Upthread: Third “D” Mission Rendezvous Mission Techniques meeting (Feb 08, 1968)
Downthread: Fifth “D” Mission Rendezvous Mission Techniques meeting—don’t miss Paragraph 5; it’s great! (Mar 01, 1968)
See list belowFEB 18 196868-PA-T-33APA/Chief, Apollo Data Priority CoordinationFourth Mission “D” Rendezvous Mission Techniques meeting
1. The first item discussed at this February 18 meeting really involved all Apollo rendezvous, which accounts for the long attendance list. The subject was whether or not to change the orbital travel between Terminal Phase Initiation (TPI) and theoretical braking from 140° to 130°. It was stated that this change would make necessary reworking the crew procedures for the 101 “C” mission flight which would delay accurate crew rendezvous training about 9 weeks. This was considered unacceptable and so the change is not being made on that flight. For all other Apollo rendezvous exercises it is intended to change to a 130° transfer angle. This change is said to have very little effect on the amount of work required to prepare for the missions; there are no changes required in spacecraft or ground guidance programs, or anything else we could think of. The only disadvantage uncovered was a slightly larger theoretical RCS propellant cost which must be cleared with the ASPO Configuration Control Board (Tindall and Contells have the action). The advantages are primarily associated with the fact that the 130° transfer angle provides nominally zero line-of-sight rates during the braking phase. This permits the crew to make those maneuvers earlier, more efficiently, and more easily. Another advantage is that is results in a higher energy transfer which reduces effect of TPI dispersions. This is particularly important in the event of failure of the ranging device— radar or VHF. Also, 130° is more consistent with making the midcourse correction at 90° after TPI as is currently proposed to take care of out-of-plane conditions more efficiently. The period following a 90° midcourse correction is thought to be about optimum. It should be noted that the 140° value had more merit some time ago when it was considered acceptable to utilize large differential altitude. More recent work on CSM rescue and other non-nominal rendezvous situations had shown it possible to maintain the Delta h below 25 miles which makes the theoretical fuel saving for the 140° transfer rather insignificant. All mission planning, crew procedures, training, etc,. associated with the “D” mission and subsequent will utilize the new 130° transfer angle unless, and until, we are unable to convince the Configuration Control Board that it's the right thing to do.
2. Associated with the “D” mission we finally all agreed to proceed assuming the nominal LM/command module separation will be made under the control of the AGS with residuals trimmed based on PNGCS. It is felt to be a safe, accurate procedure which the crew has found easy to do in their simulators.
3. We had what I thought to be an extremely fruitful discussion on how the AGS should be used throughout the rendezvous exercise one the “D” mission. Although it was obvious we did not reach agreement, I think the discussion brought this subject clearly into focus and two weeks of contemplation plus some rather simple analytic studies should make it pretty east to decide what to do the next time we get together. It was agreed that the role of the AGS on this mission should be to make most probable the return of the LM to the command module in the event of PNGCS failure. It is not intended to use it to monitor the PNCGS nor should it be compromised to get an optimum systems test on it. Therefore, the questions to be answered deal with how to keep the AGS in the best state of readiness to carry on a successful rendezvous in the event the PNCGS had failed. For example, at what times should the AGS be re-initialized from the PNCGS and when, if ever, should radar data be fed into the AGS? To give an idea of what sort of thing we are thinking about, I would like to present my proposal emphasizing that this had, by no means, been agreed upon. It is based on the assumption that the PNGCS is still thought to be working properly with an objective to keep the AGS prepared to take over in the event the PNGCS fails.
(a) Checking of the PNCGS would be by comparison with the ground computed solution only. That is, comparisons of maneuver targeting from other sources, such as the AGS, backup charts or the CSM, would not be made to commit to the PNCGS. The PNCGS solution would be used providing it was within acceptable limits of the MSFN solution.
(b) The state vectors in the AGS would be updated each time PNCGS was confirmed to be acceptable. This will likely be at each time it is committed to make the next maneuver using the PNCGS.
(c) AGS alignments would be made each time the PNCGS is realigned and each time the state vector in the AGS is updated from the PNGCS.
(d) No radar data would ever be input into the AGS as long as the PNGCS is working. This is the same procedure as I expect will be used in the lunar mission.
(e) There is no need to prepare or learn to use back up charts for CSI and/or CDH maneuvers.
In the event of a PNCGS failure I would use the AGS in almost the identical manner in which the Gemini spacecraft was flown. That is, ground targeted maneuvers up to TPI, then use of radar data in the AGS to make onboard computed maneuvers from TPI on in. And, of course, the command module could play a role here, too, probably making the TPI maneuver and/or the braking maneuver and, of course, it can compute targeting for the TPI for both itself and the LM. —Just a proposal. Incidentally, it was interesting to many of use to learn the LM has a C-band Radar beacon. This tends to increase confidence in the ground quite a bit.
4. TRW distributed copies of their first cut at the mission techniques logical flow for the rendezvous exercise up to and including the so-called insertion maneuver made by the LM to break out of the initial football rendezvous trajectory. These flow charts will probably be reviewed in detail at the next meeting.