An ion drift meter is a device used to measure the velocity of individual ions in the area of a spacecraft

Spacecraft

A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

. This information can then be used to calculate the ion drift in the space surrounding the instrument as well as the strength of any electric field present, provided that the magnetic field strength has been determined using a magnetometer

Magnetometer

A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...

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The device itself works by allowing ions to pass through an opening at the front of the instrument and measuring the currents produced by the impacts of ions in different locations on a grid at the back. The trajectories of the ions can then be determined.

Ion drift meters have been used on several spacecraft including Dynamics Explorer

Dynamics Explorer

Dynamics Explorer was a NASA mission, launched on August 3, 1981 and terminated on February 28, 1991. It consisted of two unmanned satellites, DE-1 and DE-2, whose purpose was to investigate the interractions between plasmas in the magnetosphere and those in the ionosphere...

 and CHAMP

CHAMP

CHAllenging Minisatellite Payload is a German satellite launched July 15, 2000 from Plesetsk, Russia and was used for atmospheric and ionospheric research, as well as other geoscientific applications, such as GPS radio occultation....

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