PARIS — The European Space Agency (ESA) on Dec. 7 selected Astrium UK to build the Sentinel 5 Precursor Earth observation satellite in a contract valued at 45.5 million euros ($61 million), Astrium announced Dec. 8.

Astrium UK will provide Astrium’s Astrosat 250 satellite platform for Sentinel 5 Precursor, which is scheduled for launch in 2015 into an 800-kilometer polar low Earth orbit to study atmospheric chemistry. This is the same satellite design used by Astrium for its Spot 6 and Spot 7 optical Earth observation satellites, and for Spain’s Ingenio optical reconnaissance satellite, all now in development.

Expected to weigh about 500 kilograms at launch, Sentinel 5 Precursor will carry the Tropomi tropospheric monitoring instrument under development for ESA by Dutch Space of the Netherlands, an Astrium subsidiary. The Dutch government has allocated 78 million euros for Tropomi development and data collection.

Another Astrium-owned company, Surrey Satellite Technology Ltd. of Britain, is building a spectrometer for Sentinel 5 Precursor under a separate contract valued at 10.7 million euros.

Sentinel 5 Precursor is intended to bridge the gap in atmospheric chemistry measurements between the retirement of ESA’s large Envisat satellite and NASA’s Aura satellite, and the scheduled 2020 launch of the Sentinel 5 payload aboard a polar-orbiting meteorological satellite to be operated by Europe’s Eumetsat organization.

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