Introduction and background

Reading the many books (a few of which are listed below, [2] being a good, if not the best, starter) about the epic of Apollo acquaints one with the timeline of the decision to delay the D mission (first CSM + LM flight) and instead push for a CSM-only lunar flight after the first and only successful CSM flight (C mission, Apollo 7). As an in-between flight the new bold mission was assigned the new designation, C' (C-prime) mission, and would soon become Apollo 8, a mission of so many firsts as to be often considered a close second in success to Apollo 11.

Without discussing the "politics" of Apollo management it is worth remembering that the idea to fly a lunar orbital mission started with a secret memo from George Low to Christopher Kraft, in the spring of 1968 (therefore well in advance of Apollo 7 and perhaps just after the second test of the Saturn V booster, the last test flight before the "manned ones", to use the terminology of those times). The 5th of August, Low started a series of secret meetings that culminated the 10th of August with a meeting of top management at Marshall. The meeting included therefore Von Braun and a good account is found both in [2] and [3]. The 15th of August, Samuel Phillips notified James Webb of the plan, while the latter was at a conference in Vienna with George Mueller.

From then on the clock started for a 20th of December launch of the daring mission. However the background work was still kept secret, pending the outcome of the Apollo 7 flight. After the flight, and another series of consultations, the new NASA Administrator, Tom Paine, approved on the 11th of November the C' mission and news was given to the world the following day.

The document we are going to discuss [1], available in the Downloads section of this site, is a testament of the very high confidence MPAD and MOD had in planning such an bold endeavour just a few weeks after the top managers' discussion in August. This document is a memo by the Flight Planning Branch regarding a first draft of the C' flight plan. It is interesting to compare that draft, issued the 9th of September, just one month after Gilruth, Von Braun and others were notified of the proposal, with the final version issued the 22nd of November and published in the Apollo 8 Press Kit [4].

In the following we present a discussion of the difference found between the two editions of the Flight Plan. This short research stems from the realization that the epic flight of Apollo 8 was well conceived since the very beginning, despite the pressures of the program and the novelty of it.

Discussion about the flight plan

This comparison exercise is interesting not only for the differences found, but also for the many points (most of them key decisions) which are identical in the two versions.

The first thing that appears is that there is basically no difference in the style of the draft issue and the style of the final issue. Both seem to have been typed on a standard summary flight plan form, with the same hand drawn lines. Second, it can be noted that most of the key events were well thought-out originally as they remained the same in the final version (including such details such as crew rest and eating periods, navigation exercises and surveying activities from lunar orbit). A third, more noticeable, aspect is that the original draft called for a longer flight, a total of 174 hours, against the 144 hours of the final version. Below we examine the differences in some of the details as they might be useful for further work.

General comments

There is no mention of PTC (Passive Thermal Control) maneuvers in the draft version. Sighting periods were generally longer in the draft than in the final version. The draft also proposed additional Star/Earth Horizon Sighting periods for LMP practice, all deleted in the final version.

The draft version contains references to PWR DN (Power Down) and PWR UP (Power Up) periods. These disappeared from the final version.

The draft highlights the achievement of the following distances: outbound: 15K NM (from Earth), 50K NM (from Moon) and 15K NM (from Moon); inbound: 15K NM (from Moon) and 50K NM (from Moon).

Day 1, from 00 to 24 hours

The first 24 hours are basically the same in both versions, the TEI burn is at the same time, but the first trajectory correction maneuver, MCC-1, was at TLI + 7 hrs in the draft versus TLI + 6 hrs in the final issue.

Day 2, from 24 to 48 hours

Basically no differences between the two versions. Both have MCC-2 at TLI + 25 hrs and MCC-3 at LOI - 22 hrs.

Day 3, from 48 to 72 hours

Again, not many differences between the two versions. Both have MCC-4 at LOI - 8 hrs and LOI-1 (the first braking manuver to enter an elliptical lunar orbit) at the same time. The final version has a LOI ATT CK (Lunar Orbit Insertion Attitude Check) activity scheduled 2 hours before LOI.

Day 4, from 72 to 96 hours

Most of the day is spent in lunar orbit and it is immediately evident that the lunar orbit plan remained as was originally proposed in the draft version. Noticeable is the lack of any TV activity in the draft. The LOI-2 manuever (second braking maneuver to transform the lunar orbit into a circular lunar one) is at the same time in both versions as are the various lunar landmark training exercises, the landing sites sightings and photographic activities and other similar activities. The highly critical TEI manuever (TransEarth Injection to leave lunar orbit and establish an earth return trajectory) was planned for about 15 minutes earlier in the draft version. This is probably the key to the biggest difference the the two versions.

Day 5, from 96 to 120 hours

Differences in the plans now increase. The MCC-5 manuever was originally planned at TEI + 10 hours instead of TEI + 15 hours in the final version. MCC-6, planned at TEI + 29 is delayed to the next day. Sightings before each TransEarth MCC manuever are also more detailed in the final version, with sightings performed both Star/Earth and Star/Moon before and after each maneuver (the draft version specifies just Star/Moon sightings).

Day 6, from 120 to 144 hours

As said, the final version scheduled MCC-6 at TEI + 33 hours with the same sightings pattern discussed previously. A MCC-7 at SEP - 29 hours (SEP being the separation of CM from the SM just 15 minutes before entry into the atmosphere) is not present in the final version.

Day 7, from 144 to 146 hours

The biggest difference in the two versions is found here. The final version has a nominal landing time of 147 hours and 10 minutes whereas the draft version has another full day of TransEarth coast before reaching the entry interface. The final version has MCC-7 scheduled at EI - 2 hours (the SEP event is not used in the final version) which takes the place of MCC-8 scheduled in the draft at SEP - 2 hours. Basically the two plans differ by about 24 hours all of which are concentrated in the TransEarth phase of the flight. The expected landing time in the draft version was in Day 8 at about 171 hours and 30 minutes.

Conclusions

The precise answer to this dramatic change in TransEarth trajectory duration is most likely held in a 1968 Tindallgram as well as in the related C-prime Mission Techniques. It has to do with re-entry options available and will soon be investigated. More can be said about this, therefore ... to be continued.

References 

[1] O'Neill, C' Flight Plan, Memo CF342-8M-132, 9 Sep 1968 (see Downloads section)

[2] Murray and Cox, Apollo, South Mountain Books

[3] Neufeld, Von Braun, A. Knopf Publisher

[4] Apollo 8 The NASA Mission Reports, Apogee Books

Please note that the Apogee Books replica of the final issue of the A8 Flight Plan is missing one page (page 2, from 24h to 48h in the timeline).

Timeline to the C-prime decision

02/02/2008 - Edited after proofreading by librarian.