Downthread: Third “D” Mission Rendezvous Mission Techniques meeting (Feb 08, 1968)
See list belowJAN 24 196868-PA-T-17APA/Chief, Apollo Data Priority CoordinationMission “D” Rendezvous Mission Techniques meeting
1. The second of the subject meeting was held on January 17. Some odds and ends were resolved, and one other significant operational procedure was proposed dealing with CSM operations during CSM active rendezvous.
2. G&C Division has indicated that it is proposing to execute some LM maneuvers using the AGS. The current “D” Mission rendezvous exercise includes this mode for the first and/or second maneuver. Considering the status of the AGS and the critical nature of this flight, I took the action item of finding out if we would really use the AGS in this way since it has a heavy bearing on how we utilize the guidance systems. Intuitively, it sounds nuts.
3. We continued our discussion of the preferred platform alignment to be used during the rendezvous exercise. It has been universally agreed that the alignment should be in plane and that the ORDEAL will be used with one of the 8-balls. Choice of the inertial alignment has been hard to make since there seems to be no unique advantage to any partic ular orientation. Some members of the flight crew had discussed this and arrived at a tentative proposal requiring more discussion within their organization. Their suggestion is to align the platform in such a way that the white and black hemispheres of the 8-ball coincide with the sunlit and dark hemispheres of the earth. That is, as the inertially oriented 8-ball crosses from light to dark, the spacecraft would be crossing the earth terminator from day to night.
4. Apparently, it is desired by the crew that both the command module and the LM will have the same 8-ball presentation when in a headfirst attitude. Accordingly, the REFSMMAT for each of the two spacecraft will be 90° different from each other.
5. Since earlier in the mission it is planned to perform a docked DPS maneuver, it will be necessary to align the LM platform whilst in the docked configuration. These same procedures can obviously be used in preparation for the rendezvous sequence, as mentioned before, the procedures will probably include use of the CSM attitude control system to achieve the desired orientation for viewing the alignment stars in the LM AOT, however the actual maintenance of this attitude during the alignment will probably be performed using the LM RCS.
6. Probably the most significant concept coming from this meeting dealt with the manner in which the command module should be operated during the LM active rendezvous. The importance of this is that it not only bears on the “D” mission but, if sound, would probably be used on all LM rendezvous including the lunar landing flight. The basic premise is that the most important thing we need to do is to maintain the optimum (nominal) rendezvous situations. That is, if it is impossible for some reason for the LM to execute its planned maneuvers designed to continue the coelliptic rendezvous sequence with optimum lighting, approach angles, nominal line of sight rates during braking, nominal breaking velocities, etc., as well as satisfying ground tracking constraints, then it is highly desirable that the command module execute a maneuver almost immediately to accomplish the same objective. Accordingly, the proposal under consideration is to target the command module to make a maneuver with a short time delay after the planned LM maneuver and then countdown both vehicles going through the prethrust and thrust programs such that if it is found the LM is unable to maneuver, the command module would continue its countdown and maneuver. Ed Lineberry stated that their studies have shown that almost exactly the desired conditions are achieved by the command module performing the LM targeted maneuver backwards. And so, for operational simplicity, we would target both of these vehicles to execute essentially the same maneuver using the External Delta V coordinate system, the only difference being that the command module maneuver would be backwards, and the time of ignition somewhat delayed. The question of what delay magnitude resulted in two action items. First, the flight crew was to determine the time required following ignition failure of the LM engine to evaluate the situation and establish the need for the command module to burn. It is expected this time to be about one, and no more than two minutes. The second task was for the Rendezvous Analysis Branch to perform a parametric study to show the degradation effect in terms of delta V usage, TPI time slippage, etc., resulting from various values of delay time for the command module to execute the maneuver. The basic point to be made is that we do not feel it desirable for the LM crew to spend very much time analyzing the situation, evaluating propulsion or guidance systems but rather in order to maintain a relatively nominal rendezvous situation prefer to maneuver the command module, thus making the “failure analysis” operation very much less time critical.
7. In conjunction with this operation, therefore, we would expect the LM to relay to the command module pilot the maneuver he anticipates making in External Delta V coordinate system. The command module pilot would use this targeting to prepare for the backup maneuver described above. In the event he is not called upon to make the maneuver, he utilizes that same information using the so-called Target Delta V routine (R-32) to update the LM state vector in the CMC.
8. One additional problem associated with this latter point deals with what to do if it is adjudged undesirable for the LM to trim velocity residuals in which case the maneuver passed to the CM for updating the state vectors is not accurate. There were three obvious courses of action as follows: (a) ignore the error and depend on sextant observa- tions to eliminate it, (b) reorient the LM in such a way that they are able to read out the delta V residuals in the external delta V coordinate system to be relayed to the command module, and (c) utilize the ground network taking the LM state vector from telemetry and relaying it back to the command module with the obvious time delays associated with that. This matter was not resolved and requires further consideration.
9. In order to avoid midweek travel conflicts, we have found it necessary to abandon our plan to hold these meetings every other Wednesday. The next Mission “D” Rendezvous meeting is currently scheduled for Monday afternoon, January 29, at 1:00 p.m. in Building 30, Room 3080.