Efforts to resurrect the broken reaction wheels on the Kepler space observatory have failed. The spacecraft can still do useful science but not exoplanet transit searches, which requires the extremely stable and precise pointing capabilities provided by 3 working reaction wheels.

• NASA trying to find new use for crippled Kepler telescope – Spaceflight Now
• NASA Ends Attempts to Fully Recover Kepler Spacecraft, Potential New Missions Considered – NASA