Does Elon Musk have any plans to replace using rockets for space travel? by Robert Frost
Answer by Robert Frost:
No, he doesn't. He doesn't plan to replace rockets because he knows from science class that there is no alternative.
Newton's Third Law (for every action, there is an equal and opposite reaction) requires that if we move the spacecraft forward, something has to happen in the opposite direction. Musk's electric cars comply with Newton's Third Law, because they push backwards across the ground to move the car forwards across the ground. But in space, there is no ground to push against. We comply with Newton's Third Law by ejecting mass. A rocket moves forward by ejecting a small amount of mass at a very high speed.
Momentum (P) equals the mass of an object (m) times its velocity (v).
Momentum of a system is conserved. That means that without outside influence, the total momentum of a system is constant. So, if you throw the cannonball and change its momentum by giving it a velocity in a particular direction, your change in momentum will be equal and opposite.
Tsiolkovsky came up with a rocket equation based on all of this:
The change in speed of a rocket is equal to the exhaust velocity of the fuel times the natural log of the initial mass of the rocket divided by the final mass. The final mass is the initial mass minus the fuel that was ejected out of the rear of the rocket.
So, we can make a rocket go faster by either increasing the exhaust velocity (make the exploding fuel hotter) or by ejecting the fuel out of the back of the rocket faster.
Here is the answer in Musk’s own words: