NASA Project Mercury - Wally Schirra and Sigma 7
This page is part of a series on America's first manned space program, Project Mercury. Links to all the hubs in this series can be found at the NASA Project Mercury Overview.
Schirra named his capsule Sigma 7 to reflect the engineering focus of his mission. Sigma is a mathematical symbol for summation. To Schirra, the symbol represented engineering excellence, and it also reflected the fact that his mission built on the work and experience of previous missions.
Schirra, like all of the Mercury astronauts, added the number 7 to the name of his spacecraft, to represent the seven-man Mercury astronaut team.
America's third manned orbital spaceflight took place on October 3, 1962, as part of NASA's Project Mercury.
Earlier in 1962, John Glenn and Scott Carpenter had each flown missions lasting three orbits. The goal for this flight was to double the duration to six orbits. The man chosen to do it was Mercury astronaut Wally Schirra.
All Mercury orbital missions used the Atlas-D rocket. Including unmanned test flights, this was the eighth Mercury-Atlas launch, officially named Mercury-Atlas 8. The rocket was nearly identical to those used on the two previous flights. Based on lessons learned from those missions, Schirra's Mercury spacecraft was modified, making it lighter, more fuel efficient, and, hopefully, more reliable.
Lift-off was at 7:15 a.m. EST, from Cape Canaveral, Florida. The flight lasted just over 9 hours and 13 minutes, of which Schirra was weightless for 8 hours and 56 minutes. Schirra completed six orbits as planned, and traveled a total of 143,983 miles before splashing down in the Pacific ocean at 4:28 p.m. EST.
Focus On Engineering
Despite its longer duration, Schirra's mission contained fewer scientific experiments than the previous flight by Scott Carpenter. On that flight, there had been nearly disastrous problems with capsule alignment and retrofire. Fuel consumption had also been an issue.
For the Mercury-Atlas 8 mission, Schirra's primary role would be that of test pilot. He would make an engineering evaluation of the modified Mercury spacecraft's operation and performance in orbit, and help determine if it were now ready for longer missions.
Following the flight of Alan Shepard, President Kennedy announced the goal of a manned lunar landing by the end of the decade. The ability to maneuver a spacecraft with precision while conserving fuel was vital to achieving that goal. In the wake of Scott Carpenter's fuel and alignment problems, NASA needed to demonstrate that such precision and fuel efficiency were possible. Schirra's flight plan included several control tasks that would, hopefully, prove just that.
To learn more about orbital flight and weightlessness, see: Basic Concepts of Orbital Spaceflight.
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Schirra was weightless for several hours longer than any previous American astronaut. He felt no disorientation or nausea, nor did he experience euphoria or any of the psychological responses some doctors had speculated might be triggered by extended weightlessness.
Schirra performed all spacecraft control tasks with great precision, and with even lower fuel consumption than had been expected. He was also able to accurately navigate using only visual references, such as the moon, Venus, and other stars that could be seen through the capsule window.
The only serious problem encountered during the flight was a malfunction of the spacesuit cooling system. This led to some discomfort early in the flight, but Schirra was able to make manual adjustments that fixed the problem. Schirra's performance aboard Sigma 7 gave NASA confidence in man's ability to perform as needed on future missions.
Scientific activity was reduced for this mission, but Schirra did engage in some scientific experiments, with varying levels of success. He was able to complete a series of photographs for the US Weather Bureau, but another set of earth photographs were mostly unusable, due to overexposure or excessive cloud cover. An attempt to see high-intensity ground lighting from orbit also failed because of cloud cover, as with the previous two Mercury flights.
A measurement of the amount and composition of radiation outside of earth's atmosphere was successful, and showed that an astronaut in orbit would not be exposed to unsafe levels of radiation. Also successful was a study of new materials being considered for use on future spacecraft. Eight different materials were attached to the outside of Sigma 7, to evaluate the effects of reentry on these materials.
Splashdown and Recovery
Retrofire and reentry occurred as planned, and Schirra's landing was extremely accurate, only 4.5 miles from the target site. Sigma 7 was the first spacecraft to splashdown in the Pacific ocean, where it was quickly recovered by the aircraft carrier USS Kearsarge.
Schirra chose to remain inside the spacecraft until it was aboard the carrier. Once aboard, he blew the hatch and exited the spacecraft. This was the same type of explosive hatch that had malfunctioned following Gus Grissom's splashdown, leading to the loss of the Liberty Bell 7 spacecraft.
To blow the hatch, Schirra had to hit a plunger with such force that he injured his hand. Grissom's hand was uninjured following his flight, proving that he hadn't hit the plunger to blow the hatch of Liberty Bell 7. It truly had been a malfunction.
The flight of Sigma 7 was a complete success. NASA's report following the mission called it a textbook flight. Both pilot and spacecraft had performed exceptionally well. Schirra had performed all tasks in the time allowed, with precision and fuel efficiency, and the spacecraft exhibited only one minor problem, which Schirra quickly resolved. There was now no reason not to proceed with longer missions.
In August, 1962, the Soviet Union had flown two missions of much longer duration than Schirra's flight. Vostok 3, which orbited the earth 64 times, was in space for almost 4 days, and Vostok 4 orbited 48 times on a flight that lasted almost 3 days.
By comparison, Schirra's 9 hours in space seemed small, but it was a big step forward for America's space program, and it set the stage for even larger steps that were to follow.
In addition to the sources listed on the Project Mercury - Overview page, information for this hub came from the following original source documents:
- Manned Spacecraft Center, Results of the Third U.S. Manned Orbital Space Flight - October 3, 1962, NASA, 1962
- Manned Spacecraft Center, First US Manned Six-Pass Orbital Mission (Mercury-Atlas 8, Spacecraft 16) Description and Performance Analysis, NASA, 1968