Interplanetary spaceflight or interplanetary travel is spaceflight between planets within a single planetary system. Spaceflights become interplanetary by accelerating spacecraft beyond orbital speed, reaching escape velocity relative to Earth at 11.2 km/s, entering heliocentric orbit, possibly accelerating further, often by performing gravity assist flybys at Earth and other planets. Most of today's spaceflight remains Earth bound, with much less being interplanetary, all of which performed by uncrewed spacecraft, and only just a few spaceflights having accelerated beyond, to system escape velocity, eventually performing interstellar spaceflight.