Ramjets for Space
The concept of a Bussard Ramjet or Ramscoop was proposed by Robert W. Bussard in 1960, and has been featured in science fiction books by Poul Anderson, Larry Niven, and even Carl Sagan in his Cosmos TV program. The way it works relies on near-future technologies, sometimes with just a smidgeon of fantasy.
Fuel Equation
The biggest problem with interstellar travel is fuel — the rocket equation requires nearly infinite amounts of fuel to attain a reasonable speed for travelling between the stars. The Bussard Ramjet solves this problem by using the interstellar medium as fuel, even though there isn’t very much of it out there. Between the stars there is a lot of space, but it is not truly empty, not by a long shot. The average density ranges from one molecule to one billion molecules per cubic meter — that’s 1,000,000,000 molecules per cubic meter. For reference, at sea level there are about 100,000,000,000,000,000,000,000 molecules per cubic meter. Like, I don’t know what that number is. A lot. Molecules are tiny. And when I say “molecules”, about 87% of them are hydrogen, and 8% are helium, which are the only two kinds that a Bussard Ramjet can use.
