Hi Ray and List, Last week Ray reported: "A first for me: Iridium 45 with a right antenna flare peaking at 20:23:45 > EDT that was still visible as a solar panel flare began and then peaked at > > 20:24:11. What was interesting was the slow rise and fall of the antenna > flare, > contrasted with the rather steep/fast rise and fall of the solar panel > flare. > Thanks to Robert Matson and his Iridflare for making making this a > predictable event." > You're welcome, Ray! I was wondering if you had the rise/fall durations reversed for the MMA flare vs. the solar array flare? I've seen quite a few of the latter now, and they tend to be quite gradual -- often lasting 30 seconds or more -- in contrast to the comparatively fast rise/fall of a typical MMA flare. Just last night I observed a right-MMA flare from Iridium 47 that peaked at around magnitude +1, followed 8 1/2 minutes later by a solar-array flare from Iridium 11 that reached about magnitude -0.5. The solar array flare had a very broad peak, whereas the MMA flare had a very identifiable brightest point. This behavior is what you would expect, given that the MMA's are more optically flat than the solar arrays. However, there are three factors that I can think of that might lead to abrupt solar-array flares under the right circumstances: 1. While the MMAs remain fixed relative to the spacecraft body axes, the solar arrays articulate, doing their best to track the sun. In some cases, this might cause an increase in the rate of change of the flare angle (i.e. "mirror angle"), which would decrease the flare duration. 2. Body eclipsing. Unlike the MMAs which, when viewed from the ground, cannot be eclipsed by other parts of the Iridium spacecraft, the line of sight from the ground to the solar arrays can be partially blocked by the spacecraft body. 3. Shadow entry. Just as for the MMAs, a solar array flare could be abruptly cutoff by satellite shadow entry (in which case it would be tagged by IRIDFLAR with "Pnb"). Best wishes, Rob ----------------------------------------------------------------- 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
This archive was generated by hypermail 2b29 : Mon Oct 08 2001 - 18:24:19 EDT