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INTERESTED
04-14-2001, 05:07 PM
when the shuttle leaves earth is there a right way to turn to get to say mars venus etc? And also is there a wrong way?
And I dont mean that by logging in coordinates the shuttle takes you there .

Arden Ranger
04-14-2001, 06:21 PM
Wrong forum, dude.

This belongs in GQ

flyboy
04-14-2001, 08:48 PM
Welcome to the boards, INTERESTED. In the future, you may want to check out the forum descriptions before beginning a thread, just to make sure you're posting it in the right place.

IANAPhysicist, but in answer to your question, I think it's just a matter of taking the proper trajectory upon leaving the earth's atomsphere, then, after a few orbits, firing the engines at a predetermined point, allowing you to depart orbit at a specific point. Tie a ball to the end of a string, twirl it around, then let go. The ball will fly in a straight path. Think of the ball as the shuttle, and the point at which you let go of the string as the departure from earth's orbit, and the heading the ball took flying away from you as the heading toward the destination planet. If you watch Apollo 13 you'll get a better idea.

Now the real brains in here will rip this apart and tell you how it's really done. :D

friedo
04-14-2001, 10:02 PM
I am an Official Real Brain. I know. I failed Calculus. Three times.

But flyboy is right. If you swing a ball on a string around your head, the string acts like the Earth's gravity, keeping the ball in orbit. (OK, so that's no really true, but it's a good illustration.)

Newton's Second Law says that an object in motion, not acted upon by any other force, will stay in motion (and in a straight line).

So while the space ship is in orbit, it's being acted upon by the Earth's gravity. When it fires its engines at a certain point in orbit, it travels away from the earth (helped by the momentum of the orbit; this is what astronauts are talking about when they mention "slingshotting around" the Earth.) and goes in a straight line. Once it's far enough away so the effect of Earth's gravity is negligable, it will go in a straight line forever, or until an outside force acts on it. (Smashing into another planet would work.)

Chronos
04-15-2001, 10:25 AM
As it happens, I am a physicist, and it also happens that I'm a moderator of the aforementioned General Questions forum, so I'll move the thread over there. On to the question:
First of all, to clarify, the Shuttle never goes to Mars or Venus, or even to the Moon. It stays in low Earth orbit, which for purposes of space exploration, is barely even above the surface of the Earth. That's really just a nitpick, though, as there are other spacecraft (all unmanned) that do go to Mars or Venus. The principle is simple: To get to Mars, or anywhere else farther from the Sun than the Earth, you point in the same direction that the Earth is moving in its orbit, and fire your rockets. This causes your rocket to be going faster than the Earth, so it goes into a higher orbit. This orbit will be highly elliptical, with its closest point to the Sun being the same distance as the Earth. The farthest point will depend on how hard you fired your engines. Fire them hard enough, and the outer end of your orbit will just intersect Mars' orbit, and if you timed it right, Mars will be there to meet you. Now, you again fire your rockets in the same direction that Mars is orbiting, to bring you up to the same speed as Mars about the sun, and you're in orbit around Mars.

Going "down" (closer to the Sun, like from Earth to Venus, or returning from Mars to Earth) is similar, but in reverse: First, you fire in the opposite direction from the planet's orbit, to slow yourself down. This puts you into an elliptical orbit that matches Earth at its outermost point, and matches Venus at its innermost point. Then, when you reach Venus, you slow down again, to match Venus' orbit, and go into orbit around her. Note that you don't just point your rocket straight out at Mars or straight in towards Venus: The Sun's gravity and your initial orbital speed are both considerable, and if you try to directly oppose either, you'll need extremely powerful engines, many times greater than anything we've currently got.

When one of the planets involved has a significant moon, like Earth's, you can use it for some fancy maneuvers and save a little fuel, but that gets rather complicated.

Phobos
04-16-2001, 08:12 AM
Like Chronos explained so well, it's not a matter of "turning" but rather, changing your orbit. And the fastest route is definitely not a straight line. For one thing, you're aiming at a moving target. So you need to aim for where it will be, not where it currently is.
Also, you can take advantage of gravitational slingshots to go faster (instead of using more rocket fuel). The ongoing Cassini mission to Saturn (an outer planet) actually flew by Venus (an inner planet) a couple times and the Earth once in order to get to Saturn faster.