Re: Another ISS reboost this morning ...

Date: Fri Sep 15 2000 - 07:58:33 PDT

  • Next message: Tony Beresford: "Sept 15 OBS"

    In a message dated Thu, 14 Sep 2000 20:09:56 -0500, Ed Cannon 
    <> writes:
    >Regarding NASA's Shuttle/ISS/Mir elements Web site:
    >as usual, I am having significant trouble making sense of NASA-ese, 
    >in trying to determine which is the correct ISS element set to use 
    >for tomorrow morning (about 2000/09/15.40 [or 2000/259.40 -- if 
    >I'm correct that 09/15 is day 259]), is the elset below the one 
    >(given that the next one is for epoch day 261)?
    Ed - I completely agree.  It is a chore sorting out which TLE goes with which 
    upcoming pass.  I should pass on something else Jonathan Weaver told me.  
    They used to include an explanatory line for each element set (such as "This 
    reflects the fourth reboost maneuver scheduled for X date and time), back 
    when the "predicted" elements were uploaded manually.  But those were lost 
    when they automated the system via a JAVA applet.  The system now works 
    automatically.  When NASA Mission Control decides to make an orbit change, 
    when they log that change officially into the mission timeline, the JAVA 
    applet automatically picks it up and generates new element sets for the Real 
    Time Data web page(s). 
    He added:
    >Because of this, there is
    >no easy way of being able to type in the infinite amount of possible
    >comments to describe the orbital elements coasting arc. By providing
    >you with the maneuver timeline (which we didn't use to do) you can
    >use the UTC time of a maneuver to correlate the appropriate coasting
    >arc. Thats about the best we can do given the script is now automated.
    So - that's the trick.  You figure out the UTC of the time of an upcoming 
    pass and use the TLE that most closely precedes it, as listed on the Real 
    Time Date web pages.   Unfortunately, I'm all thumbs with UTC conversions.  I 
    did it bass-ackwards.  (Does anyone know a good Mac utility that will convert 
    UTC to ordinary date and time and vice versa?)
    First, I went to the Heavens-Above web site to get the "ballpark" pass times. 
     Then I went to the NASA TV web page 
    ( to see which 
    shuttle orbit those H-A times most closely matched.  Then, with the orbit 
    number for these upcoming passes, I then compared them to the Real Time Data 
    page's listing to find which TLE matched or most closely preceded that orbit 
    But then the Real Time Data page, oddly, had replaced the shuttle orbit 
    numbers with ISS orbit numbers, confusing the hell out of me.  So I had to 
    redo everything using Mission Elapsed Time as the common denominator.  (It 
    has since then reverted back to using shuttle orbits again.)  Sigh.   :-\
    [I wonder if the NASA SkyWatch applet
    ( includes these 
    predicted TLEs when you run that?  Anyone know?  Unfortunately, I can't run 
    that until I upgrade my browser.]
    Having said all that, here's what I came up with yesterday:
    (These TLEs are based on passes predicted for the US East Coast.  While, at 
    first glance, they should be usable elsewhere, there may be better TLE 
    matches for other locations.)
    FOR FRIDAY MORNING, SEPT. 15 (Docked).
    1 26489U 00053A   00259.39327918  .00030000  00000-0  27000-3 0  9046
    2 26489  51.5803  39.3575 0004616 174.5850 185.5358 15.63975307  1093
    Same as above -- No additional TLEs listed in time for Saturday's pass.
    1 26489U 00053A   00261.24631987  .00030000  00000-0  27000-3 0  9081
    2 26489  51.5849  29.9721 0006739 215.1855 144.8857 15.62026144  1385
    FOR MONDAY MORNING, SEPT. 18 (Undocked)
    1 26489U 00053A   00262.26992887  .00030000  00000-0  27000-3 0  9106
    2 26489  51.5843  24.8014 0006802 240.2553 119.7927 15.62625557  1543
    1 25544U 98067A   00262.20597279  .00030000  00000-0  27000-3 0  9097
    2 25544  51.5847  25.1246 0006579 217.7860 142.2835 15.62036976 24556
    [Note: The reason these do not have the same epoch date is because the 
    shuttle's elements are for the final post-separation burn (MET 9/16:46 or 
    9D:16H:46M), while the ISS's elements reflect the planned undocking (MET 
    9/14:56 or  9D:14H:56M).  However, the predicted ISS elements (on the Real 
    Time Date ISS elements page) do not go by MET or shuttle orbit, so, using 
    shuttle MET, I found the shuttle coasting arc UTC for undocking (Coasting Arc 
    #10 / orbit 152), which was UTC 2000/262/03:40:28.972, and used that to find 
    the closest matching ISS TLE -- which turns out, lo and behold, to ALSO be 
    "Coasting Arc #10" (begining on orbit 2454).  Well -- you learn something new 
    -- the Coasting Arcs are coordinated.]
    FOR TUESDAY MORNING, SEPT. 19 (Undocked)
    Same as above.  No additional predicted TLEs before Tuesday.
    [Atlantis is schedule to land Wednesday morning.   But if, for some reason, 
    it did not land as planned, there is a chance both spacecraft would be 
    visible on Wednesday, too.]
    As confusing as this was, I did the best I could.   But if anyone finds any 
    errors, please, let us all know. 
    Jim Cook
    Germantown, MD
    39.2N, 77.3W
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