See list attachedJuly 3, 196969-PA-T-103APA/Chief, Apollo Data Priority CoordinationSome new ideas on how to use the AGS during Descent
This memo is to fill you in on a couple of late crew procedure changes proposed for the G mission regarding AGS operation during descent. The first is a technique to prepare the AGS for immediate ascent which can be used to quickly reinitialize the AGS LM state vector immediately after touchdown if there is any concern that the navigation during descent has fouled them up somehow. This is possible since the LM state vector on the lunar surface can be easily predicted before descent. Specifically, it involves loading some storage location through the DEDA just after the final state vector update from the PGNCS at about seven minutes before PDI. The numbers loaded would be the lunar radius (240 + 56923) and the lunar rotation (262 – 00150), which essentially constitute the entire state vector on a lunar surface. The rest of the state vector elements (241, 242, 260, 261) are all loaded zeros. None of these addresses are used during descent or descent aborts so this procedure does not conflict with anything planned. The idea is that immediately after touchdown, when the lunar surface flag is set, the crew would key in 414 + 20,000 instead of updating altitude as currently planned. This would initialize the AGS state vector with these quantities quite accurately to support an immediate ascent. This procedure is supposed to be brought to the Crew Procedures Change Control Board very soon, but I noticed that Buzz Aldrin was already doing it during the Descent simulations last week.
Everyone I have talked to feels it is a good thing to do provided it does not overload the crew.
The second possible addition to the crew timeline involves making use of the AGS DEDA display just after touchdown to provide the crew a little more information regarding his touchdown attitude condition. Bob Battey called me with a Braslau suggestion (AGS/TRW) that, since the DEDA is not used during the terminal descent, immediately after touchdown it is pos- sible to call up address 130, a component of the transformation matrix, which is essentially the cosine of the tilt angle displayed in octal. It was noted that this parameter has an interesting characteristic. If the spacecraft is perfectly vertical, the DEDA will read 40,000. If the space- craft is tilted 42°, which is the critical tilt angle, the DEDA will read just under 30,000 regardless of the direction of tilt. Display above 30,000 is okay – the bigger, the better – and below 30,000 is bad news. This convenient crossover value seems to make this a possible extra cue for the crew to quickly assess whether the spacecraft has tilted more or less than the critical tilt-over angle. So far, none of the experts I have spoken to have seen anything wrong with this idea and generally consider it a desirable thing to do. That is, the procedure should work and should provide some useful intelligence for the crew, if they get into a suspected tilt-over situation. It could certainly not be con- sidered mandatory and so the decision as to whether to do it or not to do it rests entirely on the crew's task loading during the last several hundred feet of descent. Simply, should the crew be fooling with the DEDA at this time? Ordinarily I would say no, but Buzz seems to be able to get music from that little mommy with his head turned off and both hands tied behind him.