I don't believe that you are correct. The Moon is close to earth, and might be good for some industry in the medium term, but there's nothing you can do there that you can't do with a little bit more work on orbit.
Even if you can find oxygen on the moon, nobody's found convincing evidence of nitrogen, which means that you can't grow food there, unless you import nitrogen. Now, of course, you have the same problem on orbit, but the only advantage to the Moon is that you're in a gravity well. Apart from that, it's basically a desert.
My priest on this subject is Dr. Zubrin, who advocates (rather than doing a lot of on-orbit assembly for a Battlestar Galactica Mars mission) launching two rockets, one with the return vehicle and one with the crew hab module, directly to Mars from Earth. No rendezvous in orbit, no assembly required.
It's (obviously) a bit more involved, but I suggest you check out his web site and read his plans.
Incidentally, the habs that he is talking about for Mars would also work fine on the Moon. So there's no reason not to build a couple extra and dump some crews there to do some more exploration and some real science. But, I don't believe we should depend on Luna as some sort of waystation.
All those concepts work well in wind tunnels, but have not proven themselves in long-duration flight. Yes, my rhetoric was perhaps running away with me, but the stability of the combustion system is still a huge issue with scram propulsion. I guess that would have been a better way to say it.
I don't pretend that my knowledge is comprehensive, but all the nuclear rocket proposals I've seen that look even remotely feasible involve dumping a working fluid through a hot pile. And that working fluid is now radioactive.
Just as an aside, I'm not one of those nutbags that thinks that radioisotope generators are nuclear disasters waiting to happen. I like nuclear power. Just not when I have to breathe its byproducts.
At any rate, I've never heard of a nuke rocket used as a launch system (unless you're talking about Project Orion, and if you are, you're a loony). They'll be good interplanetary drives, but they don't have the thrust for liftoff.
If there is another system out there, I'd be interested to check it out. I'd appreciate a link if you've got one.
I'm glad I sound like I know what I'm talking about. One thing I've learned, is that I definitely don't know what I'm talking about. But it's useful to be able to generate a convincing simulacrum of competence. : )
No, I don't know beans about genetic algorithms in general, or their relation to hypersonics. Would you use them for modeling the flow, or designing the shape of the engine itself?
I'd be interested in checking out the basics if you have a link handy.
Sweet! I get to cite myself! I've posted this in another thread. Should give you a grounding. Here I explain the problem with air breathing rocketry, namely the fact that you have to make the ship big and draggy in order to ingest enough air.
Man, I've been posting the CRAP out of this story...and it's all because of last semester's classwork. Almost makes me feel they're useful. : )
I think any engineer that's interested in space travel should read Robert Zubrin's "The Case for Mars". He has an axe to grind, yes, but he's also got a kick-ass plan for exploring the solar system. I heartily recommend it.
Buy it here, not at Amazon! You can also read some papers he's published that are the real meat of his proposal.
America's social experiment wouldn't have worked if it were not geographically separated from the monarchies of Europe. While I would be the last person to argue that America's system is perfect, I do believe that it's a damn sight better than even a constitutional monarchy.
There's nothing to say that the citizens of another world wouldn't go ahead and charter a new social contract. That, more than anything, is what makes me want to travel to the stars.
One big asteroid strike, and the medical programs are all gone.
We've got all our eggs in a very fragile basket. Crappy movies to the contrary, planet killer asteroids are a very big medium-term (next 200 years or so) threat.
We need to get moving.
As far as habitable planets, I suggest Mars. Then we figure out Alpha Centauri. First things first. : )
And, as far as God's saying your number's up, I think it's God's idea of a dope slap. "Didn't you guys see this coming? Why did you bury your talent in the ground?" (Yes, the second one is a Sunday school allusion. Very apropos.)
The air force thought about this in the 60's. The idea was to stick a guy in a space-suit into an egg shaped reinforced mylar bag, with a heatshield/aerobrake on the bottom. Our intrepid astronaut has in his lap and under his seat two containers of "bang foam", you know, the stuff you get at the post office where you put 'em in your box and you pull the string or whatever and they go BANG! and you have conformal packing material. Same deal, only lots more of it. Think Demolition Man car crash mode. So he de-orbits in his foam egg, pops a 'chute, and hopefully doesn't die of claustrphobia on the way down.
Can't find a link, but this was seriously considered. Might not be a bad emergency way to get out of space...but I don't want to be the first. : )
I'd be happy to scrap Shuttle and ISS, if it came with a hard budgetary commitment to explore the solar system with people. (they'll follow unmanned survey missions, of course)
Shuttle is a waste. On that, Mr. Easterbrook and I are in total agreement.
Orbital insertion? Equivalent speed is Mach 25. (of course, in orbit, there is no speed of sound, so Mach numbers don't apply, but for purposes of this discussion...)
SR-71? Mach 3. Teeny payload. However, the design we worked out used upgraded J-58 engine cores from the SR-71 to get up to scramjet operating speeds. And yes, having to fly for a long time while you accelerate is a big problem. You're burning just incredible amounts of fuel the whole time, and burning fuel to accelerate the fuel you need to burn to accelerate fuel that you need to burn to accelerate. Ad nauseam.
The other problem with air breathing rocketry is wave drag. In order to get the same thrust as a rocket, an airbreathing space craft's cross-sectional area has to be about 1.5 to 4 times as large as the rocket is to ingest enough air. Since wave drag (the primary drag force at high speeds) is very strongly dependant on cross sectional area, you swiftly get to a point of diminishing returns. Let's make up some numbers.
Rocket A thrusts at 100lbs, and weighs 10 lbs, and has (say) 10lbs of drag acting on it. That gives it an excess thrust of 80lbs to do the force=mass*acceleration thing.
Scramjet B thrusts at 100lbs, flys mostly horizontally so its weight isn't a factor (it's a lifting body), but has (say) 80lbs of drag on the airframe. So it only has a quarter of the thrust available to accelerate as our rocket, meaning it will take much longer to get to orbital insertion velocity.
In a nutshell, that is the problem with air breathing rocketry.
On short timescales and when you're not maneuvering, you're right. But, when you're trying to fly a trajectory, the changing environment in the combustion chamber makes it very difficult to keep the flame ignited. And having it not ignite is a very very very bad thing.
And yes, aerodynamic heating even for a "low speed" scramjet is a silly big problem. Now we just need to figure out how to deal with five times as much as we accelerate to Mach 25 for orbital insertion. Easy. : )
if it were broken low in the atmosphere, no. It'd just go away, probably in a very unstable manner. Forget about getting it back.
If it were broken close to the counterweight asteroid? *shudder* Bad news. The thing would wrap around the Earth three times, and cause unspeakable destruction.
Read the last 100 pages of Kim Stanley's Red Mars. Even if you don't like the rest of the book...man, that space elevator scene is cool.
Agreed on both points, yes. I just think it's important to emphasize the human development benefits of space flight, which are at least as important as the science and engineering benefits.
I do believe, however, that if we could build a compact device that grew monocrystalline lattices of, say, titanium, we'd be able to make shedloads of money. Much easier to do in microgravity than here on Earth.
Ramjets won't get us close to space, period. They top out about Mach 8.
Scramjets are a really draggy way to drive payloads at high speeds. The size of the compression ramps is huge relative to their thrust output (which is totally theoretical to begin with...the Australians kept their scramjet lit for, what? Six seconds? And that was a world class effort)
Next generation fuel-oxidizer rocketry is the way to go. The vehicles are smaller in cross section and can get out of the atmosphere faster.
Single stage air-breathing rocketry doesn't work. Multi-stage air breathing coupled with conventional rocketry has promise. With a single stage aircraft, you need at least three (and probably four) separate engine cycles to get to orbit. You need a turbojet to get to ramjet operating speeds, which will get you to scramjet operating speeds, which will get you to an altitude where you have to light a rocket to get any higher 'cuz there's no damn air. You might be able to use a rocket-ramjet in place of the turbojet, but you've still got three separate combustors with very different geometric properties.
I promise. My team and I tried to design one last semester. Looked good on paper, but our conclusion was that it wouldn't work in practice.
OK, trust me. There is NOTHING simple about aerodynamic simulations on computers. NOTHING.
And as far as justifying NASA's existence, the annual tax revenues from comm satellite-based business pay a significant amount of NASA's funding back to, say, 1950.
Let us eggheads have some money. We usually figure out how to do some wild cool (profitable!) stuff with it.
The unmanned science projects are superb, and absurdly cheap. I don't think they're in any danger. I'm worried about the high-ticket manned program, which as I've argued, is still very important regardless of its scientific value.
NASA would, ideally, be responsible for R&D and exploration, leaving private industry to exploit opportunities in LEO. Once we get launch costs to something reasonable, it won't be a big deal to launch micro-gee experiment packages to a general purpose space station, but that station should also be supporting itself with industrial revenues.
Slashdot Mirror
I don't believe that you are correct. The Moon is close to earth, and might be good for some industry in the medium term, but there's nothing you can do there that you can't do with a little bit more work on orbit.
Even if you can find oxygen on the moon, nobody's found convincing evidence of nitrogen, which means that you can't grow food there, unless you import nitrogen. Now, of course, you have the same problem on orbit, but the only advantage to the Moon is that you're in a gravity well. Apart from that, it's basically a desert.
My priest on this subject is Dr. Zubrin, who advocates (rather than doing a lot of on-orbit assembly for a Battlestar Galactica Mars mission) launching two rockets, one with the return vehicle and one with the crew hab module, directly to Mars from Earth. No rendezvous in orbit, no assembly required.
It's (obviously) a bit more involved, but I suggest you check out his web site and read his plans.
Incidentally, the habs that he is talking about for Mars would also work fine on the Moon. So there's no reason not to build a couple extra and dump some crews there to do some more exploration and some real science. But, I don't believe we should depend on Luna as some sort of waystation.
Mars Direct
Tunguska could have been bad, and it's been several tens of millions of years since the last asteroid.
No, there's no hard timescale here: But there are a lot of big near earth asteroids. I for one don't fancy rolling the dice.
Yes, I did make that number up.
All those concepts work well in wind tunnels, but have not proven themselves in long-duration flight. Yes, my rhetoric was perhaps running away with me, but the stability of the combustion system is still a huge issue with scram propulsion. I guess that would have been a better way to say it.
I don't pretend that my knowledge is comprehensive, but all the nuclear rocket proposals I've seen that look even remotely feasible involve dumping a working fluid through a hot pile. And that working fluid is now radioactive.
Just as an aside, I'm not one of those nutbags that thinks that radioisotope generators are nuclear disasters waiting to happen. I like nuclear power. Just not when I have to breathe its byproducts.
At any rate, I've never heard of a nuke rocket used as a launch system (unless you're talking about Project Orion, and if you are, you're a loony). They'll be good interplanetary drives, but they don't have the thrust for liftoff.
If there is another system out there, I'd be interested to check it out. I'd appreciate a link if you've got one.
I'm glad I sound like I know what I'm talking about. One thing I've learned, is that I definitely don't know what I'm talking about. But it's useful to be able to generate a convincing simulacrum of competence. : )
No, I don't know beans about genetic algorithms in general, or their relation to hypersonics. Would you use them for modeling the flow, or designing the shape of the engine itself?
I'd be interested in checking out the basics if you have a link handy.
Sweet! I get to cite myself! I've posted this in another thread. Should give you a grounding. Here I explain the problem with air breathing rocketry, namely the fact that you have to make the ship big and draggy in order to ingest enough air.
Man, I've been posting the CRAP out of this story...and it's all because of last semester's classwork. Almost makes me feel they're useful. : )
Only thing I want to hear from a robot on Mars is "Hey, Boss, this looks like a good place to land. Come on over."
: )
OK, that was funny as hell. Full marks. Go to the head of the class.
.sig file.
I'm so stealing that for my
I think any engineer that's interested in space travel should read Robert Zubrin's "The Case for Mars". He has an axe to grind, yes, but he's also got a kick-ass plan for exploring the solar system. I heartily recommend it.
Buy it here, not at Amazon! You can also read some papers he's published that are the real meat of his proposal.
Damn, I love it when my education comes in handy. Makes me almost forget how much debt I'm carrying. : )
Yeah. What you said. Zubrin is The Man.
I say we just cut him a check for three years of NASA budget and turn the guy loose.
Why wait?
America's social experiment wouldn't have worked if it were not geographically separated from the monarchies of Europe. While I would be the last person to argue that America's system is perfect, I do believe that it's a damn sight better than even a constitutional monarchy.
There's nothing to say that the citizens of another world wouldn't go ahead and charter a new social contract. That, more than anything, is what makes me want to travel to the stars.
One big asteroid strike, and the medical programs are all gone.
We've got all our eggs in a very fragile basket. Crappy movies to the contrary, planet killer asteroids are a very big medium-term (next 200 years or so) threat.
We need to get moving.
As far as habitable planets, I suggest Mars. Then we figure out Alpha Centauri. First things first. : )
And, as far as God's saying your number's up, I think it's God's idea of a dope slap. "Didn't you guys see this coming? Why did you bury your talent in the ground?" (Yes, the second one is a Sunday school allusion. Very apropos.)
You're right. I want the heavy, man-rated rocket for Dr. Robert Zubrin's Mars Direct mission plan.
No building stuff in orbit. Just two big damn rockets and five people spend half a year on Mars. Now THAT, my friends, is space exploration.
The air force thought about this in the 60's. The idea was to stick a guy in a space-suit into an egg shaped reinforced mylar bag, with a heatshield/aerobrake on the bottom. Our intrepid astronaut has in his lap and under his seat two containers of "bang foam", you know, the stuff you get at the post office where you put 'em in your box and you pull the string or whatever and they go BANG! and you have conformal packing material. Same deal, only lots more of it. Think Demolition Man car crash mode. So he de-orbits in his foam egg, pops a 'chute, and hopefully doesn't die of claustrphobia on the way down.
Can't find a link, but this was seriously considered. Might not be a bad emergency way to get out of space...but I don't want to be the first. : )
I'd be happy to scrap Shuttle and ISS, if it came with a hard budgetary commitment to explore the solar system with people. (they'll follow unmanned survey missions, of course)
Shuttle is a waste. On that, Mr. Easterbrook and I are in total agreement.
Orbital insertion? Equivalent speed is Mach 25. (of course, in orbit, there is no speed of sound, so Mach numbers don't apply, but for purposes of this discussion...)
SR-71? Mach 3. Teeny payload. However, the design we worked out used upgraded J-58 engine cores from the SR-71 to get up to scramjet operating speeds. And yes, having to fly for a long time while you accelerate is a big problem. You're burning just incredible amounts of fuel the whole time, and burning fuel to accelerate the fuel you need to burn to accelerate fuel that you need to burn to accelerate. Ad nauseam.
The other problem with air breathing rocketry is wave drag. In order to get the same thrust as a rocket, an airbreathing space craft's cross-sectional area has to be about 1.5 to 4 times as large as the rocket is to ingest enough air. Since wave drag (the primary drag force at high speeds) is very strongly dependant on cross sectional area, you swiftly get to a point of diminishing returns. Let's make up some numbers.
Rocket A thrusts at 100lbs, and weighs 10 lbs, and has (say) 10lbs of drag acting on it. That gives it an excess thrust of 80lbs to do the force=mass*acceleration thing.
Scramjet B thrusts at 100lbs, flys mostly horizontally so its weight isn't a factor (it's a lifting body), but has (say) 80lbs of drag on the airframe. So it only has a quarter of the thrust available to accelerate as our rocket, meaning it will take much longer to get to orbital insertion velocity.
In a nutshell, that is the problem with air breathing rocketry.
On short timescales and when you're not maneuvering, you're right. But, when you're trying to fly a trajectory, the changing environment in the combustion chamber makes it very difficult to keep the flame ignited. And having it not ignite is a very very very bad thing.
And yes, aerodynamic heating even for a "low speed" scramjet is a silly big problem. Now we just need to figure out how to deal with five times as much as we accelerate to Mach 25 for orbital insertion. Easy. : )
if it were broken low in the atmosphere, no. It'd just go away, probably in a very unstable manner. Forget about getting it back.
If it were broken close to the counterweight asteroid? *shudder* Bad news. The thing would wrap around the Earth three times, and cause unspeakable destruction.
Read the last 100 pages of Kim Stanley's Red Mars. Even if you don't like the rest of the book...man, that space elevator scene is cool.
Agreed on both points, yes. I just think it's important to emphasize the human development benefits of space flight, which are at least as important as the science and engineering benefits.
I do believe, however, that if we could build a compact device that grew monocrystalline lattices of, say, titanium, we'd be able to make shedloads of money. Much easier to do in microgravity than here on Earth.
If you wrote a thesis about a successful scramjet system, everybody would think you're a badass.
I promise, you'll spend a hell of a lot more time making the 'jet work than writing the paper.
But you feel free to be needlessly combative. Have fun.
Ramjets won't get us close to space, period. They top out about Mach 8.
Scramjets are a really draggy way to drive payloads at high speeds. The size of the compression ramps is huge relative to their thrust output (which is totally theoretical to begin with...the Australians kept their scramjet lit for, what? Six seconds? And that was a world class effort)
Next generation fuel-oxidizer rocketry is the way to go. The vehicles are smaller in cross section and can get out of the atmosphere faster.
Single stage air-breathing rocketry doesn't work. Multi-stage air breathing coupled with conventional rocketry has promise. With a single stage aircraft, you need at least three (and probably four) separate engine cycles to get to orbit. You need a turbojet to get to ramjet operating speeds, which will get you to scramjet operating speeds, which will get you to an altitude where you have to light a rocket to get any higher 'cuz there's no damn air. You might be able to use a rocket-ramjet in place of the turbojet, but you've still got three separate combustors with very different geometric properties.
I promise. My team and I tried to design one last semester. Looked good on paper, but our conclusion was that it wouldn't work in practice.
OK, trust me. There is NOTHING simple about aerodynamic simulations on computers. NOTHING.
And as far as justifying NASA's existence, the annual tax revenues from comm satellite-based business pay a significant amount of NASA's funding back to, say, 1950.
Let us eggheads have some money. We usually figure out how to do some wild cool (profitable!) stuff with it.
People shouldn't go to space to do science.
People should go to space to explore.
Both are important to us as a species.
The unmanned science projects are superb, and absurdly cheap. I don't think they're in any danger. I'm worried about the high-ticket manned program, which as I've argued, is still very important regardless of its scientific value.
NASA would, ideally, be responsible for R&D and exploration, leaving private industry to exploit opportunities in LEO. Once we get launch costs to something reasonable, it won't be a big deal to launch micro-gee experiment packages to a general purpose space station, but that station should also be supporting itself with industrial revenues.