[RADS] Fwd: T/P - Jason close encounter

Remko Scharroo remko at altimetrics.com
Thu May 8 01:58:16 CEST 2008

Dear RADS users,

I'm forwarding this message from Lee-Lueng Fu to warn you that there  
will be a data outage in the Jason-1 data.
The Jason-1 IGDR data generally makes it into RADS with a delay of  
about 3 days, so you will first notice no additional data for Jason-1  
on 10 May.
This will mean that the current cycle, 233, will remain incomplete.  
The data should pick up just before the end of that cycle.

Meanwhile, the we're up to cycle 228 with (final) GDR data.


Begin forwarded message:

> From: Lee-Lueng Fu <llf at jpl.nasa.gov>
> Date: 7 May 2008 16:52:07 EDT
> To: Ocean Surface Topography Science Team <ostst at list.jpl.nasa.gov>
> 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.
> -------------------------------------------------------------------
> -------------------------------------------------------------
> Lee-Lueng Fu
> JPL 300-323
> 4800 Oak Grove Drive
> Pasadena CA 91109
> FAX:818-393-6720. VOICE: 818-354-8167

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