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Mission or Study ID:   Mercury 4
Mercury-Redstone 4
Launch/Start Date:
Landing/End Date:
15 minutes, 37 seconds
Mercury 4 Crew Patch

Following two postponements, the second sub-orbital American flight, Mercury 4 (MR-4), was launched on July 21, 1961, into the same flight path flown by Mercury 3 and was planned as another 15-minute flight. The major objectives of the MR-4 flight were to again confirm the ability of man to fly safely into space; the astronaut for this second manned flight was Virgil ''Gus'' Grissom. The flight operations and conditions were also very similar to the first Mercury flight. The medical and technical data gathered on MR-4 added greatly to data from MR-3 and led the way for the first American orbital flight by establishing that humans could travel for brief periods into space with no lasting or major affect on their health.

As with MR-3, the life sciences objectives of the flight included the study of the effects of microgravity, launch and reentry accelerations, and gravity transition periods. Due to the short flight time of this and the previous Mercury-Redstone mission, little time was available to collect data on the physiological adaptation of the human body to space flight. Doctors and scientists, therefore, focused on monitoring physiological responses to flight to ensure that the health of the astronaut was not being compromised and to develop steps for preventing any harmful effects of space flight on future longer-duration missions.

As it landed, the Liberty Bell 7 capsule was lost and sank into the ocean. Astronaut Grissom was rescued safely, though some scientific data was lost with the spacecraft. Nevertheless, the flight was successful and reaffirmed the ability of man to fly in space and return safely.

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Experiments on this Mission