This one was an adrenaline rush, and full of countless near panic attacks. The ISS was destined to cross paths with Mars near San Diego on Monday morning, at 05:15:47 local time, yet the ground path of visibility was changing by several hundred meters every few hours over the final 24 hours, and the margin of error was approximately 100m on the ground, with the ISS being more than twice as large as Mars in apparent diameter. Add to that thick smoke and haze in CA (that miraculously let up slightly before the event), and it was a nail biter.
I'll start with the punchline. Despite several horrifying near catastrophes, it did work out! I made a short video that hits the highlights and uploaded to Youtube. Hopefully it works because I have no experience here.
Shown below is a single individual frame, of 0.35ms exposure, taken with the C9.25 Edge HD and ASI183mm at f/10. The only processing done here is stretching the levels and applying a small tonal curve, with some denoise. The ISS is brighter than Mars, but the difference is not nearly as much as with other objects. You can clearly see Syrtis Major on Mars. The very edge of one of the solar arrays is just touching the disk of Mars, so I'm calling this a transit! In fact, I like this shot because neither object is obscured, and it somewhat looks like the ISS is reaching out and grabbing Mars (or Mars is scoring a goal through the solar arrays, pick your analogy!). I had no idea what I was going to get here.
The final moments were dramatic. The ISS emerged from Earth's shadow at t-minus 40s to transit. It was already well above the horizon, but had been traveling in shadow until slightly before the transit. The ISS flickered for a few seconds, very dim, as the solar arrays started to catch the sun, and then quickly surpassed the brightness of Mars just before the transit. I started the recording at t-minus 30s. My shutter speed was 0.35ms, but I could only manage 41fps frame rate with my ROI. This was intentional, however, because I wanted to use a short and wide ROI, aligned with the long axis of the sensor along the predicted trajectory of the spacecraft, to try and get a scanning shot from right to left across the full sensor. That is exactly what happened. When I saw the ISS flash across the screen it was a very good feeling, but I could tell that the trajectory was ever so slightly below the disk of Mars. But when I looked at my image files, I was happy with the result.
Shown in the next post is a composite of each frame containing the spacecraft, blended using "Lighten" mode in Photoshop.
Edit: I also added these two images to Flickr, and the links are below.
Edited by Tom Glenn, 16 September 2020 - 05:52 PM.