““Our dependence [on space] has never been Our dependence [on space] has never been higher. In fact, it’s integrated into how we fight higher. In fact, it’s integrated into how we fight wars today so deeply that it is hard to imagine wars today so deeply that it is hard to imagine

taking space out of the equation.”taking space out of the equation.”

Gen William L Shelton, CinC USAF Space CommandGen William L Shelton, CinC USAF Space CommandSpeech to U.S. National Space Symposium, 12 Apr 11Speech to U.S. National Space Symposium, 12 Apr 11

Satellite & Data Communication for Satellite & Data Communication for Air CadetsAir Cadets

Unit AimUnit Aim

The aim of this unit is to give learners knowledge of satellite and data

communication systems and networks for Air Cadets.

CLASSIFICATIONCLASSIFICATION

UNCLASSIFIEDUNCLASSIFIED

Unit IntroductionUnit Introduction

This unit gives learners knowledge of satellite and data communication systems and networks that are required at ATC

Senior and Master Air Cadet level.

This unit introduces the principles and equipment used in satellite and data communication. It explores the types, orbits

and roles and construction of satellites, and describes the basic function of a Global Positioning System.

The unit also develops an understanding of types of data communications networks and mobile communication.

On completion of this unit a learner should:

•Know main types and roles of satellites and Know main types and roles of satellites and principles of earth orbit.principles of earth orbit.

•Know components and principles of a Know components and principles of a Global Positioning SystemGlobal Positioning System

•Know principles of data communicationKnow principles of data communication

•Know types and roles of mobile Know types and roles of mobile communicationcommunication

Learning OutcomesLearning Outcomes

UK Space PrimerUK Space Primer

ScopeScope

• The Space Environment The Space Environment • OrbitsOrbits• LaunchLaunch• The Global Positioning SystemThe Global Positioning System• The Principles of Data CommunicationThe Principles of Data Communication• The Types & Roles of Mobile CommunicationThe Types & Roles of Mobile Communication• SummarySummary• QuestionsQuestions

7

The Space EnvironmentThe Space Environment

Reference:

Chapter 1; UK Space Primer

Space CharacteristicsSpace Characteristics• No geographical boundaries

• Freedom of movement

• Unique characteristics

The Boundary Between Air & SpaceThe Boundary Between Air & Space

• 150km• Spacecraft in orbit

• 100km• Limit of aerodynamic

control

• 80km• US Definition

9

150

100

80

The Space EnvironmentThe Space Environment

• An environment characterised by:• High energy particles• Fluctuating magnetic fields• Variable temperatures• No aerodynamic forces

– The laws of orbital motion

10

Key Environmental RegionsKey Environmental Regions

11

Troposphere

Stratosphere

Mesosphere

Thermosphere

Exosphere

Magnetosphere

Terrestr

ial Weather

Space Weather

Ionosphere

Orbits - Definition of TermsOrbits - Definition of Terms

Apogee and PerigeeApogee and Perigee

ApogeeFurthest point from Earth

PerigeeClosest point to Earth

Ground TraceGround Trace

A ground trace is the projection of a satellite’s 3D orbit onto the earth’s surface as a 2D representation

Common OrbitsCommon Orbits

LEO MEO GEO

HEO

850 km101 MINUTES24,600 KPH

~20,830 km~20,830 km11 HRS 58 MIN~14,330 KPH~14,330 KPH

~36,160 km23 HRS 56 MIN~11,160 KPH

~800-40,000 km11 HRS 58 MIN

~26,000-8,000 KPH~26,000-8,000 KPH

Orbit size determines time for one orbit

Orbit size and shape also determines the speed

Earth NOT to scale !

Orbital MechanicsOrbital Mechanics• Basic Orbits Include:

• Low Earth Orbit (LEO), including sun-synchronous• Medium Earth Orbit (MEO) Also called semi-synchronous• Geosynchronous Earth Orbit (GEO) including

Geostationary.• Highly Elliptical Orbit (HEO) including Molniya

• Spacecraft obey Kepler, not Bernoulli• Satellite manoeuvres require

– Deliberate planning

– Time

– Fuel (limited)

Low-Earth Orbit (LEO)Low-Earth Orbit (LEO)

Altitude 160 – 2000 kmAltitude 160 – 2000 km

LEO Orbit – 2D Ground TraceLEO Orbit – 2D Ground Trace

Sun-Synchronous OrbitsSun-Synchronous Orbits

• Near-Polar, 97°-99° InclinationNear-Polar, 97°-99° Inclination• 760 - 860 km760 - 860 km

LEO Sun-Synchronous OrbitLEO Sun-Synchronous Orbit2D Ground Trace2D Ground Trace

Medium Earth Orbits (MEO) Medium Earth Orbits (MEO) 2D Ground Trace2D Ground Trace

• Period: 2 – 24hrs • Average = 12 hour period

• Altitude: 2000 – 35786 km, Near Circular• Average 20,800 km

GeostationaryGeostationary

Highly Elliptical Orbits (HEO)Highly Elliptical Orbits (HEO)ApogeeHigh Altitude

PerigeeLow Altitude

HEOHEO

HEO 2D Ground TraceHEO 2D Ground Trace

Orbital Example – Earth FixedOrbital Example – Earth Fixed

Orbital PertubationsOrbital Pertubations

AtmosphereOrbital Decay

Effect of the AtmosphereEffect of the Atmosphere

Height (km) Life

200 2 weeks

1000 1000yrs

36000 1Myrs

Effect of the Earth’s ShapeEffect of the Earth’s Shape

TOP VIEWTOP VIEW SIDE VIEWSIDE VIEW

15m15m

15m15m

7.5m7.5m 7.5m7.5m

EQUATOREQUATOR

12 714 km12 714 km

12 756 km12 756 km

N Pole

Orbital PertubationsOrbital PertubationsThese are subtle but accumulative effect on an orbit

• Nodal regression• The orbital plane effectively twists around the earth• This is because of the shape of the Earth. • This effect is known as Orbital Twist.

• Perigee Rotation• This effect appears as a twisting of the satellites position

relative to the Equator.• Therefore, satellites need to be managed, in effect ‘flown’.

Applications of OrbitsApplications of Orbits• LEO

• Earth Observation with resolution• Communications

• MEO Missions• Global Navigation Satellite Systems

• GEO • Communications• Earth Observation with persistence

• HEO • Communications• Earth Observation with persistence

Persistence………Persistence………

………….versus Resolution.versus Resolution

Orbital RequirementsOrbital Requirements

LEO

Coverage

Dwell Time

Revisit Time

Resolution & Power Requirements

GEO c.700

Achieving OrbitAchieving Orbit

Initial LaunchInitial Launch

Direct ascent into low altitude orbit

Data TableData TableEarth Gravitational

Force Mass of Earth Radius of Earth Orbital Height Orbital Velocity Orbital Period Energy Required to Achieve Orbit

6.67E-11 5.98E+24 6.378E+06 12 7900.7 84.7 3.133E+07

6.67E-11 5.98E+24 6.378E+06 19 7896.3 84.9 3.136E+07

6.67E-11 5.98E+24 6.378E+06 100 7846.8 86.5 3.175E+07

6.67E-11 5.98E+24 6.378E+06 200 7786.9 88.5 3.222E+07

6.67E-11 5.98E+24 6.378E+06 300 7728.4 90.5 3.267E+07

6.67E-11 5.98E+24 6.378E+06 400 7671.2 92.6 3.311E+07

6.67E-11 5.98E+24 6.378E+06 500 7615.2 94.6 3.354E+07

6.67E-11 5.98E+24 6.378E+06 600 7560.5 96.7 3.396E+07

6.67E-11 5.98E+24 6.378E+06 700 7506.9 98.8 3.436E+07

6.67E-11 5.98E+24 6.378E+06 800 7454.4 100.9 3.475E+07

6.67E-11 5.98E+24 6.378E+06 900 7403.0 103.0 3.514E+07

6.67E-11 5.98E+24 6.378E+06 1000 7352.7 105.1 3.551E+07

6.67E-11 5.98E+24 6.378E+06 1100 7303.3 107.3 3.587E+07

6.67E-11 5.98E+24 6.378E+06 1200 7255.0 109.4 3.622E+07

6.67E-11 5.98E+24 6.378E+06 20000 3888.6 710.6 5.498E+07

6.67E-11 5.98E+24 6.378E+06 35789 3075.6 1436.3 5.781E+07

Hohman Transfer OrbitHohman Transfer Orbit

Initial Orbit

Transfer Orbit

Final Orbit

On Orbit On Orbit ManoeuvreManoeuvre Basics Basics

• Attain initial on-orbit station.• Maintain assigned position (all Geo satellites).• Modify orbit to meet new mission requirements.

On-board motors (“thrusters”) are fitted to modify the satellite’s orbit to:

RepositioningRepositioning

• Primarily for GEO satellites .• Using fuel shortens life.• Takes weeks or months to complete the manoeuvre.• Takes capability away from users.

Moving satellite to a higher or lower orbit:

42

The Global Positioning System The Global Positioning System (GPS)(GPS)

2nd USAF Space Operations Squadron

System DescriptionSystem Description

Navigational Signals

Ranging CodesSystem TimeClock CorrectionPropagation DelaySatellite Ephemeris Satellite Health

Downlink DataSatellite Ephemeris DataClock Data

Uplink DataSatellite Ephemeris Corrections Clock Data Corrections

Space Segment

Control Segment

User Segment

SPACE SEGMENTSPACE SEGMENT

GPS SatellitesGPS Satellites

• 24-satellite constellation• Six orbital planes, four satellites per plane• Semi-synchronous, circular orbits (~11,000 mi)• 12-hr ground-repeating orbits

Orbital PlanesOrbital Planes

The GPS Constellation utilises the Medium Earth OrbitThe GPS Constellation utilises the Medium Earth Orbit

CONTROL SEGMENTCONTROL SEGMENT

Control SegmentControl Segment

Monitor Stations

Uplink Station

Master Control Station

Downlink S Band Up/ Downlink

Collect Range DataMonitor Navigation Services

Navigation EstimationSatellite ControlSystems Operation

Transmit: - Navigation Data - CommandsCollect Telemetry

GPS Satellite

Satellite Links Satellite Links

USER SEGMENTUSER SEGMENT

GPS ServicesGPS Services

•Standard Positioning Service (SPS)•Uses Coarse Acquisition Code (C/A Code) only•Models Ionospheric errors•Think ‘civilian GPS’

•Precise Positioning Service (PPS)•Uses C/A Code and Precision Code (P-Code) •Calculates Ionospheric errors•Has encryption capability (Y code) •Think ‘Military GPS’

52

GPS Military MissionsGPS Military MissionsNavigation• Position, Velocity and Time

• Worldwide• Any weather• Any time

Time• Users calculate GPS time

• GPS time will be within 1000ns of UTC• Time transfer to within 100ns of UTC

• Synchronizes digital communications

53

GPS PositionGPS Position

•To determine a GPS position:•Distance to satellites•Satellite orbit/position•Earth’s shape•Coordinate reference framework

54

GPS SolutionGPS Solution

55

GPS SolutionGPS Solution•c = speed of light (3x108 m/s)•tt,1, tt,2, tt,3, tt,4 = times that GPS satellites 1, 2, 3, and 4, transmitted their signals. These times are provided to the receiver as part of the information that is transmitted•tr,1, tr,2, tr,3, tr,4 = times that the signals from GPS satellites 1, 2, 3, and 4, are received according to the inaccurate GPS receiver’s clock•x1, y1, z1 = coordinates of GPS satellite 1. These coordinates are provided to the receiver as part of the information that is transmitted•Similar meaning for x2, y2, z2, etc.•The receiver solves these equations simultaneously to determine x, y, z, and tc

24

24

244,4,4

23

23

233,3,3

22

22

222,2,2

21

21

211,1,1

)()()()(

)()()()(

)()()()(

)()()()(

zzyyxxtttcd

zzyyxxtttcd

zzyyxxtttcd

zzyyxxtttcd

crt

crt

crt

crt

Coordinate FramesCoordinate Frames

57

Position DerivationPosition Derivation•GPS receivers determine position

•Cartesian Co-ordinates (X,Y,Z)•WGS-84 Ellipsoid

•Cartesian Co-ordinates are translated•Local datum (ie. OSGB-36)

•Cartesian Co-ordinates are transformed•Latitude, Longitude, and Elevation

•Elevation is determined with reference to:•Ellipsoid, Geoid, or Mean Sea Level

58

Local Mapping DatumLocal Mapping DatumA Map Datum is a coordinate reference system consisting of

unique and invariable coordinates which are based on an ellipsoid/geoid model over a portion of the earth.

59

NAD 27 ED 50ED 79 Tokyo

Indian Bngldsh

OSGB 36

Introduction to SATCOMIntroduction to SATCOM

Satellite Communication SystemsSatellite Communication Systems• Communication Satellites are used to relay information from one

point to another.

• They enable long range communications at high data rates by overcoming• The line of sight limitation of traditional communications like VHF and UHF.

• The low data rate capacity of traditional long range communication i.e. HF.

• SATCOM is used for both voice and data communications and is extremely important for both the military and commercial world (just think Sky TV), as well as society as a whole (the Global Commons)

• SATCOM does not require landline point to point connection.• Very useful for Military operations

• Very useful for work in areas of low/no infrastructure, including disaster relief.

1962 – Telstar1962 – Telstar

CategoriesCategories

• Frequency• Transponder Type• Orbit

FrequencyFrequency• Applications for frequency allocations are ratified by the International Telecommunications Union (ITU)

• NATO frequency allocations for Military Communication Satellites are:

Uplink Downlink

• UHF 290-320MHz 240-270MHz• SHF 7.9-8.4GHz 7.2-7.75GHz• EHF 43.5-45.5GHz 20.2-21.2GHz• S Band for Command, Control and Telemetry of satellites

Frequency BandsFrequency BandsDesignation Frequency

(Uplink/Downlink)

UHF 290-320MHz/240-270MHz Military

L-Band 1.6GHz/1.5GHz

S-Band 2.5GHz

C-Band 6GHz/4GHz

X-Band (SHF) 7.9-8.4GHz/7.25-7.75GHz Military

Ku-Band 14GHz/12GHz

Ka-Band 30GHz/20GHz

EHF 43.5-45.5GHz/20.2-21.2GHz Military

BeamwidthBeamwidth

Beamwidth for a 1 metre SATCOM antenna

Band Frequency Degrees

UHF 300MHz 60

SHF 8.0 GHz 2.5

EHF 40.0GHz 0.5

D

UHF CharacteristicsUHF Characteristics

• Mature Technology• Relatively Cheap• Low Data Rates• Low Gain Antennas• Good Adverse Weather Performance• Limited Anti-Jam Capability• Poor Performance in Nuclear Environment

SHF/X-Band CharacteristicsSHF/X-Band Characteristics

• Mature Technology• Inexpensive• Higher Data Rates than UHF• Higher Gain Antennas suitable for Spot Beams• Adequate Adverse Weather Performance• Some Anti-Jam Capability• Some Performance in Nuclear Environment

EHF & Ku/Ka CharacteristicsEHF & Ku/Ka Characteristics

• Less Mature Technology than SHF and UHF• Expensive• Higher Data Rates• Very High Gain Antennas for Small Spot Beams• Very Poor Adverse Weather Performance• Good Anti-Jam Capability• *Good Performance in Nuclear Environment *• UK – US MoU

CategoriesCategories

• Frequency• Transponder Type• Orbit

Transparent TranspondersTransparent Transponders

DOWNLINKUPLINK

SATELLITE

POWERAMPLIFIER

FREQUENCYCONVERTER

RECEIVER & LOW NOISEAMPLIFIER

Reconstituting TranspondersReconstituting Transponders

RECODEDDOWNLINK

CODEDUPLINK

SATELLITE

POWERAMPLIFIER

DECODER &LOW NOISEAMPLIFIER

RECODER &FREQUENCYUP-CONVERTER

FREQUENCYDOWN-CONVERTER

Store Dump TranspondersStore Dump Transponders

DOWNLINKUPLINK

SATELLITE

FREQUENCYUP-CONVERTER & POWERAMPLIFIER

FREQUENCYDOWN-CONVERTER

RECEIVER &LOW NOISEAMPLIFIER

DATASTORAGESYSTEM

CategoriesCategories

• Frequency• Transponder Type• Orbit

SATCOM OrbitsSATCOM Orbits

• Most SATCOMs are in Geosynchronous Orbit • Most of these are in GEO Stationary orbits.

• Some SATCOM systems reside in Low Earth Orbit (LEO)

• For example IRIDIUM.• Useful for global coverage including the polar

regions.