Satellites may be launched in a number of ways. They can be sprung out of a pod or rolled from the bay rather like a frisbee. They can also be literally placed in orbit by the Shuttle's "crane", the robot arm of the remote manipulator system. The Hubble Space Telescope, for example, was launched in this manner in 1990. The robot arm, which is 15 m long, extends from inside the payload bay. It has flexible joints and a snare device at the "hand" end to grip the satellites.
The Shuttle usually goes into orbit at a height of about 250 km. This is much too low for many of the satellites it launches. Most communications satellites, for example, need to orbit at 35,900 km. So these satellites have a booster rocket attached, which fires to lift them to high orbit. Shuttle-launched probes destined to explore the planets likewise carry a powerful booster (called the Inertial Upper Stage) to accelerate them to escape velocity.
The
robot arm is also put to good use in retrieving satellites from orbit.
This technique was first used in 1984 to capture a satellite called Solar
Max, which had malfunctioned only a few months after launch four years
before. After the satellite had been captured, spacesuited astronauts repaired
it. It was then relaunched by the arm and operated successfully for six
years before falling from orbit.
Shuttle
astronauts also carry out a certain amount of experimental work in orbit.
However, most scientific work on the Shuttle takes place during missions
in which the scientific laboratory Spacelab is being carried.
George Nelson carrying out an experiment (left) into crystal growth
on Discovery during the STS-26 Shuttle mission in September 1988.
Also on mission 41-C, (above) the arm is used to place in orbit the Long Duration Exposure Facility (LDEF), carrying a host of experiments.
