The Air Force’s super secret and mysterious X-37B space plane has passed a milestone reaching 600 days in Earth orbit on its latest mission. The unmanned X-37B lifted off on an Atlas V rocket from Cape Canaveral Air Force Station in Florida on May 20, 2015 on its fourth mission known as Orbital Test Vehicle-4 (OTV-4).

Watch the X-37B land

If the uncrewed spacecraft spends 74 more days aloft, it will break the duration record set during OTV-3, which touched down in October 2014.

The military space plane looks like a miniature version of NASA’s retired space shuttle orbiter. The X-37B is just 29 feet (8.8 meters) long and 9.6 feet (2.9 m) tall, and has a wingspan of nearly 15 feet (4.6 m). For comparison, the space shuttles were each 122 feet (37 m) long, with wingspans of 78 feet (24 m).

The X-37B has a payload bay about the size of a pickup truck bed that can be outfitted with a robotic arm. It has a launch weight of 11,000 lbs. (4,990 kilograms) and is powered in orbit by gallium arsenide solar cells with lithium-ion batteries. – Space.com

All three of the previous OTV missions have landed at Edwards Air Force Base in California but there are reports this flight may attempt a landing in Florida. The planned duration of OTV-4 or details of what the spaceplane is doing on this mission have not been released to the public.

Featured Image of the X-37B Courtesy of Boeing and the US Air Force