> I was looking at the GOCE satellite, and was wondering if flares off it's > solar panels are possible, I think they might be. Looking at the esa website http://www.esa.int/esaLP/goce.html I tried to piece together their intended orbit and reached the conclusion that such flares cannot be seen from the night side but that it might be possible to see daytime flares at special times and places. Here are the details: The GOCE solar panels are aligned with the orbit plane (to keep atmospheric drag and attitude disturbance as small as possible). Therefore the orbit plane has to point as normal to the Sun as is possible (to get maximum power for the solar panels) which leads to what they call a dusk to dawn sun synchronous orbit. Essentially what it means is that GOCE tries to stay close to the terminator all the time. With the declination of the Sun varying in the course of the year GOCE will not be able to fly exactly above the terminator all the time but actually experiences eclipse periods around summer and winter solstice. Interestingly these eclipse periods are asymmetric: You either have longer (up to 30 minutes) eclipses during the (Northern) winter and short (10 minutes) eclipses during the summer or the other way around - depending on how GOCE is launched (which apparently hasn't been finalized yet). Despite these eclipses GOCE never strays away from the terminator too far to allow reflexes from the solar panels to reach the night side of the Earth. But even if you are on the dayside you normally wouldn't see any flares. Only around the solstices will reflexes from GOCE's solar panels reach the (dayside) of the Earth. But here the just mentioned asymmetry comes into play: If the orbit is such that long eclipses happen during the Northern winter then you could see flares during December / January on the Southern hemisphere from Antarctica up to mid-latitudes. In that case flares on the Northern hemisphere would be restricted to Artic regions in June. If on the other hand the alternative orbit with long eclipses in the Northern summer has been chosen, it's the Northern hemisphere that gets the daytime flares down to mid-latitudes. How bright would those flares get? The GOCE solar panels are about twice as large as an Iridium main antenna - source of the famous Iridium flares. But I guess solar panels don't reflect as much light (after all their job is to convert as much light as possible into electricity). So it will probably be similar to bright Iridium flares which have been reported during daylight also. All this is based on some very quick analysis. I don't have all the information ESA mission planners have so there might be some hidden details I missed out on and which would change this analysis. But the subject seems worth pursuing. Gerhard HOLTKAMP Darmstadt, Germany ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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