NASA Office of Logic Design

NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.

2005 MAPLD International Conference

Ronald Reagan Building and International Trade Center
Washington, D.C.

September 7-9, 2005

Session G: "Digital Engineering and Computer Design:
A Retrospective and Lessons Learned for Today's Engineers"
(starts Friday morning, September 9)

Logic module welding detail.  Block II logic module design was a radical departure from Block I.  A multilayer printed board provided interconnections for 60 flat-pack dual Micrologic gates.  Each logic module held two boards, 240 gates, which doubled the packaging density.  Following the all-welded construction guidelines, Block II logic gates were welded to the multilayer board’s bonding pads. (Courtesy Eldon Hall and MIT)Eldon Hall presenting "Historic Disassembly of a Block II Apollo Guidance Computer"  
Eldon Hall of the MIT Instrumentation Lab presents
"Historic Disassembly of a Block II Apollo Guidance Computer"
at Session G of the 2004 MAPLD International Conference.
  Dr. Von Braun, seated, examining a Saturn computer in the Astrionics Laboratory at the Marshall Space Flight Center.   (March 10, 1966)

  Paul Ceruzzi, Smithsonian Air and Space Museum, Session Chairman

This workshop is a study of technical history for digital aerospace systems on topics that were critical in the 1950's, 1960's, and 1970's, which can provide lessons for today.  First held at MAPLD 2004, there was a mix of technical presentations and discussions covering an entire day.  Jack Garman will present MAPLD's first Mishap and Lessons Learned Talk, "Computer Overload and the Apollo 11 Landing."


Please e-mail me with any suggestions that you have or if you wish to participate in this session.

Workshop Participants and Talks:

Some References (will be adding more):

  1. "Flight Computer Hardware Trends," Ramon L. Alonso, MIT, and Glenn C. Randa, IBM Corp., Astronautics and Aeronautics, April 1967, pp. 30-34

  2. "Saturn V Launch Vehicle Digital Computer and Data Adapter," M. Dickinson, J. Jackson, and G. Randa, IBM Space Guidance Center, Proceedings - Fall Joint Computer Conference, 1964, pp. 501-516

  3. "Some Aspects of the Logical Design of a Control Computer: A Case Study," R.L. Alonso, H. Blair-Smith, and A.L. Hopkins, Instrumentation Laboratory, MIT, Cambridge, Mass. IEEE Transactions on Electronic Computers, December 1963, pp. 687-697

  4. "Design Principles for a General Control Computer," R. Alonso and J.H. Laning, Jr., R-276, Instrumentation Laboratory, MIT, April, 1960

  5. "Space Shuttle Main Engine Controller," Report Number NASA-TP-1932 M-360, Mattox, R. M. and White, J.B.  NASA MSFC

  6. "Computer Design Problems for the Space Environment," Dr. Joseph F. Shea, Proceedings - Conference on Spaceborne Computer Engineering, October, 1962, pp. 1-8.

  7. Journey to the Moon: The History of the Apollo Guidance Computer, Eldon C. Hall, Reston VA: American Institute of Aeronautics and Astronautics, 1996.

  8. Apollo Experience Reports

  9. "Guidance and control systems: Orbital rate drive electronics for the Apollo command module and lunar module," Parker, R. B.; and Sollock, P. E. Sep 1, 1974, NASA-TN-D-7784; JSC-S-409  Abstract: A brief record of the development and use of the orbital-rate-drive assembly in the Apollo Program is presented. This device was procured as government-furnished equipment and was used on both the lunar module and the command module. Reviews of design, development, procurement, and flight experience are included. 

  10. Annotations to Eldon Hall's Journey to the Moon," In February of 1997, Hugh Blair-Smith wrote a series of annotations to Eldon Hall's book about the history of the AGC.

  11. "Electrical Systems in Missiles and Space Vehicles," H. J. Fichtner, Astrionics Division, George C. Marshall Space Flight Center, in From PEENEMUNDE to OUTER SPACE, Commemorating the Fiftieth Birthday of Wernher von Braun, March 23, 1962, Edited by: Ernst Stuhlinger, Frederick I. Ordway, III, Jerry C. McCall, and George C. Bucher.

  12. "Special Instrumentation for Apollo Developmental Spacecraft," Alfred B. Eickmeier, NASA Manned Spacecraft Center, Houston Texas.  Aerospace Instrumentation, Volume 4, Proceedings of the Fourth International Aerospace Symposium, 1966, Edited by M.A. Perry

  13. Apollo Guidance Computer Documents

  14. Virtual AGC

  15. "The Apollo Guidance Computer: A User's View," David Scott, NASA Astronaut.  Document Courtesy of Eldon C. Hall

Some potential topics:

In the early 1960s, we reached out and had manned missions to the Moon and unmanned missions to neighboring planets.  Today we are reaching out for a manned Mars mission and to explore to the edge of the solar system.  How should the computers and digital avionics be designed?  Discuss the architecture, redundancy, reliability, and technology.

Technical Decisions:

Technical Moments:

Has the technology for digital spaceflight avionics developed in the directions anticipated?  Is technology headed in the right direction or should be corrections be made?  What is the impact of "commercial off the shelf" consumer-grade components on high reliability spacecraft design?

What is the role of "better faster cheaper?"  How does this compare to the development philosophy of earlier decades?

Failures and Troubleshooting

Man-machine interface.  As the interfaces have gotten more sophisticated over the decades, the computational and communications load have also increased.  Is the increase in resources justified?  Does the increased complexity carry unnecessary risk from design errors or will operator errors be reduced to offset that?  Do the operators have sufficient control over the machine, particularly in the case of malfunctions or off-nominal situations?

Should we have common avionics across the spacecraft in general and industry as a whole?  For Apollo, there was radically different architectures between the Saturn V and the Apollo CSM and LEM; the Apollo CSM and LEM did share common avionics.  For the Shuttle, we again see differences between the main computers and the engine controllers.  Different architectures, redundancy schemes, and technologies.  Today we continuously see (and have been seeing for decades) the call for the one set of avionics to solve all spacecraft computational problems.  Realistic goal of .ppt slide fantasy?

Design diversity.  Does the potential in the reduction of risk of common failures justify the cost, schedule, and complexity?  Does this spread the design and review and test personnel too thin?  Or is it necessary to prevent a catastrophe?  This will be addressed with respect to components, hardware design, compilers, operating systems, and applications.

What were the biggest unknowns and risks in the design of computers in the 1960s?  How were these risks managed?

Software and hardware.  The division of functions between software and hardware is always interesting and with modern logic the line between hardware and software is blurred, as a reprogrammable logic array can implement the CPU, memory, and I/O of a computer and execute the programs stored in on-chip RAM.  How were the decisions made as to the division of functions, historically?  How should they be made today?  Today, more and more functions -- including mission and safety critical ones -- are being put into software.  Are modern avionics designers heading in the right direction?

The Evolution of Arithmetic Operations in Spaceborne Central Processing Units

Redundancy and diversity.  For a manned Mars mission, how many faults should the computers be tolerant of?  Should design diversity (for both hardware and software) be employed?  Should failed modules be tossed out, replaced with spares, or repaired (electronically or with the soldering iron)?  For physical replacement, is this practical when exploiting advanced packaging technologies with on order of one thousand connections for ball grid arrays, as one example?

Design verification.  How were designs verified historically.  In today's systems, design verification is forced to rely on automated tools for databases and parameter extraction, as many device characteristics and internal architectures are proprietary and the systems are quite complex, with over 1 million gates of logic available on a single field programmable gate array?

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