I believe that the Starlink flares are not due to the motion of the specular reflection of the sun across the observer as the satellite moves along its orbit, as that would produce flares lasting 8-9 seconds rather than those observed to last one second or less. I propose, however, that the flares are a result of moving the satellite in elevation, i.e., in the sun-satellite plane, to optimize solar power input for the system including battery charging. During that time of each orbit when the satellites are illuminated by the sun; the solar elevation at the satellites varies between -20 and +42 degrees, a range of 62 degrees. To maximize output from the solar panel the satellite must re-position the plane of the solar panel, in elevation, to approximately face the sun. This re-pointing is not done continuously but in steps along the orbit at predetermined times / locations. This re-positioning, moves the surface responsible for the flares sufficiently quickly to produce the observed short duration flares from the Starlink satellites. For a 1 second duration flare only requires a satellite rotation rate of 9 milliradians / second to steer the 0.5 deg. width of the sun across an observer; for other positions of the sun the flare duration would be even shorter or if he observer is more off axis the flare would be less bright. Relative to the observer, there is an angular component that also must be satisfied, in the plane perpendicular to the sun-satellite vector in order to move the reflection out of the sun-satellite plane as most observations have been reported. The approximate difference in azimuth between the sun and the observer at the satellite was approximately 140 degrees. The range of solar elevation angles listed were for the 550 km orbit plane that included satellites 45096 & 45080 that I used. My calculations were for 1 April 2020, the observer location was Buenos Aires Argentina (see Ruben Iianza's earlier post) and I used TLEs with an epoch of 91.00001157 for both satellites. As always comments welcome! Regards, Bruce _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-lReceived on Sun Apr 26 2020 - 21:36:31 UTC
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