Apollo 10

This dress rehearsal for a Moon landing brought the Apollo Lunar Module to 8.4 nautical miles (15.6 km) from the lunar surface, at the point where powered descent would begin on the actual landing. Practicing this approach orbit would refine knowledge of the lunar gravitational field[15] needed to calibrate the powered descent guidance system[16] to within 1 nautical mile (1.9 km) needed for a landing. Earth-based observations, uncrewed spacecraft, and Apollo 8 had respectively allowed calibration to within 200 nautical miles (370 km), 20 nautical miles (37 km), and 5 nautical miles (9.3 km). Except for this final stretch, the mission was designed to duplicate how a landing would have gone, both in space and for ground control, putting NASA's flight controllers and extensive tracking and control network through a rehearsal.

The ascent stage was loaded with the amount of fuel and oxidizer it would have had remaining if it had lifted off from the surface and reached the altitude at which the Apollo 10 ascent stage fired; this was only about half the total amount required for lift off and rendezvous with the CSM. The mission-loaded LM weighed 30,735 pounds (13,941 kg), compared to 33,278 pounds (15,095 kg) for the Apollo 11 LM which made the first landing.[17] Craig Nelson wrote in his book Rocket Men that NASA took special precaution to ensure Stafford and Cernan would not attempt to make the first landing. Nelson quoted Cernan as saying "A lot of people thought about the kind of people we were: 'Don't give those guys an opportunity to land, 'cause they might!' So the ascent module, the part we lifted off the lunar surface with, was short-fueled. The fuel tanks weren't full. So had we literally tried to land on the Moon, we couldn't have gotten off."[18]

• Mass: CSM 63,648 pounds (28,870 kg); LM 30,735 pounds (13,941 kg)

LM Snoopy containing Stafford and Cernan, as inspected by Young after separation from Charlie Brown

Shortly after trans-lunar injection, Young performed the transposition, docking, and extraction maneuver, separating the command and service module (CSM) from the S-IVB stage, turning around, and docking its nose to the top of the lunar module (LM), before separating from the S-IVB. Apollo 10 was the first mission to carry a color television camera inside the spacecraft, and made the first live color TV transmissions from space.

After reaching lunar orbit three days later, Young remained in the command module (CM) Charlie Brown while Stafford and Cernan entered the LM Snoopy and flew it separately. The LM crew performed the descent orbit insertion maneuver by firing their descent engine, and tested their craft's landing radar as they approached the 50,000-foot (15,000-meter) altitude where the subsequent Apollo 11 mission would begin powered descent to actually land on the Moon. They surveyed the future Apollo 11 landing site in the Sea of Tranquility, then jettisoned the descent stage and fired the engine of the ascent stage to return to Charlie Brown Command Module. The descent stage was left in orbit, but eventually may have crashed onto the lunar surface because of the Moon's non-uniform gravitational field. Its location is unknown as it was not tracked.

During descent stage separation, the lunar module began to roll unexpectedly because the crew accidentally duplicated commands into the flight computer which took the LM out of abort mode, the correct configuration for this maneuver.[20] The live network broadcasts caught Cernan and Stafford uttering several expletives before regaining control of the LM. Decades later, Cernan said he observed the horizon spinning eight times over, indicating eight rolls of the spacecraft under ascent engine power. Recordings from the flight do not support this dramatic memory.[21] While the incident was downplayed by NASA, the roll was just several revolutions from being unrecoverable, which would have resulted in the LM crashing into the lunar surface.[20]

After Stafford and Cernan docked with and re-entered Charlie Brown, Snoopy's engine was fired to fuel depletion to send the ascent stage on a trajectory past the Moon and into a heliocentric orbit.[15][22] This maneuver was unlike the fate of the subsequent Apollo 11 ascent stage, which was left in lunar orbit to eventually crash (post-Apollo 11 ascent stages were steered into the Moon to obtain readings from seismometers placed on the surface, except for Apollo 13's ascent stage, which the crew used as a "life boat" to get safely back to Earth before releasing it to burn up in Earth's atmosphere).[22]

Snoopy's ascent stage orbit was not tracked after 1969, and its current location is unknown. In 2011, a group of amateur astronomers in the UK started a project to search for it. In 2019, the Royal Astronomical Society announced a possible rediscovery of Snoopy, determining that small Earth-crossing asteroid 2018 AV₂ is likely the capsule with "98%" certainty.[23] It is the only once-crewed spacecraft still in outer space without a crew.[24][25]

Splashdown occurred in the Pacific Ocean on May 26, 1969, at 16:52:23 UTC, about 400 nautical miles (740 km) east of American Samoa. The astronauts were recovered by USS Princeton, and subsequently flown to Pago Pago International Airport in Tafuna for a greeting reception, before being flown on a C-141 cargo plane to Honolulu.

After Apollo 10, NASA required astronauts to choose more "dignified" names for their command and lunar modules. This proved unenforceable: Apollo 16 astronauts Young, Mattingly and Duke chose Casper, as in Casper the Friendly Ghost, for their command module name. The idea was to give children a way to identify with the mission by using humor.[26][27]

The Smithsonian has been accountable for the command module Charlie Brown since 1970. The spacecraft was on display in several countries until it was placed on loan to the London Science Museum in 1978.[28] Charlie Brown's service module (SM) was jettisoned just before re-entry and burned up in the Earth's atmosphere.

After translunar injection, the Saturn V's S-IVB third stage was accelerated past Earth escape velocity and became a derelict object where as of 2020, it remains in a heliocentric orbit.[29]

The ascent stage of the Apollo Lunar Module Snoopy was jettisoned into a heliocentric orbit. On June 10, 2019, Nick Howes, a fellow of the Royal Astronomical Society, announced that he and his colleagues had located Snoopy, whose location was previously unknown, based on radar astronomy data with 98% certainty.[30]

Snoopy's descent stage was jettisoned in lunar orbit; its current location is unknown. Further, it is unclear whether the descent stage impacted the lunar surface, or if it remains in lunar orbit. Phil Stooke, a planetary scientist who studied the lunar crash sites of the LM's ascent stages, wrote that the descent stage "crashed at an unknown location",[31] and another source stated that the descent stage "eventually impact(ed) within a few degrees of the equator on the near side".[32] However, Richard Orloff and an official NASA mission summary stated simply that the descent stage entered lunar orbit, remaining silent on the question of whether the stage later impacted the Moon.[33][34] An amateur astronomy blog begun in early 2020 explored the possibility that the descent stage may still be in lunar orbit, using computer simulation.[35]

Apollo 10 space-flown silver Robbins medallion

The shield-shaped emblem for the flight shows a large, three-dimensional Roman numeral X sitting on the Moon's surface, in Stafford's words, "to show that we had left our mark". Although it did not land on the Moon, the prominence of the number represents the significant contributions the mission made to the Apollo program. A CSM circles the Moon as an LM ascent stage flies up from its low pass over the lunar surface with its engine firing. The Earth is visible in the background. On the mission patch, a wide, light blue border carries the word APOLLO at the top and the crew names around the bottom. The patch is trimmed in gold. The insignia was designed by Allen Stevens of Rockwell International.[36]

In February 2016 Discovery Channel broadcast a TV show suggesting that the mission witnessed mysterious or alien signals while on the far side of the Moon.[37] The astronauts mention the odd whistling sound that lasted nearly an hour. It was speculated that this is an evidence for UFO coverup. According to space journalist James Oberg, the sound was most probably radio interference between the command module and the lunar module landing vehicles. Describing it as "outer-space type music" was most probably due to priming, as suggested by Benjamin Radford.[38]

• 
  The S-IC first stage in the VAB
• 
  Apollo 10 during rollout
• 
  The crew poses with their launch vehicle; left to right, Cernan, Young, Stafford.
• 
  Crew boarding the command module before launch
• 
  Apollo 10 launch
• 
  Apollo 10 view of Earth rise
• 
  Lunar Module Snoopy during post-undocking inspection
• 
  CSM Charlie Brown
• 
  Lunar module about to dock with the command module
• 
  Recovery by a SH-3D of HS-4 from USS Princeton
• 
  Command module at London's Science Museum (May 2009)
• 
  Arago crater
• 
  Triesnecker crater and Triesnecker rilles
• 
  A small unnamed crater on the far side, with bright ray system
• 
  Necho crater on the far side of the Moon
• 
  High-albedo swirls within unnamed crater east of Firsov

• List of artificial objects on the Moon
• List of vehicle speed records

 This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.

Wikimedia Commons has media related to Apollo 10.

• "Apollo 10" at Encyclopedia Astronautica
• NSSDC Master Catalog at NASA
• Apollo 10 Flight Journal

NASA reports

• Apollo 10 Press Kit (PDF), NASA, Release No. 69-68, May 7, 1969 (from NASA Program History Office)
• Apollo 10 Press Kit (PDF), NASA, Release No. 69-68, May 7, 1969 (from NASA Technical Reports Server)
• The Apollo Spacecraft: A Chronology NASA, NASA SP-4009
• "Apollo Program Summary Report" (PDF), NASA, JSC-09423, April 1975
• "Table 2-38. Apollo 10 Characteristics" from NASA Historical Data Book: Volume III: Programs and Projects 1969–1978 by Linda Neuman Ezell, NASA History Series (1988)

Multimedia

• Apollo 10: "To Sort Out the Unknowns" Official NASA/JSC documentary film, JSC-519 (1969)
• Apollo 10 16mm onboard film part 1, part 2 raw footage taken from Apollo 10
• Apollo 10 Moon Orbit Orbital footage of Moon from Apollo 10
• Mission Transcripts: Apollo 10 at NASA's Lyndon B. Johnson Space Center (JSC)
• Images from Apollo 10
• Apollo launch and mission videos at ApolloTV.net