Upthread: Need to know some transearth midcourse correction (MCC) ΔV costs (Jun 28, 1968)
Downthread: Let’s move the recovery force a little (Jan 07, 1969)
See list attachedSeptember 20, 196868-PA-T-200APA/Chief, Apollo Data Priority CoordinationC’ Transearth Midcourse Correction (MCC) and Entry Mission Techniques
On September 13, we conducted a review of the Transearth MCC and Entry Mission Techniques for a lunar mission. Although, originally developed for an F or G type mission, the discussion was almost completely devoted to C'. Participation included all interested MSC organizations (including the C' flight crew) as well as representatives from North American, MIT, and Bellcomm. Some fairly significant decisions were made, which it is the purpose of this memo to report.
1. Previous to the meeting an agreement had been reached by Mr. C. C. Kraft and the flight crew that on the C' mission a non-skip reentry would nominally be utilized. It was noted, however, that in a contingency situation the full 2,500 mile reentry range might be needed for weather avoidance and, therefore, the capability was to be retained. At our meeting we determined that the full 2,500 mile range was really not a useful capability and are recommending:
a. All work should be oriented to provide capability of re- entering with ranges limited from 1200 to 1800 nautical miles. (Based on these limits the GNCS should never enter reentry P66.)
b. The useful operational footprint nominally is 1200 to 1450 nautical miles. (Simulations currently underway are expected to permit extending this to 1550 to 1600 nautical miles.) The normal reentry range for targeting and ship location purposes (i.e., PLA I) shall be 1350 nautical miles (which, if flown would preclude use of P65).
c. PLA 2 is defined as a contingency area and will be located at a range of 1800 nautical miles. PLA 2 will never be used unless PLA I is unacceptable for some reason and the G&N is working. If during attempt to reach PLA 2 the G&N fails, the crew will fly a constant G reentry until aerodynamic capture is assured and then will fly maximum range to get as close to PLA 2 as possible.
2. It seems logical that all systems tests, crew training, procedure development, etc, be limited to the above defined capability – that is, no effort should be devoted to preparing for entry ranges greater than 1800 nautical miles, at least for the C' mission.
3. Consistent with the short range reentry, it was decided at the meeting to eliminate the previously nominal, shallow entry target line. Subsequently it was decided to modify this decision to apply only to entries at velocity greater than some value to be established by C. Graves, J. Harpold, and Co. Essentially it applies to the nominal lunar flight and aborts performed some time after TLI. Henceforth, MCC-H maneuver targeting will be based on aiming for the steep target line, previously only utilized for contingencies which provide a -6.48° flight path angle at the entry interface. Use of this steep target line is considered to be compatible with a short range reentry and constraining targeting to it will substantially simplify flight controller and crew procedures.
4. The activity associated with SM/CM separation was thoroughly discussed and was finally combined with the pre-entry spacecraft attitude, horizon check. For the first time it appears we have an agreement on the timeline and crew procedures including management of the CMC for all this pre-entry activity. The separation pitch attitude has been defined as being the same as the horizon attitude check and yaw is 45° out-of- plane. Separation studies should be carried out, if they have not already been completed, to verify acceptability of this decision – not to optimize it.
5. Previously it had been proposed that the EMS would be started manually at the MCC-H computed time of .O5 g's because it was erroneously felt that the EMS Range-to-Go display could be made substantially more accurate by following this procedure. At this meeting the decision was reversed and it is now recommended that the EMS be started automatically with crew backup after a reasonable time delay, currently three seconds.
6. Two decisions were reached regarding the Transearth Injection (TEI) maneuver.
a. The criteria for switching over from GNCS to SCS will be based on providing a subsequent trajectory in which the MCC's do not exceed the remaining RCS capability.
b. The only ΔV residual requiring trimming at TEI cutoff is the x-axis and it should only be trimmed to within 2 fps.
7. It was agreed that all transearth MCC, including the first, would be performed for corridor control only, unless it is determined in real time that the predicted landing point is unacceptable for some reason (e.g., unacceptable weather or land masses within the footprint or in the PLA 2, or excessive return to base staging time). It was stated that if a maneuver is required to relocate the landing point for reasons such as noted above, the maneuver will be made large enough to provide acceptable landing conditions in the entire PLA I footprint and at PLA 2. Wherever possible, of course, the recovery ships will be removed to a new location consistant with a 1350 nautical mile entry range.
9. Incidentally, it appears that it will be decided to fly the C' mission with the GNCS up and operating continuously, if power permits. I understand MIT will endorse this as being preferable from an overall reliability standpoint.
10. The C' Mission Techniques Document shall be updated to conform with these changes and decisions.