FC5/Chairman, Ascent Phase Mission Techniques Working GroupJAN 15 196868-PA-T-6APA/Chief, Apollo Data Priority CoordinationSome thoughts about Lunar Ascent procedures
1. Charley, please excuse this memo. It's to help me remember and let some others know what we're considering.
2. Now that we have almost certainly lost LM rendezvous radar as a tie breaker for AGS/PGNCS discrepancies in velocity magnitude during lunar ascent, we will have to pin down procedures that are consistent with what's left. I assume we will utilize the VHF ranging device if it turns out to be capable under ascent conditions (that is, multipath, range, etc.). Since it is not on the telemetry downlink, I suppose it requires voice relay from the command module to the LM for the LM crews use. In addition to that, it seems highly likely that velocity magnitude difference can be detected from the DSKY and DEDA during the final stages of ascent, both onboard the spacecraft and on the ground, which will enable us to determine that a PNGCS engine shutdown will be undesirable. I refer to the situation where the AGS shows a significantly smaller velocity magnitude than the PNGCS. Accordingly, specific procedures will have to be established for preventing the PNGCS from doing the job by manually inhibiting it and by taking over spacecraft control in some way. I think we all agree it would be undesirable to switchover to the AGS. I think we also agree that it would be undesirable to have the APS “prematurely” shutdown forcing immediate re-ignition to make up the AGS displayed delta V deficiency.
4. The question before us is how and when do we evaluate the delta V deficiency, what is the limiting value, how does the crew inhibit the shutdown signal and what sort of attitude control mode will be used? Following the maneuver, what will be the procedure to determine what the situation really is, that is, AGS right/PNGCS right, and how do we handle the situation subsequent to that?
5. It would be interesting to know maximum dispersion in Ascent burn time. It would be interesting to know how long it takes to re-ignite the APS once the PNGCS has shut it down. It would also be interesting to know what sort of transient you could expect if you actually did switchover from the PNGCS to the AGS with only a velocity magnitude difference. I suppose that may not be a totally unacceptable procedure.