Subject: Sky Sensor 2000 Tracks Mir

From: (Paul Laughton)

Date: 1997/10/05

Message-ID: <>

Newsgroups: sci.astro.amateur

This evening (10/4/97) the Vixen Sky Sensor 2000 was used to track the 8:00PM pass of Mir over the San Francisco Bay Area. The Sky Sensor 2000 was mounted on a Super Polaris mount which itself was under an AP Traveler.

The latest TLE Orbital Parameters for STS86 and Mir were obtained and entered into the SS2000 via the SS2000 keypad. This was not a very difficult job. I could have used a PC for the data entry, but the keypad seemed simpler than obtaining a cable and trying to get a PC to SS2000 comm setup. I was careful to verify that each the parameters were entered properly. I was also careful to make sure that I had my exact latitude and longitude plus time-of-day entered. The SS200 manual says that a five second t-o-d error can cause a significant tracking error.

As soon as the data was entered, I could see the SS2000 was keeping track of both objects. I could watch the objects' alt/az changing in real time on the display. It was clear from the alt/az that both objects were somewhere on the other side of the world. In addition, the display was showing me the altitude and speed of the objects.

Next the mount was set up with the Polar Axis approximately parallel to the expected path of the objects. The SS2000 manual recommends doing this sort of setup for satellite tracking to avoid the OTA reversal required when crossing the meridian. In this case, the polar axis was set approximately 45 degrees east of true north.

A three-point alignment was performed using Jupiter, Altair and Arcturus. I then did a GOTO to Jupiter to watch the GRS slip around the planet's edge while waiting for the objects to come over the horizon. At just about the right time (7:59), the Mir alarm went off quickly followed by the STS86 alarm. Mir was selected and the GOTO key hit. The mount slewed somewhere off the South West near the horizon and started tracking.

Mir was sighted visually at about 10 degrees altitude and appeared to be about magnitude 2 to 3. Looking through the Traveler finder scope, I could see that Mir was being tracked a bit low of center. A couple of quick key presses centered it. I then started observing through the 22mm EP. The tracking was fairly smooth with a quick key press needed from time to time to keep Mir centered. As I watched, Mir brightened considerably to something over magnitude zero. It was a bit strange watching this bright object staying more or less stationary while the stars zooming by. It felt a bit like being in the Millenium Falcon chasing an X-Wing fighter. About the time Mir neared the meridian, the tracking started to get rough. The object stayed centered, however the tracking had become a very pronounced and fast zig-zag resulting in bright streaks rather than a bright spot. Soon thereafter, the Mir was gone over the local horizon of houses and trees. Note: the 22mm EP did not provide a lot of magnification, so no Mir detail was observed. Neither did I see STS86. Next time, I will have more confidence in the SS2000 tracking abilities and use a higher magnification EP.

After the Mir pass was over, I decided to check how well the SS2000 could locate objects being this far out of Polar Alignment. The SS2000 alignment data showed that the mount was pointed 42 degrees east of North and 3 degrees high from ideal polar alignment. A 4.8mm EP (129x) was inserted and GOTOs performed to Saturn, M31, M15, M13, M57 and M13. All appeared in the FOV. While observing M13 a nice, bright meteor flashed by. It was a very enjoyable hour with my new toy.

Cheers, Paul


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