The Space Shuttle is designed to carry large and heavy payloads into Earth orbit. But unlike earlier manned spacecraft, which were good for only one flight, the Shuttle orbiter and solid rocket boosters can be used again and again. Only the external tank is expended on each launch.
The payload bay is 60 feet (18.3 meters) long and 15 feet (4.6 meters) wide, about the size of a school bus. The bay is flexible enough to provide accommodations for unmanned spacecraft in a variety of shapes and sizes, and for fully equipped scientific laboratories such as the Spacelab. Depending on the requirements of the particular mission, a Space Shuttle can carry about 50,000 pounds (22,680 kilograms) into orbit.
The Shuttle also provides a new capability, to repair malfunctioning satellites in orbit, or return them to Earth for a more extensive overhaul and another launch. Solar Maximum Mission, a complex scientific spacecraft, was repaired in orbit at a small percentage of the cost of building and launching a new satellite. The Westar VI and Palapa B-2 communications satellites, stranded in low orbit by failures in their attached booster rockets, were recovered, returned to ground, refurbished, and later success fully re-launched on commercial unmanned vehicles. The Long Duration Exposure Facility (LDEF) remained in orbit almost six years before it was recovered and returned to Earth, where it yielded a wealth of new data on the space environment. The maiden flight of the Space Shuttle Endeavour in May 1992 successfully retrieved and repaired Intelsat-VI. One of the most spectacular shuttle flights to day, the Space Shuttle Endeavour rendezvoused with the Hubble Space Telescope in December 1993 to repair its faulty vision.
Satellites today play a major role in the fields of environmental protection, energy, weather forecasting, navigation, fishing, farming, mapping, oceanography, and many other space-borne applications. Satellites also provide world-wide communications, linking the peoples and nations of the world together. A single channel, one out of 24 on many communications satellites, can provide television coverage to most entire nations. Satellites have become an indispensable part of the modern world.
All satellites released from a Space Shuttle enter low Earth orbit. Some, such as the Hubble Space Telescope, for astronomical observations, or the Upper Atmosphere Research Satellite, for monitoring the environment, remain there throughout their working lives.
Many spacecraft, such as the weather and communications satellites that can "see" a third of the world at once, operate at a much higher level, from geosynchronous orbit. This is a flight path about 22,300 miles (35,888 kilometers) above and aligned with the equator, with a speed in orbit that matches that of the Earth's surface below. From the ground such satellites appear to hang motionless in the sky. Spacecraft reach this altitude by firing an attached propulsion unit, such as an Inertial Upper Stage (IUS), or the smaller Payload Assist Module (PAM), after deployment from the Shuttle orbiter. At altitude an on-board engine fires to "circularize" the orbit.
Interplanetary explorers launch from Space Shuttles, such as the Magellan mission to Venus, or the Galileo spacecraft to Jupiter, also use the IUS . They leave low Earth orbit on trajectories that will take them to Earth's planetary neighbors.
The Remote Manipulator System (RMS), the shuttle "arm", is a 15.2 meter (50 foot) long articulating arm that is remotely controlled from the flight deck of the orbiter. The elbow and wrist movements of the RMS permit payloads to be grappled for deployment out of the payload bay attach points or to be retrieved and secured for return to Earth. Because the RMS can be operated from the shirt-sleve environment of the cabin, an Extra Vehicular Activity, EVA, "spacewalk", maneuver is not required.
Following the successful landing of the Space Shuttle Columbia on May 6, 1993, STS-55, the Space Shuttle fleet accumulated just over one full year of flight time in space. The following payload statistics have emerged (NASA RELEASE: 93-79):
Representing only five percent of all U.S. space launches (55), Space Shuttles have carried 56 percent of all U.S. payloads to orbit (670) and 44 percent of all U.S. cargo weight to orbit (1.64 million lbs, 822 tons). The cargo weight deployed totals 756,000 lbs (378 tons).After 15 years of scientific research, technology development and satellite retrieval, deployment and maintenence, NASA has marked the shuttle program milestone with a Fact Sheet entitled, "Operating the World's Most Versatile Launch System".Fifty-one satellites have been deployed, 5 of which were recovered and returned on the same flight. Three of the 51 satellites were interplanetary probes to Venus (Magellan), Jupiter (Galileo) and the Sun (Ulysses). Three were orbiting observatories - the Hubble Space Telescope, the Gamma Ray Observatory and the Upper Atmosphere Research Satellite.
Others were communications satellites and experiment platforms such as the Long Duration Exposure facility which orbited Earth for nearly six years before being retrieved and returned to Earth. Two communications satellites, the PALAPA-B2 and WESTAR-VI, were retrieved, returned to Earth for refurbishment and relaunch.
Scientific studies aboard the Space Shuttle and in Spacelab modules carried aboard Shuttles have investigated life sciences, materials sciences, combustion science, solar science and physics, space plasma physics, atmospheric studies, biotechnology, Earth observations, astronomy and the study of the behaviors of metals, semiconductors, bio-processing and fluids in the microgravity environment of space flight. time accumulated in Spacelab science operations, alone, stands at 96 days and 13 hours, on 12 Spacelab missions.
Miscellaneous statistics include: 16 Shuttle Rendezvous Operations; 20 Shuttle Spacewalks (16 planned and 4 unplanned; 6 free-flyers); 223 hours total Shuttle EVA time; 22 Space-walking Shuttle Astronauts (46 percent of total U.S. spacewalkers); 19 Women flown in Space on Shuttle; 11 American Minority Astronauts flown; and 2 Members of Congress flown.
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