Upthread: April 9 Lunar Reentry Mission Techniques meeting (Apr 17, 1968)
Downthread: Transearth midcourse correction philosophy – a major operation break through! (Jun 03, 1968)
See list belowMAY 10 196868-PA-T-100APA/Chief, Apollo Data Priority CoordinationNo special visual reference will be provided for the final transearth midcourse correction maneuver
1. On May 7 we reviewed the need for an RTCC program change to provide a special visual reference for the crew during the last transearth midcourse correction maneuver on a lunar mission. We concluded it is not needed and that no new programming or displays are required.
2. The final transearth midcourse correction maneuver has the follow- ing characteristics. It is scheduled to occur two hour before entry. At the time, the spacecraft is location approximately on the earth- moon line about 20,000 miles from the earth. The maneuver is essentially horizontal with respect to the earth – perpendicular to the earth-moon line.
3. The primary subject under consideration was the use of the earth or the moon as a visual reference. This is partly a carry-over from using the horizon as a reference during the retrofire maneuver on earth orbital missions since they are similar maneuvers in a way – both set-up the reentry trajectory. Unfortunately located as they are with respect to a horizontal burn, the earth and moon are both located in the worst possible places for use as a burn attitude reference. Accordingly, we concluded that our best course of action is to use standard burn attitude checks such as comparison with a properly aligned SCS and stars if they are visible.
4. It should be pointed out that large orientation errors have relatively little effect on this unique maneuver since components of delta V perpendi- cular to the one we are trying to achieve don't do anything. Thus, misalign- ment merely reduces the effective magnitude of the maneuver by the cosine of the misalignment angle.