Mercury project Summary

  • Last updated on November 10, 2022

The first phase of the U.S. crewed spacecraft program in which individual astronauts were launched to extremely high altitudes (over 100 miles) and, later, into Earth orbit.

Preliminary Developments

In the decade following World War II, high-altitude atmospheric research accomplished with crewed balloon flights, uncrewed sounding rockets, and later, experimental rocket planes such as the X-15, established the feasibility of sending crewed rocket-powered vehicles beyond the upper layers of Earth’s atmosphere. These early experimental flights were followed by a number of small electronic satellites, or “artificial moons,” launched successfully into orbit. The first of these was the 184-pound Russian Sputnik 1 (launched October 4, 1957). These orbital satellites were followed almost immediately by pressurized space capsules containing live research animals wired for telemetric data (such as the dog Laika, the first living creature in space, launched aboard Sputnik 2 on November 3, 1957). Within four years, Russian cosmonaut Yuri Gagarin became the first human in space when he completed a single orbit of the earth aboard Vostok 1 (launched April 12, 1961).

In these early years of space exploration, great political emphasis was placed upon the attainment of space firsts and, in this area, the United States space program was consistently outpaced by Russian accomplishments. In fact, the space race that eventually developed between the two countries became as much a test of patriotic pride as it was a competition of scientific and technical accomplishment. In October, 1958, at the recommendation of President Dwight D. Eisenhower, the National Advisory Committee for Aeronautics (NACA) was restructured into NASA and placed under the direction of James E. Webb. By utilizing the talents of rocketry experts such as Wernher von Braun, who had headed the German army’s V-2 rocket development center at Peenemünde during World War II, the U.S. space program would eventually close the U.S.-Soviet missile gap and succeed in landing the first astronauts upon the Moon, but those successes were still years ahead.

At the Threshold of Space

NASA’s launch complex at Cape Canaveral, Florida, in use since 1947 as the Atlantic/Eastern Test Range for military and scientific rockets and missiles, became the staging ground for Project Mercury. (After November 28, 1963, Cape Canaveral was temporarily renamed Cape Kennedy to honor the memory of President John F. Kennedy, who had been instrumental in fostering America’s spaceflight ambitions.) Launch Complex 56, located near the southwestern end of “Rocket Row,” served as the launch pad for the first two Mercury-Redstone flights. Launch Complex 14, further up the eastern shore, served as the launch pad for all later Mercury-Atlas orbital flights. The Cape Canaveral site had been established near to Earth’s equator in order to save fuel by taking advantage of Earth’s rotational velocity (amounting to a gain of approximately 1,500 feet per second at the equator), thus reducing the velocity needed for a rocket to attain orbit when launched in an eastward direction.

In 1960, after a regimen of rigorous physical, technical, and psychological testing, seven military test pilots were chosen as the first Mercury astronauts: Commander Alan Shepard, U.S.N.; Captain Virgil “Gus” Grissom, U.S.A.F.; Lieutenant Colonel John Glenn, U.S.M.C.; Lieutenant Commander M. Scott Carpenter, U.S.N.; Commander Walter M. Schirra, Jr., U.S.N.; and Major L. Gordon Cooper, U.S.A.F. The seventh member of the original Mercury 7, Donald “Deke” Slayton, was grounded due to an erratic heart rate and replaced in the Mercury flight lineup by M. Scott Carpenter.

Spacecraft and Booster Rockets

Project Mercury flights utilized existing liquid-fueled launch vehicles such as the 83-foot, 30-ton Redstone rocket, and the 93-foot Atlas missile, as booster rockets. Ironically, the hefty Atlas booster, pressed into service for all of the Project Mercury orbital launches, was actually an intercontinental ballistic missile (ICBM) originally designed to deliver a nuclear warhead payload. The Redstone and Atlas rockets’ propellants consisted principally of mixtures of liquid oxygen, liquid hydrogen, and kerosene.

Mounted atop its booster rocket, the black bell-shaped Mercury spacecraft, measuring 9 feet, 6 inches long and approximately 7 feet in diameter, carried a single space-suited astronaut. Sandwiched between the shingled outer hull of the Mercury capsule and its corrugated titanium inner hull was a layer of insulation 1.5 inches thick. Every available niche inside the pressurized capsule’s battleship-grey interior was crammed with research instruments, monitoring equipment, and control switches. (Shepard once joked that the tight fit of the capsule’s interior made it seem as though the capsule was something he “put on,” rather than climbed aboard.) The first Mercury space capsule, produced by McDonnell Aircraft for automatically controlled uncrewed flights and test animals, had only a small porthole and a hatch that had to be bolted into place by hand. For the crewed model, a pilot’s viewing portal was added, along with a quick release escape hatch with explosive bolts, and a manual back-up control system for piloting the spacecraft. McDonnell also outfitted the nose of its Mercury spacecraft with a 16-foot cylindrical red abort/escape rocket capable of separating the crewed capsule from the booster and carrying it to safety in the event of a mishap; this eventuality, however, was never encountered on any of the crewed flights.

During liftoff, the Mercury astronaut was positioned flat upon his back in a seated posture, legs elevated, to better withstand the tremendous force produced by the rocket’s initial acceleration as well as the stresses of reentry, estimated to reach a maximum gravitational force (g) equivalent of approximately 8 g’s on liftoff and 11 g’s on reentry. The astronaut remained strapped into his form-fitted couch throughout the flight, which typically lasted several hours. After completing the specified number of orbits, the spacecraft was maneuvered into an ideal reentry position angle of between 5 degrees and 7 degrees approximate negative inclination with respect to the horizon. This reentry angle proved critical; a steeper reentry would cause the spacecraft to fall too fast and burn up, while too shallow an angle would cause the spacecraft to skip off into space, unable to return. After positioning the spacecraft, aft end first, the astronaut fired the retro-rockets to slow the spacecraft sufficiently for it to safely reenter Earth’s atmosphere. During reentry, the ionization effect caused by the tremendous friction heating of the capsule’s reentry through the atmosphere resulted in a brief radio blackout during which contact with the spacecraft was lost for several minutes. During those most dramatic moments of the flight, the astronaut was protected by an ablative heatshield that absorbed the searing 3,000 degree Fahrenheit heat of reentry. Finally, the spacecraft descended by parachute to a splashdown at sea to be recovered by an aircraft carrier helicopter and a team of navy divers.

Mission Highlights

Each Mercury mission focused upon resolving a specific domain of engineering and design-related problems associated with future crewed spaceflights as well as answering questions of human endurance. The basic flight data of the individual Project Mercury missions are summarized in the accompanying table.

The first two Mercury flights, Freedom 7, crewed by Shepard, and Liberty Bell 7, crewed by Grissom, were suborbital missions during which, for the most part, the spacecrafts’ systems functioned automatically, relegating the astronauts to little more than onboard observers. The spacecraft were launched along a ballistic trajectory to the fringe of outer space and returned by parachute to a recovery in the Atlantic Ocean. During the second Mercury mission, a mishap with the explosive bolts securing the capsule’s hatch caused a premature opening after splashdown that foundered the capsule and nearly drowned astronaut Grissom. (The ill-fated Liberty Bell 7 capsule, lost at sea for almost forty years, was eventually recovered from the bottom of the Atlantic virtually intact in 2000.)

On the third crewed Mercury mission, Lieutenant Colonel John Glenn became the first American to orbit Earth, completing three orbits in his 4-hour, 56-minute flight. A crisis occurred when, halfway through the mission, a sensor aboard the Friendship 7 spacecraft indicated that the capsule’s heatshield had been jarred loose. NASA Ground Control advised Glenn not to jettison his retro-rocket pack after firing, in the hope that the metal straps securing the retro-pack would help to hold the heatshield safely in place during reentry. Glenn later recounted seeing large white-hot fragments of the incinerated retro-pack hurtling past his viewing portal as he endured the awful stresses of reentry. Fortunately, Friendship 7’s heatshield held.

During the second Mercury orbital flight, the mission priority shifted from testing the spacecraft’s systems integrity, now well established, to testing the handling and performance characteristics of Aurora 7 under astronaut Carpenter’s manual control. Near the end of the mission the spacecraft became endangered by excessive fuel usage, hit the atmosphere at a steeper angle than anticipated and, consequently, missed the target recovery zone by 250 miles. After a tense search, astronaut Carpenter was recovered from a life raft, unharmed, along with his space capsule.

Less than three months after Carpenter’s flight, Russian cosmonauts Adrian G. Kikolayev (Vostok 3, launched August 11, 1962) and Pavel R. Popovich (Vostok 4, launched August 12, 1962) scored yet another space first when they maneuvered their two Vostok spacecraft to within sight of one another, completing the first crewed rendezvous in space.

The third orbital Mercury flight, Sigma 7, crewed by Schirra, logged six orbits in a superbly executed textbook flight, but during the fourth and final Mercury orbital mission a massive electrical systems failure occurred on board the Faith 7 spacecraft as astronaut Gordon Cooper completed his twenty-second orbit. Having lost all of his spacecraft’s automatic systems, Cooper flew the Faith 7 spacecraft manually to a splashdown, landing east of Midway Island in the Pacific.

Project Mercury effectively concluded with Cooper’s Faith 7 orbital mission of May 15-16, 1963. Less than one month later (June, 1963), Russian Valentina Tereshkova became the first woman in space. The 26-year-old lieutenant completed forty-nine Earth orbits, more orbits than all the Project Mercury spaceflights combined.

The engineering- and human-factors data gleaned from the Mercury spaceflights proved instrumental in the development of the later two-man Gemini spacecraft, which served as the final engineering stopgap before the Apollo Program’s lunar landings of 1969-1972.

Of the seven original Mercury astronauts, Cooper, Grissom, Schirra, and Shepard flew on later Gemini missions; Grissom was killed in a launchpad fire aboard the Apollo 1 spacecraft on January 27, 1967; Schirra flew on Apollo 7; Shepard flew on the Apollo 14 lunar landing mission; Slayton flew on the Apollo-Soyuz docking mission; and Glenn, who became a U.S. senator after ending his space career, flew as a mission specialist on the U.S. space shuttle Discovery in 2001, nearly forty years after his first orbital mission aboard Friendship 7.

  • Harding, Richard. Survival in Space: Medical Problems of Manned Spaceflight. New York: Routledge, 1989. A detailed yet accessible survey of significant medical and human factors data derived from the crewed space program.
  • Wolfe, Tom. The Right Stuff. London: Jonathan Cape, 1980. An insightful and accurate sketch of the Mercury astronauts containing exceptional characterizations that contrast their private and public lives.

Apollo Program

Wernher von Braun

Crewed spaceflight

Gemini Program

John Glenn

National Aeronautics and Space Administration

National Advisory Committee for Aeronautics


Alan Shepard


Valentina Tereshkova

Uncrewed spaceflight

Mercury Mission Highlights

AstronautSpacecraftDate of FlightDurationOrbitsShepardFreedom 7May 5, 196115 minutessuborbitalGrissomLiberty Bell 7July 21, 196116 minutessuborbitalGlennFriendship 7February 20, 19624 hours, 56 minutes3CarpenterAurora 7May 24, 19624 hours, 56 minutes3SchirraSigma 7October 3, 19629 hours, 13 minutes6CooperFaith 7May 15-16, 196334 hours, 20 minutes22

The final touches are added to the second Mercury capsule at the Lewis Hangar, now the Glenn Research Center, near Cleveland, Ohio.

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