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The performance of a rocket depends almost entirely on the velocity with which the propellant is exhausted,” he notes. Thus, “the elementary laws of mechanics – in this case relativistic mechanics, but still the elementary laws of mechanics – inexorably impose a certain relation between the initial mass and the final mass of the rocket in the ideal case… It follows very simply from conservation of momentum and energy, the mass-energy relation, and nothing else.
For our vehicle we shall clearly want a propellant with a very high exhaust velocity. Putting all practical questions aside, I propose, in my first design, to use the ideal nuclear fusion propellant… I am going to burn hydrogen to helium with 100 percent efficiency; by means unspecified I shall throw the helium out the back with kinetic energy, as seen from the rocket, equivalent to the entire mass change. You can’t beat that, with fusion. One can easily work out the exhaust velocity; it is about 1/8 the velocity of light. The equation of Figure 13 tells us that to attain a speed 0.99c we need an initial mass which is a little over a billion times the final mass.
This is no place for timidity, so let us take the ultimate step and switch to the perfect matter-antimatter propellant…. The resulting energy leaves our rocket with an exhaust velocity of c or thereabouts. This makes the situation very much better. To get up to 99 percent the velocity of light only a ratio of 14 is needed between the initial mass and the final mass.
Well, this is preposterous, you are saying. That is exactly my point. It is preposterous. And remember, our conclusions are forced on us by the elementary laws of mechanics.
All this stuff about traveling around the universe in space suits – except for local exploration, which I have not discussed – belongs back where it came from, on the cereal box.
a one-way trip of thirty-seven years (the distance to Zeta 1 or 2 Reticuli) at 99.9 percent c would take only twenty months’ crew time; at 99.99 percent c it would take only six months’ crew time. Thus even a trip to a distant galaxy such as Andromeda, two million light-years away, would take under sixty years’ crew time if the intergalactic ship somehow could manage to keep accelerating at one G, using some yet unknown technique.
Either ET is getting here by using some method that effectively circumvents the speed of light limit imposed by the fundamental laws of physics, or the ETH is flawed and should be discarded.
Originally posted by Deny777
I find it amusing to realize that there are people who spend time and energy trying to prove something is impossible instead of working towards making that thing possible. Particularly I prefer to face the Universe with a sense of wonder and a feeling that anything is possible, and even if I'm wrong, life is a lot more fun this way