The satellites are scheduled to lift off aboard a two-stage Falcon 9 rocket from Vandenberg Air Force Base on the California coast on Sunday at 9:16 a.m. EST (1416 GMT; 6:16 a.m. local California time). Watch the launch live here at Space.com, courtesy of SpaceX, or directly via SpaceX's website.
This Falcon 9's first stage has flown once before, helping loft a Taiwanese Earth-observing satellite in August 2017. The first stage landed on one of SpaceX's "drone ships" in the ocean on that occasion, but no such landing will be attempted Sunday, SpaceX representatives said.
The main purpose of Sunday's launch is getting the Paz satellite to orbit for Spanish operator Hisdesat. Paz will generate sharp radar imagery of Earth for a variety of customers, including the Spanish government, over the course of the satellite's 5.5-year mission.
The two prototype satellite-internet craft will be riding along as secondary payloads, according to documents SpaceX has filed with the Federal Communications Commission. (SpaceX has not commented publicly about the inclusion of these two prototypes, known as Microsat-2a and Microsat-2b, on Sunday's flight.)