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, Greg ----- 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 5¼" 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 > > ----------------------------------------------------------------- To unsubscribe from SeeSat-L, send a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@satobs.org List archived at http://www.satobs.org/seesat/seesatindex.html
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