Loren Pechtel

Orion was very real. In fact, a chemically powered very short range version was flight-tested, and some testing was done with test objects being propelled by a-bomb tests. The next planned test was going to be in space using an a-bomb to propel a instrument package. Atmospheric testing was banned before it flew.

None of the tests involved more than a single detonation but the test packages were being propelled properly by the bomb, not merely flung out of the blast.

Loren Pechtel

Chemical fuel will go boom when the tanks are breached and it gets mixed. Nukes won't.

Loren Pechtel

Actually, we have the technology to construct a version of a skyhook system now, although the actual engineering is far beyond what the human race is currently capable of. If you accept a sufficiently large project you can make one without superstrong materials.

Solution:

Ok, we can't build a cable long enough that can hold it's own weight. Accept this and don't try to build one that long:

In low Earth orbit build two structures. Both must go all the way around the planet. #1 is basically a maglev train, #2 is it's track. #1 needs no strength at all, #2 needs strength but the need can be reduced as low as desired by increasing the project size.

Now, slow down the track and speed up the train. Done correctly the assembly remains in orbit no matter how slow you make the track go. Once you have slowed the track to synchronous speed you can use it to support cables extending down to the ground.
You'll need several cables to balance the force out but it can be done.

Want to go higher? Build another ring and cables higher up, connect them down to the lower ring. If you want to go above geosync the train must go slower rather than faster.

As for the strength of materials needed: There are two points that must be strong. The vertical cables and the track between the anchor points of the cables. No other part of the system bears any load from the system itself (it does bear the load of any cargo, but the big problem is supporting the system, not the cargo.) To reduce the vertical strength needed make the vertical steps smaller--use more rings. Any rings in atmosphere will be more complex as they must be evacuated tubes to keep the train from burning up but they certainly can be done. To reduce the strength needed in the spans use more cables.

Both of these approaches can go basically to infinity, thus reducing the needed strength to zero. (Actual limit--the minimum size of the train. The maglev system of a train is no more than a few feet thick, however. Thus the system must be able to support say 10' of cable.)

Loren Pechtel

Actually, there is a reason for it. It's called salvage fusing. There are two reasons for it:

1) Even if you haven't reached your target yet you might be close enough to damage it.

2) By detonating you create an area that is radar opaque for a short while. If another warhead comes in through that area after the first fireball is gone the defender won't be able to track it to shoot it down.

elwoodblues

Neither of which would make any sense for a propulsion system of any kind. So, unless we're yanking warheads out of ICBM's (which, admittedly, is a possibility) and packing them unmodified in the shuttle (much less likely), it won't be a real problem.

Greg2003

Here are some really cool alternatives to nuclear propulsion that NASA has been working on:

http://www.ornl.gov/ridgelines/rocket.htm

and

http://www.space.com/scienceastronom...lsion_817.html

Mageth

A cool launch system is the laser-boosted rocket. This technology may soon be used to launch mini-satellites, and may someday be used for heavier lifts.

Some tiime back I saw this demonstrated on some television show; it was one of the coolest things I'd ever seen.

Quoting:

"The propulsion happens when beamed laser energy strikes a parabolic condensing reflector mounted on the bottom of the Lightcraft. This area is lined with a thin coat of special plastic that ablates when hit by the laser pulses, thrusting the Lightcraft upward."

Greg2003

Yes, I saw that show. It looks like the ideal method of propulsion. But I haven't heard of it advancing beyond lifting those tiny cones more than a few hundred feet in the air. And it sounds like the laser you would need to lift a shuttle type craft would be massive beyond anything yet contemplated. If there was a way to have an extremely powerful small laser that could be mounted on the craft itself, then you'd have a real live flying saucer that could float up to space without any exhuast or thunderous boom. Can anyone point us to any up to date source on this technology?

Loren Pechtel

Quite true. I was simply responding to someone who said that there would be no reason for it.

Loren Pechtel

I don't think laser has ever been intended to launch heavy stuff. The power required is simply incredible. It doesn't need to be some super laser--simply use more of them. However, it draws a *LOT* of power. One of Larry Niven's stories had a facility that threw capsules of a few thousand pounds--powered by multiple nuclear plants. Since he normally works the math in his stories I suspect he's right as to the power needed.

However, if you have an industrial presence in space, a few thousand pounds is VERY useful. That will carry a person and enough life support to get them to a station. That will deliver cargo to the station.


A laser on the craft itself doesn't make sense. The whole point of laser propulsion is that it lets you leave behind your big heavy powerplant. Thus it doens't suffer the big bugaboo of rockets--the need to haul along one's fuel.