Mercury-Redstone 4
Second U.S. human spaceflight; hatch blew prematurely after splashdown.
Mercury-Redstone 4, also known as Liberty Bell 7, was the second United States human spaceflight, launched on July 21, 1961. The suborbital Project Mercury flight was piloted by astronaut Virgil 'Gus' Grissom and lasted 15 minutes 37 seconds, reaching an altitude of more than 102.8 nautical miles (190.4 km) and flying 263.2 nautical miles (487.4 km) downrange before landing in the Atlantic Ocean. The mission is notable for the accidental explosive release of the hatch after splashdown, which caused the spacecraft to sink; Grissom was recovered safely, but the capsule was not recovered until 1999.
Quick Facts
- Insignia Caption
- Spacecraft name as painted on capsule side, with a "crack"
- Mission Type
- Test flight
- Operator
- NASA
- Mission Duration
- 15 minutes, 37 seconds
- Suborbital Range
- 262.50 nmi
- Suborbital Apogee
- 102.76 nmi
- Spacecraft
- Mercury No.11
- Manufacturer
- McDonnell Aircraft
- Launch Mass
- 2835 lb
- Launch Rocket
- Redstone MRLV MR-8
- Launch Site
- Cape Canaveral LC-5
Facts from the source article.
Lore & Background
The spacecraft, Mercury capsule #11, was designated for the second crewed suborbital flight in October 1960 and came off McDonnell's St. Louis production line in May 1960. It was the first Mercury operational spacecraft with a centerline window instead of two portholes, and featured a white, diagonal, irregular paint stripe emulating the crack in the Liberty Bell. The capsule was named Liberty Bell 7 by Grissom, the seven honoring the original Mercury astronauts, a tradition started by Alan Shepard with Freedom 7.
Liberty Bell 7 introduced an explosive hatch release designed for quick emergency exit, using standard steel bolts with drilled weak points and a mild detonating fuse. The hatch could be fired from inside by pressing a plunger or from outside by pulling a lanyard. The flight also incorporated a new rate stabilization control system for finer spacecraft handling, and a new procedure for firing posigrade rockets into the booster-spacecraft adapter to achieve greater separation velocity.
During the mission, Grissom experienced vibrations during liftoff but reported the environmental control system worked well. After splashdown, the hatch cover accidentally blew, and Grissom was at risk of drowning but was recovered safely by a U.S. Navy helicopter. The spacecraft sank into the Atlantic and was not recovered until 1999.
Reader's Guide
Mercury-Redstone 4 was a critical step in the United States' Project Mercury, demonstrating the ability to launch a second human into space and return them safely, despite a post-splashdown anomaly. The mission tested new spacecraft features, including the explosive hatch, centerline window, and rate stabilization controls, which informed later Mercury and subsequent spacecraft designs. The accidental hatch blow and sinking of Liberty Bell 7 highlighted the need for improved emergency procedures and hatch reliability. The spacecraft's recovery in 1999 provided historical artifacts for study and public display. Grissom's successful recovery, despite the incident, reinforced the viability of suborbital human spaceflight and paved the way for orbital missions.
Did You Know?
- Grissom chose the name 'Liberty Bell 7' because the capsule resembled a bell and evoked the iconic Liberty Bell, complete with a painted crack.
- The spacecraft sank into the Atlantic Ocean after the hatch accidentally blew and was not recovered until 1999.
Frequently Asked Questions
What is Mercury-Redstone 4?
Mercury-Redstone 4, nicknamed Liberty Bell 7, was the second crewed spaceflight ever flown by the United States. It took off on July 21, 1961, as part of Project Mercury and was piloted by astronaut Virgil 'Gus' Grissom.
How long did the flight last and how far did it travel?
The entire mission lasted 15 minutes and 37 seconds, carrying Grissom to an altitude above 190 kilometers. The capsule then traveled roughly 487 kilometers downrange before splashing down in the Atlantic Ocean.
What happened to the hatch after splashdown?
The hatch's explosive release mechanism fired prematurely, blowing the hatch off the capsule and flooding it with seawater. Grissom was pulled from the water unharmed, but Liberty Bell 7 sank and was not located again until 1999.
Was Gus Grissom injured during the hatch incident?
No, Grissom was extracted from the ocean safely and was not physically hurt by the premature hatch release. However, the episode added to the growing awareness of how fragile early spacecraft systems could be.
Why is Mercury-Redstone 4 considered a landmark mission?
As the second American crewed flight, it proved that a U.S. astronaut could survive a suborbital trajectory and return to Earth. The dramatic hatch failure also served as a hard-won design lesson that shaped every subsequent capsule in the program.
More in Suborbital human spaceflights 1-24
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