Although the X-37′s operations in orbit are classified, at least two of its payloads were confirmed to be an experimental electric propulsion engine and a materials exposure pallet.
The spaceplane performed a completely autonomous landing at Kennedy Space Center’s runway 15 shortly before 8am EDT, the same runway used by the Space Shuttle program. It marked the first time one of the Orbital Test Vehicle spaceplanes landed at Kennedy Space Center.
Following brief servicing on the runway, the vehicle will be towed to one of the former Orbiter Processing Facilities next to the Vehicle Assembly building. The Air Force has converted one of the old shuttle hangars for use by the OTV program to house their spaceplanes.
Measuring 29 feet long with a wingspan of 15 feet, the X-37B is a robotic spaceplane with a payload bay ideal for small payloads. While the specific milestones for this flight were classified, at least two of the experiments included the testing of an electric engine and materials exposure pallets.
The first three flights of the OTV program landed at Vandenberg Air Force Base in California, though OTV-4 became the first to land in Florida. By landing at the same spaceport which it left from, OTV operations are expected to streamline and potentially allow for faster times in between missions. One of Kennedy’s three Orbiter Processing Facilities is used by the Air Force to house the two X-37 spaceplanes in between missions.
As seen in the gifs above - taken from video of the vehicle’s landing - the spaceplane glides past a model of another famous space plane, the Space Shuttle. The Inspiration, which once sat outside the U.S. Astronaut Hall of Fame in Titusville, was moved to the SLF for restoration ahead of a nationwide tour promoting aerospace science and STEM fields.