No, liquid oxygen is a propellant. Go read Sutton 'Rocket Propulsion Elements' (5th. ed.), chapter 7, section 1:
"The term 'liquid propellant' embraces all the various liquids used and may be one of the following: (1) Oxidizer (liquid oxygen, nitric acid, etc.) [...]"
I said propellant. Fuels and oxidizers are propellants. Scramjets reduce the need for the vehicle to carry oxidizer (one kind of propellant), but they increase the mass of fuel (another kind of propellant) that must be carried. Your claim that the scramjet vehicle needs less fuel as well is just plain wrong.
High specific energy fuels like H2 do give you higher specific impulse, but they also require the vehicle to have larger tanks, since their density (not coincidentally) is lower. This increases the dry mass of the vehicle, which increases the mass you are trying to put into orbit. If you are not careful you lose more from than than you gain from the Isp increase. This is a particular problem for scramjet launchers, where the amount of LH2 required can be several times that of an equivalent launcher with rockets.
It is not a coincidence that the first stages of multistage vehicles typically use a dense fuel like RP-1 instead of LH2 -- the density advantage wins over Isp for those. Some argue that even for rocket SSTOs hydrocarbon fuels beat LH2, since the wet/dry mass ratio can be much larger.
The tradeoff studies on scramjet launcher designs have consistently optimized to the 'rocket only' solution, I am given to understand.
This is wrong. You actually need *more* fuel in a scramjet -- and the propellant tanks end up being much larger.
Airbreathing engines help the most early in the launch, since their Isp goes down with increasing speed. But early in the launch you don't care much about carrying oxygen, since it's used before the vehicle has accelerated much and therefore didn't require much previously used fuel to accelerate it.
Re:Stupid, Slightly OT Question
on
X-43A Hits Mach 7
·
· Score: 2, Interesting
Unfortunately, the drawbacks of airbreathing appear to outweigh the advantages, at least for vehicles intended to put objects into orbit.
The problem is that a scramjet trades a dense propellant (LOX) for more of a low density propellant (LH2). As a result, the propellant tanks on a scramjet vehicle would end up being larger (and heavier) than those on an SSTO rocket with similar payload. LH2 is also much more expensive than LOX, so your propellant costs go up (not that propellant cost is currently important, but your vehicle is also in a more aggressive thermal environment so it to will be more expensive.)
Worse, the effective Isp of a scramjet (after you take into account drag and gravity losses due to its lower acceleration) ends up being little better than the rocket. See Henry Spencer's comment on this.
About the only place scramjets may make sense is in hypersonic cruise missiles. The US military has a scheme for using hydrocarbon fuels, converting these fuels into hydrogen + CO in flight by partial combustion with a portion of the incoming air (that portion is slowed to a stop by a conventional ramjet inlet, with the fuel being used to keep the air relatively cool and the inlet from melting.) The H2 + CO + nitrogen is then injected into a scramjet for complete combustion.
Re:Spaceflight as a religious endeavour
on
The Wrong Stuff
·
· Score: 1
People are not genetically programmed to 'go forth and multiply.' They're genetically programmed to fuck. There's a difference -- the former is a much higher level goal than the latter. This is why there's no hardwired aversion to birth control devices.
They're already being sued for Lanham Act violation -- it's just that they probably figure that if they don't win on this, they're dead anyway.
What I want to know is if McBride/etc. are still liable under the Lanham act for their statements if SCOG itself dies (and is not around to compensate them for penalties.)
Feynman analyzes this kind of perpetual motion machine in his Lecture Notes. They don't work for fairly fundamental reasons. BTW, the collisions may be elastic, but ratchets are not!
There are other major costs. Editors are expensive. Typesetting, proofreading, marketing all are expensive.
The most important service a publisher provides, btw, is being a filter. If you look at internet-published or vanity press books, you'll be appalled at how bad most of them are. Sturgeon's law ('90% of everything is crap') is grossly optimistic.
The cost of the shuttle program would have enabled an entire fleet of HSTs to be built and launched on expendable rockets. So what if some had flaws, or failed after some years?
HST's successor, the JWST, is being launched into an orbit where it cannot be serviced.
For all this complexity, both mission losses were caused by bureaucratic ineptitude, not engineering issues.
Actually, the losses were caused by interaction of bad design with programmatic imperatives. The shuttle is too expensive to really justify its operation, so NASA is pushed into operating it in a way that inhibits addressing the safety issues.
This implies another accident of the same general kind is inevitable.
I suggest nothing be done. The shuttle is producing essentially nothing of value, so if a replacement is not much cheaper (and it's not likely to be if developed at NASA) then continuation of the manned space program at this time is just foolish.
This may force individuals to confront the sad reality that the visions of manned exploration of the solar system in their lifetimes were just bad science fiction. Too bad for them. Next time, don't be conned so easily.
Yep, future generations can see their souls bled away working as contractors for giant ossified government bureaucracies. A real inspiration for everyone.
The shuttle system has failed to meet most of the design goals that were used to justify its construction. In particular, its flight rate, reliability, and cost are all far worse than promised.
'Deficient' is an excellent word to describe the shuttle.
But, you are right, the shuttle does not need to be fixed. It needs to be abandoned.
Do you think a "they lied to us, your honor"-argument would fly in court? I think not.
IANAL, but I understand that if someone distributes to you a copyrighted item with a false copyright notice, the law says this is protection against legal action until you are informed the copyright notice is false. In particular, the SGI copyright notice on that memory allocation routine would absolve others of blame for its past distribution, even if SCO did have the rights to that code.
Conspiracy theoretic bullshit. Electrical power, heavy industry, and most other industrial resources aren't coming from space because that would be completely economically ludicrous. The cost of supporting a worker in space is orders of magnitude higher than the cost of supporting him on the ground. It would be like trying to grow bananas at the south pole -- yes, you could do it, but it would be ruinously uncompetitive.
No, in the opinion of the vast majority of scientists the 'evidence' (such as it is, being most self-contradictory) is the result of misinterpretation, error, or outright fraud.
Nonsense like this breaks out periodically in physics. Remember polywater? The '14 KeV neutrino'? The 'fifth force'? The 'Allison Effect'? 'N rays'? All of these were big in their day, but died away because there turned out not to be anything there.
This idea (using laser-produced photons for transmuting waste by photonuclear reactions) is fundamentally flawed. The efficiency of producing the photons by this mechanism sucks, and the cross section for (gamma,n) reactions is much lower than the cross section for the gammas to scatter off of (and lose energy to) electrons.
The amount of fuel necessary to do this would be completely impractical, comparable to the amount of fuel needed to launch the orbiter in the first place. It's *far* more efficient to use the atmosphere to slow down.
Observation of annihilation gamma rays places strong constraints on the amount of antimatter in the universe. For example, we can confidently say that most of this galaxy is normal matter. Were this not the case, annihilation of matter and antimatter gas in interstellar space would produce too much annihilation radiation at 511 keV (electron/positron annihilation) and at ~100 MeV (photons from neutral pion decay.)
IIRC, the smallest scale at which antimatter can dominate is galactic superclusters, but even that may now be ruled out.
Slashdot Mirror
No, liquid oxygen is a propellant. Go read Sutton 'Rocket Propulsion Elements' (5th. ed.), chapter 7, section 1:
"The term 'liquid propellant' embraces all the various liquids used and may be one of the following: (1) Oxidizer (liquid oxygen, nitric acid, etc.) [...]"
I said propellant. Fuels and oxidizers are propellants. Scramjets reduce the need for the vehicle to carry oxidizer (one kind of propellant), but they increase the mass of fuel (another kind of propellant) that must be carried. Your claim that the scramjet vehicle needs less fuel as well is just plain wrong.
High specific energy fuels like H2 do give you higher specific impulse, but they also require the vehicle to have larger tanks, since their density (not coincidentally) is lower. This increases the dry mass of the vehicle, which increases the mass you are trying to put into orbit. If you are not careful you lose more from than than you gain from the Isp increase. This is a particular problem for scramjet launchers, where the amount of LH2 required can be several times that of an equivalent launcher with rockets.
It is not a coincidence that the first stages of multistage vehicles typically use a dense fuel like RP-1 instead of LH2 -- the density advantage wins over Isp for those. Some argue that even for rocket SSTOs hydrocarbon fuels beat LH2, since the wet/dry mass ratio can be much larger.
The tradeoff studies on scramjet launcher designs have consistently optimized to the 'rocket only' solution, I am given to understand.
This is wrong. You actually need *more* fuel in a scramjet -- and the propellant tanks end up being much larger.
Airbreathing engines help the most early in the launch, since their Isp goes down with increasing speed. But early in the launch you don't care much about carrying oxygen, since it's used before the vehicle has accelerated much and therefore didn't require much previously used fuel to accelerate it.
Unfortunately, the drawbacks of airbreathing appear to outweigh the advantages, at least for vehicles intended to put objects into orbit.
The problem is that a scramjet trades a dense propellant (LOX) for more of a low density propellant (LH2). As a result, the propellant tanks on a scramjet vehicle would end up being larger (and heavier) than those on an SSTO rocket with similar payload. LH2 is also much more expensive than LOX, so your propellant costs go up (not that propellant cost is currently important, but your vehicle is also in a more aggressive thermal environment so it to will be more expensive.)
Worse, the effective Isp of a scramjet (after you take into account drag and gravity losses due to its lower acceleration) ends up being little better than the rocket. See Henry Spencer's comment on this.
About the only place scramjets may make sense is in hypersonic cruise missiles. The US military has a scheme for using hydrocarbon fuels, converting these fuels into hydrogen + CO in flight by partial combustion with a portion of the incoming air (that portion is slowed to a stop by a conventional ramjet inlet, with the fuel being used to keep the air relatively cool and the inlet from melting.) The H2 + CO + nitrogen is then injected into a scramjet for complete combustion.
People are not genetically programmed to 'go forth and multiply.' They're genetically programmed to fuck. There's a difference -- the former is a much higher level goal than the latter. This is why there's no hardwired aversion to birth control devices.
There are no planets with 'subzero cores'.
They're already being sued for Lanham Act violation -- it's just that they probably figure that if they don't win on this, they're dead anyway.
What I want to know is if McBride/etc. are still liable under the Lanham act for their statements if SCOG itself dies (and is not around to compensate them for penalties.)
Feynman analyzes this kind of perpetual motion machine in his Lecture Notes. They don't work for fairly fundamental reasons. BTW, the collisions may be elastic, but ratchets are not!
And that heat is turned into electrical energy by means of a thermoelectric generator, a kind of solid state heat engine.
No, what some companies really want is for the GPL to appear more restrictive than it is, so that companies are inhibited from using GPLed software.
There are other major costs. Editors are expensive. Typesetting, proofreading, marketing all are expensive.
The most important service a publisher provides, btw, is being a filter. If you look at internet-published or vanity press books, you'll be appalled at how bad most of them are. Sturgeon's law ('90% of everything is crap') is grossly optimistic.
I bet they're regreting going with the hybrid engine. A pressure-fed liquid engine would have
enabled them to dump all propellant in an abort.
The cost of the shuttle program would have enabled an entire fleet of HSTs to be built and launched on expendable rockets. So what if some had flaws, or failed after some years?
HST's successor, the JWST, is being launched into an orbit where it cannot be serviced.
I'm saying the manned space program does not have a value that comes anywhere close to justifying its cost.
Actually, the losses were caused by interaction of bad design with programmatic imperatives. The shuttle is too expensive to really justify its operation, so NASA is pushed into operating it in a way that inhibits addressing the safety issues.
This implies another accident of the same general kind is inevitable.
I suggest nothing be done. The shuttle is producing essentially nothing of value, so if a replacement is not much cheaper (and it's not likely to be if developed at NASA) then continuation of the manned space program at this time is just foolish.
This may force individuals to confront the sad reality that the visions of manned exploration of the solar system in their lifetimes were just bad science fiction. Too bad for them. Next time, don't be conned so easily.
Yep, future generations can see their souls bled away working as contractors for giant ossified government bureaucracies. A real inspiration for everyone.
The shuttle system has failed to meet most of the design goals that were used to justify its construction. In particular, its flight rate, reliability, and cost are all far worse than promised.
'Deficient' is an excellent word to describe the shuttle.
But, you are right, the shuttle does not need to be fixed. It needs to be abandoned.
IANAL, but I understand that if someone distributes to you a copyrighted item with a false copyright notice, the law says this is protection against legal action until you are informed the copyright notice is false. In particular, the SGI copyright notice on that memory allocation routine would absolve others of blame for its past distribution, even if SCO did have the rights to that code.
There's also the 'Clarke-Sturgeon Law': 90% of any sufficiently advanced technology is indistinguishable from crap.
Conspiracy theoretic bullshit. Electrical power, heavy industry, and most other industrial resources aren't coming from space because that would be completely economically ludicrous. The cost of supporting a worker in space is orders of magnitude higher than the cost of supporting him on the ground. It would be like trying to grow bananas at the south pole -- yes, you could do it, but it would be ruinously uncompetitive.
No, in the opinion of the vast majority of scientists the 'evidence' (such as it is, being most self-contradictory) is the result of misinterpretation, error, or outright fraud.
Nonsense like this breaks out periodically in physics. Remember polywater? The '14 KeV neutrino'? The 'fifth force'? The 'Allison Effect'? 'N rays'? All of these were big in their day, but died away because there turned out not to be anything there.
This idea (using laser-produced photons for transmuting waste by photonuclear reactions) is fundamentally flawed. The efficiency of producing the photons by this mechanism sucks, and the cross section for (gamma,n) reactions is much lower than the cross section for the gammas to scatter off of (and lose energy to) electrons.
The amount of fuel necessary to do this would be completely impractical, comparable to the amount of fuel needed to launch the orbiter in the first place. It's *far* more efficient to use the atmosphere to slow down.
Observation of annihilation gamma rays places strong constraints on the amount of antimatter in the universe. For example, we can confidently say that most of this galaxy is normal matter. Were this not the case, annihilation of matter and antimatter gas in interstellar space would produce too much annihilation radiation at 511 keV (electron/positron annihilation) and at ~100 MeV (photons from neutral pion decay.)
IIRC, the smallest scale at which antimatter can dominate is galactic superclusters, but even that may now be ruled out.