The general trajectory profile of this mission was similar to that of Apollo 14 except for a few refinements. The most significant difference was that the angle of descent to the lunar surface was increased from 14 degrees to 25 degrees. Tables 3-1 and 3-11 give the times of major flight events and definitions of the events; tables 3-111 and S-IV contain trajectory parameter information; and table 3-V is a summary of maneuver data.


The launch trajectory is reported in reference 3. Because of earth parking orbit insertion dispersions, the S-1VB instrument unit received two navigation updates prior to translunar injection. Nominally, the translunar injection maneuver is targeted to a 79-mile pericynthion. The command and service module, along with the lunar module, lower this pericynthion to 68 miles as a result of their ejection and separation from the S-IVB. Although the translunar injection maneuver was targeted to a 79-mile pericynthion, one of 139 miles was achieved. Two midcourse correction maneuvers were performed in addition to the normal vehicle separation maneuvers to reach the desired 68-mile pericynthion.

After command and service module/lunar module ejection, the S-IVB performed an evasive maneuver. Then the S-IVB, using its auxiliary propulsion system, performed two maneuvers designed to impact it at the desired lunar location of 3 degrees 39 minutes south latitude and 7 degrees 35 minutes west longitude. Initial tracking after the two maneuvers indicated that impact would be within 37 kilometers (20 miles) of the target. However, because of an error in targeting due to tolerances in the tracking vector and unexpected vehicle thrusting, the impact occurred 146 kilo meters (79 miles) from the target at 1 degree 31 minutes south latitude and 11 degrees 49 minutes west longitude.


3.2.1 Orbital Phase

The spacecraft was inserted into a 170.1-by-57.7-mile orbit around the moon using the service propulsion system. Approximately 4 hours later, the descent orbit insertion maneuver was performed, and the spacecraft was lowered to an orbit having a 58.5-mile apocynthion and a 9.6-mile pericynthion. This orbit gradually decayed, requiring a trim maneuver to adjust the orbit for powered descent initiation.





After lunar module separation, a circularization maneuver was performed placing the command and service module in a 65.2-by-54.8-mile orbit. The command and service module remained in this orbit until about 6 hours prior to scheduled lunar module ascent when a 3-degree plane change maneuver was made so that the orbital plane of both vehicles would be coincident at the time of lift-off.


3.2.2 Descent

A landing site update of 853 meters (2800 feet) downrange was incorporated at about 2 minutes into the powered descent to correct for downrange error. No other updates were necessary. The crew made at least seven site redesignations for a total change of 338 meters (1110 feet) uprange and 409 meters (1341 feet) to the right. The landing point was about 550 meters (1800 feet) northwest of the premission target point. The coordinates of the landing site are 26 degrees 6 minutes 4 seconds north latitude and 3 degrees 39 minutes 10 seconds east longitude, referenced to the Rima Hadley Lunar Photomap, Orbiter V site 26.1, First Edition, published by U.S. Army Topographic Command, April 1970 ( fig. 3-1)

3.2.3 Ascent and Rendezvous

The lunar module ascent occurred at 171:37:23 and the ascent stage was inserted into a 42.5-by-9.0-mile orbit. Some trimming of velocity residuals was required but, at insertion, the parameters were close to the desired values and a vernier adjustment maneuver was not required. The direct rendezvous technique, first used on Apollo 14, was executed nominally, and the lunar module and command and service module were harddocked about 1 hour 50 minutes after completion of the ascent maneuver.

3.2.4 Lunar Module Deorbit

Jettisoning of the lunar module ascent stage from the command and service module was delayed one revolution to permit reverifications of hatch and suit integrity. However, as a result of the delayed Jettisoning, the lunar module attitude for the maneuver was different than planned. With this change, the lunar module impacted the moon about 23.5 kilometers (12.7 miles) from the target. The coordinates of the impact point were 26 degrees 21 minutes north latitude and 0 degrees 15 minutes east longitude which is about 93 kilometers (50 miles) west of the Apollo 15 landing site.

The command and service module was to perform a 1-ft/sec retrograde separation maneuver after lunar module Jettisoning to minimize the possibility of recontact but, because of the Jettisoning delay, a 2-ft/sec posigrade maneuver was performed.

3.2.5 Orbit-Shaping Maneuver and Subsatellite Launch

In preparation for launching the subsatellite just prior to transearth injection, an orbit-shaping maneuver was performed during the 73rd lunar revolution using the service propulsion system to optimize the subsatellite orbit. The satellite was launched about an hour after the shaping maneuver into an orbit having an inclination of minus 28.7 degrees with an apocynthion of 76.3 miles and a pericynthion of 55.1 miles. The orbital lifetime is expected to be in excess of 1 year.


The transearth injection maneuver was performed at 223 hours 49 minutes. On the transearth flight, no midcourse corrections were made until about 3 hours prior to entry. A 5.6-ft/sec maneuver was performed using the service module reaction control system. The service module was separated from the command module 15 minutes prior to entry. Conditions for the entry of the spacecraft into the earth's atmosphere were nominal. The best estimate of the spacecraft landing point is 26 degrees 7 minutes 48 seconds north latitude and 158 degrees 8 minutes 24 seconds west longitude.