Quote from: Robotbeat on 11/24/2022 08:05 pmQuote from: Lee Jay on 11/24/2022 07:58 pmQuote from: InterestedEngineer on 11/24/2022 07:46 pmQuote from: TheRadicalModerate on 11/24/2022 07:03 pmI don't think letting a Starship fall over on its side in the water is viable, because there will always be wave conditions that will break it open.Why would a pressurized Starship break open falling over its side into the water?SN10 didn't even survive a hard landing on its bottom. You really think you can tip over a 16 story building into the turbulent sea and expect it to survive?Because it can be engineered (and tested) to do so.At what mass penalty?There's a reason ship hulls are 3-10 times (or more) thicker than SS's tanks.
Quote from: Lee Jay on 11/24/2022 07:58 pmQuote from: InterestedEngineer on 11/24/2022 07:46 pmQuote from: TheRadicalModerate on 11/24/2022 07:03 pmI don't think letting a Starship fall over on its side in the water is viable, because there will always be wave conditions that will break it open.Why would a pressurized Starship break open falling over its side into the water?SN10 didn't even survive a hard landing on its bottom. You really think you can tip over a 16 story building into the turbulent sea and expect it to survive?Because it can be engineered (and tested) to do so.
Quote from: InterestedEngineer on 11/24/2022 07:46 pmQuote from: TheRadicalModerate on 11/24/2022 07:03 pmI don't think letting a Starship fall over on its side in the water is viable, because there will always be wave conditions that will break it open.Why would a pressurized Starship break open falling over its side into the water?SN10 didn't even survive a hard landing on its bottom. You really think you can tip over a 16 story building into the turbulent sea and expect it to survive?
Quote from: TheRadicalModerate on 11/24/2022 07:03 pmI don't think letting a Starship fall over on its side in the water is viable, because there will always be wave conditions that will break it open.Why would a pressurized Starship break open falling over its side into the water?
I don't think letting a Starship fall over on its side in the water is viable, because there will always be wave conditions that will break it open.
Quote from: Lee Jay on 11/24/2022 08:29 pmQuote from: Robotbeat on 11/24/2022 08:05 pmQuote from: Lee Jay on 11/24/2022 07:58 pmQuote from: InterestedEngineer on 11/24/2022 07:46 pmQuote from: TheRadicalModerate on 11/24/2022 07:03 pmI don't think letting a Starship fall over on its side in the water is viable, because there will always be wave conditions that will break it open.Why would a pressurized Starship break open falling over its side into the water?SN10 didn't even survive a hard landing on its bottom. You really think you can tip over a 16 story building into the turbulent sea and expect it to survive?Because it can be engineered (and tested) to do so.At what mass penalty?There's a reason ship hulls are 3-10 times (or more) thicker than SS's tanks. Remember that Starship will ride on top of the water with less than 1 m of draft. Unless you divert into a storm I think it will be fairly resilient as long as it can maintain some pressurization. My quick estimate gives less than 1 bar to maintain a cylinder that is 50 m by 9 m and 300 t in tension even if supported only on the ends.
Quote from: eriblo on 11/24/2022 11:16 pmQuote from: Lee Jay on 11/24/2022 08:29 pmQuote from: Robotbeat on 11/24/2022 08:05 pmQuote from: Lee Jay on 11/24/2022 07:58 pmQuote from: InterestedEngineer on 11/24/2022 07:46 pmQuote from: TheRadicalModerate on 11/24/2022 07:03 pmI don't think letting a Starship fall over on its side in the water is viable, because there will always be wave conditions that will break it open.Why would a pressurized Starship break open falling over its side into the water?SN10 didn't even survive a hard landing on its bottom. You really think you can tip over a 16 story building into the turbulent sea and expect it to survive?Because it can be engineered (and tested) to do so.At what mass penalty?There's a reason ship hulls are 3-10 times (or more) thicker than SS's tanks. Remember that Starship will ride on top of the water with less than 1 m of draft. Unless you divert into a storm I think it will be fairly resilient as long as it can maintain some pressurization. My quick estimate gives less than 1 bar to maintain a cylinder that is 50 m by 9 m and 300 t in tension even if supported only on the ends.Remember, it will fall over. That impact load will drive everything. And it will be huge.
Seems like this is a problem that doesn't have to be solved if you're going with an escape capsule. We have plenty of experience making blunt bodies float, although this one would be larger and possibly top-heavier. Same thing for rough-surface landings.It's possible that there would be parachute limitations. However, if you have a propulsive system, you can arbitrarily reduce the descent speed before popping the chutes, which should reduce peak loads to something manageable.
Quote from: Lee Jay on 11/24/2022 07:58 pmQuote from: InterestedEngineer on 11/24/2022 07:46 pmQuote from: TheRadicalModerate on 11/24/2022 07:03 pmI don't think letting a Starship fall over on its side in the water is viable, because there will always be wave conditions that will break it open.Why would a pressurized Starship break open falling over its side into the water?SN10 didn't even survive a hard landing on its bottom. You really think you can tip over a 16 story building into the turbulent sea and expect it to survive?You shouldn't expect that even for perfectly calm sea in fact.The tip of 50m tall vehicle toppling sideways would impact at about 38m/s. Good luck with thin shell staying intact after that.After all the tip velocity of falling rigid stick is sqrt(3*g*l) where l is the length of the object, g is surface gravitational acceleration. This approximation (specific moment of intertia I = 1/3 * l^2) is good enough for Starship.
0:15, breaks apart after tipping.0:48, used thrusters on the top to control tipping.
Quote from: Lee Jay on 11/25/2022 02:20 pm0:15, breaks apart after tipping.0:48, used thrusters on the top to control tipping.But F9 boosters are not designed to handle a 2g lateral force, while an SS must do this as part of a normal EDL. A video compilation airliner landing failures would be just as relevant.
Quote from: DanClemmensen on 11/25/2022 02:28 pmQuote from: Lee Jay on 11/25/2022 02:20 pm0:15, breaks apart after tipping.0:48, used thrusters on the top to control tipping.But F9 boosters are not designed to handle a 2g lateral force, while an SS must do this as part of a normal EDL. A video compilation airliner landing failures would be just as relevant.If SS is coming in at a couple hundred tons, you think it's going to have thrusters on the top that can generate 2g's of lateral force, like 400 tons? Or maybe half that?
Quote from: sebk on 11/25/2022 01:34 pmQuote from: Lee Jay on 11/24/2022 07:58 pmQuote from: InterestedEngineer on 11/24/2022 07:46 pmQuote from: TheRadicalModerate on 11/24/2022 07:03 pmI don't think letting a Starship fall over on its side in the water is viable, because there will always be wave conditions that will break it open.Why would a pressurized Starship break open falling over its side into the water?SN10 didn't even survive a hard landing on its bottom. You really think you can tip over a 16 story building into the turbulent sea and expect it to survive?You shouldn't expect that even for perfectly calm sea in fact.The tip of 50m tall vehicle toppling sideways would impact at about 38m/s. Good luck with thin shell staying intact after that.After all the tip velocity of falling rigid stick is sqrt(3*g*l) where l is the length of the object, g is surface gravitational acceleration. This approximation (specific moment of intertia I = 1/3 * l^2) is good enough for Starship.And yet Falcon 9, made out of thin aluminum alloy and very nearly as tall, actually did survive this on more than one occasion. When reality shows something actually happening even without intentional engineering, it’s no longer viable to claim it couldn’t be reasonably engineered to happen intentionally.
The complexities of rotating while submerged in water and with horizontal movement of the base are beyond our meager analytic abilities, but we can calculate some more simpler sides of the problem.How many joules need to be dissipated, and how much force does it to take to cancel out the 0.5MPa of internal pressure on the tanks where the water is being impacted, thus causing buckling?With center of mass about (17-2) = 15m above the surface and a mass of 120t, mgh gives us 17.6MJ of potential energy that needs to be dissipated somehow. The bottom is under water by 2m and that water has to be moved up, and 2m*120t*9.8 gives 2.4MJ. So let's say net 15MJ of potential energy that has to go to zero.The final displacement of water will be 120t, or 120m^3 of water. This works out to 0.72m submerged height and an a water contact area of about 2.5 * 50 = 125m^2 ( per https://www.mathsisfun.com/geometry/cylinder-horizontal-volume.html )0.5MPa with an area of 125m^2 gives a max force before buckling the pressurized tanks of 62.5MN. Applied to F=ma with a mass of 120t yields a maximum acceleration of 520m/sec, or 53gs.A rough estimate of the deceleration length in water is the final displacement of the water, which here is 0.72m, so plugging that into the kinematic equations with 0.72m length, 520m/sec acceleration, final velocity zero, and solving for initial velocity, yields 27.7m/sec, and the deceleration happens over 0.053 seconds.27.7 m/sec is a free fall from 39m, which is well above the center of mass height.Given the rotation is happening in water, which slows the rotation, and the impact on the water happens at the smaller radius first (you can see the progressive splash, it's about 1-2 frames from bottom to top of F9), or about the same length of time as the deceleration above, it seems entirely plausible that pressurized Starship fuel tanks can survive falling over with its tail in water.Now, whether the header tanks or other internal plumbing can handle 53gs is another question. They did on F9, apparently (which tells me that the max force is probably less than 53gs).It's also easy to pad a precious human cargo area to handle 53gs, that kind of force is routine in car wrecks.TL;DR - abort to water landing seems feasible.