lane of the equator unless it happens 1990k). These limits vary with frequency and with the angle of that the launching site is located on the equator. The booster will elevation at which the satellite signal reaches the ground. However, have been jettisoned before this parking orbit is attained and the a limit f-145dB relative to 1 watt per m² in a sampling bandwidth second stage rocket may be detached in the parking orbit. of 4kHz is typical for frequency bands below 15GHz. Correspond- In the second phase, as the satellite is passing through the equa- ing limits apply to the power of terrestrial transmitters operating in torial plane, another rocket, called the 'perigee motor', is fired to bands in which satellite receivers operate. accelerate the satellite out of the parking orbit and into the elliptical Finally there is the problem of interference between earth stations 'transfer' orbit. This orbit has a period of about 11 hours, and the operating with satellites and the transmitting and receiving stations same inclination to the equatorial plane as the parking orbit. The of terrestrial radio systems. As usual, national governments must perigee motor casing is then discarded. Close to its apogee and resolve problems arising between stations under their jurisdiction. about 35800km above the ground, this transfer orbit passes through However, if a new earth station could suffer unacceptable inter- the equatorial plane. ference from a foreign terrestrial transmitter or vice versa, the extent In the third phase, at a time when the satellite is close to its apogee of the problem must be determined and solutions found where and about to pass through the equatorial plane, the firing of the final necessary before frequency assignments made to the earth station stage rocket, called the 'apogee motor', accelerates the satellite to a may be registered internationally (ITU, 19901). velocity of about 3kp/s and removes the inclination of its orbit. This change of velocity and direction causes the orbit to become roughly ci