The launch out of Cape Canaveral Air Force Station marked the sixth flight for the solar-powered X-37B craft - which is flown by remote control without a crew. But it could be a while before the X-37 descends from orbit to end its mission with a runway landing. The last mission that took place in 2010, lasted for two years.
The X-37B is 29 feet long (nine meters), with a wing span of 15 feet (4.5 meters).
"America Strong" is the tagline for this mission, with Space Force and ULA emblazoning it on the side of the Atlas V rocket along with the message: "In memory of COVID-19 victims and tribute to all first responders and front-line workers".
The winged spacecraft, also called the Orbital Test Vehicle, resembles NASA's old shuttles, but is considerably smaller at 8.8 metres long. The aircraft that was launched on Sunday - Operational Test Vehicle 6 - carries several USA military and NASA science experiments.
The newly-established Space Force blasted a secretive space plane into orbit from Florida Sunday for a mystery military mission.
The Air Force has two of these reusable space planes.
The drone, which resembles a smaller version of the manned space shuttles retired by the U.S. space program in 2011, was launched from Cape Canaveral in Florida, the Air Force said.
Saturday's launch was the second-ever by the U.S. Space Force and the 80th under the National Security Space Launch effort.
United Launch Alliance dedicated Sunday's launch to the health care workers and others who are working on the front lines of the pandemic. Plans have been made for a 24-hour turnaround, with a new T-zero of 9:14 am EDT; this means that the SpaceX Starlink-7 mission, scheduled of early morning May 17, will now shift to the right on the calendar as well. OTV-5 broke the record for the most time the spaceplane has spent in space at 780 days. Space Force's new recruiting video unveiled May 6 by Air Force Secretary Barbara Barrett.