accuracy of ISS / Venus transit track

From: Thomas Fly (tfly@alumni.caltech.edu)
Date: Thu Jun 03 2004 - 02:26:48 EDT

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    I'm posting this with the hope that others will compare their results with mine,
    using software they've written or own, with the ultimate goal that by June 7, as
    accurate a transit path prediction can be made as is possible.
    
    Except for the latitude & longitudes, most of the values in my results were
    never
    intended to be extremely high precision (e.g., the angle of elevation, and
    azimuth).
    
    In fact, at 5:50:53, I report an elevation angle (of the ISS as it transits
    Venus) of 1.0, while the Sun's elevation is given as 0.4, and the Sun/Venus
    separation angle is 0.2. Even allowing for rounding error, Venus (and hence the
    ISS as it transits Venus) could be no more than 0.7 in elevation, so there's at
    least half a Sun diameter of error in there, somewhere.
    
    If there's substantial disagreement with any of these results (that is, the
    latitudes & longitudes I compute), then I can post my intermediate results for
    further comparison; e.g., the ECI position of the ISS, the position of Venus,
    etc.
    
    
    The results that follow are based upon the TLE given below, posted by NASA's
    Mission Control Center on June 1 (the transit of Venus begins at about
    day-of-year 160.22); the calculations were performed at 1 second intervals.
    (Naturally, for comparisons to have any meaning, this TLE must be used.)
    
    1 25544U 98067A   04159.51921885  .00020000  00000-0  20000-3 0  9074
    2 25544  51.6331  15.0248 0005532 209.7910 150.2937 15.68809969 36809
    
    An elevation of sea-level was used in these calculations; hopefully, I'll finish
    implementing my GTOPO30 Digital Elevation Model code by June 7, that will allow
    me to calculate the transit path using accurate elevation data. However, for the
    sake of comparison, an elevation of sea-level should be used.
    
    
    The Contact times below represent "as observed by a demon at the Earth's
    center."
    
    Since Venus is close to the Earth in size, moving from the Earth's center to
    the Earth's "edge" would cause Venus to shift by about a third of its diameter,
    relative to the disk of the Sun (which would also shift relative to the stars,
    by
    about 1/3 the amount of Venus' shift).
    
    Key times: see http://sunearth.gsfc.nasa.gov/eclipse/OH/transit04.html
    
    Contact 1   5:13:29  (ISS will be on the night side of the Earth at this moment)
    Contact 2   5:32:55  Venus is first entirely silhouetted against the Sun
    Greatest    8:19:44    "   at the midpoint of its transit
    Contact 3  11:06:33    "   begins to emerge from the Sun's disk
    Contact 4  11:25:59  end of the 2004 transit of Venus
    
    
    A - seconds elapsed since somewhat arbitrary program starting time
        of 5:12:54 ("Contact 2" minus 20 minutes and 1 second)
    B - UTC time (June 8)
    
    C - elevation angle of the ISS/Venus
    D - azimuth angle of the ISS ( + is East from North; - is W from N)
    E - range (miles)
    
    F - latitude for observing the transit
    G - longitude
    
    H - sun elevation angle
    I - sun/Venus separation angle
    
    A----   B------  C--- D----- E--- F------- G-------- H---- I----
    ORBIT 1: The ISS is first seen transiting Venus as Venus transits the Sun
      166   5:15:40   1.3   66.6 1296 -10.6179   16.6564   1.2   0.3
    
    Contact 2; also represents (to 0.1) the highest elevation for any
              ISS transit of Venus
     1201   5:32:55  63.6  147.0  255  46.1773   81.6199  63.9   0.2
    
     1431   5:36:45  60.0 -166.0  263  52.1930  103.2916  60.3   0.2
     1560   5:38:54  55.0 -142.4  277  53.4559  117.4513  55.2   0.2
     1663   5:40:37  50.0 -125.9  294  53.1848  129.0865  50.1   0.2
     1757   5:42:11  45.0 -112.7  316  51.9433  139.4399  45.0   0.2
     1842   5:43:36  40.0 -102.3  344  50.0574  148.2982  40.0   0.2
     1922   5:44:56  35.0  -93.8  378  47.6828  156.0937  35.0   0.2
     1999   5:46:13  30.0  -86.7  424  44.8977  163.1224  29.9   0.2
     2070   5:47:24  25.0  -81.0  485  41.9138  169.3036  24.9   0.2
     2135   5:48:29  20.0  -76.3  566  38.8051  174.9051  19.8   0.2
     2192   5:49:26  15.0  -72.5  678  35.6822 -179.9041  14.8   0.2
     2238   5:50:12  10.0  -69.2  837  32.6552 -174.9298   9.8   0.2
     2269   5:50:43   4.9  -66.4 1068  29.7989 -169.8705   4.6   0.2
     2279   5:50:53   1.0  -64.4 1314  27.7853 -165.7539   0.4   0.2
    
    
    ORBIT 3:
    11182   8:19:16   1.6   66.7 1274  -9.9868  -29.3634   1.3   0.2
    11191   8:19:25   4.9   66.2 1075  -8.3539  -26.3397   4.7   0.2
    
    Greatest transit of Venus
    11210   8:19:44   8.4   65.9  906  -6.3542  -23.3779   8.3   0.2
    
    11222   8:19:56  10.0   65.8  839  -5.3198  -22.0455  10.0   0.2
    11267   8:20:41  15.0   65.9  681  -1.9698  -18.2882  14.9   0.2
    11324   8:21:38  20.0   66.4  566   1.7759  -14.6744  20.0   0.2
    11389   8:22:43  25.0   67.6  484   5.7591  -11.1737  25.0   0.2
    11459   8:23:53  30.0   69.3  423   9.8626   -7.7359  29.9   0.2
    11536   8:25:10  35.0   72.0  376  14.2285   -4.1223  35.0   0.2
    11617   8:26:31  40.0   75.5  341  18.6881   -0.3574  40.0   0.2
    11702   8:27:56  45.0   80.4  314  23.2314    3.6748  45.0   0.2
    11795   8:29:29  50.0   87.2  292  28.0338    8.3043  50.1   0.2
    11899   8:31:13  55.0   97.2  275  33.1626   13.9036  55.1   0.2
    12030   8:33:24  60.0  114.2  262  39.1650   21.8632  60.2   0.2
    12234   8:36:48  63.4  151.2  255  47.0528   37.0968  63.7   0.2
    13294   8:54:28   0.8  -64.5 1325  27.3823  148.1378   0.4   0.2
    
    
    ORBIT 4:
    16690   9:51:04   1.8   66.7 1265  -9.6802  -52.3954   1.4   0.2
    16699   9:51:13   4.9   66.2 1072  -8.0881  -49.4657   4.7   0.2
    16729   9:51:43   9.9   65.9  843  -5.1485  -45.2990   9.8   0.2
    16775   9:52:29  15.0   66.0  681  -1.7206  -41.4470  14.8   0.2
    16832   9:53:26  20.0   66.5  566   2.0222  -37.8361  19.9   0.2
    16897   9:54:31  25.0   67.7  484   6.0029  -34.3350  24.9   0.2
    16968   9:55:42  30.0   69.5  423  10.1614  -30.8467  29.9   0.2
    17044   9:56:58  35.0   72.1  377  14.4665  -27.2753  34.9   0.2
    17125   9:58:19  40.0   75.7  341  18.9220  -23.5018  39.9   0.2
    17210   9:59:44  45.0   80.6  314  23.4601  -19.4576  44.9   0.2
    17211   9:59:45  45.0   80.7  314  23.5127  -19.4091  44.9   0.2
    17304  10:01:18  50.0   87.5  292  28.3057  -14.7592  50.0   0.2
    17409  10:03:03  55.0   97.7  275  33.4689   -9.0728  55.0   0.2
    17541  10:05:15  60.0  115.0  262  39.4869   -0.9876  60.1   0.2
    17742  10:08:36  63.2  151.5  256  47.1997   14.1343  63.6   0.2
    17944  10:11:58  60.0 -167.3  263  52.2396   33.5070  60.4   0.2
    18077  10:14:11  55.0 -142.8  277  53.4873   48.1278  55.4   0.2
    18182  10:15:56  50.0 -125.9  295  53.1330   59.9764  50.3   0.2
    18275  10:17:29  45.0 -112.8  316  51.8355   70.1724  45.3   0.2
    18362  10:18:56  40.0 -102.1  344  49.8448   79.1689  40.2   0.2
    18443  10:20:17  35.0  -93.6  379  47.3835   86.9762  35.2   0.2
    18519  10:21:33  30.0  -86.7  424  44.5908   93.8316  30.2   0.2
    18591  10:22:45  25.0  -80.9  484  41.5326  100.0236  25.2   0.2
    18656  10:23:50  20.0  -76.3  565  38.4000  105.5577  20.2   0.2
    18714  10:24:48  15.0  -72.5  679  35.2050  110.7819  15.1   0.2
    18760  10:25:34  10.0  -69.3  838  32.1643  115.7207  10.0   0.2
    18791  10:26:05   4.9  -66.5 1071  29.2954  120.7750   4.8   0.2
    
    Lowest elevation at which my program "sees" a transit
    18801  10:26:15   0.7  -64.4 1338  27.1613  125.1682   0.4   0.2
    
    
    Contact 4, on ORBIT 5:
    22385  11:25:59  23.5   67.4  506   5.0450  -58.5304  23.3   0.3
    
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    This archive was generated by hypermail 2b29 : Thu Jun 03 2004 - 02:31:44 EDT