Observations 01 Jan 2007:
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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
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Testing a 6 inch f/5 reflector with MINTRON camera, mount modified to
run the CoSaTrak system:
For Classifed.tle:
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90013 03 564A 0433 P 20061225195004400 56 15 0543218+130537 39 +080 05
Notes:
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(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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