In waiting: French engineers inspect one of the Cluster satellites prior to its launch last Sunday. Credit: AP/MIKHAIL METZEL

After a nerve-wracking 24-hour delay, scientists are celebrating the successful launch of two of the four Cluster II satellites that will fly in formation around the Earth, sending back data on the weather in space. They were launched on Sunday at Baikonur Cosmodrome in Kazakhstan, after a last-minute hitch forced take-off to be postponed. The second pair of satellites will be launched on 9 August. Later this year scientists should start gathering data from the satellites on the structure of the Earth's magnetic field and the flow of charged particles trapped within it.