The Air Force's experimental X-37B space plane announced the end of its nearly two-year mission by creating a sonic boom on Sunday that surprised residents along Florida's Space Coast. Officials have provided only vague details about the unmanned craft's more than 700-day mission.
"Not much is known about the 30-foot-long robotic spacecraft or what it took to space," as member station WMFE reports.
The X-37B is an "orbital test vehicle" that looks like a miniature space shuttle — it even used the old shuttle runway at NASA's Kennedy Space Center when it landed Sunday. To reach orbit, it rides on an Atlas V rocket.
This was the fourth mission for the reusable vehicle, and the first time it has landed in Florida. Earlier trips have ended at the Vandenberg Air Force Base in California.
Sunday's landing sparked a flurry of tweets and questions about the sonic boom, with The Orlando Sentinel reporting that before the landing, officials had refused to confirm rumors of a pending return to Florida. The Air Force announced the landing in a tweet — after it had occurred. By then, windows had been rattled and residents had been startled.
"But it wasn't just Central Floridians who heard the spacecraft," the paper says. "Reports came from as far away as Tampa and Fort Myers."
Confirmation of the landing was met with relief in at least one household, as a resident tweeted, "CENTRAL FLORIDA HAD A SONIC BOOM IM NOT CRAZY."
The space plane has been the object of frequent speculation about its potential military uses, particularly in either surveillance or some type of combat application, as NPR's Scott Neuman reported in a roundup of theories about the craft in 2014.
The Air Force says that the program includes the testing of many technologies, from guidance and control (Sunday's landing was autonomous) to thermal protection and advanced propulsion systems. The craft is powered by gallium arsenide solar cells with lithium-ion batteries.
As WMFE's Brendan Byrne writes:
"The space plane's development began in 1999. NASA wanted to use the vehicle to repair satellites in orbit. When that proved to be too costly, the Department of Defense picked up the project as a part of its Defense Advanced Research Projects Agency (DARPA). In 2006, the Air Force announced it would develop what is now the X-37B, and launched the experimental space plane for the first time in 2010."
The craft is managed by the Air Force Rapid Capabilities Office, which describes its mission as developing "combat support and weapon systems by leveraging defense-wide technology development efforts and existing operational capabilities."
The Air Force's public information about the craft focuses on its role in researching reusable space vehicles and establishing a "space test platform for the United States Air Force."
Military space programs "are as big as NASA," astrophysicist and astronomer Jonathan McDowell told NPR's Here and Now in 2015, when the X-37B left for its most recent mission.
At the time, McDowell said there are around 20 to 25 "full-fledged spy satellites or other really secret vehicles" that orbit Earth.
The concept of militarizing space is one that's still developing, McDowell said, noting the distinction between the use of satellites solely to support on-ground operations and their use to snoop on, and even interfere with, other satellites.
Civilian satellite spotters are able to track the more than 5-ton X-37B as it orbits Earth. Fueling theories that it aids surveillance programs, trackers found that at least one earlier mission followed an orbit that took it over countries that included Iran, Afghanistan and Pakistan.