Re: ephemeris server

Jim Varney (
Tue, 31 Dec 1996 23:04:16 -0800

Walter Nissen wrote:

>Atta'boy, Jay.  It certainly seems worth the trouble to me.  It also seems 
>that an ephemeris server to run it, together with a team of computors and 
>updaters of orbits, would make a great deal of sense.

Ted Molczan replied:

>The best way to make me lose interest in this hobby is to make it into a
>job. I already have one of those, and one is enough! (Hmmm, perhaps I 
>have stumbled upon Molczan's 2nd law.)

You're right, but i think it was discovered earlier by someone who 
found that interest in the hobby remains but wanes in the 'job.'  
It should be known as Bart's Law  :)

There's no free lunch with an ephemeris server.  If the goal of the server
is to provide more accurate predictions that what we have now, then there 
are two choices.  One, you can use the simplistic, low-accuracy SGP or 
SGP4 propagators which require relatively little computing power but a 
lot of manual labor (by your orbital all-star team) in order to keep 
the predictions accurate for those objects that don't fit the SGP/SGP4 
models well.  Which means anything with an eccentric orbit, a low perigee, 
a resonant orbit or a negative pseudo-drag term.  Not to mention 'active' 
objects like STS that change their orbits frequently.

Or, two, you could run one of the expensive sophisticated propagators/
integrators on an equally expensive workstation.  That would require 
somewhat less elset-tweaking and intervention.  Choice two is a case of 
substituting money for labor.  

Which leads me to my wish for '97: that there be a new 'standard'
propagator to replace the aging SGP/SGP4, and a new elset format to go
with it.

Happy New Year

 -- Jim

Jim Varney       | 121^ 23' 54" W,  38^ 27' 28" N   |           Sacramento, CA
Member, SeeSat-L |           Elev. 31 ft.           |                         
Member, Sacramento Valley Astronomical Society      |