Satgen 578 The High Frontier by GM4IHJ (BID SGEN578) 2000-04-22 According to theory, most of our amateur radio satellites have one hundred or perhaps several hundred more years of orbiting the high frontier, before they succumb to atmospheric drag and the uncertainties of solar and lunar perturbation. But with the fate of Oscar 13 firmly etched on the tablet of amsat history, it is perhaps worth while taking an occasional look to see if all is well. Our "lowest " bird Uo11 at 655 kms altitude seems to be safe for quite a while yet. Having dropped only 20 kms in the last decade. So it is unlikely to fall foul of atmospheric drag in this relatively modest solar cycle peak. But watch out for it in the next one. The Pacsats AO16 to AO17 , have only lost about 5kms of altitude since their launch ten years ago. So while their electronics are gradually fading, they are certainly going to stay up for perhaps at least two more solar cycles. While even higher the RS birds at 1000 kms are safe for a few hundred years. All rather dull really .The satellites up even higher are in orbits which are not circular . FO20 looks like staying up for a thousand years or more. Indeed a ten year check of its apogee and perigee figures reveals less than 3 Kms of shift in a decade. Oscar ten however is always going to be different . Data from a couple of months after launch in 1983 , up to the present date, shows an interesting cycling of altitude and eccentricity. The figures are :- Year Eccentricity Apogee above earth Perigee above earth 1983 0.6038494 35487 kms 3963 kms 1990 0.5961522 35283 4163 1992 0.6071848 35570 3875 2000 0.6023670 35446 4001 So, far from coming down . AO10 appears to be cycling perigee up perigee down versus, apogee down apogee up. Thereby maintaining a very consistent length of orbit major axis = apogee + perigee + earth diameter. Dropping apogee in years up to sunspot cycle maximum then raising it after sunspot maximum. It will be interesting to see how long this oscillation continues . Not that many of us will see it, noting that Oscar ten is surely up there for many thousands of years unless aflicted eventually by the sort of perturbation which eventually sent its younger brother Oscar 13 to a fiery end. The uncertainty appertaining to Oscar 10 extends to all satellites which venture out as far as the magic 36,000kms circuit of the geostationary satellites. Unlike them Ao10 is not in a circular orbit , but it still experiences the varying gravitational pull of the Sun and the Moon as they move up and down with respect to the earths equator. Indeed, Geostationary is a relative term only. No satellite stays geostationary for very long. All the geostationaries carry large fuel tanks which on ground command, feed fuel to thrusters which push them back into a geostationary position every time they stray. Oscar 10, out of control and fuelless strays where it will . Hopefully safely, for a while yet.