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#11
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Lunar Lander
On Dec/23/2017 Ã* 7:20 PM, JF Mezei wrote :
On 2017-12-22 18:26, Fred J. McCall wrote: You'd have to design a new upper stage that allowed refueling plus a tanker stage to refuel it from. If you could refuel it, the existing RP1/LOX upper stage might even have the capability for lunar work. But we're talking hardware that would be, as yet, only a gleam in someone's eye, unlike SLS. What about the possibility of sending a the parts separately, but already fueled such that refueling is not necessary? Launch 3rd stage, service module, lander and capsule as separate launchs (perhaps combining capsule with lander), assemble pre-fueled components in orbit then go to the moon. You could also potentially combine 3rd stage with service module to reduce the weight of extra engine and use service module (with bigger tanks) for TLI. I think BFR Spaceship might be too heavy for other boosters, but you could just use it with BFR. BFR Spaceship refueled in orbit is the whole works. It can fly to the Moon, land, take off, and return to Earth. Reality check question: Apollo managed to get a capsule that fell from the Moon to re-enter earth. NASA got Shuttle to re-enter earth from as high as Hubble orbit. Space-X has gotten Stage-1 to re-enter from suborbital speed/altitude. (same with Virgin Galactic). Considering BFR will be a long fat stick instead of capsule or "space plane", how does it expect to re-enter at high speeds and remain structurally sound? Being big helps for re-entry or aero-capture. If you're big and fluffy you can spread the heat load and air pressure over a larger area. That isn't to say that re-entry of BFR will be easy. It isn't easy for a capsule, it isn't easy for a space plane and it won't be easy for BFR. Is this a question of using engines to slow down such that re-entery interface is done engine first like Falcon 9 stage-1 and engines firing long enough to slow it down to sub orbital speeds before hitting atmosphere? No, heat shields are more efficient than engines for slowing down. Would coming back from Mars create far higher speeds than coming back from the Moon, or would "catching up to Earth" result in slower speeds? You will have higher speeds coming back from Mars. Alain Fournier |
#12
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Lunar Lander
JF Mezei wrote:
On 2017-12-22 18:26, Fred J. McCall wrote: You'd have to design a new upper stage that allowed refueling plus a tanker stage to refuel it from. If you could refuel it, the existing RP1/LOX upper stage might even have the capability for lunar work. But we're talking hardware that would be, as yet, only a gleam in someone's eye, unlike SLS. What about the possibility of sending a the parts separately, but already fueled such that refueling is not necessary? Not enough grunt. Launch 3rd stage, service module, lander and capsule as separate launchs (perhaps combining capsule with lander), assemble pre-fueled components in orbit then go to the moon. You're talking an entire new stage, then. That's certainly an alternative to refueling a stage. You could also potentially combine 3rd stage with service module to reduce the weight of extra engine and use service module (with bigger tanks) for TLI. So now you need a bigger Service Module engine, as well, and you're taking a bunch of excess dry mass into lunar orbit. I think BFR Spaceship might be too heavy for other boosters, but you could just use it with BFR. BFR Spaceship refueled in orbit is the whole works. It can fly to the Moon, land, take off, and return to Earth. Reality check question: Apollo managed to get a capsule that fell from the Moon to re-enter earth. NASA got Shuttle to re-enter earth from as high as Hubble orbit. Space-X has gotten Stage-1 to re-enter from suborbital speed/altitude. (same with Virgin Galactic). Considering BFR will be a long fat stick instead of capsule or "space plane", how does it expect to re-enter at high speeds and remain structurally sound? The same way anything else does. Is this a question of using engines to slow down such that re-entery interface is done engine first like Falcon 9 stage-1 and engines firing long enough to slow it down to sub orbital speeds before hitting atmosphere? BFR Spaceship is intended to come in nose-first. They even added some little delta fins to give it better stability. Would coming back from Mars create far higher speeds than coming back from the Moon, or would "catching up to Earth" result in slower speeds? You can still kill most of the velocity with aerobraking. BFR Spaceship has a low enough density on return that a normal PICA-X heat shield on the underside is sufficient. Shuttle needed the special tiles because it was large, dense, and flying using wings and lifting body shape (all of which add drag and increase heat loads when reentering). -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
#13
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Lunar Lander
On Dec/24/2017 at 4:57 PM, Fred J. McCall wrote :
[snip] You can still kill most of the velocity with aerobraking. BFR Spaceship has a low enough density on return that a normal PICA-X heat shield on the underside is sufficient. Shuttle needed the special tiles because it was large, dense, and flying using wings and lifting body shape (all of which add drag and increase heat loads when reentering). Being large and dense is the big culprit for the high heat loads of the Shuttle. Not the added drag due to the body shape. In fact you want to have lots of drag in a re-entry vehicle, for two reasons. First and most importantly, if the re-entry vehicle has a blunt shape, air doesn't flow away as much as with an aerodynamic shape. So in effect, you have an air cushion around the vehicle and the heated shock layer (where you have the most heat) is away from the vehicle. Second, if you have a blunt shape, you will decelerate more during the earlier phase of re-entry and your speed will be lower when you reach thicker layers of the atmosphere. Alain Fournier |
#14
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Lunar Lander
Alain Fournier wrote:
On Dec/24/2017 at 4:57 PM, Fred J. McCall wrote : [snip] You can still kill most of the velocity with aerobraking. BFR Spaceship has a low enough density on return that a normal PICA-X heat shield on the underside is sufficient. Shuttle needed the special tiles because it was large, dense, and flying using wings and lifting body shape (all of which add drag and increase heat loads when reentering). Being large and dense is the big culprit for the high heat loads of the Shuttle. Not the added drag due to the body shape. In fact you want to have lots of drag in a re-entry vehicle, for two reasons. First and most importantly, if the re-entry vehicle has a blunt shape, air doesn't flow away as much as with an aerodynamic shape. So in effect, you have an air cushion around the vehicle and the heated shock layer (where you have the most heat) is away from the vehicle. Second, if you have a blunt shape, you will decelerate more during the earlier phase of re-entry and your speed will be lower when you reach thicker layers of the atmosphere. Drag generates lift. Since we don't live in a perfect universe, part of the drag does not generate lift but generates waste heat. The 'draggier' you are the more lift (and heat) you will generate. If the Shuttle didn't try to fly heat loads would be smaller. It's why wing leading edges needed special insulators. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
#15
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Lunar Lander
On Dec/26/2017 at 1:18 PM, Fred J. McCall wrote :
Alain Fournier wrote: On Dec/24/2017 at 4:57 PM, Fred J. McCall wrote : [snip] You can still kill most of the velocity with aerobraking. BFR Spaceship has a low enough density on return that a normal PICA-X heat shield on the underside is sufficient. Shuttle needed the special tiles because it was large, dense, and flying using wings and lifting body shape (all of which add drag and increase heat loads when reentering). Being large and dense is the big culprit for the high heat loads of the Shuttle. Not the added drag due to the body shape. In fact you want to have lots of drag in a re-entry vehicle, for two reasons. First and most importantly, if the re-entry vehicle has a blunt shape, air doesn't flow away as much as with an aerodynamic shape. So in effect, you have an air cushion around the vehicle and the heated shock layer (where you have the most heat) is away from the vehicle. Second, if you have a blunt shape, you will decelerate more during the earlier phase of re-entry and your speed will be lower when you reach thicker layers of the atmosphere. Drag generates lift. Since we don't live in a perfect universe, part of the drag does not generate lift but generates waste heat. The 'draggier' you are the more lift (and heat) you will generate. If the Shuttle didn't try to fly heat loads would be smaller. It's why wing leading edges needed special insulators. No. Go see https://en.wikipedia.org/wiki/Atmospheric_entry, read the "Blunt body entry vehicles" section. The most relevant sentence is: "In the United States, H. Julian Allen and A. J. Eggers, Jr. of the National Advisory Committee for Aeronautics (NACA) made the counterintuitive discovery in 1951[6] that a blunt shape (high drag) made the most effective heat shield." The draggier you are the less you need special insulators. Alain Fournier |
#16
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Lunar Lander
Alain Fournier wrote:
On Dec/26/2017 at 1:18 PM, Fred J. McCall wrote : Alain Fournier wrote: On Dec/24/2017 at 4:57 PM, Fred J. McCall wrote : [snip] You can still kill most of the velocity with aerobraking. BFR Spaceship has a low enough density on return that a normal PICA-X heat shield on the underside is sufficient. Shuttle needed the special tiles because it was large, dense, and flying using wings and lifting body shape (all of which add drag and increase heat loads when reentering). Being large and dense is the big culprit for the high heat loads of the Shuttle. Not the added drag due to the body shape. In fact you want to have lots of drag in a re-entry vehicle, for two reasons. First and most importantly, if the re-entry vehicle has a blunt shape, air doesn't flow away as much as with an aerodynamic shape. So in effect, you have an air cushion around the vehicle and the heated shock layer (where you have the most heat) is away from the vehicle. Second, if you have a blunt shape, you will decelerate more during the earlier phase of re-entry and your speed will be lower when you reach thicker layers of the atmosphere. Drag generates lift. Since we don't live in a perfect universe, part of the drag does not generate lift but generates waste heat. The 'draggier' you are the more lift (and heat) you will generate. If the Shuttle didn't try to fly heat loads would be smaller. It's why wing leading edges needed special insulators. No. Go see https://en.wikipedia.org/wiki/Atmospheric_entry, read the "Blunt body entry vehicles" section. The most relevant sentence is: "In the United States, H. Julian Allen and A. J. Eggers, Jr. of the National Advisory Committee for Aeronautics (NACA) made the counterintuitive discovery in 1951[6] that a blunt shape (high drag) made the most effective heat shield." The draggier you are the less you need special insulators. True when you're talking about blunt objects, but only because they create a compressed shockwave away from the vehicle that winds up taking the heat load. -- "Insisting on perfect safety is for people who don't have the balls to live in the real world." -- Mary Shafer, NASA Dryden |
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