A lost son and a heavenly home

 tl;dr - On the evening of Sunday, 17.11.24, the International Space Station ISS had a favourable  flyby over our hometown Bruneck. Our observation of the event was extraordinarily thrilling and at least a partial success.

After reading about a successful hunt for the ISS by our friend Sebastian Voltmer in "Sterne und Weltraum" 11/24, I sent out a call for volunteers to follow Sebastian's example on the evening of Sunday, November 17, 2024. When the time came, I was astounded by the number of students who flocked to the "torretta", the observatory of the Istituto Pluricomprensivo Brunico. Altogether, we were nine people crammed into the small space in the dome - even Felix showed up, a "long-lost son" who had not taken part in any of our activities for years. 

The "ISS crew", I mean the crew that hunted down the ISS.

The passage of the space station, currently home to seven astronauts, was scheduled for 18:34 CET, but we met more than an hour earlier. Not only were there plenty of details to discuss ahead, we were also looking forward to a special guest: Christina Oberleiter from @radioverbindet, a local school radio project. We agreed that she would quietly soak up the atmosphere, make audio recordings and conduct some interviews later on, all with the purpose of producing an enthralling report about the upcoming adventure.

The predicted path of the ISS over the sky
according to the website heavens above.

Now the thing is, I happen to be a chatterbox. While laying out the details of my plan, time flew by. When we at last had finished crosschecking various websites for the most likely trajectory, made all the necessary calculations concerning speed, exposure time, frame rate, etc., and all agreed on the most promising procedure, there were a mere 20 minutes left to the event. 

The ISS from space. The big solar panels reflect plenty of light
making the ISS a bright object in the sky.

We hurried upstairs to the dome, powered up the mount, attached our video camera and slewed to Saturn, our preselected target for careful focusing. Eighteen eyes followed the irritatingly slow motion of the little refractor telescope (oddly, it didn't seem to bother at all). At last, it came to a stop, followed by an inappropriately happy beep. Everyone's gaze swiftly turned to the display. It was pitch black. 

That was unexpected! Saturn is such a bright target and even with the optics defocused, we figured seeing some kind of glowing blob. But there was none. Immediately my eyes went up, through the slit of the dome, into the sky. Nothing to see out there. "Clouds", I muttered, disappointed. 

Change of plans: Robert rushed out of the dome into the open and looked for a suitable replacement for Saturn. What he duly reported let our hopes fade. Most of the sky was covered with mischievous veils, only Vega, the brightest star in the constellation Lyra, was out. Alright, Vega it is then! Next slew of the tiny refractor,  once more suspenseful waiting, again the familiar self-satisfied beep. Nothing! The display was dark. But wait, this time it wasn't completely pitch black. There was a very faint round glow. That must be her! That's Vega, or rather the extremely defocused image of the star. We were back in business!

Focusing wasn't a matter of a minute as usual. We had to use a Bahtinov mask and Emma painstakingly tried to nail down the perfect symmetry point of the resulting diffraction pattern on the display. All eyes were now fixed on her, on her hand turning the focusing knob, on the dancing pattern on the display. I gave a stealthy look at my mobile phone and was somewhat relieved: Five minutes left. We could still make it!

Swift and skilfull students, actually every teacher's dream.

Next, the scope slewed to eta Cygni. According to our research, the ISS was supposed to pass the star within a radius of 20 arcminutes. Felix, the long-lost son, had figured out that the best course of action would be to slew just a tiny bit to the north of the star in order to maximize the chances of getting the space station on our sensor. We trusted him. We all knew he is good at this stuff.

Next look at the mobile phone. God gracious, it's showtime already! The ISS should be above the horizon by now. "Press the record button!" Alex exclaimed "Or we'll miss it." She certainly was right, however, at that very moment my eyes fell on the disk space reading just below the record button. It read "HDD 25GB". That might sound like a lot, but we were going to take 42 frames per second, each frame weighing over 8 megapixels. "If we start too early, we will run out of disk space." "Now!" Alex insisted. Her commanding tone was almost daunting. So, I obeyed - and it was just the right decision.

I didn't worry any longer about the quickly melting away disk space. Robert was the first to spot the ISS and was now hooting in excitement. All eyes were on the bright patch of silver light rising higher and higher behind a thin veil of clouds. Beside it, only Vega and Deneb could be discerned - immobile and ethereal.

Next yelp from Alex, this time I didn't quite get the message. Turning around, my eyes met the HDD status reading: Low disk space. And the record button was off! "I've seen something whizz through the image," Alex repeated. She perceived the ... let's call it unsettledness in my eyes. Was the whole evening a failure? "I'm sure. Well, quite sure," she added.

Anyhow, there was nothing left to do up here. The ISS had ventured on, had slipped into Earth's shadow. The milk was spilled - or maybe it wasn't. We would soon know.

Moments later, everyone was assembled downstairs in the "control center". My MacBook was connected to a large 70-inch screen. It was flickeringly gasping for some free disk space, less than 300 MB remained. The video we had just taken alone was over 25 GB. If it was nothing more than a huge pile of trash, at least deleting it was going to be satisfying. 

Fortune taxed our patience. The entire clip was just over a minute long, but at 42 frames per second, going through it took a while. And then, in the very last few seconds, the ISS did indeed show up. Alex was right! The space station was on 24 out of almost 4,000 frames. Only after our rampant cheering and crowing did we realize how damn lucky we actually were.

The ISS zapping across our sensor. 

Overexposed but the irregular shape is obvious.

Christof Wiedemair