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mrandish 7 hours ago

As I said, I'm only familiar with the high level concepts of vehicle launch safety and not qualified to assess detailed scenarios. I'm just a guy interested enough to read some technical articles and skim a few linked papers several years ago when there was a lot of heat about launch safety from Boca and not much light. When there's a lot of heated rhetoric in the mass media, I find it's better to check directly in scientific and engineering sources.

I dove deep enough to a get sense that these questions have been extremely well-studied and not just by 2020s FAA and SpaceX but going back to the Shuttle and Apollo eras. The body of peer-reviewed engineering studies seemed exhaustive - and not just NASA-centric, the Europeans and Soviets did their own studies too.

Your question is reasonable and occurred to me as well. Components engineered to withstand the enormous heat and pressure of orbital re-entry should be more likely to survive a RUD scenario and subsequent re-entry burn for longer. From what I recall reading, this fits into a safety profile required to ensure very, very low risk because even if a tiny percentage of mass occasionally survives to reach the surface, the actual risk that surviving mass presents is a combination of its quantity, mass, piece size, velocity and, most importantly, where any final surviving bits reach the surface.

I recall seeing a diagram dividing the Boca orbital launch trajectory into windows, like: right around the launch pad, out over the gulf of Mexico, the Caribbean, Atlantic, Africa, Indian ocean, and so on. The entire path until it's out over empty Atlantic ocean has minimal land, people and stuff under it. The gulf of Mexico is by far the highest risk because the rocket is still relatively low and slow. A RUD there could potentially be a lot of stuff coming down. There's not a lot out there in the gulf, just a few ships and planes but the FAA closes a huge area because, while the statistical risk is very low in an absolute sense, it's still too high to take chances.

For later windows, they don't close the corridor underneath to plane and ship traffic because the rocket's much greater speed and altitude later in the flight allows more precisely modeling where the debris field will come down. There was another diagram showing a statistical model of a debris field impact zone as an elongated oval with color-coded concentric rings dividing the debris mass into classes. The outermost ring is the debris that breaks up into smaller, lighter pieces. It's the widest and longest but it's the stuff that's much lower risk because it's smaller and slower.

The smallest concentric ring in the middle is where the small amount of heavier pieces most likely to survive will come down, if any do survive. As you'd expect, that innermost ring is shifted toward the far end of the oval and is a much smaller area. The headline I took away was that there's a very small amount of higher mass debris that both A) is less likely to break up into tiny, lower mass pieces, and B) is less likely to completely burn up. This is the higher-risk mass and, due to its mass, it tends to stay on trajectory, go fastest, farthest and not spread out much. In short, the statistical model showed a very high probability of any higher risk stuff which survives coming down in a surprisingly tiny area. The overall safety model is based on a combination of factors working together so it meets the safety requirements in each window of the flight for each class of mass. The carefully chosen launch location, spacecraft design, component materials, flight path and a bunch of other factors all work together to put the small amount of higher risk stuff down somewhere that fits the safety profile of very, very low risk to people and property. Disclaimer: I've probably got some details wrong and left some things out but this is the sense I got from what I learned. I came away feeling that the safety work done on space launches is comprehensive, diligent and based on a long history of robust, peer-reviewed science backed up by detailed engineering tests as well as real-world data from decades of launches, RUDs and de-orbits.

A fun side story: a few months ago I was at the Hacker's Conference and Scott Manley ("Everyday Astronaut" on YouTube) was attending as he often does. He brought along some interesting space artifacts just to set out on a table for casual show and tell. I was able to pick up and examine a Starship heat tile that was fished out of the gulf of Mexico. It was surprisingly light weight. Sort of like a thick wall piece from a styrofoam picnic cooler. It had a very thin hard shell on one side. This shell was clearly very brittle as it had already been broken up and I was holding an index card-sized shattered piece that weighed maybe a couple ounces. This was clearly not something that was going to maintain structural integrity post-RUD. Once it wasn't packed tightly together into a smooth aerodynamic surface, it's gonna shred into tiny pieces. And that seemed by design - which apparently worked as intended because even without a RUD, at the low and slow speeds over the gulf and near the launch pad it did shatter into small, light pieces - assisted only by the rocket tipping over into the water followed by the relatively mild explosion of the remaining propellant (mild compared to an unimaginably violent orbital RUD, that is). Holding it I remembered the debris field oval diagram and thought, "this is smaller, slower, safer stuff in the outer zones."

mkl 3 hours ago | parent | next [-]

Everyday Astronaut is Tim Dodd.

mrandish 2 hours ago | parent [-]

Oops! I somehow conflated two space YouTubers who I sometimes watch and appreciate. Scott Manley is just Scott Manley on YouTube. Thanks for the correction.

gusgus01 5 hours ago | parent | prev [-]

I know this is just another reddit post so could be fake, but supposedly debris is already washing ashore in Turks and Caicos. Specifically in this post a heat shield tile, but the poster mentions other stuff on the beach. So at least some debris probably dropped nearby.

https://www.reddit.com/r/mildlyinteresting/comments/1i3na4a/...

mrandish 3 hours ago | parent [-]

As I said above, the safety model predicts some lightweight stuff with a consistency not much stiffer than tin foil and coated styrofoam could fall not that far downrange. However, that's also the exact stuff that doesn't present serious risk to people or property.

So even if those claims are true, just finding a little debris doesn't invalidate the safety model or indicate there was ever unacceptable risk. The real question is if any debris from a higher risk class fell in a place the safety model didn't predict and why. That would certainly be notable and worth incorporating into future safety models.

In the absence of solid confirmation, I'm going to stick with the model and the basic physics. If the debris is just the expected stuff, I'm sure SpaceX regrets littering the beaches and should definitely pay for some crews to pick that stuff up and trash it.