Apollo 10 (May 18–26, 1969) was the fourth human spaceflight in the United States' Apollo program and the second to orbit the Moon. NASA, the mission's operator, described it as a "dress rehearsal" for the first Moon landing (Apollo 11, two months later). It was designated an "F"mission, intended to test all spacecraft components and procedures short of actual descent and landing.
After the spacecraft reached lunar orbit, astronaut John Young remained in the Command and Service Module (CSM) while astronauts Thomas Stafford and Gene Cernan flew the Apollo Lunar Module (LM) to within (7.8 nautical miles; ) of the lunar surface, the point at which powered descent for landing would begin on a landing mission. After four orbits they rejoined Young in the CSM and, after the CSM completed its 31st orbit of the Moon, they returned safely to Earth.
While NASA had considered attempting the first crewed lunar landing on Apollo 10, mission planners ultimately decided that it would be prudent to have a practice flight to hone the procedures and techniques. The crew encountered some problems during the flight: pogo oscillations during the launch phase and a brief, uncontrolled tumble of the LM ascent stage in lunar orbit during its solo flight. However, the mission accomplished its major objectives. Stafford and Cernan observed and photographed Apollo 11's planned landing site in the Sea of Tranquility. Apollo 10 spent 61 hours and 37 minutes orbiting the Moon, for about eight hours of which Stafford and Cernan flew the LM apart from Young in the CSM, and about eight days total in space. Additionally, Apollo 10 set the record for the highest speed attained by a crewed vehicle relative to the Earth's surface: 39,897 kilometers per hour (11.08 kilometers per second or 24,791 miles per hour) on May 26, 1969, during the return from the Moon.
The mission's call signs were the names of the Peanuts characters Charlie Brown for the CSM and Snoopy for the LM, who became Apollo 10's semi-official mascots. Photo description available here . Peanuts creator Charles Schulz also drew mission-related artwork for NASA.
Framework
Background
By 1967, NASA had devised a list of mission types, designated by letters, that needed to be flown before a landing attempt, which would be the "G" mission. The early uncrewed flights were considered "A" or "B" missions, while Apollo 7, the crewed-flight test of the Command and Service Module (CSM), was the "C" mission. The first crewed orbital test of the Lunar Module (LM) was accomplished on Apollo 9, the "D" mission. Apollo 8, flown to the Moon's orbit without an LM, was considered a "C-prime" mission, but its success gave NASA the confidence to skip the "E" mission, which would have tested the full Apollo spacecraft in medium or high Earth orbit. Apollo 10, the dress rehearsal for the lunar landing, was to be the "F" mission.
NASA considered skipping the "F" mission as well and attempting the first lunar landing on Apollo 10. Some within the agency advocated for this, feeling it was senseless to bring astronauts so close to the lunar surface, only to turn away. Although the Lunar Module intended for Apollo 10 was too heavy to perform the lunar mission, the one intended for Apollo 11 could be substituted by delaying Apollo 10 a month from its May 1969 planned launch. NASA official George Mueller favored a landing attempt on ; he was known for his aggressive approach to moving the Apollo program forward. However, Director of Flight Operations Christopher C. Kraft and others opposed this, feeling that new procedures would have to be developed for a rendezvous in lunar orbit and that NASA had incomplete information regarding the Moon's mass concentrations, which might throw off the spacecraft's trajectory. Lieutenant General Sam Phillips, the Apollo Program Manager, listened to the arguments on both sides and decided that having a dress rehearsal was crucial.
Crew and key Mission Control personnel
On November 13, 1968, NASA announced the crew members of Apollo 10. Thomas P. Stafford, the commander, was 38 years old at the time of the mission. A 1952 graduate of the Naval Academy, he was commissioned in the Air Force. Selected for the second group of astronauts in 1962, he flew as pilot of Gemini 6A (1965) and command pilot of Gemini 9A (1966). John Young, the command module pilot, was 38 years old and a commander in the Navy at the time of Apollo 10. A 1952 graduate of Georgia Tech who entered the Navy after graduation and became a test pilot in 1959, he was selected as a Group 2 astronaut alongside Stafford. He flew in Gemini 3 with Gus Grissom in 1965, becoming the first American not of the Mercury Seven to fly in space. Young thereafter commanded Gemini 10 (1966), flying with Michael Collins. Gene Cernan, the Lunar Module pilot, was a commander in the Navy at the time of Apollo 10. A 1952 graduate of Purdue University, he entered the Navy after graduation. Selected for the third group of astronauts in 1963, Cernan flew with Stafford on Gemini 9A before his assignment to Apollo 10. With five prior flights among them, the Apollo 10 crew was the most experienced to reach space until the Space Shuttle era, and the first American space mission whose crew were all spaceflight veterans.
The backup crew for Apollo 10 was Gordon Cooper as commander, Donn F. Eisele as command module pilot, and Edgar D. Mitchell as lunar module pilot. By the normal crew rotation in place during Apollo, Cooper, Eisele, and Mitchell would have flown on Apollo 13, but Cooper and Eisele never flew again. Deke Slayton, Director of Flight Crew Operations, felt that Cooper did not train as hard as he could have. Eisele was blackballed because of incidents during Apollo 7, which he had flown as CMP and which had seen conflict between the crew and ground controllers; he had also been involved in a messy divorce. Slayton only assigned the two as backups because he had few veteran astronauts available. Cooper and Eisele were replaced by Alan Shepard and Stuart Roosa respectively. Feeling they needed additional training time, George Mueller rejected the Apollo 13 crew. The crew was switched to Apollo 14, which saw Shepard and Mitchell walk on the Moon.
For projects Mercury and Gemini, a prime and a backup crew had been designated, but for Apollo, a third group of astronauts, known as the support crew, was also designated. Slayton created the support crews early in the Apollo program on the advice of McDivitt, who would lead Apollo 9. McDivitt believed that, with preparation going on in facilities across the U.S., meetings that needed a member of the flight crew would be missed. Support crew members were to assist as directed by the mission commander. Usually low in seniority, they assembled the mission's rules, flight plan, and checklists, and kept them updated. For Apollo 10, they were Joe Engle, James Irwin, and Charles Duke.
Flight directors were Gerry Griffin, Glynn Lunney, Milt Windler, and Pete Frank. Flight directors during Apollo had a one-sentence job description: "The flight director may take any actions necessary for crew safety and mission success." CAPCOMs were Duke, Engle, Jack Lousma, and Bruce McCandless II.
Call signs and mission insignia
The command module was given the call sign Charlie Brown and the lunar module the call sign Snoopy. These were taken from the characters in the comic strip, Peanuts, Charlie Brown, and Snoopy. These names were chosen by the astronauts with the approval of Charles Schulz, the strip's creator, who was uncertain it was a good idea, since Charlie Brown was always a failure. The choice of names was deemed undignified by some at NASA, as were the choices for Apollo 9's CM and LM ("Gumdrop" and "Spider"). Public relations chief Julian Scheer urged a change for the lunar landing mission. But for Apollo 10, according to Cernan, "The P.R.-types lost this one big-time, for everybody on the planet knew the klutzy kid and his adventuresome beagle, and the names were embraced in a public relations bonanza." Apollo 11's call signs were "Columbia" for the command module and "Eagle" for the Lunar Module.
Snoopy, Charlie Brown's dog, was chosen for the call sign of the Lunar Module since it was to "snoop" around the landing site, with Charlie Brown given to the command module as Snoopy's companion. Snoopy had been associated for some time with the space program, with workers who performed in an outstanding manner awarded silver "Snoopy pins", and Snoopy posters were seen at NASA facilities, with the cartoon dog having traded in his World War I aviator's headgear for a space helmet. Stafford stated that, given the pins, "the choice of Snoopy [as call sign] was a way of acknowledging the contributions of the hundreds of thousands of people who got us there". The use of the dog was also appropriate since, in the comic strip, Snoopy had journeyed to the Moon the year before, thus defeating, according to Schulz, "the Americans, the Russians, and that stupid cat next door".
The shield-shaped mission insignia 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 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. "A version of this article was published concurrently in the British Interplanetary Society's Spaceflight magazine." (June 2008; pp. 220–225).
Training and preparation
Apollo 10, the "F" mission or dress rehearsal for the lunar landing, had as its primary objectives to demonstrate crew, space vehicle, and mission support facilities performance during a crewed mission to lunar orbit, and to evaluate the performance of the Lunar Module there. In addition, it was to attempt photography of Apollo Landing Site 2 (ALS-2) in the Sea of Tranquillity, the contemplated landing site for Apollo 11. According to Stafford, Our flight was to take the first lunar module to the moon. We would take the lunar module, go down to within about ten miles above the moon, nine miles above the mountains, radar map, photo map, pick out the first landing site, do the first rendezvous around the moon, pick out some future landing sites, and come home.
Apollo 10 was to adhere as closely as possible to the plans for Apollo 11, including its trajectory to and from lunar orbit, the timeline of mission events, and even the angle of the Sun at ALS-2. However, no landing was to be attempted. ALS-1, given that number because it was the furthest to the east of the candidate sites, and also located in the Sea of Tranquility, had been extensively photographed by Apollo 8 astronauts; at the suggestion of scientist-astronaut Harrison Schmitt, the launch of Apollo 10 had been postponed a day so ALS-2 could be photographed under proper conditions. ALS-2 was chosen as the lunar landing site since it was relatively smooth and of scientific interest, while ALS-1 was deemed too far to the east. Thus, when Apollo 10's launch date was announced on January 10, 1969, it was shifted from its placeholder date of May 1 to May 17, rather than to May 16. On March 17, 1969, the launch was slipped one day to May 18, to allow for a better view of ALS-3, to the west of ALS-2. Another deviation from the plans for Apollo 11 was that Apollo 10 was to spend an additional day in lunar orbit once the CSM and LM rendezvoused; this was to allow time for additional testing of the LM's systems, as well as for photography of possible future Apollo landing sites.