Re: How inaccurate are predictions made months in advance?

JAY RESPLER (JRespler@surfnj.net)
Sun, 26 Apr 1998 05:38:09 -0400

CmdrJaycee wrote:
> For example, if, hypothetically, I came up with a good pass for Mir on August
> 31, one that might be a nice highlight for a public program, should I go ahead
> and have them schedule a program for that night (even though the precise time
> might be off a bit)?  Or is the error margin so wide that Mir might not have a
> pass at all that evening?  Are we talking of error margins of minutes or hours
> (or even days) in most cases for low earth orbit satellites?

In addition to elements being old, remember that Mir maneuvers and that
will 
throw off any distant predictions.

> What about Iridium flares?  If I see a nice -7 flare predicted for mid
> September by Mike McCants' Iridflar, is there any chance that prediction might
> still be accurate for "sometime" that evening (if not for the exact "minute")?

Iridflar is by Rob Matson.  Mike wrote Quicksat.
I find that flare predictions change when elements are just a few weeks
old.


> Is it generally true that the higher up a satellite is, the more predictable
> its pass times would be months in advance (I'm thinking here of EGP, for
> example).

Yes, that's so.  I've seen NOSS with elements that are months old. Most
bright
sats are lower and will change much sooner than that.

> I just want to make sure I haven't over-reacted to the cautions about using
> *old* TLEs, that I and maybe others are missing opportunities for public
> programs by being overly concerned that predictions made so far in advance are
> totally unreliable.  Just how unreliable are they?  As long as something will
> still be visible on a given "evening," that's all I really need to know at
> this point; obvioulsy the precise timing can be refined as the date gets
> nearer.

Check the TIM column in QUICKSAT.  That will give a good indication of
how
accurate the predictions are for several week old elements.


-- 
Regards,
Jay Respler
--
            JRespler@surfnj.net 
Sky Views:  http://njsurf.com/skyviews/
  Satellite Tracker * Early Typewriter Collector
           Freehold,  New Jersey