Reports/Apollo 17/Mission report/3.0 Trajectory

The basic trajectory profile for this mission was similar to that planned for the Apollo 16 mission. The major differences, aside from those required to reach the Taurus-Littrow landing site, were those required because of a night launch, translunar injection being initiated over the Atlantic Ocean rather than the Pacific Ocean, descent orbit insertion being performed in two maneuvers rather than one, and the elimination of the orbit shaping maneuver and the satellite jettisoning event. The sequence and definition of events for the Apollo 17 mission are shown in tables 3-I and 3-II. Tables 3-III and 3-IV contain the listing and definition of trajectory parameters, and table 3-V contains a summary of the maneuvers.

[edit] 3.1 Launch and translunar trajectories

The launch trajectory is presented in reference 3. The launch azimuth was updated from 72 degrees east of north to 91 degrees 30 minutes east of north. The translunar injection differed from the original plan because of a 2-hour 40-minute launch delay. This delay resulted in the translunar coast time being shortened (accomplished automatically by the launch vehicle guidance system), so that the arrival time at the moon would remain the same as that planned prelaunch. This constant time of arrival plan simplified the crew training by providing them with only one lunar lighting condition and one set of lunar groundtracks with which they had to become familiar, resulting in a single set of conditions on which the crew could concentrate their training.

One translunar midcourse correction of 10.5 ft/sec was required and performed at the second option point. The scientific instrument module door was jettisoned about 4 1/2 hours prior to lunar orbit insertion.

[edit] 3.2 S-IVB stage

Separation from the S-IVB stage and the S-IVB evasive maneuver were completed normally. The S-IVB stage was targeted for lunar impact by two firings of the auxiliary propulsion system. Lunar impact occurred approximately 87 hours into the mission at 4 degrees 12 minutes south latitude and 12 degrees 18 minutes west longitude, about 84 miles from the planned target point. The impact was recorded by the passive seismometers at the four lunar surface experiment stations. Figure 3-1 shows the location of the S-IVB impact on the lunar surface.

[edit] 3.3 Lunar orbit

[edit] 3.3.1 Orbital phase

The lunar orbit insertion maneuver placed the spacecraft into an orbit having a 170-mile apocynthion and a 52.6-mile pericynthion. About four hours later, the spacecraft orbit was lowered to one having a 59-mile apocynthion and a 14.5-mile pericynthion. After spending 17 hours in this lower orbit, the command and service module separated from the lunar module after which the command and service module orbit was circularized into one having a 70-mile apocynthion and a 54-mile pericynthion.

[edit] 3.3.2 Descent

Five minutes after the circularization maneuver was initiated by the command and service module, the lunar module performed the second descent orbit insertion maneuver. This lowered its pericynthion to within 6.2 miles of the lunar surface. An hour later, the lunar module powered descent was initiated and the lunar module landed on the moon at 110 hours 21 minutes 58 seconds. A manual target update of 3400 feet was incorporated early in the powered descent. Later in the descent maneuver, the Commander made eight landing point redesignations. These redesignations resulted in the spacecraft landing at 20 degrees 9 minutes 55 seconds north latitude and 30 degrees 45 minutes 57 seconds east longitude on the 1:25 000-scale Lunar Topographic Photomap of Taurus Littrow, First Edition, September, 1972.

[edit] 3.3.3 Ascent and rendezvous

The planned decay of the command and service module altitude to match the lunar module trajectory at rendezvous was not realized. This was similar to the experience of the Apollo 15 mission. Because of this, an orbital trim maneuver was performed to change the command and service module apocynthion to 67.3 miles and the pericynthion to 62.5 miles. An hour later, a plane change maneuver was performed to provide the proper orbital plane for rendezvous with the lunar module.

The lunar module ascended from the lunar surface at 185 hours 21 minutes 37 seconds after having been on the lunar surface for almost 75 hours. Approximately 7 1/2 minutes later, the ascent stage was inserted into lunar orbit. The achieved orbit required a vernier adjustment maneuver of 10 ft/sec to return the orbit to the planned conditions for rendezvous. The rendezvous was then completed normally, and the two vehicles were docked at 187 hours 37 minutes 15 seconds.

[edit] 3.3.4 Lunar module deorbit maneuver

The lunar module was jettisoned four hours after docking. The lunar module deorbit maneuver began about an hour and a half after jettisoning and impact occurred at 19 degrees 57 minutes 58 seconds north latitude, and 30 degrees 29 minutes 23 seconds east longitude, about 9.9 kilometers from the Apollo 17 landing site, and about 1.75 kilometers from the planned impact point (figs. 3-1 and 4-1).

[edit] 3.4 Transearth and entry trajectory

The command and service module remained in lunar orbit approximately 43 hours after the lunar module was jettisoned. The transearth injection maneuver was initiated at 234 hours 2 minutes 9 seconds. The maneuver was so accurate that only one midcourse correction was required during transearth coast, and that was at three hours prior to entry with a differential velocity of 2.1 ft/sec.

The command and service modules were separated 15 minutes before entry into the earth's atmosphere. The command module entered the atmosphere 1200 miles from the landing point and the landing occurred 1.3 miles short of the targeted point. The earth landing coordinates, as determined from the spacecraft computer, were 17 degrees 52 minutes 48 seconds south latitude and 166 degrees 6 minutes 36 seconds west longitude.

Edits and errors by Eric Hartwell are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 license. The original NASA material is copyright-free.