Upthread: Transearth midcourse maneuvers are getting easier and cheaper all the time (Jun 18, 1968)
Downthread: C’ Transearth Midcourse Correction (MCC) and Entry Mission Techniques (Sep 20, 1968)
FM13/Chief, Mission Planning Support OfficeJUN 28 196868-PA-T-142APA/Chief, Apollo Data Priority CoordinationNeed to know some transearth midcourse correction (MCC) ΔV costs
I think we have pretty well established the transearth MCC maneuver philosophy now. As you know, it involves making small corridor correction maneuvers as their need becomes apparent. Nominally they will be made with the RCS propulsion system utilizing the SCS control system. Very large attitude errors may be tolerated during the burn.
It is necessary to establish the threshold ΔV value below which it is better not to make a maneuver but rather to wait for the next opportu- nity some eight to twelve hours later. The threshold, of course, depends on the MSFN uncertainty as a function of time and the translation ΔV cost to achieve a particular objective as a function of time. These relations are already fairly well known, but that is not the total cost. I would appreciate it if you would initiate a task assignment – probably to the Guidance and Performance Branch – to define the non-translation RCS propellant costs associated with making a maneuver of the type noted above. These could involve, among other things, the propellant required to coarse align the SCS and to orient the spacecraft to burn attitude. I recently asked Charley Parker (FDB) to establish coarse SCS alignment procedures and I would suggest that whoever is given this task coordinate with him.