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Mercury Redstone 4



Mercury Redstone 4 (MR-4, also designated Liberty Bell 7) was the second flight of an American rocket with a human on board (Virgil I. "Gus" Grissom) and the last suborbital manned flight. The objectives of MR-4 were to: (1) familiarize man with a brief but complete space flight experience, including the lift-off, powered flight, weightless flight (approximately 5 minutes), re-entry, and landing phases of the flight; (2) evaluate man's ability to perform as a functional unit during space flight by demonstrating manual control of spacecraft attitude before, during, and after retrofire and by use of voice communications during flight; (3) study man's physiological reactions during space flight; and, (4) qualify the explosively-actuated side egress hatch.

From lift-off to re-entry, operational sequences were similar to those of the first manned suborbital flight and Grissom's flight experience was similar to Shepard's in that there was a five minute period of weightlessness. As with Shepard, no ill effects resulting from this condition were reported. Control tests of spacecraft attitude in manual mode were also successfully completed and demonstrated their ease of use. The main configuration differences from the MR-3 spacecraft was the addition of a large viewing window and an explosively actuated side hatch.

During the flight, the spacecraft attained a maximum velocity of 8,270 km/hour and an altitude of 189 km. The capsule landed 483 km down range from Cape Canaveral. The duration of flight was 15 minutes and 37 s.

After splash-down, the explosive hatch activated prematurely while Grissom awaited helicopter pickup. Grissom exited the capsule immediately and remained in the water while a helicopter attempted to lift the rapidly sinking spacecraft. The attempt to raise the spacecraft failed and Grissom was lifted to another helicopter after spending 3-4 minutes in the water and transported to the aircraft carrier USS Randolph.

Despite the failure of the explosive hatch to properly function and the loss of the spacecraft, MR-4 was deemed a successful mission. Subsequent investigation into the premature firing of the explosive egress hatch resulted in more testing, but no premature firings occurred. A mechanical hatch was designed to replace the explosive hatch, but due to weight constraints was never implemented. The incident resulted in a change of procedures which required the firing safety pin to remain in place until after the helicopter hook was attached and tension applied to the recovery cable.

Liberty Bell 7 was finally raised from its resting place on the bottom of the Atlantic Ocean, some 4.8 km below the surface and 830 km northwest of Grand Grand Turk Island, in 1999 after a number of expeditions. Two expeditions to the area, in 1992 and 1993, were unsuccessful in locating the capsule. The next expedition succeeded in locating the capsule on May 2, 1999, but the cable which linked the surface ship to the submersible (which would have towed the capsule to the surface) broke, resulting in the loss of the submersible and temporarily dashing the hopes of those who intended to retrieve a piece of history. A final expedition, to recover both the submersible and the capsule, succeeded on July 20, 1999, in raising the capsule to the surface. Still attached to the capsule was the recovery line from the helicopter which tried to save it from going under in 1961. Also among the artifacts found inside were some of Grissom's gear and some Mercury dimes which had been taken into space as souvenirs.

Alternate Names

  • Liberty Bell 7
  • MR-4
  • MercuryRedstone4

Facts in Brief

Launch Date: 1961-07-21
Launch Vehicle: Redstone
Launch Site: Cape Canaveral, United States
Mass: 955 kg

Funding Agency

  • NASA-Office of Manned Space Flight (United States)


  • Engineering
  • Human Crew

Additional Information

Questions and comments about this spacecraft can be directed to: Dr. Edwin V. Bell, II



NameRoleOriginal AffiliationE-mail

Selected References

  • Grimwood, J. M., Project Mercury: A chronology, NASA, SP-4001, Wash., D.C., 1963.
  • Results of the second U.S. manned suborbital space flight July 21, 1961, NASA-JSC, Unnumbered, Houston, TX, 1961.

Other Sources of MR-4 Information/Data

MR-4 information (NASA KSC)
MR-4 Press Release images (NASA JSC)

On-line version of Results of the Second Manned Suborbital Space Flight (NASA History Office)
On-line version of Project Mercury: A Chronology (NASA History Office)

Expedition to recover MR-4 (Discovery Online)
MR-4 resoration and tour information (Kansas Cosmosphere and Space Center)

Sources of Related Information

Biography of Gus Grissom (NASA HQ)
Grissom's gravesite (Arlington National Cemetary)

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