WASHINGTON —A United Launch Alliance Delta 4 rocket carrying twin space surveillance satellites for the U.S. Air Force lifted off early this morning from Cape Canaveral Air Force Station in Florida.

The mission, known as AFSPC-6, short for Air Force Space Command-6, launched around 12:52 a.m. local time and included the third and fourth satellites in the Geosynchronous Space Situational Awareness Program, also known as GSSAP. The Air Force has said those satellites provide a kind of “neighborhood watch” for the geosynchronous belt, home to some of the Defense Department’s most exquisite and expensive satellites.

The launch went into a news blackout several minutes after liftoff.

“The first two GSSAP satellites have performed remarkably well,” Lt. Gen. Samuel Greaves, commander of the Air Force’s Space and Missile Systems Center, said in an Aug. 18 press release. “These next two satellites will add to that capability and enable us to understand more completely things what occurs in the geosynchronous orbit to a very high quality. It’s a key piece in the puzzle for space situational awareness.”

According to an Air Force fact sheet from 2015, the satellites operate in a “near-geosynchronous orbit regime” to provide accurate tracking and characterization of man-made orbiting objects. The satellites also will perform rendezvous and proximity maneuvers to allow close-up looks at nearby spacecraft. Data from the system will help with satellite collision avoidance, the fact sheet said.

More recently, on Aug. 18, the Air Force said GSSAP also can provide the location, orbit and size of satellites and space objects.

Last year, Gen. John Hyten, the head of Air Force Space Command, said that the Defense Department had used the satellites to capture “truly eye-watering” images for unspecified users while they were in test mode. The Air Force declared the program operational in October 2015.

Orbital ATK of Dulles, Virginia is the prime contractor on the program, which is thought to have a $700 million price tag.

It is unclear if these are the final satellites in GSSAP constellation.  When asked by SpaceNews if there may be more than four GSSAP satellites in the constellation, an Air Force Space Command spokeswoman said “there are no details available for constellation sizing.”