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Imagine you have a big wrecking ball swinging through the air at high speed, you throw a baseball at it and hit it head on. It seems intuitive that when the bas
by caseymarquis 6y ago
Imagine you have a big wrecking ball swinging through the air at high speed, you throw a baseball at it and hit it head on. It seems intuitive that when the baseball bounces off it, it will pick up some speed from the wrecking ball. In turn the wrecking ball will slow down the smallest amount from the collision with the baseball.
This is effectively what a gravity assist is. It's a collision with the planet. Because gravity is a weak force, and curving around a planet takes a while, it's a very gentle collision. Regardless, the result is that you pick up some momentum from the planet, and the planet slows down very slightly.
All that gravity really assists you with is increasing the duration of the collision and reducing lost energy from the collision, as the same collision head on would impart the same speed up, but would destroy your spacecraft for a variety of reasons.
They should really call it a gravity bump or something like that.
- hashkb 6y agoIsn't it more about changing trajectory without spending fuel? You don't gain or lose momentum in an absolute sense because there is no absolute sense. Play KSP.
- caseymarquis 6y agoThe size of your orbit is proportional to the energy of your spacecraft. Use manuever nodes to change the trajectory of your encounter with a planet like Eve, and notice how massively you can change the total size of your orbit (up or down, depending on the direction of the encounter). This implies a significant change in your energy during the encounter. This is from your gentle collision with the planet through its gravity field. Everyone should play KSP. :)
- WJW 6y agoYou absolutely gain or lose momentum from the gravity assist, even in KSP. Changing trajectory is just a side effect.
- z3t4 6y agoThink of it maybe as a skateboarder in a skateboard park where each pit is a planet, but because there is no friction, the skater does not lose speed, nor gain speed, relative to the skateboard park (solar system).