Message-ID: <482905AF.2030407@nasa.gov>
Date: Mon, 12 May 2008 23:06:23 -0400
From: Frank Lemoine <Frank.G.Lemoine@nasa.gov>
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To: ids.analysis.forum@cls.fr
Subject: TOPEX/Poseidon and Jason-1 Close Approaches.
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Dear Colleagues-

For the record, I provide below the status message from the OSTM project 
scientist,
Lee Fu, regarding the close approach of Jason and TOPEX. Note the 
comment that
the altimeter was turned
off during the conjunction period, however presumably DORIS data was not 
interrupted.

At least one SLR station (Riga) detected laser returns from the derelict 
TOPEX spacecraft
at about the right time.

Regards,
Frank Lemoine
=================================================================
From: Lee-Lueng Fu
Date: May 7, 2008 4:52:00 PM EDT
To: Ocean Surface Topography Science Team
Subject: T/P - Jason close encounter

Please note the following message forwarded from Glenn Shirtliffe, the 
NASA Jason Project Manager.

------------------------------------------------------------
TOPEX/Poseidon (T/P) was decommissioned in orbit in February 2006, and 
has been adrift ever since. On 07-May, T/P was about 7km (4.3 miles) 
behind Jason in the same orbit plane and was closing. In terms of time 
separation, T/P trailed Jason by about 1 second.

The relative along-track phasing between Jason and T/P will soon result 
in a period of close approaches. Ten events on 08-09 May have been 
identified where TOPEX will violate a 1-km watch sphere around Jason, 
with the closest approach of 294 meters occurring on 09-May at 0239z.

The risk of collision between the two spacecraft is exceedingly small, 
so no collision avoidance maneuver is required. However, there is a 
significant risk that when T/P drifts below Jason that it could reflect 
the Poseidon-2 altimeter signal back at Jason at almost full transmit 
power, seriously damaging the altimeter’s front-end receiver.

To mitigate this risk to the Jason mission, CNES has decided to turn off 
the Poseidon-2 altimeter on Jason for the duration of the close 
approaches between Jason and T/P. The period of the altimeter turn off 
will be from 07-May-2008 at 1752 UTC until approximately 13-May-2008 at 
0715 UTC.

During this period, no Jason OSDR or other science products will be 
available.