First Hubble, Now Kepler—Why Are NASA's Telescopes Breaking Down?

NASA has not been having much luck lately with its flagship, multimillion-dollar space telescopes.

In the past few months, the Hubble Space Telescope, Chandra X-ray Observatory and the Kepler spacecraft have all suffered technical issues that have led to the suspension of science operations.

Now, the space agency has announced that Kepler has gone back into sleep mode—in which it uses no fuel—just a few days after beginning its latest round of observations.

"Following a successful return of data from the last observation campaign, the Kepler team commanded the spacecraft into position to begin collecting data for its next campaign," a NASA statement read.

"On Friday October 19, during a regularly scheduled spacecraft contact using NASA's Deep Space Network, the team learned that the spacecraft had transitioned to its no-fuel-use sleep mode."

The spacecraft has been running dangerously low on fuel supplies for some time and has repeatedly entered sleep mode so that enough energy can be conserved to send precious data back to Earth while it remains viable.

It's possible that Kepler has finally run out fuel and will not turn back on again, although, at present, the situation is unclear.

"The Kepler team is currently assessing the cause and evaluating possible next steps," the statement said.

The fuel problems are not the only issue Kepler has been facing recently: In September, NASA announced that the aging telescope's ability to point precisely has degraded.

Nevertheless, the spacecraft was able to successfully download data from its 19th observation campaign back to Earth on October 15. The hope is that there will be enough power left to beam back the remaining data collected during the latest set of observations.

Even if this is the end of the planet-hunting spacecraft, Kepler will go down in history as one of NASA's greatest achievements. Launched in 2009 to search for Earth-sized exoplanets, it was only designed to operate for three-and-a-half years. However, the mission has lasted far longer, uncovering nearly 3,000 exoplanets in the process, revolutionizing our understanding of worlds beyond the Solar System.

An illustration of the Kepler space telescope. NASA

For example, based on data collected by the Kepler mission, scientists have estimated that there could be as many as 40 billion rocky, earth-sized exoplanets in the habitable zones of Sun-like stars and red dwarfs in the Milky Way alone.

Both Hubble and Chandra—which were launched in 1990 and 1999—have suffered technical problems recently.

On October 5, Hubble suspended science operations and entered safe mode due to a failed gyroscope (gyro)—a device that helps to point and steady the observatory's telescope—which was later found to be rotating at abnormal speeds. Safe mode puts the telescope into a stable configuration until ground control can correct the issue.

Hubble is fitted with six gyros, although usually it only uses three at any one time, with the others acting as backups. During the last Space Shuttle servicing mission in 2009, all six were replaced. However, two of these replacements had already failed, leaving just four functioning before the latest fault.

NASA announced on Monday that the gyro was now rotating at normal speeds and Hubble was closer to resuming normal science operations, although additional tests need to be performed.

Chandra, the most powerful X-ray telescope, also had problems with one of its gyroscopes: A glitch caused the observatory to go into safe mode on October 10. However, the fault was fixed relatively quickly, enabling the observatory to resume science operations on October 21.

NASA did not immediately respond to a request for comment.