Quote Originally Posted by Lord Torath View Post
The hypothetical Hydrogen Scoop Fusion Ram Jet was supposed to be able to maintain a 1G acceleration indefinitely using a huge (10,000 km) electromagnetic scoop to collect hydrogen from in front and funnel it into the ramjet. Of course, I read about it in one of those Time-Life books which were cutting edge about 2 years before they were actually published in the 1980s, if I recall correctly, so take that with a grain of salt. Half-way to your destination you were supposed to turn the ship around and re-engage in reverse. I'm not certain how well that would work if you're thrusting into your magnetic scoop, though.
You would have to reverse your engines without reversing the scoop, so just turning round wouldn't work. Anyway, what you're talking about is the so-called Bussard Ramjet (since it was first proposed by Robert W. Bussard in 1960), and the problem with it is that the interstellar hydrogen density has been found to be far lower than it was believed to be in his day, making his design as proposed completely impractical--you wouldn't get enough thrust to overcome the drag of the ramscoop.