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GPC to process both commands to the manipulator arm and arm status data for display to the astronaut. The Manipulator Controller Interface Unit (MCIU) collects data from the D&C, GPC, and manipulator arm, reformats it, and transmits it to the appropriate part of the system. In order to minimize weight and system complexity, and to retain flexibility, the MCIU utilizes a microprocessor and bi-directional serial digital data busses across the three interfaces.

The microprocessor routes GPC processed commands to the arm via fixed length message blocks, passing serially from one SPA to the next. The input latches of each SPA are consecutively loaded in response to a clock pulse from the MCIU, the data being implemented concurrently in all SPAs in response to a synch pulse. MCIU receives data from the manipulator arm joints in a similar manner, command and response data transfer occurring consecutively. Similarly, the MCIU communicates with the D&C panel. 

Back-up to the primary modes of operation, to meet orbiter safety requirements, utilizes a system of hardwired commands by-passing the GPC software and MCIU data bus system. 

SYSTEM SAFETY FEATURES

As with all manned space programs, crew safety is an overriding factor in the design of the RMS. The system is designed to be fail-safe, in that after any first failure the RMS can be operated with reduced performance to comply with Orbiter safety criterion. The RMS implements a double back-up system to primary modes of operation, both by-passing the primary chain of command through the GPC and utilizing hardwired commands to the joint drive systems. The first back-up uses a minimum of prime channel electronics, while the second back-up implements the commands through a dedicated section of the D&C Panel and a dedicated electronics unit called the Back-Up Drive Amplifier (BDA). The end effector also incorporates a back-up payload release mechanism located in series with the prime release mechanism and consisting of a spring return device actuated via a dedicated clutch as shown in Figure 6. [[not pictured on this page]] The manipulator arm is capable of being separated from the Orbiter as a last resort to assure crew safety. 

Extensive built-in test equipment (BITE) circuits perform a self-testing function, the results of which are grouped according to the criticality of failure to provide either a caution or a warning to the RMS operator, along with an audio tone. In the event of a failure the operator is provided with two methods of bringing the arm to rest. For manipulator arm failures the brakes may be applied to all joints by a single command from the D&C panel; for most other failures a safeing routine brings the arm to rest automatically by implementing zero rate demands to all joints. The operator may also initiate the safeing routine manually if desired. A dedicated GPC function provides top level system health checks to support the hardware test circuits. The GPC cautions the operator if approaching the end of a joint's travel range; if the joint continues toward its mechanical limit stops then software automatically brings the whole arm to rest.

CONCLUSIONS

Although flight tests of the RMS on board the orbiter are not scheduled until late 1979, all pre-flight analyses and tests of the system described indicate a successful design solution to a set of complex and demanding requirements. This has been achieved by the use of modularized component design and a flexible data handling system capable of accepting the inevitable modifications as the system design has matured. 

Constant attention to the requirements of a man-machine mechanism and to the safety requirements of a manned spacecraft have evolved a safe and efficient manipulator system capable of meeting the needs of the space payload community. 

ACKNOWLEDGMENTS

The authors would like to thank the National Research Council of Canada and Spar Aerospace Limited, Toronto, for permission to publish this paper. The authors would also like to acknowledge contributions of the many people at NASA Johnson Space Center, National Research Council of Canada, Spar Aerospace Limited, Toronto, Spar Technology Limited, and Canadian Aviation Electronics Limited towards a successful system design.

REFERENCES

1 Faget, M.A., Cohen, A., "Concept Design of the Payload Handling Manipulator System", JSC-09709, June 1975, NASA Johnson Space Center, Houston, Texas.
2 "Contract End Item Specification Remote Manipulator System for the Space Shuttle Orbiter Vehicle - Part I", SPAR-SG.392, Spar Aerospace Products Ltd., Toronto, Canada
3 Lindberg, G.M., MacNaughton, J.D., "Remote Manipulator System and Satellite Servicing Experiment for Space Shuttle", June 1976 AAS/DGLR International Meeting on the Utilization of Space Shuttle and Spacelab, Bonn, West Germany.
4 Sorensen, K., "Documentation of Resolved Rate Control for the MSC Shuttle Arm", Matt Memo No. 63, Aug. 1972, M.I.T.C.S. Draper Laboratory, Mass.
5 Doetsch, K., "The Remote Manipulator System for the Space Shuttle Orbiter", Sept. 1977, Jahrestagung 1977 of the Deutsche Gasellschaft fur Luft-und Raumfahrt eV, Berlin, West Germany 
6 Whitehead, G.D., Srinivas, S, Wagner-Bartak, C.G., "Manual Control Aspects of the Space Shuttle Remote Manipulator System", April 1978, XIV Annual Conference on Manual Control, University of Southern California, Los Angeles, California.
7 Brown, J.W., Whitehead, G.D., "shuttle Remote Mannipulator System Safety and Rescue Support Capabilities," Oct., 1977, XXVIII Congress of International Astronautical Federation, Prague, Czechoslavakia. 

reprinted from 
Proceedings of The Fifth World Congress on The Theory of Machines and Mechanisms - Volume 1 
published by ASME, 345 e. 47th St., New York, N.Y. 10017