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Chapter 1

INTRODUCTION

Robot is a system with a mechanical body, using computer as its brain. Integrating the sensors

and actuators built into the mechanical body, the motions are realized with the computer

software to execute the desired task. Robots are more flexible in terms of ability to perform

new tasks or to carry out complex sequence of motion than other categories of automated

manufacturing equipment. Today there is lot of interest in this field and a separate branch of

technology ‘robotics’ has emerged. It is concerned with all problems of robot design,

development and applications. The technology to substitute or subsidies the manned activities

in space is called space robotics. Various applications of space robots are the inspection of a

defective satellite, its repair, or the construction of a space station and supply goods to this

station and its retrieval etc. With the overlap of knowledge of kinematics, dynamics and

control and progress in fundamental technologies it is about to become possible to design and

develop the advanced robotics systems. And this will throw open the doors to explore and

experience the universe and bring countless changes for the better in the ways we live.

Space technology (ST) has significant impact on all socioeconomic and life aspects of

the global society and space environment represents one of the most challenging applications

of robotics as a key factor of technologies evolution. Therefore many efforts from research

groups, academia, industry and governments were applied to merge space and robotics

technologies within space robotics concept (SR). A desirable feature for space robotics

machines includes intellectual control, mobility, reconfigurable techniques, and recognition.

These features require radical innovations in computer science, mechatronics and control

technologies. The new opportunities of robotics systems in cosmic environment are considered

as hi-tech priority which requires non-trivial and constructive approaches and innovative

architectures. Obviously many important aspects ST such as specific novel communication

techniques, effect of weightlessness or autonomic behavior of SR systems cannot be verified

on-ground condition. That is why all innovative decisions need to be tested and demonstrated

in open space condition within realistic scenarios.

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1.1 Areas of Applications

The space robot applications can be classified into the following four categories:

1. In-orbit positioning and assembly: For deployment of satellite and for assembly of

modules to satellite/space station.

Figure 1.1: In Orbit Position

2. Operation: For conducting experiments in space lab.

Figure 1.2: MARS Rovers

3. Maintenance: For removal and replacement of faulty modules/packages.

Figure 1.3: Modules &Packages

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4. Resupply: For supply of equipment, materials for experimentation in space lab and for

the resupply of fuel.

The following examples give specific applications under the above categories:

Scientific experimentation:

Conduct experimentation in space labs that may include

1. Metallurgical experiments which may be hazardous.

2. Astronomical observations.

3. Biological experiments.

Assist crew in space station assembly:

1. Assist in deployment and assembly outside the station.

2. Assist crew inside the space station: Routine crew functions inside the space station and

maintaining life support system.

Space servicing functions:

1. Refueling.

2. Replacement of faulty modules.

3. Assist jammed mechanism say a solar panel, antenna etc.

Space craft enhancements:

1. Replace payloads by an upgraded module.

2. Attach extra modules in space.

Space tug:

1. Grab a satellite and effect orbital transfer.

2. Efficient transfer of satellites from low earth orbit to geostationary orbit.

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Chapter 2

SPACE ROBOT CHALLENGES IN

DESIGN AND TESTING

Robots are artificial agents with capacities of perception and action in the physical world often

referred by researchers as workspace. Their use has been generalized in factories but nowadays

they tend to be found in the most technologically advanced societies in such critical domains

as search and rescue, military battle, mine and bomb detection, scientific exploration, law

enforcement, entertainment and hospital care.

Robots developed for space applications will be significantly different from their

counterpart in ground. Space robots have to satisfy unique requirements to operate in zero ‘g’

conditions (lack of gravity), in vacuum and in high thermal gradients, and far away from earth.

The phenomenon of zero gravity effects physical action and mechanism performance. The

vacuum and thermal conditions of space influence material and sensor performance. The

degree of remoteness of the operator may vary from a few meters to millions of kilometers.

The principle effect of distance is the time delay in command communication and its

repercussions on the action of the arms. The details are discussed below:

2.1 ZERO ‘g’ EFFECT ON DESIGN

The gravity free environment in which the space robot operates possesses both advantages and

disadvantages. The mass to be handled by the manipulator arm is not a constraint in the zero

‘g’ environment. Hence, the arm and the joints of the space robot need not withstand the forces

and the moment loads due to gravity. This will result in an arm which will be light in mass.

The design of the manipulator arm will be stiffness based and the joint actuators will be selected

based on dynamic torque (i.e.; based on the acceleration of the arm). The main disadvantage of

this type of environment is the lack of inertial frame. Any motion of the manipulator arm will

induce reaction forces and moment at the base which in turn will disturb the position and the

altitude. The problem of dynamics, control and motion planning for the space robot is

considering the dynamic interactions between the robot and the base (space shuttle, space

station and satellite). Due to the dynamic interaction, the motion of the space robot can alter

the base trajectory and the robot end effector can miss the desired target due to the motion of

the base. The mutual dependence severely affects the performance of both the robot and the

base, especially, when the mass and moment of inertia of the robot and the payload are not

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negligible in comparison to the base. Moreover, inefficiency in planning and control can

considerably risk the success of space missions. The components in space do not stay in

position. They freely float and are a problem to be picked up. Hence, the components will have

to be properly secured. Also the joints in space do not sag as on earth. Unlike on earth the

position of the arm can be within the band of the backlash at each joint.

Figure 2.1: Zero ‘g’ Effect in Robotics

2.2 VACUUM EFFECT AND THERMAL EFFECT

The vacuum in space can create heat transfer problems and mass loss of the material through

evaporation or sublimation. This is to be taken care by proper selection of materials, lubricants

etc., so as to meet the total mass loss (TML) of <1% and collected volatile condensable matter

(CVCM) of <0.1%. The use of conventional lubricants in bearings is not possible in this

environment. The preferred lubricants are dry lubricants like bonded/sputtered/ion plated

molybdenum di-sulphide, lead, gold etc. Cold welding of molecularly similar metal in contact

with each other is a possibility, which is to be avoided by proper selection of materials and dry

lubricants. Some of the subsystem that cannot be exposed to vacuum will need hermetical

sealing. The thermal cycles and large thermal variations will have to be taken care in design of

robot elements. Low temperature can lead to embrittlement of the material, weaken adhesive

bonding and increase friction in bearings. Large thermal gradients can lead to distortion in

structural elements and jamming of the mechanism. This calls for the proper selection of the

materials whose properties are acceptable in the above temperature ranges and the selection of

suitable protective coatings and insulation to ensure that the temperature of the system is within

allowable limits.

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Figure 2.2: Vaccum and thermal effects

2.3 OTHER FACTORS

One of the prime requirements of space systems is lightweight and compactness. The

structural material to be used must have high specific strength and high specific stiffness, to

ensure compactness, minimum mass and high stiffness. The other critical environment to

which the space robot will be subjected to are the dynamic loads during launch. These

dynamic loads are composed of sinusoidal vibrations, random vibrations, acoustic noise and

separation shock spectra.

The electrical and electronic subsystems will have to be space qualified to take

care of the above environmental conditions during launch and in orbit. The components must

be protected against radiation to ensure proper performance throughout its life in orbit.

The space robots will have to possess a very high degree of reliability and this is to be

achieved right from the design phase of the system. A failure mode effect and critical

analysis (FMECA) is to be carried out to identify the different failure modes effects and

these should be addressed in the design by

1. Choosing proven/reliable designs.

2. Having good design margins.

3. Have design with redundancy.

2.4 SPACE MODULAR MANIPULATORS

The unique thermal, vacuum and gravitational conditions of space drive the robot design

process towards solutions that are much different from the typical laboratory robot. JSC's

A&R Division is at the forefront of this design effort with the prototypes being built for the

Space Modular Manipulators (SMM) project. The first SMM joint prototype has completed

its thermal-mechanical-electrical design phase, is now under construction in the JSC shops,

and is scheduled for thermal-vac chamber tests in FY94.

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FY93 was the SMM project's first year, initiating the effort with a MITRE

Corporation review of the existing space manipulator design efforts (RMS and FTS) and

interaction with ongoing development teams (RANGER, JEM, SPDM, STAR and SAT).

Below this system level, custom component vendors for motors, amplifiers, sensors and

cables were investigated to capture the state-of-the-art in space robot design. Four main

design drivers were identified as critical to the development process:

1. Extreme Thermal Conditions;

2. High Reliability Requirements;

3. Dynamic Performance; and

4. Modular Design.

While these design issues are strongly coupled, most robot design teams have

handled them independently, resulting in an iterative process as each solution impacts the

other problems. The SMM design team has sought a system level approach that will be

demonstrated as prototypes, which will be tested in the JSC thermal-vacuum facilities.

The thermal-vacuum conditions of space are the most dramatic difference

between typical laboratory robot and space manipulator design requirements. Manufacturing

robots operate in climate controlled, \|O(+,-)2K factory environments, where space

manipulators must be designed for \|O(+,) 75K temperature variations with 1500 W/m2 of

solar flux. Despite these environmental extremes, the technology to model and control robot

precision over a wide temperature range can be applied to terrestrial robotic operations

where the extreme precision requirements demand total thermal control, such as in

semiconductor manufacturing and medical robot applications.

Thermal conditions impact reliability by cycling materials and components,

adding to the dynamic loading that causes typical robot fatigue and inaccuracy. MITRE built

a customized thermal analysis model, a failure analysis model using FEAT, and applied the

fault tolerance research funded by JSC at the University of Texas. The strategy is to layer

low level redundancy in the joint modules with a high level, redundant kinematic system

design, where minor joint failures can be masked and serious failures result in reconfigured

arm operation. In this approach, all four design drivers were addressed in the selection of the

appropriate level of modular design as a 2-DOF joint module.

The major technical accomplishments for the FY93 SMM project are:

1. Conceptual and detailed design of first joint prototype;

2. Detailed design and fabrication of thermal-vacuum test facility;

3. Custom design of thermal-vac rated motors, bearings, sensors and cables; and

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4. Published two technical papers (R. Ambrose & R. Berka) on robot thermal design.

Figure 2.3: Robot Thermal Design

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Chapter 3

SYSTEM VERIFICATION AND TESTING

The reliability is to be demonstrated by a number of tests enveloping all the environmental

conditions (thermal and vacuum) that the system will be subjected to. Verification of

functions and tests will be conducted on subsystems, subassemblies and final qualification

and acceptance tests will be done on complete system. The most difficult and the nearly

impossible simulation during testing will be zero ‘g’ simulation.

The commonly used simulations for zero ‘g’ are

1. Flat floor test facility: It simulates zero ‘g’ environments in the horizontal plane. In

this system flat floor concept is based on air bearing sliding over a large slab of

polished granite.

2. Water immersion: Reduced gravity is simulated by totally submerging the robot

under water and testing. This system provides multi degree of freedom for testing.

However, the model has to be water-resistant and have an overall specific gravity of

one. This method is used by astronauts for extra vehicular activities with robot.

3. Compensation system: Gravitational force is compensated by a passive and vertical

counter system and actively controlled horizontal system. The vertical system

comprises the counter mechanism and a series of pulleys and cables that provide a

constant upward force to balance the weight of the robot. However, the counter

mechanism increases the inertia and the friction of joints of rotating mechanism.

3.1 PERFORMANCE ASSESSMENT AND CALIBRATION

STRATEGIES FOR SPACE ROBOTS

Predictable safe and cost efficient operation of a robotic device for space applications can

best be achieved by programming it offline during the preparation for the mission. Computer

aided design techniques are used to assure that the movement of the robot are predictable. A

software model of the robot and its work cell is made and this must be compatible with the

model of the environment in which the robot must perform. Cost efficiency requirements

dictate that a robot be calibrated, after which its performance must be checked against

specified requirements.

Proper use of miniaturized sensing technology is needed to produce a robot of

minimum size, power requirement and consumption and mass. This often requires

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minimizing the number and the type of sensors needed, and maximizing the information

(such as position, velocity, and acceleration) which is gained from each sensor.

The study of methods of assessing the performance of a robot, choosing its

sensors and performing calibration and test, ESA passed a contract with industry. Results of

this work are applicable to any robot whose kinematics chain needs accurate geometrical.

3.1.1 ROBOT PERFORMANCE ASSESSMENT

The objectives of robot performance assessment are

1. To identify the main source of error which perturb the accuracy of the arm.

2. To decide if the arm or the work cell must be calibrated.

3. To compare the expected improvement in accuracy in calibration.

The performance of the robot is assessed by making mathematical model of the

characteristics of the error source in each of its sub system such as the joint, the robot link

or its gripper. From these the effects of errors on the positioning accuracy of end effector

(the functioning tip of the robot arm) can be evaluated.

Error sources are identified by a bottom up analysis, which tale account of the

capabilities of state of the art production technology. For each robot subsystem error

sources are identified and are sorted into three categories.

1. Systematic error which do not vary with time, such as parallelism, concentricity and

link length.

2. Pseudo systematic error, which are time variant yet predictable such as temperature

induced effects.

3. Random errors, which vary with time and cannot be, predicted such as encoded noise.

Once the error source have been classified and its magnitude defined, various

statistical methods may be used to evaluate its effects when they work in combination.

Simply adding all the errors, take no account of their statistical nature and gives an estimate

which is safe but unduly pessimistic; misapplication of statistics can produce an estimate,

which is too optimistic. Accuracy of some painting mechanism is frequently estimated by

separately eliminating the root mean square value of each of the three error types identified

above and adding them. In the case of AMTS project, all error sources were considered as

statistical variables and a single root mean square error at the end effector was of interest.

The bottom up approach used to establish the contribution of each power source error source

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was validated taking the case of manipulator for which a worst case accuracy of 2.7mm was

predicted. This was very close to its average accuracy of 2mm.

3.1.2 ROBOT CALIBRATION

If the performance prediction has shown that calibration is needed to compensate for errors,

a proper calibration approach is required. Ideally, all calibration must be done on ground. In

orbit calibration procedures should be limited to crosschecking the validity of model

developed on ground and if necessary correcting for errors such as micro slip page or

pressure gradient. To keep the flight hardware simple, the in orbit calibration should be

achieved using sensors already available in the robot.

Calibration is performed in five steps:

1. Modeling, in which a parametric description of the robot is developed, introducing

geometric parameters such as link length and non-geometric parameters such as

control parameters.

2. Measurement, in which a set of robot poses (position and orientation) and encoder

data are measured using real robot to provide inputs to the identification test step.

3. Identification, which uses the parametric model and the measured data to determine

the optimal set of error parameters.

4. Model implementation, which may be done either by updating the root controller

data or by correcting the robot pose with expected standard deviation of the error.

5. Verification, that the improvement in the positioning accuracy of the robot in all

three axes have been achieved.

A method for calibrating each axes independently has been successfully developed in the

frame of the contract. This method uses independent measurements of motions along each

of the three axes. Advantage of this approach compared to others such as those requiring all

robot joints move simultaneously is that it subdivides the general problem of robot

calibration into a set of problems of lower complexity, thus achieving good stability and

numerical precession. The calibration software is parametric and is suitable for calibrating

any open robot kinematics chain.

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3.1.3 PERFORMANCE EVALUATION

As part of a verification procedure, specific performance tests were carried out on a robot

by Krypton under contract to ESA. The first was an accuracy test in which the robot had to

adapt a specified pose and aim at a point, key characteristics for predictable offline

programming. The second test evaluated the repeatability with which the robot could reach

a pose it had been taught to adopt. This is essential for performing repetitive and routine

tasks. Finally, the multidirectional pose accuracy was tested to establish the effect of random

errors and to establish the limits of calibration procedure. The performance of the robot was

measured before and after calibration. Procedures for calibrating robots on ground and in

orbit have been developed, and the performance of the robotic devices has been successfully

tested. The robot calibration procedure proved to work well resulting in an improvement in

performance by a factor of ten in some cases. The calibration software is versatile and it can

be used to calibrate and evaluate most kinematics chains ranging from a simple two axes

antenna gimbals mechanism to a ten axes manipulator. These software procedures are now

used by Krypton for applications in most motor industry and elsewhere.

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Chapter 4

STRUCTURE OF SPACE ROBOTICS

4.1 DESCRIPTION OF STURUCTURE OF SPACE ROBOTS

The proposed robot is of articulated type with 6 degrees of freedom (DOF). The reason for

6 DOF system rather than one with lesser number of DOF is that it is not possible to freeze

all the information about possible operations of the payload/racks in 3D space to exclude

some DOF of the robot. Hence, a versatile robot is preferred, as this will not impose any

constraints on the design of the laboratory payload/racks and provide flexibility in the

operation of the robot. A system with more than six DOF can be provided redundancies and

can be used to overcome obstacles. However, the complexities in analysis and control for

this configuration become multifold.

The robot consists of two arms i.e. an upper arm and a lower arm. The upper

arm is fixed to the base and has rotational DOF about pitch and yaw axis. The lower arm is

connected to the upper arm by a rotary joint about the pitch axis. These 3 DOF enable

positioning of the end effector at any required point in the work space. A three-roll wrist

mechanism at the end of the lower arm is used to orient the end effector about any axis. An

end effector connected to the wrist performs the required functions of the hand. Motors

through a drive circuit drive the joint of the arm and wrist. Angular encoders at each joint

control the motion about each axis. The end effector is driven by a motor and a pressure

sensor/strain gauges on the fingers are used to control the grasping force on the job.

4.2 DISCRIPTION OF SUBSYSTEMS

The main subsystems in the development of the manipulator arm are

1. Joints

2. Arm

3. Wrist

4. Gripper

4.2.1 JOINTS

A joint permits relative motion between two links of a robot. Two types of joints are

Roll joint – rotational axis is identical with the axis of the fully extended arm.

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Pitch joint – rotational axis is perpendicular to the axis of the extended arm and hence

rotation angle is limited.

The main requirements for the joints are to have near zero backlash, high

stiffness and low friction. In view of the limitations on the volume to be occupied by the arm

within the workspace, the joints are to be highly compact and hence they are integrated to

the arm structure. To ensure a high stiffness of the joint the actuator, reduction gear unit and

angular encoders are integrated into the joint.

Each joint consists of

1. Pancake type DC torque motors (rare earth magnet type) which have advantage over

other types of motors with respect to size, weight, response time and high torque to

inertia ratio.

2. Harmonic gear drive used for torque amplification/speed reduction. These gear

drives have near zero backlash, can obtain high gear ratios in one stage only and

have high efficiency.

3. Electromagnetically actuated friction brakes, which prevent unintentional

movements to the arms. This is specifically required when the gear drive is not self-

locking. In space environment, where the gravity loads are absent (zero ‘g’

environment) brakes will help to improve the stability of the joint actuator control

system. I.e. the brake can be applied as soon as the joint velocity is less than the

threshold value.

Electro optical angular encoders at each axis to sense the position of the end of the arm.

Space qualified lubricants like molybdenum di-sulphide (bonded film/sputtered), lead, gold

etc. will be used for the gear drives and for the ball bearings.

Figure 4.1: Joints

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4.2.2 ROBOT ARMS

The simplest arm is the pick and place type. These may be used to assemble parts or fit them

into clamp or fixture. This is possible due to high accuracy attainable in robot arm. It is

possible to hold the part securely after picking up and in such a way that the position and the

orientation remains accurately known with respect to the arm. Robot arms can manipulate

objects having complicated shapes and fragile in nature.

Figure 4.2: Robot Arms

4.2.3 WRIST

Robot arm comprises of grippers and wrist. Wrist is attached to the robot arm and has three

DOF (pitch, yaw, and roll). Wrist possesses the ability to deform in response to the forces

and the torques and return to equilibrium position after the deflecting forces are removed.

Figure 4.3: Robot wrist

4.2.4 GRIPPER

Gripper is attached to the wrist of the manipulator to accomplish the desired task. Its design

depends on the shape and size of the part to be held.

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Figure 4.4: Robot gripper

They are based on different physical effects used to guarantee a stable grasping between a

gripper and the object to be grasped. Industrial grippers can be mechanical, the most diffused

in industry, but also based on suction or on the magnetic force. Vacuum cups and

electromagnets dominate the automotive field and in particular metal sheet handling.

Bernoulli grippers exploit the airflow between the gripper and the part that causes a lifting

force which brings the gripper and part close each other (i.e. the Bernoulli's principle).

Bernoulli grippers are a type of contactless grippers, namely the object remains confined in

the force filed generated by the gripper without coming into direct contact with it. Bernoulli

gripper are adopted in Photovoltaic cell handling in silicon wafer handling but also in textile

or leather industry. Other principles are less used at the macro scale (part size >5mm), but

in the last ten years they demonstrated interesting applications in micro-handling. Some of

them are ready of spreading out their original field.

The other adopted principles are: Electrostatic grippers and van der Waals

grippers based on electrostatic charges capillary grippers and cryogenic grippers, based on

liquid medium, and ultrasonic grippers and laser grippers, two contactless grasping

principles. Electrostatic grippers are based on charge difference between the gripper and the

part (i.e. electrostatic force) often activated by the gripper itself, while van der Waals

grippers are based on the low force (still electrostatic) due to the atomic attraction between

the molecules of the gripper and those of the object. Capillary grippers use the surface

tension of a liquid meniscus between the gripper and the part to center, align and grasp the

part, cryogenic grippers freeze a small amount of liquid and the resulting ice guarantees the

necessary force to lift and handle the object (this principle is used also in food handling and

in textile grasping). Even more complex are ultrasonic based grippers, where

pressure standing waves are used to lift up a part and trap it at a certain level.

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Chapter 5

OPERATION OF SPACE ROBOTS

5.1 SPACE SHUTTLE ROBOT ARM (SHUTTLE REMOTE

MANIPULATOR SYSTEM)

5.1.1 USE OF SHUTTLE ROBOT ARM

The Solar Maximum Repair Mission (SMRM) of 1984 was the first demonstration of on-

orbit servicing by astronauts in combination with software workarounds uploaded from the

ground, and teleportation of the Shuttle Remote Manipulator System (SRMS) by an

astronaut. The Solar Maximum Repair Mission represents a "textbook" case of OOS,

involving the exchange of ORU (Orbital Replacement Unit) modules. Although the more

complex tasks were performed by astronauts on EVA (extravehicular activity), such servicing

operations may potentially be performed by robotic servicers.

The repair and servicing of the Hubble Space Telescope and other US astronaut

activities have further demonstrated the feasibility of space based servicing tasks. Indeed,

robotic servicing was an instrumental part of the early stages of the ISS programmer in which

two concepts were proposed to perform these functions - the Flight Telerobotic Servicer (FTS)

and the Orbital Maneouvring Vehicle (OMV) - but these were cancelled in the face of budget

cuts. NASA's AERCam (Autonomous Extravehicular Robotic Camera) represents a step in this

direction AERCam is a small 35 cm diameter free flying sphere comprising a camera for aiding

astronaut EVA, thrusters for attitude and translation control, and avionics developed from

astronaut MMU (manned maneuvering unit) technology. The addition of robotic manipulators

onto a larger spacecraft platform would offer free flyer servicer capabilities. The sizing of the

manipulator would be determined by EVA equivalence, one example of which is the proposed

ESA dexterous robot manipulator system:

1. Seven degrees of freedom (three degrees of freedom at the shoulder, one degree of

freedom at the elbow, and three degrees of freedom at the spherical wrist)

2. Three fingered end effector with cylindrical dimensions 10 x 15 cm

3. Control set-point rate of 100 Hz

4. Forward reach of 1m - this requires multiple grappling points on the target as full

reachability around

5. most satellites would require a reach of 4.5 - 16 m which is impractical

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6. End effector position accuracy of 0.3 mm/0.1o

7. Maximum end effector velocity of 0.1 m/s and 0.1 rad/s

8. Structural displacement compliance of 1x106 N/m and rotational compliance of

5x104 Nm/rad

9. Force/torque exertion of 200 N and 20 Nm respectively

10. Payload capacity of 500 kg in microgravity environment

Figure 5.1: ATLAS robotic servicer concept

On-orbit servicing robotics is a modern version of an old field that stems back to the origins

of science itself – Newton (1642-1729), Euler (1707-1783), Alembert (1717-1783), Lagrange

(1736-1813), Laplace (1749-1827) and Hamilton (1805-1865) all contributed to the

development of mechanics and dynamics. The primary differentiating characteristic of on-

orbit servicing robotics from terrestrial robotics is that the robotic servicer operates in

microgravity. Whereas the terrestrial manipulator is mounted onto terra firma, in space there

is no such reaction force and torque cancellation – the motion of the manipulator(s) will

generate reaction forces and moments on the spacecraft at the manipulator mounting point(s).

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Robotic free flyer manipulators are difficult to control as the spacecraft platform moves in

response to the manipulator movements.

A free-floating platform no longer permits the use of the base of the manipulator as the

inertial coordinate frame of reference. If this effect is not taken into account, the manipulators

will overshoot the target that it is attempting to grapple. A similar effect occurs with

astronauts in the microgravity environment of space.

They undergo changes in psychomotor performance and posture and their limb

movements tend to overshoot their targets until the astronaut's brain has adapted to the new

microgravity conditions (normally within two to three days). The robotic manipulator control

system must similarly compensate for operating in microgravity while implementing the

computationally intensive algorithms for trajectory interpolation, inverse kinematics,

dynamics, and force/position control of the end effector. We may apply the conservation of

momentum to the free flyer servicer system (assuming a single manipulator for simplicity) in

order to apply constraints to solve the problem, which allows us to define the center of mass

of the whole system to lie at the origin of the inertial reference frame - see Fig. 2.: The

position of the manipulator end effector with respect to inertial space may be represented by

Figure 5.2: Single arm robotic servicer

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The Shuttle's robot arm is used for various purposes.

1. Satellite deployment and retrieval

2. Construction of International Space Station

3. Transport an EVA crew member at the end of the arm and provide a scaffold

to him or her. (An EVA crew member moves inside the cargo bay in co-

operation with the support crew inside the Shuttle.)

4. Survey the outside of the Space Shuttle with a TV camera attached to the

elbow or the wrist of the robot arm.

Figure 5.3: Shuttle robot arm

5.1.2 ROBOT ARM OPERATION MODE

SRMS is operated inside the Space Shuttle cabin. The operation is performed from the aft

flight deck (AFD), right behind the cockpit; either through the window or by watching two

TV monitors. To control the SRMS, the operator uses the translational hand controller (THC)

with his or her left hand and manipulates the rotational hand controller (RHC) with his or her

right hand.

THC RHC

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5.1.3 HOW SPACE SHUTTLE ROBOT ARM GRASPS OBJECT?

Many people might think of human hand or magic hand, but its mechanism is as follows.

At the end of the robot arm is a cylinder called the end effector. Inside this cylinder equipped

three wires that are used to grasp objects. The object to be grasped needs to have a stick-

shaped projection called a grapple fixture. The three wires in the cylinder fix this grapple

fixture. However, a sight is needed to acquire the grapple fixture while manipulating a robot

arm as long as 45 feet. The grapple fixture has a target mark, and a rod is mounted vertically

on this mark. The robot arm operator monitors the TV image of the mark and the rod, and

operates the robot arm to approach the target while keeping the rod standing upright to the

robot arm. If the angular balance between the rod and the robot arm is lost, that can

immediately be detected through the TV image.

End effector and grapple fixture

Robot arm’s payload acquiring sequence

5.2 FREE FLYING SPACE ROBOTS

The figure below shows an example of a free flying space robot. It is called ETS VII

(engineering test satellite VII). It was designed by NASDA and launched in November 1997.

In a free flying space robot a robot arm is attached to the satellite base. There is a very

specific control problem. When the robot arm moves, it disturbs the altitude of the satellite

base. This is not desirable because,

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1. The satellite may start rotating in an uncontrollable way.

2. The antenna communication link may be interrupted.

One of the research objectives is to design robot arm trajectories and to control the arm

motion in such a way that the satellite base remains undisturbed or that the disturbance will

be minimum.

Figure 5.4: Free Flying Space Robots

5.3 SPACE STATION MOUNTED ROBOTS

The international space station (ISS) is a sophisticated structural assembly. There will be

several robot arms which will help astronauts in performing a variety of tasks.

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Figure 5.5: JEMRMS

The figure shows a part of ISS including the Japanese Experimental Module (JEM). A long

manipulator arm can be seen. The arm is called JEMRMS (JEM Remote Manipulating

System). A small manipulator arm called SPDM (Special purpose dexterous Manipulator)

can be attached to JEMRMS to improve the accuracy of operation.

Figure 5.6: SPDM

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5.4 SPACE ROBOT TELEOPERATION

Space robotics is one of the important technologies in space developments. Especially, it is

highly desired to develop a completely autonomous robot, which can work without any aid of

the astronauts. However, with the present state of technologies, it is not possible to develop a

complete autonomous space robot. Therefore, the teleportation technologies for the robots with

high levels of autonomy become very important. Currently, the technologies where an operator

tale operates a space robot from within a spacecraft are already in practical use, like the capture

of a satellite with the shuttle arm. However, the number of astronauts in space is limited, and

it is not possible to achieve rapid progresses in space developments with the teleportation from

within the spacecraft. For this reason, it has become highly desired to develop the technologies

for the teleportation of space robots from the ground in the future space missions.

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Chapter 6

APPLICATIONS AND ADVATAGES

6.1 SPACE SHUTTLE TILE REWATERPROOFING ROBOT

Figure 6.1: Tessellator

Tessellator is a mobile manipulator system to service the space shuttle. The method of re

water proofing for space shuttle orbiters involves repetitively injecting the extremely

hazardous dimethyl oxysilane (DMES) into approximately 15000 bottom tile after each

space flight. The field robotic center at Carnegie Mellon University has developed a

mobile manipulating robot, Tessellator for autonomous tile re water proofing. Its

automatic process yields tremendous benefit through increased productivity and safety.

In this project, a 2D-vehicle workspace covering and vehicle routing problem

has been formulated as the Travelling Workstation Problem (TWP). In the TWP, a

workstation is defined as a vehicle which occupies or serves a certain area and it can

travel; a workspace is referred to as a 2D actuation envelop of manipulator systems or

sensory systems which are carried on the workstation; a work area refers to a whole 2D

working zone for a workstation.

The objective of the TWP is

1. To determine the minimum number of workspaces and their layout, in which, we

should minimize the overlapping among the workspaces and avoid conflict with

obstacles.

2. To determine the optimal route of the workstation movement, in which the

workstation travels over all workspaces within a lowest cost (i.e. routing time).

The constraints of the problem are

1) The workstation should serve or cover all work areas.

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2) The patterns or dimensions of each workspace are the same and

3) There some geographical obstacles or restricted areas.

In the study, heuristic solutions for the TWP, and a case study of Tessellator has

been conducted. It is concluded that the covering strategies, e.g. decomposition and other

layout strategies yield satisfactory solution for workspace covering, and the cost-saving

heuristics can near-optimally solve the routing problem. The following figure shows a

sample solution of TWP for Tessellator.

Figure 6.2: TWT

6.2 ROBOTS TO REFUEL SATELLITES

The US department of defense is developing an orbital-refueling robot that could expand the

life span of American spy satellites many times over, new scientists reported. The robotic

refuel called an Autonomous Space Transporter and Robotic Orbiter (ASTRO) could shuttle

between orbiting fuel dumps and satellites according to the Defense Advanced Research

Projects Agency. Therefore, life of a satellite would no longer be limited to the amount of

fuel with which it is launched. Spy satellites carry a small amount of fuel, called hydrazine,

which enable them to change position to scan different parts of the globe or to go into a

higher orbit. Such maneuvering makes a satellites position difficult for an enemy to predict.

But, under the current system, when the fuel runs out, the satellite gradually falls out of orbit

and goes crashing to the earth. In the future the refuel could also carry out repair works on

faulty satellites, provided they have modular electronic systems that can be fixed by slot in

replacements

6.3 APPLICATIONS

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Although we have considered general robotic spacecraft issues here which are of critical

importance to the space robotics, space robotics as a discipline is focused on more specific

issues and reflects more closely the subject-area covered by terrestrial robotics. Indeed, space

robotics, like its terrestrial counterpart, is generally divided into two subject-areas (though

there is significant overlap):

1. Robotic manipulators – such devices are proposed for deployment in space or on planetary

surfaces to emulate human manipulation capabilities; they may be deployed on free-flyer

spacecraft or on-orbit servicing of other spacecraft, within space vehicles for payload tending,

or on planetary landers or rovers for the acquisition of samples;

2. Robotic rovers – such devices are proposed for deployment on planetary surfaces to

emulate human mobility capabilities; they are typically deployed on the surfaces of terrestrial

planets, small bodies of the solar system, planetary atmospheres (aerobats), or for penetration

of ice layers (cryobots) or liquid layers (hydrobots). In the following two papers, I shall

consider two case studies, one from each of these two topics: the use of manipulators

mounted onto free-flying spacecraft to provide on-orbit servicing tasks, and planetary surface

Rovers for providing terrain-crossing mobility. I have specifically selected these two case

studies to illustrate two issues – in the first, I consider the modification of traditional robotics

techniques to the space environment; and in the second, I consider how new techniques may

be borrowed from other disciplines (namely, vehicle trainability) and applied to robotic

planetary rovers.

In the developed world, highways are a critical component of the transportation network. The

Volume of traffic on the roadways has been steadily increasing for many years as society

becomes more and more mobile. However, the funding to maintain these roadways has not

been keeping pace with the traffic volume. The result is deteriorating roadways that cannot be

adequately maintained.

Conventional techniques to road repair lead to traffic congestion, delays, and

dangers for the workers and the motorists. Robotic solutions to highway maintenance

applications are attractive due to their potential for increasing the safety of the highway

worker, reducing delays in traffic flow, increasing productivity, reducing labor costs, and

increasing quality of the repairs.

Application areas to which robotics can be applied in this area include

a. Highway integrity management (crack sealing, pothole repair)

b. highway marking management (pavement marker replacement, paint re-

striping)

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c. highway debris management (litter bag pickup, on road refuse collection,

hazardous spill Cleanup, snow removal)

d. highway signing management (sign and guide marker washing, roadway

advisory)

e. highway landscaping management (vegetation control, irrigation control)

f. highway work zone management (automatic warning system, lightweight

movable barriers, automatic cone placement and retrieval)

Although relatively few implementations in highway maintenance and repair have been

attempted, some successful prototypes have been developed (Zhou and West, 1991). The

California Department of Transportation (Caltrans), together with the University of

California at Davis (UC Davis) are developing a number of prototypes for highway

maintenance under the Automated Highway Maintenance Technology (AHMT) program.

Efforts are underway to develop systems for crack sealing, placement of raised highway

pavement markers, paint striping, retrieving bagged garbage, pavement distress data

collection, and cone dispensing. One result of this effort is a robotic system, ACSM, for

automatic crack sealing along roadways (Winters et al., 1994). Shown in

Figure 3, this machine senses, prepares, and seals cracks and joints along the highway.

Figure 6.3: Automated Crack Sealing Machine

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CONCLUSION

In the future, robotics will make it possible for billions of people to have lives of leisure

instead of the current preoccupation with material needs. There are hundreds of millions who

are now fascinated by space but do not have the means to explore it. For them space robotics

will throw open the door to explore and experience the universe.

Autonomous robotic systems are critical to achieving sustainability and reliability in

NASA’s exploration mission. The current monolithic design approach to robotics offers little

room for reuse, adaptation, or maintenance on long-duration or open-ended missions.

Adopting a modular design could address these needs, by allowing a single system mass to be

reconfigured to suit each task and by reducing the number of spare parts required to achieve

redundancy. However, there are many challenges to the scalability, reliability, and usability

of such a system that a must be addressed before it could be put to use outside the laboratory.

We have presented initial prototype hardware, intended as a platform for beginning to address

those challenges. Though this hardware is still far from being immediately useful in a space

mission context, its versatility and usability is steadily increasing and we believe it may have

immediate applications in the robotics research setting. Each module implements a single

core function, reducing individual module complexity and cost and allowing a robotic system

to be tailored as needed by including special-purpose modules.

By designing for a rapid-prototyping manufacturing technology, it is easy and

inexpensive to add new module types when the existing types are insufficient or to make

incremental changes between manufacturing runs. Finally, we have described the first

components of an automated design and optimization system for modular robots, including a

modular robot simulator and an evolutionary controller optimization tool. We have presented

the results of applying this system to the optimization of a walking at, and discussed how the

system was even able to outperform the human engineer. As the capabilities of both the

robots themselves and automated design tools grow, we expect such tools to be of increasing

importance in the use of modular robots.

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REFERENCES

1. www.andrew.cmu.edu/~ycia/robot.html

2. www.google.com

3. www.space.mech.tohoku.ac.jp/research/overview/overview.html

4. www.nanier.hq.nasa.gov/telerobotics-page/technologies/0524.html

5. www.jem.tksc.nasda.go.jp/iss/3a/orb_rms_e.html

6. PRODUCTION TECHNOLOGY by R. K. JAIN

7. INTRODUCTION TO SPACE ROBOTICS by ALEX ELLERY