USA-299, also referred to as USSF-7 and Orbital Test Vehicle 6 (OTV-6), is the third flight of the first Boeing X-37B, an American unmanned vertical-takeoff, horizontal-landing spaceplane. It was launched to low Earth orbit aboard an Atlas V launch vehicle from SLC-41 on 17 May 2020. Its mission designation is part of the USA series.

The spaceplane is operated by the Department of the Air Force Rapid Capabilities Office^[2] and United States Space Force, which considers the mission classified and as such has not revealed the objectives. However an unclassified secondary satellite, FalconSat-8, was deployed from the X-37B soon after launch.^[3]

OTV-6 is the third mission for the first X-37B built, and the sixth X-37B mission overall. It flew on an Atlas V in the 501 configuration, and launched from Cape Canaveral Space Launch Complex 41.^[4] This flight is the first time the space plane has been equipped with a service module to carry additional pieces for experiments.

OTV-6 was deployed into an orbit with an inclination of approximately 44.60°.^[5]

OTV-6 landed after a record-breaking 908 days at the Shuttle Landing Facility on November 12, 2022.^[6]

A rideshare payload for the United States Air Force Academy, FalconSat-8, was deployed from the X-37B a few days into the mission. The satellite provides a platform for the academy's Cadet Space Operations Squadron to test various technologies.

Onboard experiments include:

• MEP (Magnetic gradient Electrostatic Plasma thruster), a novel electromagnetic propulsion system
• MMA (Metamaterial antenna), a low power, high performance antenna
• CANOE (CArbon NanOtubes Experiment)
• ACES (Attitude Control and Energy Storage), a commercial reaction wheel modified into a flywheel
• SkyPad, off-the-shelf cameras and GPUs integrated into a low power package

• USA-212
• USA-226