On-board Data Acquisition System - DiVA portalliu.diva-portal.org/smash/get/diva2:1340302/FULLTEXT01.pdfOn-board Data Acquisition System Conceptual Design of an Airdrop Tracking System

Linköping UniversityDepartment of Management and Engineering

Division of Machine DesignTQFT33 | Master Thesis

Master Thesis Aeronautical EngineeringSpring term 2019

LIU-IEI-TEK-A–19/03450—SE

On-board Data Acquisition SystemConceptual Design of an Airdrop Tracking System

Hanna Eriksson

Academic supervisor: Jonas DetterfeltExternal supervisor: Martin Svensson (Saab AB)Examiner: Johan Ölvander

Linköping universitetSE-581 83 Linköping, Sverige

013-28 10 00, www.liu.se

Abstract

This thesis is, on behalf of Saab AB, a pre-study of possible on-board solutions for positionmeasuring during store separation tests aimed for the test and evaluation of JAS 39 Gripen.The purpose is to replace the present ground-based system in order to achieve more effectivetrials regarding time and economy.

Three different concept development methodologies were investigated in order to findthe most suitable one for this thesis. Those were merged into one adapted methodologycontaining the following phases; Planning, Function Analysis, Concept Generation andConcept Evaluation.

The work progressed as the methodology states, and the highest amount of workwas dedicated to the Planning phase. The requirements and desiderata for the systemwere produced with an agile process, resulting in the Construction Specification List thateventually became the basis for the Concept Generation phase.

Knowledge about the technical theory needed to solve the problem was obtained inparallel with the Function Analysis and Concept Generation. The most adaptable techniquesto measure position were found out to be with the use of the Global Positioning System(GPS) or Inertial Navigation System (INS).

After an extensive work with the Concept Generation in parallel with a continuouslyupdated Construction Specification List, three concepts were developed. One concept isbased on GPS, the second one on INS and the third one is a combination of GPS andINS. All three concepts shares the same telemetry system and casing, which fulfills therequirement of simple installation and possibility to install in different stores.

In the final phase, Concept Evaluation, a comparison between the concepts was performed.Advantages and disadvantages was listed and the fulfillment of requirements was investigated.All three concepts were handed over to Saab in order to let them decide which concept(s)to further develop.

List of Figures1 A Cinetheodolite used at Denel Overberg Test Range [1] . . . . . . . . . . . 52 The INS 65210E manufactured by Measurement Specialities [2] . . . . . . . 63 The MTi-G-710 system manufactured by Xsens Technologies [3] . . . . . . . 74 The concept development process according to Ulf Liedholm . . . . . . . . . 95 The Function Analysis according to Liedholm . . . . . . . . . . . . . . . . . 106 The five-step concept generation method according to Ulrich and Eppinger [4] 117 Concept generation methods according to Ullman . . . . . . . . . . . . . . . 138 Morphological matrix according to Ullman [5] . . . . . . . . . . . . . . . . . 149 Example of an evaluation matrix according to Liedholm [6] . . . . . . . . . 1510 Example of a concept screening matrix according to Ulrich and Eppinger [4] 1611 The concept scoring matrix according to Ulrich and Eppinger [4] . . . . . . 1712 Example of a decision matrix according to Ullman [5] . . . . . . . . . . . . . 1913 The 24-satellite constellation in six orbital planes [7] . . . . . . . . . . . . . 2214 A schematic view of the control segment elements and there correlation [7] . 2315 Fundamentals of Trilateration[8] . . . . . . . . . . . . . . . . . . . . . . . . 2316 Intersection between different satellites [8] . . . . . . . . . . . . . . . . . . . 2317 Principle of real-time Kinematic [9] . . . . . . . . . . . . . . . . . . . . . . . 2518 The definition of body and global frames in relation to the object [10] . . . 2619 Example of a stable platform IMU [10] . . . . . . . . . . . . . . . . . . . . . 2620 The inertial navigation algorithm for a Stable Platform System [10] . . . . . 2621 Example of a Strap-down IMU [11] . . . . . . . . . . . . . . . . . . . . . . . 2722 The inertial navigation algorithm for a Strap-down System [10] . . . . . . . 2723 A typical light weight accelerometer [12] . . . . . . . . . . . . . . . . . . . . 2824 Example of a mechanical gyroscope [13] . . . . . . . . . . . . . . . . . . . . 3025 Visualization of the Sagnac Effect. The dashed line shows the path taken

by the beam travelling with the direction of rotation [10] . . . . . . . . . . . 3026 Coriolis effect when angular velocity is applied [14] . . . . . . . . . . . . . . 3127 Summation of the time and measurement update equations used in the

Extended Kalman Filter[15] . . . . . . . . . . . . . . . . . . . . . . . . . . . 3328 Schematic picture of a telemetry system [16] . . . . . . . . . . . . . . . . . . 3429 Comparison of antenna types . . . . . . . . . . . . . . . . . . . . . . . . . . 3630 The frequency bands defined by ITU. The range applicable in this thesis is

circled with green . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3631 Methodology adapted for this thesis . . . . . . . . . . . . . . . . . . . . . . 3732 Content of the Planning phase . . . . . . . . . . . . . . . . . . . . . . . . . 3833 Content of the Function Analysis . . . . . . . . . . . . . . . . . . . . . . . . 3934 Content of the Concept Generation phase . . . . . . . . . . . . . . . . . . . 4035 Content of the Concept Evaluation . . . . . . . . . . . . . . . . . . . . . . . 4136 Construction Specification List . . . . . . . . . . . . . . . . . . . . . . . . . 4337 Black-Box model of the system . . . . . . . . . . . . . . . . . . . . . . . . . 4438 Function/Mean-tree for the system . . . . . . . . . . . . . . . . . . . . . . . 4439 Functional flow of Concept 1 . . . . . . . . . . . . . . . . . . . . . . . . . . 4540 Functional flow of Concept 2 . . . . . . . . . . . . . . . . . . . . . . . . . . 4741 Functional flow of Concept 3 . . . . . . . . . . . . . . . . . . . . . . . . . . 48

42 Example of two fuses used in unguided bombs . . . . . . . . . . . . . . . . . 4943 Verification of the Construction Specification List . . . . . . . . . . . . . . . 5044 Gantt-schedule for the project . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Contents

1 Introduction 11.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2.1 Deliverables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Problem description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3.1 Question formulations . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3.2 Delimitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3.3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3.4 Desiderata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.4 Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.5 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Situation assessment 52.1 Present solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.2 Market analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2.1 TE Connectivity-Measurement Specialities . . . . . . . . . . . . . . . 62.2.2 Xsens Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Theory of Methodology 93.1 Concept Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.1.1 Concept generation according to Liedholm . . . . . . . . . . . . . . . 93.1.2 Concept generation according to Ulrich & Eppinger . . . . . . . . . . 113.1.3 Concept generation according to Ullman . . . . . . . . . . . . . . . . 12

3.2 Concept Evaluation and Selection . . . . . . . . . . . . . . . . . . . . . . . . 153.2.1 Concept evaluation and selection according to Liedholm . . . . . . . 153.2.2 Concept evaluation and selection according to Ulrich & Eppinger . . 163.2.3 Concept evaluation and selection according to Ullman . . . . . . . . 18

4 Theoretical frame of reference 214.1 Ballistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214.2 Position Measuring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.2.1 Global Positioning System (GPS) . . . . . . . . . . . . . . . . . . . . 214.2.2 Differential GPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244.2.3 Real-Time Kinematic (RTK) . . . . . . . . . . . . . . . . . . . . . . 244.2.4 Inertial Navigation System (INS) . . . . . . . . . . . . . . . . . . . . 254.2.5 Combined GPS/INS with Kalman Filter . . . . . . . . . . . . . . . . 31

4.3 Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344.3.1 Computer storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344.3.2 Data Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

5 Methodology 375.1 Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5.1.1 Define Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385.1.2 Situation Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5.1.3 Construction Specification List . . . . . . . . . . . . . . . . . . . . . 395.2 Function Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5.2.1 Problem Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . 395.3 Concept Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5.3.1 Combine means . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.3.2 Externally & internally search . . . . . . . . . . . . . . . . . . . . . . 40

5.4 Concept Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415.4.1 Check if requirements are fulfilled . . . . . . . . . . . . . . . . . . . . 415.4.2 List advantages and disadvantages . . . . . . . . . . . . . . . . . . . 41

6 Results 436.1 Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436.2 Function Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446.3 Concept Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

6.3.1 Concept 1 - GPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456.3.2 Concept 2 - INS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476.3.3 Concept 3 - GPS/INS . . . . . . . . . . . . . . . . . . . . . . . . . . 486.3.4 Conceptual Design of the System Casing . . . . . . . . . . . . . . . . 49

6.4 Concept Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

7 Discussion 537.1 Discussion of Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

7.1.1 Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537.1.2 Function Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537.1.3 Concept Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . 547.1.4 Concept Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

7.2 Discussion of results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

8 Conclusion 578.1 Recommendation of future work . . . . . . . . . . . . . . . . . . . . . . . . . 57

Appendices 63

A First appendix 63

Introduction

1 IntroductionThis thesis is a pre-study of possible on-board solutions for position measuring during storeseparation tests at Saab AB.

1.1 BackgroundSaab AB is a Swedish aerospace and defence company founded in 1937 [17]. One of the sixbusiness areas, Aeronautics, engages in advanced development of military and civil aviationtechnology. The most known and extensive product is the JAS 39 Gripen fighter. Gripenis a single-engine multirole fighter aircraft with a delta wing and canard configuration.

The hardware and software in the aircraft is continuously updated and there is alwaysa new version in progress. During the development of a new aircraft, test and verificationis an important part. The Flight Test and Verification department is responsible for testand evaluation of prototypes, modified aircraft and production aircraft through ground-,simulator and flight testing.

One part of the development process of a new fighter, is the integration and test ofexternal stores. Separation tests are an important part of the integration phase, both as averification of a safe separation and as a way to investigate the ballistic trajectory of thestore until it reaches the target. At the moment, these tests are performed at a specifictest area that provides advanced, stationary measuring systems. The fact that the testarea has to be reserved far in advance makes it a narrow resource. Also, the investigationand evaluation of the store’s ballistic trajectory is very time-consuming with the presentsystem.

1.2 ObjectiveThe objective of this thesis is to investigate the possibilities of replacing the present groundbased measuring system, used in external store separation trials, with an on-board system.The purpose with this substitution is to enable a more flexible separation trial process thatis more time efficient and can be performed independent on the resources available at thetest range.

1.2.1 DeliverablesThe project should produce the following deliverables:

• A report

• Possible and impossible solutions

• Recommendation of future work

1

Introduction

1.3 Problem descriptionSeparation tests of external stores are today performed at a specific test area with advancedmeasuring systems provided. These systems are stationary and requires manual operation.The test area is a narrow resource and today’s test campaigns requires a large amount ofresources. Due to these factors, the Tactical Systems and Integration section at Saab hasa desire to investigate the possibilities of an on-board system attached directly on or insidethe external store, and evaluate in which way this system could replace the present one.

1.3.1 Question formulations

Since the thesis is a concept development project, there are no specific question formulationsto answer. Though, two general questions are formulated to aid the line of argument inthe thesis.

• Given the limitations, requirements and desiderata, is there one or several conceptsthat fulfill those?

• What limitations does each concept have?

1.3.2 Delimitations

In order to assure a valuable outcome of the project within the given time frame, somedelimitations was set:

• The external store is an XXXX, unguided bomb

• The cost for material and manufacturing must not exceed 40 000 SEK per systemunit.

1.3.3 Requirements

The specification of requirements is minimal to enable a higher amount of possible solutions.These initial requirements set by Saab, are going to be more specified and extended laterin the design process:

• The installation must not have any apparent influence on the separation or thetrajectory of the load

• The product must withstand forces up to 100G without failure

• The data collected must be saved

• The system must be reliable regarding function, accuracy and construction

• It must be able to test stand alone to verify the functionality of each unit

2

Introduction

1.3.4 DesiderataSome functions are desired to fulfill in order to create value for the business. Though, thesemust not be fulfilled in order to produce a usable product.

• It should be able to monitor the data in real-time, using telemetry

• If the above mentioned function is not fulfilled, it should be possible for the pilot tosee if the system works or not, before the separation is performed

• Simple installation and possibilities to install the system in other stores than the onementioned in section 1.3.1.

1.4 PlanningThe total available time for this master thesis is 20 weeks, which corresponds to 800 hours.To make a project plan, the project was divided into different phases. An initial estimateof how much time each phase requires was made, presented below:

• Pre-study and get familiar with the problem scope: 30 h

• Planning, including planning report: 40 h

• Literature study, find a concept development method: 20 h

• Theoretical study: 50 h

• Concept development and evaluation: 250 h

• Master thesis report: 400 h

A Gantt-schedule, see Appendix A, was made in order to structure the work week by week.

1.5 MethodThis project should be performed by using a concept development method. As a beginning,existing solutions should be investigated along with an update of the requirement specificationlist. Then a research of existing concept development methods should be performed, andthe most usable method should be chosen. Using the chosen method, concepts should begenerated and the process iterated until possible and impossible solutions are found. Theconcepts should then be evaluated.

3

Situation assessment

2 Situation assessmentThe techniques required by the system to accomplish the requested measurements is alreadyused in many similar applications. For example, aircraft always has one or several differentsystems on-board that continuously measures its position and altitude. Those systemsare usually based on the Global Positioning System or Inertial Navigation Systems. Inthis section, an analysis of the current situation is presented. The present ground-basedsolution that Saab uses for these trials today are also investigated here.

2.1 Present solutionCurrently the ballistic trajectory of a store during a separation test is measured with aground system based on Cinetheodolites. A Cinetheodolite is a photographic instrumentfor measurement and collection of trajectory data. The system can provide measurementsof position and event data. [18] It uses the fundamentals of motion pictures, where thecameras are mounted with its optical axis free to move in all directions. This enables thecamera to always be aimed against the object, usually a missile or aircraft. [1]

The Cinetheodolite records the elevation angle, azimuth angle and the time of eachframe of film exposed during the tracking of an object. The film from two or moretheodolites can then be used to determine the ballistic trajectory of the object. Forthree-dimensional tracking, at least three theodolites are required, while two is enoughfor two-dimensional tracking.

Figure 1 shows an example of a Cinetheodolite used for aerospace related testing atDenel Overberg Test Range in South Africa. [1]

Figure 1: A Cinetheodolite used at Denel Overberg Test Range [1]

2.2 Market analysisThere are already several existing solutions that can meet the requirements for the on-boarddata acquisition system requested in this thesis. However, they cost too much to be valuablefor using in separation trials, since each unit of the system only can be used once.

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2.2.1 TE Connectivity-Measurement SpecialitiesAn American company named TE Connectivity-Measurement Specialities, manufacturesinertial measurement systems for several different applications. They have one system thatis adapted especially for use in a unguided Mk-80 series bomb; [2]

User Configurable Inertial Measurement System-65210EThis is a six degrees of freedom INS which contains the following components:

• three internal accelerometers

• three internal rate gyros

• two temperature sensors

• battery voltage and current monitor

• signal processor

• IRIG encoder

• optional FM transmitter

• high-capacity Li-Ion battery

Figure 2: The INS 65210E manufactured by Measurement Specialities [2]

All of these components are installed in a small cylindrical package that will fit astandard Mk-80 fuse, see Figure 2. All channels in the system are continuously measured,each sampled at 16 bits. The data is then filtered, ranged and calibrated at 42 500 samplesper second and channel. The system is suitable for harsh environments since it can operatein a temperature range between -40 to +85 degrees Celsius, and will sustain a shockof 100G. The system also contains a telemetry transmitter that can meet the desire ofreal-time data monitoring. This system fulfills each requirement specified for the desiredOn-board Data Acquisition System that this thesis aims to develop, but the cost is toohigh. [2]

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2.2.2 Xsens TechnologiesXsens is a Dutch company that develops 3D motion tracking technologies and products.They develop Attitude and Heading Reference Systems (AHRS), which provides 3D orientationdata by fusing the integrated gyroscope data with data from accelerometers and magnetometers.The aim of the fusion is to reduce the drift from the gyroscopes by compensating with themagnetic field of Earth. [3]

MTi-G-710The MTi-G-710 is a miniature AHRS based on both GPS and INS, that provides high-qualityposition, velocity, acceleration and orientation. The system has excellent heading trackingwithout requiring a magnetic field. The system can operate in rough and challengingenvironments and can sustain a shock of 2000G for 0,5 ms. The system consists of gyros,accelerometers and magnetometers. This system does not include any transmitter fortelemetry of data in real-time. [3]

Figure 3: The MTi-G-710 system manufactured by Xsens Technologies [3]

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Theory of Methodology

3 Theory of MethodologyProduct development is a complex process, which can be done using several differentmethods. The process reaches from the first idea until the final physical product. Oneimportant stage of the process is the concept development. In this chapter, some differentconcept development methodologies are explained shortly and later compared with eachother.

3.1 Concept GenerationThe first step of the concept development phase is the generation of possible solutions. Theconcept generation can in turn consist of several phases depending on the method used.In this section, three different concept generation methodologies are presented.

3.1.1 Concept generation according to LiedholmThe concept generation process consists, according to Liedholm, of three phases; ConstructionSpecification List, Function Analysis and Concept Establishment [6], showed in Figure 4.

Figure 4: The concept development process according to Ulf Liedholm

In the first step, an investigation of the problem and a break-down of specificationsshould be performed. It is, according to Liedholm, important that the constructionspecifications are solution independent, in order to hold most possibilities open early in theprocess. The next step is to specify which functions the product should have and investigatepossible means and solutions. The output from this stage is a function/mean-tree, whichis a structured way to show the functions and the alternative means to implement them.Figure 5 shows a flow chart describing the Function Analysis process. [6]

In order to define the main function, a Black-Box model should be drawn up. Thetechnical principles are then divided into transformation systems, which defines the functionsneeded to enable the main function. In the Function/Mean-tree, each technical principle isthen provided with sub-functions. For each function or sub-function, one or several meansare defined. A mean is a method of how to realize the function. [6]

9


Figure 5: The Function Analysis according to Liedholm

The third and last step of this concept development process is the establishment ofconcepts. The concepts are created by combining the appropriate means with each other,to solve the functions stated in the Function/Mean-tree. This process should be iterateduntil enough useful concept have been found.

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3.1.2 Concept generation according to Ulrich & Eppinger

The concept generation process consists, according to Ulrich and Eppinger, of five differentphases. The idea behind this approach is to break a complex problem into simplersub-problems. The five-step concept generation method is presented in Figure 6. [4]

Figure 6: The five-step concept generation method according to Ulrich and Eppinger [4]

At first, a general understanding of the problem should be developed, and if necessarythe problem should be divided into sub-problems. An ideal input to the concept generationphase is a preliminary specification list where also the customer needs have been identifiedand taken into consideration. Possible concepts are then identified by internal and externalsearch procedures. The external search aims to find existing solutions to the overall problemand the sub-problems. This research involves for example interviews with users, consultingexperts and patent searching. The output from this step is both existing concepts and newconcepts. [4]

In step four, classification trees and combination tables are used to explore the conceptsand to integrate the solution for each sub-problem to a total solution. A classification treehelps to refine the problem decomposition even more, and could for example lead to addingof a new sub-function. [4]

The last step is to reflect over the solutions and the overall process. Identify how validand useful the concepts are and what could be improved. Despite that this process ispresented in a linear manner, Ulrich and Eppinger states the importance of an iterativeconcept development process. [4]

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3.1.3 Concept generation according to UllmanAccording to Ullman, the first part of the concept generation process is to get a deepunderstanding of the function. To understand the function of existing devices are importantand a good practise is to do a benchmark. A good source of ideas are patent literature.However, it can be rough to find the relevant information when searching for patents. [19]

The main function should be divided into sub-functions in order to get a deep understandingof the product. Ullman presents a technique for functional modelling, which is very usefulwhen developing new products. It consists of 4 steps;

Step 1: Find the overall function that needs to be accomplishedThis step aims to state the overall function, based on the customer requirements.All design problems has according to Ullman, one or two functions that are mostimportant, and those should be reduced to one simple statement and implementedin a Black-Box. The Black-Box is based on the conservation of mass and energyprinciple, which means that all energy and mass that goes into the system musteither come out or be stored within system. In this step, also all interfacing objectsand fixed parameters must be identified. The designer should also identify importantinformation flows, by for example answering the question "How will the customerknow if the system is performing?". [19]

Step 2: Create sub-function descriptionsThis step aims to break down the overall function and identify all the sub-functionsneeded. Here, it is important to consider what, and not how. In this step it isimportant to ensure that no new components are mentioned. If so, step one mustbe reiterated to ensure that the specifications are complete. Let each function in thebreak-down represent a transformation in the flow of energy, material or information.Since a product have different operating sequences, it is a good idea to think of eachfunction in terms of preparation, use and conclusion.

Step 3: Order the sub-functionsThe aim of this Step is to order the functions generated in Step 2, to accomplish themain function defined in Step 1. It is important that the functions comes in a logicalorder. For example they should be arranged so that the output of one function isthe input to the next one.

Step 4: Refine sub-functionsThe sub-functions should now be decomposed even more, in order to see if thefunctions can be fulfilled by existing objects or not.

Ullman presents several different methods for concept generation, stated in Figure 7. Twoof them are going to be further explained in the following sections.

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Concept generationmethods

Basic methods Brainstorming

Brainwriting

Analogy

Extremes and inverses

Experts, reference booksand trade journals

The morphological method

Logical methods TRIZ

Axiomatic design

Figure 7: Concept generation methods according to Ullman

3.1.3.1 Morphological Method

According to Ullman [19], the morphological method is a powerful method for idea generation.It is a useful tool to create concepts of a product that is based on sub-functions formeridentified. An example of a morphological matrix is shown in Figure 8. The techniqueconsists of two steps;

Step 1: Developing concepts for each functionThe objective of this step is to find as many concepts as possible that can solve eachsub-function identified in the decomposition. Firstly, one should develop as many alternativefunctions as possible, to each already specified sub-function. Then, as many means aspossible should be identified for each sub-function. If it turns out that one of the functionsonly corresponds to one conceptual idea, that function must be further inspected, sincethere is not likely that only one concept fulfills the function. For example, check that thefunction statement does not have any nouns telling how the function should be accomplished,since a statement like that will limit the amount of possible concepts. [19]

Step 2: Combining conceptsThis step aims to combine the concepts generated in step one into overall concepts thatmeets the functional requirements. The concepts to each sub-function, listed in step 1,should now be combined into complete conceptual designs. One concept per sub-functionare chosen, and then combined into a concept design. The problem with this methodis that it probably will generate too many concepts. It also assumes that each conceptonly accomplish one function, which is rarely the case. Despite that, Ullman states theimportance of breaking down the functions in order to get a deep understanding of theconcept development. [19]

3.1.3.2 Axiomatic Design

Axiomatic Design is a system design methodology developed by Professor Nam Suh in the1970s [19]. The aim of the method is to create a logical design process where the customerneeds are transformed into functional requirements and design parameters. The axiomaticapproach is based on the relationships between four design domains: customer, function,physical and process. The relation between functional requirements and design parameters

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Figure 8: Morphological matrix according to Ullman [5]

can be described by the relation in Equation (1): [19]

FR = A×DP (1)

where A is the design matrix. [20] The Axiomatic Design method consists of twocentral axioms. The first is called the Independence Axiom and stands for the importanceof maintaining the independence of functional requirements. The design is better if thefunctional requirements are independent of each other, since a change in a specific designparameter then will impact only one single function. Therefore, the ideal situation is tohave an uncoupled design, where each functional requirement is dependent on only onedesign parameter. [19] For an uncoupled design, the relation turns out to be as stated inEquation (2) [20]. [

FR1

FR2

]=

[X 00 X

] [DP1

DP2

](2)

The second best case is to have a decoupled design, which means that the design matrixis lower triangular, as in Equation (3).[

FR1

FR2

]=

[X 0X X

] [DP1

DP2

](3)

Worst case scenario, is when each functional requirement are dependent on severaldesign parameters. This is called coupled design, and is showed in Equation (4). [20][

FR1

FR2

]=

[X XX X

] [DP1

DP2

](4)

In a coupled design, a change in one specific design parameter will effect all thefunctions, which is not the desired case. The design is much more rigid if it is uncoupled.

The second axiom is the Information Axiom, which implies the importance of keepingthe information content of the design as low as possible. Usually, the simplest design hasthe highest probability to succeed.

14


3.2 Concept Evaluation and SelectionThe Concept Selection phase is about evaluating the concepts created during the conceptgeneration, and select one or more concepts for further investigation and testing. Eventhough the amount of concepts are narrowed down, it could take several iterations of thisprocess until the final concept(s) are chosen. The amount of concepts could even increaseat a beginning, for example by creating combinations of the other concepts.

3.2.1 Concept evaluation and selection according to LiedholmThe concept selection should according to Liedholm be performed in three steps [6]:

1. Investigate whether the concepts fulfills the requirements specified in theConstruction Specification ListIf a concept does not fulfill the requirements, the concept is either to bad, or the requirementsare too strict or badly formulated. If this happens, either the concept should be rejectedor the requirements must be adjusted. [6]

2. Compare the concepts with each other by establish an evaluation matrixLiedholm states that since the knowledge about the concepts are limited at this stage, asimple evaluation method is beneficial. By using a evaluation matrix, see Figure 9, anobjective comparison between the concepts is received. Though, the result should not betaken too literal since the matrix does not tell if the concept will work or not. It is only acomparison relative each other and should be seen as a guidance. [6]

3. Choose a few concepts for further developmentThe decision of which concepts to go further with should be based on both the evaluationmatrix and the result from the previous concept review. [6]

Figure 9: Example of an evaluation matrix according to Liedholm [6]

15


3.2.2 Concept evaluation and selection according to Ulrich &Eppinger

Ulrich and Eppinger presents a two-stage concept selection methodology; Concept Screeningand Concept Scoring [4]. Both stages are based on a decision matrix which is used to helprate, rank and finally select the most qualified concepts. A six-step process should leadthe user trough each stage;

1. Prepare the selection matrix2. Rate the concepts3. Rank the concepts4. Combine and improve the concepts5. Select one or more concepts6. Reflect on the results

The Concept Screening phase is based on the method developed by Stuart Pugh, where thepurposes are to decrease the number of concepts and to improve them. In the case of morethan 12 concepts under consideration, the multi-vote technique may be used to quicklyreduce the number of solutions. Multi-voting means that every member of the conceptdevelopment team simultaneously votes for three to five concepts. Simply the conceptswith most votes are chosen to continue with the concept screening. [4]

The input to the selection matrix, see Figure 10, are concepts and criteria, where it isimportant that all concepts are presented with the same level of detail. These criteria arebased on both the customer needs and enterprise needs such as manufacturing cost. Theconcepts should be presented at the same level of detail in order to get a meaningful andcondign comparison. In this stage, the criteria are still very abstract and benefits frombeing chosen in order to distinguish the concepts. Since all criterion stated in the selectionmatrix are given the same weight, it is of high importance not to list the least importantcriteria. Otherwise, the differences among the concepts relative the more important criteriawill not be distinctly reflected in the result. [4]

All concepts are rated against a carefully chosen reference concept. The reference couldbe either one of the concepts under consideration, or a product available on the market.

Figure 10: Example of a concept screening matrix according to Ulrich and Eppinger [4]

The concepts stated in the selection matrix are then rated with "better than +", "same

16


as 0" or "worse than -", in relation to the chosen reference. A summation of the rates isthen made, and the concepts are ranked, see Figure 10. [4]

After the screening, the result is analyzed in order to find new combinations or improvementof the present ones. Since this is an iterative process, the new combinations or improvedconcepts are then stated in the same selection matrix and being scored and ranked alongwith the other ones. [4]

In order to obtain a more condign outcome from the Concept Selection, the ConceptScoring phase is performed. Here, the rating of concepts are based on the relative importanceof each criterion. The criteria former stated in the screening matrix is now provided witha weighting, in relation to a reference point. As can be seen in Figure 11, new conceptcombinations are available and a new reference is set.[4]

Figure 11: The concept scoring matrix according to Ulrich and Eppinger [4]

In the same way as in the screening phase, the concepts should then be rated. Ulrichand Eppinger recommends that all concepts are rated with focus on one criterion at thetime. Though, in this stage it is not suitable to use a single reference concept, becauseof the risk for reduction of the rating scale for some of the criteria. For example, if thereference concept is the easiest one to manufacture, all of the other concepts will receive therate 1,2 or 3 ("much worse than", "worse than" or "same as"). To overcome this problem,different reference points should be used for the various criteria. The scoring process isthen finished in the same way as the screening process; combine and improve the concepts,select one or more concepts, and finally reflection of results and the process.

17


3.2.3 Concept evaluation and selection according to Ullman

According to Ullman, the goal of the concept selection process is to "expend the leastamount of resources on deciding which concepts have the highest potential for becoming aquality product". He states that the central problem in this is to choose which concept tofurther develop, without knowing that much about it. At this stage, it will be less riskyto refine a number of concepts before limit oneself to one of them. On the other hand,this approach will require more resources and will also lead to less investigation of eachconcept. [19]

Ullman calls this phase of the concept development for Concept Selection, and statesthat it is a combination of comparison and decision making. The comparison can be madein two different ways. Either it is absolute, which means that the concepts are comparedto a target set by a criterion, or it is relative, by comparing the concepts with each other.[19]

As a first step, Ullman propose that the evaluation can be made based on feasibilityjudgement. One of the three following reactions will emerge when looking at each concept:(1) it is not feasible and will not work; (2) it might work if something else happens; (3)it is worth considering. This method will result in a better outcome the more experiencethe engineer has. Before rejecting any of the ideas that seems "not feasible", the concepthas to be carefully considered in order to find why it is not feasible. The concepts that arejudged to be worth considering are usually the hardest ones to evaluate, which makes theengineering experience essential. [19]

When the intuition phase is done, the remaining concepts will be further evaluatedin a go/no-go screening. This evaluation is based on the customer defined criteria andthe technology readiness level. By reformulating the customer needs to questions, theycould be answered with go or no-go. The readiness level of a product tells how mature thedesign is, and is a good technique to refine the concept evaluation. A technology that isnot mature enough to be implemented in the design will result in an expensive and timeconsuming process, and the risk of a bad product as outcome is high. Ullman suggests sixmeasures that can be applied to determine the maturity of a design: [19]

1. Are the critical parameters that control the function identified?2. Are the safe operating latitude and sensitivity of the parameters known?3. Have the failure modes been identified?4. Can the technology be manufactured with known processes?5. Does hardware exist that demonstrates positive answers to the preceding fourquestions?6. Is the technology controllable throughout the product’s life cycle?

Ullman states that if the answers of these questions are negative, it is a good idea toadd a consultant to the team, in order to expand the knowledge field. [19]

Further, to evaluate the concepts even more, Ullman suggests a decision-based method[19], see Figure 12. The method is simple and effective for comparison of concepts. Itis based on Pugh’s method, earlier mentioned in Section 3.2.2. Each concept is scoredwith a weight relative to another, regarding the ability to meet the criteria set by thecustomer. One concept is chosen as a reference, to which the other are compared with.The method is an iterative process and new alternatives are often found. According to

18


Ullman, the outcome of the process is most valuable if every member of the team performsit independently, and then compares the results with each other.

Figure 12: Example of a decision matrix according to Ullman [5]

19

Theoretical frame of reference

4 Theoretical frame of referenceIn this thesis, the bomb that should be positioned are both unmanned and unguided. Sinceit is not dirigible, it is of high importance to be aware of the behaviour that the bomb showsthrough the air and at the impact. Even though the manufacturer of the bomb guaranteesthe behaviour of it, Saab needs to ensure that it works as desired even after the integrationto a new aircraft. At this point, the desire of an on-board system for determination ofthe ballistic trajectory of the bomb arises. In this section, the technical theory required tosolve the problem is going to be examined and presented.

4.1 BallisticsBallistics is the theory about the behaviour and effects of thrown bodies or launchedprojectiles through the air. When analyzing thrown bodies, the effects of air resistance isoften neglected and the Earth’s gravitation is considered as the only force acting on thebody. This assumption gives a symmetrical parabolic trajectory through the air. However,in the real case the body is also affected by aerodynamic drag caused by the resistance ofthe air, resulting in an asymmetrical parabolic path with the highest point closer to itspoint of impact. This is especially important to consider when analyzing the motion andtrajectory of a projectile. [21] The drag contribution emerged by the air varies with thevelocity and altitude of the projectile. By measuring the projectile’s position along thetrajectory, the ballistics of it can be calculated. The knowledge of the ballistic behaviourcan then be used to adjust the rear sight of a projectile to ensure the correct point ofimpact. [21]

4.2 Position MeasuringReal-time determination of position is a fundamental prerequisite for many applicationsin today’s society, not least in aviation and automotive industry. There are many waysto accomplish the positioning, more or less suitable depending on the application. Lately,the interest in unmanned air vehicles (UAV) has increased rapidly [22]. The positiondetermination of those vehicles are of high importance due to the fact that they are notcontrolled by an on-board pilot.

4.2.1 Global Positioning System (GPS)The Global Positioning System (GPS) is a navigation system based on satellites. Thesatellites was originally put into orbit by the U.S. Department of Defense in 1973, and aretoday available for both military and civilian use. The satellites are available anywherein the world, 24 hours per day. GPS works in all types of weather and consists of threesegments: Space Segment; Control Segment and User Segment. [7]

4.2.1.1 Space Segment

There are always at least 24 satellites available, placed in six orbital planes, see Figure 13.The inclination relative to the equator is 55◦and there are four satellites in each orbital

21


plane. This 24-satellite constellation ensures the users ability to view at least four satellitesat the time, at any time and any point on Earth. At some optimal time slots, up to 12satellites can be used at the same time, which increases the accuracy highly. [23] Thesatellites operates at an altitude of 20 200 km and each satellite circles the Earth twice aday. The number of operational satellites are continuously increased, and as of 9th January2019, there were 31 satellites in operation. [7]

Figure 13: The 24-satellite constellation in six orbital planes [7]

Each satellite has its unique signal and orbital parameters. By sending those to a GPSreceiver, the precise location of the satellite can be determined. The receiver can then byusing this information calculate the exact position of the object. Once the position of theobject is found, other information such as speed, time and bearing can be calculated. [24]

In order to track the two-dimensional position (longitude and latitude) of an object, aGPS receiver on the object must be in contact with the signal of at least three satellites.In cases where the three-dimensional position should be determined (longitude, latitudeand altitude), a minimum of four satellites are required. [7]

The GPS originally sends data on two different frequencies:

L1 = 1575.42 MHz

L2 = 1227.60 MHz

The civil frequency, L1, is used for both civil and military use, while the L2-signal onlyis available for military applications. The military uses the civil signal to send P-code(Precision-code) in order to increase the safety and lower the risk of the signal to beintruded. The L1 frequency sends C/A-code (Coarse/Acquisition-code). [23]

4.2.1.2 Control Segment

The control segment of the GPS is the Operational Control System (OCS), which includesa master control station, monitor stations and ground control stations [23]. These elementsand there correlation is shown in Figure 14. The main purposes of the OCS is to track thesatellites for determining the orbit and clock, synchronize the time of the satellites, andupload the data.

There are in total 16 monitor stations available. Each of these tracks the positionof all satellites passing overhead. [7] There are two mathematical ideas behind the GPSpositioning network; Trilateration and Pseudorange. [25]

22


Figure 14: A schematic view of the control segment elements and there correlation [7]

Trilateration calculates the position of an object by measuring the distance fromdifferent satellites to the object. The object’s GPS receiver acquires a specific time anddistance from each satellite available at the moment. Since the location of all satellites areknown, this distance gives information about where the object is located. The distance toeach satellite is known, though the angle is still unknown. This means that the object canbe located anywhere on the circle with a radius equal to the distance from the satellite,see Figure 15.

Figure 15: Fundamentals of Trilateration[8]

To get the exact two-dimensional position of the object, the same process must bedone with two more satellites. Each satellite is at the center of a circle and where theyall intersect is the position of the object, see Figure 16. Though, the Earth is threedimensional, which means that the GPS satellites broadcast signals as a sphere, shown inFigure 16. The three-dimensional position of the object can be determined by using foursatellites. The point where all four spheres intersect is the position of the object. [25]

Figure 16: Intersection between different satellites [8]

The other mathematical idea, Pseudorange, is the time the signal takes to travel fromthe satellite to the receiver, multiplied with the speed of light. Equation (5) states theformula for pseudorange P s, where T is the time of the receiver clock, T s the time of the

23


satellite clock, and c is the speed of light (=299 792 458 m/s in vacuum).

P s = (T − T s)c (5)

Since the atomic clock on the receiver is not totally reliable, clock errors often occurs,thereby the range definition pseudo. At least four satellites must be used to solve thepseudorange equation and find out the three-dimensional position of the receiver. Withfour unknowns and four equations the method of least-square is used to determine theobject’s position.

4.2.1.3 User Segment

The user segment consists simply of the GPS receiver equipment, which receives thesignals from the satellites and uses the transmitted information to calculate the user’sthree-dimensional position.

4.2.2 Differential GPS

Differential GPS (DGPS) is an improvement of the original Global Positioning Systemwhich provides highly improved position accuracy. DGPS uses fixed ground-based referencestations to adjust the real-time GPS signals in order to eliminate the pseudorange errors.

When the satellite signals are travelling through the atmosphere heading to the GPSreceiver, they are subjected to delays. Since the pseudorange is based on the travel timeof the signal, this results in an incorrect pseudorange which leads to errors in the positionmeasurements. A relative small time delay can lead to a large position error which meansthat the continous changes in the atmosphere can result in a very inaccurate positiondepending on the present conditions. [26]

The Differential GPS can either be integrated directly in the GPS receiver used in theobject, or it could be added afterwards when post processing the data. In the latter case,the GPS receiver just collects all measured positions and the time for each measurement.This data can then be processed afterwards and merged with the corrections made by thereference station.

4.2.3 Real-Time Kinematic (RTK)

Real-Time Kinematic is a carrier-based ranging method that gives a higher accuracy thanthe code-based GPS technique. The basic concept of the RTK technique is to reduce andremove the common errors that occurs due to atmospheric changes. [9] By using a carrierwave signal instead of a code-signal as used in GPS, a more precise signal change can beobtained. This enables knowledge about exactly when the signal was changed, which givesa much higher timing resolution. When merging the real-time and corrected signals, thetime change is highly accurate which means that a very precise position can be calculatedby comparing the distance between satellite and receiver. [27] Figure 17 shows the principalof Real-Time Kinematic.

24


Figure 17: Principle of real-time Kinematic [9]

4.2.4 Inertial Navigation System (INS)An Inertial Navigation System (INS) is a device that uses motion sensors, rotational sensorsand a computer to measure and calculate the three-dimensional position, velocity andacceleration of an object. Usually, the motion sensors are accelerometers and the rotationalsensors are gyroscopes. The accelerometers and gyros provides measures of the object’sacceleration and angular velocity. By receiving those measures, the navigation computercan then calculate the relative position, orientation and velocity of the object. The INS issuitable for a wide range of applications, such as navigation of aircraft, missiles, spacecraftand marines. The largest difference between the GPS and INS is that the GPS generatesan absolute position using a known coordinate system, while the INS generates the positionrelative to the last known point. [28]

By definition, an INS consists of two essential parts; the Inertial Measurement Unit(IMU) and the navigation computer. The IMU comprises the accelerometers and gyrosthat performs the measurements and serves the navigation computer with information. [28]An important aspect when talking about INS is how the reference frames are defined. Inthis thesis, the reference frames are defined as shown in Figure 18; the navigation system’sreference frame as the body frame, and the frame of reference in which the navigation ismade as the global frame. [10]

The IMUs can be divided into two main categories; Stable Platform Systems andStrap-down Systems, where the only difference is the frame of reference where the accelerometersand gyros are operating.

Stable Platform SystemsIn a Stable Platform System, the inertial sensors (accelerometers and gyros) are mountedon a platform that are always held aligned with the global frame of reference. [10] Thismeans that the part where the sensors are attached is isolated from all angular motionscreated by the object, for example an aircraft. [29] The platform is mounted using gimbals(frames), which allows the platform to be free in all three axes, shown in Figure 19.

25


Figure 18: The definition of body and global frames in relation to the object [10]

Figure 19: Example of a stable platform IMU [10]

The gyroscopes attached to the stable platform detects eventual rotations and reportsthose to the torque motors which then rotates the gimbals to maintain the platform alignedwith the global frame. [10] Due to many rotating parts and a complex physical shape, themaintenance of a stable platform IMU is expensive and time-consuming [30].

Figure 20: The inertial navigation algorithm for a Stable Platform System [10]

26


The orientation is tracked by reading the angles between the gimbals using the anglepick-offs. The position of the object can be calculated by integrating the accelerometersignals twice. Before the signals from the accelerometers are integrated, they are correctedfor the gravitational impact. The inertial navigation algorithm for a Stable PlatformSystem is presented in Figure 20.

Strap-down SystemsIn a Strap-down System, the inertial sensors are mounted rigidly, or "strapped down", tothe frame of the object, shown in Figure 21. [30]

Figure 21: Example of a Strap-down IMU [11]

This enables the INS platform to follow the movements of the object which it is attachedto. Hence, the sensors are measuring the acceleration and angular velocity in the bodyframe. A Strap-down System are in general less complex than a Stable Platform System,both regarding physical shape and computation. [10] Through less moving parts, themaintenance and reliability over time is improved. Even though the Strap-down Systemsrequires more accurate inertial sensors and more computing power, the benefits of lowercost, complexity and weight make these systems the optimal choice within aviation. [30]

Figure 22: The inertial navigation algorithm for a Strap-down System [10]

Figure 22 shows the inertial navigation of a Strap-down System. The physical principlesare the same as for the stable platform showed in Figure 20. For the Strap-down System,the orientation is determined by integrating the gyroscope signals. The accelerometersignals are transformed into global coordinates using the orientation obtained from theintegrated gyro signals. When the global acceleration signals are obtained, the positioncan be determined by the same procedure as the Stable Platform IMU. [10]

27


4.2.4.1 Accelerometer

An accelerometer is an electromechanical device that measures proper acceleration. Properacceleration is the acceleration of a body relative its own rest frame, meaning the coordinatesystem in which the body is at rest. The forces measured by an accelerometer can be bothstatic, for example gravitational forces, or dynamic to sense movement and vibrations.[31] An accelerometer in free fall measures an acceleration of 0 m/s2, while one placed onthe Earth’s surface will read -9.82 m/s2. In the case of free falling, both the mass andthe casing are falling by the action of gravitational forces, which means that the relativedifference is zero. When placed on the surface of Earth, the forces acting on the casing iszero while the mass is effected by the gravitation, resulting in a negative acceleration. [28]

Normally, an accelerometer consists of some type of capsule with a weight inside.The capsule is firmed into the object which acceleration should be measured, while theweight inside is loose. Due to the inertia of the weight, pressure forces, drag forces anddisplacements occurs between the weight and the capsule, which then transforms intoelectrical signals. A simple accelerometer usually consists of a mass attached to a spring,that measures the deflection and converts it into acceleration. Accelerometers can be usedin many different applications such as geology, navigational and inertial guidance systems,smartphones and industrial vibration measurement. [32] Figure 23 shows a typical lightweight accelerometer.

Figure 23: A typical light weight accelerometer [12]

The position x of an object at any time t can be determined by estimating theacceleration of the object, as stated in Equation (6),

x(t) =

t∫0

t∫0

a(t)dtdt+

t∫0

v0dt+ x0 (6)

where a is the acceleration of the object, v0 is the initial velocity of the object and x0the object’s initial position. [33] The acceleration a, can by using accelerometers bemeasured directly. Though, one problem with accelerometers is the large amount of errorsthat occurs in the measurements. The extent and impact of these errors must be takeninto consideration when using this device for applications where the accuracy is a criticalparameter. The direct output from an accelerometer is an electrical signal proportional tothe acceleration of the device, often measured in voltage. [33] A simplified model of themeasured voltage is

Vm(t) = S(1 + δS)a(t) + Vb + δVb (7)

where

28


S is the sensitivityδS is the sensitivity errorVb is the voltage biasδVb is the voltage bias error.

By rearranging Equation (7) to solve for the measured acceleration, Equation (8) is obtained.[33]

am(t) =Vm(t)− Vb

S= a(t) + δSa(t) +

δVbS

(8)

The initial velocity and position (v0 and x0) are assumed to be zero at t = 0. CombiningEquation (6) and (8), and integrating twice gives the time dependent position of the objectas

x(t) =

t∫0

t∫0

am(t)dtdt =

t∫0

t∫0

a(t)dtdt+ δS

t∫0

t∫0

a(t)dtdt+δVbS

t∫0

t∫0

dtdt. (9)

The first term of Equation (8) is the data desired to obtain the position of the object.The second and third terms are the internal errors that occurs in the sensor. It can beseen from these terms that the errors are time dependent and increases quadratically withtime. This results in a rapidly growing error over time. For example, a position error of0.1225 meters after one second, has growth to an error of 3 meters in five seconds. Anaccelerometer with a three-axis sensor can measure the position in all three dimensions(latitude, longitude and altitude). [33]

In general, an accelerometer by itself is not a good option for position measuring ofan aircraft, due to the large gravitational variations. Those variations gives very unstabledata and the accuracy becomes low. Though, using accelerometers in combination withgyroscopes and a computer (INS) is usually a good choice for aircraft applications, due tothe high accuracy obtained.

4.2.4.2 Gyroscope

A gyroscope is a device which uses gravity to measure and determine orientation of anobject. There are a lot of different types of gyroscopes, for example mechanical, opticaland vibrating. The most conventional one is the Mechanical gyroscope, which consists ofa spinning wheel mounted on two gimbals, showed in Figure 24. The gimbals allows thewheel to rotate in all three axes. The Conservation of Angular Momentum principle, allowsthe wheel to remain stationary and resist changes in orientation. By using angle pick-offs,showed in Figure 19, the angles between the gimbals can be measured, and the orientationof the object can be identified. A large disadvantage with mechanical gyroscopes is that themoving parts causes friction, which results in a higher maintenance cost and less accurateoutput results over time. [13]

Unlike the mechanical one, the Optical gyroscopes and MEMS (Micro-Electro-Mechanicalgyroscopes) measures angular velocity. A fibre optic gyroscope consists of a large coil ofoptical fibre, and measures the angular velocity by using the impact of light. The basicprinciple is based on the Sagnac Effect. The theory describes the physical effects thatoccurs when two light beams are fired into the coil in opposite directions. If the coil isstationary, both beams will travel the same path in the same time, independent on thedirection. Though, if the coil is under rotation, the direction of travel of the beams will

29


Figure 24: Example of a mechanical gyroscope [13]

govern the path and travel time around the coil. The beam travelling against the directionof rotation will have the shortest path and travel time, showed in Figure 25. [34] Whenthe beams reaches the exit of the coil, they are combined into one, due to the phase shiftcreated by the Sagnac Effect. By measuring the intensity of the combined beam, it ispossible to determine the angular velocity. [10] In comparison with the mechanical gyros,the optical ones are easier to maintain due to no moving parts. The accuracy of an opticalgyroscope is dependent on the size, larger ones has higher accuracy. [10]

Figure 25: Visualization of the Sagnac Effect. The dashed line shows the path taken by the beamtravelling with the direction of rotation [10]

A Ring Laser Gyro (RLG) uses the Sagnac Effect as well, with the difference thatinstead of optical fibre, mirrors are used. In modern aircraft the RLG is the predominantgyroscope type used. [30]

Another gyroscope type is the MEMS, which is a combination of mechanics and electronics.A MEMS is using vibrating elements to measure the Coriolis effect, which is the principleforce that acts on a mass moving with a velocity v in a frame of reference that is rotatingwith an angular velocity ω. [10] The simplest variant of a MEMS gyroscope consists oftwo masses oscillating and constantly moving in opposite directions, showed in Figure26. By applying an angular velocity, the Coriolis force on each mass will act in oppositethe direction. This will result in capacitance change, that is proportional to the angularvelocity. [14]

30


Figure 26: Coriolis effect when angular velocity is applied [14]

There are many advantages with these gyroscopes, such as the small size, low weight,few parts and low power consumption. Despite that, they are not suitable for applicationswhere high accuracy is required, for example in aircraft. [10]

4.2.5 Combined GPS/INS with Kalman FilterIn reality, both the INS and GPS data comes with inaccuracies. The GPS is highlydependent on location and time, since the number of available satellites varies through theday. These outages can be reduced by the use of an Inertial Navigation System, since theINS are using dead computation and are totally independent on external sources. The INSon the other hand, often contains low-cost inertial sensors that exhibits large errors. Thoseerrors can be compensated using position and velocity data from a GPS. The combinationof GPS and INS, with the use of a Kalman filter, results in a high-accuracy real-timenavigation system. [35]

A Kalman filter is a set of mathematical algorithms, that based on a multitude ofincomplete or uncertain measurements can measure the state of a dynamic system. Kalmanfilter can be used for many different applications, but are most valuable for systems whichare continuously changing. One example of such system is an INS used to continuouslymeasure the position and velocity of a moving object. The Kalman filter can then producecorrect and accurate information about the object’s position and velocity, based on a seriesof imperfect observations made by the inertial sensors. The filter can estimate the currentoptimal state of a system, by combining the measured output with a known model of thedynamic system. [36]

The position and velocity measurements from the GPS or inertial sensors, comes as arange of possible positions and velocities for each time stamp. Some of the data pointsmight be true, and it is the Kalman filter’s task to find out which position and velocity thatis real. The filter assumes that the positions and velocities are random and distributed bynormal distribution. The basic representation of the Kalman filter is a linear estimator, andis only applicable on linear systems. In order to filter the data for navigation systems asINS or GPS, the Extended Kalman filter must be used, which linearizes about an estimateof the current mean or co-variance of the variables. [15]

31


Define the state x ∈ Rn of the object as a vector of the position and velocity. Due tothe non-linearity, the process is governed by the non-linear stochastic difference equation

xk+1 = f(xk, uk, wk) (10)

with a measurement z ∈ Rm that is

zk = h(xk, vk). (11)

In Equation (10) and (11), the random, normal distributed variables wk and vk representthe process and measurement noises. The non-linear function f(•) in the differenceequation (10) relates the time at step k to the state at step k+ 1. The non-linear functionh(•) in the measurement equation (11) relates the state xk to the measurement zk. [15]Since the values of the noise wk and vk is not known at each time step, the state andmeasurement equations can be approximated without them as

xk+1 = f(xk, uk, 0) (12)

andzk = h(xk, 0) (13)

In order to linearize an estimate about Equation (12) and (13), new governing equationsare defined: [15]

xk+1 ≈ xk+1 +Ak(xk − xk) +Wkwk (14)

zk ≈ zk +Hk(xk − xk) + Vkvk. (15)

The new variables used in Equation (14) and (15) are described in Table 1. [15]

Table 1: Description of variables used in Kalman equations

Variable Descriptionxk+1 and zk actual state and measurement vectorsxk+1 and zk approximate state and measurement vectorsxk a posteriori estimate of the state, from a previous step k)Ak the Jacobian matrix of partial derivatives of f with respect to xWk the Jacobian matrix of partial derivatives of f with respect to wHk the Jacobian matrix of partial derivatives of f with respect to xVk the Jacobian matrix of partial derivatives of f with respect to v

The predicted error is defined asexk≡ xk − xk (16)

and the measurement residual asezk ≡ zk − zk. (17)

By the use of Equation (16) and (17), the governing equation for the error process canbe stated as

exk+1≈ Ak(xk − xk) + εk (18)

andezk ≈ Hkexk

+ ηk (19)

32


where εk and ηk are new random variables with zero mean, presented below together withthe approximated probability distribution for the error prediction exk

p(exk) ∼ N(0, E([exk

eTxk])

p(εk) ∼ N(0,WQkWT )

p(ηk) ∼ N(0, V RkVT )

Combining Equation (16), (17) and (19) results in a posteriori state estimate for thenon-linear process as

xk = xk + ek. (20)

Given the approximated probability distributions and letting the predicted value of ekto be zero, gives

ek = Kkezk (21)

where Kk is the Kalman gain, that minimizes the a posteriori error covariance defined asPk = E[ekek

T ]. On of the forms that minimizes the error covariance is stated in Equation(22). For more details about the derivation of the gain can be found in [37].

Kk = PkHkT (HkPkHk

T + VkRkVkT )−1 (22)

Substituting Equation (21) into (20) with the use of Equation (17) results in

xk = xk +Kk(zk − zk). (23)

All equations derived and stated in this section, finally leads to the time update andmeasurement update equations for the Extended Kalman Filter. [15] The final equationsare summarized in Figure 27.

Figure 27: Summation of the time and measurement update equations used in the ExtendedKalman Filter[15]

33


4.3 Data AcquisitionThe aim of the system is to measure and collect information about the position and velocityof the store, from separation to impact. The information should both be stored andtransmitted to a ground station in real-time.

4.3.1 Computer storageA posteriori analysing and verification of results are often desired in flight testing. Therefore,the data measured during the test must be collected and stored in some way. The mostsuitable way to accomplish this is to use a data logger or a SD card.

A data logger is an electric device that records data over time or relative a location,either with built in sensors or via external sensors. The logger is usually a small, batterypowered digital processor with an internal memory. One benefit with using a data loggeris the ability to collect data during a long time upon activation. [38]

Secure Digital (SD) is another way to collect and store the data acquired by the sensorsin the data acquisition system. A SD-card is a non-volatile type of computer memoryoften used in portable devices. [39] The most significant difference compared with thedata logger is that a SD-card does not require constant power in order to retrieve andstore data. Therefore, it is often the most suitable type of memory in applications wherethe battery capacity is limited. [40]

4.3.2 Data TransmissionTransmitting data from an aircraft to a ground station enables real-time analysis andverification of the present system, which is often valuable in flight testing. Within theaircraft industry, telemetry is often used as a general description for transmission of data.As well in the health technology sector, telemetry is a valuable tool used for example incontinuous heart rate monitoring.

Telemetry is an automated communication process where measured data are wirelesstransmitted from the object of measurement to a receiver station. For space and aircraftapplications, long distance telemetry systems are used. In long distance telemetry, usedfor example in flight testing, data from the different sources are sampled and sent over aunified channel.

Figure 28: Schematic picture of a telemetry system [16]

A telemetry system consists of a transmitter and a receiver, with corresponding antennas.The transmitter collects the measured data from the sensors in the system, unifies them intoone data package and sends them to a telemetry receiver unit. The receiver acquires themeasurement data and outputs a filtered data stream. [16] Dependent on the applicationand the required accuracy of measurements, the data could be further processed afterwards,for example with Differential GPS as mentioned before.

34


4.3.2.1 Friis’ Transmission Equation

There are a large amount of different transmitters, receivers and antennas on the market.Which components to use are highly dependent on the specific application. In the caseof a flight test, the maximum range between transmitter and receiver is often specifiedsince the altitude of flight is known. In other cases, the knowledge about the length of thetransmission range is desired, in order to specify where to place the receiver antennas for aspecified system. Independent on which parameter that is unknown, the relation betweentransmitter power, receiver power and range is the same. Equation (24) is called Friis’Transmission Equation [41],

PR = PTGTGR

(λ

4πR

)2

(24)

where

PR is the receiver power [W]PT is the output power from the transmitter [W]GR is the receiver antenna gain [-]GT is the transmitter antenna gain [-]R is the range between transmitter and receiver antennas [m]λ = c

f is the wavelength of the signals [m].

The equation states the relation between the power received from one antenna whentransmitted from another antenna. [41] Each antenna has a gain, which is simply aperformance parameter that describes how much power that is needed to convert radiowaves into electrical power (receiving antenna) or convert input power to radio waves(transmitting antenna). [42]

By examine Equation (24), it is obvious that the receiver power is dependent on all otherparameters in the data transmission system. The choice of antennas is highly dependenton the actual application of use. There are two main types of antennas; Omnidirectionaland Directional. An Omnidirectional antenna radiates and receives signals equally wellin all horizontal directions, while a Directional one is able to focus the signal receptionin a particular direction. [43] A high gain means a high directivity, in other words howdirectional the antenna’s radiation patterns is. [44] Therefore, an antenna with high gainis suitable in cases where the desired signal direction is exactly known. For applicationswhere there are several receiving units or moving objects, a low gain antenna is better touse since the radiation pattern is more spread.Figure 29 shows two different types of antennas, one Omnidirectional (dipole) and oneDirectional (yagi), with the corresponding signal patterns in the horizontal direction.

4.3.2.2 Frequency Range

When sending data between two objects, the signals are sent over a specific frequency, whichbasically represent the number of cycles per unit time. Depending on application, either ahigh or low frequency is most suitable. The International Telecommunication Union (ITU)has divided all available frequencies into bands with different frequency ranges. [45] Asstated in Figure 30, there are nine frequency bands [45], although only two of them are

35


Figure 29: Comparison of antenna types

appraised to be suitable for the acquisition system developed in this thesis. This is basedon the required distance of communication along with the volume of data to be sent.

Figure 30: The frequency bands defined by ITU. The range applicable in this thesis is circledwith green

In general, a lower frequency results in a longer range due to its ability to go aroundobstructions in the atmosphere. Lower frequency radio waves exhibit low signal attenuation,which means that the gradual loss of flow intensity through a medium is low. A higherfrequency requires the receiving and transmitting objects to be within line of sight witheach other, which means a lower range. However, more data can be sent on a higherfrequency since the update rate is higher.

36

Methodology

5 MethodologyBased on the concept development processes presented in Section 3, an adapted methodologywas produced for this thesis. The methodology, presented in Figure 31, includes partsfrom the different methods developed by Liedholm, Ulrich & Eppinger, and Ullman. Itwas divided into four general phases; Planning, Function Analysis, Concept Generationand Concept Evaluation.

Figure 31: Methodology adapted for this thesis

The methodology adapted for this thesis was mostly based on the concept developmentprocess according to Ulf Liedholm [6]. However, the Concept Generation phase evolved byLiedholm was here divided into two comprehensive phases in order to separate the problemdefinition and the concept generation. The Function Analysis was made fully according toLiedholm’s method, where the problem was decomposed into functions and sub-functionsby creating a Black Box and a Function/Mean-tree.

The Concept Generation phase was a combination of Liedholm’s and Ulrich & Eppinger’smethods. As Liedholm states, the concepts should be established by combining the meansdefined in the Function/Mean-tree [6]. Ulrich and Eppinger suggests a less structured waywhere the developer should search for solutions by interviewing lead users and search forpatents [4], which has been the most useful idea-generator in this project. To evaluatethe concepts a requirement check was made according to Liedholm, and then a list ofadvantages and disadvantages was produced.

37

Methodology

5.1 PlanningAccording to Figure 32, this phase aims to output a Construction Specification List basedon the task definition and present solution. The objective and problem description of thisthesis are defined and presented in Section 1. The objective was identified in accordancewith Saab along with the University’s requirements for the thesis.

Figure 32: Content of the Planning phase

5.1.1 Define TaskIn order to understand the problem and get the ability to define the objective, a criticalreview of the problem was made. The following questions were analyzed in accordancewith Liedholm’s concept development process [6]:

• What is the problem?

• Who has the problem?

• What is the goal?

• Which side-effects should be avoided?

• What are the limitations to solve the problem?

5.1.2 Situation AssessmentThe situation assessment performed is presented in Section 2, where a description of thepresent solution also is made. The market analysis investigates the existing solutions onthe market that meets the requirements for the system. The market within the area iswell distributed since the use of navigation systems occurs in many different applications.There are two main parts of the market; military sector and civilian sector. Althoughthis thesis aims to develop a system for military use, the main focus has been to findcomponents from the civilian sector. This is mainly due to the economical factor, since itearly in the market analysis became obvious that components with the same performancecan be found within both sectors but with very different pricing.

38

Methodology

5.1.3 Construction Specification List

Based on the task definition, with some inspiration from the market analyze, a detailedConstruction Specification List was made. The requirements defined by Saab at thebeginning of the project was mostly functional and no details was specified. Therefore,the amount of work dedicated to the production of the Construction Specification Listhas been higher than predicted. Some of the requirements have been defined after theconcept generation, since the components in the concepts have limited the design. Theexact specifications for the system and each component has not yet been defined. Thisis due to the fact that Saab still does not know how good the performance need to bein order to fulfill the purpose of the system. Therefore, the specifications are producedenough strictly to be able to build a prototype of the system and test it in order to seewhich parameters and components that possibly needs improvement.

5.2 Function AnalysisIn order to decompose the problem and define the main function and sub-functions, aFunction Analysis was performed.

Figure 33: Content of the Function Analysis

5.2.1 Problem Decomposition

The first step of the analysis was to define a simplified visualization of the system by usinga Black-Box. This is, according to Liedholm [6], a good way to define the main function,input and output of a system.

The technical principles of the system were identified based on the requirements anddesiderata defined in the Construction Specification List together with the overall purposeof the system. The questions answered in the task definition were used as a foundation forthe principles. Each technical principle can be seen as a function that should be fulfilledby the system. The functions were then combined with one or several means, which arethe tools able to execute the function.

5.3 Concept GenerationThe concept generation is the most central part of this project, though it is a quite straightforward process.

39

Methodology

Figure 34: Content of the Concept Generation phase

5.3.1 Combine meansAfter production of a detailed Construction Specification List and a break-down of theproblem, the generation of possible solutions was started. According to Liedholm [6],concepts can be elaborated by creating combinations of the means appurtenant eachfunction specified in the Function/Mean-tree. Some of the means were used in more thanone concept and some of them were combined into one solution.

5.3.2 Externally & internally searchThe second part of the concept generation phase consists of external and internal searchfor information and inspiration, in accordance with Ulrich and Eppinger’s theory [4]. Inthis project, some of the external search consisted of inquiries by experts from differentareas at Saab. Navigation systems are an important part of an aircraft, which meansthat there are a lot of competence within this area at Saab. This has been utilized in thegeneration of ideas that eventually led to the three final concepts. Also, information fromexperts at other companies has been collected, for example UMS Skeldar who themselvesuses telemetry systems to navigate their vehicles.

The actual techniques of navigation suitable for the system that should be developedare nothing new, which made the market analysis very useful for the concept generation.By looking into already existing solutions a high amount of inspiration on how the problemcan be solved was received.

The internal and external search have in this thesis gone hand in hand since the projectis performed by one single person. The internal search consisted mostly of search foradequate components to meet the requirements for the system. Since there are a highamount of available components within the navigation domain, the search was delimitedby the economical factor.

40

Methodology

5.4 Concept EvaluationTo examine the quality of the produced concepts, a two-step evaluation was performed asstated in Figure 35.

Figure 35: Content of the Concept Evaluation

5.4.1 Check if requirements are fulfilledThe first step of the evaluation was to investigate the fulfillment of the requirementsspecified in the Construction Specification List. The concepts were not yet fully specified,which according to Ullman [19] is a usual problem at this stage of the process.

Liedholm states the importance of acquainting oneself with the concepts and analyzethe possibilities before making any decisions [6]. This was made by analyzing each conceptseparately and comparing the solution with the requirements and desiderata.

As Ullman proposes [19], a feasibility judgement was made with the goal to emerge oneof the three following reactions; (1) it is not feasible and will not work; (2) it might workif something else happens; (3) it is worth considering. All three concepts were assignedwith the last one since they are all worth considering and develop further. Liedholm aswell states that the personal intuition can be used for the evaluation of concepts [6].

The requirement fulfillment check was performed in accordance with Ullman’s [19]go/no-go screening. The requirements were reformulated into questions in order to investigatewhether they were fulfilled or not.

5.4.2 List advantages and disadvantagesIn order to evaluate the quality of the concepts further, the advantages and disadvantageswere investigated. The concepts are in this stage compared relative each other, whichmeans that "simple solution" refers to simple in comparison with the other two.

The advantages and disadvantages were found partly by investigating existing solutionsthat are using the same techniques. By doing an external search for each mean used in theconcepts, conclusions could be drawn about negative and positive effects of the solution.Since the techniques used are well established at the market, it was easy to find evaluationsand test results for similar solutions. The information received from the internal searchmade in an earlier stage did as well contribute to the evaluation.

Liedholm states that if a concept receives too many disadvantages, it should be investigatedif it is possible to improve it [6]. In this case, none of the concepts were considered toobad and all of them were kept as previous developed.

41

Results

6 ResultsThe output and results from the concept development phases stated in the methodologyare presented in the following section.

6.1 PlanningDue to the absence of detailed requirements from Saab, the specifications were compiledwith an agile process with incrementally development of new requirements, along withimprovement of existing ones. For simplification, the requirements were sorted by differentgroups; Functional, Environmental and Technical. Some of the specifications listed mustnot be fulfilled in order to produce a usable product, and are therefore noted with a "D"for Desired. The functional, environmental and technical requirements and desiderataspecified for the system are displayed in the Construction Specification List in Figure 36.

Figure 36: Construction Specification List

43

Results

6.2 Function AnalysisThe main function, input and output was defined in a Black-Box, shown in Figure 37. Theinput to the system is data from satellites and information about the store’s position. Themain function is to measure the position in real-time in order to determine the trajectoryof the store. The system should output information about altitude, longitude, latitude andairspeed.

Figure 37: Black-Box model of the system

The technical principles that were identified are Measure 3D Position, Telemetry ofData in real-time and Withstand Harsh Environment, all defined as functions in theFunction/Mean-tree showed in Figure 38. Each function (dark grey box) was combinedwith one or several means specified below it in the tree.

Figure 38: Function/Mean-tree for the system

The first technical principle, Measure 3D Position, was solved by two different meansin the Function Analysis, GPS and INS. According to this, one concept based on theGlobal Positioning System and one concept based on a Inertial Navigation System wasproduced. Also, one concept with a combination of both GPS and INS was created. Thetwo remaining technical principles were constructed in an equal way for all three concepts.The three concepts created were developed based on the Function/Mean-tree, which inturn was inspired by the market analysis.

In order to solve the third technical principle, withstand the harsh environment thatarises in the store at the separation moment, a casing was designed to insulate the system.The main focus when designing the casing was to ensure a simple installation in the store,and hold the possibility of installation in different stores open. The unguided bombs wherethese systems should be used, consists of a missile-shaped steel casing with a fuse inside.The fuse works as a detonator and contains explosive charge.

44

Results

6.3 Concept GenerationThe Concept Generation process explained in Section 5.3 resulted in three concepts,presented below. The advantages and disadvantages found in the Concept Evaluationare presented adjacent to each concept description.

6.3.1 Concept 1 - GPSThe first concept is the most simple one, based on the Global Positioning System. Itconsists of a GPS sensor that receives data from satellites and outputs information aboutthe position and velocity. If the GPS sensor has a built-in data logger, all measured datawill be saved on that. If the GPS sensor does not have this, an external SD-card is requiredto save the data.

The GPS sensor are connected to a telemetry transmitter, which receives all collecteddata. The position- and velocity data are then, via the transmitter, streamed to a groundstation with a receiver. During a flight test, it is possible to view the data from the on-boardsystem in real-time at this station. This enables real-time evaluation of the bombs ballisticbehaviour. The functional flow of Concept 1 is visualized in Figure 39.

Position VelocityCollect satellite

dataGPS sensor Transmitter

Position Velocity

Receiver

Figure 39: Functional flow of Concept 1

The GPS is commonly used in navigation and measurement applications, which results ina broad market of different sensors. This makes Concept 1 a convenient solution if thedesire is to have a simple system with few components. By using a sensor that supportspost-processing of data using Differential GPS, the accuracy of the result can be highdespite the basic system.

45

Results

The following advantages and disadvantages summarises the function of Concept 1:

ADVANTAGES:

• Simple solution

• Low-cost solution

• High accuracy can be reached by post-processing the data

DISADVANTAGES :

• Possibly loss of GPS-reception under the wing

• Data-quality dependent on time, day and location (satellite-dependent)

46

Results

6.3.2 Concept 2 - INSThe second concept is based on an Inertial Navigation System (INS), consisting of gyroscopesand accelerometers. The number of those components are dependent on which configurationthat is chosen; either one 3-axis accelerometer and one 3-axis gyro, or three single-axisaccelerometers and three single-axis gyros. Accelerometers are navigating in an inertialreference frame, which means that the data measured needs to be transformed into thecorrect coordinate system. The gyroscopes are used to keep track of the direction in whichthe accelerometers are pointing.

The acceleration and directional data received from the sensors are sent to the navigationcomputer, where the axis transformation is performed. By integrating the accelerationtwice, the position and velocity for the object are obtained.

In the same way as in Concept 1, the position- and velocity data are sent to thetelemetry transmitter, which in turn streams the data to the ground station.

Acceleration Orientation

Accelerometers

Transmitter

Position Velocity

Orientation

Receiver

Gyroscopes

Collectacceleration &directional data

Axistransformation

Position Velocity

Orientation

NAVIGATION COMPUTER


In general, Inertial Navigation Systems gives highly accurate results, which makes themsuitable for aircraft navigation. INS is the most commonly used navigation techniquewithin aviation industry. Though, a high quality INS is expensive and therefore not the firstalternative in all flight applications. As distinct from the GPS, an INS is also measuringthe orientation of the object. This can be useful when information about the rotationalmovements of the object through the air is desired.The following advantages and disadvantages summarises the function of Concept 2:

ADVANTAGES:

• Independent of location - always functional

• Measures orientation as well

DISADVANTAGES:

• Integration drift - only accurate for a short period of time

• Vibrations may cause flaws in information data

47

Results

6.3.3 Concept 3 - GPS/INSThe third concept is a combination of the two previous ones, using both GPS and INS.In the same way as is Concept 2, acceleration and directional data are measured withaccelerometers and gyroscopes. This data are axis-transformed and integrated in thenavigation computer, which then outputs position-, velocity and directional data.

In parallel with the accelerometer and gyroscopes, an GPS measures the position aswell. The data from the INS and GPS are merged with the use of an Kalman Filter. Thefilter uses the measurements from the sensors and calculates, together with a known modelof the dynamic system, the current optimal state of the system. The Kalman filter canestimate a position with high accuracy even with imperfect or uncertain measurements.

Acceleration Orientation

Accelerometers

Transmitter

Position Velocity

Orientation

Receiver

Gyroscopes

Collectacceleration &directional data

Axistransformation

GPS sensor Collect satellitedata

Position Velocity

estimates

estimates

Kalman filter

Correctednavigationparameters

PositionVelocity

Orientation

NAVIGATION COMPUTER


The corrected navigation parameters are saved by using an SD-card. In the same way asin the other concepts, the data are then transmitted to a ground station where it can beanalyzed in real-time. This concept also outputs information about the object’s orientation,which comes with the advantages mentioned in the description of Concept 2.

48

Results

The following advantages and disadvantages summarises the function of Concept 3:

ADVANTAGES:

• Higher accuracy without need for post-processing

• Fast sampling rate

• Can analyze the separation moment as well

• The GPS ans INS compensates for each other’s faults

DISADVANTAGES:

• High-cost

• More components required

6.3.4 Conceptual Design of the System CasingIn order to ensure that the system can withstand the harsh environment that occurs insidethe store during the separation, a casing was designed. The main focus for this design isto fulfill the requirement of simple installation and also hold the possibility of installationin other stores open.

Figure 42: Example of two fuses used in unguided bombs

The flight test aimed to be performed with the system developed should be performed withunloaded bombs. Thus, the fuse is not included in the bomb body during those tests. Inorder to simplify the installation of the on-board system, the casing is therefore designedin the same way as the fuse; a cylinder-shaped aluminium case. This enables the systemto easily replace the fuse during these flight tests. The dimensions of the cylinder arethe same as the original fuse, and the mounting threads as well. This enables an simpleinstallation in all unguided bombs, since they have the same fuse.

To preserve the system during high G forces and vibrations, an isolating material shouldbe enfolded around the system components within the cylinder. An appropriate materialfor this is not yet investigated.

49

Results

6.4 Concept EvaluationThe concepts were evaluated by investigating whether the requirements were fulfilled ornot. Some of them were not possible to verify since the concepts are still general and thefulfillment is dependent on which specific component that is chosen. The concepts weremarked with a colour with the following meaning:

• Green - requirement/desiderata fulfilled

• Yellow - requirements/desiderata not yet possible to verify

• Red - requirement/desiderata not fulfilled at the moment.

Figure 43: Verification of the Construction Specification List

The different requirements and desiderata are verified according to:

#1 To ensure that the installation does not have any influence on the separation, allof the components are installed inside the fuse space inside the bomb. The separationwill therefore not be affected since nothing is attached on the outside of the store.As well the center of gravity does not change since the system replaces the fuse.

50

Results

#2 The system will not affect the trajectory of the store since the center of gravitywill be unchanged. Also, the fact that no components are attached on the outside ofthe store will ensure that the aerodynamics does not change.

#3 The system, independent on component type, is independent of the aircraft.It is therefore possible to test it before installing it in the bomb and installing thebomb to the aircraft.

#4 The data can be saved in different ways. As mentioned in the concept description,either an SD-card or a data logger is included in the system. An other possiblesolution for concept 2 is to use a complete INS with a data logger built in thenavigation computer. For concept 3, a complete GPS/INS with a built in datalogger could be an alternative.

#5 Whether the reliability of 95 percent is fulfilled or not is yet not possible toverify, since it requires several trials to be performed with the final built system.

#6 All three concepts developed includes a telemetry-system, which contributesto the fulfillment of this desideratum.

#7 The desideratum that the pilot should be able to verify the functionality of thesystem before separation is not fulfilled. This is due to the fact that the telemetryis connected to a ground station and not the aircraft. The main reason to this isregulations according additional aircraft antennas. Though, this is still in one wayfulfilled, since the aircraft has radio contact with the ground station, which in turnhas contact with the system in the store.

#8 The system is easy to install in the bomb since it is designed to fit in the fusespace. Since the fuse is replaced by the system, it is also easy to attach with thesame threads.

#9 & #10 The accuracy of the position and heading are still not yet possibleto verify, since it depends in the specific components chosen. For example, thereare many different GPS sensors available at the market with different performance.Though, a study of possible sensors for all three concepts are investigated and listedin Appendix B (Saab Confidential).

#11 The system is possible to install in several different bombs in the Mk80-series,since they have the same fuse. The possibility to install in other types of bombs arebig since the system could be inserted in a casing with another shape or size as longas it fits. Whether the system can be easily installed in a store without a fuse is notinvestigated in this thesis.

#12 This requirement is not yet possible to verify, since it depends on the specificcomponents chosen. However, the investigation of possible components that wasmade, attached in Appendix B (Saab Confidential), shows that there are componentsavailable that fulfills this. Also, the insulating casing will help the components to

51

Results

withstand the forces.

#13-#15 Those requirements are all dependent on the specific components chosen.They have all been investigated, and there are components available that fulfills allof these, see Appendix B (Saab Confidential). The requirements are though not yetverified since the final concept and components are not chosen.

#16 Since the casing is designed in the same way as the fuse, it is densely andtherefore waterproof.

#17 This requirement is verified by investigating if there are any batteries thatcould power a telemetry-system that should deliver an output power of 1 W and stillmanage the weight and space limits. Also the position measuring sensors are in needof power, but they requires a very small amount and therefore the output power ofthe telemetry transmitter is the limiting parameter. For example, a battery with anominal voltage of 3,6 V and 10 Ah (Ampere hours), could output 1 W for 36 hours.A battery like this will weight around 100 grams and have a size of 6x3x3 cm.

#18 An investigation of suitable components for the system was made, see AppendixB (Saab Confidential). This shows that a typical GPS sensor has a weight of around30-40 grams. A typical 3-axis accelerometer weights around 80 grams and a completeGPS/INS system weights around 100 grams.

#19 This requirement is fully dependent on which transmitter that is chosen. Thereare several transmitters available that could output 1 W. How many Watts that arerequired is also dependent on which antennas that are used, which is not investigatedyet.

#20 This requirement depends on the the specific components in the system andare therefore not yet verified.

52

7 DiscussionThis chapter aims to discuss the methodology used for the thesis. The results achievedfrom the concept development are also discussed and critically reviewed.

7.1 Discussion of MethodologyThe methodology elaborated in this thesis consists of four phases that are going to bediscussed in this section.

7.1.1 PlanningThe task and appurtenant requirements were at the beginning of the project defined bySaab based on their need of the product. The root of the problem and purpose of thesystem were well defined from the start. Though, the requirements were mostly functionaland did not define the limitations or boundaries of the requested system. Due to this, theamount of work dedicated to the production of the Construction Specification List washigher than expected. It became obvious early in the project that the system requirementsmust be more specific and substantial in order to be able to produce a useful design. Asthe Planning phase progressed, the problem did grow and became more complex in theinterim. This made the Planning phase more extensive than expected.

At the end, the conclusion can be drawn that the majority of the time spent on thethesis was applied to the Planning. This is in accordance with the desire from Saab, sincethey at the beginning requested a pre-study within the area in order to find out if theproblem is possible to solve. Though, the planning made in the beginning of the projectwas not taking this aspect into consideration, and the time spent on each phase is not inaccordance with the Gantt-schedule showed in Figure 44.

The situation assessment was pretty straight forward and progressed as planned. Though,the absence of detailed requirements made it complicated to search for existing solutions.It was hard to search for information about existing solutions when the desired solutionwas not fully specified.

7.1.2 Function AnalysisTo get a simple and explicit picture of the system, the problem was decomposed. At first,a Black-Box was made in order to visualize the system clearly. The Black-Box method wasprimarily chosen since it is a simple way to define the input, output and main function ofa system. It is also recommended by both Liedholm [6] and Ullman [19], which makes thechoice even easier to motivate. However, the system may be too complex to get a valuableresult from the Black-Box. Also, the method seams to be adapted for a more mechanicalsystem or product. This gets obvious in the definition of input, which is usually some kindof energy or work. In this thesis, the system does not really have any input, which makesthe Black-Box a bit misleading.

The technical principles defined in the Function Analysis is based on the ConstructionSpecification List and the purpose of the system. Probably, it would have been possible to

Discussion

define more technical principles if there had been more specific requirements available atthe time. Though, at this stage of the project a Function/Mean-tree at the general levelis sufficient in order to start a Concept Generation.

The Function/Mean-tree was very valuable for the Concept Generation. The meansproduced to solve each sub-function could easily be combined in order to develop differentconcepts. If the system had been even more composed in the Function Analysis, theoutcome had probably been a higher amount of concepts. But as stated before, this hadclaimed more detailed specifications.

7.1.3 Concept Generation

All concepts were generated by combining the means from the Function/Mean-tree, whichin turn had been created with inspiration from the internal and external search. Theexternal search seemed to be a good way to gather information since the navigationtechniques are commonly used both within Saab and at the civilian market. It turnedout to be very useful in the Concept Generation.

The way to create solutions by combining means in order to solve each sub-functionindependently, was successful since the sub-functions are not related to each other regardingfunctionality. Each sub-function is functional by itself, and therefore it was good togenerate concepts with this in mind.

7.1.4 Concept EvaluationIn this project, the techniques to solve the problem are rather limited to the ones used inthe concepts produced. This made the amount of concepts quite low and the evaluationprocess even more difficult since there were less to sift out. The evaluation was mostlya check of how good the concepts fulfills the requirements and desiderata. Some of therequirements were at this stage of the project not possible to verify, since they requiretesting of the system.

7.2 Discussion of resultsThe pre-study performed resulted in a concept development where three concepts wereproduced. As mentioned before, the largest limitation has been the absence of detailedrequirements. However, based on the aim for this thesis, the amount of concepts and thematurity of each solution seems feasible and enough.

The concepts developed are quite similar to each other. The only thing that distinguishthem is the technique used to measure the position. It is possible that there are othersuitable solutions for position measuring than the ones used, but based on the researchmade there are no reason not to settle for the solutions found.

Only one design was developed for the casing of the system. This seemed to be themost valuable way to fulfill the requirements of simple installation and possibility to installin different types of stores. The room inside the bomb is very limited, which makes theamount of possible solutions low. Since the fuse is excluded in the separation tests thissystem is designed for, the best and most simple solution is to use the fuse-space. This alsoenables the desideratum of possibility to install in different stores, since all the unguided

54

Discussion

bombs has the same size of fuse, independent on bomb size. This also enables an easyinstallation since the space and attachment is already in place.

All requirements are either fulfilled or not yet possible to verify. The ones that not yetcan be verified are mostly the ones that are fully dependent on which specific componentthat is used. Though, if assuming that only components that fulfills the environmentaland accuracy requirements are chosen, almost all requirements are fulfilled.

The only desideratum that is not fulfilled is the one that specifies that the pilot shouldbe able to verify the functionality of the system before separation. This is due to thefact that the telemetry is chosen to be linked to a ground station, and not to the aircraft.This could have been solved by sending the data from the system to the aircraft instead,but was limited by regulations regarding additional aircraft antennas. The function of thedesideratum is however fulfilled even so, since the pilot has contact with the ground stationduring the test.

The choice of antennas used for the GPS and telemetry are not investigated due tolimited time. Since the antenna gain has a very large impact on the quality of the data,this need to be accurately examined.

Which solution that is the most suitable remains unknown. The main factors that willdetermine this is the required performance and the economy. The most high performancesolution is Concept 3, but it is also the most expensive one. Therefore, the exact performancerequired need to be determined before choosing which solution is the best. The best wayto find this out is to realize the concepts into prototypes and perform a flight test tosee how the system behaves and how the data-quality becomes with the different sensors.Therefore, the concept selection is delegated to Saab for further investigation and all threeconcepts are handed over in order to let them decide the desired outcome.

Another aspect is if there is a desire to use this system in other flight tests as well.For example, if using Concept 2 or 3, also the rotational movement of the object can beanalyzed. This could be useful for separation trials for an object with a continuously shiftedCenter of Gravity (CG). Another application suitable for those concepts is to analyse theseparation moment of the store, in order to ensure that the store does not hit the aircraft.

By taking the last mentioned in to account, the further analyze of desired performancegets even more important. If the system can be useful for other applications as well, thebudget can probably be increased, which will in turn increase the accuracy and functionalityof the system.

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Conclusion

8 ConclusionIn this chapter, the question formulations stated in Section 1 are going to be responded.

Given the limitations, requirements and desiderata, is there one or severalconcepts that fulfill those?Yes, three concepts have been carried out. All of the concepts developed have the potentialto fulfill all requirements and desiderata. They are all dependent on which sensors thatare chosen.

What limitations does each concept have?Concept 3 is the most high performance one, which will give the most accurate result.This concept is also the most rigid one since the different sensors are compensating foreach others deficits. The only limitation of this concept is the high-cost.

Concept 1 is limited by the fact that the GPS sensor may loose reception when attachedunder the wing. This can result in a loss of data after the separation, dependent on thelock-time of the sensor.

Concept 2 does not have any limitations in the collection of data. Though, the dataquality and accuracy may be bad after a while due to an eventual integration drift.

8.1 Recommendation of future workSince this thesis was a pre-study within a larger project at Saab, the aim of the wholeproject is not yet fulfilled. Some recommendations of how to proceed to reach the desiredresult are presented here.

The three concepts developed should be further investigated regarding their function.Since they are all component dependent, the best way to accomplish this is to performtesting. As a first step, each component in the concepts could be tested by itself. Forexample, a suitable GPS sensor could be tested in order to investigate the reception underthe wing and the lock-time after loss of reception. This will give a better view of thedesired performance of the sensors. The same concerns the accelerometers and gyroscopesin the INS.

By using Frii’s Transmission Equation (presented in Section 4), a suitable telemetrysystem can be found. The best way is to specify either the transmitting components orthe receiving components, and then calculate the required performance of the other ones.Also, an accurate investigation of suitable antennas needs to be performed. When suitablecomponents have been found according to the equation, the system should be tested to seeif the data stream has the required quality.

In conclusion, the concepts and their associated components should be evaluated withground- and flight-testing. This will lead to achievement of the project’s purpose withinthe desired time frame. Also, the possibilities of using this system for other flight testapplications should be investigated in order to increase the value even more.

57

References[1] Perkins C. Flight Test Manual. 2018;.

[2] 65210E Inertial Measurement System with External Inputs Data Acquisition - TMKit.TE Connectivity - Measurement Specialities; 2017. Available from: https://www.te.com/usa-en/product-CAT-RIN0010.html?source=header-match#guest-click.

[3] Mti-G-710. Xsens, Initial Sensors; 2019. Available from: https://www.xsens.com/products/mti-g-710/.

[4] Ulrich K, Eppinger S. Product Design and Development. 3rd ed. McGraw-Hill; 2003.

[5] Ullman D. The Mechanical Design Process. Int. ed. McGraw-Hill; 2010.

[6] Liedholm U. Systematisk konceptutveckling. Linköping University; 1999.

[7] The Global Positioning System; 2017. Available from: https://www.gps.gov/systems/gps/.

[8] Trilateration vs Triangulation - How GPS Receives Work. GIS Geography;. Availablefrom: https://gisgeography.com/trilateration-triangulation-gps/.

[9] An Introduction To GNSS, Chapter 5: Real-Time Kinamatic (RTK). NovatelInc.; 2019. Available from: https://racelogic.support/01VBOX_Automotive/01General_Information/Knowledge_Base/How_does_RTK_(Real_Time_Kinetic)_Work%3F.

[10] Woodman O. An introduction to inertial navigation. Computer Laboratory; 2007.

[11] Andrisani D. Fundamentals of Strapdown Inertial and PGS-Aided Navigation; 2002.

[12] PiezoStar Miniature Triaxial Accelerometer; 2018. Available from: https://www.kistler.com/en/product/type-8766a/.

[13] Maxwell G. Atom Interferometer Gyroscopes; 2015. Available from: https://www.slideshare.net/MaxwellGregoire/gyroscopes-grad-talk-2.

[14] Esfandyari J, Nuccio RD, Xu G. Introduction to MEMS gyroscopes; 2010. Availablefrom: https://electroiq.com/2010/11/introduction-to-mems-gyroscopes/.

[15] Welch G, Bishop G. An Introduction to the Kalman Filter;.

[16] System Technology. Datatel Telemetry; 2019. Available from: https://www.datatel-telemetry.de/en/system-technology/systems.

[17] About SAAB, history; 2019. Available from: https://saabgroup.com/about-company/f.

[18] Cinetheodolites. Denel Overberg Test Range; 2019. Available from:http://www.denelotr.co.za/products--services/range-instrumentation/optical-systems.

59

https://www.te.com/usa-en/product-CAT-RIN0010.html?source=header-match#guest-click

https://www.te.com/usa-en/product-CAT-RIN0010.html?source=header-match#guest-click

https://www.xsens.com/products/mti-g-710/

https://www.xsens.com/products/mti-g-710/

https://www.gps.gov/systems/gps/

https://www.gps.gov/systems/gps/

https://gisgeography.com/trilateration-triangulation-gps/

https://racelogic.support/01VBOX_Automotive/01General_Information/Knowledge_Base/How_does_RTK_(Real_Time_Kinetic)_Work%3F



https://www.kistler.com/en/product/type-8766a/

https://www.kistler.com/en/product/type-8766a/

https://www.slideshare.net/MaxwellGregoire/gyroscopes-grad-talk-2

https://www.slideshare.net/MaxwellGregoire/gyroscopes-grad-talk-2

https://electroiq.com/2010/11/introduction-to-mems-gyroscopes/

https://www.datatel-telemetry.de/en/system-technology/systems

https://www.datatel-telemetry.de/en/system-technology/systems

https://saabgroup.com/about-company/f

https://saabgroup.com/about-company/f

http://www.denelotr.co.za/products--services/range-instrumentation/optical-systems

http://www.denelotr.co.za/products--services/range-instrumentation/optical-systems

REFERENCES

[19] Ullman D. The Mechanical Design Process. 3rd ed. McGraw-Hill; 2003.

[20] Krus P. Engineering Systems Design, Lecture notes; 2017.

[21] 3.3: Projectile Motion. Physics, Libre Text; 2019. Available from: https://phys.libretexts.org/Bookshelves/University_Physics/Book%3A_Physics_(Boundless)/3%3A_Two-Dimensional_Kinematics/3.3%3A_Projectile_Motion.

[22] Malysheva J. Integrated aircraft navigation system. 2014;.

[23] Hofmann-Wellenhof B, Lichtenegger H, Collins J. GPS Theory and Practice. Fifth,revised ed. SpringerWienNewYork; 2001.

[24] What is GPS?; 2017. Available from: https://www8.garmin.com/aboutGPS/.

[25] The Physics of GPS - Trilateration. Quantum Technologies;. Availablefrom: https://www.stem.org.uk/system/files/elibrary-resources/2018/08/Quantum%20Tech_Teacher%20guide_GPS%20and%20Trilateration.pdf.

[26] How does DGPS (Differential GPS) work?. Ragelogic Spacecenter; 2019. Availablefrom: https://racelogic.support/01VBOX_Automotive/01General_Information/Knowledge_Base/How_does_DGPS_(Differential_GPS)_work%3F.

[27] How does RTK (Real Time Kinamatic) work?. Ragelogic Spacecenter; 2019. Availablefrom: https://racelogic.support/01VBOX_Automotive/01General_Information/Knowledge_Base/How_does_RTK_(Real_Time_Kinetic)_Work%3F.

[28] Inertial Navigation Systems (INS) explained. Oxford Technical Solutions;. Availablefrom: https://www.oxts.com/what-is-inertial-navigation-guide/.

[29] Inertial Navigation System (INS) (Part one). Flight Literacy;. Available from: https://www.flightliteracy.com/inertial-navigation-system-ins-part-one/.

[30] Inertial Navigation System (INS). SKYbrary; 2017. Available from:https://www.skybrary.aero/index.php/Inertial_Navigation_System_(INS)#Stabilised_Platform_INS.

[31] Goodrich R. Accelerometers: What they are and how they work; 2013. Availablefrom: https://www.livescience.com/40102-accelerometers.html.

[32] Plitnik G. Accelerometers. Salem Press Encyclopedia of Science; 2018.

[33] Position Determination using Accelerometers; 2015. Available from: http://kionixfs.kionix.com/en/document/AN013%20Position%20determination%20using%20Accelerometers.pdf.

[34] A Simple Description of the Sagnac Effect. Physics Insights;. Available from: http://www.physicsinsights.org/sagnac_1.html.

[35] Hide C, Moore T, Smith M. Adaptive Kalman Filteringfor Low-cost INS/GPS; 2003. Available from: https://www.cambridge.org/core/journals/journal-of-navigation/article/adaptive-kalman-filtering-for-low-cost-insgps/7D17D4A198ED56F06C7F590E90467BC3.

60

https://phys.libretexts.org/Bookshelves/University_Physics/Book%3A_Physics_(Boundless)/3%3A_Two-Dimensional_Kinematics/3.3%3A_Projectile_Motion



https://www8.garmin.com/aboutGPS/

https://www.stem.org.uk/system/files/elibrary-resources/2018/08/Quantum%20Tech_Teacher%20guide_GPS%20and%20Trilateration.pdf

https://www.stem.org.uk/system/files/elibrary-resources/2018/08/Quantum%20Tech_Teacher%20guide_GPS%20and%20Trilateration.pdf

https://racelogic.support/01VBOX_Automotive/01General_Information/Knowledge_Base/How_does_DGPS_(Differential_GPS)_work%3F

https://racelogic.support/01VBOX_Automotive/01General_Information/Knowledge_Base/How_does_DGPS_(Differential_GPS)_work%3F



https://www.oxts.com/what-is-inertial-navigation-guide/

https://www.flightliteracy.com/inertial-navigation-system-ins-part-one/

https://www.flightliteracy.com/inertial-navigation-system-ins-part-one/

https://www.skybrary.aero/index.php/Inertial_Navigation_System_(INS)#Stabilised_Platform_INS

https://www.skybrary.aero/index.php/Inertial_Navigation_System_(INS)#Stabilised_Platform_INS

https://www.livescience.com/40102-accelerometers.html

http://kionixfs.kionix.com/en/document/AN013%20Position%20determination%20using%20Accelerometers.pdf



http://www.physicsinsights.org/sagnac_1.html

http://www.physicsinsights.org/sagnac_1.html

https://www.cambridge.org/core/journals/journal-of-navigation/article/adaptive-kalman-filtering-for-low-cost-insgps/7D17D4A198ED56F06C7F590E90467BC3




REFERENCES

[36] Pham-Van T, Nguyen-Van T. 15-State Extended Kalman Filter Design for INS/GPSNavigation System; 2015.

[37] Maybeck P. Stochastic Models, Estimation and Control, Volume 1; 1979.

[38] Data Loggers. Intab AB; 2019. Available from: https://intab.se/en/products/data-loggers.

[39] Rouse M. Secure Digital card (SD card); 2017. Available from: https://searchstorage.techtarget.com/definition/Secure-Digital-card.

[40] An Introduction to SD Standards. SD Association; 2019. Available from: https://www.sdcard.org/developers/overview/index.html.

[41] Friis H. A Note on a Simple Transmission Formula. 1946;.

[42] Understanding Antenna Gain. Telewave Inc.; 2018. Available from: https://www.telewave.com/2018/02/08/understanding-antenna-gain/.

[43] Omni-Directional Antennas vs Uni-Directional (Yagi) Antennas:Which Is Right for You?. Alex B. and James N.; 2019.Available from: https://www.wilsonamplifiers.com/blog/omnidirectional-antennas-vs-unidirectional-yagi-antennas-which-is-right-for-you/.

[44] Directivity. Antenna-theory; 2015. Available from: http://www.antenna-theory.com/basics/directivity.php.

[45] Nomenclature of the frequency and wavelength bands used in telecommunications.International Communication Union; 2015. Available from: https://www.itu.int/dms_pubrec/itu-r/rec/v/R-REC-V.431-8-201508-I!!PDF-E.pdf.

61

https://intab.se/en/products/data-loggers

https://intab.se/en/products/data-loggers

https://searchstorage.techtarget.com/definition/Secure-Digital-card

https://searchstorage.techtarget.com/definition/Secure-Digital-card

https://www.sdcard.org/developers/overview/index.html

https://www.sdcard.org/developers/overview/index.html

https://www.telewave.com/2018/02/08/understanding-antenna-gain/

https://www.telewave.com/2018/02/08/understanding-antenna-gain/

https://www.wilsonamplifiers.com/blog/omnidirectional-antennas-vs-unidirectional-yagi-antennas-which-is-right-for-you/

https://www.wilsonamplifiers.com/blog/omnidirectional-antennas-vs-unidirectional-yagi-antennas-which-is-right-for-you/

http://www.antenna-theory.com/basics/directivity.php

http://www.antenna-theory.com/basics/directivity.php

https://www.itu.int/dms_pubrec/itu-r/rec/v/R-REC-V.431-8-201508-I!!PDF-E.pdf

https://www.itu.int/dms_pubrec/itu-r/rec/v/R-REC-V.431-8-201508-I!!PDF-E.pdf

A First appendix

Figure 44: Gantt-schedule for the project

63

Documents

On-board Data Acquisition System - DiVA portalliu.diva-portal.org/smash/get/diva2:1340302/FULLTEXT01.pdfOn-board Data Acquisition System Conceptual Design of an Airdrop Tracking System