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 Question: ---------- 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 unit (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. Cheers Greg ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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