George Dyson and Project Orion

[AdamI]

I'd like to suggest a guest: George Dyson, son of Freeman Dyson, to talk about project Orion and nuclear propulsion.

This is relevant to the UFO topic because it provides some counterargument to the common SETI argument that "you can't travel that far." Project Orion shows that it was technically feasible to travel to the planets using 50s/60s technology, and probably to the stars today... at least if we were willing to blow up a few a-bombs.

For some background, visit these links:

BBC - BBC Four Documentaries - To Mars by A-Bomb

George Dyson on Project Orion | Video on TED.com

Torrents of the BBC documentary are around, and I'd highly recommend tracking it down.

This would be hard to get, but it'd be fantastic. Not really a paranormal topic, but relevant and really a fascinating and forgotten chapter of history.

 

[Gareth]

Stan Fiedmans latest book "Flying Saucers and Science" deals with this stuff. So while it isnt the most captivating read for people that have read a few things, if there is one thing it doesnt fail on its the explanation of space travel using nuclear fusion / fission.

Some really fascinating stuff.

 

[AdamI]

I haven't read Friedman's book, but it sounds pretty good.

I think it's important to point out that "fantasy physics" are not required to explain travel between relatively nearby stars. There are quite a few stars within our local stellar neighborhood that are sun-like that could be reached in sane amounts of time using nuclear propulsion:

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The rough rule is that it takes about 1G of acceleration for one year to get you to about 2/3 C, the speed of light. A more detailed explanation is here:

travel at Light speed

So 1G for about 2 months gets you a bit past 0.1C, 10% the speed of light. There are 14 stars within 100 years travel time at that speed, three of which are sun-like. I've read analyses that say that Orion could do that, though I've lost the URLs.

So you could almost get to 14 stars using 1960s technology.

I'm not a "believer," but I definitely don't think the "you can't travel that far" flies as a way to rule out the ETH. Someone with, say, twice our life span and who spent their surplus GDP on exploration and research instead of war could definitely do it.

 

[Dolphtesla]

I have always wondered, is there little bits of rock and dust out there to run into at those speeds? I am guessing not due to the fact that Voyager has not been obliterated.

Does the gravitational field of larger bodies kind of keep it tidy out there? Because at 10% the speed of light, I would imagine a piece of dust striking the craft would cause some damage!

 

[Mothra]

Maybe if a large physical object with mass (Yes I know light atoms have mass, just humor me) was moving at the speed of light, it might create some sort of wake around itself. Maybe a distortion of some kind that would interrupt trajectories on a molecular level.

Then again, maybe I just don't know what the hell I'm talking about.

 

[AdamI]

Yes, you would need shields, but they would not have to be solid. I've read proposals such as heavy molecule (e.g. fluorocarbons with heavy metal groups) gas clouds sprayed out in front of the craft coupled with large superconducting electomagnets. First, objects that the craft hits in its journey are vaporized by the gas for the same reason that things vaporize on re-entry... think about how fast this gas cloud is going. Second, the charged particles resulting from the vaporization of objects are deflected around the craft by a magnetic field. The magnets could also help recollect and recycle the gas. Colliding with a gas cloud traveling at 0.1C would vaporize most anything except very large objects, and those could perhaps be spotted and avoided by maneuvering jets.

Assuming that Einstein is right, the big problems in interstellar travel are:

a) You can never come home to the same time period that you left from, so it's more or less a one-way trip for you.

b) You have to either live for a long time, have a generational ship, or go into hibernation. All are possible but difficult.

c) The technology of the ship must be designed for very long life and to be repaired in flight. You must have facilities on board to synthesize replacement parts, which means probably very flexible microfab manufacturing technologies. We're on the verge of stuff like this now, so this is do-able.

d) Propulsion with enough energy density to accelerate you to some meaningful fraction of the speed of light. From what I've read, Orion-style nuclear propulsion, nuclear-powered ion drives, and other similar techs could do it. They're all nuclear though, since nuclear energy is the only thing with enough energy/mass ratio to enable you to carry enough fuel to go that fast.

e) Since you need a decent size ship and nuclear propulsion, you have to get a bunch of tech at least into orbit or onto a nearby moon to assemble and fly the thing. Launch from your planet using conventional rockets is expensive, and barring anti-gravity or something else revolutionary you're stuck with them. See: The Cold Equations Of Spaceflight You *could* ground-launch a nuclear pulse drive like Orion and lift something with the mass of Chicago in one go, but the environmental consequences are... not pleasant. (But wow what a show!)

I've done a decent amount of reading obviously, but I'm not a physicist. However, what I've read has convinced me that interstellar travel between nearby stars (on the order of < 20 light years) is possible. Hard, slow, and expensive, but possible. We could do it with present technology if we wanted to spend an amazing amount of money. If we weren't stupid and we didn't spend all our surplus GDP on tribal warfare, I could see it happening.

 

[AdamI]

Along the lines of this discussion:

Nearest planetary system boasts two asteroid belts - space - 27 October 2008 - New Scientist Space

This is 10.5 light years away, so it would take (with speeding up and slowing down) probably about 150 years to reach at 0.1C.

 

[0uterj0in]

A fictional account of a such a "nuke" craft: Anathem. In which the ship uses a kind of gravel exoskeleton as a shield.

 

[AdamI]

I love Neal Stephenson... too bad I don't have much reading time these days.

Actually, as I was going home from work today a thought popped into my head regarding something I said above. It's a bit of a tangent, but interesting.

I mentioned several times that someone who didn't spend their surplus GDP on tribal warfare might end up doing something like this. It seems to me that this is an argument for peaceful alien visitors. It seems likely that warlike aliens would spend most of their surplus wealth fighting each other back home. They would never spend so much on something as "useless" (to the warmongers) as a crazy one-way interstellar pilgrimage into the unknown.

So who knows... while the light speed and conservation of momentum barriers might seem like no fun, maybe we're lucky they are there. Maybe the fact that interstellar travel is Hard-with-a-capital-H acts as a filter to keep the gun-happy yahoos safely confined to their own solar systems.

 

[marduk]

From Wikipedia:

If a spaceship could average 10 percent of light speed, this would be enough to reach Proxima Centauri in forty years. Several propulsion systems are able to achieve this, but none of them is reasonably affordable.
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From what I understand, economics is as great a barrier as technology. A "swingby" shot at least at something like .01C should be doable -- this is where the probe actually isn't captured by the target star but shoots on by it and therefore does not require energy or mass to decelerate into orbit.

Shielding would be an issue but may not be worth the reaction mass. For example, the Daedalus project's proposed shield weighed 50 tons (9mm thick x 35 meters wide). If it were up to me I'd simply send a bunch of disposable robot probes and hope for the best. If the probes were small enough across perhaps a 9mm shield 3 meters wide would be light enough.

The science folks are probably far more interested in checking out Mars and Encaledus (possible candidates for ET life) where the probe could get there in years and at a fraction of the energy required. Plus they could stay there a lot longer (witness Spirit and Opportunity). Compare this with a probe's transit through a system at .1 to .01C which would be days or weeks at best. You'd also be hoping to get close enough to any planet to image it while you shoot through the system at between 30M and 3M m/sec.

Economically it might make a lot more sense to build a space-based telescope that could actually image earth-sized planets in enough detail that we could see directly (via spectral analysis) if organic elements like chlorophyll were present. The great advantage there is that you could point the thing at any number of systems and upgrade it at will.

Then you would know where to go and probably have some more advanced propulsion ideas on how to get there.

For fun, check out Project Longshot proposed by the US Naval Academy:
Page F30: Project longshot, an unmanned interstellar probe to Alpha Centauri