Sunday, 13 January 2008

Lacrosse 2 manoeuvre, and bad luck with a stopwatch

Yesterday was a very clear day, so in twilight I set up the ETX-70 to gather positional data on Lacrosse 2 (91-017A), the NOSS 3-3 (05-004 A & C) duo and the NOSS 3-4 (07-024A & C) duo.

I had adapted the home-made piggyback camera adapter slightly, so it can also funtion as a rest for my 5 mw green laserpointer. The drawback of the ETX-70 is that it doesn't come with a finderscope, so I use the laser to point the telescope. A 5 mw green laser gives a tens of meters long visible beam at night pointing to where you point the scope if you shine it parallel to the scope tube. Simple, and works like a charm.

Unfortunately, after succesfully observing passes of NOSS 3-3 A & C and Lacrosse 2 I must have hit a wrong button on the stopwatch by mistake. When I had pointed the telescope to the point near where NOSS 3-4 A & C should pass and took up the stopwatch, I discovered to my horror that it was no longer running and had no lap times in it's memory! I lost all gathered points so far.

Next, in the confusion of having to start up the stopwatch anew just before the NOSS 3-4 duo pass, I lost that pass.

Now, I can't quite stand such things happening, it makes me very irritated for a while. Luckily my neighbours have double-pane glass, so probably they did not hear my swearing...

What saved the night was that before turning to the telescope, I had triggered the Ixus camera in addition during the Lacrosse 2 (91-017A) pass. The trail showed up faint but well enough defined to measure against the late twilight sky, which meant I had an image providing two positions.

After data reduction, it turned out that the satellite was 17.3 seconds early relative to Mike's 07357.17849791 TLE. On the 6th of January, the difference to this TLE was 1 second. So I reckoned 91-017A must have made a manoeuvre recently. Which, it turns out, it indeed did, a small manoeuvre changing the mean-motion slightly on or near the 6th. What I had missed was that Mike had just issued and update of the 91-017A orbit incorporating the manoeuvre yesterday morning.
That 91-017A still does manoeuvre, points out it is still alive and probably still being used for reconnaisance almost 17 years after it was launched.

(click image to enlarge)

Lacrosse 2 (91-017A) crossing through Cygnus 17.3 seconds early

I set my alarm-clock to see if it would still be clear in the morning (allowing me in that event to catch amongst others Progress M-61). But alas, it had become overcast.

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