Re: C* 1953, C* 1933 family and solar panels

Bart De Pontieu (BDP@MPE.MPE-GARCHING.MPG.DE)
Sat, 04 Feb 1995 22:26:59 +0100 (CET)

Walter Nissen wrote in seesat/115 :

>> Subject: 88- 50 A (Cosmos 1953) discovered flashing
>Whoops!  Didn't I mention C* 1953 at some point?  It is presently one of
>the more spectacular objects in the C* 1933 family.  If there are no
>earlier reports of flashing, then the ones below tell a very, very
>interesting story.  And I am embarrassed for not (?) reporting it.

Thanks for the report, Walter. The flash period database (PPAS) of the Belgian
Working Group Satellites (BWGS) did not contain any 'flash'-observations of 
88- 50 A. 
This means that either :

a. You didn't report them.

or

b. I failed to transmit your observations through to Tristan Cools (who 
   collects the flash period observations for the BWGS, and is not yet on 
   Internet). I may have refrained from sending them through if they were 
   not in the PPAS format. (for details on that format, 
   send a message with Subject: archive get ppas/ppas4.txt to 
   seesat-l-request@iris01.plasma.mpe-garching.mpg.de)

>1)  These large, valuable payloads use propellant to stabilize during
>their useful life.

I wonder how many satellites use propellant to stabilize. What about
gyros and magneto-torquers/reaction wheels? 
 
>2)  At some point, possibly terminating their useful life, they suffer
>catastrophic failure of attitude control, often (?) due to exhaustion of
>the propellant supply.  

Or failure of the gyros (remember the gyro-problems HST suffered from?) ?
 
>3)  Thereafter, eddy currents within the object and the Earth's magnetic
>field slow the rotation and eventually end virtually all the flashing,
>except for, (is this the right term?), synodic effect.

The term 'synodic effect' is, I think, usually used to indicate the 
difference between the *flash* period (measured by the observer) and the
*rotation* period. If the flashing has virtually ended, this means the
rotation period has become extremely long, longer than the duration of a
pass.

>I'm most interested in receiving observations of these, including radio
>monitoring to confirm operational intervals.  BDP was kind enough to
>provide the PPAS observations (in overwhelming quantity.  I keep trying).

The BWGS (reachable on the Internet through me) is also very interested in 
receiving observations of these, or in fact any flashing satellite :-) 
 
>According to BDP, you can see full solar panel reflection from an
>operating satellite.  I question this based on efficiency (it has to be
>pointed at the Sun)

Other mission constraints can cause a slight inclination of the solar
panels with respect to the direction of the sun, I've been told. A 25
degree deviation from the optimal causes only a 10% reduction in energy
received. In case a 25 degree deviation is present, you could see a 'full
solar panel reflection' for phase angles down to 130 degrees (depending
on the exact geometry). Hardly impossible, I'd say.
 
> and experience (I can't think of many examples of
>really bright flashers). 

Haven't there been reports of extremely bright flashes from HST and Topaz
on sci.astro?

Cheers,
   Bart