Mercury Program - astronomy.

Mercury Program - astronomy. I INTRODUCTION Mercury Program, first United States manned space program, conducted from 1961 to 1963. Named for the fleet-footed messenger of Roman mythology, the Mercury program was intended to put a manned spacecraft into Earth's orbit and to investigate a human being's ability to survive and work effectively in the harsh environment of space. During the program's two-year span, six astronauts were launched into space and safely returned to Earth. The program employed more than 2 million people from government agencies and the aerospace industry. The Mercury program marked the entry of the United States into the "space race" with the former Soviet Union to send a person to the Moon. The Soviets had already moved ahead in the race by sending a dog named Laika into orbit aboard Sputnik 2 in 1957 and had launched the first manned spacecraft in 1961. II SPACECRAFT The first Mercury spacecraft was a single-passenger, cone-shaped capsule, 2.0 m (6.6 ft) long and 1.9 m (6.2 ft) in diameter, with a 90-cm-long (35-in-long) cylinder mounted on top. The spacecraft weighed 1.9 metric tons at launch. Fastened to the cylinder was a 5.8-m-long (19.2-ft-long) escape tower designed to separate the spacecraft and its astronaut from the rocket in case of launch failure. To return the Mercury capsule to Earth, a retro-rocket system was attached that produced the reverse thrust necessary to slow the craft enough to take it out of orbit. The blunt end of the capsule was covered with a heat shield to protect the craft from the extreme heat experienced during its rapid reentry into Earth's atmosphere. The opposite end of the capsule housed the drogue and main parachutes, used to stabilize and slow the craft after it had entered the atmosphere. The capsule was designed to land in the ocean and remain afloat until it could be recovered by an aircraft carrier or destroyer. During the course of the Mercury program, two different launch vehicles were used, each originally designed for military purposes. The United States Army's Redstone rocket was used to launch the first two Mercury spacecraft into suborbital flight. This rocket was developed by a group of engineers under the direction of the German American scientist Wernher von Braun. The Redstone's Rocketdyne A-6 engine consumed immense quantities of an alcohol-water mixture and liquid oxygen to produce a thrust of 35,100 kg (78,000 lb)--sufficient to lift the Mercury capsule and its astronauts above Earth's atmosphere for a short time. In order to boost the spacecraft into orbit, however, a more powerful rocket was needed. Mercury scientists used the United States Air Force's Atlas rocket, which was originally designed to be an intercontinental ballistic missile (see Guided Missiles). This rocket used 115,200 kg (256,000 lb) of liquid oxygen and kerosene to produce a thrust of 162,000 kg (360,000 lb). The Atlas was a one-and-a-half stage booster that used three Rocketdyne engines: Two engines dropped away during the spacecraft's ascent; the central engine lifted the craft the rest of the way into orbit. Most of the equipment inside the Mercury spacecraft was built using existing technology, although some new systems were designed in order to increase reliability and safety. Mercury scientists developed a new automated system to measure the astronaut's blood pressure. Other new instruments were used to sense the amount of oxygen in the spacecraft and the amount of carbon dioxide in the astronaut's pressure suit. Early astronauts were carefully monitored to assess their reactions to the foreign conditions in space. Engineers tested the astronauts' ability to control the spacecraft manually, especially the retro-rockets used to return the craft to Earth. In later missions, astronauts were tested on their ability to perform a variety of orbital maneuvers. III MISSIONS On May 5, 1961, 23 days after the Russian cosmonaut Yuri A. Gagarin became the first human being to be launched into space, Alan B. Shepard, Jr., a lieutenant commander in the U.S. Navy, became the first American astronaut to fly in space. A Redstone rocket launched the Freedom 7 capsule containing Shepard to a height of 187 km (116 mi) above Earth's surface. The mission ended with a splashdown in the Atlantic Ocean 15 minutes 22 seconds later. Virgil I. Grissom, a U.S. Air Force captain, was the second American to fly in space. His Liberty Bell 7 capsule was launched aboard a Redstone rocket on July 21, 1961. The flight lasted only 15 seconds longer than Shepard's mission. Although his capsule malfunctioned after splashdown and sank in the Atlantic Ocean, Grissom managed to escape. The capsule was recovered from the ocean floor in 1999. On February 20, 1962, six months after Soviet Major Gherman S. Titov became the second human being to orbit Earth, John H. Glenn, Jr., a lieutenant colonel in the U.S. Marine Corps, circled the planet in the Friendship 7. The capsule was launched by an Atlas rocket and orbited Earth three times. It splashed down in the Atlantic Ocean after 4 hours 55 minutes. On May 24, 1962, U.S. Navy test pilot Malcolm Scott Carpenter orbited Earth in a flight lasting 4 hours 56 minutes. His Aurora 7 capsule splashed down about 320 km (about 200 mi) off course and began taking on water. Carpenter was rescued from an inflatable life raft about two hours later. Lieutenant Commander Walter M. Schirra, Jr., of the U.S. Navy was launched aboard the Sigma 7 spacecraft on October 3, 1962. Schirra orbited Earth six times and splashed down after 9 hours 13 minutes. Test pilot L. Gordon Cooper, Jr., of the U.S. Air Force was the sixth and last person to fly under the Mercury program. His Faith 7 capsule, launched on May 15, 1963, circled Earth 22 times. His flight lasted 34 hours 19 minutes and enabled scientists to evaluate the effects on the human body of spending more than one day in space. Cooper landed his capsule manually after an electrical failure disabled his reentry equipment. Cooper's flight marked the end of the Mercury program. The program set the stage for the more ambitious Gemini program, which developed the skills and technology that would ultimately land human beings on the Moon. Contributed By: Dennis L. Mammana Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.