Jupiter slingshot orbital mechanics, illustration. Probes and spacecraft sent to explore other planets can be accelerated or slowed down with gravitational ('slingshot') assists from planets. An example of this is the use of Jupiter shown here. At upper left, a probe with velocity V1 (blue line) approaches a planet moving with velocity V2. The probe swings into orbit (upper right, and burns its engine at periapsis (the point of closest approach, lower left). At lower centre, the result for an acceleration (achieved by approaching the same direction as the planet is moving), is to gain twice the value of V2. At lower right, the result for a deceleration (achieved by approaching the planet from behind), is to lose twice the value of V2.