Description of L2 in STC

[Rob Seaman]

Hi Hervé,

> L2 point is 1,500,000 km not 150,000... just a factor 10 father ;-)
> 
> And this is only a rough estimate since a satellite moves along an orbit around this point (a Lissajous for Herschel, another kind for JWST :
> http://www.stsci.edu/jwst/overview/design/orbit.html )

I read the 150000 km to mean a tolerance about the L2 point.  Knowledge of the observation epoch will index into the moving location of L2, and he's saying that high precision beyond this isn't needed for this application.  The part about constructing "their own complex location" (I think) implies that separately conveyed knowledge of the particular spacecraft's orbital parameters (epicycles within epicycles if you will) can later recover the precise location in the solar system.

I'd be interested to learn how STC represents the precise location for complex situations like this, but not all applications require that such precision be carried around with each individual data product.

Rob
---
> Le 16/04/2011 01:05, Roy Williams écrivait :
> 
>> Arnold and DM group
>> Can you advise on Wil's question, that has come up on the VOEvent RFC page?
>> Thank you
>> Roy
>> 
>> -------- Original Message --------
>> Subject: Re: Can you help with VOEvent2?
>> Date: Thu, 14 Apr 2011 11:49:04 +0200
>> From: William O'Mullane <womullan at sciops.esa.int>
>> To: Roy Williams <roy.williams at ligo.org>
>> CC: Nicholas A Walton <naw at ast.cam.ac.uk>, Lukasz Wyrzykowski
>> <wyrzykow at ast.cam.ac.uk>, "R.Burgon" <r.burgon at open.ac.uk>
>> 
>> in 3.4.2 ObservatoryLocation
>> You should add "L2 = within 150000 KM of Earth Sun Lagrange Point 2" or
>> something there are enough missions going out there even if you suggest
>> space missions can construct their own complex location later.