Hidden Histories: Cancelled Mercury Missions
Project Mercury was NASA's first manned space program and was responsible for sending the first six Americans into space. It flew a total of 26 missions from 1959 to 1963, but some that were originally planned never took place. This post will talk a little bit about some of the Mercury flights that got cut during the program's duration.
In the earliest days of the Mercury Program, NASA planned to qualify their new Mercury spacecraft with a series of balloon flights. It was essentially their own version of the Air Force's Project Manhigh. Scheduled to take place from July 1959 to January 1961, these flights would carry the capsule to the very edge of space then release it in order to test recovery systems before making a recovery at sea. The final flights were also set to be manned at last up to 24 hours. In March 1959, the project was cut back to two balloon flights to qualify the spacecraft at altitudes up to 15 miles (24 km). On May 22, it was cancelled entirely when the agency realized they could obtain all necessary data using the altitude wind tunnel at the Lewis Research Center in Cleveland, Ohio. Interestingly enough, the Soviet Union had their own series of analogue Vostok capsule tests. Misconstrued stories of piloted test flights, along with Soviet secrecy, spawned allegations of "phantom cosmonauts", or people who perished during spaceflight and whose deaths were covered up by the Soviet Union. These stories are entirely false though some of the pilots who are claimed to have been killed were actual test pilots.
Mercury-Redstone 3A is the name given to the original Mercury-Redstone 3 mission, which would have launched on March 24, 1961 and put an American in space before the Soviet Union. The crew and spacecraft, Alan Shepard and Freedom 7, remained the same— the only difference is the launch date. After problems with the Mercury-Redstone 2 booster, which launched the chimpanzee Ham on a suborbital flight in January 1961, Wernher von Braun demanded further unmanned tests of the Redstone before allowing men to fly it. The main problems were structural feedback to the control system, instrument vibration, and thrust control malfunction. A Mercury boilerplate capsule was launched on Mercury-Redstone Booster Development (BD) and the test was flawless. After an 8.5 minute-long suborbital flight, the Redstone booster was approved for manned flight. This was the last time a Redstone would launch uncrewed.
Mercury-Redstone 5 & 6
Mercury-Redstone's 5 and 6 were crewed suborbital flights scheduled for late summer and autumn respectively. They were both cancelled in the summer of 1961 after the full-day Soviet Vostok 2 flight completed by Gherman Titov. Delays in the program resulted in planned Redstone flights occurring relatively close to the anticipated manned Atlas flights. The original Project Mercury plan had all astronauts making initial suborbital flights in preparation for longer Atlas missions. NASA figured additional suborbital flights would look silly compared to the Soviet's orbital journeys so they cut the two planned Redstone flights following Grissom's Mercury-Redstone 4. John Glenn was slated to fly MR-5 and Deke Slayton would have flown MR-6 . The actual Redstone that would have been used for MR-6 is now on display in the Heroes & Legends building at the Kennedy Space Center in Florida.
Mercury-Atlas 7 Delta 7
Mercury-Atlas 7 carrying the Delta 7 spacecraft was the planned second crewed orbital flight and was cancelled in March 1962. It would have been a three-orbit mission flown by Deke Slayton, who was accepted not only as an astronaut but as an Air Force pilot with a minor heart fibrillation. It all began when John Glenn's wife refused to make a television appearance with Vice President Lyndon B. Johnson after a launch scrub of Glenn's historic orbital flight. Rumors spread in the Pentagon that Glenn had a secret medical condition, possibly one effecting his heart. In the process of investigating Glenn, Slayton's own heart condition came up. The flight surgeons ran some tests and informed him he was not medically qualified to fly in space; if his heart could not handle the stresses of spaceflight, he would be completely alone and in grave danger. If not for the cancellation of MR-6 and the scrub of MA-6, Slayton just might have gotten to fly before the Apollo-Soyuz Test Project in 1975. His removal from active flight status is the primary reason he became Chief Astronaut shortly after. Mercury-Atlas 7 launched on its three-orbit mission on May 24, 1962 and was flown by Scott Carpenter in his Aurora 7 spacecraft.
Mercury-Atlas 10 was the second planned day-long Mercury orbital flight. It was cancelled after the success of Mercury-Atlas 9 in the spring of 1963 for being too risky but was scheduled to launch in October of the same year. The pilot would have been Alan Shepard and his spacecraft would have been Mercury capsule number 15B, callsign Freedom 7 II. Walt Williams, a NASA deputy associate administrator during Project Mercury, as well as Shepard and others at the Manned Spacecraft Center wanted a 3-6 day long Mercury endurance mission. If flown, it would have been the first American endurance record . The mission also would have covered the biological objectives of the first two crewed Gemini missions. NASA decided to undertake another manned mission in the event MA-9 was a failure. Cooper's 18-orbit flight was a success, despite the multitude of things that went wrong, and achieved all the goals MA-10 was proposed to fulfill. This and budgetary pressure brought about the end to Project Mercury in order to move onto Project Gemini, and MA-10 was officially cancelled on June 12 by Administrator James Webb. The following day McDonnell's remaining work for Mercury was terminated. Coincidentally, Shepard was removed from flight status that October due to Meniere's disease— if NASA had chosen to go through with the mission, it more than likely would have been flown by someone else. In September 1967, the Smithsonian Institute received the spacecraft and it is now on display at the Udvar-Hazy Center in Chantilly, Virginia. This exhibit is one of only two remaining Mercury spacecraft in orbital configuration. Not only is the retropack still attached to the aft end of the capsule, but its parachutes are still packed inside the nose section.
MA-10 capsule on display with "Freedom 7 II" visible on its side (Smithsonian)
Like all subsequent space programs, both crewed and uncrewed, Project Mercury underwent a number of mission changes during its short duration. Some were a result big issues, such as fierce competition on the other side of the world, while others were the result of internal concerns. These incidents are what shaped Project Mercury and its iconic missions.
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 Both Glenn and Slayton were bumped to orbital flights after the termination of MR-5 and 6.
 The first American endurance record was not set until 1965 when Gemini 5 stayed 8 days. They broke the Soviet record of 5 days set by Vostok 5 in 1963.
“Mercury Capsule 15B, Freedom 7 II.” Mercury Capsule 15B, Freedom 7 II | National Air and Space Museum, https://airandspace.si.edu/collection-objects/capsule-mercury-15b/nasm_A19680241000.
“Mercury Redstone BD.” NASA Space Science Data Coordinated Archive, https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=MERCRBD.
Moore, Roger E. "No Go: Project Mercury Missions and Spacecraft That Never Left Earth." 2001.
Wade, Mark. “Your Flight Has Been Cancelled.” Encyclopedia Astronautica, http://www.astronautix.com/y/yourflighthbeencancelled.html.