Obs 01 Jan 2007-correction 25Dec 2006

From: Greg Roberts (grr@telkomsa.net)
Date: Tue Jan 02 2007 - 05:08:12 EST

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    Observations 01 Jan 2007:
    -------------------------------
    
    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
    
    
    Correction one observation made 25 Dec 2005:
    
    29651 06 057A   0433 P 20061225190945500 56 15 0935233-664022 39  +070 05
    
    
    --------------------------------------------------------------------------
    
    Testing a 6 inch f/5 reflector with MINTRON camera, mount modified to
    run the CoSaTrak system:
    
    
    For Classifed.tle:
    ------------------
    
    90013 03 564A   0433 P 20061225195004400 56 15 0543218+130537 39  +080 05
    
    Notes:
    ---------
    
    (1) I modified a super Polaris equatorial mount to an altazimuth
        mounting by pointing the polar axis vertically and the declination
        axis parallel to the ground,adding a stepper motor to each axis
        and running the system using the CoSaTrak electronics/software.
        Conditions were very poor - very thick cirrus and few stars visible.
        However I was able to carry out sufficient tests to determine whether
        it was worthwhile using a 6 inch f/5 reflector as the "camera".
    
    (2) I was able to find #90013 without much difficulty- a geostationary
        satellite about magnitude +8 and was able to determine what I wanted
        to know.
    
    (3) The field of view was 28.4 x 22.4 arc minutes. Despite very thick
        cirrus and full moon I could see stars on the monitor down to at
        least 14th mag. with a 1.92 second integration- in fact I could
        see more stars than the program GUIDE displayed. With dark skies
        and smoother/smaller stepping size I am confident that I can reach
        mag +16 or fainter.
    
    (4) I am not happy with the system.
        The gearing I used for the CoSaTrak modification was selected so
        that I would make no changes to the  mounting itself so space was
        limited in which to make the changes. The result is that the
        stepping increment was too course making it a bit difficult to
        centre objects. The setting accuracy  of CoSaTrak ( as a result of
        backlash in gears/belts etc) is not good enough to ensure the object
        would be in the field of view-  typically I found an error of about
        half a degree in elevation (levelling error?) and about 5 minutes of
        arc in azimuth. Due to mechanical limitations caused by the super
        polaris mount I do not have full coverage of the sky which means
        the telescope can collide with the motors/pier etc and could cause
        severe damage. Finally there are so many cables involved that its
        bound to get ripped apart when fouling part of the system.
    
    (5) Whilst the system gives pleasing views of astronomical objects like
        the Great nebula in orion (Messier 42), exposures show the course
        stepping of the motors so effectively blur the exposure.
    
    (6) So what next?
        Mel Bartels system can drive a CoSaTrak system - the electronics
        are essentially identical- and uses micro-stepping whilst CoSaTrak
        can only go to half-stepping. This will result in  smoother
        stepping. Mels system can also drive an altazimuth mounting ( but
        cannot do satellite tracking). However due to the danger of
        shearing cables/stripping gears etc due to sky access limitations
        I am now contemplating returning the mount to an equatorial system
        and using Mels software for an equatorial since basically all I
        want is a GOTO system for finding geostationary or high altitude
        satellites.
        Mels system should be capable of better setting accuracy as it uses
        the Taki system for determining instrument pointing errors and is
        not as fussy as CoSaTrak as regards levelling errors etc. Since I
        also want to take "pretty" astronomical images the use of an
        equatorial mounting will avoid the field rotation one finds when
        using an alt-azimuth mounting.
    
     7) Irrespective of what I use I will have to add a relatively wide
        angle CCD finder - for this I will use a Watec camera I have which
        will be ideal for the job. With a field of about 2-3 degrees I
        should be able to determine where I am pointing should the
        electronics pointing not be accurate enough.
    
    8)  Sorry a long story but might help others contemplating doing
        something similar.
    
    9)  Happy New Year!
    
    Cheers
    Greg
    
    
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