Upthread: Results of the June 11 Apollo Software Configuration Control Board (ASCCB) meeting (Jun 12, 1968)
Downthread: AGS program changes (Jul 26, 1968)
See list attachedJUL 1 196868-FM-T-144PA/Chief, Apollo Data Priority CoordinationResults of the June 25 Apollo Spacecraft Configuration Control Board (ASCCB) meeting
This memo is to inform you of things that happened at the June 25 ASCCB meeting. Some were quite significant.
1. There was a long discussion about minimum impulse APS burns and the associated propellant system freeze up problem. Actually, there is only one circumstance we know of that involves a short burn, namely after Abort Stage very early in powered descent. It is expected that workaround procedures may be developed to take care of this. Action had been given to the Mission Techniques Task Force to see that this is done.
2. It was reported that the VHF hardware and software have exactly the same range constraint – 327 nautical miles. I had been concerned that the hardware was capable of working at greater ranges and that the computer program would be limiting. This is not the case. I am still curious, however, as to whether or not the computer program should pay any attention to the “data good” discrete. Since both the astronaut and the rendezvous navigation program provide good data editing, I really don't see why we should fool with it. I would be interested in anyone's comments on this, how about you – Math Physics Branch?
3. PCR's 206 and 207 consist of 30 pages of GSOP, Chapter 4, changes and comments to make the document like the coding. They were both approved provided no coding changes were required as a result of that.
4. Two PCR's were submitted associated with the Colossus stroking test. The first – PCR 208 to provide a stroking test terminate verb – was disapproved since the probable crew action, in the event of trouble, would be to turn off the engine. PCR 209 was approved to change the restart protection such that it would terminate the test rather than to recycle into it again.
5. PCR 210 changed the DPS throttle recovery limit in Luminary. This is a zero impact program change to put two parameters in erasable memory. It was approved.
6. PCR 211 is to provide the Colossus lift-off monitor routine with protection against an erroneous lift-off signal. It was added to the Colossus 2 requirements since it would have cost four days to provide it in Colossus.
7. PCR 214 is a Luminary program change costing four days to take advantage of the recent DSKY light alterations for landing radar evalua- tion. It was, of course, approved.
8. PCR 438 was an MIT proposal to add a PIPA threshold to Colossus. MIT felt this was necessary to avoid unacceptable error during entry and to provide good range and range rate information during the final stages of the rendezvous. The errors MIT quoted for sustained operation of the Average G far exceeded those we had estimated. Fred Martin was to verify their accuracy. In the meantime, I would suggest Claude Graves and Ed Lineberry each contact MIT to make sure they are familiar with the situation. My personal opinion is this program change is probably not needed. GPB's memo, 68-FM73-29A, of June 26 seems to confirm this too.
9. PCR 439 is an MIT proposed simplification to Colossus deleting the “preferred attitude flag” in the alignment programs since they felt it is unnecessary. I must say they sound convincing to me and this PCR was approved for immediate implementation unless someone comes forward with a reason not to do it. Apparently, a similar Luminary PCR will soon be submitted.
10. An MIT proposal (PCR 441) to add a routine to permit the easy loading of a new lunar landing site location was disapproved, since it would cost two days and we could not figure out when it would be used.
11. PCR 468 to change the Target ΔV routine (R32) into a Colossus program (P76) was approved at the cost of two days impact. The reason for this was to avoid the danger of a restart clobbering the spacecraft state vector. You recall it is much easier to restart protect a pro- gram than it is an extended Verb. A similar change will be proposed for Luminary.
12. PCR 470 added a program (P68) to Luminary which will do the same sequence of operations which previously occurred when the crew hit “proceed” at the end of the landing phase descent program (P65, P66, or P67). This change would preclude an inadvertent engine shutdown before landing and would also insure that the crew would not be locked out from proceeding through the programs in an orderly way if the PGNCS navigated state vector had an erroneous attitude. The impact of two days was accepted.
13. Another significant program change (PCR 472) makes the APS abort program (P71) almost exactly the same as the DPS abort program (P70). It also makes the Verb 37 entry into P71 affectively the same as an “Abort Stage.” That is, other initialization ????????? MIT had previously provided will be omitted. This was a zero impact ???????? simplification and readily approved.
14. PCR 478 improves the LM RCS thrusting-into-orbit processor by the addition of a gravity term. The improvement prevents insertion at too low an altitude. It was approved at the cost of one day impact.
15. PCR 475 would modify the Landing Analog Display Routine (R10) in Luminary such that the program will drive the tape meter and cross pointers while in Programs 12, 70, and 71. Approval was recommended for this additional capability at the cost of one day.
16. Myron Kayton (GCD) is submitting a Sundance PCR (No. 221) to change the rendezvous radar test routine such that the data will be collected at a higher frequency. This extremely late proposal was brought about by the realization that the time is extremely short during which the rendezvous radar test could be made as the “D” mission LM passes over the White Sands Missile Range – apparently less than half a minute. It is apparent that either a program change will be required, a location other than White Sands Missile Range must be used, or that the test objective must be modified. These alternate courses of action will be submitted to the Apollo Program Manager's Change Control Board once the Sundance impact has been terminated.
17. MIT officially informed us that the lunar landmarks selected by MCC are completely unsuitable and the lunar landmark selection routine (R35) has been rendered relatively useless as a result. MIT even proposes that R35 should be eliminated.
18. There was a lengthy discussion regarding the FCSD request for raw rendezvous radar data on the DSKY. FSD intends to coordinate this to make sure the simplest possible program change may be defined based on the crew requirements and MIT's program constraints. (Incidentally, MIT apparently intends to propose an official PGNCS constraint limiting the use of P20 to ranges greater than five miles.)
That's it – at least the things I think would interest you most – it was quite a productive meeting wouldn't you say?