First, skip down below the fold and look at the pictures.
Then c'mon back and read on . . .
On November 20, 2008, the International Space Station (with Space Shuttle Endeavor docked) passed almost directly overhead as seen from Rutherford College, NC. It occured to me that there wouldn't be that many more chances to see the Shuttle and the ISS together since the Shuttle flleet is set to be decommissioned within a couple of years. So then I thought I should try to get a decent picture as they sailed by in deep twilight. Then I realized that if I used a long enough lens, the ISS would leave a wide and perhaps interestingly detailed streak since it is now big enough to be resolved at easily achievable image scales.
And that reminded me that during a pass some months ago, I had seen intricate detail on the ISS through the eyepiece. It was dazzlingly bright. Since the ISS is sitting in full sunlight during a visible pass, it could be photographed at very high shutter speeds at which blurring would be minimal. That's when things got intricate.
I put the DSLR behind the 5-inch F6 Astro-Physics refractor. I mounted an Orion ST-80 on top with a 20x eyepiece. As twilight deepened, I focused the A-P on Vega and then aligned the ST-80 with the A-P. Whatever I could see in the ST-80's eyepiece would be somewhere on the DSLR's chip. The closer to the center the better, but why be picky?
A detailed chart from Heavens-Above.com helped me anticipate one small chunk of the sky through which the ISS would sail -- just "inside" the eastern wingtip of Cygnus. Checking the possible framing with Guide 8 software, I identified a couple of stars I could line up on and wait.
I put a remote release on the Canon DSLR and set the camera to "bulb." I wanted the ISS to trail into the frame. As it passed my marker star, I would close the shutter. Then I planned to spin the shutter speed dial from "bulb" to some small fraction of a second (1/4000 or so). And unclamp the RA and Dec axies of the G11 mount. And flip the telescope across the meridian so I could more readily see into the eyepiece as I tried to track the ISS into the trees to the NE of the observing site. Meanwhile, I would hand the remote control to Amy who was going to push and hold the shutter button on it whenever I said, "Now," as the ISS came in and out of view in the ST-80's eyepiece. I set the camera to record high quality JPEGs so there'd be no chance of running out of buffer space. I'd rather have had RAW frames to process, but decided I might need more chances than the buffer would allow and, in any case, I wanted as many images to stack as I could get. (The image scale of the 50D at 762mm is about 1.3 arc seconds per pixel, which works out to about 8 feet when the ISS is overhead, so I thought there ought to be plenty of detail to work with.)
There were some clouds as the moment approached. I decided to use 1/2500 rather than 1/4000s. I decided to use ISO 800 rather than ISO 200 or 400 since I couldn't imagine the 50D's modest noise would be my limiting factor. I thought imperfect focus and blur from imperfect tracking would be far more likely problems. In 1/2500 second, the ISS would move 17 feet; almost all of that motion would be cancelled by my panning with the station, so I really didn't expect image motion to be a prob...
And oh good lord, here it comes, out of the trees. Dead on the predicted line. I opened the shutter and watched alongside the guide telescope. Yeppers: exactly on its predicted track. I leaned into the eyepiece. The ISS burst into view and passed my marker star. I wasted a few brain cycles being amazed, then I closed the shutter. Total exposure: 16s. I handed Amy the remote control. Spun the shutter speed dial. Stood up, dosey-doed under the camera cable and around the mount. Unclampled both axles. Flipped the telescope over the RA axis, put an eye to the tracking telescope and was on the target more easily than I expected to be. I said, "Now!" and Amy pushed the button. The Canon stated clicking off images and I never once said "Stop" until the ISS disppeared behind our tallest pine 32 seconds and 204 frames later (that's 6.4 fps if anyone's counting). Clouds took most of the images, but >70 have the ISS and Endeavor on them, and of those more than half are pretty decent. I've taken the best three consecutive frames and stacked them for better resolution in the images below.
For once, a photo came together pretty much as planned. Here's what you have: the ISS trails into the frame and the sharpest obtainable image at the same scale is composited just beyond the end of the streak. It's a time-compressed photo of the ISS and Endeavor sailing through the stars of Cygnus. The gap as shown below would correspond to a fraction of second's travel while the real gap was 42-43 seconds (during which time the ISS passed well into Virginian "air space" and my pixel scale changed from 8 to more like 14 feet per pixel). I gave up a lot of image scale in the interest of a dramatic image. If there's a next time, I'll make a point of trying for the detailed images nearer the zenith.
Full frame, reduced for web display:
The interesting bits, blown up for your viewing pleasure:
I think the data can be tortured refined to produce a better (smoother,
sharper...) photo in a day or so, but for a first look, it's not bad. There's
another good pass on Saturday, but it's much earlier in the evening. We'll
see if I can do anything with it.
Trivia: this photo was made on the 10th anniversary of the start of the ISS's construction ("the Russian-built, NASA-financed Zarya module that marked the beginning of station assembly...was launched from the Baikonur Cosmodrome in Kazakhstan aboard a Proton rocket at 1:40 a.m. EST on Nov. 20, 1998," according to CBS News). There were ten people on board when I made this photo; eight inside and two outside the ISS. I observed three satellites or bits of debris preceding the ISS in orbit. The brightest was an easy naked eye object, 3-4 mags fainter than the ISS and preceding it by a couple of minutes. Two much fainter thingawidgets shared the eyepiece a few arc minutes ahead of the station. Lunch wrappers?
© 2008, David Cortner