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Interstellar Hydrogen Prevents Light-Speed Travel?
garg0yle writes "As if relativity wasn't enough to prevent us traveling at light speed, Professor William Edelstein of the Johns Hopkins University School of Medicine is now claiming that the interstellar hydrogen, compressed in front of the ship, would bring the journey to a shocking end. 'As the spaceship reached 99.999998 per cent of the speed of light, "hydrogen atoms would seem to reach a staggering 7 teraelectron volts," which for the crew "would be like standing in front of the Large Hadron Collider beam."'"
Some numbers! If the ship is just 100kg with cargo, then you need 6.36e22 J to get to .99999998c assuming 100% efficiency. About 1.4e21 J hits earth everyday from the sun. So a earth sized solar panel will collected the energy required in about 4 and half days. All assuming no energy losses.
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I wondered why they didn't run them in series. Cumulative thrust would have put the ship closer to light speed.
Not necessarily. You are actually fusing those hydrogen atoms, turning them into helium. The output of one ramjet has less hydrogen than went into it. Yes, you could fuse that hydrogen/helium exhaust into heavier elements but it won't release as much energy. Basically you'll be adding mass to your spacecraft by putting another engine on but you won't be increasing your thrust as much as you may think.
You might eke out a bit more acceleration with another engine in series but it's probably not worth it. You don't want to put them in parallel on a small ship either, for several reasons. For example, the magnetic fields that funnel material into the engine are supposed to extend in a cone far in front of the engine. Two engines that are close together will have their magnetic fields interact, complicating the management of those fields. Another concern would be properly adjusting those engines to maintain even thrust on both sides. When you're traveling at a significant fraction of the speed of light a slight variation in the hydrogen input of one engine could tear apart your spaceship pretty easily.
Sapere aude!
And if you actually read the Wikipedia article you link to, rather than just drooling over the qualifications of the inventor, you'll find that as people have actually began to seriously study it - there are now significant doubts as to how well it will work. (Even assuming we figure out how to do the parts Bussard handwaved into existence, like the magnetic scoop.) In addition, even if it does work, it may be subject to the problems outlined in TFA.
Accelerating to 99.999998% of light speed in 3.5 hours would be a somewhat dizzying experience. Especially since you'd actually experience an acceleration equivalent to going to 5000 times light speed in a pure Newtonian universe. We're talking more than 500.000km/s^2 here -- or 50 million g.
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