Re: Different flash period for 95 58B?

Bart De Pontieu (BDP@MPE.MPE-GARCHING.MPG.DE)
Wed, 17 Jan 1996 01:11:11 +0100 (CET) 

Matthew Francey <mfd@angoss.com> writes in seesat-l/1475 :

>this brings up a small question:  asteroid observers can determine, to some
>extent, the spin axis of the body by digesting light curve data acquired
>under different viewing geometries.  has this been attempted for objects
>in earth orbit?  would it even be useful to do?

It has been attempted with varying degrees of success almost since the
beginning of the space age. I can give you a list of references, if you're
interested (+ I have xeroxes of all the articles, some of them are in pretty
hard-to-find publications like technical notes of NASA, etc...). 

R.H. Giese published 2 or 3 papers in the 1960's, as did
H.R. Simpson, both of whom use timings of specular reflections. Their
efforts were limited by the computer technology of the that time.
Williams (and Meadows) published a few articles at the end of the 1970's
which assumed diffuse reflections and used amateur visual observations from 
the UK. Their measurements were based on magnitude estimates of the maximum
and minimum magnitude of a tumbling rocket. Though he finds some interesting
results, I think the required accuracy in estimating the magnitudes is just
a bit too high to make this method practical.

The most recent professional effort that I am aware of is by Graham Appleby
of the Satellite Laser Ranging Team in Herstmonceux. He used the telescope
that is usually used for geodetic research (observing sats like 86- 61 A/EGP)
and obtained a rotation axis for 87- 41 B, a notorious Zenit flasher, by
using recorded photometric data. This is not really in the realm of amateur
observations, but that may change in the next few years. I think it's safe
to say that in the 60's there were more efforts to use visual data to
determine a satellite's attitude since it was sometimes the only way of
knowing where the satellite was pointing to. I remember an article about 
Tiros 1 by Bandeen and Manger in Journal of Geophysical Research.

There have also been some publications in German. Notni and Oleak worked
on this problem in 1959 already, applying it to the Sputnik 3 rocket.
Hermann Boehnhardt (currently working in ESO) told me he published some
results (in German) during the seventies.

R.J. Gregg from Escondido, California has been trying to promote a
satellite observing project in high schools all over the US. In this
project the goal would be to observe the Pageos rocket (66- 56 B) in 
order to obtain the direction of the rotation axis. I haven't heard
from Rachan in a long time, so I don't know what the current status of
his project is. Maybe he's even on seesat-l ?

Finally, I've published some stuff on a new method for determining 
rotation axis directions from timings in Flash, the english language
newsletter devoted to satellite observing. I described the results of
observations of Mike McCants, Walter Nissen and myself, with which we
were able to determine the direction axis of 91- 29 B and 82- 40 J (if
memory serves me well). I am preparing an article for a refereed journal
on this work. We (= the flash period observers of the BWGS) have also
started a project to follow-up on this work, called DRAP (Determination
of Rotation Axis Project) in which we follow just a few sats intensively.
This project is currently dormant, but we hope to get it started again in
spring. You will hear more about it than you would probably like on 
seesat-l :-)

As to your question whether it would be even 'useful to so', I think that
is ultimately a question of taste. Is it useful to know that some
asteroids rotate and in which direction the rotation axis points ? It
surely is, though I'm not too interested in it. I'm more interested in sats,
and am very much interested in trying to understand what happens with
discarded rockets, rotation-wise. There seem to be a few puzzles left, one
of which are the 'accelerations' you hear so much about on seesat-l these
days. I believe measuring the rotation axis during such an acceleration will
greatly improve understanding of the process involved. 

But, and now I will finish this long message, measuring flash periods and
playing around with the data is *fun*, and that's probably the first and
foremost reason why the 35 BWGS observers keep measuring flash periods.

Cheers,
   Bart