DRA-report: 95- 32 B top-priority

Bart De Pontieu (BDP@MPEPL)
Sun, 05 May 1996 22:20:35 +0100 (CET)

I would like to ask that all flash period observers mark 95- 32 B (23604,
Cosmos 2315 r) as absolute top-priority. I am now restarting the DRA project
(Determination of Rotation Axis) with 95- 32 B currently as the only satellite
that we track. In a few weeks time I may consider adding some other satellites.
Note though that you should still send in your DRA obs of any other object
you happen to see/record. It's just that 95- 32 B should get highest 
priority as far as DRA obs go.

Using the DRA observations of Walter Nissen and Leo
Barhorst during April, I was able to relatively accurately determine the
direction of its rotation axis on 4 days. I would like to follow up on this
object so that we can track the motion of the rotation axis as a function
of time. 

I am preparing a longer article for the upcoming issue of Flash (which will
be placed on the VSOHP Web-pages at the end of this month) about the analysis
of the observations. The observations of Walter on April 11 and 18 both
happened to show a synodic anomaly, which allowed me to determine the
rotation axis with an accuracy of 0.5 degrees (note that my earlier analysis
of Walter's April 11 obs was off by a few degrees, since I placed him in
Maryland, instead of in Ohio :-). The observations of Leo (20th)
and Walter (21,22) were combined in pairs to get a rough idea of the direction
of the rotation axis (with an estimated accuracy of 5 to 10 degrees). There
are still two general solutions for the rotation axis which I can not 
discriminate, even though they are not at all times at opposite ends. The 
motion of the rotation axis is nicely visible in a GIF I put in the 
ftp-archive of Oxford. Location:
ftp://ftp.physics.ox.ac.uk/pub/sat/bwgs/9532b.gif

Or get it uuencoded through e-mail by sending a message with the words 
"archive get obs/9532b.uu" (without the quotes) in the SUBJECT field to
SeeSat-L-request@iris01.plasma.mpe-garching.mpg.de

The GIF shows a projection of the celestial globe with a coordinate grid
of right ascension (running from -180 to +180) and declination (-90 to 90).
Overplotted on the grid are the positions of solution 1 of the rotation
axis (full black dots, connected by lines), solution 2 (stars, connected
by lines) and the position of the normal to the orbital plane (crosses).
The rotation axis moves at about 3 to 4 degrees per day, which is of the 
correct order of magnitude if one assume the torque due to the gravity gradient
plays an important role in the temporal evolution of the rotation axis
direction. 

What happened in April, I think, is that Walter had the good fortune to
observe 95- 32 B at a time that its rotation axis was pointing at a 
direction which roughly coincided with the direction of the bisectrix 
between the vectors satellite-sun and satellite-observers. This allows the
observer to see a synodic anomaly. Some time later the rotation axis had
moved through that region and the synodic anomalies disappeared. The
subsequent observations did not show any synodic anomalies, but a clear
synodic effect, allowing relatively precise determination of the rotation
axis. 

I will in the near future try to develop a model that integrates the temporal
evolution of the direction of the rotation axis using theoretically derived
values for the external torques acting on the rocket body. This could lead
to a decision on which solution describes the real rotation axis.

What I need for my DRA analysis is:
Date of obs, location of observer (latitude and longitude), start time of
the obs, and all times of the flashes measured with respect to the
start time. The times should be given with an accuracy of 0.1 seconds.

Preferred are *long* series of timings. The best would be to track the
satellite from horizon to horizon. If you have a chance to observe the
satellite several times on successive days, try to observe passes that
do not have the same illumination conditions. E.g. don't always observe
low northbound passes, or only zenital passes. Try to vary as much as you
can, this greatly improves the accuracy of the determination of the rotation
axis. 

95- 32 B is currently not visible from moderate northern latitudes, but
will become visible in the middle of May, in the mornings. This visibility
period lasts until the end of July for observers at +50 degrees latitude.
It would be great if we could collect a great number of observations
until then.

Most recent elements from OIG:

1 23604U 95032B   96124.06755442 +.00000015 +00000-0 +00000-0 0 01083
2 23604 082.9054 132.8796 0027245 139.5609 220.7581 13.73606451041583

And if this helps your motivation, your observations will be used for 
(acknowledged) an article which I am preparing for a refereed scientific 
journal.

I am always available for questions/remarks.

Cheers,
    Bart
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Bart De Pontieu --  Max-Planck-Institute for extraterrestrial Physics, Garching
bdp@mpepl.plasma.mpe-garching.mpg.de -- http://www.rzg.mpg.de/~bdp/eurosom.html
        "Can you take me back where I belong ?" -- Lennon/McCartney
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