“Safety tends to not be on the front burner until it really needs to be on the front burner.”
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Maybe it’s time to reassess the risk of space junk falling to Earth
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Probably nothing much. They aren't big enough to do structural damage to larger buildings, and hitting a person directly is unlikely.
SpaceX will have to do an expected casualties calculation, but the risk is likely still well below FAA and NASA thresholds.
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Every doer is responsible for their own personal safety. That's basically rule number one in any safety training class. Keep yourself safe. Now we'll cover all the things you need to do to keep yourself safe.Ah, yes, people who are concerned about safety. Those would be the checkers, not the doers.
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normally butters
Ars Praefectus
They're not so much worried about capsule/trunk recollision after separation. SpaceX had a separation sequence that worked just fine after deorbit burn for Dragon 1 cargo missions, and all the trunks from those missions came down quickly in a predictable area.
This issue is a "regression" in Dragon 2, both the crewed and cargo versions, and it's all about NASA's risk assessment methods for calculating loss-of-mission and loss-of-crew probabilities. There's some risk, probably very small but nonzero, that the trunk jettison might fail, and it remains attached or stuck to the capsule. If that occurs after deorbit burn, like Dragon 1, that would very likely result in an unsuccessful reentry. With the Dragon 2 procedure, if the trunk jettison fails, they have time in a stable orbit to try some maneuvers to shake the trunk loose or other contingency procedures.
In other words, the trunk is jettisoned earlier for mission assurance reasons, to slightly lower the LOC probabilities that were so important to Commercial Crew certification. NASA and SpaceX knew that unpredictable trunk reentry would be a consequence of this decision, but they overestimated the demiseability of the trunk. Or the other way to put it is that they prioritized a risk to the mission over a risk to the general public.
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Crew Dragon has propellant reserves for an abort, and on missions where you don't perform an abort, enough for a propulsive landing after re-entry. They have tons (literal) of propellant reserves, so much so that they needed to add a fourth parachute. That's also the reason Starliner performs its own circularization, not just to ensure disposal of Centaur, but to burn off all that excess propellant.
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Even that is not a reasonable criticism. Debris reenters all the time, and that is entirely acceptable so long as the risk is properly assessed and remains below the regulatory threshold.
Nobody has shown that the unexpected hazard creates an unacceptable risk. Doing so is the first step, before fixing anything.
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I think you're missing their point: they're not focusing on the likelihood, they're focusing on the (metaphorical) impact; the damage one of the panels these size would cause is enough that it's not something that can be treated as negligible, and the same focus needs to be given to it as to denser materials.
Given the amount of earth that is covered by water it would probably be reasonable to assume that all dragon trunks have had the same amount of debris fail to burn up?
There's been just over 20 launches, there's been 4 instance's of debris that have been found. Given 70% ocean and a good % of land that isn't scoured by humans day to day it would seem like we've found about the right amount of debris in that case.
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This is a serious risk given the huge constellations companies like SpaceX are lofting. I worry it's not getting attention because it's inconvenient to people's visions of the future, which assume that dumping unlimited amounts of debris into the atmosphere is consequence free. Much like people used to assume about dumping waste into the ocean.
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leaving residual compounds that may be harmful to ozone — https://doi.org/10.1073/pnas.2313374120
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How would insurance incentivize SpaceX? It would have coverage for any loss and would be less connected to the financial harm. It isn't like SpaceX wouldn't have the money to cover the harm directly.
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As I commented in the other thread, this paper is looking too narrowly at the problem. Iron oxide also depletes the ozone layer, and there's a hell of a lot more iron in meteorites than there is aluminum. Plus all the nickel, silica, etc.
The real question is how much satellite debris affects ozone compared to meteorite debris, and whether this will have a meaningful effect on net ozone concentrations.
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This is a bit like the argument that volcanos release CO2, which was Rush Limbaugh's argument for why global warming was a hoax. It's true as far as it goes, but iron meteorites have been entering the atmosphere as long as Earth's been around and are part of the existing balance. Launching large amounts of aluminum is new, much like how burning fossil fuels effects the existing CO2 balance.
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So much this. I hope someday soon Ars (and other organizations) will learn that X, along with being a safe-haven for fascists, has not been a reliable place for news for ages. Please follow Prof. Lawler at https://mastodon.social/@sundogplanets
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Thus my second paragraph. I'm all for doing the research and figuring out what the risk is. My criticism is that they're currently making too narrow of a comparison.
As I said in the other thread - Getting a PhD is generally about becoming an expert in the tiniest slice of narrow sub-specialties. This is not training for "big picture" thinking. Can a PhD be a big picture thinker? Absolutely - but the degree has nothing to do with it.
Your Rush comparison just a strawman which makes you look bad. There was nothing in my post indicating that I think this risk is a hoax.
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Is it? There have been hundreds of Starlinks deorbited, and AFAIK nobody has ever found debris. About 20 Crew Dragon trunks, and debris was found 4 times.
That indicates to me that the demisability of Starlinks appears to be good, and the demisability of the Crew Dragon trunks appears to be poor.
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A few people have linked to that paper, but there is a problem. As far as I can tell, it does not once mention ozone. In fact, the abstract finishes with this sentence (emphasis added):
"The influence of this level of metallic content on the properties of stratospheric aerosol is unknown."
Now, I know quite a few people doing work on the kinds of chemical reactions that can occur on atmospheric particulate matter, and am familiar enough with their work that I'm absolutely not willing to rule out some reaction or sequence of reactions that could affect the ozone layer.
But the cited paper does NOT appear to raise this possibility. So I'd really like to know where the "may be harmful to ozone" is coming from.
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Do we know if these are specifically crew dragon trunks or do we count all Dragon 2? because there have been a LOT more than 20 Dragon 2 missions
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I believe crew Dragon lands in the Gulf of Mexico off Pensacola, and Cargo Dragon lands in the Pacific. The trunk would have to fall significantly short to hit land along those tracks. (assuming the Gulf of Mexico track is from Southwest to Northeast). Hitting boats, on the other hand...
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Could be all Dragon 2. Do you know if they use the same trunk jettison procedure?
Edit: Looks like we could possibly add 13 Cargo Dragon 2 flights. That really doesn't change the math in a meaningful way.
~33 re-entries, debris found 4 times. (Dragon 2)
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~300 re-entries, debris found 0 times. (Starlink)
Could this change in the future with larger Starlinks? Sure. But the evidence so far seems to be that the Dragon 2 trunk is far more likely to have a debris problem.
Hm. I wonder if the Feds should start requiring a real, all-up demisability test for these LEO megaconstellation satellites, not just calculations.
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There's 'only' been 24 orbital launches of dragon 2, including the one currently docked to the ISS, so 23 returns to earth where the trunk is discard. I wouldn't call that a lot more than 20.
The most recent return was CRS-30 on the 30/04/24 so the trunk for that might be still up there (unless it was the one recovered in May, though the delay seems to be longer than a month, based on the Victorian one, so that could have been from crew 7. I'm unsure if there has been any confirmation?)
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Full up as in components in a hypersonic plasma tunnel (which are quite rare), or full up as in toss one in orbit and watch it fall? I'm not sure how you would manage the latter. Have some extra propulsion module to let you target some area, and have a radar ship parked underneath? Maybe use the missile test range off Hawaii, with USN support?
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Rideshare on a rocket into orbit, controlled re-entry to target an appropriate missile range with appropriate tracking, optics, etc. I initially thought about Hawaii, but someplace like White Sands would make it easier to find debris...
It really wouldn't need to be all that expensive.
Any significant changes to the satellites being put up would require a re-test.
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I just tried streaming IFT-4 from X, for a couple of people mildly interested but not following very closely. It was an absolute and unmitigated embarrassment: the stream stuttered and buffered the entire bloody time; even setting it to 240p didn't make it stutter any less. Was pretty much damn near unwatchable (and the narration was certainly near-unintelligible as a result.) What a great job, Elon, promoting SpaceX so effectively and exclusively through such an incredibly crappy platform...
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I don’t think it would take much of a re-design - just add an FTS type device to the trunk and design it to go off when the acceleration (deceleration) level exceeds a certain threshold after it has been jettisoned. That way you’re able to increase the exposed surface area early on without risk of spreading debris in LEO. I would probably trigger it at about 1 g, but possibly earlier would be fine too.
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An unfair way. I would say rather they felt the risk to the mission was a higher probability than the risk to the general public.
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They also probably aren't very deadly. Their density is low, their terminal velocity is low, they likely don't weigh much, and they probably tumble aggressively, lowering the terminal velocity even more. And in my experience (I've picked up the remains of a few CFRP [carbon fiber reinforced plastic] aircraft after accidents), the pieces tend to be very floppy; their ̷s̷t̷r̷e̷n̷g̷t̷h̷ stiffness is dependent on their shape.
I wouldn't want to be hit by one, but it'd probably be somewhat worse than being hit with a similarly sized piece of cardboard.
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Umm, yes, every piece of a Starlink satellite is designed to burn up. The FAA insisted, and refused to allow early Starlink satellites to launch until they could demonstrate 'demisability' to the FAA's satisfaction; SpaceX had to remove some components (specifically lenses) from them to get launch approval because SpaceX couldn't show they would be destroyed during re-entry. This has been discussed on Ars in the past.
Further, Starlinks are designed to actively de-orbit themselves. There's no guarantee this will always happen, but so far, quite a few Starlink satellites have in fact done so. I don't know how accurately they can target their re-entry, given the low thrust of their argon rocket engines, but it seems likely they make an effort to 'demise' them in the South Pacific graveyard.
As for concerns about 'harmful chemicals', SpaceX payloads max out around 10t to LEO per launch. Per annum, that's perhaps 1000t/year (as of last year). Every year, something like 40,000t of meteorites are destroyed in Earth's atmosphere. That includes a lot of iron, carbon, aluminum, silicon, etc., and likely in similar proportions to Starlink satellites, excepting iron (more in meteorites) and heavy metals (probably more in meteorites, excepting a few like gallium, copper, and gold). At least for now, absent some evidence of harm or harmful quantities, screaming that 'the sky is falling!' seems premature.
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Speaking for myself, criticism of Musk/SpaceX isn't verboten, but you better bring your 'A' arguments. Sadly, we get a lot of the credulous 'C-' arguments, ad nauseum, and have low tolerance for crap or off-topic comments.
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The giant piece that stuck itself into the ground vertically like a giant cleaver from space looked like it might have left a mark.
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I tend to find the problem is a combination of some people not having internalized what a douche Musk is, while others want to interject it into places where we’re just talking about rockets. To me, there’s a middle ground, where the nuance of reality lies.
As an only slightly-related example, every discussion of Wagner’s music doesn’t have to include a discussion of his influence on Nazism, but at the same time yes... he and his art did have an influence on Nazism, and that’s sometimes is relevant.
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I was about to comment on that. On the other hand, though, you would’ve had to have been hit directly. It’s not like it gouged out a big crater affecting everything for meters around or tumbled along the ground for many meters.
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There have been 30 CRS missions total (12 Dragon, the rest Dragon 2) so far, and 12 crewed Dragon 2 launches (7 NASA and 4 commercial).
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This, 100%. While i do not like Musk as a person, but that is also what I have thought about 100% of the CEOs I have ever met. You pretty much have to be a complete asshole to make it to that level.
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Well, Musk is a particularly putrid piece of work, IMHO. Even as far as big company CEOs go. But rockets are rockets and CEOs are CEOs. Only sometimes are both relevant at the same time in the same conversation.
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Not sure what you are meaning here, but I do not like Musk either. I do acknowledge that Elon has made some crazy good decisions.
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Depends on the proximity to a person or structure when it hits terra firma I guess.
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The difference being that accidental triggering of the LOX kerosene in the planned way won't guarantee the death of a crew, but the same happening to explosives rigged to shred the capsule absolutely will.
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This is a good simple explanation of the threat to the ozone layer that burning up satellites will cause. For those confused.
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