The LM can handle big Descent plane changes but required protection against APS abort fuel depletion

See list attachedJUL 18 196868-PA-T-160APA/Chief, Apollo Data Priority CoordinationThe LM can handle big Descent plane changes but required protection against APS abort fuel depletion

We have recently verified that the LM has a substantial capability to translate out of its initial orbital plane during powered Descent at very little cost. That is, whereas previously a limit of 0.3° had been quoted, it now appears that 1° or more is probably possible with- out effecting the performance of the guidance equations, the landing radar, the visibility of the crew during landing, nor are the ΔV costs excessive. This capability gives us more than adequate assurance that it will not be necessary to perform a plane change trim burn on DOI day. And that's darn important!

In order to take advantage of this capability, however, it appears that something may have to be done to limit the yaw steering the LM would do in the event of an APS abort during powered Descent. As currently pro- grammed, the PGNCS would attempt to guide the LM all the way back into the CSM plane. If the abort were to occur at “hover” or after touch- down, the APS ΔV cost could be excessive (i.e., 1° costs approximately 80 fps and could result in fuel depletion prior to obtaining a safe orbit). Obviously the thing we must do is to achieve the targeted in- plane conditions in the case of an abort. We can take care of the plane change after the LM is in orbit, perhaps using the CSM. Therefore, it seems necessary to make a (hopefully) rather small change to the APS abort program (P71) which would limit the extent of the out-of-plane steering. MPAD and MIT people are both in the process of studying this and we plan to recommend specific action very soon. Something similar will be needed in the AGS too, I suppose.