[preachadaq]

I have been reading lately about project Orion. The government was running the numbers on how feasible nuclear engines were for travel in outer space. In 1946 they estimated they could get to alpha centauri in 1,000 years.

I find it interesting that they were playing with tech like this all the way back then. They have considered so many different possibilities, haven't they?

An interstellar ark to colonize outer space.

Notice their strategic use of all the rare earths.

http://en.wikipedia.org/wiki/Project...ear_propulsion)
http://en.wikipedia.org/wiki/Interstellar_ark
http://en.wikipedia.org/wiki/Project_Daedalus

They considered colonizing outer space.

Project Orion was a study of a spacecraft intended to be directly propelled by a series of explosions of atomic bombs behind the craft (Nuclear pulse propulsion). Early versions of this vehicle were proposed to have taken off from the ground with significant associated nuclear fallout; later versions were presented for use only in space.

A 1955 Los Alamos Laboratory document states (without offering references) that general proposals were first made by Stanislaw Ulam in 1946, and that preliminary calculations were made by F. Reines and Ulam in a Los Alamos memorandum dated 1947.[1] The actual project, initiated in 1958, was led by Ted Taylor at General Atomics and physicist Freeman Dyson, who at Taylor's request took a year away from the Institute for Advanced Study in Princeton to work on the project.

By using energetic nuclear power, the Orion concept offered high thrust and high specific impulse, or propellant efficiency, at the same time. As a qualitative comparison, traditional chemical rockets—such as the Saturn V that took the Apollo program to the Moon—produce high thrust with low specific impulse, whereas electric ion engines produce a small amount of thrust very efficiently. Orion would have offered performance greater than the most advanced conventional or nuclear rocket engines then under consideration. Supporters of Project Orion felt that it had potential for cheap interplanetary travel, but it lost political approval over concerns with fallout from its propulsion The Orion nuclear pulse drive combines a very high exhaust velocity, from 20 to 30 km/s, with meganewtons of thrust.[4] Many spacecraft propulsion drives can achieve one of these or the other, but nuclear pulse rockets are the only proposed technology that could potentially deliver both (see spacecraft propulsion for more speculative systems). Specific impulse measures how much thrust can be derived from a given mass of fuel, and is the standard figure of merit for rocketry.

Since weight is no limitation, an Orion craft can be extremely robust. An unmanned craft could tolerate very large accelerations, perhaps 100 g. A human-crewed Orion, however, must use some sort of damping system behind the pusher plate to smooth the instantaneous acceleration to a level that humans can comfortably withstand – typically about 2 to 4 g.

The high performance depends on the high exhaust velocity, in order to maximize the rocket's force for a given mass of propellant. The velocity of the plasma debris is proportional to the square root of the change in the temperature (Tc) of the nuclear fireball. Since fireballs routinely achieve ten million degrees Celsius or more in less than a millisecond, they create very high velocities. However, a practical design must also limit the destructive radius of the fireball. The diameter of the nuclear fireball is proportional to the square root of the bomb's explosive yield.

The shape of the bomb's reaction mass is critical to efficiency. The original project designed bombs with a reaction mass made of tungsten. The bomb's geometry and materials focused the X-rays and plasma from the core of nuclear explosive to hit the reaction mass. In effect each bomb would be a nuclear shaped charge.

A bomb with a cylinder of reaction mass expands into a flat, disk-shaped wave of plasma when it explodes. A bomb with a disk-shaped reaction mass expands into a far more efficient cigar-shaped wave of plasma debris. The cigar shape focuses much of the plasma to impinge onto the pusher-plate. Just thinking about it

[preachadaq]

Of course today we have thorium reactors, the japanese have a very small one that can be used locally for power....

[irresseni]

100g acceleration for 1 minute gets one to rough constant velocity of 100,000 miles per hour. In space vaccum, zero gravity, the ship would travel about 2.4 million miles per earth day. It would take such a ship well over a month just to reach our sun, let alone travel outside our solar system.