# Gravity Assist: Acceleration At Its Easiest

Have you ever wondered how a spacecraft can accelerate to such a high velocity while combatting the extreme force of gravity? Well, what if I told you that the spacecraft is not combatting gravity to the degree that you may think, in fact, it is working alongside it.

When considering a spacecraft that is heading to... let's say... the moon, we see that the kinetic energy of the spacecraft needs to be incredibly large in order to achieve the final height of the moon and still have a smooth landing (please email Dr. Voss with any questions :) ).

For those of you who are like, "Bailley, I do not have a clue what potential or kinetic energy is," I have the answers for you. Imagine a canon loaded with a soccer ball. The maximum height of the soccer ball is 20 meters. At the bottom of the 20 meters, or when y=0, the total energy of the system is purely kinetic. The formula for kinetic energy is 1/2(mass)(velocity)^2. At the top of the 20 meters, when the velocity is 0 m/s, the energy is purely potential. The formula for potential energy is (mass)(9.8)(height above the ground).

Back to spacecrafts! Using the fly-by technique that NASA uses to launch their spacecrafts, the momentum of the spacecraft can be added or subtracted to increase or decrease the energy of the orbit to ensure that the velocity of the spacecraft is the calculated amount.

Why is this important? The answer is not super straightforward, but using gravity to assist the takeoff of a spacecraft to manipulate the energy of the spacecraft shows how we can use the forces around us to advance technology in the future!

Sources:

My Winter Term Physics class with Dr. Voss :)

__https://www.planetary.org/articles/20130926-gravity-assist__

__https://www.space.com/38226-how-gravity-assists-work-osiris-rex.html__