In orbital mechanics and aerospace engineering , a gravitational slingshot , gravity assist maneuver , or swing-by is the use of the relative movement ( e.g. orbit around the sun ) and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft , typically in order to save propellant , time , and expense .
A gravitational slingshot , gravity assist maneuver or swing-by is the use of the relative movement and gravity of a planet to alter the path and speed of a spacecraft , typically in order to save fuel , time , and expense .