True, but in space, aside from the big gas planets, there really isn't that much of it. Even in the pseudo-scientific technical manuals for Star Trek, they don't claim for such a system to be that effective in producing the quantities needed to sustain a long duration, let alone fast, trip.
Here's a scientific article on the idea: http://en.wikipedia.org/wiki/Bussard_ramjet
And some scientific stuff:
"The collected propellant can be used as reaction mass in a plasma rocket engine, ion rocket engine, or even in an antimatter-matter annihilation powered rocket engine. Interstellar Space contains an average of 10 (to the -21st power) kg of mass per cubic meter of space. This means that the ramjet scoop must sweep 10(to the 18th power) cubic meters of space to collect one gram of ions per second."
In other words, 10,000,000,000,000,000 cubic Km to get one gram.
For fun, in imperial: 62,137,119,200,000,000 cubic miles for all of 0.00220462262 pounds of it.
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Probably why it usually shows up on relativistic ships in sci-fi.
The faster you're going, the longer your volume is, and the less width you need on your scoop to sustain things.
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the Helium 3 isotope wouldbe a very efficent reaction mass for Macross drives-and it is present in the atmospheres of the gas-giant planets.Also,I believe the waste produced by fusing Helium 3 is good old H2O. I think it wouldn't be difficult to harvest with Macross level tech(I believe the major difficulty is GETTING to the gas giant planets) .Addenum-I just saw on one of those Lunar landing hoax BS websites that there is 10 billion tons of Helium 3 on Luna-deposited by the solar wind.