Gemini Program - astronomy.

Gemini Program - astronomy. I INTRODUCTION Gemini Program, series of American piloted spacecraft launched to develop the techniques necessary to send humans to the moon. Gemini's specific objectives were to rendezvous and dock with a second orbiting vehicle; learn how to keep astronauts and equipment in space for up to two weeks; develop and test controlled reentry into the earth's atmosphere and precision landing in the Atlantic or Pacific Ocean; and enable astronauts to leave the spacecraft while in space. Conducted between April 1964 and November 1966, the Gemini program successfully prepared the National Aeronautics and Space Administration (NASA) to send an astronaut to the moon in the Apollo program. Gemini included 12 missions: 2 unpiloted (1 and 2) and 10 piloted (3 through 12); all were launched from Cape Canaveral, Florida. II SPACECRAFT AND SUPPORTING SYSTEMS The Gemini spacecraft consisted of two modules: The reentry module and the adaptor module. The reentry module contained the pressurized cabin section with two astronaut seats. A heat shield, which protected the craft from the intense heat caused by reentering the earth's atmosphere, was attached to this module. The reentry module was equipped with the controls used to rendezvous with target vehicles in space, along with the rockets needed to send the spacecraft out of orbit and toward the earth and the parachute used to slow the spacecraft's descent through the atmosphere. The reentry module was 3.4 m (11 ft) long and 2.3 m (7.5 ft) in diameter at its base. The adaptor module contained equipment for orbital operations and the 20 rockets needed to maneuver the spacecraft in space and send the capsule out of orbit. The adaptor module was 2.3 m (7.5 ft) long and 3.1 m (10 ft) in diameter at its widest point. The total weight of the two modules at launch was about 3000 kg (about 7000 lb). Unlike spacecraft in the earlier Mercury program, which used automatic programming to control each phase of the mission, Gemini spacecraft were controlled by the pilot. Gemini spacecraft were launched using a military Titan II intercontinental ballistic missile (ICBM) rocket with some minor modifications, including added backup systems for flight control and electrical systems. NASA engineers also added a Malfunction Detection System to the rocket to sense major problems during launch and to transmit appropriate information to the astronaut crew, who used it to decide whether to abort the launch. The Mission Control Center (MCC) based in Houston, Texas, was staffed with flight controllers and support personnel who specialized in every aspect of a Gemini mission, including spacecraft systems, flight operations, flight procedures, support systems such as communications and space suits, and science experiments. During the Gemini program, the worldwide spacecraft tracking and communications network, which MCC used to stay in periodic contact with the astronauts in orbit, was in its trial stages. In addition, MCC operations were developed and verified and these methods were later used essentially unchanged during the Apollo program. III GEMINI MISSION HIGHLIGHTS The basic flight profile for Gemini missions began with launch to a low orbit above the earth. Depending on the specific objectives of each mission, orbital operations included one or more of the following phases: spacecraft systems evaluation, which consisted of making sure equipment performed properly; rendezvous, in which the astronauts maneuvered their spacecraft to meet another spacecraft while in orbit; docking, or locking two spacecraft together; combined vehicle maneuvers, in which two docked spacecraft maneuvered as one; extravehicular activity (EVA), when a crew member left the capsule and moved about in space; and space experiments, including earth science experiments and studies of the effects of weightlessness and other aspects of spaceflight on astronauts. After orbital operations were completed, the spacecraft reentered the earth's atmosphere to a parachute landing in the Atlantic or Pacific Ocean. The landing site of the spacecraft could be adjusted by using the aerodynamic lifting capability of the spacecraft. This steering capability was directed either by the astronauts in response to cockpit displays or automatically by the onboard computers. This technique permitted a precision touchdown within a 73,000 sq km (28,000 sq mi) area. The first Gemini mission was launched April 8, 1964, and the last mission was launched on November 11, 1966. During this 31-month period, 12 missions were launched, with the 10 piloted missions averaging a launch every 60 days. The Gemini program accomplished all of the goals NASA had set for it. During six piloted missions (6 and 8 through 12), ten rendezvous were completed with three different types of target vehicles and seven different rendezvous techniques. Nine dockings with the Agena target vehicle, a special stage of an Atlas rocket launched into orbit to act as a passive target for Gemini missions, were completed over four missions (8 and 10 through 12). Three missions (4, 5, and 7) set records in duration, lasting 4 days, 7 days, and 14 days, respectively. Controlled reentry into the earth's atmosphere followed by landing at a predetermined location was demonstrated on the final seven missions; the average miss distance from the target landing site was 6.3 km (3.9 mi)--on the last five missions, this distance was reduced to 3.8 km (2.3 mi). Four missions (8 and 10 through 12) demonstrated control of the docked Agena target vehicle by the Gemini spacecraft. These included nine major propulsive maneuvers by the Agena to make significant orbit changes of the docked combination. A total of nine extravehicular activity sessions were performed by five astronauts, the first by Edward White, II, during Gemini 4, on June 3, 1965. During four EVAs, the astronaut opened the spacecraft hatch but remained fastened to the seat. The five other EVAs were umbilical excursions into free space, in which the astronaut left the spacecraft but remained tethered to it by a cord that supplied oxygen from the spacecraft's supply. These umbilical EVAs lasted for an accumulated total of 6 hours and 1 minute outside the spacecraft. Gemini used several systems new to spaceflight operations. These included high-performance thrusters to maneuver in orbit and onboard radar for navigating relative to other spacecraft during rendezvous and docking procedures. The Gemini program also demonstrated that fuel cells could be brought into space and used while in orbit for electrical power. It showed that the onboard guidance system worked, as did the docking system, extravehicular space suits, and other equipment. During the ten piloted Gemini missions 52 supplemental space experiments were performed. As part of these experiments, the astronauts took an extensive array of photographs of the earth. These images provided the first real insight into the value of space photography for the fields of geology, oceanography, and weather. Gemini photos were the first images that indicated the fragility of the earth's resources and may be Gemini's most lasting legacy. Contributed By: David R. Scott Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.