Upthread: Mission “D” Rendezvous Mission Techniques meeting (Jan 24, 1968)
Downthread: Fourth Mission “D” Rendezvous Mission Techniques meeting (Feb 18, 1968)
See list belowFEB 8 196868-PA-T-30APA/Chief, Apollo Data Priority CoordinationThird “D” Mission Rendezvous Mission Techniques meeting
1. We had our third “D” Mission Rendezvous Mission Techniques meeting on January 29. I am afraid it was a rather frustrating meeting for everyone. But on second thought—what's new?
2. One thing we did accomplish, which I consider significant, is that everyone agrees the command module should be operated during the LM active rendezvous as proposed in the last minutes, that is, target the CSM to make slightly delayed mirror image LM rendezvous maneuvers. Ed Lineberry reported that for the CSM mirror image LM maneuvers with one minute time delays are quite acceptable for maintaining the rendezvous situation. Accordingly, it is proposed that as a nominal procedure we target the command module with the LM computer maneuvers to be executed with a one minute time delay in the event the LM is unable to maneuver. There is a refinement under consideration to be made in the procedure. Namely, we will establish preflight small delta V biases to be added by the CSM crew to the LM maneuver relayed to him by voice. It is anticipated these do not add significant complexity to the operation and may avoid dispersions which, although acceptable, are probably unnecessary. If future study shows this refinement to be a poor one, it will be dropped.
3. Morris Jenkins reported that the mission plan should probably be changed to make the two short APS burns with RCS interconnect instead since they contribute little useful knowledge to APS or PNCGS performance and do introduce some minor disadvantages. He stated that these maneuvers are not necessary to meet any mission requirement. This is someone else's business. Of course, we'll be interested in the results.
4. It has been proposed that the initial separation of the command module from the LM be performed in a manner similar to that currently planned for the lunar landing mission. On that mission one-half revolution before DOI the command module will make a radial 1 fps maneuver downward which puts it slightly in front of and at the same altitude as the LM at the time of DOI. On the “D” mission this separation maneuver would occur one-half a revolution before the initiation of the rendezvous sequence which starts with a 40fps LM maneuver radially upward. The big question was which vehicle should make this 1 fps maneuver—the command module as on the lunar landing mission or the LM to avoid perturbing the command module state vector. Of these two relatively weak considerations, the latter seems more valid and so I propose that we carry this maneuver as LM active until some overwhelming disadvantage is uncovered. Obviously, the maneuver would be carried out using RCS propulsion and the Average G program (P-47). The command module would update its version of the LM state vector with the Target Delta V routine (R-32).
5. Considerable discussion centered on spacecraft activities between this small preparation maneuver and the initialization of the football rendezvous one-half revolution later. Everyone agreed that the LM should carry out an undocked fine alignment of its platform during the darkness period it enters about 15 minutes after separation. It is probable that some LM radar checks should also be made, but it was agreed that these checks should be performed in some way that avoids modifying the state vectors in the LGC. It was the concensus that these rendezvous radar observations could potentially do harm to the state vector, but could certainly not improve it.
6. By far the most time at this meeting was spent on selection of the desired platform orientation for this exercise. Everyone agrees it must be in plane, but it soon became evident that the final choice of the in-plane components must be rather arbitrary, since there is no really significant advantage to any of those currently proposed. This is particularly true since it is intended to utilize the ORDEAL to drive the ball, thus obscuring the alignment used. In the absence of agreement, then, I would like to propose the following:
a) that a single inertial orientation (REFSMMAT) be used through- out the entire rendezvous sequence.
b) that the orientation be specified by ground computations using the “desired REFSMMAT” mode as opposed to using some onboard computed alignment.
c) that the orientation be determined associated with the final LM TPI of the entire rendezvoud exercise,
d) that the platform alignment be similar to that encountered in the lunar landing mission, that is, 0, 0, 0 on the inertial ball when the LM is oriented to coincide with local vertical at TPI or some soon-to-be specified number of minutes prior to TPI. The value “10” was suggested.
e) that command module alignment be either identical to or different from the LM by an integer number or 90° increments.
It is to be noted that, with both vehicles operating, voice communication between them and the ground and command uplink capability will be difficult at best during station passes and the objective in this proposal is to keep the operation-voice communications, procedures, etc., —as simple as possible—to avoid situations where a clear understanding by all parties involved is jeopardized.
7. There was a brief discussion of clock synchronization of the two spacecraft. It was not clear what the effect of non-synchronization is, although it was reputed possible for the ground to synchronize them within fractions of a second. This matter requires more thought.
8. If anyone comes, we'll get together again at 1:00 p.m. on February 18. One thing to be discussed is the proposed change of the terminal phase transfer angle (wt) from 140° to 130°— which probably applies to all flights.