The pioneering planet-hunting Kepler Space Telescope has finally reached the end of its service life and will be switched off permanently. NASA announced today that the aging, unmanned spacecraft, which has so far been responsible for the discovery of over 2,700 exoplanets, has run out of the propellant needed to keep it from tumbling and must be retired.

Today's announcement comes after a series of bold efforts to keep Kepler operating after nine years in deep space. Launched on March 6, 2009, at 7:49 pm PST atop a United Launch Alliance Delta II rocket from Space Launch Complex 17B at Cape Canaveral Air Force station in Florida, Kepler is currently in an Earth-trailing orbit around the Sun.

The Kepler mission was originally slated to last only 3.5 years, but hunting for planets outside the Solar System requires long, repeated observations of other stars and Kepler encountered higher than normal noise levels, so the mission was extended until 2016. Unfortunately, in 2012, the craft suffered he first of a series of failures of the reaction wheels that keep Kepler pointed in the right direction.

This nearly ended the Kepler mission because the chemically-powered attitude thrusters didn't have enough propellant to keep the spacecraft stable for very long. However, NASA devised a way to use the telescope's solar panel to act as a sail to balance out the pressure of the solar winds and maintain the craft on a stable attitude.

This solution worked and allowed for new mission extensions, though it did reduce the telescope's efficiency, and in June this year the propellant levels dropped to critical levels. Despite this, NASA managed to prolong Kepler's life in a series of observation/hibernation maneuvers that got in the maximum number of observations while buying time for the onboard computer to transmit the last of its data back to Earth.

According to NASA, the Kepler mission is so far responsible for the confirmed discovery of 2,723 exoplanets with more to follow as the data continues to be analyzed. Meanwhile, Kepler itself will be turned completely off, including its radio transceiver, so that stray transmissions won't be able to accidentally blind other spacecraft or the Deep Space Network of tracking stations on Earth.

"As NASA's first planet-hunting mission, Kepler has wildly exceeded all our expectations and paved the way for our exploration and search for life in the solar system and beyond," says Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate in Washington. "Not only did it show us how many planets could be out there, it sparked an entirely new and robust field of research that has taken the science community by storm. Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars."

See our Kepler feature article for a full run down of the mission's history and achievements.

Source: NASA