On Mars I could walk into space. Up Mount Olympus above the atmosphere and jump. Could I do that on earth?

Question

Assuming we had a mountain that high! The real question is - do we need these phenomenal sized rockets? A hot air balloon would get you 20 miles up - nearly half way. My mountain would be just a 70 mile walk!

Answering one of the answers: I just want to stay in orbit and therefor do not need escape velocity. Hence my assumption that being above the atmosphere was crucial - no drag. I now understand that being up there would still let me sink back, so I would need forward thrust to maintain an orbit.
Still think that if hot air will get me 20 miles up there's an easier way to get into orbit than blasting our way up there!!

Answer 1

You won't "sink back", you'll fall back at the normal acceleration. The closer you are to the surface, the faster you have to travel to stay in orbit. 20 or 70 miles is nothing. The drag of the atmosphere is negligible compared to the force of gravity.

A rocket lifting off is 20 miles high in a few tens of seconds. Starting at that altitude is of little benefit.

Answer 2

Well, you couldn't jump into space from My Olympus or any mountain on Earth. They're simply too low for that.

But there's a huge difference between getting up there (by Spaceship 1, for instance), barelly touching space and then falling back to Earth on the one hand, and orbiting on the other.

For that, you must have these huge rockets.

On a somewhat related matter; it would be possible to climb to orbit slowly, as opposed to the rather violent, headlong rush that we use right now. But the downside is that it would require even bigger rockets. So big, in fact, that this, though possible, is completely impractical.

edit: now that you mention it, there have been proposals that a payload might be lifted to some great height by balloon, then blasted into orbit by rocket. I don't actually know why this hasn't been tried yet, but I can guess; the technical details are probably daunting. For instance, it would take quite a balloon to lift any reasonable payload and rocket. For that matter, spaceship 1 uses a similar idea. It merely uses an airplane to lift it up high rather than a balloon.

Answer 3

Do you want to leave the atmosphere (no air), or escape the earth?

The "scale height" of the earth's atmosphere is about 9 km. That's the height at which the pressure or density drops to about 1/3 of the value at sea level. So, if you climbed Mt everest, (~9km) indeed you'd be pretty close to that value.

On the other hand, if you want to actually jump and not come down, the issue is more about velocity than height. While pressure is an exponential decay as a function of altitude above the earth surface, gravity goes as 1/r^2 where r is the distance from the center of the earth. Since you're about 6000 km from the center of the earth while sitting at your computer, even climbing to the top of everest gives a pretty small change, percentage wise. So if you jump on top of that mountain, you still come down same as if you were on the ground.

Those fancy rockets are for getting you high enough, and the speed large enough so that the earth's gravity can't slow you down enough to fall back to earth.

Answer 4

You could jump from Mount Olympus, but you'd fall back on Mount Olympus. You need to achieve "escape velocity." Rockets are the best (cheapest) way that we can do it now - from either Earth or Mars, or the Moon for that matter - remember the LEMs blasting off from the Moon?

Answer 5

Staying in orbit would probably be tougher than achieving escape velocity. You would need to attain orbital velocity, which is a pretty big jump, even on Mars. The problem is one of energy. You need more than you've got. That's why we build rockets.

Answer 6

Just being outside the atmosphere doesn't enable you to leave the planet so easily. The atmosphere isn't what is holding you down.