RE: Can Someone Predict This?

From: Ted Molczan (molczan@rogers.com)
Date: Tue Apr 16 2002 - 09:59:32 EDT

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    Art Glick requested assistance in predicting precise ephemerides for his
    post-undocking STS/ISS pass on 2002 Apr 17 UTC:
    
    http://satobs.org/seesat/Apr-2002/0197.html
    
    Here is how I approach this problem:
    
    First find out the undocking time. The flight plan is available at both
    CBS News and Spaceflight Now. Here is the latter:
    
    http://www.spaceflightnow.com/station/sts110/fdf/110plan.html
    
    Undocking is scheduled for 2002 April 17 at 2:39 PM EDT = 18:39 UTC. I
    am going to go to a NASA page that provides planned 2-line elements
    several days in advance, so I need to convert the above date and time to
    the 2-line epoch format: yyddd.dddddddd
    
    Where yy is the last two digits of the year = 02
    
    ddd. is the day of the year; 2002 Apr 17 = day 107
    
    .ddddddddd is the fraction of the day; 18:39 UTC = (18 X 60 + 39) / 1440
    = .777083
    
    Putting it all together, the undocking epoch is 02107.777083
    
    Now, let's go to NASA's shuttle elements page and find the element set
    that is later than the undocking and closest in time prior to Art's
    pass, which he told us is 6h 14m after undocking:
    
    http://spaceflight.nasa.gov/realdata/sightings/SSapplications/Post/JavaS
    SOP/orbit/SHUTTLE/SVPOST.html
    
    I found this set:
    
    1 27413U 02018A   02107.88243482  .00071000  00000-0  10050-3 0  9028
    2 27413  51.6362 355.8852 0009700 343.6021  16.4819 15.58484112  1439
    
    Now, I need to check the flight plan for any reboosts prior to
    undocking, so back to Spaceflight Now:
    
    http://www.spaceflightnow.com/station/sts110/fdf/110plan.html
    
    I see that a reboost is planned for 2002 Apr 17 at 7:19 AM EDT = 11:19
    UTC. I covert this to 2-line epoch format = 02107.4715278, and go to
    NASA's ISS elements page, in search of an elset after the reboost that
    is closet to the time of Art's pass:
    
    http://spaceflight.nasa.gov/realdata/sightings/SSapplications/Post/JavaS
    SOP/orbit/ISS/SVPOST.html
    
    Here it is:
    
    1 25544U 98067A   02108.45973608  .00070138  00000-0  83646-3 0  9026
    2 25544  51.6373 352.9945 0007995 352.1898   7.9131 15.58003683  4756
    
    My ephemeris generator reports that Art's post-undocking shuttle pass on
    2002 Apr 17 will culminate at 86 deg elevation, azimuth 221 deg, at
    20:48:21 EDT, followed about 5.5 s later by ISS. At that point, their
    angular velocity will be 1.09 deg/s, so they will appear about 6.0 deg
    apart. Of course, they will appear closer together at all other points
    during the pass.
    
    I caution that the elements on the above NASA pages may revised (in fact
    they were revised as I typed this message, changing the STS-ISS
    separation at culmination from 3.8 deg to 6.0 deg!), so for precision
    work, it is necessary to review before the pass.
    
    Now I have to get back to work.
    
    Clear skies!
    Ted Molczan
    
    
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