Using the laws of space
Once the probe has been propelled in the right direction, it may still have a long way to travel.
To achieve the momentum it needs, a probe relies on the laws of space. As it orbits around the Sun or other planets it encounters, it moves as a result of universal gravitation.
Interplanetary exploration therefore seeks to exploit the mutual attraction between objects in space to adjust a probe’s trajectory and velocity.
To achieve the momentum it needs, a probe relies on the laws of space. As it orbits around the Sun or other planets it encounters, it moves as a result of universal gravitation.
Interplanetary exploration therefore seeks to exploit the mutual attraction between objects in space to adjust a probe’s trajectory and velocity.
The Mariner 10 probe launched in 1973 was the first to use gravity to change its trajectory and get from Venus to Mercury.
The trajectory on the right includes the Venus flyby. On the left, the direct trajectory to Mercury, requiring a much more powerful launcher.
Animation: how gravity assist work (CNES)
Animation: a few missions' trajectories (ESA website)
Spacecraft may also be equipped with motors and thrusters, which are only fired occasionally to make minor corrections to their trajectory, orbital plane or attitude.
