Orbital Focus - International Spaceflight Facts and Figures
carousel image
STSS Demonstrator Mission

Tyneside, UK
2022 Aug 15
Monday, Day 227

Curated by:

STSS Demonstrator:


Description of missile detection and interception system

STSS Demonstrator home page
Ground Station Frequency Lock - A Special Case

During the course of a pass by this location of STSS Demonstrator SV2 on 2009 November 17, the normal Doppler curve was disrupted by a sudden change of frequency that reverted after a short time.

At 23:27:13 UTC, the received frequency suddenly hopped downward by 38 kHz. Then, at 23:28:38, the status quo was restored when it jumped upwards by 41 kHz. It was as if the satellite's receiver had responded to, and locked onto, an uplink for a few seconds but the large frequency jump indicated that it was not the usual nearby ground station to the Zarya location.

Lock to Thule


1 - The jump was quite large and downward in direction initially, suggesting that SV2 had passed by the ground station sometime earlier and that the relative Doppler shift was negative. Had it been the nearby UK ground station then a much smaller change would have been involved.

2 - The downward and upward steps were unequal, re-inforcing the idea that a ground station was involved. The larger upward step indicated that SV2 had moved further away from the ground station during the locked-on period and that the relative Doppler shift had become more negative.

3 - At the time, SV2 was close to the northern apex of its orbit and to the north of the UK, having just passed along the US eastern seaboard and across the Atlantic Ocean.


Given the clues above, the inference is that the particpating ground station was a long way from the UK and to the west. At the time the event occurred, the only land masses to the west of Europe visible to SV2 were the extreme NE coast of Canada, Greenland, and Iceland. Of these, the most likely location for the uplink transmission was Greenland.

Modelling the effect of an uplink from the western coast of Greenland produces very similar results to those observed, suggesting the source of the uplink was the Air Force Satellite Control Network ground station at Thule.
Copyright © Robert Christy, all rights reserved
Reproduction of this web page or any of its content without permission from the website owner is prohibited