Upthread: AGS program changes (Jul 26, 1968)
Downthread: Results of the October 8 Apollo Spacecraft Software Configuration Control Board (ASSCCB) meeting (Oct 16, 1968)
See list belowSeptember 23, 196868-FM-T-201FM/Deputy ChiefResults of September 17 Apollo Spacecraft Software Configuration Control Board (ASSCCB) meeting
The first three hours of this marathon meeting were devoted to imple- mentation of the descent program in LUMINARY. The currently approved plan is to implement the one-phase descent scheme proposed by Floyd Bennett and his merry crew. However, MIT has been directed to implement it in such a way that it would be possible to fly the old two-phase technique – if desired. Almost all effort is to be devoted to the one-phase technique with only one day's worth of testing included for the two-phase – and no design improvements are to be developed or included in the two-phase. What this really means is that at the cost of one day's worth of testing we have provided some cheap insur- ance for being able to change back later if we have to. If the decision were made to use the two-phase, a considerable amount of additional testing would be required and at that time, program deficiencies might be uncovered revealing that that capability does not really exist.
Several things that interested me about the new one-phase are:
1. The decision of which way to go – one or two-phase is made pre-flight and an option flag is set in erasible memory before launch.
2. The much smoother attitude time history of the one-phase scheme may very well permit the DPS trim gimbal to do all the steering, substan- tially reducing RCS usage.
3. MIT is providing a crew option via the DSKY for manually changing from P63 to P64 in the event they want to do that earlier than the auto- matic switch.
4. High-gate is now being defined as the time at which the landing radar position is changed.
MPAD has submitted a Program Change Request (PER 249) to eliminate a lock-out of the landing radar data above 35,000 feet (estimated altitude). This vas a two part change since it is necessary to fix a program to allow the data to be read and also necessary to change the weighting function such that data above 35,000 feet is not given a zero influence on the state vector. Since the proposed change was estimated to cost three days schedule impact, Floyd Bennett was requested to rewrite his PCR to simplify the requirement while achieving the same end results. Essentially, it amounted to replacing the 35,000 foot boundary with a 50,000 foot boundary. In addition, it is necessary that I verify that the rendezvous radar powered flight designate routine (R29) can be eliminated as a requirement and thus be made uncallable from the descent programs. Subsequent to the meeting I did that and have informed FSD.
Guidance and Control Division brought in two PCR's (Nos. 224 and 248) which influence the processing of the landing radar data. One changed the reasonability tests and the other provided a delay in utilizing landing radar data for four seconds after the LGC receives a “data good” discrete because it takes that long for the landing radar output to converge on the true value after lock-on. Both were approved at a cost of one day each.
MIT was requested to determine the impact of changing the descent program such that it would be possible for the crew to command all four RCS jets in the minus X direction immediately upon touchdown in order to smoosh the LM into the lunar surface and keep it from turning over while the DPS belches to a stop. Ain't that the damnest thing you ever heard?
Flight Crew Support Division presented a proposal to modify COLOSSUS II to permit the crew to manually steer the TLI burn in the event of a SIVB IU failure. No action will be taken on this until the technique is approved by Mr. Low's CCB.
A really ancient PCR, No. 132, submitted by the crew to provide a VHF ranging data good discrete light, was finally disapproved since the spacecraft will not be modified to provide the additional DSKY lights which would have been used for this.
Tom Gibson presented their proposal, which was approved, for the follow- on spacecraft programs. A so-called COLOSSUS I Mod A will be prepared, which is basically the COLOSSUS I program with all known anomalies corrected plus the following three simple program improvements:
2. Backup integration
3. An improvement on the mark incorporation.
It is planned that a tape release of this program will occur on December 1, at which time mission operations testing (Level 6) can be started along with rope manufacture. This program will be used for the D mission.
A COLOSSUS II program is also now being developed which starts from the COLOSSUS I Mod A baseline to which CSI/CDH will be added. I suppose it will also include anomalies uncovered too late for the Mod A version. MIT's estimate of tape release for this program is February 1, 1969. It is felt that this program can probably be made ready for Spacecraft 106 – that is, the flight after D, whatever that is. VHF ranging, incidentally, should also be available on spacecraft 106.