ane, to become inclined to it. The inclination grows at about 0.86° per annum if not corrected, causing daily excursions of 51.3.3 Orbital perturbations and their correction the satellite north and south of its nominal position. The pressure of solar radiation and solar wind on a geostationary In time, natural forces change the orbits into which satellites are satellite cause the orbit, initially circular, to become somewhat initially put. These perturbations are most significant and most elliptical. The effect is seasonal, a build up of ellipticity at one time thoroughly characterised for geostationary satellites. of year being neutralised by a change in the contrary sense at Non-uniformity of the gravitational field of the Earth causes the another time of year. Ellipticity causes the satellite to seem to period of a geostationary satellite, initially exactly equal to one oscillate daily east and west of its nominal position. The effect sidereal day, to increase or decrease so as to accelerate the satellite increases with the area of cross-section of the satellite and it is big towards either of two stable points, at 77° east longitude or 108° enough to be significant if the satellite is large. Spacecraft technology 51/7 Injection into final orbit Boost phase Injection into transfer orbit Final geostationary Transfer orbit satellite orbit Figure 51.2 Flight profile to the goestationary satellite orbit Significant movement of a satellite, east or west of its nominal thrusters as were used for the final adjustment of the orbit during the position, is likely to cause interference to or from another network launch procedure; the amount of fuel required for this is relatively operating in the same frequency band and using a neighbouring small. The ITU Radio Regulations require geostationary satellites satellite. Drifts due to the Earth's gravitational field can be corrected using frequency bands allocated to the fixed satellite service to be throughout the life of a satellite by means of the same Hydrazine maintained