Residents in Central Florida got an early wake-up call from outer space on Sunday morning, May 7. Their weekend slumber was cut short by a mysterious sonic boom, which as it turns out was caused by the X-37B mini space shuttle.

The unmanned spacecraft landed at the Kennedy Space Center in Cape Canaveral after orbiting our planet for the past two years.

The X-37B reusable space plane began its mission — the Orbital Test Vehicle mission 4 or OTV-4 — on May 20, 2015, when it was launched with an Atlas V rocket from Cape Canaveral Air Force Station.

The exact details of this mission are shrouded in mystery; suffice to say the U.S. Air Force mentioned the space shuttle was engaged in "on-orbit experiments" aiming to gather data for the scientific and space communities.

"The landing of OTV-4 marks another success for the X-37B program and the nation," said Lt. Col. Ron Fehlen, the space shuttle's program manager.

X-37B's Unexpected Booming Return

U.S. Air Force tweeted about the X-37B homecoming on Sunday morning at 7:57 a.m., posting photos and video footage of the military space plane.

The 11,000-pound mini space shuttle, measuring 29 feet in length, completed its fourth mission in orbit and safely returned to Earth, setting another space flight endurance record for this type of vehicle. This weekend's landing marks the secretive spacecraft's first arrival in Florida, after the OTV-3 landed at Vandenberg Air Force Base in California in 2014, just like the previous two missions of the X-37B. Although the space plane was rumored to land in Florida earlier this year, in February, Air Force officials hadn't confirmed the spacecraft's itinerary.

"Our team has been preparing for this event for several years, and I am extremely proud to see our hard work and dedication culminate in today's safe and successful landing of the X-37B," said Brig. Gen. Wayne Monteith, commander of the 45th Space Wing.

After the mysterious sonic boom caused by the Florida landing, people turned to social media to describe the morning's experience and find out the source of the racket. X-37B's return caused quite a commotion among residents in the vicinity of the landing site. However, Central Floridians weren't the only ones startled by the big boom, as it was reportedly heard even in Tampa and Fort Myers.

The Orbital Test Vehicle's Secret Mission

According to an official statement, the X-37B mini shuttle is "an experimental test program" designed to operate and develop "technologies for a reliable, reusable, unmanned space test platform" created for the U.S. Air Force. The purpose of the OTV is to establish renewable spacecraft technologies that can benefit America's future space explorations.

Another objective of the X-37B is to perform on-orbit experiments and gather data for scientists back home to analyze. The X-37B is the first space vehicle since NASA's Shuttle Orbiter able to bring experiments back to Earth for further examination. With the completion of its fourth mission, OTV-4, the mini space shuttle now has an additional 700+ days' worth of experimentation under its belt.

However, the military space plane was designed for an on-orbit time of at least 270 days, which means the X-37B can stay in space for much longer. This unmanned shuttle is the newest and most advanced re-entry spacecraft and was created to be launched to low altitudes in our planet's orbit, with the mission to "perform long duration space technology experimentation and testing."

The OTV-4 mission lasted for 718 days, bringing up the program's total number of days spent in space to 2,085. The X-37B's fifth mission is scheduled to launch from Cape Canaveral later this year.

Among the technologies the U.S. Air Force tested with the X-37B program are: advanced guidance, navigation and control, thermal protection systems, avionics, high temperature structures and seals, conformal reusable insulation, lightweight electromechanical flight systems, advanced propulsion systems, advanced materials and autonomous orbital flight, reentry and landing.

"The hard work of the X-37B OTV team and the 45th Space Wing successfully demonstrated the flexibility and resolve necessary to continue the nation's advancement in space," said Randy Walden, the director of the Air Force Rapid Capabilities Office, which manages the program.

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