Robert Clark asked: > My reading of the discussion on the "Misty" type satellites > suggests they are difficult to track visually. > So how are these orbital elements so accurately determined > to the degree that the amount of orbital decay they are > experiencing can be determined? The object in question is readily tracked because is not a Misty satellite. It is either debris or a decoy resulting from the launch of what is now believed to be Misty 2 (1999-028A / 25744), which was launched in May 1999. In June 1999, hobbyists began tracking an object from that launch that was fairly intrinsically bright, in a 63.4 deg, 2700 km x 3100 km orbit, which seemed like it might be the payload. Initial speculation was that it was an IMINT satellite of KH-11 lineage, sent into a higher than usual orbit, to obtain increased dwell-time and wider area coverage of targets, at reduced resolution - a need that had been identified as a result of experience during Operation Desert Storm. This theory began to fall apart in 2002, with the discovery of the object's high area-to-mass ratio, which makes it more likely to be debris than a payload, as I reported in the following post, which I believe you have read: http://satobs.org/seesat/Aug-2002/0045.html In the above post, I also discussed the object's other debris-like characteristic: it rotates, unlike most payloads, which are 3-axis stabilized. Initially, its period of brightness variation was about 150 s, which had decreased to 116 s after three years. By the summer of 2005, it had decreased below 80 s; since then it appears to have been increasing: http://satobs.org/seesat_ref/99028C_period_of_var/99028C_period_of_var_3.jpg If the object were a spin-stabilized payload, then I would expect its rate of rotation to remain much more nearly constant. In late 2005, we changed our designation of the high object from 1999-028A / 25744 to 1999-028C / 25746, in recognition that it could not be the primary payload, and most likely is debris, or a decoy, intended to draw attention away from Misty 2, which most likely would have gone to a quasi 65 deg, 700 - 800 km orbit, like that of its predecessor. We should have made the switch sooner, but finally acted when it became clear that using the original ID was creating confusion among those not familiar with the evolution of our understanding of this object. Based on its observed brightness, 99028C probably has a cross-sectional area of about 50 m^2. Assuming it presents an equivalent area to the sun, then its mass is about 560 kg, based on its area-to-mass ratio of about 0.09 m^2/kg, derived from analysis of solar radiation pressure perturbations. For the object to be a primary Titan IV-B class payload, it would have to be very massive, and have a large surface area facing the sun, to account for its area-to-mass ratio. I estimate that a manoeuvrable Titan IV-B payload in excess of 10,000 kg (dry mass) could reach the 63.4 deg, 2700 km x 3100 km orbit of 99028C, which would require a sun-facing surface area of about 900 m^2. I cannot imagine an NRO spacecraft so-configured. The JWST (James Webb Space Telescope), has a mass of 6200 kg, and a sunshield of 220 m^2, resulting in a sun-facing A/m of 0.035 m^2/kg, well short of 99028C's value. Of course, unlike NRO telescopes, JWST is designed for ultra-high IR sensitivity, requiring it to have the large sunshield. Also, JWST is 3-axis stabilized. Ted Molczan ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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