Project Mercury



Project Mercury was the first human spaceflight program of the United States. It ran from 1959 through 1963 with the goal of putting a human in orbit around the Earth. The Mercury-Atlas 6 flight on February 20, 1962, was the first American flight to achieve this goal.[1]

The program included 20 unmanned launches, followed by two suborbital and four orbital flights with astronaut pilots. Early planning and research were carried out by the National Advisory Committee for Aeronautics (NACA),[2] but the program was officially conducted by its successor organization, NASA. Mercury laid the groundwork for Project Gemini and the follow-on Apollo moon-landing program.

The project name came from Mercury, a Roman mythological god often seen as a symbol of speed. Mercury is also the name of the innermost planet of the Solar System, which moves faster than any other and hence provides an image of speed, although Project Mercury had no real connection to the planet.

Goals and guidelines
The goals of the program were to orbit a manned spacecraft around Earth, investigate the pilot's ability to function in space and to recover both pilot and spacecraft safely.[3]

NASA also established program guidelines: existing technology and off-the-shelf equipment should be used wherever practical, the simplest and most reliable approach to system design would be followed, an existing launch vehicle would be employed to place the spacecraft into orbit, and a progressive and logical test program would be used.

Project requirements for the spacecraft were that it must be fitted with a reliable launch escape system to separate the spacecraft and its astronaut from its launch vehicle in case of impending failure; the pilot must have been given the capability of manually controlling the attitude of the spacecraft; the spacecraft must carry a retro-rocket system capable of reliably providing the necessary impulse to bring the spacecraft out of orbit; a zero-lift body utilizing drag braking to be used for reentry; and that the spacecraft design must satisfy the requirements for a landing on water.[4]

Contractors
On October 7, 1958, T. Keith Glennan, the first administrator of NASA, approved the Mercury project.[5] [6] On December 17 Glennan announced Project Mercury publicly.[7]

On December 29, 1958 North American Aviation was awarded a contract to design and build Little Joe launch vehicles to be used for altitude flight testing of the Mercury launch escape system.[8] In January 1959 McDonnell Aircraft Corporation was chosen to be prime contractor for the Mercury spacecraft, and the contract for 12 spacecraft was awarded in February. In April seven astronauts, known as the Mercury Seven or more formally as Astronaut Group 1, were selected to participate in the Mercury program.

In May 1959 North American Aviation delivered the first two Little Joes, and in June, an Atlas D launch vehicle named [|Big Joe] was delivered, for use in a suborbital heat shield test flight. In July, the planned use of the Jupiter rocket as a suborbital launch vehicle was changed to the Redstone.[9] In October General Electric delivered to McDonnell the ablative heat shield designated for installation on the first Mercury spacecraft. In December the launch vehicle for Mercury-Redstone 1 was ready to begin static tests installed on a test stand at ABMA.

In January 1960 NASA awarded Western Electric Company a contract for the Mercury tracking network. The value of the contract was over $33 million.[10] Also in January, McDonnell delivered the first production-type Mercury spacecraft, less than a year after award of the formal contract. On February 12, Christopher C. Kraft, Jr. was appointed to head the Mercury operations coordination group.[11] In April, the first spacecraft was delivered to Wallops Island for the beach-abort test. The test was completed successfully on May 9.[12]

Interior and control
Because of their small size, it was said that the Mercury spacecraft were worn, not ridden. With 1.7 m³ of habitable volume, the spacecraft was just large enough for the single crew member. Inside were 120 controls: 55 electrical switches, 30 fuses and 35 mechanical levers.[13] The spacecraft was designed by Max Faget and NASA's Space Task Group.[14] [15] :26–28

Despite the astronauts' test pilot experience NASA at first envisioned them as "minor participants" during their flights, causing many conflicts between the astronauts and engineers during the spacecraft's design. Nonetheless, contrary to other reports, the project's leaders always intended for pilots to be able to control their spacecraft, as they valued humans' ability to contribute to missions' success.<sup class="reference" id="cite_ref-exun7_14-1">[15] <sup class="reference" style="white-space:nowrap;">:23–25 John Glenn's manual attitude adjustments during the first orbital flight were an example of the value of such control.<sup class="reference" id="cite_ref-exun7_14-2">[15] <sup class="reference" style="white-space:nowrap;">:33 The astronauts requested—and received—a larger window and manual reentry controls.<sup class="reference" id="cite_ref-exun7_14-3">[15] <sup class="reference" style="white-space:nowrap;">:24–25

Mission profile
During the launch phase of the mission, the Mercury spacecraft and astronaut were protected from launch vehicle failures by the Launch Escape System. The LES consisted of a solid fuel, 52,000 lbf (231 kN) thrust rocket with three engine bells mounted on a tower above the spacecraft.<sup class="reference" id="cite_ref-exun7_14-4">[15] <sup class="reference" style="white-space:nowrap;">:28 In the event of a launch abort, the LES would fire for one second, pulling the spacecraft and astronaut away from the launch vehicle and a possible explosion. The spacecraft would then descend on its parachute recovery system. After booster engine cutoff (BECO), the LES was no longer needed and was separated from the spacecraft by a solid fuel, 800 lbf (3.6 kN) thrust jettison rocket that fired for 1.5 seconds.

After a successful liftoff, the spacecraft fired three small clustered solid-fuel, 400 lbf (1.8 kN) thrust rockets for 1 second to separate the spacecraft from the launch vehicle. These rockets were called the posigrade rockets<sup class="reference" id="cite_ref-exun7_14-5">[15] <sup class="reference" style="white-space:nowrap;">:28 (point D on illustration).

The spacecraft were only equipped with attitude control thrusters; after orbit insertion but before retrofire they could not change their orbit. There were three sets of high and low powered automatic control jets and separate manual jets, one for each axis ([|roll, pitch, and yaw]), and supplied from two separate fuel tanks, one automatic and one manual. The pilot could use any one of the three thruster systems and fuel them from either of the two fuel tanks to provide spacecraft attitude control. The Mercury spacecraft was designed to be completely controllable from the ground in the event that something impaired the pilot's ability to function. Heat shield and retropack. Small red posigrade rockets can be seen between retrograde rocketsThe spacecraft had three solid-fuel, 1000 lbf (4.5 kN) thrust retrorockets that fired for 10 seconds each<sup class="reference" id="cite_ref-exun7_14-6">[15] <sup class="reference" style="white-space:nowrap;">:28 (point F on illustration). One was sufficient to return the spacecraft to Earth if the other two failed. The firing sequence (known as ripple firing) required firing the first retro, followed by the second retro five seconds later (while the first was still firing). Five seconds after that, the third retro fired (while the second retro was still firing).

There was a small hinged metal flap at the nose of the spacecraft called the spoiler.[pic.] If the spacecraft started to reenter nose first (another stable reentry attitude for the spacecraft), airflow over the spoiler would flip the spacecraft around to the proper, heatshield-first reentry attitude, a technique called shuttlecocking. During reentry, the astronaut would experience about 8 g-forces on an orbital mission, and 11–12 gs on a suborbital mission.

Initial designs for the spacecraft suggested the use of either beryllium heat-sink heat shields or an ablative shield. Extensive testing settled the issue – ablative shields proved to be reliable (so much so that the initial shield thickness was safely reduced, allowing a lower total spacecraft weight), and were easier to produce — at that time, beryllium was only produced in sufficient quantities by a single company in the U.S. — and cheaper. The surface of the heat shield had a coating of aluminum with glassfiber in many layers. As the temperature rose to 2,000 °F (1,100 °C) the layers would evaporate and take the heat with it. The spacecraft would become hot but not harmfully so.<sup class="reference" id="cite_ref-HowMercuryWorked_17-0">[18] Freedom 7 recovered by helicopter. Notice landing bag beneath spacecraftAfter re-entry, a small, drogue parachute was deployed at 21,000 ft (6.4km) for first lowering of speed. The main parachute was deployed at 10,000 ft (3 km), further slowing the spacecraft in preparation for landing. Just before hitting the water, a landing bag inflated from behind the heat shield to reduce the force of impact. Upon landing, additional bags inflated around the nose of the craft to keep the capsule upright in the water, and the parachutes were released. Once the recovery helicopter hooked onto the spacecraft, the astronaut blew the escape hatch to exit the capsule. It was also possible to exit the capsule through the nose cone.<sup class="reference" id="cite_ref-HowMercuryWorked_17-1">[18]