Kepler, NASA’s planet-finding spacecraft, about to run out of fuel

All good things must end. So it is with Kepler, the plucky space telescope that discovered thousands of planets despite significant malfunctions. NASA announced that the spacecraft will run out of fuel in just a few months, according to an article on

“Our current estimates are that Kepler’s tank will run dry within several months — but we’ve been surprised by its performance before! So, while we anticipate flight operations ending soon, we are prepared to continue as long as the fuel allows,” said Charlie Sobeck, a system engineer on the Kepler team.

In the meantime, Sobeck’s team intend to grab all the scientific data Kepler can still get. They plan to transmit that information before the fuel tanks run dry.

“We even have plans to take some final calibration data with the last bit of fuel, if the opportunity presents itself,” he said.

Even though Kepler’s time is drawing to a close, the data it collected will remain relevant for years to come. Researchers are still sifting through its voluminous archive in search of potential planets.

In nine years, Kepler has identified 2,342 planets. The space observatory has accounted for two-thirds of all known exoplanets.

In addition, the space telescope has spotted 2,245 possible candidates for exoplanets that require follow-up. (Related: NASA’s alien-hunting probe discovers 100 new planets orbiting stars outside our solar system.)

Kepler trucks on despite age, malfunctions

Kepler was launched in 2009. Its mission was to seek out exoplanets in a certain part of the Cygnus constellation. Its photometer checked stars for brief moments of dimness caused by the passage of exoplanets.

Before the space telescope entered orbit, there were very few known rocky exoplanets that were smaller than the Earth. Kepler’s data showed that such rocky planets are actually very numerous.

Costing $600 million, Kepler’s original two-year mission was extended. Disaster struck during its fourth year, when the gyroscope “wheels” that aimed it started malfunctioning.

By 2013, three of its four gyroscopes no longer worked properly. Kepler could not keep itself pointed at Cygnus.

NASA therefore devised the new K2 mission, where Kepler swiveled itself between different patches of sky every three months, a period of time called a “campaign” by the team. Doing so shortened its orbital period but allowed it to keep hunting for exoplanets.

“Initially, the Kepler team estimated that the K2 mission could conduct 10 campaigns with the remaining fuel. It turns out, we were overly conservative. The mission has already completed 16 campaigns, and this month entered its 17th,” remarked Sobeck.

Even as successors approach, Kepler will keep working

Kepler has no gas gauge, so the team is forced to estimate its remaining fuel stock. It’s biggest advantage is its position in deep space; the telescope is nowhere near a planet that has tempting ice-covered moons.

That’s what doomed the Galileo and Cassini space probes once they started running on fumes. NASA deliberately crashed them into Jupiter and Saturn, respectively, in case they hit one of the icy moons orbiting those planets.

“We can afford to squeeze every last drop of data from the spacecraft — and ultimately that means bringing home even more data for science. Who knows what surprises about our universe will be in that final downlink to Earth?” Sobeck asked.

Kepler’s successors are on the way. The Transiting Exoplanet Survey Satellite (TESS) is expected to launch in April 2018.

The mission of the new NASA satellite is a full-sky survey covering a minimum of 200,000 stars. It will concentrate on exoplanets around stars that are brighter and closer for Kepler.

After TESS comes the James Webb Space Telescope. With a launch date of 2019, it will work alongside ground telescopes to follow up on TESS’ observations.

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