Hacker News Reader

Hacker News

Comment by MegaButts | Hacker News Reader

Parent Full thread

MegaButts

That's part of the reason there's just so much junk flying around in orbit.

https://en.wikipedia.org/wiki/Kessler_syndrome

View on HN

If you read the article, SpaceX specifically designed the process to avoid orbiting junk.

Yup, spacex stuff is all LEO. Without input it all crashes into the atmosphere in a few years (3 I believe)

If you read the article, it's not just that they operate at LEO, but the launch process begins at even lower altitudes so that they can quickly deorbit any problem satellites.

Would spacex be liable if one of their satellites hits your car or house?

Small satellites like Starlink burn up in athmosphere. But if you're curious about liability laws for falling satellites, here's the relevant UN convention: http://www.unoosa.org/pdf/gares/ARES_26_2777E.pdf

That convention makes states (i.e. national governments) liable, but doesn't by itself make SpaceX liable. I assume SpaceX would be liable under ordinary tort law in the U.S., irrespective of the convention. At least for claims against U.S. nationals, the convention is probably mostly irrelevant; it's purpose is to act as a backstop in case compensation can't be found using normal legal procedures--e.g. courts won't otherwise hear a claim (AFAIU, the U.S. is relatively liberal in permitting foreign entities to sue in domestic courts for all manner of situations, and to do so on equal footing), or the entity is unable to pay compensation, in which cases the state signatory effectively acts as a guarantor for all the entities within its jurisdiction.

> That convention makes states (i.e. national governments) liable, but doesn't by itself make SpaceX liable.

The US is liable for any damage from space SpaceX causes in a different country. If it hits a house in the US, that's a completely different question.

If there’s so little atmosphere that a Starlink doesn’t burn up before it hits your car, the ICE engine would have trouble running anyway.

How modified would a Tesla Cybertruck need to be to run on the moon?

If I had to guess, probably quite a bit. I doubt the battery cells or the electronics would hold up under hard vacuum.

I recall a story posted here that if you put an iPhone in helium it will break the MEMS components inside of it and it will fail to boot, and that's still at 1 atmosphere.

The battery is already sealed, and 1 atmosphere isn't a lot of pressure to contain. It might even be able to be pressurized to quite a bit less. Regarding the electronics, engineering-wise that's a solved problem. And it would only need the drivetrain and charging electronics.

I suppose that a wider track would be useful in 1/3 G, but that is a mod that off-roaders have been doing at home for decades. Ditto ride height and wheel size.

I would not be surprised to see a Cybertruck offloading from a Starship someday, maybe even on a private mission after Artemis finishes.

Yes. But they're designed to burn up on entry. I think it's been mentioned on HN that the delay in their laser link network was due to the need to redesign the laser component to ensure it would break up.

When people say something will "burn up on reentry", a phrase that I've heard almost all of my life but never really given much thought too, how burnt are we talking? Surely it doesn't just completely atomize?

Here's a video of a satellite (a very large one) reentering: https://www.youtube.com/watch?v=OhBw5yaR_SU

And here's a timelapse in a hypersonic plasma test chamber: https://www.youtube.com/watch?v=q_AcG4ZQItg

(Keep in mind the pieces that come off are still going to keep being heated even after they seperate.)

It largely does atomize yes, depending on the material. Which is why they're designed out of materials that will do this.

I don't know specifically but as a layman I'd imagine the satellite breaking up into smaller and smaller pieces due to the rapid heating and the "wind resistance"(?) from making contact with the atmosphere at high speeds.

I'd also imagine that at some point in this breaking-up-process the pieces are small enough to sublimate from the extreme heat, i.e. "burning up".

You know how racecars spectacularly fly to pieces when they crash? That is by design - as it rapidly sheds energy. Same thing applies to things that "burn up on reentry", so long as you prevent the thing from coming down as one solid lump of glowing hot metal - the surface area to mass ratio renders the fragments harmless.

I wonder if anyone has ever tested the whole thing about field mice surviving a drop from any height due to their low terminal velocity... those bat bombs in WWII don't count.

Do you remember, back when SpaceX used aluminum grid fins, when you'd see a Stage 1 re-entering, and you could watch the grid fins erode away in realtime video?

Think of that, but for, well, everything.

I’d love to know more about this too.

Yeah, I mean to be specific your homeowners' insurance would pay you directly for "falling debris", but then they would go sue SpaceX to get their money back.

This reminds me of an episode of Jim Henson's TV series Dinosaurs where a space rock hits the Sinclairs' house, and the insurance refuses to pay out. Because they had "meteor" insurance, so their house would only be covered if it was floating in the upper atmosphere at the time of the strike. Instead, the insurance said their house was hit with a meteorite (a meteor that reached the ground), which wasn't covered under their policy.

It wasn't a meteorite when it hit the house, only when it hit Earth. I know, hit me with the downvotes.

I think their house was made of earth (rock).

They should have argued that it hadn't yet hit the ground when it hit their house.

Probably? But I imagine that won't/can't happen because the satellite is likely designed to burn upon reentry. It would seriously surprise me if no regulatory body thought of this before they sent thousands into LEO.

If you can build your house, or drive your car, at that altitude I rather think you'd be the one being liable! :D

(based on the fact these satellites are designed to burn up completely upon re-entry into Earth's atmosphere and so no 'chunks' reach the surface)

I don’t think this is true. Looking at this: https://i.stack.imgur.com/pMchk.jpg from UN, objects above 500km take ~25 years to decay from orbit. They reportedly start at 550km, so I wonder how they hope to achieve 3 years of deorbit without active control.

That infographic is a very simplified view of a complex subject. Here's a more detailed overview: https://www.spaceacademy.net.au/watch/debris/orblife.htm

Bear in mind that Starlink is much lighter and "draggier" than typical artificial satellites. Based on publicly available data, I get a ballpark figure of roughly 20 kg/m^2 for the ballistic coefficient of a tumbling Starlink satellite.

Just eyeballing the graphs in the link I provided, that corresponds to a lifetime of something like 2-9 years, depending on solar conditions.

That's wrong. There were four missions that were deployed to apogees above 300 km, but most are deployed to 250km and below. That means that satellites that fail tend to burn up quite quickly, in a few years.

Here's a chart of deployment apogee and perigee.

https://twitter.com/planet4589/status/1491256299002155012/ph...

It depends on density and cross section (and solar flux); a 500km orbit can be 2-30 years, depending. That's all basically still in the "self-cleaning" domain. Being rather dense and flat, I'd expect Starlink to be on the lower end of that range.

http://www.spaceacademy.net.au/watch/debris/orblife.htm

The Starlink "0.9" batch was launched in May 2019. Most reached operational altitude; those that did not decayed quite early, as expected. Those that remained operational have by now been deliberately dropped, but some 5 seem to have become unresponsive at a more-or-less operational altitude.

See dashboard at https://forum.nasaspaceflight.com/index.php?topic=49936.200

Starlink-43 is the first of those to fully decay, reentering around 26 January. https://in-the-sky.org/spacecraft.php?id=44257

Starlink-24 is probably going to be the slowest of that cohort. It might have a couple years left. https://in-the-sky.org/spacecraft.php?id=44257

Natural decay in <5 years is really quite fast as these things go.

And we inhale it all. (Yes, I know it's insignificant; all things start insignificantly.)

About 15,000 tonnes of material enter the Earth's atmosphere each year from meteors. I know the makeup of satellites vs. random meteors isn't exactly the same, but it's probably not concerning in terms of pollution sources, and it's really hard for me to imagine it getting there.

When you consider the century-long global effort burning 2-3 billion gallons of oil every day to raise CO2 from 320ppm to 420ppm, you get a sense of the scale involved.

Yea ~0.033% to 0.040% took ~879,000,000,000,000 kg of carbon with the oceans sucking up another 590 Gt, and land taking 528 Gt from 1750 to 2012. We added another 0.004% in the last 10 years.

Just wait until you learn just how much random space stuff enters Earth’s atmosphere in any 24 hour period

Someone already mentioned burning oil, I'd like to also mention coal which makes oil look very clean by comparison. Coal is a few ppm uranium, arsenic, and other unpleasant metals (this is from memory, but it has lot of impurities). We burned literally billions of tons of it, putting thousands or tons of these metals into the atmosphere in the process.

Also, leaded gasoline

this argument is pretty general; you're a priori attempting to prove that "acknowledged insignificant things are actually significant". This feels too strong!

There is no guarantee of this. Very possible the satellites can break up and cause junk/collisions. They are too bright and block astronomers already:

https://static.independent.co.uk/s3fs-public/thumbnails/imag...

https://www.labroots.com/trending/space/22175/spacex-starlin...

TFA says space junk shouldn't be a problem with the launch method they used

>SpaceX deploys its satellites into these lower obits so that in the very rare case any satellite does not pass initial system checkouts it will quickly be deorbited by atmospheric drag. While the low deployment altitude requires more capable satellites at a considerable cost to us, it’s the right thing to do to maintain a sustainable space environment.

Need third party analysis of that, personally

The search term "Gabbard diagram" should tell you all you need to know. Especially if you find some animated ones. Here's a particularly nice one:

https://www.youtube.com/watch?v=5ijKirDjwOU

The Gabbard diagram is a way of expressing the orbital locations and decay of the particles produced as a result of an orbital collision. Note how higher objects tend to stay high for a long time, but low objects (below about 600km) drift lower at an appreciable timescale, and once they're below about 500km they fall the rest of the way very very quickly.

Starlink satellites deploy to 550-km orbits.

Edit: Oh, these were launched into a 210-km orbit, which combined with the higher atmospheric density due to the geomagnetic storm, basically dragged them back down before they could raise to their normal orbit. Oof.

Even more strongly, SpaceX launches to a ~200km orbit and has the satellites raise themselves. This way any satellites without attitude control deorbit immediately.

Also, the vast majority of SpaceX satellites will be at 350km.

Your numbers are a bit on the low side.

They start off at a 350 km ( https://in-the-sky.org/spacecraft.php?id=50803 was launched earlier this year).

They then raise them to about a 550 km orbit for its operational lifetime ( https://in-the-sky.org/spacecraft.php?id=45102 )

And then they lower it a bit, and it decays more rapidly ( https://in-the-sky.org/spacecraft.php?id=44249 )

Another one that didn't go operational - https://in-the-sky.org/spacecraft.php?id=44282 - you can see it go up, fail, get lowered, and decay.

The VLEO orbit for Gen2 is 340km, and will comprise the bulk of the satellites.

https://en.wikipedia.org/wiki/Starlink#cite_note-sn20170917-...

> SpaceX has two constellation applications pending FCC approval — one for a 4,425 satellite constellation operating in Ka- and Ku-band from around 1,200 kilometers, and another for 7,518 V-band satellites flying between 335 and 345 kilometers.

I am not aware of any Starlink satellites currently in either of those two orbits.

Yes, I used future tense in my comments.

How about linking to the original source rather than a poor copy? https://www.reddit.com/r/space/comments/ld4vlq/gabbard_diagr...

Also: https://www.youtube.com/watch?v=aRUaENzxH44

Analysis of what, exactly? The physics of the orbits they are in are pretty well understood. You can track the orbital altitudes (and failures/disposals) here: https://planet4589.org/space/stats/star/starstats.html

well, exactly that, to me that meant "any source aside from SpaceX" and you provided it so thanks.

Many third parties have analyzed it. FCC, Nasa, their competitors, and others.

To the people that provided third party analysis, thank you, to everyone else, be like those people.

Reply on news.ycombinator.com