3.0 TRAJECTORY
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.
3.1 LAUNCH AND TRANSLUNAR TRAJECTORIES
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 LUNAR ORBIT
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.
TABLE 3-1.- SEQUENCE OF EVENTS
TABLE 3-II. - DEFINITIONS OF EVENT TIMES
TABLE 3-III.- TRAJECTORY PARAMETERS
TABLE 3-IV.- DEFINITION OF TRAJECTORY AND ORBITAL PARAMETERS
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.
TABLE 3-V.- MANEUVER SUMMARY
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.
3.3 TRANSEARTH AND ENTRY TRAJECTORY
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.