Yesterday, I commented that there may be evidence of recent small orbit-raising manoeuvres by Lacrosse 4. Additional observations will resolve the question. I would not be surprised to find that Lacrosse 4 performs periodic altitude-maintenance manoeuvres over its entire life. Previous Lacrosses have not done so; however, Lacrosse 4 already differs from them in that its initial orbit is somewhat higher, and apparently more circular. The higher, more circular orbit appears to have been made possible by launching on the Titan IV-B, which has greater payload mass capability than the Titan IV-A used for previous Lacrosses. One obvious result, was the much higher parking orbit, 580 X 683 km, compared with 435 X 686 km for Lacrosses 2 and 3. All things being equal, this would have enabled Lacrosse 4 to use less propellant to achieve the present higher orbit, than previous Lacrosses used to reach their lower orbits. Assuming the same initial propellant load as previous Lacrosses, there would be a surplus available for orbit maintenance. Titan IV-B's greater capacity might well have been used in part to increase the mass of Lacrosse 4, some of which could be additional propellant for orbit maintenance. There is a precedent for maintaining highly circular, near constant altitude orbits, among four well-known civilian SAR (synthetic aperture radar satellites. ERS-1 (91050A / 21574) maintained a near-constant altitude until 2000 day 68. Most of its orbital history can be found here: http://hea-www.harvard.edu/QEDT/jcm/space/elements/disk4/21500/S21574 The element to look at is the mean-motion, which was always held near 14.3224 rev/d (revolutions per day): 1 21574U 91050A 99244.18650952 +.00000365 +00000-0 +15145-3 0 09698 2 21574 098.5527 317.3575 0001108 110.7193 249.4111 14.32243231425064 ERS-2 (95021A / 23560) behaves the same as ERS-1: http://hea-www.harvard.edu/QEDT/jcm/space/elements/disk4/23500/S23560 JERS 1 (92007A / 21867) maintained a near-constant altitude until about 1998 day 282: http://hea-www.harvard.edu/QEDT/jcm/space/elements/disk4/21800/S21867 Radarsat 1 (95059A / 23710) also maintains a near-constant altitude: http://hea-www.harvard.edu/QEDT/jcm/space/elements/disk4/23700/S23710 If Lacrosse 4 adopts this mode of operation, then prediction likely would be even easier than it is now, since the effects of drag would be all but eliminated. Of course, this is all speculative, but that is part of the fun of satellite sleuthing. Ted Molczan ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
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