On Friday, an Atlas V rocket will launch another satellite for the US military — one aimed at giving advanced warning of missile launches from space. The probe going up is called SBIRS GEO-4, for Space Based Infrared System, and it’s the fourth satellite of its kind to go into a high orbit around Earth. As its name implies, the satellite is designed to use infrared to spot the heat coming from potential missiles launched on Earth, giving the US an early heads-up on strikes.

The Atlas V, made and operated by United Launch Alliance, launched the three previous SBIRS satellites that all went to the same orbit. These satellites sit about 22,000 miles above the Earth’s surface, in an orbit known as geostationary orbit. Up there, satellites match the speed of the Earth’s rotation, so they seem to hover over the same patch of land at all times. From this height, the SBIRS satellites also give information that helps with the US missile defense systems and data about what kinds of launches are happening on the ground.

The launch is set to take off on Friday from Cape Canaveral Air Force Station in Florida at 7:48AM ET. It was originally scheduled for Thursday evening, but ULA delayed the launch due to a valve problem that prevented propellant loading. ULA’s coverage will begin around 20 minutes before the launch window opens, so check back then to see if this rocket gets off the ground.

Update January 18th, 7:27PM ET: This post was updated twice after the launch was delayed.

https://www.theverge.com/2018/1/18/16905796/atlas-v-rocket-launch-missile-detecting-satellite-watch