The U.S. Air Force's secret X-37B spaceplane on March 25 broke the world space endurance record by a spaceplane.

The X-37B, whose current mission is identified as OTV-4, exceeded the current record of 674 days in orbit to reach 675 days on March 25. The former record for the longest time spent orbiting the Earth by a spaceplane capable of a return flight was set by the OTV-3 mission.

Like Us on Facebook

OTV-4 blasted-off from Cape Canaveral Air Force Station in Florida on May 20, 2015 aboard a United Launch Alliance Atlas V rocket. As with the previous three OTV missions, the Air Force remained tight-lipped about the true purpose of the OTV-4 mission. Speculation abounds, however.

The previous X-37B record of 674 days in space was set by OTV-3, which launched from Cape Canaveral Air Force Station on December 12, 2012 and landed at Vandenberg Air Force Base on October 17, 2014. The X-37B was originally designed for orbital missions lasting 270 days.

The U.S. Air Force left open the possibility of landing the X-37B on the space shuttle landing strip at Kennedy Space Center in Florida.

There are persistent reports the Air Force is testing a working version of the controversial EmDrive electromagnetic thruster aboard the OTV-4 mission.

If true, the report of an EmDrive aboard the X-37B might help explain why the spaceplane remains in orbit well past its announced mission life of 200 days.

Also called a radio frequency (RF) resonant cavity thruster, an EmDrive or Em Drive uses no reaction mass and emits no directional radiation to generate thrust. British aerospace engineer Roger Shawyer designed the EmDrive in 2001 and has promoted the idea through his company, Satellite Propulsion Research.

While the Air Force hasn't confirmed speculation an EmDrive is being tested aboard the spaceplane, what is certain is the X-37B is testing a prototype "Hall Effect Thruster" (HET) in support of the Air Force's Advanced Extremely High Frequency (AEHF) communications satellite program.

The U.S. Department of Defense said operational Hall Effect Thrusters or Hall Thrusters will propel military satellites (milsats) in Earth orbit or power future spacecraft on interplanetary voyages.

TagsU.S. Air Force, X-37B spaceplane, OTV-4, 675 days, OTV-3