US Air Force's secretive X-37B plane returns to earth after 718 days – what was it doing up there?

Washington: Central Floridians woke up to the sounds of a sonic boom when US Air Force`s secretive X-37B aircraft returned to Earth after being in the space non-stop for 718 days.

The touchdown of the Orbital Test Vehicle mission 4 (OTV-4) at the Kennedy Space Center has added to the mystery that has surrounded the X-37B programme ever since the launch of the aircraft in 1999. While OTV-1 spent 224 days in space the subsequent mission OTV-2 and OTV-3 operated for 468 days and 675 days respectively.

OTV-4 was the fourth and longest-running mission run by the US Air Force`s Rapid Capabilities Office. The programme began as a NASA project but was later transferred to the Pentagon.

The US Air Force has two X-37B planes built by Boeing and they are deceptively very small in size, at least when compared to a space shuttle.

This X-37Bs also lift off vertically as a space shuttle and glide back to the earth in a planned sequence, just like other space shuttles made by NASA.

Though the unmanned X-37Bs measure just 9 feet 6 inches in height and are 29 feet 3 inches long, the aircraft carries a phenomenal level of awe on its wings.

The US Air Force has been very secretive about what exactly are the mission for which X-37B spends these long periods of time in the space.

The payload that is carried by plane has been the biggest mystery of all. A report in airspacemag.com says that before the launch of OTV-4 in 2015, the Air Force had, for the first time, revealed two of the payloads: a NASA materials science experiment and an ionizing thruster being tested for the Air Force.

Though the announcement did give some understanding about the hush-hush project, there is no official word forthcoming – expectedly – on what the aircraft was up to when it flew around us in a near-Earth orbit for close to two years. The US Air Force insists that the aircraft is being used to conduct “experiments” but what sort of experiments remains a mystery.

So, here's a look at all the theories doing the rounds.

Sensors and Surveillance

The most believable inference that has been drawn by experts is that X-37B was deployed to conduct tests and experiment on advanced surveillance sensors. Given the low orbit, it flies in, the spacecraft can be quickly the spacecraft can be quickly manoeuvred to any precise location, faster than satellites, and start beaming live visuals to the bosses in Pentagon!

“The smart money is on advanced surveillance sensors. The Air Force has never mentioned them directly, but everyone seems confident that they’re flying,” the airspacemag.com writes in an article.

Space bombing

Conspiracy X-37B may have the capabilities to drop bombs from outer space or shoot down/interfere with other satellites to cripple the enemy in the event of a war. However, other reports, like one by Popular Mechanics, have rejected the idea on the basis of the fact that changing an aircraft's orbital plane requires a great amount of thrust and that will in turn increase fuel consumption and reduce the range of the aircraft.

Spy satellites and spying on China's space station Tiangong-1

With the NASA working on several projects to reduce the size of satellites and yet maintain the same level of operational efficiency, some theories have claimed that X-37B may be sending out small reconnaissance satellites to place them as 'American spies' in the space.

Some other reports had claimed in 2015 that the X-37B was aimed at keeping track of China's Tiangong-1 space station from close quarters. However, owing to their different trajectories around the globe, that report was junked by experts as impossible.

Whatever may be X-37B's mission in the space, the entire programme has triggered fears that it may the start of the weaponization of space.

Watch video:

The #X37B #OTV4 is the newest and most advanced re-entry spacecraft. Find out more about today's landing here: https://t.co/GUGgOMQiYg pic.twitter.com/HfHHVnWhYc — U.S. Air Force (@usairforce) May 7, 2017

Land, air and sea – and now space!