United Launch Alliance (ULA) has launched its Atlas V rocket as part of a clandestine mission being carried out by the fledgling US space force.
The rocket carrying a X-37B space plane lifted off from the Cape Canaveral Air Force Station, in Florida, on Sunday, one day after bad weather scuppered initial launch plans.
The space plane, also known as an Orbital Test Vehicle (OTV), will deploy a small satellite into orbit and test power-beaming technology, among carrying out other experiments.
"This X-37B mission will host more experiments than any other prior missions," Secretary of the Air Force Barbara Barrett said earlier this month.
Sunday's liftoff marks the beginning of a sixth mission for the ULA vehicle. On its last flight, which ended in October 2019, the craft spent 780 days in Earth's orbit.
The length of the current mission is unclear.
The latest venture was meanwhile dedicated to front line workers battling the coronavirus pandemic and those affected by it.
A message including the words "America Strong" was emblazoned on a banner placed in the vicinity of the rocket as it took off.
"We were honored to partner with the US Space Force to dedicate this mission to first responders, front-line workers, and those affected by Covid-19," Gary Wentz, vice president of government and commercial programmes at ULA, said in a statement.
"It is truly a unique time in our history and I want to thank the entire team for their continued dedication and focus on mission success," he added.
The Space Force officially became a new branch of the US military in December, and has been described by President Donald Trump as "separate but equal" to the Air Force.
The newly-established force launched its first national security satellite in March.
The other US military branches are the Army, Navy, Coast Guard and Marine Corps.
