USA 129 does a Mark Twain!
We were wrong: USA 129 is still alive!
Greg Roberts observed it from S-Africa last night, after a dedicated 2.5 hour plane scan, and observed it over two passes. A quick fit to his observations by Ted Molczan suggests that the perigee of the satellite might have been brought significantly down, to 240 km (was 310 km). More observations are needed to say anything more about this.
This is something new. I really did not expect USA 129 to manoeuvre into a new orbit.
It should be noted that Ted Molczan already had a hunch about this: as USA 129 was running a bit late when Greg observed it on Jan 27th, Ted felt this could indicate it had made a manoeuver in the hours just prior to Greg's observation. It is now clear he was right: kudos to Ted!
The question now is: what does it mean? Do they have some new purpose for the satellite? At its age of 17+ years, that would be amazing! This is option #1 and perhaps the preferred option. The new orbit appears to be sun-synchronous, which is preferable for an operational optical reconnaissance satellite.
Or is this all in preparation for a de-orbit later (option #2)?
If they are running low on juice for example, they might have opted to bring the perigee of USA 129 down as far as possible and next use natural decay to bring down USA 129 even more, to say 150 km, and then do a final de-orbit burn (option #3). This is a scenario a bit similar to what NASA did with UARS in 2011 (except that they could not do a final de-orbit burn and had it re-enter uncontrolled, something which I don't expect for USA 129). But that is (extremely) wild speculation.
It will be interesting to see what happens with USA 129 the coming days, weeks and months.
Another interesting moment will be reached in two days from now: will USA 129's younger sister ship USA 186 (2005-042A), indeed be boosted into a more circular orbit, as I expect?