Spacecraft computer program newsletter

See list belowDEC 18 196767-FM-T-124FM/Deputy ChiefSpacecraft computer program newsletter

1. This memorandum is to make sure you are up to date on spacecraft computer programs. As you undoubtedly know, an Apollo Software Configuration Control Board, chaired by Chris Kraft, has been estab- lished. I am the MPAD representative and Stan Mann is the alternate. There have been three meetings so far in which we have discussed and taken action on quite a large number of proposed Program Change Requests (PCR) for all of the manned mission programs.

2. SUNDISK – Sundisk, the earth orbital command module program, has been completely finished and has gone through Level 5 testing. A tape has been delivered to Raytheon which they could use to manufacture the actual flight ropes. It is not our current intention, however, to make flight ropes from that tape since there are a number of changes that have been identified as necessary and some time is available to implement them. Following is a list of program changes that MIT has been directed to complete in time to send another tape to Raytheon on February 1.

a. PCR #3 – Flight Crew people stated that attitude error indica- tion during the first 10 seconds of flight for use as an abort cue is mandatory for crew safety. Currently, the launch program does not start outputting attitude error signals until 10 seconds after lift off at which time a comparison is made with boost polynomials pre- pared preflight. This program change will provide a signal to the FDAI needles proportional to the difference between present attitude and that attitude which existed at receipt of the lift off signal by the computer.

b. PCR #24 – The orientation of the CSM rendezvous radar transponder had been modified on Spacecraft 103. This program change takes into account its new alignment in determining preferred attitude of the space- craft during the rendezvous phase of the mission.

c. PCR #37 – An error was found in the formulation of the Lambert guidance which caused long duration burns such as TPI using the RCS pro- pulsion system to be in error. This obvious deficiency is being corrected.

3. SUNDANCE – Sundance, the earth orbital LM program, currently scheduled for delivery on March 15 had one PCR (#30) approved the other day. The time the DPS should operate at 10% thrust (currently fixed at 26 seconds) will be moved into erasable memory such that it can be modified if some other value is found to be more suitable. This change is part of an effort underway to reduce DPS constraints from both the standpoint of guidance system accuracy and buildup of helium tank pressure. Another change (PCR #39) which the crew is anxious to have implemented deals with providing an automatic attitude control of the spacecraft during the latter phases of rendezvous such that the spacecraft Z-axis would be maintained within 5° of boresight on the command module in addition to the 30° “dead band” currently implemented.

4. LUMINARY – The changed to the IMU alignment program for Luminary have been approved and MIT is implementing these simplifications to the crew procedures.

MIT has also been requested (PCR #4) to provide limited throttling of the DPS about the fixed high thrust throttle point during powered descent to compensate for thrust dispersions and, thus, permit a significant fuel saving. The impact for this change had been determined to be unacceptable for the first release of Luminary and MIT has been directed to implement it as soon as possible on some later version.

5. COLOSSUS – Schedule impact for the simplifications to platform align- ment procedures requested by the crew for the command module (PCR #16) was determined to be unacceptable for the first release of Colossus. Accord- ingly, in this case too, MIT has been directed to implement them as soon as possible – probably to be included in the second release.

6. There are a small number of other piddling modifications that have been approved which I am not going to mention here, Also, I am not going to list those which have been disapproved or delayed and I recommend that if there are some program changes in which you have special interest you get in touch with proper personnel of the Flight Software Branch. The same advice goes for additional information on those I have noted here, since my understanding is often rather limited. But I did want to make you aware of the more significant items.