X-37B
The X37-B space plane is the closest American counterpart to China's proposed projectU.S. Air Force courtesy photo

There are only a handful of secret missions launched in recent years that no one seems to know anything about. There was a launch in January by SpaceX, which was officially "lost", but that was a spy satellite, one might never get to know what really happened. The US Air Force's(USAF) X-37B is one such mission.

All that is known about this mission is that it is a drone that flies at the edge of space and stays in orbit for months. What it does up there, where it's flying, its payload and other details are shrouded in mystery. The only time it comes to the public eye is when it lands and takes off. The fifth and now ongoing mission is reported to have approached a new milestone that three out of four of its predecessors have successfully met and even exceeded the benchmark of staying one year in continuous orbit, reports SpaceflightInsider.

USAF operates this secretive spacecraft/drone — also called the Orbital Test Vehicle (OTV). The craft vehicle itself looks like the Space Shuttle, albeit, a shrunken down minature version. This mission was launched atop a SpaceX Falcon 9 rocket in September last year.

Falcon 9 launch
The OTV 5 launch by SpaceX from the Kennedy Space Center- Spetember 2017. The booster core was also landed successfully after launchSpaceX

The mission, OTV-5, was launched around the time when hurricane Irma was raging and thought to be the right time to launch in a small window of opportunity, notes the report. Irma, later went on to cause some minor damage to the Kennedy Space Center's launch complex.

Little information about the mission has actually been made public. One part of the X-37B's payload is reported to be the Advanced Structurally Embedded Thermal Spreader's (ASETS-II) upgraded, second version. It has hardware designed for thermal management system tests which are optimised for the environment in space. It was reportedly developed under the vigil of the Air Force Research Laboratory (AFRL).

The OTV-5 mission also carried a number of small satellites into orbit, notes the report. Finer details are kept secret but it is not always under wraps as there are several amateur astronomers and star gazers who frequently catch the drone in flight. People seem to know where the X-37B is but no one knows what it is doing up there. Falcon9 deposited the drone at an altitude of about 354 km, inclined 54.5 degrees to the equator.