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.

AGC - Saturn V LVDC Comparison

The documents below, courtesy of Eldon C. Hall, discuss an evaluation of the Apollo Guidance Computer and its potential replacement with the Saturn V Launch  Vehicle Digital Computer.


July 3, 1963

The Apollo guidance system presently uses a computer being designed by MIT and manufactured by Raytheon.  As a result of a recent Guidance and Navigation review, the Office of Systems has recommended to MSC that consideration be given to replacing the MIT computer by the computer presently being developed for the S-IB and S-V vehicles.  This computer, which is called the Saturn TMR (Triple Module Redundancy) computer, is being developed by IBM under the direction of MSFC.  This recommendation has been jointly studied by MSC and the Office of Systems.

Guidance Computer for Apollo

MEMORANDUM for the Acting Manager, Apollo Spacecraft Project Office

David W. Gilbert
Manager, Spacecraft Systems
Guidance and Control
July 9, 1963

Recent studies by MSC, MIT, Bell Comm., and IBM have defined the relative characteristics of the present MIT-Raytheon Computer and the proposed IBM-TMR Computer being planned for Saturn V.  The action being proposed by Headquarters now is to develop the TMR Computer so that it can be used for the Spacecraft also.  In evaluating this action further, some additional information needs to be developed and some decisions or ground rules established.  These are discussed as follows ...

Results of Planning Meeting for Apollo Spacecraft Guidance and Navigation Review

MEMORANDUM for Distribution

David W. Gilbert
Manager, Spacecraft Systems
Guidance and Control
September 30, 1963


The following is a brief description of the issues in question:

  1. ... it was decided that an investigation should be made to determine if the Saturn V Triple Module Redundant Computer made by IBM should be used instead of the Apollo Guidance Computer made by MIT-Raytheon
  2. ... to determine if the current MIT Guidance and Navigation System with the GAEC Abort Guidance System should be used in the Lunar Excursion Module, or if a new lightweight, doubly redundant Guidance and Navigation System should be developed with radar o the ascent stage for use as an Abort Guidance System.

The attached agenda has been developed for the October 7 meeting in order to allow the Executive session to resolve the issues.

Critique of IBM Apollo Study Report - IBM #63-928-129 - 1 Oct 1963

Massachusetts Institute of Technology
Instrumentation Laboratory
October 7, 1963

The following is a collection of comments on the use of the Saturn V guidance computer as a back-up for the MIT AGC.  Although it is not intended to be complete, the preliminary evidence presented makes clear that the IBM computer is neither suitable nor capable of performing the Apollo mission as it has been defined.  It is indeed unfortunate that the portion of the BELLCOMM staff which has been an enthusiastic supporter of the IBM computer did not discern these obvious deficiencies in the many months of their association with the IBM and MIT staffs.


Eldon Hall
October 8, 1963

  1. Mechanical Problems
  2. Reliability Problems
  3. Thermal Problems
  4. Input - Output Problems
  5. Programming Problems

In summary: What they presented is probably too big as it is. It is very likely they will need more memory than already estimated.  They will probably have to change their design (machine instruction codes) in order to be able to do the job at all.  It is very likely the weight, volume, and power that they have quoted is lower than required for the machine that they proposed in the report.

Note to Mr. Webb

R.P. Young, Executive Officer
August 20, 1963
(tif format)

With regard to the LEM guidance system, you and Dr. Seamans have recently approved the procurement plan and sole source justification to have this work done by MIT and the AC Sparkplug-Raytheon-Coleman industrial support team.  At the present time, OMSF has asked that this be held in abeyance and no announcement be made because they now have underway a study by Bellcomm to see if it would be wiser to design a new system based on the present state of the art rather then use the MIT system which was based on the state of the art two years ago.

Saturn V/Apollo Spacecraft Guidance Computer Development Programs

Samuel C. Phillips
Brigadier General, USAF
April 28, 1964

I have scheduled a meeting at Headquarters, NASA on May 7, 1964, in connection with the Procurement Plan submitted by the Manned Spacecraft Center for the development of a modification of the Saturn V triple modular redundant computer for the Apollo spacecraft.  Discussions at this meeting will include ...


Saturn V/Apollo Spacecraft Guidance Computer Conference

Samuel C. Phillips
Major General, USAF
May 14, 1964

I would like to express my appreciation for your contribution to the discussions of May 7, 1964, concerning our spacecraft and launch vehicle computer development programs.  As a result, I believe all participants have a much better understanding of our joint problems.  I would encourage continued inter-Center information cross-flow including participation in each other's design reviews.

The following is a summary of actions resulting from the meeting ...

Saturn V Guidance Computer for use as Apollo back computer

TO: NASA Headquarters, Attention: Deputy Director, Apollo Program, MA

FROM: PA/Manager, Apollo Spacecraft Program Office [Joseph F. Shea]

August 1, 1964

I would like to summarize the status of our actions resulting from the May 7, 1964 meeting with you, as outlined in reference (a).
  1. The completion of our guidance and control studies confirmed our suspicion that we would require only one Apollo Guidance Computer.  Thus, system reliability can be met with a simplex primary computer in the Block II guidance and navigation system.  ...
  2. Our study with MSFC and Bellcomm on the utilization of the spacecraft computer in the launch vehicle indicates that ...
  3. As a result of the above, we would like to uncouple our backup effort from MSFC as discussed in reference (b).  ...

Documents to get: IBM APOLLO STUDY REPORT NO. 63-928-129, 1 Oct 1963

Apollo Guidance Computer and Other Computer History

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