In recent years, several hobbyists have been tracking the Titan Launch Dispensers, which were the specialized upper stages used to deploy the second generation NOSS. Originally, they were intended for Shuttle launch, and so were named Shuttle Launch Dispenser: http://www.nrl.navy.mil/pao/pressRelease.php?Y=1997&R=7-97r Photos are available here: http://www.globalsecurity.org/space/systems/sbwass_n.htm There have been open source references to SLDCOM, an apparent contraction of the dispenser's original name and the description of the payload it hosts, which is believed to be experimental communications, so that is the name we use for them. GlobalSecurity.org's John Pike reported on SLDCOM's communications payload in 2000: http://www.globalsecurity.org/space/systems/sldcom.htm The approximate orbit of the SLDCOMs emerged in the late 1990s: 63.4 deg, 1200 x 11600 km, 270 deg argument of perigee, as I mentioned here, in this Sep 2000 post: http://www.satobs.org/seesat/Sep-2000/0242.html At the time, I had a fairly good idea of the probable SLDCOM orbital planes, based upon their launch dates, hobbyist tracking of 91076A and 96029A while still in LEO, and information filed by the U.S. with the U.N.; however, several more years passed before they could be tracked. By 2002, Greg Roberts had improved the sensitivity of his video tracking system, enabling him to track the objects from his excellent vantage point (near perigee) in South Africa. Greg is a major contributor of observations, as are David Brierley and Peter Wakelin. Peter mainly uses his CCD camera for these faint objects, which has been another key enabling technology. A few hobbyists make telescopic observations, including Mike McCants, who also has generated almost all of the 2-line elements from the team's observations. The objects were first tracked as unknowns, but could readily be identified by referring to the aforementioned estimated orbital planes. 91076A's use of a 5.5 rev/d orbit instead of a 6 rev/d orbit was a surprise. It was identified by a process of elimination, since 90050A and 96029A were accounted for. A further surprise came in the spring of 2003, when 96029A went missing after several weeks out of sight of observers. We guessed that it had manoeuvred to an orbit similar to that of 91076A. I believed there might be some advantage to tracking and studying the objects quietly - at least until 96029A could be tracked again - so at my request, we delayed making the elements and observations public. Tracking of 96029A resumed in 2006, which was found to have manoeuvred to the 5.5 rev/d orbit, as we had suspected. Also in 2006, a piece of debris turned up, which Mike McCants identified as having originated from 91076A. It is fairly strongly perturbed by SRP, revealing a high area to mass ratio. Also, it is intrinsically bright, so perhaps it is a piece of thermal blanket. We eventually added both pieces to the list of unknowns, as 90064 and 90065, respectively; however, from here on 96029A will be referred to by its real ID. The latest orbits of all four SLDCOM objects being tracked are as follows: SLDCOM 1 0.0 0.0 0.0 5.1 v 1 20641U 90050A 07030.66518297 .00000000 00000-0 00000-0 0 04 2 20641 63.4203 113.1674 4028367 268.3743 91.6257 6.02570819 07 SLDCOM 2 0.0 0.0 0.0 5.3 v 1 21775U 91076A 07048.63525490 .00000000 00000-0 00000-0 0 01 2 21775 63.3559 235.6202 3325559 266.6278 93.3722 5.53394918 07 SLDCOM 2 deb 0.0 0.0 0.0 4.1 v 1 90065U 06629B 07056.67525164 -.00000076 00000-0 -67469-1 0 08 2 90065 63.3134 225.2698 3277609 271.3766 88.6234 5.53955279 03 SLDCOM 3 0.0 0.0 0.0 5.6 v 1 23893U 96029A 07023.74104674 .00000000 00000-0 00000-0 0 09 2 23893 63.4683 7.8791 3315345 264.7452 95.2548 5.52844075 06 To-date, no debris from 91076A has been officially catalogued, so we will continue with the 90065 / 06629B designation for the piece that we are tracking. 90050A's ground track repeats daily, after 6 revs. 91076A and 96029A originally were in similar orbits, but subsequently manoeuvred so that their ground tracks repeat every 2 days, after 11 orbits. Ted Molczan ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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