how visible is a pass?

Walter Nissen (dk058@cleveland.Freenet.Edu)
Fri, 2 Oct 1998 11:00:15 -0400 (EDT)

In response to one of my occasional Mir/Shuttle/(ISS) alerts for Cleveland 
and DC, one of my correspondents, who has not been asked for permission to 
disclose his identity, writes: 
 
> Thanks for the note. Why does www2.gsoc.dlr.de only list the 9:42 pm ED= 
> T pass 
> while www.hq.nasa.gov/osf/mir/a.html only lists the 8:20 pm EDT pass fo= 
> r 
> tonight. 
> I would think that both passes should be visible naked eye and both sit= 
> es 
> should list 
> both passes. Just curious. thanks. 
> = 
 
I respond here because my answer may be of interest to some part of the 
SeeSat-L readership. 
 
For some reason, your mailer didn't generate plain ASCII text. 
 
I don't think I've ever used either site which you mention, so I can only 
comment generally. 
 
The problem of screening passes for visibility is a central problem. 
Generating a correct rating is very, very difficult.  Even with such a 
rating, a cutoff must be imposed.  Implemented programs are far from 
ideal, often very far from ideal.  Most do not actually rate, but merely 
impose various criteria.  Unless these criteria are very elaborate, they 
will be quite imperfect. 
 
Superficially, each pass must have violated some criterion. 
 
My ancient and reliable version of QuickSat generates: 
 
  41.374  81.864  840.    Nissen, OH            1950 17.5  2 F F F F F 
***  1998 Sept 29  *** Times are UT ***   0 2 1031 
16609 Mir Complex                       .1  -3 
 
 H  M  S  TIM AL AZI C   U  MAG   REVS  HGT SHD  RNG  EW PHS  R A   DEC 
 0 26  8   .1 42 331 C  62  -.1   40.8  371 224  541 2.2 106 1410  68.7 
 2  0  1   .1  8 307    71  4.9   41.8  370  28 1507  .7 140 1341  32.6 
 
At an unfavorable phase angle, the second pass of Mir was most likely even 
more difficult than suggested by the predicted altitude and magnitude. 
 
Because the GSOC site generated an incorrect time, it must have been given 
incorrect data, probably observer location data; or have had a bad or old 
elset for Mir; or (not strongly indicated by this example) use very rough 
criteria. 
 
Cheers. 
 
Walter Nissen                   dk058@cleveland.freenet.edu 
-81.8637, 41.3735, 256m elevation 
 
--- 
 
On 1901 September 14, President William McKinley died of a gunshot wound. 
45 days later, 1901 October 29, assassin Leon Czolgosz was executed for the 
crime, as the American people put the matter behind them and got on with the 
business of the country.  Of course, there were fewer lawyers then, and 
less concern then for the rights and privileges of a little guy than for 
the rights and privileges of a president now.