A videometer is a European designed automatic docking system that guides an

Automated Transfer Vehicle The Automated Transfer Vehicle, originally Ariane Transfer Vehicle or ATV, was an expendable cargo spacecraft developed by the European Space Agency (ESA), used for space cargo transport in 2008–2015. The ATV design was launched to orbit fiv ...

(ATV) towards the docking port of the Russian

Zvezda Service Module ''Zvezda'' (russian: Звезда, meaning "star"), Salyut programme, ''Salyut'' DOS-8, also known as the ''Zvezda'' Service Module, is a module of the International Space Station (ISS). It was the third module launched to the station, and ...

of the

International Space Station The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...

(ISS).{{cite news, title=State of the art in automatic rendezvous, url=http://www.esa.int/esaMI/ATV/SEMZ2O57ESD_0.html, publisher=

European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...

, date=2 April 2004 The ATV uses relative

global positioning system The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...

(GPS) in order to close in on the ISS up to a distance of 249 m. Thereafter the ATV uses two videometers, together with additional data from

telegoniometer A Telegoniometer (a type of goniometer) is a device for varying the phase relationship(s) among two or more antennae in an array. This is for steering the directionality of the array without physically moving the antennae. the telegoniometer is ...

s, to automatically complete the docking maneuver. Both videometers are active during rendezvous with one acting as a back-up. Retroreflectors located on the aft end of Zvezda module accurately reflect pulsed laser beams emitted by the videometer on the front of the ATV. The spot patterns of laser light returned from the passive reflectors are analysed by the image processors on the ATV to give its relative position and orientation to the ISS. The beam travel time to the videometer's 26 retroreflectors, contained in a 25mm cube, compute the distance between the two spacecraft and thus allowing it to identify, approach and mate to Zvezda’s docking mechanism.

References

Components of the International Space Station