After unpacking two Soyuz rockets from shipping crates, Russian workers at the Guiana Space Center are testing and assembling the boosters before moving the vehicle to the launch pad this summer.

Workers attach one of the Soyuz rocket's strap-on boosters to the core stage. Credit: Arianespace

Two Soyuz 2-1a rockets were transported from Russia to French Guiana in November, and engineers are putting the launchers together for the first time in a new integration building near the Soyuz launch pad, which is still under construction.

Each Soyuz rocket includes four strap-on boosters, a core stage and a third stage, all fueled by kerosene and liquid oxygen. A Fregat upper stage will be added atop the Soyuz to inject satellites into specific orbits.

The ongoing testing will involve bolting the pieces together to test out procedures inside the integration building, which mimics similar Soyuz infrastructure at other launch sites, according to Arianespace, the Soyuz rocket's commercial operator in Kourou.

If a new mobile gantry is finished by July, the workers will move one of the vehicles to the launch pad for combined tests of the booster and the ground facilities.

Antonio Fabrizi, the European Space Agency's director of launchers, said there are tight schedules leading to the liftoff of the first Soyuz rocket from the space center, which normally hosts launches of Europe's Ariane 5 rockets.

European space officials are planning to launch medium-lift Soyuz rockets and the new lightweight Vega booster from French Guiana to augment the heavy-lift Ariane 5 workhorse.

Multiple shifts of workers are constructing the gantry, but it is uncertain whether the facility will be ready for the first Soyuz launch by September.

The launch of the HYLAS communications satellite for Avanti Communications of the United Kingdom is still scheduled for September, but there is no room for error in the schedule, Fabrizi said.

Two more launches of the French Pleiades Earth observation satellite and a pair of Galileo in-orbit validation navigatoin spacecraft were expected before the end of the year, but those flights are likely to slip into early 2011.

In an interview with Spaceflight Now, Fabrizi said he anticipates the long-delayed HYLAS launch will occur well before the end of the year.

The most recent schedule slips were caused by the late delivery and construction of the launch pad's mobile gantry, a unique piece of equipment not used for Soyuz launches at the Baikonur Cosmodrome or the Plesetsk Cosmodrome in Kazakhstan and Russia.

The Soyuz launch pad in Kourou, French Guiana. Credit: Arianespace

For Soyuz fights from Kourou, the three-stage booster and its Fregat upper stage will be put together inside the integration building before rolling out to the launch pad. Payloads will be added once the rocket reaches the pad and is erected vertically inside a 164-foot-tall tower. The gantry will be rolled back to a distance of around 250 feet from the rocket in the hours before liftoff.

The operations concept is drastically different than existing Soyuz preparation procedures, in which the rocket is fully assembled on its side, towed to the launch pad on a train, then lifted upright a few days before flight.

CNES, the French space agency, is overseeing the gantry construction with a team of European and Russian contractors.

Once the structure is topped out, officials are planning to add exterior panels and a maze of cables, plumbing and cranes for launch operations.

The Soyuz launch pedestals, fueling systems and umbilical swing arms were installed at the pad last year.