"SpaceShipTwo could be single stage to SUBorbit"
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From: Jeff Findley on 14 May 2010 11:16 "J. Clarke" <jclarke.usenet(a)cox.net> wrote in message news:hsjhh3112ob(a)news4.newsguy.com... > On 5/14/2010 12:05 AM, Jorge R. Frank wrote: >> On 05/13/2010 05:08 PM, J. Clarke wrote: >>> On 5/13/2010 4:04 PM, Jeff Findley wrote: >>>> "Pat Flannery"<flanner(a)daktel.com> wrote in message >>>> news:6vGdnRW146eIxXHWnZ2dnUVZ_tOdnZ2d(a)posted.northdakotatelephone... >>>>> On 5/13/2010 9:10 AM, LSMFT wrote: >>>>>> What happened to the X-30? >>>>> >>>>> And since when did 50,000 feet become outer space? >>>>> I like the part about it using a "liquid chemical propulsion system", >>>>> without specifying what those chemicals are exactly. >>>>> You could certainly make a ground takeoff rocket plane that could >>>>> climb to >>>>> 50,000 feet, but since numerous types of jet aircraft are capable of >>>>> flying to 50,000 feet also, what would be the point of doing this? >>>> >>>> The promises made by X-30 were absolutely silly, in retrospect. A >>>> vehicle >>>> which can cruise at hypersonic speeds is going to be very different >>>> than a >>>> vehicle which can accelerate to orbital speeds, yet somehow X-30 was >>>> being >>>> sold as able to do both (makes me think of the SNL skit for Shimmer, a >>>> floor >>>> polish and a dessert topping). >>> >>> So let's see, a vehicle that can cruise at Mach 20 is going to be >>> different from one that can accelerate to Mach 25 how, exactly? >> >> If you haven't figured it out on your own, it is not going to be worth >> anyone's time to explain it to you. But the quick-and-dirty is that >> cruising at Mach 20 with an airbreather is going to require remaining at >> an altitude where there is enough O2 to keep the engine going, which >> radically increases the total heat load. > > Which heat load goes into the fuel and out the exhaust. > >> Whereas a Mach 25 accelerator >> will only spend a brief amount of time in the Mach region where a >> scramjet will do any good, so it will need two additional propulsion >> systems: one to accelerate to the minimum speed to light the scramjet, >> another (necessarily rocket-based) to take over for the final boost to >> orbit once the scramjet is useless. The additional weight of having >> three propulsion systems more than outweighs the advantages of the >> airbreather. > > You seem to have missed the point. > >> IMO scramjets are daft for either mission. It's at times like this that >> I really miss Henry Spencer. He could explain this far more eloquently >> than I could. > > So what do you recommend for Mach 20 cruise if scramjets are "daft" for > it? That's a little like Peter Pan asking "What would you recommend for human flight besides fairy dust?". Neither fairy dust nor runway to Mach 20 hypersonic air breathing engines exist. The difference between the two is that one is obviously pure fantasy even to non-engineers where the other is only an obvious fantasy to those who know enough about engineering to crunch the numbers for themselves and realize that the math just doesn't work out. In an apples to apples comparison, rocket engines for orbital launch vehicles beat even drawing board air breathing launch vehicles for the reasons which Jorge states. Math always trumps faith when it comes to engineering. Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon
From: Jeff Findley on 14 May 2010 11:19 "J. Clarke" <jclarke.usenet(a)cox.net> wrote in message news:hshuh902r54(a)news1.newsguy.com... > On 5/13/2010 3:53 PM, Jeff Findley wrote: >> "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message >> news:hshi7c030ls(a)news4.newsguy.com... >>> On 5/13/2010 1:10 PM, LSMFT wrote: >>>> Robert Clark wrote: >>>> What happened to the X-30? >>> >>> Clinton. >> >> X-30 was way too much for NASA to do in one huge leap and would have >> required billions more dollars just to try to make it work. The state of >> the art in hypersonic propulsion still isn't where it would need to be to >> build X-30 today (note that X-30 was cancelled more than two decades >> ago). >> Hypersonic propulsion is one of those promising looking technologies >> that's >> been "only a few years away" for many decades. > > Uh, it's not there because Clinton pulled the plug on it. NASP was a research playground which was producing little to no flight hardware, and certainly wasn't producing flying testbeds (i.e. real X-planes testing real engines on real test flights). Killing a research program which was sucking up billions of dollars without producing any actual flown hardware was a prudent move, IMHO. Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon
From: J. Clarke on 14 May 2010 15:10 On 5/14/2010 11:19 AM, Jeff Findley wrote: > "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message > news:hshuh902r54(a)news1.newsguy.com... >> On 5/13/2010 3:53 PM, Jeff Findley wrote: >>> "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message >>> news:hshi7c030ls(a)news4.newsguy.com... >>>> On 5/13/2010 1:10 PM, LSMFT wrote: >>>>> Robert Clark wrote: >>>>> What happened to the X-30? >>>> >>>> Clinton. >>> >>> X-30 was way too much for NASA to do in one huge leap and would have >>> required billions more dollars just to try to make it work. The state of >>> the art in hypersonic propulsion still isn't where it would need to be to >>> build X-30 today (note that X-30 was cancelled more than two decades >>> ago). >>> Hypersonic propulsion is one of those promising looking technologies >>> that's >>> been "only a few years away" for many decades. >> >> Uh, it's not there because Clinton pulled the plug on it. > > NASP was a research playground which was producing little to no flight > hardware, and certainly wasn't producing flying testbeds (i.e. real X-planes > testing real engines on real test flights). Killing a research program > which was sucking up billions of dollars without producing any actual flown > hardware was a prudent move, IMHO. You have to do the research before you can produce the "flying testbeds".
From: J. Clarke on 14 May 2010 15:23 On 5/14/2010 11:03 AM, Jeff Findley wrote: > "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message > news:hshuh912r54(a)news1.newsguy.com... >> On 5/13/2010 4:04 PM, Jeff Findley wrote: >>> "Pat Flannery"<flanner(a)daktel.com> wrote in message >>> news:6vGdnRW146eIxXHWnZ2dnUVZ_tOdnZ2d(a)posted.northdakotatelephone... >>>> On 5/13/2010 9:10 AM, LSMFT wrote: >>>>> What happened to the X-30? >>>> >>>> And since when did 50,000 feet become outer space? >>>> I like the part about it using a "liquid chemical propulsion system", >>>> without specifying what those chemicals are exactly. >>>> You could certainly make a ground takeoff rocket plane that could climb >>>> to >>>> 50,000 feet, but since numerous types of jet aircraft are capable of >>>> flying to 50,000 feet also, what would be the point of doing this? >>> >>> The promises made by X-30 were absolutely silly, in retrospect. A >>> vehicle >>> which can cruise at hypersonic speeds is going to be very different than >>> a >>> vehicle which can accelerate to orbital speeds, yet somehow X-30 was >>> being >>> sold as able to do both (makes me think of the SNL skit for Shimmer, a >>> floor >>> polish and a dessert topping). >> >> So let's see, a vehicle that can cruise at Mach 20 is going to be >> different from one that can accelerate to Mach 25 how, exactly? >> >>> The fact of the matter is that LOX and liquid fueled rocket engines are >>> really good at accelerating vehicles to orbital velocity. >> >> No, actually they aren't. They can do it, but "really good"? No. > > Show me an air breather that can do better. I didn't say an air breather could do better, I said that chemical rockets aren't "really good" at getting to orbit. > Better yet, show me an air > breather which can actually fly at Mach 20, which is what NASP was sold as > being able to do. I'm sorry but I don't get your point here. You seem to be arguing that if we haven't done something in the past that there's no point in trying to do it in the future. >>> Air breathers, >>> not so much. The machinery required to compress enough air for use in an >>> engine optimized for rocket like acceleration would be large and heavy. >>> So >>> much so that just bringing your own LOX in a tank turns out to be a net >>> win. >> >> X-30 was intended for Mach 20 cruise. At Mach 20 orbit isn't that far >> away. > > But you can't get there with air breathing engines. You *must* switch to > engines burning oxidizer carried on board. Now you're talking about two > different sets of engines to maintain. No, you have no need to do that. None at all. You cruise to Mach 25, go into a ballistic trajectory, and at apogee you use a small rocket to perform a circularizing burn. > Either that or you're talking an even *more* complicated engine that can do > both. Considering that we have yet to develop a hypersonic air breathing > engine without a rocket mode, this is a stretch, to say the least. So you're saying that because the current prototypes work in a particular way, there's no point in continuing development? >> You don't need "rocket like acceleration" if you are cruising at speeds >> that high. >> >> And you don't need any "large and heavy machinery" to "compress enough >> air". >> >> Scramjets work. Get used to it. > > B.S. Scramjets are a research project, not an off the shelf commercial > technology. Anyone who tells you otherwise is selling you snake oil. Straw man. Atomic bombs are not "an off the shelf commercial technology" so by your logic they don't work either. > On the other hand, liquid fueled rocket engines suitable for use in orbital > launch vehicles have been available since the late 1950's. So what? > They are off the > shelf technology today. So what? > There is no shortage of companies today which will > sell you fully developed liquid fueled rocket engines which are currently > being used on existing launch vehicles. So what?
From: Marvin the Martian on 14 May 2010 21:44
If all you guys want to do is just go up and fall back down for the ride and to get "astronauts wings" and bragging rights you've been in space, build a fracken rail gun. Let's see... 50,000 ft =~ 15,000 meters, so your energy per unit mass would be 150 kJ/kg = v^2/2 => v^2 = sqrt(300 kJ/kg) = 546 m/s At 2g, acceleration, you'd need to accelerate for 28 seconds, and your rail gun would need to be =~ 16 km long. Should be do-able. Much of the cost of real estate could be reduced by making the initial part of the ride circular. |