SanDiegoAtheist

Most of our interplanetary probes have had some form of nuclear material on board (I believe both Voyagers powered their instruments through heat exchangers powered by plutonium decay). It's the only power source that can last long enough for a mission outside the inner solar system. Solar panels are pretty ineffective, as the solar flux drops rapidly.

As to the skyhook (an elevator to orbit) - it's a great idea, but way beyond our means at this point, as a skyhook requires a terminus in geostationary orbit to prevent torque on the elevator cable. We're not quite up to being able to manufacture 24000 miles of ~100 ft thick cables in orbit with tensile strengths of spidersilk (not to mention...imagine if something went wrong. I'd hate to be anywhere on the EARTH if 24000 miles of cable suddenly started dropping from the sky with orbital velocities).

My guess for the next improvement in reusable spaceflight will be something like a combined ramjet/rocket. Use conventional propulsion to get to altitude, cut in the ramjet to boost to suborbital speeds & altitude, then ignite the rocket to finish the push to orbital velocity/altitude. That's well within our technological capacity given a few more years of r&d, and would result in huge savings with regards to payload costs for delivery to orbit (I'd guess a reusable ramjet rocket would probably be only a few percent of the cost of our current payload delivery methods).

Cheers,

The San Diego Atheist

Greg2003

That's a much better way to go, I think, and in line with the 2001 vision of space flight. But there's always the Russian space shuttle which could launch a larger payload than ours and supposedly could take you to the moon and back.

SanDiegoAtheist

Nukes are a lot harder to detonate than explosives. It's simply not possible to 'accidentally' detonate a nuke by exploding something near it (unless the arming/detonating mechanism is designed to allow for 'shock' detonation, which I can't think of any reason for).

You could throw subcritical masses of uranium or plutonium around all day, pile them in one place, stomp on them, and do anything else you please with them and wind up with nothing more than lethal radiation burns for your troubles. Creating a sustained chain reaction requires a lot of precision in how you put the subcritical masses together so that they don't just immediately fly apart from the original reaction.

Cheers,

The San Diego Atheist

Mageth

Beanstalks/space-elevators have been kicked around for decades. I think Clarke uses them in his writing, and I know Heinlein uses them extensively in Friday.

(Some of the material below sourced from here.)

Konstantine Edouardovitch Tsiolkovski wrote an 1895 paper 'Day-Dreams of Heaven and Earth' in which he discussed possible ways of escaping from the earth. One way he considered was the building of a high tower, and he described what would happen as one ascended it:

"On the tower, as one climbed higher and higher up it, gravity would decrease gradually; and if it were constructed on the Earth's equator and, therefore, rapidly rotated together with the earth, the gravitation would disappear not only because of the distancefrom the centre of the planet, but also from the centrifugal force that is increasing proportionately to that distance. The gravitational force drops. . . but the centrifugal force operating in the reverse direction increases. On the earth the gravity is finally eliminated at the top of the tower, at an elevation of 5.5 radii of the earth (36000 km)."

A Soviet engineer, Yuri Artsutanov, first developed the idea in 1960 or thereabouts. Some American engineers independently developed the idea a bit later, apparently unaware of Artsutanov's work. Clarke used space elevators first in 'The Fountains of Paradise' in the early '70s, although, quite unknown to Clarke, Charles Sheffield wrote and submitted for publishing a somewhat similar book using a space elevator (Web Between The Worlds) shortly before Clarke's book was published (Clarke wrote a foreword to Sheffield's book detailing the similarities between the books and that it was to be understood that it was not a case of plagiarism).


Here's another good site.

elwoodblues

The point is that fissible materials do not burn like rocket fuel. You can take a lump of plutonium or uranium and bash it, toast it, electrify it, and it will do nothing but irradiate you (just as it would if it were just sitting there). You need a very special arrangement, done just right, to create a chain-reaction (a nuclear explosion). It is improbable to the extreme that this would come about by accident in some sort of explosion. The fissible materials would be scattered; as I said, the explosion would be dirty. But the fissible materials would not 'blow up' in any sense of the phrase.

The retarded monkeys come in for some kind of design where an accidental explosion would result in a critical mass forming from the remainder of the fuel. That'd be a damned silly design, and ridiculously unlikely to boot.

Greg2003

OK, OK, I get it now. But it would be fun to see what retarded monkeys come up with.

elwoodblues

lol, I'd like to see that too.

Loren Pechtel

Orion had a problem with fallout but a catastrophic failure of the booster isn't going to detonate the warheads it's carrying. Properly designed nukes don't go off unless you want them to no matter how hard you bang them about.

Loren Pechtel

I have a big problem with Bush proposing it--I strongly suspect ulterior motives. Had Clinton proposed it I would have said "fine". So long as they are detonated far enough away that the debris doesn't come back there's nothing wrong with it.

Loren Pechtel

You're describing NERVA, although that was based on using hydrogen, not water. You would get a far lower ISP out of it if you used water. At it's best NERVA is only about 3x the ISP of chemical rockets and this means runnning your reactor just below melting. Nice but nowhere near what Orion could do.

The critical factor with rockets is not so much total energy but the velocity of the exhaust. Consider the shuttle--the engines run *FAR* too rich--half the fuel is being thrown away unburnt! However, hydrogen is lighter than oxygen, the increased exhaust velocity is worth more than the lost energy.