Space probe

A space probe is an unmanned spacecraft that, unlike Earth observation satellites and space telescopes, is sent on a journey to one or more objects of study in the solar system. In the obvious context of space exploration, the term may also be abbreviated to "probe", thus forming composites with target object names, for example "lunar probe" or "Mars probe".

Especially for flights to destinations beyond Mars and Venus, spacecraft flight requires the ability to make large velocity changes (delta v). Course corrections are made after the initial survey of the orbit and at various distances from the target. Spacecraft navigation is performed using the Doppler effect and signal travel times to an accuracy sometimes less than one meter in position and less than one centimeter per hour in velocity.

Due to long signal propagation times for control commands, space probes must have systems that make them independent of ground stations to a certain extent. This is especially true for attitude control and sequencing of orbital maneuvers and observations.

The power supply for space probes to the moon and inner planets is usually provided by solar cells buffered by an accumulator. Space probes for the flight to outer planets often use radionuclide batteries for the power supply, since solar cell surfaces become increasingly inefficient with increasing distance from the sun. However, progress in solar cell technology makes it possible to supply even a space probe at Jupiter with energy from solar cells (see: Juno).

Depending on the task, space probes are divided into:

• Flyby probes - Probes that perform only one flyby of a celestial body to make observations along the way and in the vicinity, and then may have another destination.
• Orbiter - Probes that take up an orbit around a celestial body, sometimes at a Lagrange point.
• Lander - probes that land on a celestial body.
• Sample return - Probes that return samples from a celestial body, particles collected in space, or manufactured samples to Earth.

Sufficiently soft-landed probes or parts of them that remain on a celestial body and are equipped with a passive element retroreflector are used as survey points and for measurements of dust deposition and the transparency of the atmosphere.

See also

• List of space probes