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
Because there is no air in space.
This is basically it.
Flying through air slows you down through wind resistance.
In space there isn’t really much to slow you down.
In space any little bit of extra engine use adds to your speed.
In the air you need to constantly run your engine just to keep moving at the same speed.
In space once you are in motion, you will stay that way. A spacecraft on some course will keeping going at that speed and course forever unless some outside force acts on it. Spacecraft can basically cost at a constant speed towards their destination without having to burn any fuel.
On earth you are constantly being slowed down by friction. Air resistance means that if you stop your engine for a moment you will slow down. You can do clever tricks with gliding to use the air resistance to extend your range somewhat, but you can’t just keep going forever.
Another problem with air is that it really gets in the way if you are starting to really fast.
As you go faster and faster the friction from the air becomes more and more and you don’t just have to work harder and harder to keep going at that speed, the friction with the air also starts heating up your craft. If you go at speeds many, many times the speed of sound the heat from the friction becomes a real technical problem, which is why spacecraft returning to earth and entering the atmosphere at extremely high speeds get heated up so much that they are in danger of burning up.
Going fast in the air is hard and dangerous.
On the other hand going fast in space is almost required.
Technically if you reach an altitude of 100km above the ground you have reached space. But if you want to to stay there instead of simply falling back down to earth you either have too keep running your engines the entire time or you have to enter into an orbit.
An orbit is basically going so fast sideways that you continue to miss the ground as you fall down. If you are in orbit you won’t have to run any engine or anything you just stay where you are at more or less the same altitude or speed you have (at least for circular orbits).
However orbits require orbital speeds and those are really fast.
To stay in orbit a speed is required that you wouldn’t be able to achieve while in the atmosphere.
The Space Station goes around the earth at what would be something like two dozen times the speed of sound in air near the ground.
Such speeds are very hard to achieve and sustain inside the air and necessary to stay in orbit.
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