Fw: CoSaTrak, etc

From: Greg Roberts (grr@iafrica.com)
Date: Wed Dec 24 2003 - 12:10:27 EST

  • Next message: chiayk1: "unid flasher near Beta Ceti 12/24/03"

    Willie Koorts, my partner in the crime of satellite tracking, has
    this to add to the subject of CoSaTrak and TLE's. I always pass
    onto him anything of interest from SeeSat or Dsat.
    Best wishes,
    ----- Original Message -----
    From: "Willie Koorts" <wpk@saao.ac.za>
    To: "Greg Roberts" <grr@iafrica.com>
    Sent: Wednesday, December 24, 2003 11:25 AM
    Subject: CoSaTrak, etc
    > Hi Greg
    > Here's my contibution to the discussion.  I have not had a chance to read
    > today's mails so I may repeat things already said.  Feel free to edit
    > this out from my mail if so.
    > Cheers
    > Willie
    > Hi All
    > At the moment I am too snowed under with work to be subscribed to any
    > mailing lists, even SeeSat which I always found one of the best lists for
    > staying on topic, only minor flame wars, etc.  Also one of the friendliest
    > lists I have even subscribed to.
    > Anyway, Greg has passed on some of the recent discussions on ideas on what
    > to do if we loose the availability of satellite elements.  I found this
    > very interesting and with my previous involvement with Greg in developing
    > a computerised tracking system for the amateur (CoSaTrak), I would like to
    > add a few ideas to the "melting pot", highlighting this angle.
    > Firstly, I want to agree with the positive responses raised here.  I am
    > currently inactive mainly due to family and work commitments but could
    > easily see myself easily inspired to more regular observing if a serious
    > need arises to contribute to a "worthy cause".
    > Greg mentioned some aspects of the contribution a CoSaTrak system has to
    > offer in the way he had refined his system to provide very accurate
    > results.  In general, CoSaTrak offers two modes of following a satellite,
    > "full tracking" or "slew-and-wait" tracking.
    > Full tracking actually follows the satellite properly such that it stays
    > put in the middle of the eyepiece/camera field with the stars drifting
    > past in the background.  As Greg said, to get a smooth track, this mode
    > can be quite demanding on the mechanical accuracy and steadiness of the
    > mounting.  The higher the magnification, the more the chance of seeing the
    > vibration from the stepper motors, particularly on a high culmination
    > track.  The choice of gear ratio here becomes a compromise between
    > smoothness of track and maximum slewrate achievable, leaning towards high
    > ratios.
    > Slew-and-wait (SAW) tracking simply slews the mount (on command, eg a
    > keystroke on the keyboard or press of a handset button) to the next
    > previously predicted position of the satellite.  The mount would typically
    > be slewed ahead of the satellite (to a nice starfield, stationary in the
    > eyepiece/camera field) and then wait for the satellite to pass through the
    > field before slewing ahead again (on command).  Greg has mostly been using
    > this mode of tracking in recent times.  This mode is not very demanding on
    > the quality/accuracy of the mounting or the need for high gear ratios, as
    > along as the mount can be pointed to a degree or so (depending on your
    > FOV, obviously).
    > In both modes, the program allows the mount to be moved while tracking, by
    > using the arrow keys on the keyboard or pressing buttons on a handset, eg
    > to centre the satellite in the FOV or a better starfield.  This is how
    > Greg sometimes chase after an unknown satellite that suddenly enters the
    > FOV while waiting or crossing the track of the satellite being tracked,
    > however this method has it limits.
    > One function provided by CoSaTrak is, with the press of a key or handset
    > button, to record instantaneous position/time information like the PC
    > clock, the mount's Alt/Az position, the corresponding RA/DEC position, etc
    > and subsequently writing this to a text file to disk.  We have never
    > tested the accuracy of this function which will obviously depend on things
    > like the eyepiece/camera FOV, the accuracy of the mount, how well the
    > mount has been set up and calibrated, etc - best suited for a (semi)
    > permanent setup like Greg's.  Although this will be far from the accuracy
    > of measuring positions w.r.t. the starry background, this method might be
    > accurate enough for mass positions of many satellites.  The big advantage
    > of this method would be the lack of reductions afterwards - the file
    > format can be arranged to be a standard output directly.  After accurately
    > setting the PC clock and setting up the mount, the operator would then
    > simply need to centre the satellite on the eyepiece crosshair or target on
    > the TV monitor before pressing the "record" button/key.  As said, to
    > obtain good results would be quite demanding on hardware.
    > Since SAW tracking is much less demanding on an accurate mount, very much
    > simpler systems can be built that should be capable of producing the same
    > accuracy as Greg currently gets.  Such computerised mounts will ideally be
    > fitted with lightweight, low light level video cameras like Greg's rather
    > than telescopes.  The advantage would be even smaller mounts, only
    > requiring tiny motors, eg old 5" floppy drive motors which are (were?)
    > available in abundance.
    > As Greg pointed out, our systems were mainly built from bits found in our
    > (well stocked) junk boxes which make them difficult to mass produce but
    > I'm sure that with some sourcing of readily available commercial parts, an
    > affordable system good enough for SAW tracking is possible.  The next
    > trick would be to automate the time-consuming task of measuring the video
    > tape afterwards but probably easily solvable by the combined software
    > expertise on SeeSat.
    > Sorry for the long-winded mail.
    > Regards
    > Willie
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