Re: test of iss pass across the moon tonight

From: Thomas Fly (thomasfly@j2ee-consultants.com)
Date: Sat May 17 2003 - 10:41:48 EDT

  • Next message: Thomas Fly: "Re: test of iss pass across the moon tonight"

    I had some time this morning to plot Kevin's comparisons: http://iss-transit.sourceforge.net/images/comparisons.gif
    
    Lacking an actual observation, one can't say which track is the most accurate.  However the moon's angular size is about 0.009
    radians, so at a distance (to the ISS) of 543 miles, the transit path would be 4.9 miles wide, and any of these tracks would result
    in a near dead-center transit.  The primary difference isn't really one of accuracy, but the fact that my track prediction- based
    upon the SVPOST element sets- was made several days in advance (I normally make 10 day forecasts, which are updated as NASA updates
    the SVPOST page).
    
    One can infer from the existence of the SVPOST page, and the apparent accuracy of predictions based upon it, that NASA has a more
    refined orbital model for the ISS than SGP4, and that (for the benefit of people like me), they distill that refined model down into
    SGP4 model 2-line element sets.
    
    A picture is worth a thousand rows of numbers...
    
    ----- Original Message -----
    From: "Kevin Fetter" <kevin_fetter@hotmail.com>
    To: <SeeSat-L@satobs.org>
    Sent: Thursday, May 15, 2003 1:10 PM
    Subject: test of iss pass across the moon tonight
    
    
    > I did a test to see how close tomas fly's path was.
    >
    > Using this latest orbit.
    >
    > ISS (ZARYA)
    > 1 25544U 98067A   03135.48473194  .00011619  00000-0  15101-3 0   127
    > 2 25544  51.6307 184.5710 0006298 116.4433 319.0011 15.59274485255903
    >
    > For example tom gives
    >
    > 1-------  2-----  3------  4--  5--------  6---------  7 8---- 9----
    > 2:55:35  23.327  168.109  543  46.6558 N,  56.4769 W  n -23.7 179.4
    > 2:55:36  23.288  168.193  544  46.7058 N,  56.4035 W  n -23.7 179.4
    > 2:55:37  23.250  168.278  544  46.7557 N,  56.3300 W  n -23.6 179.4
    > 2:55:38  23.212  168.362  545  46.8057 N,  56.2563 W  n -23.6 179.4
    > 2:55:39  23.173  168.447  545  46.8556 N,  56.1825 W  n -23.5 179.4
    > 2:55:40  23.135  168.532  546  46.9055 N,  56.1085 W  n -23.5 179.4
    >
    >
    > I got
    >
    > 16 May 2003 02:55:35.00            46.547            -56.651
    > 16 May 2003 02:55:36.00            46.597            -56.578
    > 16 May 2003 02:55:37.00            46.647            -56.505
    > 16 May 2003 02:55:38.00            46.697            -56.431
    > 16 May 2003 02:55:39.00            46.747            -56.358
    > 16 May 2003 02:55:40.00            46.797            -56.284
    >
    >
    > Rob's program gives
    >
    > 2003/05/16  2:55:35   46.5463    -56.6498
    > 2003/05/16  2:55:36   46.5963    -56.5767
    > 2003/05/16  2:55:37   46.6464    -56.5035
    > 2003/05/16  2:55:38   46.6964    -56.4301
    > 2003/05/16  2:55:39   46.7465    -56.3566
    > 2003/05/16  2:55:40   46.7965    -56.2830
    >
    > My results are close to rob's, but not tom's. But since he would have used a
    > different orbit, then he gets different results.
    >
    > Kevin
    >
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