A gravity assist is a fundamental technique utilized in astrodynamics that allows a spacecraft to change its velocity or trajectory relative to the Sun or another primary body without expending significant onboard propellant. The maneuver operates by exploiting the gravitational influence of a massive celestial body, such as a planet or large moon. As the spacecraft passes near this body, it interacts with the planet's gravitational field, resulting in a change in the spacecraft's momentum and energy. This interaction can redirect the spacecraft onto a new path or accelerate it to higher speeds, efficiently lowering mission costs and extending operational range by harvesting the kinetic energy of the assisting body.