Launching Satellites Into Orbit

Placing a satellite into geosynchronous orbit requires an enormous amount of energy. The launch process can be divided into two phases: the launch phase and the orbit injection phase.

The Launch Phase
During the launch phase, the launch vehicle places the satellite into the transfer orbit--an eliptical orbit that has at its farthest point from earth (apogee) the geosynchronous elevation of 22,238 miles and at its nearest point (perigee) an elevation of usually not less than 100 miles as shown below in Figure 7.

The Orbit Injection Phase
The energy required to move the satellite from the elliptical transfer orbit into the geosynchronous orbit is supplied by the satelliteís apogee kick motor (AKM). This is known as the orbit injection phase.

Figure 7: The Elliptical Transfer Orbit

Launch Vehicles
There are two types of launch vehicles: expendable rockets, which are destroyed while completing their mission, and the Space Shuttle, which is reusable.

Expendable rockets for communication satellites have three stages. The first stage contains several hundred thousand pounds of a kerosene/liquid oxygen mixture, plus a number of solid fuel rocket boosters that produce a tremendous display of flame--and ear splitting noise--as the rocket lifts off the pad. It raises the satellite to an elevation of about 50 miles. The second stage raises the satellite to 100 miles, and the third stage places it into the transfer orbit. After the satellite is placed in its transfer orbit, the rocketís mission is complete, and its remnants fall to earth. The satellite is placed in its final geosynchronous orbital slot by the AKM, which is fired on-command while the satellite is at the apogee of its elliptical transfer orbit. Figure 8 shows a picture of the Atlas IIAS expendable satellite launch vehicle.

Figure 8: The Atlas IIAS Expendable Satellite Launch Vehicle

The Space Shuttle shown in Figure 9 performs the functions of the first two stages of an expendable launch vehicle. The satellite--together with the third stage--are mounted in the cargo bay of the shuttle. When the shuttle reaches its orbital elevation of 150 to 200 miles, the satellite and third stage assembly are ejected from the cargo compartment as shown in Figure 10. Then the third stage is fired, placing the satellite into the elliptical transfer orbit. At the apogee of the transfer orbit, the satelliteís AKM moves the satellite into its designated geosynchronous orbital slot. After all of its cargo has been jettisoned, the shuttle returns to earth for refurbishing and reuse.

Figure 9: The Space Shuttle Reusable Launch Vehicle

Figure 10: The Space Shuttle Cargo Bay

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Copyright William Cook, 1996
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