RE: Viewing circumstances for Endeavour & ISS

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Sun May 15 2011 - 04:28:24 UTC

  • Next message: Brad Young: "BY Obs May 15"

    Joe Rao asked:
    
    > I have a question concerning viewing  circumstances of Endeavour relative to
    > the ISS for this upcoming  mission:  If the launch comes off on schedule,
    > then according to the  Master Flan Plan outlined by William Harwood at the
    > Spaceflightnow.com site, the orbiter is scheduled to undock from the ISS
    > at 11:53 p.m. EDT on May 29.
    > 
    > For the next 283 minutes, Endeavour will fly in close  proximity around the
    > ISS, but will finally begin moving away in earnest at  4:36 a.m. EDT on May 30.
    > 
    > As it turns out, from NYC, there will be a  31-degree high pass of the ISS
    > in bright twilight scheduled about 14 minutes  later.  Anybody want to venture
    > an educated guess what the distance  between the two vehicles (in miles/
    > kilometers) might be at that time?
    > 
    > Will they be too close together to discern as two separate objects  without
    > optical aid?
    
    The pre-flight estimated orbital elements may be helpful in providing an approximate answer:
    
    http://spaceflight1.nasa.gov/realdata/sightings/SSapplications/Post/JavaSSOP/orbit/SHUTTLE/SVPOST.html
    
    In principle, comparing the final docked TLE with the one after the final separation should provide a reasonable
    estimate of the separation between ISS and Endeavour during the New York pass. This is the latest available docked TLE:
    
    1 00134U          11149.46839051  .00020000  00000-0  20000-3 0  9212
    2 00134  51.6449 256.6685 0004050 340.0490  20.0515 15.75846599  2055
    
    I also considered the immediate post-undocking TLE:
    
    1 00134U          11150.16593341  .00020000  00000-0  20000-3 0  9221
    2 00134  51.6467 253.0815 0004948 342.4954  17.6039 15.75906166  2160
    
    Here is the TLE after the final separation:
    
    1 00134U          11150.41955913  .00020000  00000-0  20000-3 0  9282
    2 00134  51.6442 251.7701 0002335 345.7065  14.4033 15.76536145  2200
    
    The latest docked TLE and the immediate post-undocking TLE are about 10 km apart at undocking, which seems too much, so
    I decided to use the latter as the proxy for ISS. That is not ideal, since it includes the small delta-V of undocking,
    but it's probably the best available. (I also tried using NASA's predicted ISS TLE, but the resulting separation seemed
    far too great.)
    
    On the New York pass of May 30, at 04:48 EDT, the immediate post-undocking TLE and the TLE after final separation are
    1.5 km apart, almost entirely in altitude above the Earth. At culmination, that would result in a difference in
    elevation above the horizon of about 0.11 deg.
    
    
    > Even better . . . the following morning (May 31) at  around 3:38 a.m. EDT,
    > the ISS will move out of the Earth's shadow and  quickly climb to an altitude of
    > 85-degrees. Endeavour will likely be  "leading" the ISS; any guesses by how many
    > seconds or degrees?
    
    Here is the predicted TLE:
    
    1 00134U          11151.37037687  .00020000  00000-0  20000-3 0  9298
    2 00134  51.6447 246.8702 0002422 350.8916   9.2204 15.76528862  2355
    
    Endeavour would lead ISS by about 30 s. At culmination, that is equivalent to about 38 deg along-track.
    
    The above elements almost certainly will be revised throughout the mission, so I recommend checking them a few days
    before undocking to see whether these estimates hold up.
    
    Ted Molczan
    
    
    
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