Re: ISS Transit prediction problems?

From: Kevin Fetter (kfetter@yahoo.com)
Date: Sun Aug 31 2003 - 08:23:37 EDT

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    --- satcom <john@satcom.freeserve.co.uk> wrote:
    
     Tom , I think your visual pass yesterday was a high elevation one and I
    > agree how big the station seems during these transits....in excess of 10" or
    > so.
    
    This is one person wrote after seeing a transit I told him to watch
    
    Right on 
    schedule, it entered the Sun's disc at about position 4 o'clock and exited 
    at about position 10 o'clock, taking perhaps 1.5 seconds to cross.  The 
    amount of detail at 50x was utterly astounding... its solar collection 
    panels were all sharply defined rectangles, the cells of the main 
    cabin-bodies visible, AND THE WHOLE APPEARANCE WAS THAT OF A SMALL DRAGONFLY 
    WITH FOUR WINGS.  In fact, the transit was almost over by the time I 
    realized that this small, highly detailed "insect" was not a dragonfly, but 
    was in fact the ISS target!   WOW!!
    
    The iss is a big satellite.
    
    Tom wrote
    
    I thought I saw a speck go across the sun... but a few seconds later,
    an upside-down T went zipping across, startling me for a number of reasons,
    including how large it appeared to be!
    
    Doesn't suprise me.
    
    Using this data on the iss
    
    Dimensions: Width: 73 meters (240 feet) across solar arrays 
    Length: 44.5 meters (146 feet) from Destiny Lab to Zvezda; 52 meters (170 feet) with a Progress
    resupply vessel docked 
    Height: 27.5 meters (90 feet 
    
    So the length is 44.5 m
    
    So if the iss is 500 km away, then
    
    x =44.5/17
    
    = 2.617647059 
    
    divide by the distance to the iss
    
    so x= 2.617647059/500
    
    = 0.005235294 Degress across
    
    So 0.005235294*3600
    
    Which works out to be 18.84705882
    
    So at a distance of 500 km, the iss appears to be roughly 18.8 arc seconds in length.
    
    So a solar panel at the same distance apprears to be 
    
    roughly 30.9 arc seconds across.
    
    See it's can appear big :)
    
    Kevin
    
    
    
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