You lost me Bjorn, Zing! right over my little bean! Russ ----- Original Message ----- From: "Björn Gimle" <b_gimle@algonet.se> To: "SeeSat" <SeeSat-L@satobs.org> Sent: Tuesday, September 17, 2002 8:08 PM Subject: Flash period vs RPM; was Re: ATLAS CENTAUR R/B (#10779U) > ... and there is the synodic effect: If it IS doing 12 rpm, then > it is rotating 360*12 deg/min or 6*12 = 72 deg/s, and the > reflection up to twice that speed. > > Since the satellite moves (a few degrees) during these 6 seconds, > it may send the reflection to you a fraction earlier, or later. > > Now if you observe a pass where the axis is nearly perpendicular > to the orbit and to your line-of-sight, and the Sun somewhere > near the plane of these two vectors, and the satellite happens to > move at 0.72 deg/s, you would see a 0.5 % increase or decrease in > the visual period, so it would have a flash period of 5.025 or > 4.975 s. (If the rotation is slower, the relative effect is > correspondingly larger). > > If you can observe one pass culminating "moving left", and the > next one "moving right", and see a larger difference between > their flash periods (at culmination) than what a similar estimate > gives, you are pretty sure that you have been timing fractional > rotations. > > If the geometry is less than ideal, it is more difficult to draw > conclusions, but you should use a stopwatch with 50/100/300 > memories, and plot the observed times vs. the computed ones, > using the less distorted period at the start or end of the track, > to see a stretched "S" or "Z" shape displacement of the flash > times (like an arctan() or arccot() function. > > In a long "Determination of Rotational Axis" project several > years ago, Bart de Pontieu (SeeSat founder) showed that with > accurate "simultaneous" observations from two locations, and/or a > lucky pass of the rotation axis near one observer, the true > position of the axis, and thus the speed and direction of > rotation, could be computed. > > > Next time, I'll wait till the next morning to give details ; ) > > ...and I should think twice, at least, instead of sending incomplete replies. > > > And Bjorn, I'm confused. If the sat is spinning one revolution and flashes, > > and it takes 4.66 seconds to complete another revolution and flashes again, > > wouldn't that be 12.88 RPM? Or is the satellite showing me two reflective > > surfaces per revolution and I must divide by two? Help! > > > ... > > > ----------------------------------------------------------------- > 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 > ----------------------------------------------------------------- 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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