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Comment by nickff | Hacker News Reader

It's considered unwise to leave uncontrolled vehicles in orbit, as they may hit other uncontrolled vehicles (or natural objects) and create debris.

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An orbit like parent post is talking about is barely an orbit and more like an escape trajectory that just barely fails to escape.

Would need lot of extra fuel to raise altitude for an escape trajectory. Fuel either brought up the gravity well at launch or later refueled in orbit. Of course not all satellites are designed to allow in-orbit refueling. Maybe an reusable orbital tug might be something that someone will come up with.

It doesn't have to be one vehicle. You can launch 10 falcon 9s (perhaps even using the same booster) and have them take turns pushing.

The ISS weighs 450 tonnes.

Ten Falcon 9s (with 8 tonnes to GEO each, expended) couldn’t move it into a parking orbit. There literally isn’t enough current lifting capacity on Earth to do this.

You're trying to calculate this with weird units. ISS escape velocity orbit would require about 3200m/s delta-v. Yes, with chemical rockets this is like 800 tons of fuel. But you don't really need the high thrust of big chemical rockets. You could do it with ion engines which have a specific impulse between 10x to 100x higher than chemical rockets, bringing the total cost way down. It would take much longer, but it could be done.

Do you realize that 10 F9 flights means 10 new second stages and on those second stage someting has to sit and that something whatever that is - is completely dwarfed by ISS and it would have to be a new dedicated vehicle consiting of mostly fuel just to deorbit the sucker in one go.

Original plain AFAIR was to use several Progress vehicles.

And going to graveyard orbit with something like ISS is not just a few whole times more difficult but at least an order of magnitude more.

Yeah, but this is the ISS we're talking about. Obsolete commsat number 723, sure, no one's going to care about deorbiting it, but the ISS has historic and cultural significance. Raise it a bit to a parking orbit, everything else can keep track of where it is, and a thousand years from space archaeologists can explore it.

Or pack it inside otherwise empty Starships a few segments at a time and fly it down intact to put in a museum.

> Raise it a bit to a parking orbit

That's not “a bit” and the fact that it’s the ISS and not a typical satellite is among the reasons it is impractical.

The ISS will burn up in the atmosphere within very few years unless periodically boosted up.

Boosting it all the way up to a more long-term graveyard orbit (i.e. several hundred kilometers) would consume a lot of fuel compared to a planned deorbit.

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.

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