Waterside view of Delta 4 GPS 2F-6 Launch

The covert follow-on satellite program that will serve as a replacement to the nation’s surveillance “eyes” from space begins launching in 2018 from Vandenberg Air Force Base in California.

United Launch Alliance is set to retire part of its rocket family Thursday with the final flight of the Delta 4 rocket’s “single stick” configuration, a mission set for liftoff from Cape Canaveral carrying a new GPS navigation satellite into orbit for the U.S. Air Force.

A United Launch Alliance Delta 4-Heavy rocket climbed into space Sunday with NASA’s Parker Solar Probe on a daring mission to explore the atmosphere of the sun. Liftoff from Cape Canaveral occurred at 3:31 a.m. EDT (0731 GMT).