It isn't as much fun to take adventurous road trips without Melinda - she hasn't felt like straying far from home with the new chemo drug, so I'm looking for fun from the back yard! I noticed the other day on Spaceweather that the International Space Station (ISS) was to make an excellent pass tonight. In fact, it was to go within 1 degree of our zenith - right over Tucson! The map is shown at left - it was to move from the NW down towards the SE before disappearing into the earth's shadow, all this happening in a dark sky.
Normally I look for mountaintops to shoot down from - I've never tried shooting upwards with high-resolution in mind. These days lots of amateur astronomers are imaging the ISS through telescopes, some as it passes over the disk of the sun or moon, the ultimate perhaps being Thierry Legault, who developed an autoguider to keep the image stabilized for high-resolution video. I was thinking I wanted to use the TEC refractor, perhaps with a barlow to expand the image scale a bit more.
So in preparation to the pass this evening, I went through my collection of auxiliary optics, particularly Barlow lenses that I could adapt to camera use. The TEC by itself (140mm F/7 = 980mm focal length) is about 1 meter focal length, and I located a 2X from Explore Scientific and 5X Tele-Vue Powermate. I set up the scope in the front yard, where there is a partial view of Finger Rock up in the Catalina Mountains, about 7.5 miles away according to Google Maps. Shown at left are views by a 300mm lens, then the TEC alone and with 2X and 5X Barlow. While the ISS is physically larger than a football field, at 250 miles altitude, it is still smallish. From an examination of the various combos and resultant sharpness, I decided to go with the 2X Barlow. The 5X, while making the image larger, doesn't have any better sharpness (likely limited by daytime seeing in these exposures), and the resultant smaller field-of-view would likely make it more difficult to track the moving ISS. The final setup is shown at right. On the telescope side I needed to add an extender to reach focus, then the 2X Barlow, then the camera adaptor.
The ISS pass was about an hour after sunset, so there was plenty of time to check focus on the moon and a few bright stars before the Space Station made its entrance. At left is a single frame of the moon at full camera resolution with the TEC 140 with 2X Barlow. Finally the ISS rose above some clouds in the NW, and I aimed and took a few shots at 1,000th of a second, and checked the brightness - appeared about right at the ISO of 1600 (maxed out), so kept at it, tracking the best I could manually while snapping frames. As it approached the zenith, I stopped and rotated the alt-az mount manually to pick it up again as it continued SE. It was when I first picked it up after the zenith move that I got a few frames in 10 seconds and stacked three of them as shown at right here. I'm no expert on the ISS layout, but the vertically stretched objects are the solar cells, the main spar running horizontally in this image. While not much compared to Legault's efforts above, it is a fun first step. Legault uses a 14" telescope, so stepping up in size would help in larger image scale as well as keeping exposures short. We'll see...
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