In order to unambiguously express the speed of a spacecraft, a
frame of reference must be specified. Typically, this frame is fixed to the body with the greatest
gravitational influence on the spacecraft, as this is the most relevant frame for most purposes. Velocities in different frames of reference are not directly comparable; thus the matter of the "fastest spacecraft" depends on the reference frame used. Because of the influence of gravity, maximum velocities are usually attained when a spacecraft is close to its primary body: either just after launch, at a point of closest approach (
periapsis), or during the early stages of
atmospheric entry. Parker Solar Probe.jpg|
Parker Solar Probe (artist rendering), fastest spacecraft relative to the Sun New Horizons spacecraft model 1.png|
New Horizons (artist rendering), fastest spacecraft upon departing Earth ApolloX CommandModule London.jpg|
Apollo 10 CSM Charlie Brown, fastest crewed vehicle relative to Earth ==See also==