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"The reason it's hard to get to orbit isn't that space is high up. It's hard to get to orbit because you have to go so fast." https://what-if.xkcd.com/58/ http

by ash 12y ago

"The reason it's hard to get to orbit isn't that space is high up. It's hard to get to orbit because you have to go so fast." https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/

keypusher 12y ago
I don't entirely buy this. You don't get to go any slower if you are going to Mars, which is not orbiting the Earth in any way. Or if I just want to escape Earth orbit and go drift in space, why do I need to be moving fast relative to the Earth? Why can't I be moving slowly but steadily away?
- dragonwriter 12y ago
  > Or if I just want to escape Earth orbit and go drift in space, why do I need to be moving fast relative to the Earth? Because gravity. If you aren't going fast relative to Earth, you aren't going to escape Earth orbit [0]. Heck, if you aren't going fast relative to Earth, you aren't even going to be in Earth orbit [1], you are going to be falling back to the surface. [0] http://en.wikipedia.org/wiki/Escape_velocity http://en.wikipedia.org/wiki/Escape_velocity [1] http://en.wikipedia.org/wiki/Orbital_speed http://en.wikipedia.org/wiki/Orbital_speed
- scott_s 12y ago
  Everyone's responses are spot-on. But I can understand that it still may not be intuitive to you. The difficulty is that we see pictures and videos of our satellites and shuttles in orbit, and they look peaceful and serene. What's missing from those images and videos is a visceral feel that they are going over 17,000 mph. If they went less, they would leave orbit, and hit the Earth. Objects in orbit are not "outside" of Earth's gravity; they are not just up there, just floating in space. The reason they don't "fall to Earth" is that they are falling to Earth. Constantly. It's just that their horizontal speed relative to the Earth is so large that they are - literally - falling around the Earth.
- lukeschlather 12y ago
  The premise of your question is wrong. If you are in Earth orbit, you are moving fast. It's actually being in orbit that allows you to move slowly away, because you can take as long as you want to apply the force. If you're not in orbit you have to quickly apply enough force to escape Earth's influence in one go or you will fall back to Earth.
- jameshart 12y ago
  I can highly recommend having a play with Kerbal Space Program to get an intuitive grasp of orbital mechanics. Basically, if you don't go fast enough, you're going to come back down to earth. Once you get to a speed that's fast enough that you aren't going to come back to earth, you'll find you are now in orbit around the sun, in a path remarkably similar to the one the earth is on. To get to Mars you need to get up into a higher orbit around the sun, so you need to go even faster.

by ash 12y ago

"The reason it's hard to get to orbit isn't that space is high up. It's hard to get to orbit because you have to go so fast." https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/

keypusher 12y ago

I don't entirely buy this. You don't get to go any slower if you are going to Mars, which is not orbiting the Earth in any way. Or if I just want to escape Earth orbit and go drift in space, why do I need to be moving fast relative to the Earth? Why can't I be moving slowly but steadily away?

dragonwriter 12y ago
> Or if I just want to escape Earth orbit and go drift in space, why do I need to be moving fast relative to the Earth? Because gravity. If you aren't going fast relative to Earth, you aren't going to escape Earth orbit [0]. Heck, if you aren't going fast relative to Earth, you aren't even going to be in Earth orbit [1], you are going to be falling back to the surface. [0] http://en.wikipedia.org/wiki/Escape_velocity http://en.wikipedia.org/wiki/Escape_velocity [1] http://en.wikipedia.org/wiki/Orbital_speed http://en.wikipedia.org/wiki/Orbital_speed
scott_s 12y ago
Everyone's responses are spot-on. But I can understand that it still may not be intuitive to you. The difficulty is that we see pictures and videos of our satellites and shuttles in orbit, and they look peaceful and serene. What's missing from those images and videos is a visceral feel that they are going over 17,000 mph. If they went less, they would leave orbit, and hit the Earth. Objects in orbit are not "outside" of Earth's gravity; they are not just up there, just floating in space. The reason they don't "fall to Earth" is that they are falling to Earth. Constantly. It's just that their horizontal speed relative to the Earth is so large that they are - literally - falling around the Earth.
lukeschlather 12y ago
The premise of your question is wrong. If you are in Earth orbit, you are moving fast. It's actually being in orbit that allows you to move slowly away, because you can take as long as you want to apply the force. If you're not in orbit you have to quickly apply enough force to escape Earth's influence in one go or you will fall back to Earth.
jameshart 12y ago
I can highly recommend having a play with Kerbal Space Program to get an intuitive grasp of orbital mechanics. Basically, if you don't go fast enough, you're going to come back down to earth. Once you get to a speed that's fast enough that you aren't going to come back to earth, you'll find you are now in orbit around the sun, in a path remarkably similar to the one the earth is on. To get to Mars you need to get up into a higher orbit around the sun, so you need to go even faster.