I've checked Marco's picture and data from the Lacrosse 5 disappearance on 26-JUL-06 he observed and did some simple calculations. At the time of disappearance, the sun's elevation as viewed from Lacrosse 5 was 7.5 degrees meaning that the satellite was illuminated from well below. This seems to rule out shadowing by the solar panels. The sun's direction was almost directly to the left of the spacecraft. A large radar antenna running along the lower left side of the spacecraft would indeed shadow the remaining satellite under these conditions. If the antenna surface reflects specularly (and John Locker reporting his *glint* before his observation of disappearance may just have been on the edge of this reflection for a moment) Lacrosse 5 would vanish from view unless you can observe the flare. The reason Lacrosse 5 doesn't do it all the time is that on most days the sun would come from different directions than the left side and thus shining around the radar antenna (at least partially). If this is the case we would have an easy way to predict these disappearances: Check when the elevation of the sun as viewed from Lacrosse 5 is between 7.5 and 9 deg. (the upper limit is just a guess - it would need to be established by observation) and when the sun's azimuth is such that it comes from the left side of the spacecraft within a (still to be determined) margin (maybe one can use the Beta Angle of the orbit instead - something greater than 65 deg maybe). Does anybody have a compact list of all the Lacrosse 5 disappearance observations done so far so we can do more checks? Gerhard HOLTKAMP Darmstadt, Germany ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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