All of the planets in our solar system, including the gas giants, fit between the earth and the moon with a little bit of room to spare.
http://i.imgur.com/CLqdeKf.jpg
People severely underestimate the distance to the moon!
http://i.imgur.com/CLqdeKf.jpg
People severely underestimate the distance to the moon!
Getting to the moon from LEO takes less than half the delta-v that it takes to get to LEO, and WAY less fuel (because by this time you've dropped so much weight getting to LEO)
So the real problem will always be the stupidly inefficient method by which we conduct space flight. We send all of our supplies out of an enormous gravity well with a thick atmosphere.
Imagine what we could build if we already had everything in space for us already.
The only way we'll be able to become truly space-fairing is if we either become an astroid-mining civilization, or if we build something that lets us virtually ignore Earth's gravity well, like a space elevator.
Watching the launch today, I couldn't help wonder why they don't use standard jets to get the vehicle to a height where a rocket could take over.
The highest a jet has flown is about 37km and LEO is considered to start at about 160km. That 37km though in my mind would be the toughest and most fuel costly to ascend.
Would it not save both weight and money to use jets and fixed wings up through the low altitudes before turning to rockets for the higher altitude ascent?
They are the two big approaches to cheap space being done now. 1) Be cost-effective at making rockets, 2) launch from jets. My money is on #1, which SpaceX is doing, but #2 has some things going for it that could prove me wrong. #2 is also strictly limited in just how big you can make a payload, while for #1 you can get up to around 200 ton payloads before things start working against you.
Since they don't need to achieve anywhere near the required velocity to enter LEO, they can use a much smaller solid-fuel rocket engine and launch from a jet.
LEO isn't that far away, but it goes by _really_ quickly. And getting going that fast requires a lot of propellant mass, and that's judged by the tyranny of the rocket equation.
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.
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.
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.
For yet more perspective - an astronaut on the ISS in LEO is at most a couple of hours from the ground-based facilities in an emergency, probably more accessible than researchers at the South Pole. Sending people to Mars (on the order of magnitude of a year round trip, with very limited opportunities for early return) would require them to carry with them not only more expensive redundant systems, but also more advanced medical equipment and repair systems than anyone has had to carry into space before (which requires yet more mass, and hence a bigger and better launcher).
Of course, Orion itself doesn't deal with any of these issues - it's meant to be used for ascent and Earth return only, and to be attached to the larger systems that deal with the challenges of a Mars journey. Which indicates pretty well how little of the engineering work has been done towards NASA's Mars mission.
True, but it doesn't actually cost very much to do so. The cost of fuel for getting into orbit is only 0.3% of the total cost for the rocket [1], so if we could rapidly re-use them, we could potentially launch them every day of the year for not a lot of money.
[1]http://www.space.com/21386-spacex-reusable-rockets-cost.html
if we're talking about probes, the delta V aspect becomes a lot more fun when you consider the web of gravity slingshots that can be pulled off to up your dV