A U.S. military space plane landed in California on Friday, after spending almost two years in orbit conducting secret on-orbit experiments.
The unmanned aircraft, called the X-37B Orbital Test Vehicle mission 3, or OTV-3, landed at the Vandenberg Air Force Base, located 9.2 miles northwest of Lompoc, California, at 9:24 a.m. PDT (12:24 a.m. EDT).
The plane returned to Earth after spending approximately 674 days in space during its secret mission, extending the total number of days spent on-orbit for the OTV program to 1367 days, according to a statement from the Vandenberg Air Force Base.
"The X-37B is the newest and most advanced re-entry spacecraft," the Air Force said in the statement. "Managed by the Air Force Rapid Capabilities Office, the X-37B program performs risk reduction, experimentation and concept of operations development for reusable space vehicle technologies."
The X-37B spacecraft is a miniaturized version of the space shuttle, according to air base. They said that the spacecraft launched from Cape Canaveral on December 11, 2012, aboard an Atlas V rocket.
The spacecraft carried along with it some avionics equipment, fuel, and a mysterious cavity around the size of a truck bed. People expected that this cavity might contain some sensors, experiments, hardware, or some bacterial colonies or a bomb.
The U.S. Air Force hasn't specified the purpose why this unmanned spacecraft was sent into space. Some people think that the spacecraft is an orbital weapons platform intended to take out satellites.
"The mission is our longest to date and we're pleased with the incremental progress we've seen in our testing of the reusable space plane," said the program manager of the mission in a statement. "The dedication and hard work by the entire team has made us extremely proud."
Colonel Keith Balts, 30th Space Wing commander, said that the 30th Space Wing and their mission partners have worked hard to make preparations for safe landing of the spacecraft, according to the Vandenberg Air Force Base.
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