NASA’s Spitzer Space Telescope is finally nearing the end of an absolutely incredible journey. The spacecraft has been peering deep into space for well over a decade and a half, and it’s outlived its original planned mission timeline by over 11 years. In that time, it’s made some incredible discoveries and offered scientists new insights into the workings of some of our nearby planetary neighbors as well as distant objects we can only dream of one day visiting.

Now, with it’s planned decommissioning scheduled for Jan. 30, 2020, NASA’s Jet Propulsion Laboratory is taking a look back at its incredible journey, while offering some technical insight into why the still-functional telescope will have to be shut down.

Spitzer is an infrared telescope, meaning that it doesn’t see things in the same way that, say, the Hubble telescope does. It senses heat rather than visible light and that allows it to see things that are undetectable by optical telescopes. This has made it incredibly useful for spotting very distant stars and spotting various features of the Milky Way that would otherwise go unnoticed.

Unfortunately, its mission is coming to an end sooner rather than later, and the biggest bummer of all is that the telescope will still technically be functional when NASA finally pulls the plug. But why?

NASA’s JPL offers some background: “Spitzer orbits the Sun on a path similar to Earth’s but moves slightly slower. Today it trails about 158 million miles behind our planet – more than 600 times the distance between Earth and the moon. That distance, along with the curve of Spitzer’s orbit, means that when the spacecraft points its fixed antenna at Earth to download data or receive commands, its solar panels tilt away from the Sun. During those periods, the spacecraft must rely on a combination of solar power and battery power to operate.”

This would be fine, if not for the fact that the distance between the telescope and Earth continues to grow. In the many years since it launched, NASA has had to adjust the telescope’s solar array dramatically in order to ensure it can maintain power while communicating with Earth. Even then, it can only send data back for a period of about two-and-a-half hours before it has to adjust itself once again.

The unfortunate reality here is that the spacecraft just isn’t efficient enough to warrant further use and, as of January 2020, NASA will have to shut it down for good.