By all rights, NASA’s Kepler spacecraft should have stopped working long ago. The observatory launched in 2009 with the aim of finding out how common exoplanets are throughout the universe. It turns out: very common. Mechanical failures forced NASA to change Kepler’s mission profile, but it still kept working until a few months ago. NASA was unsure if Kepler could go on, but the spacecraft just woke up to begin a new observational campaign.
Kepler uses the transit method to detect exoplanets. That means it has to watch vast swaths of the sky for weeks in order to track small light dips that could indicate an exoplanet passing in front of its host star. That became much more difficult in 2013 when a second of four reaction wheels failed in the spacecraft. At that point, Kepler could no longer maintain its orientation to point at the same area over time.
Since 2014, Kepler has been engaged in its secondary “K2” mission. This allows NASA to balance Kepler for several weeks a few times per year using the remaining reaction wheels and pressure from the solar wind. The original Kepler mission identified 2,244 candidate exoplanets with 2,327 of them confirmed. Kepler’s K2 phase resulted in 479 candidates exoplanets and 323 confirmed. Together, that’s most of the roughly 4,000 known exoplanets.
This part of the mission doesn’t require fuel, but Kepler needs to use its thrusters to orient its antenna toward Earth for beaming data back. NASA placed the telescope into hibernation mode over the summer to ensure it would have enough fuel left to send back data from its 18th observation. NASA got all the data back late last month and started a new observational campaign on August 29th.
NASA originally only expected 10 campaigns in K2, but there’s no fuel gauge on the spacecraft. Engineers are merely estimating what’s left in the tank based on past usage. It’s possible Kepler won’t have enough fuel to send back the data it’s currently collecting in the 19th campaign, but NASA isn’t giving up.
In the most recent mission update, NASA reports that one of Kepler’s thrusters isn’t working correctly, so its ability to reorient could be limited. NASA says it will continue monitoring the spacecraft throughout the current campaign. Even if Kepler can’t manage another full campaign, the agency’s Transiting Exoplanet Survey Satellite (TESS) is ready to pick up where it left off.
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