It’s easy to say “Lets put Hubble on the ISS”, but when you get to the details it becomes clear that not only is not possible, or practical, but not a good idea in the first place. The ISS is the last place you want the HST. You don’t want it even close. Even having it ½ orbit away would probably cause problems. I suspect the ISS would leave a trail of pollution streaming out all around it s orbit. Do they do urine dumps? Anyplace humans go garbage tends to collect. Fortunately the Hubble is at 370 miles. The ISS is at 245 miles now. Hopefully that’s far enough away the keep from contaminating the HST. I would think even though their orbits cross you would think the orbit of anything floating away from the ISS would immediately begin to decay, keeping it away from the HST.