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Comment by bell-cot | Hacker News Reader

> NASA announced SpaceX has been selected to develop and [emphasis mine] deliver the U.S. Deorbit Vehicle that will provide the capability to deorbit the space station and ensure avoidance of risk to populated areas.

> The single-award contract has a total potential value of $843 million. The launch service for the U.S. Deorbit Vehicle will be a future procurement.

So...with $843M, what could SpaceX come up with? In Gwynne's shoes, I'd be looking to develop a vehicle with far wider application than a 1-off LEO deorbit burn.

And, given the inability of most of SpaceX's competition to reliably delivery anything to orbit, I suspect that NASA has similar hopes.

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Couldn’t we put it in a super long orbit that means it will revisit earth in a million years or something? Might be a nice surprise for whoever is around at that point.

Answered in their FAQ[1]:

> Decommissioning by boosting an object to a higher “graveyard” orbit to extend orbital lifetime is often done with smaller satellites operating near geostationary orbits (~36,000 km in altitude). This is not a realistic target for space station decommissioning because of the large mass of the space station and distance from its operational altitude to a “graveyard” orbit. Existing propulsive assets (spacecraft) do not have the capability to raise the space station’s altitude to such a high target.

[1] https://www.nasa.gov/faqs-the-international-space-station-tr...

For perspective, the ISS is currently orbiting at 400km altitude. Typical graveyard orbits are just beyond geostationary, so lets call it 36500km.

Orbits get somewhat emptier beyond 2500km altitude, but you'd still risk spent rocket stages or defunct satellites hitting the ISS if you don't go all the way out beyond geostationary. Maybe you can stay at lower orbits if you dock a vehicle that can provide thrust for obstacle avoidance even after the main station powers off.

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

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.

Does it have the delta v and structural strength for a maneuver like that in its current configuration? I agree it would be cool to put it in deep freeze for a few thousand years.

Structural strength shouldn't be an issue, but it doesn't have the delta-v. They would probably need to find a way to attach some ion engine tug to it.

It's far more expensive, in the orbital mechanics sense, to do anything like that than to "simply"* nudge an end-of-life satellite just enough to push into the atmosphere, when it's starting from an already-low orbit.

*(The engineering here is not very simple)

Like Snoopy!

https://skyandtelescope.org/astronomy-news/astronomers-might...

Can you imagine, people rebuilding the society after collapse and this thing resembling the images in some very old artefacts returns from the skies.

... moving at like a billion miles an hour before vanishing back into the blackness before humanity can react.

... that might explain Oumuamua!

It would take a massive amount of energy to eject such a huge structure from very low orbit out of Earth orbit completely.

can you protect an orbit with the "One Small Step to Protect Human Heritage in Space Act"?

Such a shame. Can’t we dismantle it and bring the pieces down in Starship flights? The American parts would look great at the Udvar Hazi. As for others, each one can be delivered to its country of origin.

I’m assuming anything that did fit in a shuttle could fit inside a Starship.

Not sure Russians would like that though. I’m betting they would prefer their pieces deorbited.

I'm not sure how much they can carry on re-entry. More heating etc., and more weight when doing the landing.

They’re going to enter mars atmosphere with a full payload at a faster speed so I think it could handle it.

Mars has less than 1% the atmosphere of earth. That makes it easier in some ways and more difficult in others. I don't think you can really judge the performance when landing on Earth by looking at the performance when landing on Mars.

Mars has less gravity and less atmosphere, so its not a comparable situation.

thats the intention, its hardly a proven.

Also they’d need more fuel for the de-orbit burn.

> So...with $843M, what could SpaceX come up with? In Gwynne's shoes, I'd be looking to develop a vehicle with far wider application than a 1-off LEO deorbit burn.

So that would probably point to "Starship, possibly with a lot of fuel loaded onboard, docks with ISS, and then feathers its maneuvering jets to push the ISS into a guided re-entry into the Pacific Ocean."

Its going to be Starship again surely, with the right docking stuff to attach to the ISS.

Or a modified Dragon?

You don't need a lot, just something lined up on the correct axis with enough engines and fuel to slow the station down enough to fall out of orbit. The station has its own propulsion (on Zvezda & Zarya, I believe) even with most of its station keeping being down by Progress etc. There's no reason they couldn't loft something with an F9 (23t to LEO) or maybe FH (64t to LEO). With the fact that it's going to burn up in atmo anyways, you can strip a lot out of the existing cargo dragon.

You can slowly deorbit anything with enough time/fuel. It's just a matter of how fast NASA wants to make it happen to assure it lands in a specific spot and doesn't breakup too much while still in "orbit" (see also: atmo + solar panels).

According to https://forum.nasaspaceflight.com/index.php?action=dlattach;... (PDF)

> The deorbit vehicle will need to provide at least 3236 N thrust to hit the target delta-v within a 60-minute time period.

Each Draco on Dragon can deliver 400N, there are 16, that's 6400N. So unless I've missed some math somewhere, a Dragon could do the deorbit. Ignoring the fact that they probably haven't burned those engines for an hour. Also fuel required for that manuver.

>Also fuel required for that manuver.

Ah yes, that pesky detail of the rocket equation.

Super complex, but could the fuel & thrusters be staged -- waiting in lower orbits -- so you don't have the mass of all of them at once?

It could, but it's never been done before. SpaceX just tested some fuel transfer in zero-G for the first time with their second Starship test.

Modified Dragon seems like the simplest option. Dock and then burn retrogade while attached. Probably not nearly that simple in reality though.

If anything I'd like SpaceX to attach some cameras that live-stream the ISS breakup through Starlink the way they've been filming their re-entries.

Maybe the extra cost is to look into bringing it down without destroying it. Would be good to study it for data on long term spacecraft.

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