After over nine years, the Kepler Space Telescope mission may be coming to an end. The reason: out of fuel. NASA engineers have determined that the unmanned deep space probe has only enough propellant left in its attitude control system to keep it properly oriented for a few more months. When this runs out, the spacecraft will no longer be able to collect data or transmit it to Earth.

Launched from Cape Canaveral Air Force Station Launch Complex 17B atop a Delta II rocket on March 7, 2009, the Kepler Space Telescope has already exceeded it first mission life many times. Its original mission estimate was for three and a half years, but this was extended as it continued to seek out extrasolar planets as it circled the Sun in its Earth-trailing orbit about 94 million mi (151 million km) from home.

In 2013, it seemed as if the mission had come to a final end when the reaction wheels that hold the spacecraft steady failed, but NASA came up with a fix that allowed Kepler to use the solar winds to balance its attitude like a boat setting its sails to keep it on course. Though the telescope could now only point in one direction and it wasn't as stable as before, the new K2 mission let Kepler continue operating through 17 three-month campaigns.

According to NASA, Kepler is now up against a much harder deadline as it runs out of the propellant used to keep it pointing in the right direction for both observation and maintaining contact with mission control back on Earth. Though there's no way to directly measure how much propellant is left, engineers are monitoring the spacecraft for signs like a drop in tank pressure that will indicate when the end is imminent.

The present estimate is that Kepler has only a few months of life left, but NASA stresses that the spacecraft has already survived and functioned much longer than originally estimated and may do so again. With this in mind, the project team will continue to collect data about candidate exoplanets for as long as possible, with a final set of commands ready for the spacecraft to carry out a series of calibration exercises as the end nears.

NASA has not said what the final fate of Kepler will be. Because it is a deep space probe that won't pass near any planets, it poses no physical hazards in the foreseeable future, but it is usual for deep space missions to power down completely to prevent their radio transmitters from accidentally blinding deep space tracking networks.

Source: NASA