Apollo 10 Service Module Returned to Earth Instead of Orbiting the Sun

Summary: The Apollo 10 service module returned to Earth Monday, May 26, 1969, instead of orbiting the sun in a bounce maneuver off Earth’s atmosphere.

Interior view of the John F. Kennedy Space Center’s Manned Spacecraft Operations Building (MSOB) shows transfer of the Apollo 10 mission’s cone-shaped command module and cylindrical-shaped service module to integrated work stand number one for mating to spacecraft LM (lunar module) adapter (SLA), Jan. 31, 1969; NASA ID S69-19190: Generally not subject to copyright in the United States, via NASA Image and Digital Library

The Apollo 10 service module returned to Earth Monday, May 26, 1969, for a landing in the Pacific Ocean, instead of orbiting the sun in a skipping maneuver off Earth’s atmosphere.

According to the National Aeronautics and Space Administration’s (NASA) Apollo 10 Mission Report, released August 1969, the Apollo 10 mission numbered as “. . . the tenth in a series of flights using specification Apollo hardware and . . . the first lunar flight of the complete spacecraft” (2.0, page 2-1), according to NASA’s Apollo 10 Mission Report, released August 1969. The Mission Report stated the mission’s purpose as confirmation of the upcoming July 1969 Apollo 11 mission in “. . . all aspects of the lunar landing mission exactly as it would be performed, except for the actual descent, landing, lunar stay, and ascent from the lunar surface.”

Range Zero, defined as “the integral second before lift-off,” occurred Sunday, May 18, 1969, at 16:49:00 Greenwich Mean Time/Coordinated Universal Time (11:49 p.m. Eastern Standard Time; 12:49 p.m. Eastern Daylight Time). The eight-day mission successfully ended 193 hours 39 minutes (193:39 Ground Elapsed Time GET) after liftoff with the hoisting of the spacecraft’s command module onto prime recovery ship USS Princeton Monday, May 26, at 18:28 GMT/UTC (1:28 p.m. EST, 2:28 p.m. EDT).

The spacecraft’s command and service modules had separated prior to the command module’s scheduled re-entry into Earth’s atmosphere. Separation of the two modules took place Monday, May 26, at 16:22:26 GMT/UTC (11:22 p.m. EST, 12:22 p.m. EDT), according to freelance space writer Richard W. Orloff’s NASA-published Apollo by the Numbers (2000: page 88). The jettison of the service module occurred 191 hours 33 minutes 26 seconds (191:33:26 GET) after liftoff and 29 minutes 57 seconds prior to the command module’s re-entry into Earth’s atmosphere.

NASA’s Apollo 10 Mission Report explained that firing of the service module’s reaction control system (RCS), after separation, was intended “. . . to insure that the service module would not enter and endanger the command module and the recovery forces” (6.10: page 6-5). Approximately 370 seconds of firing time “. . . should have resulted in a positive velocity change of 370 ft/sec, sufficient to have caused the service module to enter the earth’s atmosphere and then skip out (because of the shallow flight-path angle and near parabolic velocity). The resulting trajectory would either have been a heliocentric orbit or an earth orbit with an apogee in excess of a million miles.”

The service module, however, did not bounce off Earth’s atmosphere for entry into a heliocentric, or sun-centered, orbit. Instead, the service module re-entered Earth’s atmosphere. Its impact point in the Pacific Ocean, at 19.14 degrees south latitude and 173.37 degrees west longitude, was distanced “about 500 miles uprange from the command module.” The service module impacted the South Pacific Ocean southeast of the Vava’u archipelago in the northern Kingdom of Tonga.

The Mission Report found that the effective velocity change after separation could not have been 370 feet per second (fps). The Report calculated that, with “. . . separation attitude and service module weight of 13, 072 pounds, an effective velocity change of only 55 ft/sec would have resulted in an impact at this location.”

Hypothesized scenarios of unstable attitude or premature firing termination were presented and rejected. “Six-degree-of-freedom simulations have shown that tumbling during the firing is very unlikely, and past experience and ground testing of the reaction control thrusters indicate that a premature thrust termination is not probable,” the Mission Report explained. “Although recontact between the two modules was virtually impossible because of the out-of-plane velocity at separation, no conclusive explanation for the uprange impact location can be given at this time” (6.10: pages 6-5 to 6-6).

The takeaway for the Apollo 10 service module’s return to Earth instead of bouncing into a sun-centered orbit is that its unexpected impact point in the South Pacific Ocean fortunately was located approximately 500 miles uprange from the command module’s splashdown.

artist’s concept of Apollo spacecraft’s command module (CM)-service module (SM) separation; NASA ID S66-05101, NASA ID S66-10991: NASA Johnson Space Center, via NASA

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Interior view of the John F. Kennedy Space Center’s Manned Spacecraft Operations Building (MSOB) shows transfer of the Apollo 10 mission’s cone-shaped command module and cylindrical-shaped service module to integrated work stand number one for mating to spacecraft LM (lunar module) adapter (SLA), Jan. 31, 1969; NASA ID S69-19190: Generally not subject to copyright in the United States; may use this material for educational or informational purposes, including photo collections, textbooks, public exhibits, computer graphical simulations and Internet Web pages; general permission extends to personal Web pages, via NASA Image and Digital Library @ https://images.nasa.gov/details-S69-19190

artist’s concept of Apollo spacecraft’s command module (CM)-service module (SM) separation; NASA ID S66-05101, NASA ID S66-10991: NASA Johnson Space Center, via NASA @ https://www.hq.nasa.gov/alsj/S66-05101.jpg; Program Summary, Overviews, and Supplementary Material: 1966-7 Mission Event Illustrations > Apollo Mission Events, Scans courtesy Mike Gentry and Jody Russell, NASA Johnson, via Apollo Lunar Surface Journal @ https://www.nasa.gov/history/alsj/alsj-MissionEvents.html (specific image URL @ https://www.nasa.gov/wp-content/uploads/static/history/alsj/S66-05101.jpg)

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