Re: flares from GOCE satellite ?

From: Gerhard HOLTKAMP (
Date: Thu Apr 28 2005 - 17:10:09 EDT

  • Next message: Ted Molczan: "RE: Titan IV B-30 Tracking stations"

    > 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
    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 
    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:

    This archive was generated by hypermail 2b29 : Thu Apr 28 2005 - 17:21:14 EDT