At one point they planned on using ion thrusters to try and keep the ISS in a stable orbit. I wonder how many it would take to push it into a graveyard orbit? Most of the energy for ion thrusters comes from solar, which the ISS has plenty of.

- "Most of the energy for ion thrusters comes from solar, which the ISS has plenty of."

The ISS rather has very low power relative to its mass. About 1/50th the power/mass ratio of the Dawn probe, for instance. This approach would take multiple decades, with the ISS as it currently is.

It's worth remarking there's never been a spacecraft to date that's attempted a solar-electric spiral out starting from low Earth orbit. (The Boeing 702 satellites can spiral from GTO to GEO at least—though those have, again, far higher power/mass ratios than the ISS).

A deorbit would create a huge amount of chemicals in the atmosphere that are very harmful to the ozone layer. It might be worth sending up a few more rockets to give a big enough push to send the ISS into the sun (along with said rockets).

https://www.space.com/starlink-satellite-reentry-ozone-deple...

https://www.space.com/deorbiting-impact-on-earth-atmosphere-...

Why the sun? In terms of delta-V that's the hardest target to hit in the entire solar system, since you have to zero out all of earth's orbital velocity.

My KSP-fu tells me that you could definitely get a corona-crossing periapsis without zeroing out the velocity relative to the sun. You aren’t trying to land on the bastard.

That much delta v would take a few hundred rockets, not a few. You’d probably cause way more pollution from all those rockets.