RE: Observations - Unexpectedly Bright Satellites

Ted Molczan (molczan@fox.nstn.ca)
Sat, 19 Oct 1996 10:17:10 -0400

3432P@VM1.CC.NPS.NAVY.MIL wrote:

>Robert Sheaffer asked if #13003 Radio Rocket has ever been observed
>as bright as Mag 3.5.  I've only seen it three times, and each time
>it was dimmer than Mag 5.  It took me many tries before I saw it the
>first time -- I was expecting something much brighter.  The
>QUICKSAT.MAG file gives it a standard magnitude of 3.5, so perhaps
>you had an optimum pass with the rocket body oriented perfectly to
>reflect the sunlight.  

First, Robert did not indicate how exhaustive a search
he conducted for matching objects. For the purpose of
this reply, I assume he used at least a recent issue
of the xxx.n2l files, and checked all of the objects in
the file.

The standard magnitudes in Quicksat.mag are maximums,
at 1000 km, 50 percent illuminated. At the time of
Robert's observation, the Radio r (81120G/13003) was
about 1970 km distant, and about 37 percent illuminated.
This would result in a maximum magnitude of:

3.5 + 2.5 * log10((1970/1000)^2 *0.5/0.37) = 5.3

My program, Predict 1.7, predicts a magnitude of 7.3, but
this was based on a mean std mag, so a maximum that it
2 mags brighter is believable. However, the observation was
1.8 magnitudes brighter than the predicted maximum. 81120G 
is one of many Tsyklon stages in orbit; so I checked 
quicksat.mag to find the range in maximum magnitude - I found:

max
mag  count
3       2
3.5    89
4     155
4.5    36
5      15
5.5    14
6      18
6.5     4

So it would be much more probable for the standard magnitude to 
have been fainter than brighter; however, the Quicksat manual
states that satellites can be brighter than the predicted maximum
magnitude if they reflect the sun better than expected at a given
phase angle. In my experience, a related factor is azimuth and
elevation. 

I have observed that many objects flare up in brightness when
observed high in the W or NW, not long after twilight. I believe 
it occurs when the object is at about the same azimuth as the sun.
Those circumstances existed at about the time of Robert Sheaffer's
observation. I recommend scheduling observations of 81120G under
similar conditions to see if it flares up.

In conclusion, I believe that although the probability is low, the
observed object could have been 81120G. Further observations may
help resolve the question. Also, others may be able to comments on
their experience observing Tsyklon stages.

Ted Molczan