The European Space Agency has just received the first signal from its Rosetta spacecraft in over two years. Ground controllers placed the solar-powered Rosetta spacecraft into sleep mode in June, 2011 to conserve power while the vehicle looped far from the sun. The dangerous - and apparently successful - maneuver allowed the spacecraft to synchronize orbits with its ultimate target, Comet 67P/Churyumov-Gerasimenko.
During its hibernation, heaters periodically warmed the delicate electronics inside the spacecraft. To keep its solar panels pointed toward the sun, the craft was put into a slow spin. Since Rosetta couldn't contact Earth during its sleep period, scientists and engineers back on Earth could only wait and hope that the extraordinary efforts to keep the spacecraft warm had actually worked.
Over the next few days, ground controllers will check the spacecraft subsystems for functionality. If no major issues are found, Rosetta will continue its epic journey across the solar system that began in March, 2004 and included three Earth fly-bys, a Mars fly-by, and two asteroid fly-bys. Rendezvous with its ultimate target will occur in August, 2014. Rosetta carries a small lander that will attempt to "dock" with the comet soon after arrival, the first time a spacecraft has attempted a soft comet landing (NASA's Deep Impact was the first "hard" comet landing back in 2005).
Congratulations to the Rosetta team!!
(Disclaimer: Your Denver Space Industry Examiner has assisted the science team for the ALICE instrument aboard Rosetta. ALICE is a compact ultraviolet imaging spectrometer that has flown on several spacecraft, including the New Horizons mission to Pluto).