[UPDATED] MUOS 4 has been moved to its operational position at 75 E

MUOS 4 imaged while still in its check-out position at 172 W on 27 September 2015

Since September 2015, I have been periodically covering MUOS 4 (2015-044A), a newly launched military communications satellite in geostationary orbit. It was launched on 2 September 2015 and initially placed at 172 W, just west of Hawaii. This position was temporary: it is the "check-out position" where the satellite is initially placed, well situated with regard to key monitoring stations, to check if it is working okay. It stays there for a few months until this check-out is complete: then it is moved to its operational position. In the case of MUOS 4, it is known (see my earlier post and this unclassified publication) that the operational position assigned to MUOS 4 is at 75 E, south of India.

At the start of December 2015, it was announced that check-out had been completed and that the satellite would be moved to its operational position in the spring of 2016.

When I checked upon MUOS 4 on 4 December 2015 using the 0.51-m telescope of Warrumbungle obs in Australia, it was still at 172 W. For various reasons I did not get to check that position again until a few days ago. When I imaged that location on March 1, 2016, using the same Warrumbungle telescope, MUOS 4 was no longer there. It had been moved somewhere between December 4 and March 1.

This is confirmed by observations of the Russian ISON network. I received two of their MUOS 4 elsets for mid February 2016, which show the satellite drifting westwards at a rate of about 3 degrees/day. From the drift rate I reconstruct from these elsets, I find that the move from 172 W to 75 E started near 23.0 January 2016. At this drift rate, it should have reached its designated operational slot at 75 E 37 days later, on 29.0 February 2016.

[UPDATE 11 March 2016:  On March 8, Greg Roberts in South Africa recovered MUOS 4 at 74.8 E, very close to the expected position]