TELESCOPE TRACKING

Alphonse Pouplier (pouplia@interpac.interpac.be)
Fri, 18 Aug 1995 11:38:07 +0200 (MET DST)

 The folowing text was sent in july to SEESAT-L. 
 But, as several seesat-l users ask for it, I send it again: 

 HOW I TRACK THE ARTIFICIAL SATELLITES WITH MY TELECOPE

 I often make demonstrations of the system I use to aim
 my telescope onto a point where a satellite should pass
 and then track it. 
 In August 1992 (night of the 4th to the 5th), with five
 friends (namely Bart De PONTIEU, Chris STEYAERT and
 Tristan COOLS), near my house of Esparron in Provence,
 we could use that system and track 21 satellites during
 the same night. The last one was the rocket of COMSTAR 4
 which was 25,000 Km far and gave a flash every 40 sec.! 
 The telescope is a NEWTON D=130 mm F=720 mm on an
 ALT-AZ. MOUNT. 
 The 2 motions (alt. and az.) are controlled by step-motors
 and my computer. 
 On the same mount, I fit a CCD VIDEO CAMERA
 (6 mm x 4.5 mm matrix) with an russian objective
 F=85 mm 1/f=2. I can with it record the passages on tapes. 
 At a meeting in Loon-op-Zand, I could show on such a
 record the flashes of COBE. 
 One can also fit on the same mount binocculars, other
 optics, and so watch at the satellite with several people. 
 You can find an article about my works in S&T of
 august 1993 :"My robotic AstroScan". 
 I could record a passage of MIR when the Sun was only 1 deg. 
 under the horizon! At the end of that passage, it's very
 interesting to see MIR amongst the branches of a tree. 
 MIR remains centered in the TV screen, appearing and
 disappearing behind the moving branches. 
 To prepare an observation-night, it takes me now less time
 than to write these explanations... 
 1) By means of my program "PIAP", I make a selection of the
 satellites I want to know if they will be visible,
 when and where. That selection is made from both
 "MOLCZAN"-file (which gives the standard magnitude) and
 another file GSFC.TXT I download frequently from the Dave
 RANSOM's BBS. 
 2) By means of my program "ANALyse", for all the satellites
 of my selection, I create a file called "PASSAGES.DAT" in
 which are the instants of visibility with Az., Alt., Alt.Sun,
 Hgt., Dist., and the current magnitude if out of earth's
 shadow. 
 3) By means of my program "PREPAR" I can easily choose
 for each satellite the instant I want the tracking to be
 started according to alt. and az. The same program makes
 a file which will be used by the computer during the
 session of observation: The chosen instants are sorted
 chronologically. The direction of the satellite is given by
 means of "Increasing or decreasing azimuth, increasing or
 decreasing altitude". 
 Those three things takes me less than 20 min. for one night
 and up to 100 (one hundred) satellites. 
 On site: 
 I make the setup of my telescope in 5 minutes because it is
 an ALT.-AZ. mount. I use therefor a spirit level, fixed on
 the top of the mount. If the level is horizontal for any
 azimuth it means that the main axis (azim-axis) is vertical. 
 As you can see in the article of S&T, I tried several
 kinds of mounts, even a spheric one for the AstroScan. 
 At my opinion, the alt-az mount is the most convenient
 for several reasons at the contrary of an equatorial mount
 or a mount centered onto the center of the satellite curve: 
 1) It's very easy to balance. So it can support several
 optics. 
 2) With a Newton telecope, the eye-piece is always horizontal. 
    No need of ladders, steps, leg motions, etc. 
 3) It's easy to reach any point of the sky from
    0 to 90 deg. altitude in any azimuth. 
 4) The setup can be made anywhere, even in day-light, in a
    few minutes. No need of Polaris or Bigourdan. 
 5) Even without the control of the step-motors by the
    computer, it can be used the following way: A lot of prgrams
    give alt. and azim. So by means of the graduation circles,
    it's easy to aim the telescope onto the right point of the
    sky where the satellite will be passing. 
 Everything I use (Computer, step-motors, camera, recorder,
 etc...) is on 12v cc. So, if my car is not too far, I don't
 need the main 220v current. 
 The screen of the computer gives me in graphics
 (like with "LOGIS-CIEL") the aspect of the current sky,
 centered on the location where the first satellite
 is expected. I choose a known star for initialization. 
 The screen gives also the remaining time in minutes and,
 if I want it, a list of interresting things to be seen
 while waiting (M31, M13, Albireo, etc...)
 So in the mean-time, I can aim automatically the telescope
 in order to allow my friends to admire what they want. 
 When it remains only 5 minutes for the passage of the
 expected satellite, the computer beeps. 
 Then I ask it to aim onto the the point where the stellite
 will be passing. When aimed there, the telescope does't move
 anymore. Everybody is at his ocular. One of us has in his
 hand a kind of "track-ball" which will allow him to start
 the tracking when the satellite will appear in his field. 
 The computer beeps on a frequency. For the 60 last seconds,
 another frequency, for the 10 lest seconds, another one,
 suspense...! at the predicted instant, another beep. 
 So it's easy to see if the satellite is ahead or delayed. 
 The same track-ball gives the possibility to make
 corrections if the satellite is not well centered in the
 ocular. 
 Another program, called "VOIRSAT" (the one I sent to
 SEESAT-L as MIRVIS01.EXE) is also very interresting: 
 One example: 
 One night, we were tracking a satellite with Mr Paul
 PAQUET, the director of the Belgian Royal Observatory. 
 As the satellite remain centered, the celestial objects
 are passing in the ocular. We could see a planetary nebulae
 passing. Later on, when our observations were finished,
 we used then my program "VOIRSAT" to identify it. 
 VOIRSAT shows the sky in graphics (like with "LOGIS-CIEL"),
 stars up to magnitude 5, moon (with its phase), planets
 and the 110 Messier objects. But also the satellite moving
 amongst them! And it's very easy to identify any object near
 which it is passing. 
 Alphonse POUPLIER
 47 Chemin des Vignerons
 5100 WEPION Belgium
 Phone or FAX: ..3281460567 (BBS on request)
 E-Mail: pouplia@mail.interpac.be