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#21
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National Aerospace Plane (X-30) announced 20 years ago
In article ,
"H2-PV NOW" wrote: Wings are cheaper than fuel. Before last year's oil price gouging carbon-fiber fabric was down to $0.94 square foot for 6kx6k 2,000,000 psi, wholesale in volume lots. The cost of 10,000 square feet of wings in material costs was less than buying a Piper Cub used. Now Exxon got their price raise and it costs a NEW Piper Cub. Comparing an air breathing winged vehicle to a VTVL all rocket vehicle the VTVL has the following advantages. Low landing speed of about 3 mph, vs 220 mph for a winged lander. The vehicle has about 10% less hardware (no wings or wheels). Because there are no wings or wheels they can't fail (Shuttle). Hardware costs are in the neighborhood of $1000 per kilogram, and propellents $0.50 per kilogram. With these numbers the break even point for cost is at 250 flights per year for a vehicle designed for a ten year life, and it will be a long time before we have shuttles running that schedule. No specialized runways required to land. In an emergency it can land on any firm level ground (DC-X). Wings are of use only for the first two minutes of a mission, and the last one minute. Wheels are used only the last 30 seconds of the flight. Many engineers and managers like wings and wheels because they are a known quantity. They don't like the Buck Rogers stuff, at least until someone else does it, then it will be all the rage. -- Mike Swift Two things only the people anxiously desire, bread and circuses. Decimus Junius Juvenalls |
#22
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National Aerospace Plane (X-30) announced 20 years ago
mike Williamson wrote:
Wings do not allow for less energy to be used to orbit a craft- while they provide lift they do not provide any energy. In fact, since they also generate drag, a winged vehicle would almost certainly require more fuel to reach orbit, since the tubular design will have less drag to overcome. Careful here. Wings do indeed save energy; this is because wings have a lift/drag ratio, the drag is approximately equal to the engine thrust, and so thrust can be reduced- reducing the propellant needed to carry the vehicle whilst within the atmosphere. The root cause of the energy saving is that the vehicle uses wing to throw air downwards relatively slowly; the slow speed represents lower energy needed to carry the vehicle; the high exhaust speed of rocket engines uses more energy (since energy goes as a square law on the exhaust velocity), although it saves propellant mass. Even with Apollo, studies showed that a lifting approach did indeed increase payload (although the payload increase was very marginal.) The big downside of wings is after you leave the atmosphere- wings push up dry mass, and then it is very easy to lose everything that was gained during ascent and then some; a good mass ratio is essential particularly toward the end of the burn. Mike |
#23
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National Aerospace Plane (X-30) announced 20 years ago
"dan" wrote in message ups.com... Various attempts have been made to design hypersonic airbreathing engines. The X-43 is probably the only one to fly, even briefly. The problem with scramjets is that they tend to be efficient only in a narrow range of speeds; great for a cruise missile but not for orbital launch. The liquid air cycle (i.e. hotol) is less speed sensitive but there's no easy way to carry enough cooling capacity to actually liquify all the air you need. Best bet might essentially be a cooled-inlet turbojet. Wings can be useful for thrust-limited designs, but a launch vehicle goes through the speed regiemes quickly and above about 30 KM wings aren't much use. After attacking the SSTO problem for awhile, at some point a two-stage solution begins to look more practical. Why bother with air breathing, winged vehicles at all? Why not consider a conventional, rocket powered VTVL TSTO? Such a design wouldn't even need an altitude compensating engine (i.e. aerospike), since the first stage would be optimized for low altitudes and the second stage for vacuum. Jeff -- Remove icky phrase from email address to get a valid address. |
#24
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National Aerospace Plane (X-30) announced 20 years ago
"dan" wrote in message oups.com... In other words, the high cost of fuel isn't what makes spaceflight expensive when launch costs fare more than the cost of fuel for the launch. Exactly. Almost all the cost for the Shuttle is the maintenance needed between flights. Some parts, like the SRBs, are completely disassembled, stripped to bare metal (even the nuts and bolts), inspected for cracks, and remanufactured. The Orbiter requires months of inspections and maintenance. But these aren't the inevitable result of the vehicle being reusable; they're with us because the Shuttle was designed before we had any actual flight experience with many of the critical systems, particularly the TPS and SRBs. Actually, the problem really was with the SRB's themselves. As with many orbiter systems, they were chosen because of their low development costs, not because NASA thought they would have low per flight costs. Also, the TPS on the orbiter isn't the only labor intensive system. There are also the SSME's (their high chamber pressure drove them to a design that's bleeding edge), the APU's (toxic propellants), the RCS/OMS systems (which use toxic propellants), and etc. Jeff -- Remove icky phrase from email address to get a valid address. |
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National Aerospace Plane (X-30) announced 20 years ago
"Mike Swift" wrote in message ... In article , David Given wrote: [...] SpaceShipOne only got 1/3rd the way there and that wasn't SSTO, it was two staged, carried on White Knight. No. No, it didn't. SS1 reached Mach 3. Orbit is about the equivalent of Mach 25. That's 1/8 of the way. Actually it much worse than 1/8 of the way. In terms of energy that eight to one velocity increase takes 128 times more energy. As you can see SpaceShipOne was far from getting to orbit. The intention was never to get it into orbit. The question to ask yourself, is if NASA were given the task to create a reusable vehicle to carry three people to 50 miles altitude and back, what would *that* have cost? Ask the same question only substitute any large aerospace contractor for NASA. Jeff -- Remove icky phrase from email address to get a valid address. |
#26
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National Aerospace Plane (X-30) announced 20 years ago
dan wrote:
The liquid air cycle (i.e. hotol) is less speed sensitive but there's no easy way to carry enough cooling capacity to actually liquify all the air you need. Best bet might essentially be a cooled-inlet turbojet. Alternately, there is SABRE. http://en.wikipedia.org/wiki/SABRE Which might be that "cooled inlet turbojet" you mentioned. After attacking the SSTO problem for awhile, at some point a two-stage solution begins to look more practical. Yes, though sometimes the SSTO looks tempting, like when you find a very lightweight dense fuel design. Mike Miller |
#27
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National Aerospace Plane (X-30) announced 20 years ago
Ian Woollard wrote:
mike Williamson wrote: The big downside of wings is after you leave the atmosphere- wings push up dry mass, and then it is very easy to lose everything that was gained during ascent and then some; a good mass ratio is essential particularly toward the end of the burn. Mike Which is another excellent reason to look at TSTO rather than STSO with current technology. -- Malcolm Street Canberra, Australia The nation's capital |
#28
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National Aerospace Plane (X-30) announced 20 years ago
*From:* "Ian Woollard"
*Date:* Wed, 15 Mar 2006 19:42:39 -0000 mike Williamson wrote: Wings do not allow for less energy to be used to orbit a craft- while they provide lift they do not provide any energy. In fact, since they also generate drag, a winged vehicle would almost certainly require more fuel to reach orbit, since the tubular design will have less drag to overcome. Careful here. Wings do indeed save energy; this is because wings have a lift/drag ratio, the drag is approximately equal to the engine thrust, and so thrust can be reduced- reducing the propellant needed to carry the vehicle whilst within the atmosphere. The root cause of the energy saving is that the vehicle uses wing to throw air downwards relatively slowly; the slow speed represents lower energy needed to carry the vehicle; the high exhaust speed of rocket engines uses more energy (since energy goes as a square law on the exhaust velocity), although it saves propellant mass. Even with Apollo, studies showed that a lifting approach did indeed increase payload (although the payload increase was very marginal.) The big downside of wings is after you leave the atmosphere- wings push up dry mass, and then it is very easy to lose everything that was gained during ascent and then some; a good mass ratio is essential particularly toward the end of the burn. Mike So the obvious approach is a two-stage one - fly the wings and atmospheric engines away once they no longer serve a good purpose. Spaceship One on steroids... |
#29
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National Aerospace Plane (X-30) announced 20 years ago
In article .com,
"dan" wrote: Exactly. Almost all the cost for the Shuttle is the maintenance needed between flights. Some parts, like the SRBs, are completely disassembled, stripped to bare metal (even the nuts and bolts), inspected for cracks, and remanufactured. Could you please give an example of an SRB segment that has been reused, including the flight on which it was first used, and the flight on which it was reused. -- Bruce | 41.1670S | \ spoken | -+- Hoult | 174.8263E | /\ here. | ----------O---------- |
#30
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National Aerospace Plane (X-30) announced 20 years ago
Derek Clarke wrote:
So the obvious approach is a two-stage one - fly the wings and atmospheric engines away once they no longer serve a good purpose. The problem is that the optimum staging speed is about 3km/s. But the wings are normally only good for maybe mach 3 or so (1km/s); after that structural heating problems start to really get interesting. So you're compromising your first stage when you stick wings on in several different ways. Spaceship One on steroids... Yes, but it might be observed that Spaceship One took two stages to do what one stage can do. Even Rutan admitted that a lot of the tech he used was because it was stuff that *he* knew how to do, rather than because it was inherently better (but he did have some good ideas, the pivoting tail structure seems to be a reasonably good idea.) |
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