2017 Mar 24
Friday, Day 83
While monitoring SGLS Channel 10 for signals from the STSS Demonstrator Satellites, a novel signal turned up 2009 Sep 25, obviously a satellite because of the well-defined Doppler curve.
A search of possible candidates turned up NOAA 11 as the possible source. Pass times on subsequent days confirmed the identification.
Discovery of Transmissions
It was first detected from here 2009 Sep 25 a little after noon UTC. About five hours later it was detected on a pass across the continental US by Lyn Kennedy in Texas.
Transmission seems not to be continuous as it not detected on all passes. Whether on or off seems independent of lighting conditions on the orbit.
It is unlikely that it has recently come back on air, it has probably just not been noticed as there are few observers regularly monitoring S-band. Its discovery now is down to concentrating on SGLS 10/2247.5 MHz in the search for the STSS Demonstrators satellites.
NOAA 11 is not a new satellite, having been launched 1988 Sep 24. It was deactivated 2006 Jun 16 and its status according to NOAA is "power depleted, batteries disconnected, transmitters turned off......".
Like other old satellites, something has occurred to cause electricity to reach the transmitter. NOAA 11 seems to be spinning which produces the effect of the signal switching on and off every few seconds. In the trace below, the time interval between successive switch ons is about 8s and the cycle is not regular. Lyn Kennedy timed the cycle period and concluded that it averages 7.4s.
The plot below shows a whole transit. Between 13:08 and 13:10, it completed 14 cycles of switching, equivalent to 8.5s per cyle.
NOAA's Use of 2247.5 MHz
Since the discovery of NOAA 11 on this frequency, the currently active NOAA 18 has turned up also but with a clean signal. In the operational manual, 2247.5 MHz is said to be used during the ascent phase of the mission and as a backup route for data from the TIP instrument aboard the satellites.
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