The precise details of these experiments are closely guarded. In the Air Force statement, only the program "re-usable spacecraft technologies for risk reduction, trial and operation development concepts," he revealed.
This is the fifth X-37B spacecraft launched into orbit over the last decade, and each flight is longer than the previous one.
"Our team is getting ready for this event and I am proud of the hard work and dedication that today's safe and successful landings have resulted in the landing of the X-37B." General Doug Schiess said in a statement Sunday.
Each mission was highly confidential, leading to speculation that the public could be used for espionage activities or testing space weapons.
Here's what we know about the X-37B: The boat is designed to test a new navigation system, as well as to test the Earth's atmosphere and methods for safe reconstruction.
The X-37B spacecraft is about 29 feet (8.8 meters) long and 9.5 feet (2.9 meters) high with a wing opening of about 15 feet (4.5 meters).
Airplanes also have a unique design. They rushed into orbit on powerful rockets and left to fulfill their mission. When they return to Earth, they are horizontally contacted on a runway, such as a commercial aircraft or space shuttle orbit that comes for landing.
The new landing plane was launched into space on a SpaceX Falcon 9 rocket in September 2017. In a Sunday press release, the Air Force announced its readiness to launch its sixth X-37B mission in 2020.