See list belowJUN 3 196868-PA-T-114APA/Chief, Apollo Data Priority CoordinationLunar Rendezvous Mission Techniques
1. On May 28 we finally kicked off the Lunar Rendezvous Mission Techniques business. Because of the imminence of missions “D” and “E”, we started on those first some months ago. Now I wish we hadn't because they are so darned complicated. I have a feeling the lunar rendezvous can be finished up quicker than they can and, of course, some of the things we are planning to do in the lunar operation should influence how to go on the development flights.
2. This meeting was devoted to establishing some ground rules upon which we can base our work as well as making a cursory survey of anticipated problem areas requiring special attention. This memo will do little more than list these items. Some of the assumptions are debatable, of course, and if ultimately proven wrong, will require changing some things. However, we have got to get started somewhere.
3. The following is a list of the ground rules we established:
a. Assume Luminary (the LM spacecraft computer program) will remain as designed today for the lunar missions.
b. Assume Colossus (the command module spacecraft computer program) will be the same as designed today, plus the addition of the CSI and CDH rendezvous targeting programs and the addition of IMU pulse torquing.
c. Assume the VHF ranging device on the command module is operational.
d. Assume the “G” mission lunar rendezvous operation is as currently planned. That is, it should be completed within approximately one revolution. The coelliptic differential altitude is 15 n.m. and the terminal phase transfer angle is 130°.
e. Assume LM liftoff shall be on-time only. That is, there is no launch window.
f. Assume MSFN rendezvous assistance (that is, participation) is minimal as long as the situation remains essentially nominal.
g. Assume all in-orbit LM maneuvers will be made with the RCS propulsion system.
h. Assume both spacecraft will update the LM state vector based on their rendezvous navigation.
i. Assume that if an out-of-plane situation exists after LM ascent, all necessary maneuvers will be made prior to TPI to establish an in- plane rendezvous situation during terminal phase.
j. Assume all plane change maneuver targeting to be executed by either vehicle will be done by the CSM based on its sextant tracking.
4. The following is a list of problem areas, some large and some rather trivial for which we must seek answers:
a. By far the most significant is the problem of how to handle the out-of-plane situation. More on this later in the memo.
b. What is the source of the LM state vector in the command module computer after LM insertion?
c. Should frequent VHF range ambiguity tests be made by the crew as a standard procedure?
d. Should we include onboard determination of radar angle bias in the PGNCS?
e. Should rendezvous radar data be input to the AGS?
f. Should in-orbit platform alignments be performed by either spacecraft after LM insertion into orbit?
g. Should the CSM be targeted for a Hohmann Transfer to protect against a low LM insertion orbit as a standard (that is, nominal) procedure?
5. I believe for the first time the question of how to handle the out- of-plane situation on the lunar rendezvous is being attacked. Primarily as a result of our beloved three gimbal platform (choke) any difference in the LM and CSM orbital planes becomes difficult to handle. Current estimates of MSFN targeting uncertainty for the LM ascent plus LM PGNCS errors during ascent assure us that an out-of-plane situation will exist. Therefore, a basic question to be resolved is – should we plan as a nominal procedure in the timeline to make a maneuver specifically for getting the two vehicles into the same plane. The alternate, of course, is somehow to pick up pieces of the out-of-plane by incorporating out- of-plane components into the CSI/CDH/TPI burns as much as we can and then take care of the rest of it in the terminal phase midcourse maneuvers. Most of us are inclined to think we should provide a special maneuver probably using the command module. Of course, this idea immediately leads to another, namely why not eliminate the command module plane change prior to LM ascent and incorporate both that and the dispersions picked up during ascent into a single burn performed after sufficient in-orbit rendezvous navigation to determine the actual situation. There is a sort of philosophical question here since if everything worked perfectly, no post-ascent plane change would be required if we made the CSM maneuver before ascent. It was the opinion of the majority, I think, that we would be naive to think that everything will work perfectly. Some of the basic questions to be answered in order to make this important decision deal with its effect on rendezvous navigation and the impact of an extra maneuver on the timeline. For example:
a. How does this effect rendezvous radar navigation?
b. How does this effect VHF rendezvous navigation?
c. If we pulse torque the platforms, will that introduce unacceptable errors in the rendezvous?
d. What platform orientation should be used in the CSM before and after the plane change?
e. How does this effect the command module mirror image maneuver targeting?
f. What is the maximum plane change delta V which can be left until terminal phase? (This also has implications on RCS delta V residual trimming and possible use of SPS only.)
g. Should the out-of-plane maneuver be made at its natural node or should two burns be planned instead?
h. Should we plan any out-of-plane yaw steering during ascent?
i. One important matter which Ed Lineberry will discuss with Milton Contella (FCSD) prior to the next meeting regards selection of optimum TPI time, currently set at 20 minutes before darkness. The question is how undesirable from a lighting standpoint is it to move nominal TPI time later – perhaps even to midpoint of darkness – in order to give more time in the rendezvous sequence to perform the plane change maneuvers.
6. Well, there are a lot of questions and few answers. As I noted previously, its impact is so great on everything, we really must decide what to do about the plane change before we can get anywhere. So that's what we'll talk about at the next meeting – June 12th.