Monday, 30 September 2013

A farewell to GOCE

In the past, I have observed ESA's gravity probe GOCE (2009-013A), the Gravity field and steady state Ocean Circulation Explorer, a number of times (e.g. here, here, here, here and here), usually as a rather faint object producing brighter specular flares near culmination.

 click image to enlarge

This weekend I tried again, spurred to do so by some people at ESA's ESOC in Darmstadt. The reason was that GOCE does not have much lifetime left. It's ion engine will run out of Xenon and cut-off somewhere mid- to end October, and the expectation is that the spacecraft will then re-enter and disintegrate in the atmosphere within 2 to 3 weeks. Some 250 kilo of the one-ton spacecraft might survive re-entry, divided over 50+ fragments.

The Goce orbit already had been brought down in November 2012: its orbital altitude currently is no  more than 225 km. As a result, it currently zips across the sky at high speed. Because of the low altitude, it is visible in twilight or very shortly after twilight only.

The image above shows GOCE over the roof of my home in Leiden center in deep evening twilight of  Sunday 29 September. It was visible with the naked eye, but only barely.

The image was shot with an EF 2.0/35mm lens and because of the bright twilight sky I used a short exposure of 2.5 seconds. The elevation of the spacecraft was around 40 degrees, passing east of me. The sky background shows stars in Andromeda: about halfway of the chimney and the GOCE trail you can see the fuzzy glow of M31, the Andromeda nebula.

I had also tried to image the spacecraft the evening before (Saturday the 28th), but Murphy struck. I was a bit late in checking for passes that day (in twilight already) and discovered that the only visible pass would happen within minutes of me checking for passes! So I ran outside, grabbed the camera, slammed it on the tripod, aimed it...and forgot to take off the lens-cap....

That particular pass, in a somewhat darker late-twilight sky and at a higher elevation through Cygnus, was a nice one, where GOCE was clearly visible to the naked eye. GOCE was racing through the sky, about the fastest you will ever see a satellite move in the sky. Quite apt for "the Ferrari among the satellites"!

This might have been my last view of GOCE ever: over the coming days the passes will become increasingly more unfavourable for my location.

It will be interesting to follow the satellite to decay once its engine has cut off. The ESOC people told me they will try to put it in a fine-pointing mode just before it does so, but there is a possibility that at one point it will lose attitude and will start tumbling.


Mohamed Goneam said...
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OrbitalGroove said...

Thank you for this goodbye picture! I spotted GOCE only 1 time, on December 6,2012 while flew over the Alps, heading North ( +/- 40° √©lev. East shore from my place ). True that it's "Space-Ferrari" ! Was so fast, and a reddish faint sunlit trajectory on a perfect winter sky...I had goosebumps spotted the most beautiful spacecraft ever built!
No more sightings since, cause of clouds, or work :( Bye GOCE !!