Re: Site information why elevation.. (fwd)

=?ISO8859-1?Q?Bj=F6rn_Gimle?= (b_gimle@algonet.se)
Thu, 10 Jun 1999 18:06:14 +0200 (CEST)

My apologies - my comment was in two parts, terribly formatted, and the first part sent to the wrong recipient!


> This all presumes the elements and predictions have that kind of
> accuracy. ... I mean do your common week old elements for a LEO satellite calculated
> with SGP4 give you a positional accuracy around 100 meters, or 1 meter,
> or 1000 meters??

Your prediction elsets may be bad, but from high-precision 
observations you can generate better elsets. Of course, if 
the observations are spread out over time (or the elsets 
used long after the observations) they are subject to the 
inherent approximations in the elset/prediction model, and 
the variability of solar flux/atmosphere and magnetism.

> My experience with the shuttle and MIR is that when you use the "latest"
> elements for both objects (but dated just one day apart) when they are
> actually docked, give positions up to 5 km apart. That's .3 degrees at

... and my experience is that published elsets are bad in period and even more
in drag, fluctuating much more than the physical reality. 
If you take observations ( I've done it with KHs and Lacrosses) or predictions
near (a  tracking station along the orbit at) the epoch, for several elsets
to generate one new elset, it can be valid within about 1 km or less during
the period (tried it with Starshine).


Björn



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-- bjorn@tt-tech.se (office)  b_gimle@algonet.se (home)      --
--                            http://www.algonet.se/~b_gimle --
-- COSPAR 5918, HAMMARBY, 59.298 N, 18.104 E, 55 m           --
-- SeeSat-L / Visual Satellite Observer Home Page found at   --
-- http://www.satellite.eu.org/satintro.html       --