Hi All, After a bit of coding, I've determined the sun beta angles for the Iridium double flares listed below, and they are all in the range where the Iridium solar arrays do not point at the sun: > 2 Mar '01 IR36 19:40:30 m-3.4 az 129.7, el -35.9, beta 58.44 > 3 Mar '01 IR 7 19:34:10 m+3 az 127.1, el -36.0, beta 59.78 > 3 Mar '01 IR51 19:34:30 m-2 az 126.7, el -35.9, beta 59.82 > 4 Mar '01 IR61 19:37:05 m+1 az 128.4, el -38.5, beta 61.15 > 5 Mar '01 IR35 19:30:40 m+0 az 124.1, el -39.5, beta 62.52 5 Mar '01 IR35 19:30:50 m-3 az 123.3, el -38.6, beta 62.52 (Last data point corresponding to Michael Gill's observation has been updated to reflect his corrected ground site coordinates -- thanks Michael.) In all of these cases, the solar panel gimbal "rule" in effect is that the azimuth gimbals are locked down at +/-40 degrees, and the elevation gimbal swings 0-360 degrees maximizing the solar incidence angle. The combined action of the azimuth/elevation gimbals is a bit messy to model because it is not an alt-azimuth mount. When the gimbal azimuth is not zero, rotation about the elevation axis causes the solar array normal to sweep out a cone rather than a great circle. The solar array gimbal azimuth can actually be computed from the above derived az/el data using the following equation: gimbal_az = 90 - ACOS(SIN(Az)*COS(El)) For example, in the first case az=129.7, el=-35.9. Plug into the above and you get gimbal_az = 38.6. The other gimbal azimuths compute to 40.2, 40.5, 37.8, 39.7 and 40.8. This seems to confirm the azimuth 40 lock-down rule. Note that if the beta angle trend above continues, it will soon reach 65 degrees, in which case the azimuth gimbals will be locked at 90 degrees and the elevation gimbals locked at 0 and 180 degrees. In this configuration, nighttime solar-array flares will no longer be possible. I'll work on coding the solar arrays into IRIDFLAR, though I suspect that the solar array pointing is not maintained nearly as accurately as the spacecraft orientation since it is not critical for the arrays to point precisely at the sun. This means that the solar array glint brightness will not be very predictable, but I should at least be able to flag ~when~ to look for it. Cheers, Rob ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
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