Adam said:L

>why muck about with a fusion reactor?

It's doubtful that anything else is practical.

>The damn things weigh too much and the radiator
>would be ridiculously huge.

The vehicle would be mostly fuel tank and radiator. A real starship could easily be mistaken for a small asteroid.

>Unless someone can crack the aneutronic fuels and have
>a direct power-conversion system.

Neither are likely to happen. Aneutronics require too high a temperature to ignite. The best bet is probably a deuterium fusion reaction in a magnetic bottle directly driving a plasma propulsion system.

>Use the fusion technology we know and love - fusion
>bomblets! An Orion/Daedalus style craft is more doable
>and such a damn easy interstellar drive.

Daedalus is based upon an aneutronic fuel cycle along with laser or particle beam ignition (both are nonoptions for a real starship). Orion is just silly (dropping lots of little self detonating atomic bomb behind a pusher plate).

>Tack on a magnetic-sail and you don't even need fuel at
>the destination.

A practical magnetic field decellerator would cause structural failure and/or impossibly high magnetic fields.

>Dyson reckoned an exhaust velocity of ~ 0.03c was
>doable, so 0.1c final V is not a huge stretch.

Dyson is almost as over rated as Carl Sagen (NOBODY is more over rated than Carl Sagen). I don't understand why people pay so much attention to him.

>Build Enzmann-class starships in orbit around Saturn or
>Uranus out of fuel mined from the planet, haulled up by
>NTR-powered ramscoops.

Never heard of Enzmann-class starships. Ramscoops presuppose proton-proton fusion reactons which can only occur in stellar cores (fusion cross sections are ridiculously high).

>With sufficient closed-loop ecology and manufacturing a
>starship fleet could cruise the Galaxy indefinitely,
>dropping off excess population [willing, mind] at suitable >planets.

Nope, cosmic rays require 6 feet of concrete to shield against (not an option for a startship). DNA based life is incompatible with interstellar travel due to cosmic ray damage.

>Or wait a bit until laser-sails or particle-beam propulsion
>become cheap enough and get a push to a decent speed
>say ~ 0.5c or so.

Wrong again... Robert Forward is almost as over-rated as Dyson. His light sails are ridiculous nonsense (they require 1000 km. diameter frensel lens).

>Or nano-facture pellets with a bit of self-guidance and
>fling them at a starship at whatever speed you want and
>boost up to near-light speed.

How about closing your eyes and tapping your heels together three times?

>Eventually any determined group could buy a starship [or >get one sponsored by a government happy to see them
>leave] with a closed-loop manufacturing system and go
>off to colonise any bit of the Galaxy.

My guess is a civilization is probably good for about 20 starships before it times out or runs out of resources.

>Who needs FTL? TV script writers.

You got it. That's why science ficition is currently in the toilet. The best science fiction was written over twenty years ago, e.g. Clark, Asimov, Niven, Campbell/Herbert, Vance, Panshin, Lindsay, Haldeman....

Gary