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Date: Tue, 12 Oct 2010 15:26:51 -0400
From: Frank Lemoine <Frank.G.Lemoine@nasa.gov>
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Subject: [ids.analysis.forum] Jason-1 EOL Discussion Continued & Future
 Orbits Beyond Jason-3 for Jason-CS

Dear IDS Analysis Forum:

I forward below the comments from Luca Cerri (CNES)
regarding the Jason-1 End of Life proposals, and the new
orbits being proposed for the Jason-CS missions.

These topics will be discussed at the OSTST (Ocean surface
topography Science Team) meeting in Lisbon next week, October
18-22, 2010.

Those attending the meeting should be prepared to provide their
thoughts or comments on these issues (Apologies for the duplication
of posts for those who have seen this message more than once).

Best regards,
Frank Lemoine
NASA GSFC
================================================================
================================================================


Dear all,

As most of you already know, we have been asked to give our advice as
Jason POD team on  

1) a possible change of orbit for Jason-1, and a possible change of
orbit for 
the upcoming Jason-CS mission. (see attached slides in the zip folder)
2) how to maintain a 1 mm/yr drift accuracy for the Jason series,
particularly in 
preparation for Jason-3. 

 We will do our best to find the time at the end of the POD splinter in
Lisbon to 
discuss these issues and either I or Frank will present a 1 or 2 slides
summary of the 
discussion. 

Concerning issue number 1 , especially for Jason-CS, the main point in
my opinion is that
a drastic change in the orbit geometry will make the solution react
differently to errors 
in dynamical models (some examples follow below). In particular, this
would have an impact
in the calval analysis between Jason-3 (classic T/P orbit) and Jason-CS
(new orbit), 
at the 1-cm level. For example, some inconsistencies are reported now
when comparing Jason 
with Envisat data, even if orbit solutions for both missions share
common models and 
processing strategies.

Concerning issue number 2 , the POD contribution to the drift error
budget can be reduced 
by regularly reprocessing the entire series of orbits with the best
available standards.
In the near future that means updating GDR-C orbits with ITRF2008 and
the latest generation 
of GRACE-derived time varying gravity field (special care should be
taken in handling drifts 
from these tvg models). 
In order to reprocess jason orbits in ITRF2008, we will need a
consistent GPS constellation 
solution throughout the entire Jason-1 and Jason-2 lifetime. 
Willy, can JPL provide this as it was done when we switched to ITRF2005?


Thank you in advance for your comments and inputs!

Best regards

Luca

========================================================================
===============

Some comments on ISSUE NR 1 
- Moving Jason-1 to a long-repeat geodetic orbit (1288 km altitude ?
TBC) 
- Moving Jason-CS to a completely different orbit , the candidate orbit
shortlist
  would is (A=altitude, i=inclination, c=repeat cycle)
  A878_i66_c10, A926_i67_c13, A801_i71_c22 (from CLS study) 
  A640_i78_c20, A820_i78_c20, A942_i78_c20 (from UHH study) 

- Decreasing Jason-1 altitude of about 50 km should not have a large
impact on POD.
We should check however if the change in ground-track and the
long-repeat nature 
of the new orbit will require an update to SAA model

Few examples of causes of incosistencies between Jason-3 and the
follow-n Jason-CS

- Lowering the orbit while keeping similar inclination will decrease the
beta angle period.
Radial errors induced by SRP model deficiencies will not have identical
patterns between 
Jason-3 and the following Jason-CS mission

- different platform and different attitude regime might also completely
change 
the surface forces scenario that we are used to with the Jason series. 

- Depending on the satellite configuration, lower orbit means higher
drag and we might be 
at a new solar max by Jason-CS launch (2017 or so)

- Lower altitude means higher sensitity to errors in the time-varying
gravity field.
Different inclination might change the typical order-one pattern that we
have on jason.

- We might argue that with an "agressive" reduced dynamic approach we
would be able to 
compensate most of these errors on both Jason-3 and Jason-CS. But for
this we would need 
full GPS capability (no SAA loss) on both satellites and probably
ambiguity fixing processing 
schemes. Will both GPS receiver be adapted for such a challenge? 


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