Quote from: CMac on 05/29/2023 01:21 pmI'm thinking that this idea got baked in at that point in time and then maybe people didn't return to it as a consideration with the thought "they already tried this and it wasn't practical"Or more to the point - for most every other launch vehicle, it simply isn’t necessary.
I'm thinking that this idea got baked in at that point in time and then maybe people didn't return to it as a consideration with the thought "they already tried this and it wasn't practical"
Quote from: Herb Schaltegger on 05/29/2023 01:35 pmQuote from: CMac on 05/29/2023 01:21 pmI'm thinking that this idea got baked in at that point in time and then maybe people didn't return to it as a consideration with the thought "they already tried this and it wasn't practical"Or more to the point - for most every other launch vehicle, it simply isn’t necessary.Bingo. Everyone is happy to use watercooled (and not evaporative cooled in the vast majority of cases) diverters for engine test stands, but it's (thus far) not been needed for launch mounts.
More than 32,500 5/32-inch holes in the B-2 Test Stand flamedeflector direct more than 240,000 gallons of water a minute tocool rocket engine exhaust during a hot fire test. About another92,000 gallons of water per minute will be sprayed through 92nozzles to provide vibro-acoustic suppression protection duringSpace Launch System core stage testing. This also will help toshield the stage from radiant heating and other thermal effects. The water system nowis capable of delivering 335,000 gallons per minute to the B-2stand via 96-inch pipes
My question here was going to be "What does the B-2 test stand at Stennis use for the 8 minute SLS tests?" as that's all I am aware of with comparative levels of craziness. As always, the internet provideth:https://www.nasa.gov/sites/default/files/atoms/files/b-stand-poster.pdfQuoteMore than 32,500 5/32-inch holes in the B-2 Test Stand flamedeflector direct more than 240,000 gallons of water a minute tocool rocket engine exhaust during a hot fire test. About another92,000 gallons of water per minute will be sprayed through 92nozzles to provide vibro-acoustic suppression protection duringSpace Launch System core stage testing. This also will help toshield the stage from radiant heating and other thermal effects.
More than 32,500 5/32-inch holes in the B-2 Test Stand flamedeflector direct more than 240,000 gallons of water a minute tocool rocket engine exhaust during a hot fire test. About another92,000 gallons of water per minute will be sprayed through 92nozzles to provide vibro-acoustic suppression protection duringSpace Launch System core stage testing. This also will help toshield the stage from radiant heating and other thermal effects.
We can estimate the thermal energy of the exhaust, and this gives us an upper limit on the amount of water needed to dissipate that energy. Probably not going to get to that upper limit, but a ceiling is nice.The exhaust kinetic energy rate is 650kg/sec * 33 * 0.5 * 332502= 113GW.We know that the engines are about 59% efficient in converting the chemical energy to kinetic energy, so this leaves us with 41/59 * 113GW = 78GW of thermal energy in the exhaust stream.The heat of vaporization of water is 2.25 MJ/kg. Thus to absorb all the thermal energy would require a flow rate of 78GW/2.25MJ/kg = 35t/second, or 35m3/sec. (I'm not including the heat required to heat water from 20->100C because I'm looking for orders of magnitude here)Note this is the upper limit. Most the heat is escaping in the exhaust stream that is bouncing off of the stagnation layer, and that stream is moving so fast it's going to not have very much time to turn the water into steam below the exhaust mount. I suspect 3.5t/sec would be more than sufficient.
AIUI, the stagnation layer doesn't get rid of the downward force from the thrust; there's still 75,000 kN of force that will be trying to toss the water in your pool into Mexico. What the stagnation layer does do is reduce the amount of insanely hot, insanely fast gases that would otherwise scour whatever surface is resisting the thrust.
I have a couple of questions concerning the stagnation layer above the steel plate of the Starship OLM that I hope you can help me with. So the way I understand it is, spewing water up through the steel plate will do two things: it keeps the plate cold to prevent an internal steam explosion and it creates a stagnation layer of steam above the steel plate that pushes most of the rocket exhaust to the sides away from the steel plate. Effectively this means that the steam stagnation layer does most of the job of protecting the launch surface and not the steel plate, right?So my question is, if the steel plate doesn’t really do much, why not just remove it and build a simpler and safer system in the form of a deep pool of water? In both cases, the rocket exhaust would flash-boil water to create the steam stagnation layer that protects the launch surface. In the case of a pool we just don’t pump it up to meet the rocket exhaust. We just need to make sure that the pool holds at least the same amount of water as we are pumping up through the steel plate so that the stagnation layer doesn’t disappear.If we use the numbers that InterestedEngineer estimated we can get a feel for how large and deep a pool would have to be:Quote from: InterestedEngineer on 05/11/2023 12:19 amWe can estimate the thermal energy of the exhaust, and this gives us an upper limit on the amount of water needed to dissipate that energy. Probably not going to get to that upper limit, but a ceiling is nice.The exhaust kinetic energy rate is 650kg/sec * 33 * 0.5 * 332502= 113GW.We know that the engines are about 59% efficient in converting the chemical energy to kinetic energy, so this leaves us with 41/59 * 113GW = 78GW of thermal energy in the exhaust stream.The heat of vaporization of water is 2.25 MJ/kg. Thus to absorb all the thermal energy would require a flow rate of 78GW/2.25MJ/kg = 35t/second, or 35m3/sec. (I'm not including the heat required to heat water from 20->100C because I'm looking for orders of magnitude here)Note this is the upper limit. Most the heat is escaping in the exhaust stream that is bouncing off of the stagnation layer, and that stream is moving so fast it's going to not have very much time to turn the water into steam below the exhaust mount. I suspect 3.5t/sec would be more than sufficient.So, the heat from the rocket exhaust will at most evaporate ~35m3 of water every second when we assume that no part of the exhaust is pushed away. For a pool with a diameter of 13m (The OLM legs are 16m apart) that means the booster would vaporize ~0.3m of water every second. For a launch like the first orbital flight test of Starship, where the booster fired for ~8s before lift off, we’d need a pool at least ~2m deep to not empty the pool but that's feasible to build.Then there is of course the pressure from the rocket exhaust. Because we are not pumping the water up to meet the rocket exhaust, some of the rocket exhaust must always be in contact with the water surface to create the steam stagnation layer. This contact is obviously quite violent so additional water will be blasted away compared to the steel plate solution.I find it difficult making a good conservative estimate on how much water is blasted away as this effect is a careful balance between creating steam from the rocket exhaust, and steam preventing the exhaust from reaching the water. Perhaps some of you smart people have an idea for a good estimate?My gut feeling is that the total water removal rate from vaporizing water and blasting it out of the pool is less than what the heat from the rocket would remove if all of it was used to vaporize water (the 35m3/s mentioned above). If so, a pool concept would be a viable alternative to the steel plate solution SpaceX is building, but gut feeling ain’t much to build on.
Quote from: edzieba on 05/30/2023 07:48 amQuote from: Herb Schaltegger on 05/29/2023 01:35 pmQuote from: CMac on 05/29/2023 01:21 pmI'm thinking that this idea got baked in at that point in time and then maybe people didn't return to it as a consideration with the thought "they already tried this and it wasn't practical"Or more to the point - for most every other launch vehicle, it simply isn’t necessary.Bingo. Everyone is happy to use watercooled (and not evaporative cooled in the vast majority of cases) diverters for engine test stands, but it's (thus far) not been needed for launch mounts.My question here was going to be "What does the B-2 test stand at Stennis use for the 8 minute SLS tests?" as that's all I am aware of with comparative levels of craziness. As always, the internet provideth:https://www.nasa.gov/sites/default/files/atoms/files/b-stand-poster.pdfQuoteMore than 32,500 5/32-inch holes in the B-2 Test Stand flamedeflector direct more than 240,000 gallons of water a minute tocool rocket engine exhaust during a hot fire test. About another92,000 gallons of water per minute will be sprayed through 92nozzles to provide vibro-acoustic suppression protection duringSpace Launch System core stage testing. This also will help toshield the stage from radiant heating and other thermal effects. The water system nowis capable of delivering 335,000 gallons per minute to the B-2stand via 96-inch pipesAlso video of a flow test, link starts at the diverter portion of the test:
So, more than 2 months after Elon said the repair was going to take 1-2 months, there's over 2 meters of exposed rebar under the OLM, we're waiting for concrete, and the steel plates and water system after that.Am I the only one who's just completely sick of his entirely insane time estimates? He's either the dumbest person on Earth (the evidence would indicate otherwise) or just lying about those time estimates. Why? Is it to push his people harder?