[ackydoodles]

From the FAQ:

Q: Why did you choose fusion based propulsion for Project Icarus?

A: Well, we thought about it and we realized that the only appropriate power source for an imaginary starship was a likewise imaginary one. And while there are certainly many options in the field of imaginary power generation, we rejected some of the main contenders for a variety of reasons.

"Maxwell's Demons" would have alienated both the new-agey spiritual sci-fi crowd and also the fundamentalists because it sounds medieval and just evil at the same time.

"Dilithium crystals" was taken. The zero-point people are bunch of wack jobs and we certainly didn't want to be tarred with that brush. "Fairy wings" just sounds too wussy for our tastes.

So, you see, there aren't all that many choices of power left for an imaginary starship. Fusion sounds just about right, especially if you say is slowly, with gravitas, like "fuuuuuuusion".

[ctdonath]

Tangent: fusion will require carrying...how much hydrogen? I once calculated that trying to gather it along the way (interstellar hydrogen) is pointless, as a 1m^2 swath from here to Alpha Centauri would net 0.01g of the stuff.

ETA: Yup, I was considering the Ramjet design. Scale of the scoop overwhelmed itself trying to acquire enough to function. I was just startled at how little interstellar hydrogen there is; I knew it wouldn't be much, but 0.01g in ten million cubic kilometers was even less than I'd assumed.

[lutusp]

> ... how much hydrogen? I once calculated that trying to gather it along the way (interstellar hydrogen) ...

FWIW this is an old sci-fi idea / plot device called a Bussard ramjet:

http://en.wikipedia.org/wiki/Bussard_ramjet

But this isn't meant to dispute your calculations. The linked article comes to the same conclusion: it's not feasible, too little interstellar hydrogen.

[ackydoodles]

Most notional implementations of the Bussard Ramjet depend upon some sort of heretofore undiscovered force field rather than a physical structure to collect hydrogen, because size matters.

Naturally, a very large force field ramjet will deplete interstellar hydrogen along the main routes between stars, leading to a situation known as "peak hydrogen", and possibly prompting the invasion of developing hydrogen-rich planets on some sort of flimsy pretext.

Most scientists working on imaginary spacecraft projects therefore eschew the Bussard, correctly anticipating the moment when, shortly after the leader gives a speech on the deck of a starship in front of a huge "Hydrogen Accomplished" banner, the price of hydrogen rises to over $5 a gallon and starships are all left to rust in the front yard.

[lutusp]

Yep. And shortly after his victory speech, the leader is heard to loudly complain that he's been "misunderestimated".

[dennisgorelik]

> from here to Alpha Centauri would net 0.01g of the stuff

... and yet that 0.01g of stuff would produce lots of friction and heat if spaceship flies with 10%+ of light speed...