Downthread: Third Mission “C” Rendezvous Mission Techniques meeting (Feb 07, 1968)
See list belowJAN 24 196868-PA-T-16APA/Chief, Apollo Data Priority CoordinationSecond Mission “C” Rendezvous Mission Techniques meeting
1. On January 17 we held our second Mission “C” Rendezvous Mission Techniques meeting. I feel we have this mission phase pretty well in hand conceptually. There are a number of numerical limits yet to be set.
2. It is evident that limits must be set regarding the magnitude of the delta V residuals following the NCC₁ maneuver which we would trim out with the RCS. That is, if they are small we will trim them. If they are large we will not trim them but will account for the disper- sions they create with the NCC₂ maneuver. This limit must be estab- lished. It is expected to be in the order of 10 fps which is not an unlikely value using the present PNGCS design and thrust alignment uncertainties. Residuals at NCC₂ and NSR must be trimmed. If excessive, the alternative is to abandon the rendezvous, thus, the rendezvous RCS red line will probably fix the limit.
3. It had been established that the ground would update the state vectors of both the command module and the S-IVB at two times during the rendezvous exercise. The first is prior to the NCC₁ maneuver and the second is prior to the NCC₂ maneuver. We have now established the time tag for each of these state vectors as follows: the first command module state vector will be time tagged 6 minutes before the NCC₁ maneuver and the first S-IVB state vector will be time tagged 6 minutes after the NCC₁ maneuver. Time tags for the state vector update prior to NCC₂ for the command module will be 6 minutes before the NCC₂ maneuver and for the S-IVB will be 6 minutes after the NSR maneuver. External delta V targeting parameters will be related to the crew at the same time the state vector updates are made.
4. Two platform alignments will be made during this exercise, one in preparation for the NCC₁ maneuver and one in the time period between NCC₂ and NSR. Orientation of the platform for the entire rendezvous exercise shall be such that at the TPI time as predicted at the beginning of this mission phase the spacecraft FDAI 8-ball would read 0, 0, 0 when the spacecraft is in a horizontal, heads up, wings level, in plane attitude.
5. The 8-ball orbit rate torquing device (ORDEAL) will be used, of course. Although the primary mode is for the crew to determine initiation ????? time onboard the spacecraft, it is also desirable that the ground have the same capability as a backup. Ed Lineberry was given the action item of establishing precisely how the torquing rate parameter was to be computed on the ground. This will be specified in mathematical equation format probably as a function of spacecraft attitude and optimized for rendezvous.
6. The event timer will not be set up to run continuously throughout this mission phase but rather will be used to countdown to each of the burns. The only exception is that the crew will start it counting up at the TPI maneuver.
7. We had a lengthy discussion regarding the TPI maneuver. Specifically, there were two things which must be done. A decision must be made in real time as to whether to use the spacecraft computed TPI maneuver or the ground computer maneuver. Following this decision there is the task of executing one or the other. As a result it was identified as necessary for the ground to transmit to the crew two sets of TPI maneuver targets— one for comparison with the PNGCS and one for execution if the PNGCS is declared NO GO. In order to make the comparison in the order of 9 to 12 minutes before TPI, the best PNGCS output for the crew to use is the TPI maneuver in the external delta V coordinate system from the P-41 RCS thrust program. Therefore, for compatibility the ground will transmit the same parameters for comparison purposes. If the crew determines the PNGCS is all right they will execute the onboard determined maneuver using P-41. The second set of targets transmitted from the ground will be used only if the PNGCS solution is declared unsatisfactory. These are delta V's which the crew should see count up in the DSKY as they utilize P-47 to execute the maneuver manually with the spacecraft X-axis boresighted on the target and with wings level. The ground computation will assume that spacecraft attitude in addition to compensating for the 7½° control axis rotation from the body axis. Burn duration of these delta V's will also be sent to permit execution with SCS if the PNCGS maneuver capability has failed.
8. It is our understanding that the navigation W-matrix which governs the weighting given the optical observations are automatically initialized in the spacecraft whenever new state vectors are transmitted from the ground via P-27, or when the crew manually requests re-initialization. It is our desire that the W-matrix be at its initialization values at the time the first sextant observations are obtained following NSR. Since state vectors were transmitted prior to NCC₂ with no subsequent sextant observations it is our understanding the W-matrix should still be at its initialization state at that time. If that is not the case, the crew must re-initialize them after NSR but only then. Specifically, it is judged undesirable to re-initialize following the TPI maneuver.
9. It is currently planned that the one and only midcourse correction will be set up to occur 20 minutes after TPI. We did not have time to discuss this maneuver or the terminal braking but will do so at the next meeting. Of particular interest is the desirability of braking and what to do next. Also, what is the state of the S-IVB at that time? In order to avoid conflict with midweek travel, the next meeting will be held starting at 9:00 a.m. on February 2—already breaking that nice schedule I set up!
10. Subsequent to this meeting I discussed our conclusions with Tom Stafford and Donn Eisele, who both concurred as of this time.