I already spotted the ISS in front of the sun two times last year.
This was my first try:
And this my second (where I was late and only got the ISS on one picture):
Planning and realizing the shooting was big fun and quite tricky and thrilling. The space station is chasing past the sun/moon in the wink of an eye (transit time 0.6 s in the first picture) and my biggest problem was to find an exact and reliable time basis (continuous shooting begins to stutter after a few seconds so that the remainig time window for shooting the series is extremely short. I finally noticed that all my smartphone apps and "internet atomic clocks" all differed and were not exact enough and I ended up listening to the analog telekom time signal (is "speaking clock" the name?) to calibrate my Iphone timer. I shot from a tripod and did not use my K5 at that time but an Olympus OM-D E M5 with a 300 mm lens (1st Picture) and a Pentax/Sigma 70-200 mm F2.8 and 2x TC (2nd picture) because it provides crop-factor 2x, 10 fps and a tilt monitor.
Compared with the sun the moon is another challenge but it helps a lot that I can start from my balcony this time. I have to hope for a clear sky and enough contrast of the moon against the sky that will be very bright because the transit happens 4 minutes before! sunset. I plan to attach the OM-D to the 80/480 scope and put it onto the DEC-Unit of the Star Adventurer mount. With lessons learned I plan to film with 30fps instead of continous shooting. The OM-D has an interesting "lossless" digital zoom in film mode (similar to crop-mode of the K1) that doubles the film Resolution without loosing detail compared to the uncropped photo. So I do not have to look at the watch because the Mount keeps track and the camera films self-reliant. And I can perhaps produce a HQ moon picture with ISS by using Autostakkert to stack thousands of film frames later.
I then also plan to mount the K3 II in parallel on the other (counterweight-) side of the Star Adventurer's L-bracket and attach my Pentax 400mm F5.6 plus perhaps the 1.2 x TC. I want to fire the K3 II manually with remote control in RAW and continuous shooting mode. Because it is riding on the mount I do not have to care for re-adjusting and can concentrate on the right moment......
....and if all my plans bust with upcomming clouds or missing contrast I go, drink a beer and wait for the next 2! transits of the ISS in front of the sun that occur in this June at my place. I find it most amazing that there are 3 transit events within 2 weeks that I can watch from my balcony
. I think the possibility for this must be one in millions - so please wish me lots of luck and clear skies!