Gravity can speed spacecraft — or slow them
Spacecraft can use planetary gravity assists to change speed while saving fuel. The Voyager probes accelerated during outer-planet flybys, while the Parker Solar Probe decelerated after flying by Venus.
How planetary gravity assists speed up or slow down spacecraft
Spacecraft can use planetary gravity assists to change speed while saving fuel. The Voyager probes accelerated during outer-planet flybys, while the Parker Solar Probe decelerated after flying by Venus.