At 7:42 p.m. Eastern time on Friday, January 20, an Atlas V rocket streaked across the sky and into space from its launch pad at Cape Canaveral Air Force Station in Florida. The United Launch Alliance Atlas V rocket carried an infrared surveillance satellite into high-Earth orbit for the U.S. Air Force. This satellite, the third of its kind to enter Earth’s orbit, is a Space-Based Infrared System GEO Flight 3 satellite.

The SBIRS payload in this launch consists of two components, explains First Lieutenant Nick Walton on ULA’s webcast: a scanner and a step-starer. “The scanning sensor scans the globe twenty-four seven, and provides global strategic missile warning,” he says. While the scanning sensor sweeps the globe, looking for anything out of the ordinary, the step-starer can closely monitor more pinpointed areas without interfering with the scanner’s accuracy.

In short, this satellite network can provide the Air Force with an early warning system in the event that a foreign power fires missiles at the United States.

Initially scheduled for 7:46 p.m. on January 19, ULA delayed the launch because it needed to work on issues affecting sensors on the rocket, Loren Grush reports for The Verge. Then the launch was scrubbed altogether because an aircraft came within the rocket’s range.

But on Friday, everything went according to plan. The Atlas V rocket operated nominally, and the SBIRS satellite was deployed into high orbit.

This launch, the first of ULA’s 2017 season, is the third SBIRS satellite to go into space, becoming part of the existing network. But it won’t be the last. The U.S. Air Force plans to launch more of these missile detection satellites to provide greater global coverage. Since the SBIRS satellites are purely defensive, the Air Force wants to put more units into orbit so they’ll be able to quickly detect and respond to any threats.

You can watch the entire webcast here: