GOES-S Turns ‘Seventeen’

GOES-S was launched on March 1, 2018 into a Geostationary Transfer Orbit (GTO).  This mission unlike many we follow was not classified but does use the Lockheed Martin A2100 satellite bus.  A favourite of the US military, so studying it on a non-classified mission could prove interesting.

Active Doppler Curves!

Unlike what we have seen in the past with A2100 buses GOES-S had a very dynamic Doppler curve.  Locked curves, unlocked and even states in between it seemed.  We’re still not sure what all this activity meant but we are carefully considering its meaning.

Pass 1: Dynamics reveal themselves for the first time, brief periods of what appear to be unlocked behaviour reveal the true Doppler behaviour and allow for radio tracking (white dots).
Pass 2: Still intense dynamics on the TT&C downlink.

Final Approach to GEO

As GOES-S reduced its Mean Motion on almost every apogee, there came a time when it was likely going to go for GEO insertion.  Unfortunately this timing occuring after Sun rise at my location.  But prior to that I was able to track the satellite both visually and by radio as it approached its final GTO apogee.

Screenshot - 18-03-12 - 01-11-06 AM
GEOS-S hours before it arrive in GEO orbit as seen visually.  This is five frames superimposed to see the difference between the stars and the interlopers…
GOES-S animation as it approaches GEO orbit.

GOES-S entered eclipse and I reduce my observations and derived a TLE as Space Track always seemed to be at least a day or more behind current spacecraft activity.  My efforts told me to aim at 99W for the next apogee.

At about March 12, 2018, 18:47 UTC, GOES-S became GOES-17 by arriving in GEO orbit. Notice the abrupt change in Doppler characteristic from a sinusoidal pattern to almost flat line.  The end of the sinusoidal pattern is characterized by period, for a couple of hours, that seems somewhat chaotic as it presumably fired its thrusters for the last push to GEO.

Mystery of the Wobbly Doppler Curve…

GOES-S displayed a very dynamic Doppler curve, the most dynamic we’ve seen.  To be fair we largely follow the classified launches so this demonstrates some kind of difference in how the military and security establishment control their spacecraft versus the civilian variations.   The answer may be in the TDRS constellation.

GOES-S like a fine upstanding young lass takes the time to visit the retired TDRS-1, 13969 just before making a run for GEO.

Ironically, during the rise of GOES-S it passed by a retired TDRS-1, 13969 and presumably dead satellite data relay mission.  You can’t seem to swing a faulty coax patch cord these days and not hit a ‘dead’ NASA satellite!

Author: Scott Tilley

Amateur visual and radio astronomer, radio amateur VE7TIL

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