Quote from: meekGee on 10/20/2018 11:53 pmGiven that the skydiver design is relatively new...>https://forum.nasaspaceflight.com/index.php?topic=46395.msg1860063#msg1860063Langley, 1959. Skip to 1:20
Given that the skydiver design is relatively new...>
At least for the short term a BFS boost away is probably the best that can be achieved with the current design. The one good thing is that with the current engine design it does have enough thrust to break away even if slower than a conventional LAS.Beyond that the best temporary option is likely to be send crew up on Dragon to dock with an orbiting BFS. This approach also has the advantage that if BFS does suffer heat shield damage on takeoff the crew can use the same Dragon they came up on to get back down.In fact that's a huge potential safety advantage for BFR as a system. If necessary, SpaceX could provide Dragon lifeboats for early missions and it would provide both an LAS for takeoff and a second heat shield for reentry if needed.
Some people seem to think putting a LAS on BFR/BFS is comparable to putting it on a capsule design where the capsule is at the top of a rocket with two or more other stages.It's not comparable. The design of BFR/BFS is so much different that any sort of "LAS" on BFR/BFS would be so much different from an Apollo-style LAS that it's really not very useful to compare them.There are a lot of ways to achieve safety. A system like Saturn V/Apollo had certain risks that it made sense to mitigate with a tower on top of the capsule. That only made sense because (1) the Saturn V had risks that couldn't be mitigated other ways; and (2) the fact that there was a very small, already separate, vehicle on the top of the stack made this kind of LAS reasonable in terms of additional cost and risk.Neither of those is true of BFR/BFS. Trying to apply the same solution to a very different situation isn't a good idea.The primary question shouldn't be "should BFR have a launch escape system". The primary question should be "what is the best way to mitigate risk on BFR/BFS"?
Agreed you can't LAS the BFS, since it's an entire second stage...But a p2p vehicle can be built so the cabin is separable, and then using the rather large guidance thrusters that are already required for landing the whole BFS in wind - the numbers don't prohibit it.You'd end up escaping and parachuting a 30-ish ton cabin, but that's not impossible.
I know this thread is long and some may not have read all. What I proposed was a "launch/entry escape cabin" multiple abort modes from launch to entry, some try to twist that fact.... Please refrain from thinking of the Apollo methodology and replace it with the "saucer separation of the Enterprise" in philosophy; just as "Elon was inspired by Tintin" in his redesign... Sci-fi visionaries have moved many to push the limits of rigid-thinking...
Quote from: docmordrid on 10/21/2018 12:52 amQuote from: meekGee on 10/20/2018 11:53 pmGiven that the skydiver design is relatively new...>https://forum.nasaspaceflight.com/index.php?topic=46395.msg1860063#msg1860063Langley, 1959. Skip to 1:20Saw it back when originally posted. Tiny lightweight model in very subsonic fully dense flow. As relevant as Goddard's rockets to an F9...Nobody claimed SpaceX invented vertical landings either - but I didn't see any geniuses here suggest the skydiver as an option for BFS, or even recognize it for what it was when shown it on a slide before the 2018 talk.So yeah, skydiver is completely new for BFS, and the rest of my post stands, even in light of that video. (Which is awesome on its own merit, before being unearthed to show nothing SpaceX does is original)-----ABCD: Always Be Counting Down
Quote from: meekGee on 10/21/2018 12:58 amQuote from: docmordrid on 10/21/2018 12:52 amQuote from: meekGee on 10/20/2018 11:53 pmGiven that the skydiver design is relatively new...>https://forum.nasaspaceflight.com/index.php?topic=46395.msg1860063#msg1860063Langley, 1959. Skip to 1:20Saw it back when originally posted. Tiny lightweight model in very subsonic fully dense flow. As relevant as Goddard's rockets to an F9...Nobody claimed SpaceX invented vertical landings either - but I didn't see any geniuses here suggest the skydiver as an option for BFS, or even recognize it for what it was when shown it on a slide before the 2018 talk.So yeah, skydiver is completely new for BFS, and the rest of my post stands, even in light of that video. (Which is awesome on its own merit, before being unearthed to show nothing SpaceX does is original)-----ABCD: Always Be Counting DownPlease refrain from trying to imply a negative motivation and agenda to my posting of the video. It was posted to demonstrate the the control methodology was investigated looked sound and SpaceX's variation for BFS is a great concept... We all stand on the shoulders of giants... Leave pride out of it...
Semmel - A mars ship is designed for months of travel, it has cabins, and a common area upfront. It has an ECLSS. It has mars-surface provisions.A P2P vehicle is designed for hour-long flights. It has seats packed up like in a jetliner, and a luggage/cargo area.Once you have a p2p vehicle, you can't send people to Mars with it. Even 12 hours flights in a jetliner are hard to take. But 3 months?My observation is that the p2p requirements are much more amenable to a LAS, since the cabin area is compact.A stage-wide LAS even if were possible would also have the issue of how to land a fueled stage in an unknown site. If its just the cabin, there's a smaller issue with post landing fire and tip over.And, you can call it star trekky, but it's just a variation on capsule separation which is a proven thing. Based on a 737 mass breakdown, I called it ~20-30 tons. That's not insane.
Quote from: meekGee on 10/21/2018 03:30 pmSemmel - A mars ship is designed for months of travel, it has cabins, and a common area upfront. It has an ECLSS. It has mars-surface provisions.A P2P vehicle is designed for hour-long flights. It has seats packed up like in a jetliner, and a luggage/cargo area.Once you have a p2p vehicle, you can't send people to Mars with it. Even 12 hours flights in a jetliner are hard to take. But 3 months?My observation is that the p2p requirements are much more amenable to a LAS, since the cabin area is compact.A stage-wide LAS even if were possible would also have the issue of how to land a fueled stage in an unknown site. If its just the cabin, there's a smaller issue with post landing fire and tip over.And, you can call it star trekky, but it's just a variation on capsule separation which is a proven thing. Based on a 737 mass breakdown, I called it ~20-30 tons. That's not insane.I know, and your logic is sound, no argument from me. But I dont think p2p is a design driver for BFR. Therefore it cannot be used to decide whether a LAS is needed or not. If it was design driving, Musk might risk to compromise the Mars goal with BFR. I dont think he would do that. Obviously it is an assumption on my part that p2p is not a design driver, it was never explicitly stated. But then, making it a design driver is inconsistent with the presentations we have got. And I am happy to change my view, in light of better evidence when and if we get it. I hope the soon(tm) to be held AMA on reddit shines some light onto it.
Quote from: Semmel on 10/21/2018 07:59 pmQuote from: meekGee on 10/21/2018 03:30 pmSemmel - A mars ship is designed for months of travel, it has cabins, and a common area upfront. It has an ECLSS. It has mars-surface provisions.A P2P vehicle is designed for hour-long flights. It has seats packed up like in a jetliner, and a luggage/cargo area.Once you have a p2p vehicle, you can't send people to Mars with it. Even 12 hours flights in a jetliner are hard to take. But 3 months?My observation is that the p2p requirements are much more amenable to a LAS, since the cabin area is compact.A stage-wide LAS even if were possible would also have the issue of how to land a fueled stage in an unknown site. If its just the cabin, there's a smaller issue with post landing fire and tip over.And, you can call it star trekky, but it's just a variation on capsule separation which is a proven thing. Based on a 737 mass breakdown, I called it ~20-30 tons. That's not insane.I know, and your logic is sound, no argument from me. But I dont think p2p is a design driver for BFR. Therefore it cannot be used to decide whether a LAS is needed or not. If it was design driving, Musk might risk to compromise the Mars goal with BFR. I dont think he would do that. Obviously it is an assumption on my part that p2p is not a design driver, it was never explicitly stated. But then, making it a design driver is inconsistent with the presentations we have got. And I am happy to change my view, in light of better evidence when and if we get it. I hope the soon(tm) to be held AMA on reddit shines some light onto it.... unless the LAS is only implemented on p2p... Not as an afterthought, but as one of the differentiators.After all, p2p is supposed to launch people really often.Tanker, cargo, and deployer never will.BFS mars will carry people, but will operate on a two year (minimum) cycle, and will involve people undertaking the risks of Mars.Since p2p will be transporting regular folk on a scheduled service, the whole concept of risk is different. It really has to be as safe as a plane. I don't mind if BFS flies without a LAS, but once p2p exists, I can't see why not use it for earth ascent, with BFS launching just full of mars-bound cargo.-----ABCD: Always Be Counting Down
Quote from: meekGee on 10/21/2018 08:10 pmQuote from: Semmel on 10/21/2018 07:59 pmQuote from: meekGee on 10/21/2018 03:30 pmSemmel - A mars ship is designed for months of travel, it has cabins, and a common area upfront. It has an ECLSS. It has mars-surface provisions.A P2P vehicle is designed for hour-long flights. It has seats packed up like in a jetliner, and a luggage/cargo area.Once you have a p2p vehicle, you can't send people to Mars with it. Even 12 hours flights in a jetliner are hard to take. But 3 months?My observation is that the p2p requirements are much more amenable to a LAS, since the cabin area is compact.A stage-wide LAS even if were possible would also have the issue of how to land a fueled stage in an unknown site. If its just the cabin, there's a smaller issue with post landing fire and tip over.And, you can call it star trekky, but it's just a variation on capsule separation which is a proven thing. Based on a 737 mass breakdown, I called it ~20-30 tons. That's not insane.I know, and your logic is sound, no argument from me. But I dont think p2p is a design driver for BFR. Therefore it cannot be used to decide whether a LAS is needed or not. If it was design driving, Musk might risk to compromise the Mars goal with BFR. I dont think he would do that. Obviously it is an assumption on my part that p2p is not a design driver, it was never explicitly stated. But then, making it a design driver is inconsistent with the presentations we have got. And I am happy to change my view, in light of better evidence when and if we get it. I hope the soon(tm) to be held AMA on reddit shines some light onto it.... unless the LAS is only implemented on p2p... Not as an afterthought, but as one of the differentiators.After all, p2p is supposed to launch people really often.Tanker, cargo, and deployer never will.BFS mars will carry people, but will operate on a two year (minimum) cycle, and will involve people undertaking the risks of Mars.Since p2p will be transporting regular folk on a scheduled service, the whole concept of risk is different. It really has to be as safe as a plane. I don't mind if BFS flies without a LAS, but once p2p exists, I can't see why not use it for earth ascent, with BFS launching just full of mars-bound cargo.-----ABCD: Always Be Counting DownThen you have a second problem: you need to design the LAS such that it is both non-interfeering with the Mars BFR design AND optional. So a capsule nose for instance is not possible, it would require a completely different structural design than one that does not have a capsule nose. But thats off topic for this thread, where technical solutions are beside the point of whether the LAS is needed or not.
Quote from: Lemurion on 10/20/2018 08:10 pmAt least for the short term a BFS boost away is probably the best that can be achieved with the current design. The one good thing is that with the current engine design it does have enough thrust to break away even if slower than a conventional LAS.Beyond that the best temporary option is likely to be send crew up on Dragon to dock with an orbiting BFS. This approach also has the advantage that if BFS does suffer heat shield damage on takeoff the crew can use the same Dragon they came up on to get back down.In fact that's a huge potential safety advantage for BFR as a system. If necessary, SpaceX could provide Dragon lifeboats for early missions and it would provide both an LAS for takeoff and a second heat shield for reentry if needed.Putting Dragon on BFR/BFS in a way that it could function as an LAS is completely infeasible. It would be an enormous design change, and it would increase risk more than it would decrease it.
My suggestion was to launch the crew separately on Dragon, which already has an LAS. Dragon would then dock with BFS in orbit and the crew would transfer. They could then either return on BFS or via Dragon-- It provides an LAS on the way up and a potential lifeboat for a second way back. At no time does it include strapping a Dragon to BFS as an LAS.
Quote from: Lemurion on 10/21/2018 08:59 pmMy suggestion was to launch the crew separately on Dragon, which already has an LAS. Dragon would then dock with BFS in orbit and the crew would transfer. They could then either return on BFS or via Dragon-- It provides an LAS on the way up and a potential lifeboat for a second way back. At no time does it include strapping a Dragon to BFS as an LAS.Way too expensive for mars colonization. Would require of tens of Falcon 9 / dragon launches (probably with expendable upper stage) to fill a BFS.
Quote from: hkultala on 10/26/2018 07:11 amQuote from: Lemurion on 10/21/2018 08:59 pmMy suggestion was to launch the crew separately on Dragon, which already has an LAS. Dragon would then dock with BFS in orbit and the crew would transfer. They could then either return on BFS or via Dragon-- It provides an LAS on the way up and a potential lifeboat for a second way back. At no time does it include strapping a Dragon to BFS as an LAS.Way too expensive for mars colonization. Would require of tens of Falcon 9 / dragon launches (probably with expendable upper stage) to fill a BFS.Certainly not too expensive for the earliest shakeout flights of BFS when there will likely only be minimal crew. This might also be a good idea for very early test flights of BFS in NEO where BFS goes up unpiloted and does extended on-orbit stays to test out life support, refuelling, heating & cooling, and all the other things it's going to have to do in space for nearly a year. There's zero chance the first time an inhabited BFS spends 2 years in vacuum will be the first flight to mars. They're going to park a couple of these in orbit and monitor and test systems near home for extended periods of time. BFS space stations are going to be a thing if for no reason beyond testing before Mars.Dragon is an absolutely excellent way to put people on & off BFS in the earliest test phases until a proven flight history exists. Once the numbers show it's not needed, you stop doing it.