How much rocket fuel would be needed to accelerate a conventional space rocket to half lightspeed?
Best Answer: Using the space shuttle main engines to get a one kilogram space craft up to 50% the speed of light would take 3 followed by 14,476 zeroes kilograms of propellant. That is way, way more than the mass of the whole UNIVERSE! You calculate this with the rocket equation. You need the exhaust velocity of the engine. The space shuttle engines have an exhaust velocity of 4.5 kilometers per second. The speed of light is 300,000 kilometers per second, so half that is 150,000. The propellant needed to get a payload to that speed is the mass of the payload times e to the 150,000/4.5 power. That is e to the 33,333 power. "e" is the base of the natural logarithm, and is equal to about 2.7. So to get one kilogram up to 4.5 kilometers per second takes 2.7 kilograms of fuel, and to get up to twice that speed you need 2.7 * 2.7 = 15. That is more speed than you need to get to orbit, so the space shuttle needs less than 15 times its own weight in fuel to go to orbit. To get up to 33,333 times as fast, you need to multiply 2.7 times itself 33,333 times, and the number you get is more than the mass of the entire universe. This means it is absolutely, physically impossible to use conventional rockets to get any where near the speed of light.
Last Updated: 28 Sep 2016
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