sojourner Posted April 13, 2017 Share Posted April 13, 2017 2 hours ago, Frozen_Heart said: Shush. You'll give elon ideas. It's an old video. The trunk stays attached to the first stage now. It comes back with every returned first stage. Link to comment Share on other sites More sharing options...
Spaceception Posted April 13, 2017 Share Posted April 13, 2017 1 minute ago, sojourner said: It's an old video. The trunk stays attached to the first stage now. It comes back with every returned first stage. I thought it was called the interstage. Link to comment Share on other sites More sharing options...
Brent Kerman Posted April 13, 2017 Share Posted April 13, 2017 Trunk is on dragon before reentry. Link to comment Share on other sites More sharing options...
sevenperforce Posted April 13, 2017 Share Posted April 13, 2017 7 minutes ago, sojourner said: It's an old video. The trunk stays attached to the first stage now. It comes back with every returned first stage. The interstage is between the first stage and the second stage; the trunk is between the second stage and the Dragon capsule. The trunk stays with the capsule on orbit and is jettisoned shortly before re-entry. Link to comment Share on other sites More sharing options...
sojourner Posted April 13, 2017 Share Posted April 13, 2017 Doh, my bad for posting after just waking up. Wasn't thinking straight. Link to comment Share on other sites More sharing options...
Spaceception Posted April 13, 2017 Share Posted April 13, 2017 10 minutes ago, sojourner said: Doh, my bad for posting after just waking up. Wasn't thinking straight. I think we've all been there Link to comment Share on other sites More sharing options...
tater Posted April 13, 2017 Share Posted April 13, 2017 (edited) Someone at NSF made an interesting point regarding the vacuum Merlin engines, and possible use of landing. They are ground tested without the bell extension added (giving credence to the claim up thread that the bell might not even be able to stay intact at sea level with the engine running)... the interesting point was that if it is bolted on after testing, it could equally be jettisoned after the reentry burn, using the engine as tested (now MUCH shorter, too) for landing. Look at the SSTU engines, above. You can see where the bell extension is added on the vacuum versions. It's not a cheap part of the engine, but it is none the less cheaper than letting the entire stage 2 burn up as it does now eventually. Edited April 13, 2017 by tater Link to comment Share on other sites More sharing options...
tater Posted April 13, 2017 Share Posted April 13, 2017 (edited) Is the added refurb cost (replacing the bell extension at minimum) cheaper than adding X superdraco engines, including the lost payload capacity opportunity cost, etc.? EDIT: I honestly had not been aware how thin the nozzle extension was, most is apparently ~0.3mm thick (!?) according to one of the pages I found. Edited April 13, 2017 by tater Link to comment Share on other sites More sharing options...
Kryten Posted April 13, 2017 Share Posted April 13, 2017 13 minutes ago, tater said: EDIT: I honestly had not been aware how thin the nozzle extension was, most is apparently ~0.3mm thick (!?) according to one of the pages I found. It's a niobium-based alloy, so it's still going to be pretty expensive. Not so much from raw materials cost, but from manufacturing costs. Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted April 13, 2017 Share Posted April 13, 2017 37 minutes ago, tater said: EDIT: I honestly had not been aware how thin the nozzle extension was, most is apparently ~0.3mm thick (!?) according to one of the pages I found. That can't be right, can it? ZERO POINT THREE MILLIMETERS?! How thick is aluminum foil, for reference? It's got to be containing some serious pressures! Link to comment Share on other sites More sharing options...
sevenperforce Posted April 13, 2017 Share Posted April 13, 2017 12 minutes ago, CatastrophicFailure said: That can't be right, can it? ZERO POINT THREE MILLIMETERS?! How thick is aluminum foil, for reference? It's got to be containing some serious pressures! Household aluminum foil usually comes in at around 0.016 millimeters. So the niobium alloy nozzle is almost twenty times thicker. 53 minutes ago, tater said: Is the added refurb cost (replacing the bell extension at minimum) cheaper than adding X superdraco engines, including the lost payload capacity opportunity cost, etc.? EDIT: I honestly had not been aware how thin the nozzle extension was, most is apparently ~0.3mm thick (!?) according to one of the pages I found. Yes, it's very thin. You can cut it with kitchen shears, although it would ruin the shears. It's so thin that there is a stabilization ring around it, to keep it from being warped while it is in the interstage. Once stage separation and startup happens, the heat causes the stabilization ring to expand and fly off. You can see it in most of the SpaceX webcasts. 1 hour ago, tater said: Someone at NSF made an interesting point regarding the vacuum Merlin engines, and possible use of landing. They are ground tested without the bell extension added (giving credence to the claim up thread that the bell might not even be able to stay intact at sea level with the engine running)... the interesting point was that if it is bolted on after testing, it could equally be jettisoned after the reentry burn, using the engine as tested (now MUCH shorter, too) for landing. It's not a cheap part of the engine, but it is none the less cheaper than letting the entire stage 2 burn up as it does now eventually. Great idea, but it still wouldn't work. The first stage is 22.2 tonnes dry. The second stage is 4 tonnes dry. The first stage is already coming in on a suicide burn with a TWR > 1 at minimum throttle; the thrust-to-weight ratio would be more than five times greater with the smaller second stage. Link to comment Share on other sites More sharing options...
tater Posted April 13, 2017 Share Posted April 13, 2017 (edited) The only difference is not the extension, however. The mass flow is also lower, right? Wonder how much lower the base thrust is with the "wrong" bell size/shape? Edited April 13, 2017 by tater Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted April 13, 2017 Share Posted April 13, 2017 16 minutes ago, sevenperforce said: Once stage separation and startup happens, the heat causes the stabilization ring to expand and fly off. Ah, so THAT'S what that is! Thank you! Link to comment Share on other sites More sharing options...
sevenperforce Posted April 13, 2017 Share Posted April 13, 2017 (edited) 22 minutes ago, tater said: The only difference is not the extension, however. The mass flow is also lower, right? Wonder how much lower the base thrust is with the "wrong" bell size/shape? Mass flow difference is roughly 1-2%. The engines are significantly different -- the combustion chamber is a different shape and the throat leading to the nozzle is wider -- but SL thrust would be about the same. In fact, the Merlin 1D Vacuum might not actually be able to throttle as low at SL as it can in vacuum without choking in the nozzle, since the throat is wider. 12 minutes ago, CatastrophicFailure said: Ah, so THAT'S what that is! Thank you! Yeah, I wondered this as well, then got pilloried over at NSF when I asked in one of the threads. Edited April 13, 2017 by sevenperforce Link to comment Share on other sites More sharing options...
tater Posted April 13, 2017 Share Posted April 13, 2017 Clearly they need a plan B then for recovery, lol. Link to comment Share on other sites More sharing options...
sevenperforce Posted April 13, 2017 Share Posted April 13, 2017 7 minutes ago, tater said: Clearly they need a plan B then for recovery, lol. SuperDracos, probably. Link to comment Share on other sites More sharing options...
Mad Rocket Scientist Posted April 13, 2017 Share Posted April 13, 2017 1 hour ago, CatastrophicFailure said: That can't be right, can it? ZERO POINT THREE MILLIMETERS?! How thick is aluminum foil, for reference? It's got to be containing some serious pressures! It probably contains surprisingly low pressures, as the entire point of a de Laval nozzle is to lower pressures of exhaust products to external pressures, which means that in space the exhaust should have very little pressure. Link to comment Share on other sites More sharing options...
sevenperforce Posted April 13, 2017 Share Posted April 13, 2017 45 minutes ago, Mad Rocket Scientist said: It probably contains surprisingly low pressures, as the entire point of a de Laval nozzle is to lower pressures of exhaust products to external pressures, which means that in space the exhaust should have very little pressure. Yep. And the bell is actually pressure-stabilized during the burn. Link to comment Share on other sites More sharing options...
tater Posted April 13, 2017 Share Posted April 13, 2017 Aviation Week says that BE-4 testing happens in the next 3-8 weeks. One is already in the test stand, they have two more engines ready to ship to the test facility in TX, and they have 2 test stands, total. Link to comment Share on other sites More sharing options...
Frozen_Heart Posted April 13, 2017 Share Posted April 13, 2017 I reckon the best way of doing it will be to add the heatshield onto the front and have a few superdracos pointing forwards. The stage lands on its nose. Would avoid the problem of the main engine facing re-entry. Link to comment Share on other sites More sharing options...
tater Posted April 13, 2017 Share Posted April 13, 2017 Seems like dumping the extension would make sense regardless of what is doing the landing burn, since it's likely to not like the stress, anyway---that or landing on the nose as @Frozen_Heart says. Link to comment Share on other sites More sharing options...
magnemoe Posted April 14, 2017 Share Posted April 14, 2017 11 hours ago, Spaceception said: I thought it was called the interstage. Interstage stays on first stage and it reused, they have even mounted the grind fins on it. Trunk is dropped. As I understand its needed during an abort to keep dragon aerodynamic stable, they will then drop it and bottom will point forward. Sounds a bit weird as the new shepard does not need an trunk for abort and it uses just an stupid solid fuel engine. I guess dragon 3 will have an integrated trunk, it will also give more flexibility as I assume you could have an hatch to the non-pressurized compartment letting you install an pressurized cargo module if needed or perhaps an air lock for eva Link to comment Share on other sites More sharing options...
Wjolcz Posted April 14, 2017 Share Posted April 14, 2017 Seems like someone's already done it in KSP 3 years ago: Link to comment Share on other sites More sharing options...
kerbiloid Posted April 14, 2017 Share Posted April 14, 2017 (edited) @BahamutoD did this Spoiler Upd.: P.S. They are just trying to reproduce what was KSP mainstream years ago. Edited April 14, 2017 by kerbiloid Link to comment Share on other sites More sharing options...
sevenperforce Posted April 14, 2017 Share Posted April 14, 2017 9 hours ago, magnemoe said: Interstage stays on first stage and it reused, they have even mounted the grind fins on it. Trunk is dropped. As I understand its needed during an abort to keep dragon aerodynamic stable, they will then drop it and bottom will point forward. Sounds a bit weird as the new shepard does not need an trunk for abort and it uses just an stupid solid fuel engine. I guess dragon 3 will have an integrated trunk, it will also give more flexibility as I assume you could have an hatch to the non-pressurized compartment letting you install an pressurized cargo module if needed or perhaps an air lock for eva I have not yet seen a concept I like for an integrated Dragon 3/second stage. Link to comment Share on other sites More sharing options...
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