Satgen362 Ao13 not same Jianbing By GM4IHJ 2 March 96 Following up the story of the imminent demise of Chinese sat Jianbing ( Satgens 360 and 361), several readers ask " Is Oscar 13 going the same way "?. The answer is not just yet, as the following table shows :- Oscar 13 Changing orbit parameters Date 93314 95049 95088 95287 95334 96035 96053 Perigee 805 676 642 493 446 395 380 kms Apogee 38001 38130 38163 38311 38358 38410 38424 kms Major 51561 51562 51561 51561 51560 51561 51560 kms axis Eccen .721396 .726373 .727676 .733465 .735286 .737265 .737841 ratio Period 686.6 686.6 686.6 686.6 686.6 686.6 686.59 mins Perigee .22 .87 .74 1.0 .77 .83 kms /day decrease Comparing with the Jianbing table in satgen361. Both apogee high point and perigee low point are decreasing fast with Jianbing. Because the perigee is getting deeper into the atmosphere where air drag reduces its ability to climb back to a high apogee. So Jians orbit is getting less eccentric and becoming circular. This a typical pattern due to atmospheric drag. Contrast this with the Ao13 table above. As its perigee decreases its apogee increases. Indeed the sum total of apogee height plus perigee height plus earth diameter = orbit major axis , is not changing at all. Meanwhile eccentricity is rising , getting less circular . So as yet there is no sign that atmospheric drag is having much effect on Ao13. The changes in Ao13s orbit are still being caused by the attraction from the Sun and perhaps the Moon. But watch out. Over the next few months if drag starts to affect Ao13 , you will begin to see the sum of apogee, perigee and earth diameter reducing , and you should see eccentricity begin to reduce just as it is with Jianbing. Thereafter if Ao13 takes up the pattern shown by Jianbing, it is doomed eventually ,to follow Jianbing into oblivion. You can use the BASIC program given in satgen 361 to work out all the parameters shown in these tables, by enteringt each new set of Ao13 Keplerian elements as they are published, thereby predicting for yourself, exactly what is happening. EMAIL TO GM4IHJ address after 2 Mar 96 :- gm4ihj@branegan.demon.co.uk The old address (gm4ihj@delphi.com) will close finally at end March 96