Sue Wheatley asked: > Tonight I saw two objects about 2 degrees apart, traveling in > the same line. The trailing object flared for about 8 seconds > to a -4 or brighter, and then dimmed to match the magnitude > of the first (about 3rd mag). Did I see USA 160? The visual appearance you observed is consistent with other recent reports that have been posted here, so my guess is that you did see USA 160 and its companion. If you can provide the date, time and a rough position or track, I could be more certain. > And if so, was the first member of the duo a satellite or debris? Two payloads appeared shortly after launch on 2001 Sep 08, and have been tracked ever since. We know they are payloads because both have manoeuvred. Thus far, only three pieces have been officially catalogued, only one of which is a payload: 2001-040A 26905 USA 160 2001-040B 26906 ATLAS 2AS CENTAUR R/B 2001-040C 26907 USA 160 DEB Hobbyists are routinely tracking the Centaur plus two payloads. We have not detected any other objects in or near the orbital plane. Until the situation becomes clearer, we have assigned one of the payloads to the 26907 catalogue number, which officially is debris. Every one of the first and second generation NOSS triad members shed a small piece of debris at the time of deployment that is too faint to be tracked with binoculars. So it is quite possible that 26907 actually is debris. If not, then perhaps the catalogue entry is erroneous and it really is one of the two payloads. The two payloads appear to be about as bright as the second generation NOSS, and they behave similarly in that most of the time they are around magnitude 5 or 6 at best, but occasionally brighten to magnitude 3 or 4. The recent flaring is less common, but has been observed, as I pointed out in an earlier message. The big mystery is the absence of a third payload to complete the standard NOSS triad. Second generation NOSS deployments typically took about 28 days. The triad members were carried on a manoeuvrable payload dispenser, which placed them in the exact orbits required to form the familiar "flying triangle". The 01040A launch almost certainly did not involve the use of a payload carrier. The payloads seem to have been deployed separately from the Centaur. Alternatively, they could have been joined together at separation from the Centaur, and subsequently separated from one another. For the first couple of months or so, both payloads remained in about the same plane, but made numerous small manoeuvres, such that at times they drifted apart and at other times they station-kept at a variety of distances, often much farther apart than standard NOSS. Eventually, they manoeuvred to the present close separation, and adjusted their inclination slightly, such that their ascending nodes no longer precessed at the identical rate, thus causing them to drift apart. Once they reached the present separation, about 0.24 deg, one or both manoeuvred to equalize their precession rates. The present planar and along-track separation is close to that of an operational NOSS triad, but without the third member. It has been my guess that the third member is attached to one of the two payloads, awaiting deployment at some time. I am increasingly doubtful of that possibility, because it seems that the opportune time to deploy the third member arose weeks ago, when their planar separation was stabilized. Perhaps there are other conditions that must be met for the third payload to be deployed. Or, it may be that only two payloads were launched. That seems unlikely, because the relative position of the two payloads looks like too much like a normal triad with one member missing. Another possibility, which I am increasingly leaning toward, is that three payloads were launched, but that one failed to separate and is a write-off. That could explain the couple of months of frequent manoeuvring - perhaps engineers were evaluating novel operating modes in an effort to salvage as much of the designed operational capability as possible. These objects are widely believed to track the positions of ships at sea by triangulating on their radio transmissions. (This is a surveillance mission, not a navigation mission.) My guess is that the novel operating modes did not sufficiently improve the quality of the data, so the operators decided to proceed to manoeuvre the objects to something like the standard relative positions. One reason for doing so might be that they have accumulated considerable experience over the years in working around the failure of a single triad member, which provides the most confident basis for making the best of the present situation. Another Atlas 2AS launch is scheduled for launch from VAFB in 2002 November, which I suspect carries the same payloads as the 01040A Atlas 2AS. That should settle the present mystery. If we see a repeat performance, then most likely it was always intended to change from a NOSS triad to a doublet. If a triad is launched, then that will almost certainly confirm that one of the 01040A's payloads failed to separate. Ted Molczan ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www.satellite.eu.org/seesat/seesatindex.html
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