A mysterious blank space carpenter’s plane manoeuver by the US Air Force has passed its600th dayin orbit – but we ’re still not any wiser on what it ’s actually doing up there .

The   Boeing X-37B distance plane , also called the Orbital Test Vehicle ( OTV ) , was launched on May 20 , 2015 , from Cape Canaveral in Florida . This is the fourth mission in the program , and the second for this fomite . The previous longest missionary station in the program hold up 675 day , from December 11 , 2012 , to October 17 , 2014 .

Despite the programme ’s spaceflight spending almost 2,000 day in orbit in totality , the purpose of the space carpenter’s plane remains mystifying . The X-37B is a belittled vehicle , measuring 8.8 meters ( 29 foot long ) , about four time smaller than the Space Shuttle . Like the Shuttle , it also has a shipment bay , which can use a robotic arm .

The plane set in motion vertically on a rocket and lands horizontally back on a rails . It ’s also solar - powered , which is how it has been able-bodied to stay in orbit for so long , travel at 28,000 kilometer per hour ( 17,500 miles per hour ) .

We do screw some of the loading these space vehicle have carried into orbit . On this launching , there is known to be a NASAmaterials science experimentand an ion thruster . But the overall finish of the infinite plane is n’t clear .

One theory is that the plane is testing thrusters in a relatively low domain ( about 320 kilometers/200 miles ) , with a view to place reconnaissance satellite here in the hereafter to get higher resolve effigy of the ground . Or it may already be perform   reconnaissance mission .

harmonise to the US Air Force’swebsite , the “ principal objectives of the X-37B are twofold : reusable spacecraft technology for America ’s time to come in space and operating experiments which can be returned to , and prove , on Earth . ” But many think it may dish another purpose , too .

At any rate , it ’s middling cool that there is a working space planer in orbit . Even if we may never know what it ’s really up to .