Boeing 
 
 The intriguingly long voyage of the unmanned X-37B has come to a conclusion at last. But the mystery of the mission lingers on. 
 
 Boeing 
 
 The US Air Force space plane, one of just two X-37B vehicles in the Pentagon's inventory, landed Friday morning under the auspices of the 30th Space Wing at Vandenberg Air Force Base in California after 674 days in space -- that is, 22 months. 
 
 And that's about all that the space plane's handlers would say about the mission, aside from the terse statement that it "conducted on-orbit experiments." 
 
 "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," the Air Force said in a statement. 
 
 The Air Force also said it plans to start the next X-37B mission sometime in 2015, launching from Cape Canaveral in Florida. 
 
 Almost as remarkable as the length and the hush-hush nature of the mission is one of the signature skills of the Boeing-built X-37B -- the unmanned spacecraft flies autonomously on its return trip to Earth. 
 
 The Air Force has said precious little -- ever -- about its X-37B missions, leading to wide-ranging speculation about what the diminutive space vehicle has been up to up there, or is building toward. Theories hit on everything from terrestrial surveillance to satellite launches (or, conversely, satellite killing) to weapons platform aimed at ground targets. 
 
 Or it could be more mundane: these could simply be shakedown cruises to see how a space plane, one with no human aboard, fares on extended junkets into orbit and back. It can't be easy to work all the kinks out of the algorithms that enable a space plane to maneuver in orbit, and in re-entry and landing, without a human at the controls. 
 
 The boilerplate description on the Air Force's fact sheet is not exactly illuminating: "The primary objectives of the X-37B are twofold: reusable spacecraft technologies for America's future in space and operating experiments which can be returned to, and examined, on Earth." 
 
 Measuring 29 feet long, with a wingspan of less than 15 feet and a cargo bay equivalent to that of a pickup truck, the 11,000-pound X-37B looks like a junior version of NASA's space shuttles. That's not really a coincidence, since both trace their roots to the space agency's research into lifting-body flying machines. In fact, the X-37B program was a NASA project until 2004, before it was shifted first to the Defense Advanced Research Projects Agency and then on to the Air Force. 
 
 This was the third spaceflight of an X-37B, also known as the Orbital Test Vehicle, since missions began five years ago. The first, which ended in December 2010, lasted 224 days, and the second, which ended in June 2012, endured for 469 days, or a year and four months. 
 
 This latest mission began December 11, 2012, when an Atlas V rocket carrying the space plane lifted off from the Cape Canaveral Air Force Station in Florida. 
 
 There are two OTV craft in the X-37B fleet. The one that flew on the just-ended mission is OTV-1, which also carried out the first of the flights to date. Confusingly the numbers in the the OT-x designations seem to be used loosely both for the spacecraft (-1 and -2) and for the missions (-1, -2, and now -3). 
 
 NASA last week said it has entered into an agreement with the Air Force's X-37B program for use of the Kennedy Space Center's Orbiter Processing Facility (OPF) Bays 1 and 2 -- former space shuttle hangars -- to process the X-37B for launch. Boeing is performing construction upgrades in those facilities that are targeted to be complete in December. 
 
 But the flights of the X-37B -- however many eventually take place -- could just be the groundwork for the next generation of space plane. 
 
 In July, DARPA took a first step back into the game, announcing the start of design work toward the XS-1, which also would be a reusable unmanned vehicle for "aircraft-like access to space." The agency didn't mind mentioning potential payloads: "XS-1 seeks to deploy small satellites faster and more affordably, and develop technology for next-generation hypersonic vehicles." 
 
 It's probably not too much of a surprise that Boeing is in the mix, winning a $4 million preliminary design contract for its concept of the XS-1. (Teamed with Boeing is Blue Origin, the spacecraft-minded company owned by Amazon CEO Jeff Bezos.) The other two Phase 1 contracts went to Northrop Grumman (working with Virgin Galactic) and to Masten Space Systems (working with XCOR Aerospace). 
 
 Late on Friday, Boeing declared its own cheery but unrevealing sentiments ("the X-37B program performs risk reduction, experimentation and concept of operations development for reusable space vehicle technologies") about the return of the X-37B. 
 
 "We congratulate the Air Force Rapid Capabilities Office and the 30th Space Wing at Vandenberg Air Force Base on this third successful OTV mission," said Ken Torok, Boeing director of Experimental Systems. "With a program total of 1,367 days on orbit over three missions, these agile and powerful small space vehicles have completed more days on orbit than all 135 Space Shuttle missions combined, which total 1,334 days." 
 
 Update October 18 at 7:38 a.m. PT: Added photos, along with comment from Boeing. 
 
 Boeing ||||| CAPE CANAVERAL, Fla. (Reuters) - The U.S. military’s experimental X-37B space plane landed on Sunday at NASA’s Kennedy Space Center in Florida, completing a classified mission that lasted nearly two years, the Air Force said. 
 
 The unmanned X-37B, which resembles a miniature space shuttle, touched down at 7:47 a.m. EDT (1147 GMT) on a runway formerly used for landings of the now-mothballed space shuttles, the Air Force said in an email. 
 
 
 
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 The Boeing-built space plane blasted off in May 2015 from nearby Cape Canaveral Air Force Station aboard an Atlas 5 rocket built by United Launch Alliance, a partnership between Lockheed Martin Corp (LMT.N) and Boeing Co (BA.N). 
 
 The X-37B, one of two in the Air Force fleet, conducted unspecified experiments for more than 700 days while in orbit. It was the fourth and lengthiest mission so far for the secretive program, managed by the Air Force Rapid Capabilities Office. 
 
 The orbiters “perform risk reduction, experimentation and concept-of-operations development for reusable space vehicle technologies,” the Air Force has said without providing details. The cost of the program is also classified. 
 
 The Secure World Foundation, a nonprofit group promoting the peaceful exploration of space, says the secrecy surrounding the X-37B suggests the presence of intelligence-related hardware being tested or evaluated aboard the craft. 
 
 The vehicles are 29 feet (9 meters) long and have a wingspan of 15 feet, making them about one quarter of the size of the National Aeronautics and Space Administration’s now-retired space shuttles. 
 
 Slideshow (4 Images) 
 
 The X-37B, also known as Orbital Test Vehicle, or OTV, first flew in April 2010 and returned after eight months. A second mission launched in March 2011 and lasted 15 months, while a third took flight in December 2012 and returned after 22 months. 
 
 Sunday’s landing was the X-37B’s first in Florida. The three previous landings took place at Vandenberg Air Force Base in California. The Air Force relocated the program in 2014, taking over two of NASA’s former shuttle-processing hangars. 
 
 The Air Force intends to launch the fifth X-37B mission from Cape Canaveral Air Force Station, located just south of the Kennedy Space Center, later this year. ||||| The record-shattering mission of the U.S. Air Force's robotic X-37B space plane is finally over. 
 
 After circling Earth for an unprecedented 718 days, the X-37B touched down Sunday (May 7) at the Shuttle Landing Facility at NASA's Kennedy Space Center in Florida — the first landing at the SLF since the final space shuttle mission came back to Earth in July 2011. The landing occurred at 7:47 a.m. EDT (1147 GMT). 
 
 "Today marks an incredibly exciting day for the 45th Space Wing as we continue to break barriers," Air Force Brig. Gen. Wayne Monteith, the 45th SW commander, said in a statement. "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." [The Mysterious X-37B Space Plane: 6 Surprising Facts] 
 
 The U.S. Air Force's X-37B Orbital Test Vehicle mission 4 (OTV-4) is seen after landing at the Shuttle Landing Facility of NASA's Kennedy Space Center in Cape Canaveral, Florida on May 7, 2017. The unpiloted space plane spent a record 718 days in space during its classified mission. Credit: U.S. Air Force 
 
 The just-ended mission, known as OTV-4 (Orbital Test Vehicle-4), was the fourth for the X-37B program. All four launched from Florida's Cape Canaveral Air Force Station, and the first three landed at Vandenberg Air Force Base in California. But Air Force officials have said they want to consolidate X-37B launch and touchdown operations on Florida's Space Coast, so today's landing might be the first of many at the SLF. 
 
 "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," Randy Walden, the director of the Air Force Rapid Capabilities Office, said in the same statement. "The ability to land, refurbish, and launch from the same location further enhances the OTV's ability to rapidly integrate and qualify new space technologies." 
 
 The Air Force is known to possess two X-37B space plane vehicles, both of which were built by Boeing. The 29-foot-long (8.8 meters) X-37B looks like NASA's now-retired space shuttle orbiter, only much smaller; indeed, two X-37Bs could fit inside a space shuttle's cavernous payload bay. 
 
 The X-37B launches vertically and comes back to Earth horizontally for a runway landing, as the space shuttle did. 
 
 Most of the X-37B's payloads and activities are classified, leading to some speculation that the space plane could be a weapon of some sort, perhaps a disabler of enemy satellites. But Air Force officials have always strongly refuted that notion, stressing that the vehicle is simply testing technologies on orbit. [The X-37B's Fourth Mystery Mission in Photos] 
 
 Technicians in protective gear work on the U.S. Air Force's X-37B Orbital Test Vehicle after its successful landing at NASA's Kennedy Space Center Shuttle Landing Facility in Cape Canaveral, Florida on May 7, 2017. NASA's massive Vehicle Assembly Building is visible in the distance at top right. Credit: U.S. Air Force 
 
 
 
 Space weapon tests: It's a secret project to make war in space. 
 
 Space surveillance: It's the world's best spysat platform. 
 
 Space tech tests: The U.S. military is pushing the robotic spaceflight frontier. 
 
 Peaceful uses in space: The X-37B is quiet because it's a robot and doesn't talk. 
 
 
 
 "Technologies being tested in the program include advanced guidance, navigation and control; thermal-protection systems; avionics; high-temperature structures and seals; conformal, reusable insulation, lightweight electromechanical flight systems; and autonomous orbital flight, re-entry and landing," Capt. AnnMarie Annicelli, an Air Force spokeswoman, told Space.com via email in March. 
 
 "Also, the Air Force Research Laboratory (AFRL), Space and Missile Systems Center (SMC), and the Air Force Rapid Capabilities Office (AFRCO) are investigating an experimental propulsion system," she said. 
 
 Outside experts generally agree with the Air Force's claims, saying it's unlikely that the X-37B is doing anything aggressive or nefarious on orbit. Some observers have suggested that, in addition to the roles cited by Annicelli, the vehicle may be testing sensors for the National Reconnaissance Office, which operates the United States' fleet of spy satellites. 
 
 Each X-37B flight has been longer than the last. OTV-1 lifted off on April 22, 2010, and spent 224 days in space; OTV-2 launched on March 5, 2011, and orbited Earth for 468 days; and OTV-3 began on Dec. 11, 2012, and lasted 674 days. (OTV-4 lifted off on May 20, 2015.) 
 
 Though OTV-4 set an X-37B program record, the mission fell far short of the overall mark for longest spaceflight mission. Some Earth-observing satellites have operated for decades, and NASA's twin Voyager 1 and Voyager 2 probes are still sending data home, nearly 40 years after their 1977 launches. 
 
 Editor's note: This story was updated Monday, May 8 to include the landing time for X-37B contributed by reporter Irene Klotz. 
 
 Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com. ||||| After a record-shattering 22 months in space, the U.S. Air Force's mysterious X-37B space plane returned to Earth on Friday (Oct .17) in a smooth landing at Vandenberg Air Force Base in California. The 674-day mission launched in December 2012, but the purpose of the top secret spaceflight has been classified. The X-37B space plane landing was completely automatic and captured in images and video. You can see those amazing images here in this Space.com gallery. 
 
 Here, the X-37B is serviced by a ground crew wearing protective suits after its successful landing on Oct. 17. The winged robotic spacecraft landed at 9:24 a.m. PDT at the Vandenberg Air Force Base to end its 22-month mission. The mission originally launched on Dec. 11, 2012. The U.S. Air Force Rapid Capabilities Office oversaw the mission, which marked the third X-37B flight since 2010. Credit: Boeing. 
 
 The X-37B space plane is also called the Orbital Test Vehicle (or OTV) in Air Force parlance, with its latest mission known as OTV-3. Here, the spacecraft swoops down toward the runway at Vandenberg during its pinpoint landing. [See more X-37B photos from the OTV-3 mission.] 
 
 The images here were provided to the Air Force by Boeing, which built the two X-37B space planes using its Phantom Works division. You can see some more amazing views of the landing here: 
 
 Another view of the X-37B space plane landing on Oct. 17 as it approaches the Vandenberg runway. Credit: Boeing 
 
 This view of the X-37B space plane landing is actually a still from an Air Force video of the landing captured on the runway at Vandenberg. The X-37B space plane that flew the OTV-3 mission was actually making its second spaceflight. The spacecraft launched on the first X-37B mission, called OTV-1. in 2010 and spent 225 days in space on that flight. This latest mission puts its time in space at 899 days. Credit: Boeing. 
 
 Another view of the X-37B space plane landing. While the X-37B may look like a version of NASA's space shuttles, the military space plane is actually much smaller. Two X-37B vehicles could fit inside the 60-foot payload bay of a NASA shuttle. Credit: Boeing. 
 
 The X-37B space plane zooms by a camera during the successful landing of the OTV-3 mission at Vandenberg Air Force Base in California. A recovery team was standing ready to receive the spacecraft after its 674-day spaceflight. Credit: Boeing. 
 
 Recovery crew members work on the X-37B space plane after the vehicle's successful landing on Oct. 17. The recovery crew is responsible for processing the X-37B vehicle to make sure the vehicle is safe to be towed back to its hangar for additional work. Credit: Boeing. 
 
 Here, the recovery crew is working on the aft of the X-37B, which houses its tail fins, rocket engine and other vital systems. The X-37B spacecraft has its own small payload (which is about the size of a pickup truck bed) and a solar array to generate power during long space missions. The black tiles and panels along its nose, wings and belly serve as a protective heat shield during re-entry. Credit: Boeing. 
 
 The scale of the X-37B space plane is clear in this view of the spacecraft as it is being serviced by a recovery crew. The spacecraft is about 29 feet (8.8 meters) long and 9.5 feet (2.9 m) tall. It has a wingspan of about 15 feet (4.6 m). Credit: Boeing. 
 
 An American flag waves over the runway landing site for the U.S. Air Force's third X-37B space plane mission as recovery crew members work to process the spacecraft after its 674-day flight in this official mission photo. Credit: Boeing. 
 
 Above, the X-37B sits on the Vandenberg runway after its smooth landing on Oct. 17. Credit: Boeing. 
 
 This last photo from Boeing gives us a departing look at the X-37B on the runway at Vandenberg Air Force Base. The landing on Oct. 17 marked the successful second flight of this particular X-37B vehicle, proving its viability as a reusable spacecraft. A second X-37B vehicle was used to fly the OTV-2 mission for the Air Force in 2011. 
 
 So far, all X-37B missions have launched from Cape Canaveral Air Force Station in Florida and landed at Vandenberg Air Force Base in California. The Air Force has been studying the potential of using NASA's former space shuttle landing site at the Kennedy Space Center for Florida landings of the X-37B spacecraft. 
 
 Email Tariq Malik at tmalik@space.com or follow him @tariqjmalik and Google+. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.
– The Air Force owns two X-37B space planes, and one of them is finally back on the ground after a nearly 2-year-long secret mission. While the what is unknown, the how long is clear: 718 days in orbit, reports Space.com, with the unmanned plane landing Sunday morning at NASA's Kennedy Space Center in Florida—and flying into the record books. It was the Air Force's fourth such mission since April 2010 and the longest to date. A fifth is planned for 2017, reports Reuters. There's plenty of speculation about what the 29-foot-long plane, which looks like a mini-space shuttle, is up to up there. Reuters cites one group's belief that the secrecy indicates intelligence-related hardware tests are being conducted. An Air Force fact sheet offers up this much: "The primary objectives of the X-37B are twofold; reusable spacecraft technologies for America’s future in space and operating experiments which can be returned to, and examined, on Earth." One cool fact: Though its mission is classified, its location isn't, thanks to what Space.com refers to as "keen-eyed amateur astronomers." The site offers a satellite tracker when missions are active, and notes the X-37B "usually looks like a star of middling brightness moving across the sky."