Two of the four reaction wheels on the spacecraft's stabilising systems have failed meaning it cannot orientate itself to observe distant stars with sufficient accuracy.
Speaking to the Associated Press, deputy project manager Charles Sobeck, said: "We can't point where we need to point. We can't gather data."
Kepler can operate fine on just three wheels as it had been since a first failed in July of last year.
Then in January 2013 Nasa nervously announced a second wheel was showing "increased friction" - knowing if that too failed then the mission would be in jeopardy.
Orbiting the sun 40 million miles away from Earth, Kepler is too far away to be repaired like the Hubble Telescope has been in the past.
Kepler has been in space since 2009 and has identified 134 planets in that time two of which are similar enough to Earth in their size and distance from their star to host life.
It has already performed beyond expectations, completing its primary mission in 2012 when Nasa decided to extend its task through to 2016.
The telescope detects planets by measuring the tiny changes in light emitted from distant stars as planets move in front of them.
Data from the Kepler mission has been extrapolated to suggets there are 17 billion Earth-sized planets in our galaxy alone.