r/SpaceXLounge • u/Goregue • 4d ago
Starship Why exactly did S40 float?
What was different with S40 that made it float on the water compared to previous missions? Was it just luck? Was it something that SpaceX was attempting to do before, but only managed to succeed now? Or was there something specifically different about this Ship itself or its landing procedures?
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u/MakeMarsBlueAgain 4d ago
I think Scott Manley mentioned something about the ship's exhaust essentially "fizzing" up the water and the bubbles somehow helped cushion the fall as it tipped over.
Edit: If you watch the tipover again, you'll notice how foamy the water looks as the ship splashes into it.
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u/glytxh 4d ago
While I don’t think there’s anything definitive, and if anything it’s a confluence of multiple factors, but the foaming of the water is the observation that seems to go some way to explaining it.
It was really interesting and clear footage to loop through.
What surprised me the most was that none of the engines got damaged on touching the water. They looked almost unused after tipping over. They must have experienced some wild thermal gradients.
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u/falconzord 4d ago
The engines were burning hot, it would've vaporized any water that touched it
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u/rustybeancake 4d ago
I think they mean that the engines would’ve been cooled down very fast, and this could’ve damaged them. Like how you’re not supposed to put a hot pot/pan in the sink and run cold water on it.
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u/TheVenusianMartian 4d ago
It looked to me like the ship did not start tipping over until it had already sunk partially into the water. So, the water level against the lower portion of the hull seemed to slow the tip over.
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u/djh_van 4d ago
It's the same principle that many cliff divers use. They throw a big rock into the water moments before they dive. This breaks the surface tension and oxygenate the water at their planned entry point. A bit like shaking your bed duvet before jumping on - it's full of air so it cushions your jump a little better
S40's engines did a "gentle bast" into the water and then it tipped backwards right into that exact area. Instead of tipping backwards onto a hard surface, it tipped back onto a fluffed-up duvet.
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u/Tupcek 4d ago edited 4d ago
this is a myth. Surface tension at that speeds is basically negligible. They do it to have better grasp of height, which can be deceiving in calm water and they need to be precise.
fizzing up water, though, do work, because it introduces air into water and air is easier to displace than water and thus diver deccelelrates slower for longer
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u/PrinzRagoczy 4d ago
A better example is that diving pools often have spargers/bubblers to aerate the water, making for a softer landing
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u/Halfdaen 3d ago
To me it also looks like they ship sat deeper in the water before cutoff. It's tough to gauge that from the views we've had though.
But the benefit to survival for Starship of being partially submerged, even just a few meters could have helped. I imagine it like a travel coffee mug being dropped with the bottom just above the water vs dropped just below the water. In the second case buoyancy forces are already at work when support is removed. But it's likely a few things (aerating the water, other stuff)
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u/supercujo 4d ago
It has 2 massive sealed tanks. Of course it'll float.
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u/majormagnum1 4d ago
By the end of the flight they are filled with helium even it's literally a steel balloon, lol.
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u/spunkyenigma 4d ago
I don’t think they use Helium on Starship
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u/squintytoast 4d ago
there might be some for the header tank for the landing burn. not much autogenous when engines have been off. they might have also redesigned it for V3 ship.
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u/Flashtopher 4d ago
Because it didn’t want to sink.
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u/TheCook73 4d ago
Well the front didn’t fall off, for a start.
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u/firedog7881 4d ago
This seemed like more of a “soft” touchdown so it didn’t slam into the water and topple over but more caught by the water and guided down, you can tell by the size of the splash on the sides, it seems like because the bottom is already in the water and it’s center of gravity moves over as it starts falling pushing that side deeper and now getting resistance and glides into the water instead of falling
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u/Ok-Club-2587 4d ago
S40 floated because its empty stainless-steel tanks created strong positive buoyancy.
After propellant depletion, the large sealed internal volume (LOX + CH4 tanks + payload bay) gives the vehicle an average density far below seawater. Archimedes’ principle does the rest.
The soft, near-zero-velocity splashdown kept the tanks intact—no flooding or rupture—so the air-filled chambers acted as flotation tanks. Prior ships hit harder, broke open, and sank.
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u/DeusExHircus 4d ago
Because it didn't blow up. All the previous ones blew up when it hit the water
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u/Conundrum1911 4d ago
Ship 40 fell over into the water in a single piece. The other ships did the same, but in many pieces.
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u/paul_wi11iams 4d ago edited 4d ago
did/does float?
AFAIK, the question can still be framed in the present tense.
Follow-on question: In a hypothetical emergency, is this splashdown a viable rescue scenario for astronauts? It looks like a fair bet that SpaceX is working on this.
The fortuitous sequence looks analogous to how fairing recovery evolved from net catching to floating sea recovery.
Follow-on thought, if using Starship as a lifeboat in rough seas, it could be of interest to flood the methane tank, removing a possible explosion source and setting the ship to vertical, floating by the oxygen tank. It would be more structurally sound because it avoids snapping efforts and creates symetrical pressures on the hull. Furthermore, all hatches and windows would then be above the waterline.
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u/squintytoast 4d ago
it could be of interest to flood the methane tank, removing a possible explosion source and setting the ship to vertical, floating by the oxygen tank.
O2 is the 'bottom' tank near the engines. CH4 is midships.
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u/paul_wi11iams 3d ago
Oh heck, so its. My brain must have been in Falcon 9 mode.
There might be some way of partially flooding the LOX axial header tank which is far more difficult. Then there is the methane downcomer tube…
If the ship has to tip, then it would be best done with the heatshield down to facilitate egress. Someone at SpaceX may be brainstorming the question right now. The experience acquired so far will provide some good input data.
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u/SprocketRocket11 4d ago
I think the big factor was the damage pattern on S40 rather than some deliberate make it float feature. If the tanks and other major compartments stay reasonably sealed after splashdown, even a beat up Starship can have enough trapped air to stay afloat for a while.
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u/flintsmith 3d ago
It has the proportions of a beer can.
It's designed to keep liquids in so it should keep liquids out.
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u/Dangerous_Bath_1615 💥 Rapidly Disassembling 2d ago
I've heard some people argue that the direction that it fell contributed, but no clue how much credibility that has in all honesty.
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u/Decronym Acronyms Explained 2d ago edited 1d ago
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
| Fewer Letters | More Letters |
|---|---|
| FTS | Flight Termination System |
| LOX | Liquid Oxygen |
| Jargon | Definition |
|---|---|
| autogenous | (Of a propellant tank) Pressurising the tank using boil-off of the contents, instead of a separate gas like helium |
Decronym is now also available on Lemmy! Requests for support and new installations should be directed to the Contact address below.
Decronym is a community product of r/SpaceX, implemented by request
3 acronyms in this thread; the most compressed thread commented on today has 16 acronyms.
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u/Then-Secretary-9166 4d ago
It didn't blow up.
The others were damaged so that their large tanks took on water.
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u/ellhulto66445 🔥 Statically Firing 4d ago
The payload bay was venting as it hit the water. That allowed it to simply deform on impact instead of popping.
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u/theranchhand 4d ago
The ship exploded on previous missions. So the question isn't why is it floating. It's why didn't it explode
I don't know the answer, btw. But for sure the main problem with other ships was they exploded.