Lunar Ascent preparation

See list attachedJUL 16 196868-PA-T-151APA/Chief, Apollo Data Priority CoordinationLunar Ascent preparation

1. At the July 3 Lunar Ascent Mission Techniques meeting we cleaned up the last of the main open items for the phase of the lunar landing mission from LM touchdown to liftoff. We are now ready to go to press for that part of the mission and will hold a world-wide review of it before the end of the month.

2. Most of the discussion was devoted to establishing the CSM timeline prior to LM Ascent. Much to my surprise, the CSM requires about eight hours (four orbits) to prepare for LM Ascent. Involved is all of the work associated with determining the position of LM with respect to the CSM orbit and with making a plane change if it is necessary. Time required for the LM to get ready is less than two and one-half hours unless rendezvous radar tracking is required. In that case, the LM crew would have to start powering up the PGNCS about three hours before liftoff, in order to track the command module during its last pass over- head. It is necessary for either the command module to track the LM on the lunar surface using the sextant or, if that is not possible, for the LM to track the command module using the rendezvous radar. The data thus obtained is required to target the CSM plane change or the LM Ascent. In the timeline that we settled on, the sextant tracking of the LM would be done three revolutions (approximately six hours) before Ascent and the CSM plane change, if it is required, would be performed one and one-fourth revolutions (approximately two and one-half hours) before liftoff. If the command module pilot is unable to track the LM with the sextant it will be necessary for us to target the command module plane change based on MSFN tracking and navigation, realizing that that the resultant CSM orbit may be as much as 0.3° away from the LM position as a result of MSFN inaccuracies. It is only in this event that we would require the LM to track the CSM with the rendezvous radar to obtain the data the ground would use to determine the out-of- plane steering the LM should execute during Ascent. It is only in the event that the command module is unable to track the LM that both the command module plane change and LM Ascent out-of-plane steering would be performed.

3. The other thing we firmed up was the logic defining when to use the command module SPS to make a pre-Ascent plane change vs. yaw steering the LM into the command module orbit during Ascent. The rule we established was that if the LM is less than half a degree out of the CSM orbital plane, the LM would take care of it during Ascent at an APS propellant cost of approximately 19 fps. If the plane change required is greater than half a degree, the command module would be used. Thus, the minimum SPS burn would be 50 fps. The maximum should be no more than 200 fps, depending on the location of the landing site and the inclination of the plane. These limits represent burn times between three and thirteen seconds.