BREMEN, Germany — Astrium Space Transportation will oversee development of an atomic clock test program using two new-generation atomic clocks to be operated aboard the international space station under a contract with the European Space Agency (ESA) announced July 19.

Under the contract, valued at 35 million euros ($45 million), Astrium’s orbital systems division of Germany will oversee the Atomic Clock Ensemble in Space (ACES) system, which is scheduled for a late-2013 launch to the station aboard a Japanese HTV unmanned cargo carrier. Once fitted onto the external payload facility that is part of Europe’s Columbus laboratory at the space station, ACES is expected to operate for two years.

The ACES program, in development for several years, includes two types of atomic clocks to be launched together. The first, called Pharao, was developed by the French space agency, CNES. It is a laser-cooled cesium clock designed specifically for use in a microgravity environment. The second, developed by the Observatory of Neuchatel, Switzerland, is a hydrogen maser clock. ESA is also using passive hydrogen maser technologies — in addition to more-conventional rubidium clock technology — on the four Galileo In-Orbit Validation positioning, navigation and timing satellites to be launched in 2011.

The performance of the two ACES clocks will be compared, and also compared to ground-based atomic clocks through a microwave network that is also part of the contract with Astrium.

ACES is being financed by ESA’s human spaceflight directorate, which manages the agency’s space station and microgravity research programs.

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