PARIS — One of four French electronic-intelligence satellites flying in formation in low Earth orbit was forced to perform a collision-avoidance maneuver after U.S. and French space tracking radars determined that it was on a collision course with a large piece of orbital debris, the French air force said.

The satellite that had to be moved is one of four identical 120-kilogram Elisa demonstrator satellites launched into a 694-kilometer low Earth orbit in December 2011.

With French naval and German ground-based precision space-surveillance radars out of service for several months for maintenance, the French military deployed two of its less-precise ground radars, located in Sommepy in northeast France and Solenzara on the island of Corsica in the Mediterranean, to track what the French air force said was a dead satellite.

French officials said the object in question was a dead U.S. Defense Department weather satellite named Defense Satellite Application Program — or Defense Meteorological Satellite Program — Block 2 F3, which was launched in March 1966. The satellite is now in an orbit with a perigee of 592 kilometers and an apogee of 816 kilometers.

Initial word of the possible collision came through the usual channel — an early warning from the U.S. Strategic Command’s Joint Space Operations Center, JSPOC, which uses a near-global network of ground and space-based surveillance sensors to track satellites and debris.

>The French space agency, CNES, took the JSPOC data and added information from the French Graves bi-static radar and the French Defense Ministry’s space surveillance division.

A more typical sequence for determining the position of an orbital object in Europe is to use the Graves radar to make wide-field surveys of objects and then to use the French Monge naval vessel to train its radar on the object in question.

Similarly, the German TIRA radar has been used with Graves to home in on specific objects in low Earth orbit.

But both Monge and TIRA are out of service for planned maintenance that will last until midyear, a French government official said.

The French air force, in a summary of the Feb. 28 collision-avoidance maneuver described in its in-house publication, Air Actualites, said the Elisa E12 was judged to be at high risk of collision with a large piece of space debris.

The French government official said a decision to maneuver a satellite is made when the likelihood of collision is judged to be equal or higher than one in 2,000.

CNES’s in-house orbital tracking service, called CAESAR, or Conjunction Analysis and Evaluation Service Alerts and Recommendations, monitors about 20 satellites, mainly — but not exclusively — French government spacecraft. It describes its role as a “middleman” between JSPOC and satellite owners, much like the Conjunction Assessment Risk Analysis team at NASA’s Goddard Space Flight Center.

CAESAR, based in Toulouse, France, is one of several space surveillance and tracking agencies in Europe that are expected to form a consortium to provide a European space-tracking capacity for the European Commission. The program, budgeted at 70 million euros ($96 million) over seven years starting in 2014, is viewed as a complement to the much more elaborate and costly U.S. JSPOC service delivered to satellite operators worldwide.

Peter B. de Selding was the Paris bureau chief for SpaceNews.