An eccenctric flasher

Bruno Tilgner (Bruno_Tilgner@compuserve.com)
Sat, 10 Jul 1999 13:36:12 -0400

On 4 June 1999 at 20:33 UTC, while doing astrometric work on minor planets,
Swiss amateur astronomer Stefano Sposetti (known to SEESATTERS for his
remarkable photos of the ASTRA satellites) caught by chance a flashing
object which at first sight appeared to be a geostationary satellite but
quickly turned out to be a small object in a highly eccentric orbit which
happened to be near its apogee.

I could identify it as 92072F (catalog # 25151). It is a piece of debris
of the Ariane 4 launcher which put the US communications satellite Galaxy 7
into geostationary orbit in 1992. The orbit of 92072F is highly eccentric
(e = 0.625) with an inclination of 6.6 degrees. The apogee height was about
22 587 km, the perigee height 313 km, and the period 395 min. When the
object was observed, it was roughly at a distance of 22 230 km.

It is interesting to note that the main payload has the catalog number 22205.
This would suggest that the debris has been detected much later (in 1998).

The object showed a distinct flash pattern with brighter and fainter flashes.
The interval between successive bright or successive fainter flashes was
1.16 sec, i.e. it was a very rapid flasher.

The magnitude of the bright flashes is estimated at 9 mag and those of the
fainter ones at 10 mag.

A picture can be seen at the URL http://www.astroinfo.ch/aida/sposetti.
The filename is string_of_pearls.jpg.

On 7 July the object could be observed again at a position within 2 arcsec
of that calculated with the latest TLE from OIG. However, the brightness
was much fainter (about 13 mag) and there were no flashes with the exception
of one noticeable increase of brightness during the 20 sec exposure.

This object presents a challenge to experienced observers with the appropriate
equipment. It can be observed not only from Europe but also from the western
hemisphere. It appears advisable to observe it near its apogee.

We are attempting to capture the object again in order to check whether the
observed flashes were merely due to an exceptionally favourable phase angle
and orientation of some shiny surface or whether there is a more complex
pattern. We would also be interested to know if somebody has observed objects
in this kind of orbit and whether the approximate size and shape of 92072F
are known.


This is a joint message by Stefano Sposetti (who is not subscribed to
SEESAT) and myself. His address is;

Stefano SPOSETTI
CH-6525 Gnosca
spo@dial.eunet.ch
http://www.astroinfo.ch/aida/sposetti/



Bruno Tilgner
Saint-Cloud, France
Bruno_Tilgner@compuserve.com