sh1pman Posted July 11, 2018 Share Posted July 11, 2018 6 hours ago, Serpens Solidus said: On F9 /o\ Inflatable heat shield? Normal heat shield below PAF that gets decoupled somehow? Ballutes? Reentry at 8 km/s will be much much hotter than their booster reentry. Quote Link to comment Share on other sites More sharing options...
cubinator Posted July 11, 2018 Share Posted July 11, 2018 15 minutes ago, sh1pman said: Reentry at 8 km/s will be much much hotter than their booster reentry. A good step towards 14 km/s... Quote Link to comment Share on other sites More sharing options...
Wjolcz Posted July 11, 2018 Share Posted July 11, 2018 39 minutes ago, sh1pman said: Inflatable heat shield? Normal heat shield below PAF that gets decoupled somehow? Ballutes? Reentry at 8 km/s will be much much hotter than their booster reentry. There was an idea someone posted in this thread and it looked like a ballute around the engine. So I'm guessing it would reenter "nose" first. It would be interesting if instead of that the second stage had half of the interstage left on it (to protect the engine) and a pair of wings. Then the engine (assuming they modified the fuel tanks to deflate somehow) could be moved into the stage to control the center of mass. Maybe, just maybe they could land it on a runway that way. I doubt it will ever happen but I'd like to see that. I hope I'm not repeating myself. Quote Link to comment Share on other sites More sharing options...
sh1pman Posted July 11, 2018 Share Posted July 11, 2018 6 minutes ago, Wjolcz said: ballute around the engine. Still have to protect the engine against heat. Quote Link to comment Share on other sites More sharing options...
zolotiyeruki Posted July 12, 2018 Share Posted July 12, 2018 Is the re-entry heating worse than what the engine experiences during ascent/orbital insertion? It makes sense to have the second stage enter engine-end-first. That way the acceleration due to drag will force all the fuel down towards the engines, just like it is during ascent. No need for ullage motors. Another question: does it need to re-enter at 7km/s? Why not do a big retro burn? Let's do the math. The empty mass of the 2nd stage is 3.9 tons, and it carries about 92.5 tons of fuel. Let's say it keeps the last 10% of its fuel*, and has a mass of 13 tons. Assuming an Isp of 300, that means it could slow down from 7km/s down to 3.5km/s before hitting the atmosphere. Is that slow enough that the engine wouldn't need extra protection against the heat? * yes, I know that this would impact the payload capacity to orbit, but a lot of payloads are well under the 22.8 tons capacity anyway Quote Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted July 12, 2018 Share Posted July 12, 2018 46 minutes ago, zolotiyeruki said: Another question: does it need to re-enter at 7km/s? Why not do a big retro burn? Let's do the math. The empty mass of the 2nd stage is 3.9 tons, and it carries about 92.5 tons of fuel. Let's say it keeps the last 10% of its fuel*, and has a mass of 13 tons. Assuming an Isp of 300, that means it could slow down from 7km/s down to 3.5km/s before hitting the atmosphere. Is that slow enough that the engine wouldn't need extra protection against the heat? It’s not just the heat, it’s the dynamic pressure. AKA hypersonic air drag and all the nasties it brings. And that MVac engine Bell is fragile as heck. Watch during a launch, just after staging, you’ll see a metal stiffening ring come loose from the end of the Bell. You could easily dent it with a hammer, it’s so thin. Protecting that is gonna be the big trick for re-entering a second stage. Doing a big retro burn is a likely way of doing this, but then it’ll still have to deal with the much higher G-forces from plunging faster into the thicker air, and most likely nose first, directing that force in a way it wasn’t designed for, in order to protect that engine Bell. And then you have the whole messy business of center of mass due to that heavy engine at the back. Realistically, I have no idea how they’re gonna pull this one off. Quote Link to comment Share on other sites More sharing options...
sh1pman Posted July 12, 2018 Share Posted July 12, 2018 45 minutes ago, zolotiyeruki said: Is the re-entry heating worse than what the engine experiences during ascent/orbital insertion? You serious? It's like a thousand times worse. Ballistic reentry is 2200-2500 deg C heating. Everything that's not a heat shield will melt, even the combustion chamber. The engine is also regeneratively cooled during ascent. Quote Link to comment Share on other sites More sharing options...
YNM Posted July 12, 2018 Share Posted July 12, 2018 (edited) 4 minutes ago, CatastrophicFailure said: it’s the dynamic pressure. AKA hypersonic air drag and all the nasties it brings. I was wondering whether SpX has data for this on their existing engines. Sure the heat is massive but what I'm more concerned so far is the fragile nature of the engine bells. You don't want to return it home in useless state I guess, unless cutting off and replacing the bell is part of the plan (which I've heard somewhere). Edited July 12, 2018 by YNM Quote Link to comment Share on other sites More sharing options...
zolotiyeruki Posted July 12, 2018 Share Posted July 12, 2018 Thanks for clearing up my misconceptions. Could an inflatable donut-shaped heat shield slow it down enough before it hits the denser atmosphere and the accompanying dynamic pressure? Quote Link to comment Share on other sites More sharing options...
tater Posted July 12, 2018 Share Posted July 12, 2018 Quote Link to comment Share on other sites More sharing options...
StarStreak2109 Posted July 12, 2018 Share Posted July 12, 2018 When I remember the hubbub they made when discussing to admit LNG freighters to one German Northsea port... Like the danger of the freighter turning into a giant fuel-air-bomb... Now imagine that truck going caboom... I hope for longterm they have an alternative logistics concept... Quote Link to comment Share on other sites More sharing options...
Scotius Posted July 12, 2018 Share Posted July 12, 2018 It's empty It is being transported to Boca Chica, where it will be covered in insulation and cooling equipment. Maybe even buried undergound? And only then filled up with LOX. Trying to haul such big tank loaded with cryogenically liquified oxygen would be all kinds of logistic nightmare. Quote Link to comment Share on other sites More sharing options...
Xd the great Posted July 12, 2018 Share Posted July 12, 2018 About the bfr, how does spcaeX plan to do the flip maneouver during landing? Stalling a plane is not always a great idea. Try to imagine a boeimg 747 lands propulsively. Quote Link to comment Share on other sites More sharing options...
Wjolcz Posted July 12, 2018 Share Posted July 12, 2018 (edited) 2 hours ago, Xd the great said: About the bfr, how does spcaeX plan to do the flip maneouver during landing? Stalling a plane is not always a great idea. Try to imagine a boeimg 747 lands propulsively. I've been wondering this myself. I only see 2 solutions (or one if you combine them): RCS and some sort of airbrakes on the nose being activated just after the reentry when the air is still not dense enough to counteract the flip manouvre + moving weight. Considering that most of the weight is on the bottom half of the spaceship it might as well stabilize itself well enough. Maybe the wings and split flaps are enough to keep it from stalling during reentry. Or maybe the flight profile will look like this: the ship reenters just like the shuttle did, dives and pulls up until it's going vertically up, let the gravity do the work and bring the ship back down then fire up the engines and land. I'm pretty sure exactly this is what is showed in their Martian landing simulation. Let me find it real quick. Edit: Yep. You can see it going down, gaining lift and then up again. I can imagine the final approach will probably be much steeper on Earth since the atmosphere is denser. Edited July 12, 2018 by Wjolcz Quote Link to comment Share on other sites More sharing options...
Xd the great Posted July 12, 2018 Share Posted July 12, 2018 Sounds dangerous to me. Probably gonna stick to the dragon capsule. Quote Link to comment Share on other sites More sharing options...
Val Posted July 12, 2018 Share Posted July 12, 2018 Moved ½ page of SLS posts to the NASA thread. Quote Link to comment Share on other sites More sharing options...
YNM Posted July 12, 2018 Share Posted July 12, 2018 4 hours ago, Xd the great said: Try to imagine a boeimg 747 lands propulsively. You need extra jets. Or a really s*** engine. Quote Link to comment Share on other sites More sharing options...
Xd the great Posted July 12, 2018 Share Posted July 12, 2018 Yeah, about that, none of the planes are in a stall while landing/docking Quote Link to comment Share on other sites More sharing options...
YNM Posted July 12, 2018 Share Posted July 12, 2018 4 minutes ago, Xd the great said: none of the planes are in a stall while landing/docking Not for the second, yes for the first. Quote Link to comment Share on other sites More sharing options...
MinimumSky5 Posted July 12, 2018 Share Posted July 12, 2018 Yes, technically the Harrier is in a stalled state, but it's still landing horizontally, and hasn't had to perform a flip in order to land on it's tail, and it's not had to endure Mach 25+ speeds in the upper atmosphere, and it hasn't done all of that hundreds of times. Quote Link to comment Share on other sites More sharing options...
Rakaydos Posted July 12, 2018 Share Posted July 12, 2018 1 hour ago, Xd the great said: Sounds dangerous to me. Probably gonna stick to the dragon capsule. Obligitory "We've been able to do this since the 90s" Quote Link to comment Share on other sites More sharing options...
magnemoe Posted July 12, 2018 Share Posted July 12, 2018 21 minutes ago, Rakaydos said: Obligitory "We've been able to do this since the 90s" Yes, add that spacex has thought this trough a lot, they added the delta wing to be able to land on both earth and mars. Now I'm a bit skeptical about part of BFR, mostly the lack of escape system as rockets will not be passenger plane safe. This is also something who will be extensively testing then they start testing the upper stage. Quote Link to comment Share on other sites More sharing options...
Wjolcz Posted July 12, 2018 Share Posted July 12, 2018 44 minutes ago, Rakaydos said: Obligitory "We've been able to do this since the 90s" I keep forgetting that having enough gimbal makes you fly however you want. Quote Link to comment Share on other sites More sharing options...
YNM Posted July 12, 2018 Share Posted July 12, 2018 1 hour ago, MinimumSky5 said: but it's still landing horizontally, and hasn't had to perform a flip in order to land on it's tail, and it's not had to endure Mach 25+ speeds in the upper atmosphere, and it hasn't done all of that hundreds of times. It's only handling Mach 3 on Mars. And trying to fly on Mars is like trying to keep yourself full by eating air. Not to forget the TWR of BFR upon landing on Mars is probably way above that of Harriers. It's not flying, it's just a really s*** blanket. Quote Link to comment Share on other sites More sharing options...
tater Posted July 12, 2018 Share Posted July 12, 2018 Quote Link to comment Share on other sites More sharing options...
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