Satgen 542 Satellite Inclination 4 by GM4IHJ (BID SGEN542) 1999-08-14 Until recently most satellites kept well away from the Van Allen Radiation belts. Some stayed below 1200 kms altitudes , some loitered well above the belts at high altitude and high inclination before conducting a high speed dash through the belts and out again, while other stayed up above 30000 kms altitude well above the tops of the belts. But times change, and there are advantages to be had by going to intermediate height orbits, provided your orbit is circular and sticks to the less dense sections of the belts using an orbit with an inclination of 45 degs or even better 55 degs inclination. A situation in which your satellites electronics have to have expensive radiation protected microchips, but which does allow you to operate with a large earth viewing footprint, thereby reducing the number of satellites you need for simultaneous whole earth coverage. Such a system is proposed for ICO the third entrant in the satellite mobile phone market. While Iridium operates in a low altitude high inclination orbit which needs 66+ satellites, and Globalstar in a slightly higher altitude but lower inclination orbit needs 48 satellite for near whole earth coverage, the ICO Global Communications satellites will have 10 satellites , in two orbit planes , inclination 45 degs ,altitude 10335 kms. Where ICO will need some radiation protection and error detection/correction software, but which is worth it for the 55 degs plus, good earth viewing radius , with full earth coverage even at a modest 45 degs inclination orbit. Already up in higher altitude circular orbits are the satellites of the Global Positioning system . Their orbit of 54 degs inclination at 26,600 kms is chiefly necessary because you need to see several satellites simultaneously in order to get an accurate navigation fix. It could be asked why the ICO mobile phone satellites could not go higher, and get well clear of the radiation hazard. The problem for the ICO satellites is signal transit time , to and from the satellites down to the earth bound mobile units. At 26,000 kms up plus 26,000 kms down again the delay this would cause in telephone conversations would be quite marked. So ICO accepts the need for expensive microchips and stays lower albeit at an orbit inclination which does give some reduction in radiation dosage, as compared with a lower inclination equatorial orbit. Far above the earth orbiting at 36000 kms altitude in the Geosynchronous orbit , the true geostationary satellites have very low values of orbit inclination . Although they do get pulled north in the northern summer and south in the northern winter by Solar gravity, such that observed in a telescope or a long time exposure camera you can see some orbit inclination, which controllers correct from time to time. While the far less numerous geosynchronous satellites at the same altitude have deliberately introduced orbit inclination of up to 20 or 30 degs , so that they trace out a daily loop over targets in the northern and southern hemisphere . A feature which is favoured by the military intelligence community.