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Clean Nuclear Launches?
AKAImBatman writes "When it comes to launching millions of pounds of material into space, nearly everyone knows about the Orion Project. Blow up a series of nuclear bombs under your dairy-aire and ride the explosion on up. Unfortunately, the Orion spewed out so much radiation that it just wasn't a feasible launch option. If we want commuter trips to space, we're going to have to find another way. Well, it turns out that NASA's been doing quite a bit of research on Gas Core Nuclear Rockets, an ultra-powerful nuclear rocket that puts out almost no radiation. This research has spurred a fascinating new generation of ideas on reaching the cosmos. Could inexpensive cruises to the moon happen within our lifetimes?"
(article text, minus pictures)
Opening the Next Frontier
by Anthony Tate
Part 1: The Frontier Spirit
America loves its legends. George Washington in Valley Forge. The Wild West. World War II. The Man on the Moon.
But lately, it seems the legends have stopped.
Sure, we have the Internet to play with now, and computers are changing the world in ways we can scarcely grasp as of yet. The Soviet Union is no more, and despite our current travails with terrorism, a certain comfortable familiarity has us in its grip.
Where is the next legend? Where is the next frontier? Or are we just going to go comfortably off into retirement?
If the 'entertainments' of the kids these days are any indication, no way.
Extreme sports, fun little things like 'base jumping' and other diversions indicate that the next generation of Americans are harkening back to their roots in a big way. America is ready for the next challenge, refreshed, revitalized, and shaking off old fears and inhibitions.
But what could have caused our recent doldrums?
Why have we not gone back to deep space, that logical 'Final Frontier,' for so many years after Apollo? I believe it was a confluence of several factors, most of which have now passed, that caused us to huddle close to the bosom of Mother Earth for these past decades.
Part 2: What went wrong.
To be blunt, it was the 70's.
After the turbulent change of the 60's, the 70's were just a hard time for America. The Cold War dragged on and on, no end in sight. Vietnam was a horrible, bloody mess, deeply misunderstood to this day, and bitterly divisive even in the aftermath. Watergate destroyed the faith of millions in their own government. The Oil Embargo shocked the economy as well, causing the nightmarish condition of 'stagflation.' Cultural upheaval became the norm as gains in civil rights were cemented into place.
With that litany of bad news, there is little wonder that the public lost interest in space. When you are scared for your job, your children, and whether or not your paycheck next year will still cover the rent, idealism and exploration goes out the window.
Also, lets be honest, landing on the Moon in the 1960's was an incredible feat. That entire rocket, the whole plan, was designed, built, and flown using less computing power than you have in your PC. Genius level effort was used to make that program possible, and the chance of disaster was perilously high, even by the comparatively relaxed standards of the day. In other words, Saturn was ahead of its time, by many years.
If it wasn't for the Cold War imperative to beat the Soviets, we'd probably be looking to go to the Moon right about now, all things considered.
Add in the fact that science itself was throwing up massive roadblocks, and there is little surprise to be had from the seeming 'retreat from space.' The rocket fuel used in the Saturn V moon rocket at launch was BETTER than the rocket fuel used to launch the Space Shuttle today. Why is that? Well, it's simple: The chemical fuels used in the Saturn V are among the best fuels that chemistry allows. Science is remarkably inflexible: unlike in the movies we can't just 'whip up' better rocket fuels. Chemistry is pretty stubborn that way.
So, exploring further in space was not important to the country while we had other problems to deal with, and making rockets better than the SaturnV was pretty much impossible.
So, NASA went sideways for a while. The Space Shuttle is a remarkable system, but it is at its core a compromise. So while it is good at many things, it is great at nothing. But nonetheless, the Space Shuttle kept America in space, and slowly we were building momentum to move forward once again away from the Earth.
Then Challenger blew up (and now we've lost Columbia and her crew as well).
Now, to the doughty folks who made Apollo fly, that disaster would have been a learning experience, and development would have continue
My understanding is that the clean nuclear propulsion systems presently under serious consideration don't provide a high enough thrust/weight ratio to actually lift a spacecraft off the surface of the Earth. Rather, their primary use would be for entirely space-born craft, which would be assembled in orbit and zip around the solar system without actually ever touching down anywhere.
This space unintentionally left unblank.
From dictionary.com:
2 entries found for derriere.
derriere also derriere ( P ) Pronunciation Key (dr-ar)
n.
The buttocks; the rear.
Also:
No entry found for dairy-aire.
It's like the difference between a segway and a segue. One is a normal word used in English, the other is an amalgam coined for some other purpose.
What is music when you despise all sound?
- The ribbon would end up fluttering down and wouldn't be dangerous at all
- The counterweight would fly off into space
- Any load ON the ribbon would be a different matter, but hey, the space shuttles fell without causing planet-wide destruction.
Also, the base of the ribbon would probably be a floating platform in the middle of an ocean, so any falling load would be extremely unlikely to hit land.A gas core nuclear reactor has a high ISP (meaning it's very efficient), but it does not have a particularly high thrust. That means it's great for cruising and orbital work, but it's not a launch engine like Orion could be.
I hate when I see this arguement.
Look at some of the more recent space elevator designs.
Basically, the elevator would be made out of a ribbon so light and with such a surface area that it would fall to the earth like a peice of paper. At least that section of the ribbon that doesnt burn up while entering the atmosphere.
A space elevator isnt like the ones you read about in Kim Stanley Robinsons Mars trilogy.
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And would dispersal be greater if the nuclear reactor went critical?! Thought so...
Here's where education is important. Do you understand what "going critical" is? Very specifically, it's a build up of heat from a "melt-down". (A "melt-down" being when a nuclear reaction gets out of control and produces excessive amounts of heat.) Usually reactors are highly contained units. All that extra heat builds up pressure that has to go somewhere. Thus the containment itself can produce a big explosion. Still, it's more like an industrial boiler exploding than a nuclear bomb. The only radiation is from any radioactive material that gets ejected. (Usually not much, and cleanup isn't too large of an issue.)
Now in a nuclear rocket, specifically a Nuclear Thermal Rocket, heat is what we want. Assuming the reaction goes beyond the safeguards (which should be impossible), you can simply increase power to the turbopumps and flow more fuel through the reactor. This will end up providing far more thrust than originally intended (read: serious KICK IN THE PANTS), but the melt-down will not become critical.
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I think you need to have a look at Liftwatch. There are a lot of announcements such as these. There are nanotube advancements almost every month, and a whole bunch of universities and corporations worldwide are throwing rather large sums at putting it under heavy research. A 1km cable with 2% CN loading was already constructed a while ago. Smaller stretches were already made with 5% loading at the time the NIAC phase II was written, and was mentioned in said paper.
You neither need to grow a 35000km buckytube, nor do you need to reach a 100% CN-loaded ribbon.
Composites will be made with a higher and higher CN loading, and once a certain percentage is reached (feel free to check the NIAC 2 paper which draws this line quite clearly), you'll have elevator-worthy material. At the rate CN loading in composites has been increasing in the past decade or so, we should [hopefully] have elevator-worthy material in about 2 years.
Cheers.
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If going "critical" means that it has gone beyond the safeguards and is melting the containment safeguards (which is what I meant..) then who's to say the pumps (or any other piece of equipment) wouldn't just melt?
Because the Turbopumps are in a different part of the craft. Did you read the article? Turbopumps push a steady stream of fuel from the tanks to the core where the core heats the material to PLASMA. Don't suppose you know how hot plasma is, do you? I'll try to explain it this way: The reactor is DESIGNED to run under what would be considered melt-down conditions in a normal reactor. More heat from the reactor means more energy transfered to the fuel, which means more thrust. If you cut the thrust, the backend of your rocket will melt and fall into the ocean. The ocean will provide a new moderator that will stop the reaction completely. The reactor will still be contained in its shielding, so little to no radiation will be exposed to the underwater environment. (Not that underwater volcanos don't already put out enough of that.)
But that's all besides the point, the point was, if it DID go critical, and it DID explode, that would be inherently WORSE then if the shuttle just blew up.. You said:
"Thus the containment itself can produce a big explosion"
Doesn't that one statement agree with what I'm saying?!
No. Because you took two different designs and equated them. Nuclear engine != Nuclear powerplant. A powerplant exists under pressure. It can only operate within certain heat tollerances before a boiler explosion (and it IS a boiler explosion) happens.
A nuclear engine exists in a state where ALL the heat is being transferred to fuel. More heat is actually a GOOD thing in the engine as it provides more thrust. The problem with a runaway reaction (which doesn't just happen by itself, sorry to say) is control. You're now sending your astronauts on a trip to the moon when all they wanted was to achieve orbit. That's a problem. In many ways that's less of a problem than a failed chemical booster which would simply explode, or fail, or just about anything else. Assuming the craft survived the initial failure (not likely), a chemical booster helpfully drops you back to Earth at terminal velocity, on an unknown vector.
With a little education, you should be MORE scared of chemical rockets than nuclear ones.
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That is right, the US self-destructed a rocket right after launch and the RTGs survived intact, were recovered and the material was in good enough condition to be reused.
Nuclear propulsion is our ticket off this rock. The only thing in our way is ignorance of the technology.
Oh, and yes, IAARS.
"It takes considerable knowledge just to realize the extent of your own ignorance." - Thomas Sowell
No one said that. In fact, when that question was asked, the answer was "Okay, so we have to build it strong enough so that can't happen." And they did - the WTC was capable of withstanding an impact by the largest jet transport that existed at the time of its construction.
In fact the WTC towers were capable of (mostly) surviving 9/11, if only there had been better fire retardants on the supporting columns - which had been recommended repeatedly, particularly after the 1993 attacks. Nobody said that was a worry for another day, either, they just didn't want to pay for it.
So, bad example.
-Graham
part(s) of the core of Chernobyl 4 melted down. (though i'm not entirely sure if this was due to a runaway reaction producing too much heat, or due to external heating from the graphite moderator fire started by the steam explosion. nor am i sure which would be the worse thing.)
what basically happened was that the molten core material had to melt its way through its containment (what there was of it). in the process, of course, it became diluted with molten whatever-it-had-just-touched matter. this can't go on forever without the core matter going subcritical; the "china syndrome", melt-through-the-planet scenario presupposes some mechanism for the fissile material to stay homogenous and concentrated, and i for one can't think of any.
As far as meltdowns go, you forget one thing. As the core melts surrounding materials, it mixes with them and this causes a certain amount of moderation, slowing down the nuclear reaction. Many new reactor designs incorporate moderating materials directly into the containment vessel so that even under a full and uncontrolled meltdown, the moderation caused by these materials is enough to slow the reaction and prevent a breach. New reactors can survive an full catastrophic failure of all systems simultaneously and still not allow a breach of the containment system.
Allow me to rephrase. NERVA got up to 75,000 pounds of thrust out of the TEST rockets. The GCNR rockets are far more efficient, plus we can boost efficiency by use of particle accelerators on the plasma. Thus we can get MORE THRUST with THE SAME REACTION MASS that is used for chemical thrusters.
Think of the nuclear rockets as ultra-powered chemical rockets. Somehow we've managed to get the hydrogen to higher velocities than was previously possible with a simple chemical reaction.
BTW, Force = Mass * Velocity2. So more velocity at the expense of mass will improve our thrust. Obviously there's an upper limit to how much velocity we can obtain, so we need to throw more mass. But if you consider that a nuclear engine can throw the same amount of mass as a chemical engine (minus some "light" electrons lost in plasma conversion), then we have greater overall force coming from our nuclear than our chemical reaction. Although, to be exact we're both throwing and pulling against the plasma. First we create the plasma which is exhausted (throwing). Then we use EM accelerators to pull on the plasma on the way out. The "pull" transfers that much more energy from the mass to the craft.
That being said, I am NOT a rocket scientist, so I can't give you exact numbers. However, the article I linked to in the story does give quite a few numbers, and a bit of googling will produce even more exact numbers. (I've seen some right down to the force per molar mass on usenet. Since I wasn't going to be building one of these things myself, my eyes kind of glazed over at that.)
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