Rakaydos Posted January 22, 2019 Share Posted January 22, 2019 40 minutes ago, Terwin said: Hmm, Methane might be a problem if you are getting above 1200f as it looks like methane will ignite at about 600c(1112f) ( https://www.sciencedirect.com/science/article/pii/0304389484850013 ) Cutting structure and tank costs to 1/60 does not sound like a bad thing... Ignite with what? there's only so much oxygen at the altitudes where aerobreaking happens. Quote Link to comment Share on other sites More sharing options...
Nivee~ Posted January 22, 2019 Share Posted January 22, 2019 17 hours ago, CatastrophicFailure said: Kowalski, analysis? Skipper, this looks like the mockup of the Revolutionary Frustum Donut patented in 1967, ditching the traditional toroidal shape. The idea was abandoned after a mass police panic when the Toroidal Donut company threatened to stop selling donuts.. <Private, in the background, looking cute> What should I do, Skipper?? Quote Link to comment Share on other sites More sharing options...
tater Posted January 22, 2019 Share Posted January 22, 2019 Quote Link to comment Share on other sites More sharing options...
tater Posted January 22, 2019 Share Posted January 22, 2019 (edited) https://www.popularmechanics.com/space/rockets/a25953663/elon-musk-spacex-bfr-stainless-steel/ Sorry, @RedKraken already posted this! Edited January 22, 2019 by tater Quote Link to comment Share on other sites More sharing options...
Ozymandias_the_Goat Posted January 22, 2019 Share Posted January 22, 2019 Musk says that stainless steel will be lighter because they need to use less; apparently the strength of his high chrome-nickel content alloy is increased by 50% at cryogenic temperature. Though, I am under the impression that carbon fiber is four times less dense than stainless steel 300 series. Can you really omit so much material, so that the weight breaks even? Additionally, he talk about a “regenerative heatshield”, which leaks fuel in between two layers of the shield. However, although I will admit I do not know of this ever being used for a heat shield, didn’t the sr-71 do something very similar, leaking fuel onto its skin to seal gaps as the airframe expanded under severe heat? Quote Link to comment Share on other sites More sharing options...
Terwin Posted January 22, 2019 Share Posted January 22, 2019 2 hours ago, Rakaydos said: Ignite with what? there's only so much oxygen at the altitudes where aerobreaking happens. If you are compressing air in front of your ship, you are concentrating any oxygen that might be there. I don't know how much of the methane will have oxygen to burn with or how much that will counteract the regenerative cooling, but at the very least it sounds like something that needs to be looked at and tested as it 'might be a problem'. 1 minute ago, Ozymandias_the_Goat said: Musk says that stainless steel will be lighter because they need to use less; apparently the strength of his high chrome-nickel content alloy is increased by 50% at cryogenic temperature. Though, I am under the impression that carbon fiber is four times less dense than stainless steel 300 series. Can you really omit so much material, so that the weight breaks even? Additionally, he talk about a “regenerative heatshield”, which leaks fuel in between two layers of the shield. However, although I will admit I do not know of this ever being used for a heat shield, didn’t the sr-71 do something very similar, leaking fuel onto its skin to seal gaps as the airframe expanded under severe heat? SR-71 had very tight tolerances for the super-sonic regime, as such, when the surface of the plane was not being heated by passing super-sonic air, it fit together poorly and leaked a lot of fuel. It was not really for cooling purposes. I think the issue is that you need the carbon fiber to be a certain strength when being heated or cooled, and the steel has a sufficiently larger heat tolerance that even though the frame is heavier, they can reduce/eliminate the (heavy)heat-shield that the carbon fiber would need. Perhaps if you think of it more as a heat-shield that removes the need for the carbon-fiber structural elements than as a straight replacement for the carbon-fiber? Quote Link to comment Share on other sites More sharing options...
tater Posted January 22, 2019 Share Posted January 22, 2019 He's talking about perforations to the outside on the windward (TPS, though in this case it's hot structure/active TPS) side. Quote Link to comment Share on other sites More sharing options...
Mad Rocket Scientist Posted January 22, 2019 Share Posted January 22, 2019 Still sounds to me like the carbon fiber was just not working how they hoped. What's really surprising is how cheap steel is though, I knew carbon fiber was horribly expensive, but I didn't know how cheap steel was. 3 hours ago, CatastrophicFailure said: This. This right here. Stainless or no, stuff like this is usually built in clean room, yes? I would think there’d be a huge risk of dirt, rocks, small desert creatures and other foreign contaminates getting into the thing. It’s all fun and games until some hapless frozen pigeon gets sucked into a turbo pump. "Part of the Merlin’s qualification testing involves feeding a stainless steel nut into the fuel and oxidizer lines while the engine is running—a test that would destroy most engines but leaves the Merlin running basically unhindered." https://www.airspacemag.com/space/is-spacex-changing-the-rocket-equation-132285884/?page=2 Quote Link to comment Share on other sites More sharing options...
MaverickSawyer Posted January 22, 2019 Share Posted January 22, 2019 9 minutes ago, Mad Rocket Scientist said: "Part of the Merlin’s qualification testing involves feeding a stainless steel nut into the fuel and oxidizer lines while the engine is running—a test that would destroy most engines but leaves the Merlin running basically unhindered." https://www.airspacemag.com/space/is-spacex-changing-the-rocket-equation-132285884/?page=2 Benefits of a gas generator cycle. If they tried that with Raptor at full power, I personally guarantee they'd have nothing left of the test stand in under a second. Staged combustion is EXTREMELY intolerant of errors or flaws... just ask the teams behind the NK-33 and Aerojet Rocketdyne's conversion of them for use on Antares... According to the incident report... Quote "The explosion was triggered when rotating and stationary components in part of the turbopump came into contact. “This frictional rubbing led to ignition and fire” in the turbopump, and thus the explosion, the report states." That was an ox-rich staged combustion engine. Full-flow, like Raptor, is likely to be even less tolerant of abuse. Quote Link to comment Share on other sites More sharing options...
KSK Posted January 22, 2019 Share Posted January 22, 2019 4 hours ago, CatastrophicFailure said: This. This right here. Stainless or no, stuff like this is usually built in clean room, yes? I would think there’d be a huge risk of dirt, rocks, small desert creatures and other foreign contaminates getting into the thing. It’s all fun and games until some hapless frozen pigeon gets sucked into a turbo pump. Totally. Macerated pigeon would make a dreadful propellant - the ISP hit would be awful. Tis a serious point though. Presumably it gets taken back into the (then completed) hangar for installing the actual flight engines and other important bits and pieces. Meanwhile they're building the stainless steel bits in parallel with the hanger? Although that's total speculation on my part. Quote Link to comment Share on other sites More sharing options...
tater Posted January 22, 2019 Share Posted January 22, 2019 (edited) Edited January 22, 2019 by tater Quote Link to comment Share on other sites More sharing options...
magnemoe Posted January 22, 2019 Share Posted January 22, 2019 5 hours ago, CatastrophicFailure said: This. This right here. Stainless or no, stuff like this is usually built in clean room, yes? I would think there’d be a huge risk of dirt, rocks, small desert creatures and other foreign contaminates getting into the thing. It’s all fun and games until some hapless frozen pigeon gets sucked into a turbo pump. Booster parts are not clean room items. Yes manufacturing facilities are clean just like plane construction sites. Space hardware like satellites are usually clean room because of optic and solar panels. Yes you could put satellite into an foil cocoon Quote Link to comment Share on other sites More sharing options...
sh1pman Posted January 22, 2019 Share Posted January 22, 2019 Subcooled liquid (~100K) turned to gas (110K) and then to very hot gas/plasma (1750K) in milliseconds, then vented away. Kinda like a liquid ablator. Quote Link to comment Share on other sites More sharing options...
XB-70A Posted January 22, 2019 Share Posted January 22, 2019 Here are some (terrible) shots of the SLC-39A taken today: 21 km away (awful) From the Saturn V hangar, 6.3 km away. Somewhat a bit better but the viewing angle is really bad from there. Then the only one with an average view of it: Drivers are always slowing down to show alligators, or a nest of bald eagles to the tourists, I wish they could do it for big Falcons too... Quote Link to comment Share on other sites More sharing options...
tater Posted January 22, 2019 Share Posted January 22, 2019 41 minutes ago, sh1pman said: Subcooled liquid (~100K) turned to gas (110K) and then to very hot gas/plasma (1750K) in milliseconds, then vented away. Kinda like a liquid ablator. I've seen estimates of the mass of methane required for the reentry phase that vary from 5-nearly 20 tonnes. Still, props are cheap, and the steel apparently has a lower mass than CFC + TPS, anyway. In fact, even 20 tonnes might simply equal a TPS mass, so this might be "free" from a mass standpoint. Super exciting to watch this take shape. Quote Link to comment Share on other sites More sharing options...
sh1pman Posted January 22, 2019 Share Posted January 22, 2019 1 minute ago, tater said: Still, props are cheap, and the steel apparently has a lower mass than CFC + TPS, anyway. In fact, even 20 tonnes might simply equal a TPS mass, so this might be "free" from a mass standpoint. It does fit the description of something “delightfully counter-intuitive”. Quote Link to comment Share on other sites More sharing options...
Ultimate Steve Posted January 22, 2019 Share Posted January 22, 2019 7 minutes ago, tater said: 51 minutes ago, sh1pman said: I've seen estimates of the mass of methane required for the reentry phase that vary from 5-nearly 20 tonnes. Still, props are cheap, and the steel apparently has a lower mass than CFC + TPS, anyway. In fact, even 20 tonnes might simply equal a TPS mass, so this might be "free" from a mass standpoint. One concern I have is re-entries that are not from LEO. Are your 5-20 ton estimates for LEO or not? Because if it's 5-20 from LEO it's going to be a whole lot more coming back from the Moon or Mars. Quote Link to comment Share on other sites More sharing options...
sh1pman Posted January 22, 2019 Share Posted January 22, 2019 (edited) 9 minutes ago, Ultimate Steve said: it's going to be a whole lot more coming back from the Moon or Mars. Also applies to any regular (ceramic tiles) or ablative TPS. Another benefit of liquid cooling is that it’s waaay easier to refill the coolant (fuel) than to replace the tiles/ablator. ESPECIALLY on other planetary bodies (wishful thinking) Edited January 22, 2019 by sh1pman Quote Link to comment Share on other sites More sharing options...
Ultimate Steve Posted January 22, 2019 Share Posted January 22, 2019 17 minutes ago, sh1pman said: Also applies to any regular (ceramic tiles) or ablative TPS. Another benefit of liquid cooling is that it’s waaay easier to refill the coolant (fuel) than to replace the tiles/ablator. ESPECIALLY on other planetary bodies (wishful thinking) Correct. I'll admit I hadn't considered the whole refueling thing, that does make it much easier. However, I'd think that per kg, a dedicated heat shield material is better at dealing with heat then liquid methane. I don't know how much better, though. And past a certain point, I'm guessing that the reduced mass of a dedicated TPS would outweigh the simplicity and other advantages that methane has. The question is, is that point before or after interplanetary trips? Quote Link to comment Share on other sites More sharing options...
sh1pman Posted January 22, 2019 Share Posted January 22, 2019 4 minutes ago, Ultimate Steve said: However, I'd think that per kg, a dedicated heat shield material is better at dealing with heat then liquid methane. I don't know how much better, though. And past a certain point, I'm guessing that the reduced mass of a dedicated TPS would outweigh the simplicity and other advantages that methane has. The question is, is that point before or after interplanetary trips? No idea, honestly. I guess it depends on the heat shield material, reentry speed and profile, vehicle shape and probably a hundred other things. Quote Link to comment Share on other sites More sharing options...
MaverickSawyer Posted January 22, 2019 Share Posted January 22, 2019 I strongly suspect after. Think about it... Rocket engines use actively cooled walls in the hottest areas, right? It'd be easier from a production standpoint to use ablative cooling, but they use regenerative cooling instead because it's more reliable. Quote Link to comment Share on other sites More sharing options...
Rakaydos Posted January 22, 2019 Share Posted January 22, 2019 44 minutes ago, MaverickSawyer said: I strongly suspect after. Think about it... Rocket engines use actively cooled walls in the hottest areas, right? It'd be easier from a production standpoint to use ablative cooling, but they use regenerative cooling instead because it's more reliable. From a recently posted talk by TomMueller, SpaceX's chief rocket scientist engineer, the ablatives on the MErlin 1A were a pain in the ass. The best materials for ablatives had crappy stress-resiliance- half the nozzles they cast came out of the oven already cracked from cooling. That does not sound like "easier from a production standpoint" continues into... Quote Link to comment Share on other sites More sharing options...
Xd the great Posted January 22, 2019 Share Posted January 22, 2019 1 hour ago, Ultimate Steve said: One concern I have is re-entries that are not from LEO. Are your 5-20 ton estimates for LEO or not? Because if it's 5-20 from LEO it's going to be a whole lot more coming back from the Moon or Mars. How about adding extra PICA-X not picachu for shielding? Quote Link to comment Share on other sites More sharing options...
tater Posted January 22, 2019 Share Posted January 22, 2019 5 minutes ago, Xd the great said: How about adding extra PICA-X not picachu for shielding? Not with active cooling venting methane through pores to the outside. Quote Link to comment Share on other sites More sharing options...
MaverickSawyer Posted January 22, 2019 Share Posted January 22, 2019 Y'know, just had a bit of a brainwave... Ablative heat shields outgas to carry away the heat, right? I can't remember if the outgassing has an impact on the shock front, but if it does... Maybe there's an advantage to the venting of methane on the windward side... Something like gas film cooling in a rocket engine, perhaps? Quote Link to comment Share on other sites More sharing options...
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