A few days ago, I attributed the recent decline in this object's rate of decay to the increase in its perigee height, as its argument of perigee moves toward 270 deg. However, I forgot to check on a potentially more significant factor: whether perigee was in eclipse or in sunlight. Since USA 129's orbit is moderately eccentric, most of its decay occurs as it passes through a small portion of its orbit nearest perigee, about 280 km altitude. At altitude's well above about 200 km, atmospheric density is much lower at night than in daylight. As it turns out, USA 129's perigee precessed into eclipse about 2005 July 24, and by Aug 9 a wide area surrounding perigee was fully eclipsed, by which time a steep decline in the rate of decay was evident. USA 129's perigee will exit eclipse about Sep 1, and by Sep 15 the entire region near perigee, where most of the decay occurs, will be sunlit. By that time, the rate of decay is likely to be two to three times the recent values, depending upon solar activity. USA 129 15.0 3.0 0.0 5.3 v 1 24680U 96072A 05232.90910473 .00006238 00000-0 82127-4 0 05 2 24680 97.9612 295.4226 0524801 310.8678 44.8154 14.73856458 06 Arc 2005 Aug 15.89 - 20.92, WRMS residuals = 0.017 deg Brief Introduction To TLEs And Satellite IDs: http://www.satobs.org/element.html Ted Molczan ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Sun Aug 21 2005 - 14:29:56 EDT