How is it that we engineer vehicles in space to travel for millions of miles at absurdly fast speeds? When we can only have vehicles on earth (jets) travel for thousands of miles at lower speeds? Why is the gap SO BIG?

Question

We can send vehicles/rovers to space and have them travel at very high speeds for millions of miles to other planets. But vehicles on earth (jets/planes) have significantly shorter range and speed. Why is this? ELI5

In: Physics

Answer 1

Air resistance slow object down and the faster it goes the more air resistance increase. So the engine accelerate the Jets, but by doing that more and more of the power of the engine goes to counter the air resistance. At one point the power of the engine will be equal to the air resistance and the Jets won’t be able to go faster. For a land vehicle like a car you have the air resistance and the friction of the ground.

In space you don’t have air resistance or friction. So all the power of the engine goes toward accelerating the spacecraft. If you stop the engine of a Jet, it will slow down, but it doesn’t happen for a spacecraft, nothing slow it down. So if you keep your engine running you will continue to go up in speed indefinitely. Well technically at some point when it reach closer to the speed of light the inertia go up and the engine have an harder and harder time accelerating the spacecraft, but we are far far from this kind of speed, so this effect is almost undectable at the speed of our current spacecraft.

The same principle explain the range. We don’t need our engine to run throughout the whole trip, we can turn them on, burn our fuel and the spacecraft will keep going at the same speed even with the engine turn off. We can’t do that on earth, we need enough fuel to keep the engine running all the time.