International Space Station on 26th Feb 2012

[ejwwest]

Taken with Canon 40D DSLR attached to Celestron EdgeHD 925 at prime focus.

[Sam]

Very cool!

[ejwwest]

Here's a closeup:

International Space Station by ejwwest, on Flickr

[Ponoobersie]

How on earth did you manage that?!? with the rate of speed that travels?!? very well done!

[ejwwest]

The technique is to point the telescope at a point the ISS is predicted to pass through. I set the camera on high burst rate (6.5 fps is the fastest on my Canon 40D) JPEG (not RAW as the buffer fills up too quickly) at 1/1000 of a second exposure at ISO 1600. As the ISS enters the field of view of the finder, then set the burst going and stop when it leaves. There are typically 3 shots with the ISS in the frame when overhead but I got 4 on this pass as I (coincidentally) had the camera oriented diagonally to its path. Quite a bit of the structure such as the various modules, support trusses and solar panels is clearly visible.

To find out where it is going to pass through, the approach I use is to use Heavens Above (Heavens-Above Home Page) or Calsky (http://calsky.org/) to find a star the ISS is going very close to and tracking on that (HA has stars to about mag 6, Calsky much fainter). With a GOTO scope I don't need to use a star but get coordinates from Calsky and go to that coordinate and wait. Clearly focussing and seeing are now the limiting factors in how good an image one can get but for these shots I used the crescent moon to get a sharp focus.

With a GOTO scope one problem is aligning it whilst still twilight (which is usually the conditions for an evening pass) even if the pass itself is in the dark. Usually there are not enough bright stars visible in the twilight to accurately align and then ensure the scope is properly polar aligned: there often is not enough time.

For this pass, I managed to use Venus and Jupiter as alignment points and by then I could use bright stars such as Betelgeuse, Castor, Capella and Rigel as calibration stars. This allowed me to then enter the coordinates that I'd extracted from Calsky.org to get very close to the passthru point. Without properly polar aligning, there was still sufficient drift that I had to re-position the scope a couple of minutes before the pass just so I could be sure the scope would still be pointed at the right area.

This works fine for a DSLR like mine with a 30'x20' FOV (on my EdgeHD 925 scope). I would like to try with my 640x480 CCD camera but that has such a narrow FOV that I can't be confident the ISS will actually pass through. I tried this on Saturday night's pass and failed. I also tried this on a predicted pass through Jupiter last Monday but it was too light to accurately align and I couldn't see Jupiter through the thin cloud. I'll try again when there's a prediction of a very close pass to a bright enough star AND I have time to actually align very accurately.

I also have quite a few shots of ISS passes across the Sun. For these, aligning isn't the problem but knowing when it's coming through when you can't see it. For these use a GPS and start the burst about 1s before the predicted transit and stop about a second after (the transits are usually over in less than a second).

Some examples up here: International Space Station - a set on Flickr

[Zul]

Fantastic!