The Fregat M upper stage for Starsem's Soyuz launch of the MetOp-B weather satellite is undergoing its checkout in preparation for a May 23 liftoff from Kazakhstan's Baikonur Cosmodrome on the Arianespace affiliate company's 25th commercial mission.

Built by Russia's Lavochkin Research and Production Association, the Fregat M stage is an autonomous and highly flexible orbital vehicle that can be restarted up to 20 times in flight - enabling it to carry out complex mission profiles.

For Starsem's upcoming flight, Fregat will place MetOp-B into polar orbit, joining the nearly identical MetOp-A spacecraft - which was launched in October 2006 by Starsem on another Soyuz mission from Baikonur Cosmodrome.

A total of three MetOp-series spacecraft are being developed as a joint undertaking between the European Space Agency and EUMETSAT (the European Organisation for the Exploitation of Meteorological Satellites), providing continuous weather observations until 2020.

The upcoming Starsem launch will use a Soyuz 2 modernized version of Russia's medium-lift workhorse launcher, which also is in service with Arianespace at the Spaceport in French Guiana.