Orbital Mechanics

Most people don’t have a strong grasp of what space-flight is like. People think that space works the same as flying. You turn left and you’ll go left. Turn right to go right. On Earth, there’s the air that makes an airplane move, the ground allows a car to move, but what is there in space?

Nothing.

The vacuum of space provides the most direct representation of basic physics:

• Every Action has an equal and opposite reaction.
• An object at rest will stay at rest.
• An object in movement will stay in movement.

In space, just spinning your ship doesn’t make it turn. Turning off your main drive won’t make you stop.

Manuevers in the Vacuum

Let’s assume for a minute that there was nothing else in the universe except your ship and some magical light to see by. You turn your main drive on for a minute, the g-forces, the acceleration, tells you the ship’s moving. When your ship accelerates - especially fast - it’s moving faster than you are and that makes thrust-gravity. It could make you press down against the deck or fly into a wall.

Turn the drive off and it’s no longer accelerating, but it’s still moving.

If we put a giant billboard out ahead of your ship, it’d fly right on by it, even without the drive running. And you’d keep on moving like that forever. There’s nothing to make your ship stop. No drag and no gravity.

Let’s try to turn.

Spin the ship sideways and what happens? You’re still going the same direction you were before. Without the main drive, the direction your facing means nothing. So we’ll kick on the main drive. We’re going really fast to the side now, right? Not quite. We didn’t turn, but we did nudge our course by a few degrees, it’s the start of a turn.

To go directly sideways, we’d have to turn the ship around so we can cancel out our initial thrust and start actually moving sideways.

On the Earth, your car tires push against the ground and that makes you turn. Airplane wings push on the air. In space, there’s nothing to push against. Your direction and thrust influences the direction you go, but it’s not magic.

Relative Movement

The other side of the equation is more simple: your movement is relative.

Two ships flying in a formation, under thrust, going the exact same direction will keep going in that direction. If one of those ships flips to a braking burn, it looks like flying away - but - that’s not completely true. The ship with the brakes? It’s just slowing down. It could take it days to come to a complete stop. It’s still going the same direction, just a little slower.

Your movement in space is relative to the speed and direction you’re already traveling.

How Orbit Works

And then there’s orbit. Gravity.

Gravity is the one thing that’ll effect your space craft all the time. This also means that the shortest route between two points isn’t necessarliy a straight line either. In space, we aim for where an object is going to be and we have to work with our orbits.

When you watch a rocket launch, it doesn’t go straight up the entire time. A rocket starts by going straight up and then it leans onto its side until it’s in level flight. This manuever is how a ship gets into orbit.

An orbiting ship is flying faster than it’s falling.

If you just dropped an object in the air far above a planet, it would fall down from gravity and hit the planet. If that object moved a little to the side, it would still hit the planet, but what if it moved a LOT to the side? It would shoot over the horizon, fall a little, keep moving for the horizon, keep falling. It’s in orbit.

Play

Here’s a really cool demonstration of how orbit works.