Mir Marathon / computer-assisted tracking

Mon, 2 Jun 97 15:38:09 PDT

Greetings everyone.

About a week ago I mentioned that some observers might be able to have
a Mir Marathon, with a chance to see up to 6 passes in one night.  I
had an oppourtunity to see six Mir passes Saturday night, but clouds
wiped out one low pass (elevation 5 deg) so I had to settle for 5.  The
first and last passes were spectacular.  I was at a dark sky site, Fremont
Peak, south of the San Francisco bay area, along with several dozen amateur
astronomers and members of the public attending a star party at the
observataory there.  The first pass exceeded -3 mag, low in the SE about
35 minutes after sunset, and had an excellent phase angle.  Everyone
seemed to enjoy the pass, and quite a few of the people asked questions
about how fast it was moving, how high, when was it launched, etc.  When
I told them it was going around the earth every 1.5 hours, but was staying
sunlit the whole time, they expressed amazement (and some skepticism until
I explained why).

The last pass for the night was about 1 hour before sunrise, with Mir
streaking by almost directly overhead.  Too bad I was the only one at the
mountaintop crazy enough to stay awake to see it!

I saw 89 satellites that night, most of which were small debris pieces
not visible to the naked eye.  I glimpsed a few satellites I hadn't planned
on, since one bay area astronomer brought his 8-in Meade LX-200 scope
that was being driven by the C-Sat satellite tracking software (more info
about C-Sat is available at www,skyshow.com).  At first he had problems
getting the rig to track correctly, but by adjusting a few parameters
he managed to get it working ok. As a test, I suggested he try to track a
few dim debris pieces and the scope slewed to the correct locations and
tracked them very well.  It's not capable of keeping a satellite dead-center
as it tracks; It uses a "leap-frog" method where after the satellite passes
through the field of view, the scope slews ahead a bit and stops, waits for
the satellite to travel through again, and then repeats the process.

I found that the leap-frogging would make it difficult to make accurate
flash measurements if the satellite is moving rapidly, but as the slant range
increased the scope could keep the object within the .4 deg field of view,
even when it was slewing ahead.  A few other objects were tracked, including
the recently launched Goes geostationary weather satellite, and the Vanguard
2 rocket body, before the batteries on the laptop computer (a 50mhz 486) began
to wear down (they weren't fully charged to begin with).

Overall, I was impressed with C-Sat, but the configuration has a few
problems;  Due to the way the Meade scope is designed, sometimes when
tracking a satellite it would have to stop and begin slewing all the way
around almost 360 degrees before it could continue tracking.  I was told
that this was necessary to avoid stretching some sort of electrical cord
on the scope.  The interface seemed workable, but could use improvement
in the way a satellite is selected.  It has no point-and-click ability
to select a satellite from the list of objects currently above the horizon;
You must enter the NORAD (USSPACECOM these days) number manually.  This
will probably be fixed once it is converted from an MS-DOS application to
to Windows, which I'm told is in the works.

Another problem that really isn't C-sat's fault is that fresh elements
are a must when you are tracking a moving object and only looking at
about a .5 deg field.  We tried to lock onto Lacrosse 2 as it made a pass,
but the elements for this classified object were too old (48 days) for
it to cope.

There are some mechanisms that allow you to adjust the scope a bit as
it tracks to compensate for variances, but with Lacrosse it was beyond
the scope of the software to bring it into view.

I was having a lot of fun with that C-sat/Meade combo for about 1/2
hour, until we had to shut down the laptop for the night.  With a heavy
heart, I trudged back to my low-tech 4.5 inch second-hand newtonian
(my "Satellite Bazooka") and resumed my manual, and now seemingly
archaic, satellite hunting.  As I close in on my goal of seeing 2000
different objects, I can't help wondering how much more quickly I could have
done so had I had such a rig when I started observing two years ago; but
then again, I've had a wonderful time bagging satellites the old-fashioned
way, and have learned more about the night sky in the process.  Some of
the stars that used to be anonymous are now old friends that I know by
name, thanks to Rob Matson's Skymap.  Rob, I know I told you last month I'd
be registering Real Soon Now, so I'm publicly promising to send in my
contribution this week!  Just in case anyone else wants to register their
copy, the address has recently changed to:

Rob Matson
SkyMap Software Registration
232 Santa Ana Ave.
Belmont Shore, CA 90803

Please excuse the 'commercials'.  I'm not affiliated with C-sat or Skymap
in any way.

 Craig Cholar    3432P@VM1.CC.NPS.NAVY.MIL
 Marina, California
 36 41' 10.3" N,  121 48' 17.9" W     (+36.6862, -121.8050)      UTC -7