Blastoff was expected just after 8:30 a.m. ET, Saturday, but instead, a live video feed suggests the next window for the rocket to get off the ground won't be reached until closer to 10:30. On May 17, 2020, at 13:14 GMT, the unmanned, autonomous spacecraft lifted off from Space Launch Complex 41 at Cape Canaveral Air Force Station in Florida atop a specially modified Atlas V 501 rocket.
It is the plane's sixth mission in space.
The Air Force, which own two X-37B vehicles, has historically been reticent to comment on the capabilities of the X-37B and what it does during its extended time in space, aside from hosting scientific experiments.
The X-37B runs various missions for the USA, though its specific aims are actually classified.
The launch was held following protocols because of tight restrictions on access to the Air Force station because of the COVID-19 pandemic. However, a senior vice president for X-37B developer Boeing, Jim Chilton, noted that each mission for the craft has been progressively longer.
The most recent mission ended in October 2019, after 780 days in orbit, bringing the X-37B programme's time in space to more than seven years. "We have to stop the live broadcast early so we don't provide adversaries too much data about the flight".
This was the 84th flight of the Atlas 5 since it entered service in 2002.
The Air Force said OTV 6 will carry more experiments than any of the previous X-37B missions.
One of the experiments will test the effect of radiation on seeds and other materials, according to AFP. However, the livestream cut out afterwards due to the extreme secrecy surrounding the capabilities of the X-37B, said ULA chief executive officer Tory Bruno.
Another experiment from the U.S. Naval Research Laboratory will transform solar power into radio frequency microwave energy, with the goal of transmitting that energy to the ground.
In its five flights the X-37B spent 2,865 days on orbit.
When the X-37B completes its mission, it autonomously cruises back to Earth and lands on a runway.