Obs 23 May 2006 re XSS-11

From: Greg Roberts (grr@iafrica.com)
Date: Wed May 31 2006 - 07:44:46 EDT

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    Observations 23 May 2006:
    Cosatrak 1 (Computerised satellite Tracking System).
    MINTRON low light level CCD surveillance camera (0.005 lux typical
    in non integration mode) and 0.00005 lux in STARLIGHT mode with 128
    frame integration.
    Used with 145mm focal length f/2.5 lens,integrating for 128 frames
    which is equivalent to an exposure of 2.56 seconds per image.
    Site 0433 : Longitude 18.51294 deg East, Latitude  33.94058 deg S,
    Elevation 10 metres - situated in Pinelands (Cape Town), South Africa
    Has XSS-11 done an orbit change ?
    Based on observations reported by me on 23 May it was thought that
    XSS-11 had performed an orbit change.Since then I have been unable
    to locate this satellite and there is now some uncertainty as to what
    has happened,if anything, and until XSS-11 is found again there is
    a question mark. The possibility has been raised that I may have
    made a timing error of about 13 seconds.
    I have very strong doubts about this due to the nature of how my
    tracking system operates. There are four time displays all set
    against GPS at start of tracking session and the clocks running
    are as follows:
    (1) GPS time display
    (2) Time display from a crystal oscillator controlled clock
    (3) Time display on monitor from a crystal controlled video time display
    (4) Computer Time display which controls CoSaTrak and has a slow drift
        of about 3 seconds over a 5 hour period
    (5) Oscilloscope display of time error between GPS signal and crystal
        controlled oscillator - increases to about 10 milliseconds over a
        5 hour period
    These I check frequently during a tracking spell to make sure nothing
    has changed and to my best recollection I have never had a difference
    larger than expected, so I am 99.99% certain there was not a time error
    greater than a few milliseconds in the clocks or greater than 0.1
    seconds in the video display time as the time is displayed to 0.1
    second resolution.
    There is a remote possibility that GPS was wrong (!) as all systems
    are set against GPS. I think this possibility can be ruled out as none
    of the other satellites observed on the 23rd May had large time errors.
    The satellite was predicted to appear at 16h57m30sec UT at azimuth 171.70
    degrees and elevation 18.16 degrees. At the predicted time I did not see
    the satellite, and as is my habit, I start CoSatrak tracking on the
    prediction which increases my magnitude capability from about mag +8
    to +12. After tracking for about 50 seconds I has still not seen anything
    on the monitor so stopped the track at 16h58m25sec UT. I then waited
    and at 16h58m34sec a satellite appeared in the field of view travelling
    in the correct direction. I then moved the mount to the next predicted
    position and when the satellite appeared I started the autotrack. This
    was at 16h58m55s UT and made a note in my observing log " satellite about
    10 seconds late". It was the correct object ( or one in very similar
    orbit) because the CoSaTrak predicted track for XSS-11 would have soon
    shown a deviation from that observed.
    The following positions were obtained ( I re-measured all this without
    referring to my previous observations as I did not want to introduce any
    possible bias.)
    28636 05 011A   0433 G 20060523165857400 56 15 1900286-840524 39  +075 05
    28636 05 011A   0433 G 20060523165957600 56 15 1008049-791502 39  +075 05
    28636 05 011A   0433 G 20060523170057700 56 15 0918083-552017 39  +075 05
    28636 05 011A   0433 G 20060523170208200 56 15 0901463-190343 39  +075 05
    28636 05 011A   0433 G 20060523170307000 56 15 0853475+051548 39  +075 05
    28636 05 011A   0433 G 20060523170404600 56 15 0847286+203614 39  +080 05
    28636 05 011A   0433 G 20060523170439200 56 15 0844024+270621 39  +080 05
    The satellite was running about 13 seconds late on prediction and a fair
    distance from the predicted track as follows:
    16h58m57.4s UT  offset from predicted track 13.5 arc minutes
    16h59m57.6s UT  offset from predicted track 19.7 arc minutes
    17h00m57.7s UT  offset from predicted track 25.4 arc minutes
    17h02m08.2s UT  offset from predicted track 24.0 arc minutes
    17h03m07.0s UT  offset from predicted track 20.3 arc minutes
    17h04m04.6s UT  offset from predicted track 15.7 arc minutes
    17h04m39.2s UT  offset from predicted track 13.5 arc minutes
    I stopped tracking at 17h05m29s UT when I "ran" into some trees.
    Okay thats the "evidence". All I can conclude is that the satellite was
    running 13 seconds late and this is also borne out by the large offset
    from the predicted track.
    Now to find the satellite again :-))
    Sorry for the long discourse - might be of interest to some.
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