Upthread: Second Mission “C” Rendezvous Mission Techniques meeting (Jan 24, 1968)
Downthread: Fourth Mission “C” Rendezvous Mission Techniques meeting (Feb 21, 1968)
See list belowFEB 7 196868-PA-T-29APA/Chief, Apollo Data Priority CoordinationThird Mission “C” Rendezvous Mission Techniques meeting
1. Based on our two previous meetings, TRW had prepared the first version of the mission techniques flow diagrams for the “C” Mission Rendezvous. This meeting on February 2 was devoted to going through that flow. As usual, in spite of the fact we thought we had everything all worked out, we ran into numerous items requiring further resolution.
2. The first discussion involved the logic associated with determining whether or not a pre-phasing maneuver need be made prior to the actual rendezvous exercise itself. This maneuver is only necessary if dispersions are far in excess of expected. It is intended to assure no collision of the CSM and the S-IVB regardless of whether the first maneuver in the rendezvous sequence, NCC₁, is performed or not. In the nominal flight plan the closest approach is something like 60 miles, and after finally finding out what this was all about we set the GO/NO GO test for this maneuver based on the criteria that the predicted closest approach should never become less than 5 miles. This value was made small in order to make the likelihood of the maneuver extremely small but was made large enough to compensate for any inaccuracy in orbit determination and maneuver dispersions.
3. A number of us were surprised to find that a Sextant tracking rendezvous navigation exercise has been planned by Flight Crew Support people prior to the first maneuver in the rendezvous sequence (NCC₁). Apparently, it had been in the timeline all along but somehow we had not noticed it. Previously, we had all agreed on the desirability of rendezvous navigator with the sextant following the NCC₁ maneuver as a spacecraft systems test and, perhaps more important, as on-the-job training for the crew prior to the real thing an orbit later. I guess they are going to keep the earlier exercise in the timeline too, but it was emphasized that it is a low priority activity and if it interferes with anything else it should be the first to go.
4. In the sequence of preparing for the NCC₁ maneuver which occurs within a few minutes of exiting a darkness period, we have included a final fine alignment of the platform followed by a sextant/star check made with the spacecraft in the inertial NCC₁ maneuver attitude. The objective of this star check was to provide assurance that the whole guidance system is operating correctly, at least to the extent of having gotten the spacecraft into the proper attitude for the maneuver. It was agreed by everyone that on-time execution of the NCC₁ maneuver is of highest priority and the crew people felt that not less than 13 minutes should be allotted to prepare for it. Accordingly, a ground rule was established that the crew would do this fine alignment of the platform and then proceed to the sextant/star spacecraft inertial attitude check, if time permitted, but that either or both would be terminated or eliminated completely when the Time-to-Go to the maneuver reached 13 minutes. It was also agreed if the sextant/star check was performed and inertial attitude error exceeded .9° that this was indication enough that something was wrong and the entire rendezvous sequence would be delayed at least one rendezvous revolution.
5. Considerable discussion ensued regarding the NCC₁ and NCC₂ maneuvers, particularly with regard to whether or not residuals should be trimmed. As of not it is planned that in order to save RCS fuel only small residuals in NCC₁ would be trimmed and large residuals would be left to be taken care of by NCC₂, more than likely utilizing the SPS engine. As reported previously, Ed Lineberry's people are in the process of analyzing the situation parametrically to permit selection of the actual test numbers defining “small” and “large residuals.” Two things agreed on were:
a) Since the NCC₁ and NSR maneuvers are approximately one revolution apart it is possible that any out-of-plane residual in NCC₁ can be easily and cheaply removed at NSR. Therefore, it does not seem reasonable to do any trimming in the out-of-plane direction at NCC₁.
b) The matter of how small an NCC₂ maneuver should be made with the SPS was tentatively resolved by saying that the SPS would be used for any maneuver it could handle including use of the minimum impulse mode. This, it would be used for maneuvers in the order of 10 to 15 fps and greater. It was emphasized, too, that whatever residuals do occur at NCC₂ must be trimmed with RCS in order to maintain an optimum rendezvous solution.
6. There is some concern about use of the SPS on this first manned mission, particularly these first maneuvers. For example, is there any problem in making three SPS burns within one revolution? And, can one of them be a minimum impulse burn? That is, is there a freezing problem or something? Any comments on this would be appreciated.
7. That is all I can remember that happened. The next meeting is scheduled for Friday, February 16, at 9:00 a.m. in Building 30, Room 2032B.