At 10:09 9/06/06, Tom Wagner wrote: >About satellite orbit eccentricity. What's the advantage of a satellite having a permanent highly eccentric earth orbiting orbit? > >What general kind of satellites have them? I see that some Delta satellites do. The DELTA-4 R/B, although, not a working satellite, has an eccentricity in the TLE that's listed as being about 0.7! Tom, there are a large number of scientific satellites in eccentric orbits. They are divided into two main sorts. Firstly astronomical observatories in the X-ray region and satellites investigating the magnetosphere. The first class are in sufficiently high orbits near apogee that they are outside the radiation belts, so they can work for long periods without electronic glitches and radiation tracks on their imagin detectors. Examples are Chandra ,XMM-Newton and Integral X-ray/gamma ray observatories. Examples of the second type are the 4-member cluster satellites of ESA, the Tc-1 and 2 satellites of PRC, and a hosts of earlier launches. In this case the varying radius gives over time samples of the magnetosphere from top to bottom, from the region facing the sun to the distant tail end of the magnetosphere. In addition to these spacecraft there is a lot of junk in eccentric orbits. Most but not all launches leave the upper stage of geostationary comsats in the transfer orbit. This quite common orbit reaches from rather low circular orbit to an apogee at the geostationary height. The payload has to use ita own means to circularize the orbit, and zero the inclination. The GPS launches also result in the third stage being left in a transfer orbit with an apogee at 20,000km. Incidentally the USA has used the Molniya orbit for comsats and signal intelligence satellites. Greg Roberts reports on quite a few on this list. Tony Beresford ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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