This morning, the United Launch Alliance (ULA) successfully launched a Boeing-built satellite into orbit as part of the U.S. Air Force’s Global Positioning System (GPS).

This $131 million satellite was the final addition to the Air Force’s most recent 12-satellite GPS series, known as the Block IIF satellites.

GPS satellites are operated by the Air Force and provide global positioning, navigation and timing services both for the military and civilian users. We can all access GPS from our phones because of this very constellation.

Back in 1978, the first GPS satellite was launched into orbit. Since then, the Air Force has improved their satellite design and released new versions of GPS satellites in blocks. Starting with Block I, the Air Force has moved through Block IIA, Block IIR, Block IIR-M, and today they’ve completed the launch of their Block IIF series.

While only 30 GPS satellites are currently operational, 50 have been launched in total. The most recent group of Block IIF satellites were launched between May of 2010 and today.

Col. Steve Whitney, the director of the Global Positioning System Directorate, said that the last leg of launches had “one of the most aggressive launch schedules of the last 20 years.” There were 7 Block IIF satellites launched in just over 21 months.

The GPS Block IIF satellites were launched to improve the accuracy of GPS. Col. Steve Whitney, the director of the Global Positioning System Directorate, said that before the Block IIF series, the accuracy of GPS could be off by 1 meter. With the new Block IIF satellites in place that error is down to 42 centimeters.

The change won’t mean much to the average civilian, but it could mean the difference between life and death for the military who uses GPS to guide munition to specific targets.

In order to make room for today’s satellite, the Air Force will move one of the older Block IIA satellites that was launched in 1990 out of its orbit. Impressively, the satellite is still operational and will continue to serve the GPS constellation as a back-up satellite.

Now that Block IIF is up and running, the Air Force will shift its focus to the next series of Block III satellites for the GPS-3 constellation. Block III satellites will continue to improve the accuracy and reliability of GPS navigation and will have upgraded anti-jamming and security capabilities for military signals.

Maintaining an up-to-date fully functioning GPS is pertinent to national security. For these reasons, selecting a company to launch these assets is an important decision. There’s been some controversy recently over which company (ULA or SpaceX) should launch the Air Force’s next block of satellites. The decision has not yet been made.

The first GPS 3 satellites are scheduled to be launched in 2018.