Mission controllers last night sent a command to the Kepler spacecraft, NASA's unprecedented planet hunter launched last month, to eject its dust cover, effectively opening the telescope to the heavens.

Kepler, now some two million miles (three million kilometers) from Earth, will trail our planet in an orbit around the sun, observing a patch of sky for three-plus years in search of possible companion planets around a group of 100,000 stars. The spacecraft bears the largest space-borne camera ever, a photometer composed of 42 charge-coupled devices (CCDs), to monitor those stars for periodic dips in stellar brightness that occur as orbiting planets block a portion of the stars' light from Kepler's view.

The photometer had been protected during launch and initial flight by a spring-loaded oval dust cover (centered in image above) held in place by a latch, according to NASA. When engineers at the Laboratory for Atmospheric and Space Physics in Boulder, Colo., sent a command to break a wire and release the latch at 10:13 (Eastern Daylight Time) last night, Kepler's cover popped off and drifted away. (See animation below.)

The cover also provided a dark environment for calibrating Kepler's photometer and removing sources of inherent noise. "We have thoroughly measured the background noise so that our photometer can detect minute changes in a star's brightness caused by planets," Bill Borucki, the mission's principal investigator, said in a statement.

NASA says that with the spacecraft's science instrument now receiving light, only a few weeks of calibration remain before Kepler begins its hunt for extrasolar planets. According to Alan Boss, author of The Crowded Universe and a member of the Kepler science team, the spacecraft won't have any conclusive evidence of habitable planets for years, but larger, hotter planets should be spotted in relatively short order.