Ignition of the Soyuz rocket. Photo: ESA

At 18:39 local time (1239 GMT; 0839 EDT) today, the steppes of Kazakhstan reverberated with the roar of rocket engines as a Soyuz-Fregat launch vehicle lifted off from pad 6 at Baikonur Cosmodrome with its precious payload of two Cluster satellites. "We have lift off!" came the confirmation on the public address system.

Within minutes, the white, dart-shaped Soyuz, emblazoned with a giant blue Cluster logo on the fairing, had disappeared into the blue evening sky, its passage witnessed solely by a rapidly dissipating trail of smoke.

Out of sight of the watching crowds, the protective fairing around the Cluster satellites was jettisoned and the first two Soyuz rocket stages consumed their fuel, separated and fell away, enabling the slimmed down booster to soar beyond the atmosphere and into the blackness of space.

Finally, less than 9 minutes after the dramatic launch from the historic cosmodrome, the Fregat upper stage and its Cluster payload (together known as the Upper Composite) separated from the third stage of the Soyuz booster.

Within seconds, the Fregat main engine ignited for about 3 minutes 45 seconds, inserting the upper stage and the satellites into a 200 km circular parking orbit.

Soyuz climbs into the sky. Photo: ESA

24 minutes into the mission, the Upper Composite drifted into the Earth's shadow and out of radio contact with the ground. For the next half an hour, the Cluster satellites relied solely on their onboard batteries for power.

The next major milestone came 1 hour 15 minutes after lift-off, when the Fregat main engine fired for the second time. This extended burn, which lasted 9 minutes 42 seconds, propelled the Upper composite into a 251 km x 18,053 km elliptical orbit.

Minutes later, the Fregat thrusters fired to spin up the entire stack, then the Fregat sent a command to operate the springs used to separate its Cluster payload.

First to push away was Samba, followed 10 seconds later by the gentle departure of Salsa. Free at last to go their own way, the spacecraft began to transmit telemetry to the ground station at Kiruna in Sweden.

To the delight of everyone at Baikonur and the European Space Operations Centre in Darmstadt, the spacecraft seemed to be in good health and ready for their prolonged journey to operational polar orbit during the week ahead.

"It's fantastic", said John Credland, ESA's Head of Scientific Programmes Department.

The stage is now set for the second act in the Cluster launch drama, with the next pair of spacecraft scheduled for lift-off from Baikonur on August 9.