Hacker News Reader

Hacker News

Comment by bufferoverflow | Hacker News Reader

Parent Full thread

bufferoverflow

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

View on HN

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

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

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

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.

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

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.

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

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?

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?

I’d love to know more about this too.

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".

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.

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.

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.

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.

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.

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.

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

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).

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'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...

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.

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.

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...

Reply on news.ycombinator.com