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#11
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Were liquid boosters on Shuttle ever realistic?
"Greg \(Strider\) Moore" wrote:
"Fred J. McCall" wrote in message .. . There is no such thing as assembly line production 'spewing out' rocket engines. It made sense to use Merlin engines because the idea was to have three identical cores for Falcon Heavy, sort of like what Delta IV Heavy does. In the event, Musk found they couldn't do that and that they couldn't just use three Falcon 9 cores for Falcon Heavy. The side boosters are now different from the central 'core'. What are the differences? Last I knew the side boosters for the primary flight are B1023.2 and B1025.2 (i.e 2nd flight for those two boosters) It's mostly got to do with mechanical loading. The side boosters are close (but not an exact match) for what they fly on Falcon 9. They're only slightly modified so as to be able to take structural loading from the attachment points on the sides rather than straight down through the center of the core. The center booster requires a lot more structural work to stand loads, both the side loads from the two attached boosters and the increased load on the front of the booster from the second stage and payload. Musk himself has said that he doesn't necessarily expect the first launch attempt to reach orbit and would consider it getting far enough away to avoid pad damage a win. Look at how many Falcon 9 launches failed before they got a success. According to Musk, Falcon Heavy was "shockingly difficult" to develop. It was originally supposed to use fuel cross-feed among the three cores, but that proved too difficult and was dropped. It was originally supposed to be three 'standard' Falcon 9 cores (with Falcon 9 eating the additional structure) but now the center booster is different from the side boosters. Yes, it really is rocket science... -- "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 |
#12
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Were liquid boosters on Shuttle ever realistic?
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#13
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Were liquid boosters on Shuttle ever realistic?
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#14
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Were liquid boosters on Shuttle ever realistic?
Jeff Findley wrote:
In article , says... Yes, but the difference isn't as preposterous as your case makes it sound. LH2/LOX is going to be around 50% more expensive for engines for 'similar' performance. The ability to stage higher and faster because of Isp differences makes up for some of that (because you're either carrying a smaller mass of fuel or because you're carrying the same mass of fuel and it burns longer). You then have to adjust that for tank weight and aerodynamic drag from the need for bigger volume tanks. There are 'sweet spots' in there where LH2/LOX is competitive and there are hypothetical cases that make LH2/LOX look even worse than one would expect. GENERALLY, a higher density exhaust (from a denser fuel) makes sense for a first stage, but that's not always the case or Delta IV wouldn't look like it does. While you're making valid points, do note that Delta IV is the (far) more expensive launch vehicle compared to Atlas V. Is it? When I look at cost numbers they're both around $13k/kg of payload. ULA plays games with the cost of Atlas V by giving 'incremental cost' of an additional launch while charging all the pad support, etc, to USAF contract. LOX/LH2 may not cost much more in the engine department, but the costs start mounting when you consider everything else which has to go into the (larger, better insulated) first stage and all of its associated plumbing. That includes all of the headaches involved with buying, storing, and loading large amounts of LH2 into the first stage at the pad (the upper stage is tiny by comparison). That's why ULA wants to drop Delta IV as quickly as it can. It's too expensive and simply can't compete, even with Atlas V, made by the same company. LOX/LH2 makes very little sense as a first stage propellant combination due to the many disadvantages that quickly drive up costs compared to pretty much any other (sane) liquid fuel. Actually, they aren't built by the same company (one is Boeing and one is LockMart, although both are sold through the joint venture ULA) and they want to get rid of Atlas V, too. In fact, Atlas V is the one they really want to get rid of because it uses Russian RD-180 engines. LOX/methane is the fuel of choice for new development today because it offers a good compromise on density and performance. Plus in its liquid form it can share a common bulkhead with LOX without a lot of (any?) insulation on the bulkhead. And yes, having common engines and common fuel/oxidizer on both the lower stage and upper stage simplifies manufacturing and operations, lowering costs. So that's a win for LOX/methane as well. But practically no one in the methane/LOX game is using common engines among all their stages. ULA will be using BE-4 and SRBs on the first stage and LH2/LOX on the second stage. New Glenn uses BE-4 on the first two stages and LH2/LOX on the third stage (when used). There are two versions of the BE-4, one sea level optimized and one vacuum optimized. The same is true of the Raptor engine SpaceX will use and once again SpaceX is the only one using the same engine everywhere. SpaceX pays the price for not having a high energy LH2/LOX upper stage by refueling on orbit. In a world where SpaceX has set the bar very low on cost, everyone is scrambling to optimize on cost rather than performance. Henry Spencer used to call optimizing for performance the "performance uber alles" mindset which came along with former German engineers who were used to designing missiles rather than launch vehicles. That still holds today. In the old days you almost had to go for performance because the payloads and dry weight of the vehicles were always right at the edge. Even SpaceX has done some of that, going with superchilled RP1 to improve performance. I don't think Henry invented that phrase, as it was pretty commonly used by a lot of people back in the day, but I can't prove he didn't, either. -- "Insisting on perfect safety is for people who don't have the balls to live in the real world." -- Mary Shafer, NASA Dryden |
#15
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Were liquid boosters on Shuttle ever realistic?
Jeff Findley wrote:
In article , says... It does not necessarily mean that it is the optimal design from an engineering point of view. It's the design that makes the most business sense. It may not even be that. Certainly no one here is advocating 'optimal engineering design' as a GOAL, although that usually makes the most business sense. Depends on what you mean by "optimal engineering design". For example, missiles are optimized for long storage times and for minimum size and mass for a fixed payload size. The requirement to store them on subs and in smallish launch facilities drives the requirements. But, they are not in any way shape or form designed for minimum manufacturing costs. In terms of overall program costs, that's just not a big consideration. Most aerospace stuff isn't designed for "minimum manufacturing costs" because we just don't build enough of them to do that. Put those same engineers on a launch vehicle program and they'll design an "optimum" launch vehicle with different engines on every stage, maximum ISP engines (at the bleeding edge of what the materials can take), and stages which have to be transported by barge and by over- sized cargo aircraft. Different stages will have different fuels driving up handling complexity and costs at the launch pad. All those little things add up to launch vehicles which are far more expensive than they need to be. Why? Because "we've always done things that way" and "performance uber alles"! Not necessarily. Depends on what the requirements are. If you're a commercial outfit trying to compete for launch business, you're going to want to drive overall costs per launch down. That might make you decide on designs that don't push the envelope as hard because they're cheaper to build because you can use cheaper materials and fuels that are cheap and don't require expensive storage and handling facilities. Or it might drive you to more expensive practices so that stages are reusable, using more expensive materials and squeezing more performance so that you have capability left to get the stages back. On the other hand, if your primary business is government payloads you're not going to have to compete as hard to get a share (because the government won't want all its eggs in one basket) and you might just push pure performance harder because you can afford to do it. Back in the 1940's and 1950's, there wasn't a lot of choice but to push performance because nothing less would get **** on orbit. That doesn't mean modern missile engineers are obtuse (or even that the old time ones were). The revolution brought by SpaceX (and somewhat by Blue Origin) isn't at all technology driven. There was no magic breakthrough technology that drove down costs (like SABRE engines). There is absolutely nothing technically challenging about how they've designed their engines and launch vehicle stages (to date anyway). But what they have done is optimize for lower cost at every step of the process. Lower development costs, lower testing costs, lower build costs, lower transportation costs (Falcon stages are transported by semi-truck), lower integration costs (horizontal integration), and etc. Actually they haven't. Superchilled RP1 drives up costs in order to improve performance. Going for reusability drives up manufacturing costs and design costs because you have to make things that can be used dozens of times without attention (so you need better materials and tighter designs without pushing for extra performance, figure out some way to avoid 'coking' on an RP1/LOX engine, etc). It's the normal engineering evolution of launch vehicles that was stalled while most payloads were government. On top of that, both SpaceX and Blue Origin are pursuing reusability with a tenacity never before seen in the industry (space shuttle SRBs and orbiters were refurbished after flight over many months, so they don't really count). That will be the next step towards even cheaper access to space. BFR and the BFR Ship are sort of the end result of that. Reliability of airliners with the ability to do hundreds of flights with only routine servicing is the goal. -- "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 |
#16
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Were liquid boosters on Shuttle ever realistic?
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#17
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Were liquid boosters on Shuttle ever realistic?
JF Mezei wrote:
On 2017-10-24 23:02, Greg (Strider) Moore wrote: What are the differences? Last I knew the side boosters for the primary flight are B1023.2 and B1025.2 (i.e 2nd flight for those two boosters) Musk said that the reason Falcon Heavy is so late is that they had underestimated the structural changes needed to the rocket because of different loads (and heavier payload at top). Whether they retrofitted existing stage 1s as boosters (and the core stage) or built new ones, reusing only engines, I have no idea. That's because you're either not paying attention or you have the memory of a mayfly, Mayfly. It's been mentioned several times that the side boosters are 'used', which means they're original Falcon 9 equipment that has been retrofitted. The center booster is apparently new build. Perhaps the modifications required for the center booster are too extensive to economically use old Falcon 9 stages. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
#18
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Were liquid boosters on Shuttle ever realistic?
Jeff Findley wrote:
In article , says... Actually they haven't. Superchilled RP1 drives up costs in order to improve performance. Going for reusability drives up manufacturing costs and design costs because you have to make things that can be used dozens of times without attention (so you need better materials and tighter designs without pushing for extra performance, figure out some way to avoid 'coking' on an RP1/LOX engine, etc). It's the normal engineering evolution of launch vehicles that was stalled while most payloads were government. As far as engines go, this isn't really true. All liquid fueled engines are designed to be fired multiple times, at least on the test stand. That's how they're qualified. Henry Spencer used to say (paraphrasing here), there is absolutely nothing fundamental about a liquid fueled rocket engine that makes it expendable. Well, actually it is. You go into engine design knowing how many 'refires' the engine needs to stand. If it needs to stand 3 with some safety margin, the robustness required is a lot less than if it needs to stand up to 36 of them with the same safety margin. That is going to drive up manufacturing costs (which you hopefully get back through the savings by reusing hardware). Same goes for tanks and plumbing. They pretty much have to be "certified" for a certain number of fill and drain cycles even if they're "expendable" in order to account for tanking tests, aborts, and etc. And they have to be "certified" for a magnitude (or multiple magnitudes in the case of something like BFR) more fill and drain cycles if they're supposed to be reusable. Solids on the other hand are single use, excepting for complete tear down to component parts accompanied by extreme cleaning. Solids are expensive for what they bring to the table when compared to liquids, even if you fully expend all hardware. I really don't understand ULA's love affair with them. -- "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 |
#19
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Were liquid boosters on Shuttle ever realistic?
JF Mezei wrote:
On 2017-10-25 07:13, Jeff Findley wrote: On top of that, both SpaceX and Blue Origin are pursuing reusability with a tenacity never before seen in the industry (space shuttle SRBs and orbiters were refurbished after flight over many months, so they don't really count). That will be the next step towards even cheaper access to space. In fairness, SpaceX is likely at the same stage now that NASA was when it had flown a Suttle orbiter 2 or 3 times. Doing costly turn-around examinations in order to gauge how much work will really be needed in the future. Until it has reflown enough stages, AND SpaceX releases some number of the work/costs involved in turning stages around "in production", nobody outside of SpaceX know how cost effective turning stages around is. SpaceX doesn't need to release anything. You can look at what they charge customers for expending a stage vs allowing it to be recovered and what discount they offer for using a 'used' stage to get some idea of the costs. It may very well be a no brainer either way (eg: 50% cheaper than new stages or 75% cheaper than new stages ) So the question becomes how MUCH will SpaceX revolutionlize launch industry, not whether it will or not. Look at the manufacturing cost for a new stage, which we can estimate from what they charge for a launch. Even if you have to do a complete tear down it's going to be cheaper to reuse than to buy new. This was even true for the Space Shuttle (look at what a new Shuttle Orbiter cost). -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
#20
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Were liquid boosters on Shuttle ever realistic?
JF Mezei wrote:
On 2017-10-26 16:21, Fred J. McCall wrote: That's because you're either not paying attention or you have the memory of a mayfly, Mayfly. It's been mentioned several times that the side boosters are 'used', which means they're original Falcon 9 equipment that has been retrofitted. In his recent Australian speech, Musk explicitely said that ALL of it had to be re-engineered, hence the delay for Falcon Heavy. The original expectation close to what you described. Except what you're getting from his statement is not what he said. Are the engines different? No. OK, that's already NOT "all of it re-engineered". Are the tanks, piping, or electronics different? No. There's more. Mayfly, we KNOW that the two side boosters are 'reused' from Falcon 9. It's been announced. The boosters have been identified. It's been talked about here before. We also know there are structural changes required in order to handle getting loads from the side attachment points vs straight down through the axis of the booster. There will obviously be software changes, but that's 'just software'. Does your brain reset to factory fresh every time you get a new fact? -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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