The second Boeing X-37B orbital test vehicle (OTV-2) launched into space on 5 March, riding atop a United Launch Alliance Atlas V rocket from space launch complex-41 in Cape Canaveral, Florida.
The flight is a follow-up to the 270-day mission of the OTV-1 that ended on 3 December, with the spacecraft de-orbiting and landing at Vandenberg AFB, California.
US Air Force officials have declined to answer questions about whether any payloads have intended to be tested or deployed with either OTV-1 or OTV-2.
Instead, the USAF has confirmed both spacecraft are being used to understand the flight characteristics of the X-37B. A statement released after the launch of OTV-2 adds the spacecraft will be tested for landing in higher winds after it de-orbits in several months.
"We'll also be looking at the performance of its advanced thermal protection systems and tiles, solar power systems and environmental modelling," LtCol Troy Giese, X-37B program manager, says in a statement.
The X-37B launches come under the rapid capabilities office, and are officially described as aimed at demonstrating a reusable, unmanned testbed for orbital missions.
The latest mission will enable enable the capabilities office to "further experiment with the vehicle and its ability to operate in low-Earth orbit," says Craig Cooning, vice president and general manager of Boeing space and intelligence systems.
The latest mission involved launching from the Atlas 501 rocket configuration, which includes a 5.1m-diameter payload fairing. The RD AMROSS RD-180 engine served as the booster, with the Centaur upper stage bowered by the Pratt & Whitney RL-10A engine.