RE: smap 15-003A/40376

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Sun, 7 Jan 2018 13:03:11 -0500
Tristan Cools wrote:

> My first satellite observation of 2018 today at 16:56UTC: 2015-03A/40376 or
> the NASA satellite Smap is tumbling with a period of about 1s.  No
> chronograph with me.
> 
> The satellite was already a failure almost 6 months after launch, it had a
> large dish antenna.  I wonder, with a tumble like that why it hasn't been
> torn of in the meantime...

I suspect that the regular variation in brightness is due to the satellite's rotating antenna:

https://smap.jpl.nasa.gov/system/internal_resources/details/original/178_SMAP_Handbook_FINAL_1_JULY_2014_Web.pdf

"The L-band SAR and radiometer share a 6-m mesh deployable offset-fed reflector antenna that rotates at 13 to 14.6 rpm
to provide high spatial resolution with a 1000 km measurement swath that enables global coverage every 2-3 days..."

SMAP Antenna Beam Footprint: https://smap.jpl.nasa.gov/resources/61

The L-band radar failed in July 2015, but the radiometer continued to operate, presumably still fed by the rotating
antenna:

https://www.nasa.gov/press-release/nasa-soil-moisture-radar-ends-operations-mission-science-continues

Ted Molczan


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Received on Sun Jan 07 2018 - 12:03:58 UTC

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