Hi All

Gary has - unintentionally, I'm sure - used fighting words. Here's my response...

Adam said:L

>why muck about with a fusion reactor?

It's doubtful that anything else is practical.

Reply...
We still can't do controlled fusion, so I'm not sure what "practical" means.

>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.

Reply...
And all dead weight. I reckon we can do a LOT better.

>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.

Reply...
He3-D reactions aren't too far beyond current fusion attempts, and a direct exhaust fusion drive has to be a LOT more efficient than power converters and plasma drives.

>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).

Reply...
Laser/particle beam systems have been extensively studied and they're still live options for starships. "Daedalus" is rough draft 25 years old, but the same general idea is still valid.

"Orion" isn't silly. It's a seriously practical design. The original design team had most of the problems licked.

>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.

Reply...
Bullshit. Go look at Zubrin's paper at NASA's NIAC web-site.

>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.

Reply...
He and colleagues designed the first practical starship and also predicted what an advanced Type II civilization would look like. The fact that none have been detected yet is negative evidence for advanced ETIs.

>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.

Reply...
Robert Enzmann was a NASA brain in the '60s. He designed huge starships driven by multiple "Orion" pulse drives and fuelled by D-D frozen in a huge sphere forward of the crew section. Rick Sternbach popularised the idea in some classic starship paintings in the '70s.

Ramscoops presuppose proton-proton fusion reactons which can only occur in stellar cores (fusion cross sections are ridiculously high).

Reply...
Not Bussard ramscoops. Nuclear-ramjet Scoop-ships propelled by Nuclear Thermal Rockets to gather up fuel from Jovian-class planets.

>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.

Reply...
Bullshit again. Cosmic ray damage can be mitigated by wrapping fuel around the living quarters and also by huge magnetised loops to deflect most of the cosmics.

>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).

Reply...
WHo said Forward light-sails? Other designs exist at doable size ranges needing only ~hundred metre lenses. With a magnetic loop to make the sail rigid and act as the brake at destination such designs can reach decent speeds.

>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?

Reply...
It's a few technology cycles away but it can be done by a reasonable extrapolation of techniques.

>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.

Reply...
If we don't industrialise the Solar System then we won't launch one. Not even a probe.

>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

Reply...
Maybe. A multitude of forgettable hacks wrote while they got established. And all the hacks, now, imitate the greats.

All the good writers today have to write against the background of the computer revolution and the end of the Cold War. They have to write in an era which no one predicted - space can be done, but no one can think of a good, immediate reason to do it en masse.

When Clarke wrote his short story version of "Earthlight" - his only space war story - he set it c. 2015. In 1950 he could imagine just about every planet colonised 40 years after the first Moon landings [c. 1975], and sufficiently developed to fight for independence. In the novel he pushed it forward to c. 2115, but "The Sands of Mars" and so many other stories into the 1960s had optimistic timetables.

Heinlein imagined the airline style space-travel of "Space Jockey" to follow maybe a decade after the foundational events of "The Man Who Sold the Moon". In his "Future History" he could set "Farmer in the Sky" on a Ganymede explored by 1985, with its terraforming beginning in 1998!

Neither writer could have imagined the Moon left abandoned for +30 years and a manned flight to Mars postponed to c. 2050 (maybe!) No wonder SF struggles.

Adam