Another Apollo spacecraft computer program status report

This is another of my gripping reports on the status of the Apollo spacecraft computer programs and the associated matters based on my weekly visit to MIT on June 28 and 29.

AS-204: Debugging of the AS-204 program is reaching its final stages with most of the operational sequences now working. It is anticipated that the so-called “B release” tapes should do an adequate job of supporting the spacecraft systems tests in the Cape altitude chamber. The major capabilities not yet checked out and working in the “B release”, which is actually just the best assembly of this program existing at 4 p.m., June 30, and delivered to Raytheon for rope manufacture, are the prethrust and thrust programs for the deorbit maneuver (other similar programs are working and so it is expected these will be O.K. very soon) and the auto positions of the optics. Many displays have not yet been checked for accuracy yet either.

It is to emphasized that the “B release” is certainly not flight-worthy, and there is no intention of using it for that. In addition to the fact that programming bugs still exist, it is virtually certain that, with improper treatment, the program will bomb out; that is, excessive restrictions still exist as to how it must be used by the operator. The system should be made more foolproof–if I may use that expression–before it is committed to flight.

AS-205: As you know, every effort is being made to use the final AS-204 program, as is, for the AS-205 flight, although it is highly probable that certain changes will be forced upon us. Of course, this is not to suggest that known program deficiencies–bugs–that are uncovered after release of the flight tapes for AS-204 will not be corrected. I am referring here to the addition of new capabilities. MIT presented us with four documented recommendations for deletion of new requirements which, if accepted by MSC, would permit using the AS-204 program. These changes are as follows:

a. Side-force computations during launch phase. It is anticipated that we will accept MIT’s recommendation and delete this requirement.

b. The capability for the crew to orient the spacecraft during SPS maneuvers in either a heads-up or heads-down attitude. This requirement was originally requested for the AS-204 program but was rejected for schedule reasons with the implication that it would be added into the AS-205 program. Although final disposition must await discussion with interested MSC personnel, it is our current intention to accept MIT’s recommendation and not provide this capability, unless it is mandatory for the mission.

c. Modification of the program to do the S-16 experiment. This program provides the automatic control of spacecraft attitude to the fine degree of accuracy required to carry out this “trapped particles” experiment. It is anticipated to not be within the astronauts’ capability to follow the rather complicated attitude profile manually, which means that failure to include this program would, in effect, eliminate the capability of doing this experiment. Although MIT recommends deleting this entire requirement, they do offer an alternate proposal. They suggest that a duplicate set of AS-204 flight ropes be manufactured for AS-205 which would be used for all initial spacecraft testing. Then starting on August 1, two AS-204 programmers would start work on the program which would provide this new attitude control capability. Since the AS-204 program completely absorbs the available computer storage, it is necessary that some processor be eliminated if this change is to be made. MIT is recommending that the processor to be eliminated be a non-flight program used for prelaunch activity rather than reducing the in-flight capability of the guidance system. This certainly seems logical to me, also. Therefore, it would be included in one of the six rope modules which is otherwise devoted entirely to preflight pad activity. Upon completion of the development of this processor, a seventh rope would be manufactured to replace one of the six original ropes at some time in the midst of the preflight pad activity after the spacecraft tests requiring that rope have been completed, Unless the flight schedule slips, it would not be possible to supply the final version of the flight program–that is, all six rope modules in their final configuration–on schedule.

If my understanding of the priority of the experiments is correct, I would guess that MIT’s recommendation to delete this requirement must be rejected and that we will follow their alternate proposal. The obvious disadvantages are that the ropes must be changed on the pad, and, of course, there is the expense of making an additional rope module.

d. Changes to the telemetry down-link in support of the S-17 X-ray astronomy experiment. MIT, through direct conversations with the S-17 experimenter, have been led to the conclusion that it is possible to obtain the information required without change to the onboard computer program. It does require, however, that during the experiment the crew call up on their DSKY display the three quantities defining spacecraft attitude, which automatically results in this information being included in the downlink. Since this data may be asynchronous and for other reasons, it is probable that special ground programs must be developed for use in the ACR facility of the MCC to support the real time operations of the experimenter. We were told that somebody in the Flight Control Division is coordinating all of this MCC support, although I personally had never heard of it before and neither had Carl Huss.

In summary, it is anticipated that at least two of the four known requests for modification to the AS-204 program to support AS-205 shall be deleted, with a third (item “b” above) as a possible candidate. The fourth and biggest change will probably have to be made and, as noted above, will require the manufacture of an extra rope module to be assembled into the spacecraft during final prelaunch activities.

AS-206: MSC people most expert on the AS-206 mission, including Carl Huss of Mission Planning and Analysis Division and Dave Reed of the Flight Control Division, discussed the overall AS-206 program with the MIT people in an attempt to reduce MSC requirements to an absolute minimum for this program. The purpose of this was to assist to the maximum extent our overall effort to have this program available on schedule. Although the deletions made save in the order of 2½ man-months of programming activity, which in itself is a worthwhile accomplishment, apparently we did not influence the pacing items of this program; and, as a result, the AS-206 schedule was not significantly improved. Obviously, further effort will be required. The discussions did have the benefit of reviewing the flight time-line in great detail, which brought to the surface a number of unresolved questions which were taken care of and which should at least permit MIT to proceed as quickly and efficiently as possible in their work. Although we did not satisfy our primary objective–that is, schedule improvements–on this occasion, the meeting was extremely valuable in these other respects.

AS-501: One entire day was spent discussing the AS-501 program, which is also slated for one-month late delivery. As reported in a previous note to you, our apparent best approach for the AS-501 and 502 programs was to use the AS-202 program with minimum modification. This is the course of action we have adopted and were thus able to improve the schedule from a three-month late delivery to a one-month late delivery. (Note: It is not entirely certain if a “one-month late delivery” is truly that since it is highly likely that the AS-202 program could be used for initial spacecraft checkout at the Cape with very little loss of efficiency since these programs will be so similar.) Without going into detail on the program changes to the AS-202 program for use on AS-501, I would like to emphasize that NASA/MSC has to bend so far over backwards in an attempt to reduce requirements on the AS-501 program that we look like a double pretzel. We have eliminated almost all real time abort and alternate mission capability, an item which must be discussed in detail with our management. In addition to that, we have adopted a course of action which seriously perturbs other interfacing activities, which is annoying, to say the least, if not on the verge of being unacceptable. Use of the AS-202 program means that much of the work which has gone on for the RTCC programs, the CCATS programs, and the Remote Site Data Processing programs, goes straight into the trash can. In effect, we have forced these activities, which were progressing in an orderly, businesslike manner, onto a crash basis to make them compatible with the onboard system. It is galling that the “good guys,” who have really been doing the job right, are forced into the position of seeing their efforts go right down the drain, and then to be forced into a crash effort to make up for deficiencies with another system. On the other hand, there seems to be no choice in the matter for this particular mission.

AS-502: It was our intention to use the AS-501 program virtually intact for AS-502, however, there were some discussions which were completely over my head indicating that this may not be entirely possible, particularly associated with the large out-of-plane maneuvers and associated special platform alignments required in the AS-502 mission. Carl Huss intends to work this over as soon as possible to determine the true situation in order to allow us to move on.

Other mission programs were not discussed on this visit, and so I don’t have much of anything to report here.

Other matters: Shortage of programming development personnel continues to be the most pressing problem at MIT. However, steps are being taken at this time which seem, at least partially, effective and so, although we should remain concerned and alert, I see no useful action for us to take at this time. MIT has been successful in recruiting people from within MIT as well as obtaining offers of assistance, including short term, from several contractors which will go a long way toward relieving this serious situation. Steps are also being taken to clear the building of non-software oriented personnel to accommodate the build-up.

The major item which I am still concerned about and which is not, in my opinion, obtaining adequate attention is the Program Development Plan. I discussed this with MIT management, informing them, in my opinion, that the situation was still entirely unacceptable in all of these areas. If I don’t see evidence of real improvement within the next couple of weeks, rest assured that you will hear about it–if you aren’t deaf.

Terms & Abbreviations


see Apollo 1


Originally scheduled as the first unmanned flight of the LM, it was cancelled after the Apollo 1 fire. The AS-206 launch vehicle, a Saturn 1B, was used to launch Skylab 2 on May 25, 1973.

Apollo 1

Originally designated AS-204, Apollo 1 was scheduled to be to launch on February 21, 1967 as the first manned Apollo mission. During a test on January 27, 1967, a fire in the crew compartment killed the three Apollo 1 austronauts, Gus Grissom, Ed White, and Roger Chaffee. This fire resulted in reappraisal of just about every goal, procedure, and schedule of the Apollo program.


The "Display and Keyboard" interface through which the astronauts controlled their guidance computers.


Mission Control Center. Popularly known as “Houston” (as in “Houston, we have a problem”)


Massachussets Institute of Technology. In these memos, MIT is shorthand for the MIT Instrumentation Laboratory, created and led by avionics pioneer Charles Stark Draper. It is now known as the Charles Stark Draper Laboratory and became independent of MIT in 1973.


Manned Spacecraft Center. Now known as Johnson Space Center.


Real-Time Computer Complex. The IBM computing and data processing system at MSC.


Service Propulsion System, the large engine of the Service Module that was used to enter and exit lunar orbit, as well as make course corrections while going to and from the moon.