The International Space Station is a floating mechanical laboratory, and with almost everything mechanical, sometimes things fall apart. It's just the way things are.
Since things sometimes fall apart, they need to be fixed by humans so they can then be used again. This is exactly what happened on the ISS, as astronauts Andrew Morgan and Luca Parmitano were given the job of going on a spacewalk to fix the coolant pumps on the Alpha Magnetic Spectrometer. The cosmic ray detection instrument was out of commission due to the cooling system failing, but since this past Saturday's spacewalk, the instrument might just be ready for use.
After the initial spacewalk, both astronauts decided to double-check the coolant system to make sure their work was 100%. To their surprise, there was actually a leak found in the cooling system, and after discovering this, the leak was repaired. The Alpha Magnetic Spectrometer is valued at around $2 billion dollars and is designed to shine some light on what dark matter actually is and how it works. NASA believes that since the repairs have been successful that the Alpha Magnetic Spectrometer should work until the end of the ISS's lifespan.