Maneuver Analysis
The parameters derived from the best estimated trajectory for each spacecraft maneuver executed during the translunar, lunar orbit, and transearth coast phases are presented in table 7-11. Tables 7-III and 7-IV present the respective pericynthion and free-return conditions after each translunar maneuver. The free-return results indicate conditions at entry interface produced by each maneuver, assuming no additional orbit perturbations. Tables 7-V and 7-VT present the respective maneuver summaries for the lunar orbit and the transearth coast phases.
7.4.1 Translunar Injection
The pericynthion altitude resulting from translunar injection was 896.3 miles, as compared with the preflight prediction of 718.9 miles. This altitude difference is representative of a 1.6 ft/sec accuracy in the injection maneuver. The associated free-return conditions show an earth capture of the spacecraft.
7.4.2 Separation and Docking
The command and service modules separated from the S-IVB and successfully completed the transposition and docking sequence. The spacecraft were ejected from the S-IVB at 4 hours 17 minutes. The effect of the 0.7-ft/sec ejection maneuver was a change In the predicted pericynthion altitude to 827.2 miles. The separation maneuver performed by the service propulsion system was executed precisely and on time. The resulting trajectory conditions indicate a pericynthion altitude reduction to 180.0 miles, as compared to the planned value of 167-7 miles. The difference indicates a 0.24-ft/sec execution error.
7.4.3 Translunar Midcourse Correction
The computed midcourse correction for the first option point was only 17-1 ft/sec. A real-time decision was therefore made to delay the first midcourse correction until the second option point at translunar injection plus 24 hours because of the small increase to only 21.2 ft/sec in the corrective velocity required. The first and only translunar mid-course correction was initiated on time and resulted in a pericynthion altitude of 61.5 miles, as compared with the desired value of 60.0 miles. Two other opportunities for midcourse correction were available during the translunar phase, but the velocity changes required to satisfy planned pericynthion altitude and nodal position targets were well below the levels at which normal lunar orbit insertion can be retargeted. Therefore, no further translunar midcourse corrections were required. The translunar trajectory was very similar to that of Apollo 10.
J.bA Lunar Orbit Insertion and Circularization
The lunar orbit insertion and circularization targeting philosophy for Apollo 11 differed from that of Apollo 10 in two ways. First, targeting for landing site latitude was biased to account for the orbit plane regression observed in Apollo 10; and secondly, the circularization maneuver was targeted for a noncircular orbit of 65.7 by 53.7 miles, as compared with the 60-mile-circular orbit targeted for Apollo 10. A discussion of these considerations is presented In section 7.7. The representative ground track of the spacecraft during the lunar orbit phase of the mission Is shown in figure 7-2.
The sequence of events for lunar orbit insertion was initiated on time, and the orbit achieved was 169.7 by 60.0 miles. The firing duration was 4.5 seconds less than predicted because of higher than predicted thrust (see section 8.8).
The circularization maneuver was initiated two revolutions later and achieved the desired target orbit to within 0.1 mile. The spacecraft was placed into a 65-7- by 53.8-mile orbit, with pericynthion at approximately 80 degrees west, as planned. The R2 orbit prediction model predicted a spacecraft orbit at 126 hours (revolution 13) of 59.9 by 59.3 miles. However, the orbit did not circularize during this period (fig. 7-3). The effects of the lunar potential were sufficient to cause this prediction to be in error by about 2.5 miles. The actual spacecraft orbit at 126 hours was 62.4 by 56.6 miles.
7.4.5 Undocking and Command Module Separation
The lunar module was undocked from the command module at about 100 hours during lunar revolution 13. The command and service modules then performed a three-impulse separation sequence, with an actual firing time of 9 seconds and a velocity change of 2.7 ft/sec. As reported by the crew, the lunar module trajectory perturbations resulting from undocking and stati on—keeping were uncompensated for in the descent orbit Insertion maneuver one-half revolution later. These errors directly affected the lunar module state vector accuracy at the initiation of powered descent.
7-4.6 Lunar Module Descent
The descent orbit insertion maneuver was executed at 101-1/2 hours, and about 57 minutes later, the powered descent sequence began. The detailed trajectory analysis for the lunar module descent phase is presented in section 5.1. The trajectory parameters and maneuver results are presented in tables 7-H and 7-V.
7.4.7 Lunar Module Ascent and Rendezvous
The lunar module ascent stage lifted off the lunar surface at 124:22:00.8 after staying on the surface for 21 hours 36.35 minutes. Lunar orbit insertion and the rendezvous sequence were normal. The terminal phase was completed by 128 hours. The detailed trajectory analysis for ascent and rendezvous is presented in sections 5-6 and 5.7. Tables 7-H and 7-V present the trajectory parameters and maneuver results for these phases.
7.4.8 Transearth Injection
The transearth injection maneuver was initiated on time and achieved a velocity change of only 1.2 ft/sec less than planned. This maneuver exceeded the real-time planned duration by 3.4 seconds because of a slightly lower-than-expected thrust (see section 8.8). The transearth injection would not have achieved acceptable earth entry conditions. The resulting perigee altitude solution was 69.4 miles, as compared with the nominal value of 20.4 miles.
7.4.9 Transearth Midcourse Correction
At the fifth midcourse-correction option point, the first and only transearth midcourse correction of 4.8 ft/sec was made with the reaction control system, which corrected the trajectory to the predicted entry flight-path angle of minus 6.51 degrees.
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