View Full Version : nuclear engines
I was reading in popular science and at the nasa site about a form of propulsion using a nuclear reaction to heat liquid nitrogen into a gas, which would expand out and push the ship along. The question I have is if this could be used to help ships enter orbit, since these engines are estimated to be 2-3 times as powerfull and effecient as chemical propulsion it could save launch costs. Would this work?
07-08-99, 01:15 PM
Technically, it would work. Politically, no. Environmentalists would absolutely have a cow, and for once I'd agree with them. An active nuclear reactor moving at high speed through the air is not something I want to be near.
Mind you, I am all for nuclear energy in space, such as RTG's or reactors launched inert. As long as fuel rods are adequately packaged against a launch explosion, and inserted into reactor safely away from Earth, I think nuclear engines are an excellent idea. Too bad some people go ape at the very word "nuclear" - without the slightest understanding of the technical issues.
Nuclear engines would be good for long trips, where high specific impulse and fuel economy are important. This would involve interplanetary missions, mostly.
For launching things, nuclear engines are not practical. As Laticia points out, they present an environmental hazard. But, they are also bulky, and unlikely to be competitive with air-breathing, maglev-assisted and beamed-energy solutions that actually utilize the Earth's atmosphere to push themselves onto orbit. This saves both on engine complexity and weight, and on fuel weight (resulting in compounded savings from smaller and lighter fuel tanks, smaller overall form factor, less air friction, therefore even less fuel required, and so on.)
I am; therefore I think.
While I see your points about the bulkiness and enviroment risks, by using liquid nitrogen, there isnt a risk of a large explosion like the challenger. In the article i read about this type of engine its mentions that radiation isnt released beacause of the magnetic fields that keep the fissioning uranium in place. Couldnt those magnetic fields also be used to act as control rods, and remove/add uranium as needed? And another idea i had is to use the engine as a nuclear reactor to power the ship while all the heat is being created to vaporize the liquid nitrogen, and when the engine isnt being used it could be used as a regular reactor. I realize to that this would be fairly impractable to provide thrust for a ship the size of the space shutte, but perhaps one much larger? Such a large ship could be more effeicent for the building of space stations. The modules that are being used to construct the ISS all have a high surface area to volume ratio, and since there is a lot of "armour" needed to protect the crew from the hazards of space wouldnt it be better to make modules with a high volume compared to surface area.
As far as i know the concepts nasa has in mind such as mag lift shuttles are intended to transport small packages such as sattelites.
Look I know these ideas and questions may sound dumb to some of you, but I am still in high school and am trying to find out if some of my ideas are plausible at all.
07-09-99, 05:21 AM
Since you're in high school, can you figure out what the shape is that gives the minimal surface area for a given volume?
Hint: nature knows.
Well, I too am in Highschool, i believe you are referring to the sphere if i'm not mistaken.
a sphere, and im not just copying anton.
the volume to suface area ration also increases when the size of the sphere increases. Now can someone please answer my other questions?
hey thanks a lot for the nice replies to the rest of my questions. Knew i could count on you guys.
Sorry bob for making you feel ignored. I was kinda hoping someone else would discourse on the topic. Oh well, it's Boris to the rescue!! (paa-parampampam-paaaa!!!)
1) Magnetic fields, and indeed anything electromagnetic, cannot serve as a total protection against fission radiation. That is because among the byproducts of fission are neutrons -- which are electrically neutral. To completely shield any nuclear reactor, you would have to put an impervious barrier around it which would absorb the escaping energetic particles. Read: "lots of weight".
2) A crash can be caused by any odd component, not even necessarily the propulsive one. But the end-result is unavoidably the same: radioactive material in the atmosphere.
3) Again, magnetic fields are not usable as control rods. Control rods in fission reactors absorb neutrons; they are typically made of graphite. I think what you might be confusing this with is the fusion reactor, or more accurately the toroidal plasma confinement systems. In these machines, electrically charged and superheated plasma is trapped by magnetic fields and forced to produce helium nuclei every now and then, thereby creating energy. However at present such reactors haven't even yielded positive energy output on the ground even in their most advanced versions, requiring constant maintenance and certainly being too big and fragile to put on a spaceship.
4) Someday, we will probably have vehicles larger than the shuttle, and exceeding its cargo capacity by orders of magnitude. However, at present even a shuttle launch costs (if my memory doesn't fail me) around $300 million! Building something even larger would mean it would be even more expensive to support. I don't believe our space technology has reached the point when scale begins to provide economy. In addition, our reliability record is too dismal to plan of trying to routinely send up ships that might cost many billions of dollars (which means the shuttles weren't such a great idea, actually). I think NASA has the right idea now with the 'smaller, faster, cheaper' approach (or whatever the heck it is) -- it is cheap to make mistakes with inexpensive craft; and once we have made enough mistakes to learn something, then perhaps it will be time to raise the stakes...
I am; therefore I think.
[This message has been edited by Boris (edited July 12, 1999).]
Thanks a lot boris, even though my idea was a flop I'm glad that you took the time to explain why. The only material I've been able to find on that subject was quite thin, so I wasnt too clear on how it worked.
OH well mabye the X-33 and X-34 will make space access reliable enough to build large scale space shuttles.
Don't worry about asking dumb questions, Bob. I'm the King of Dumb Questions, and I graduated from high school in '73.
07-13-99, 02:51 AM
sorry bob, wanted to get back on this, became rather busy, but Boris did a fine job so hey!