Seventh “D” Mission Rendezvous Mission Techniques meeting

See list belowAPR 2 196868-PA-T-87APA/Chief, Apollo Data Priority CoordinationSeventh “D” Mission Rendezvous Mission Techniques meeting

1. At the seventh “D” Mission Rendezvous Mission Techniques meeting on March 25, we spent most of our time discussing activity in the football rendezvous, specifically, under what circumstances and how to abort. It turned out that the same ground rules and techniques probably apply equally well to the pseudo-TPI maneuver halfway through the rendezvous exercise. I think we've gone a long way getting these things pinned down.

2. In the first paragraph I would like to clean up a couple of old open items from some previous meetings.

a. FCD had been requested to look into the RTCC/MCC capability to be sure it was possible for the flight controllers to compute and relay to the crew the CSM gimbal angles to point the LM AOT toward a selected star in order to carry out a docked LM platform alignment. Bill Fenner reported that this capability does exist. Out of this discussion came the suggestion that we should probably prepare some sort of crew chart giving pseudo- sextant shaft and trunnion angles for the AOT as a function of the docking ring index reading in order that the crew could do this job themselves.

b. We spent a little time discussing the required accuracy of LM/CMS clock synchronization for the rendezvous exercise. It was concluded that misalignment of these two spacecraft clocks in excess of one second should not product any significant problem in the rendezvous except as an opera- tional annoyance. In conclusion, it seemed as though the current mission rule is fine. Specifically, either clock should be reset by the ground whenever it gets out of synchronization with the ground by more than one- half second. Thus, in the worst case, the LM and CSM clocks could conceivably be one second apart.

c. In order to avoid confusing of terminology, it was decided the maneuvers would be referred to as follows: the small one or two fps burn to separate the two spacecraft from one another initially, to avoid station keeping, shall be called the “separation” burn. The much larger maneuver, which starts the LM on the initial football rendezvous, will be called the “phasing” burn.

d. Regarding the phasing burn, it was restated that this maneuver may be executed with targeting established preflight, that is, it will not be updated in real time. It was noted that the AGS will be used for executing the burn and the PNGCS will be operated in a follow-up mode using P-30/P-40. It was emphasized that, because of the difference between AGS and PNGCS, the external delta V targeting parameters will be slightly different for each.

3. The rest of the meeting was devoted to the football rendezvous. We spent some time discussing the sort of trajectory-oriented system failures which would cause us to abort the rendezvous exercise and to return the LM to the CSM immediately. It was important to establish which of the systems may have failed because, obviously, the manner in which we would perform this rendezvous would be significantly influenced by the status of the spacecraft systems.

4. The following is a list of trajectory-oriented system failure which would force us to abandon the rest of the rendezvous exercise:

a. Rendezvous radar failure

b. LM PNGCS failure

c. CSM G&N failure

d. RCS jet failures

e. DPS failure to start when attempting to do insertion burn.

5. Based on those abort situations we arrived at the following general conclusions regarding how the rendezvous should actually be performed:

a. It was decided that whichever spacecraft was having the systems problem should be the passive vehicle for TPI and the subsequent midcourse corrections. It may or may not be desirable for that vehicle to perform the braking maneuver depending on the situation. It was noted that the systems problem referenced to is not necessarily one of those listed above, but could just as well be some other critical system such as, ECS, fuel cells, etc. The reason for this conclusion is:

(1) To relieve the crew with the problem spacecraft of rendezvous activity in order that they may devote full attention to the problem.

(2) To use the spacecraft which has all of its systems still working to do the rendezvous.

Of course, I am sure there will be some exceptions to this rule, although, I hope not too many. One probable exception would be a failure of the LM PNGCS, but with the rendezvous radar still working. Under this circumstance it would probably be preferable for the LM to be the active vehicle since it has superior observational data (the RR) and a guidance and control system (the AGS) adequate to carry out the maneuvers.

b. We had a lengthy discussion regarding whether the rendezvous should be carried out with the rendezvous transfer angle of 80°, 90° or to use the standard 130°. It was finally concluded that we should use the 130° transfer for the following reasons:

(1) The lighting conditions are superior. Specifically, that rendezvous would occur in darkness for the shorter transfer, unless the ???????????????????????????????????????? and this is not ??????? thing ????? which ???????? the proper lighting conditions for the rest of the rendezvous exercise.

(2) More time is available for obtaining rendezvous navigation observations after TPI.

(3) Use of 130° provides the standard rendezvous approach for which all training, crew backup charts, etc.. have been prepared. It was noted that under some conditions it would be desirable to delay making the TPI maneuver for a revolution or two, depending on the spacecraft systems problem. That is, as long as the LM remains in the football orbit, condi- tions remain relatively constant for each successive revolution.

c. It was also concluded that ordinarily it would be preferable not to stage the DPS for the following reasons:

(1) Primarily it seems very desirable in an emergency situation to retain all possible consumables in the LM to avoid getting into a time critical situation. It is recognized that to perform an active rendezvous with the LM unstaged does present some problems and costs additional RCS, but in the general case, this is probably an acceptable penalty.

(2) A secondary consideration for not staging the DPS is that it will eliminate the concern of a possible recontact.

6. It was also concluded that a nominal mission planning change should be made to provide the best possible abort conditions and that the magnitude of the phasing maneuver should be increased about 50 percent in order to provide a reasonable large range rate at the braking maneuver. The current plan provides a closing velocity of about 13 fps, whereas it is generally agreed that it should be in excess of 20 fps. Morris Jenkins has the responsibility for getting the mission plans changed to increase the phasing maneuver from 40 fps to something in excess of 60 fps to provide this characteristic. Actually, since this will result in an abort delta h very near nominal, it was recommended that the magnitude of the phasing maneuver be chosen to make delta h exactly the same as that ???? so that all nominal terminal phase work will be directly applicable.

7. Based on all of the above, we concluded that as a standard operating procedure during the football rendezvous the CSM should be targeted and prepared to execute the TPI if an abort is necessary.

8. As noted in the first paragraph, after looking over the results of our discussions of aborts from the football, there seems to be no reason the same conclusions do not apply equally well to aborts from the first half of the rendezvous exercise at the overhead TPI opportunity. At least we will proceed using these techniques for both cases for now. Furthermore, if the “E” mission rendezvous is made identical to the “D,” as now appears probable – of course, all of this will apply to that flight too.