NASA's planet hunter shakes off reaction wheel woes and gets back to work

No more stress for TESS

NASA has confirmed that the Transiting Exoplanet Survey Satellite (TESS) has recovered from a reaction wheel problem and resumed making observations.

The spacecraft dropped into safe mode on April 23 following an issue that occurred earlier in the month. The latest safe mode was triggered by a failure to dump momentum from TESS's reaction wheels, which requires using the spacecraft's propulsion system. The system had not been successfully repressurized following the earlier safe mode event on April 8.

Once the issue was corrected, TESS resumed science operations. However, the team still needs to figure out what caused the April 8 upset, which occurred during scheduled engineering activities.

TESS has four reaction wheels for fine pointing and its mission is to monitor millions of stars for temporary drops in brightness. "This first-ever spaceborne all-sky transit survey will identify planets of all sizes," according to MIT, which leads the NASA mission.

TESS was launched in 2018 atop a SpaceX Falcon 9 rocket and is currently in its second mission extension. As of April 18, the observatory had discovered 432 planets and 7,138 planet candidates.

The spacecraft is in a highly elliptical orbit, with its lowest point 67,000 miles (108,000 km) from the Earth and its highest 232,000 miles (373,000 km) away. Therefore, it is safely positioned away from the hazards of the Van Allen radiation belts and well above the geosynchronous orbit used by many communication satellites.

During its two-year primary mission, the observatory imaged approximately 75 percent of the sky, finding 66 new exoplanets – worlds outside the solar system – and 2,100 candidates requiring confirmation from astronomers. Dr Patricia Boyd, TESS Guest Investigator Program Lead at NASA Goddard Space Center, declared the mission "a roaring success."

However, things are starting to stack up for the spacecraft, which is well into the bonus science period of its lifetime. In October 2022, the spacecraft entered safe mode following a surprise reset of its flight computer. The cause of the first problem in April 2024 remains unknown.

A third extension for TESS, which will take the mission from September 2025 to September 2028, is contingent on the outcome of the 2025 Astrophysics Senior Review. The project has invited input from the scientific community on priorities for the proposed extension. ®

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