It looks like something out of a sci-fi film. But don't be fooled, because this aircraft is every bit as real as it looks weird.
The world's largest aircraft by wingspan has successfully completed its first flight in California, the US space transportation firm behind it says.
The plane built by Stratolaunch has two fuselages and a wingspan of 117 metres (the size of a football field). It flew for 2.5 hours over the states Mojave Desert.
"What a fantastic first flight," Stratolaunch's chief executive Jean Floyd said in a statement on Saturday.
"Today's flight furthers our mission to provide a flexible alternative to ground launched systems."
Stratolaunch was established in 2011 by late Microsoft co-founder Paul Allen. It aims to make access to orbit more affordable and accessible by launching satellites into space from aircraft, rather than from the ground.
On Saturday its aircraft took off from the Mohave Air and Space Port, about 150 kilometres north of Los Angeles. It flew at altitudes up to five kilometres and performed numerous manoeuvres including a simulated landing approach. "We all know Paul would have been proud to witness today's historic achievement. It reached speeds of up to 304km/h and an altitude of 17,000 feet, the Stratolaunch team said.
"The flight itself was smooth, which is exactly what you want the first flight to be," Evan Thomas, a test pilot with Scaled Composites, who flew the Stratolaunch, said to the New York Times.
"And for the most part, the aeroplane flew as predicted, which is again exactly what we want."
The aircraft is a remarkable engineering achievement and we congratulate everyone involved," said the late billionaire's sister Jody Allen, who is also the chair of his philanthropic trust.
According to the New York Times, the aircraft has been designed to carry rockets to blast commercial satellites into space.
"The aeroplane felt really nice on the touchdown, gear felt good," Thomas said. "We had a couple of corrections to line up in the slowdown and ended up rolling to a stop pretty much where we wanted to coming off the runway.
"So it was overall fantastic."
Microsoft, a mammoth plane, and the man behind the machine
With a wingspan stretching beyond the length of two Olympic swimming pools has undertaken its maiden flight in the US.
The six-engine Stratolaunch jet took-off from California on Saturday local time (Sunday AEST).
It is designed to carry as many as three satellite-laden rockets under its wings, which stretch about 117 meters.
Founded by the late Microsoft billionaire Paul Allen, Stratolaunch is vying to be a contender in the market for air-launching small satellites.
"We all know Paul would have been proud to witness today's historic achievement," Chair of Vulcan Inc. and Trustee of the Paul G. Allen Trust, Jody Allen said.
"The aircraft is a remarkable engineering achievement and we congratulate everyone involved."
Stratolaunch aircraft first emerged from its Mojave hangar in 2017 and underwent ground tests, including taxiing and rolling down a runway at near-takeoff speeds.
The jet is powered by the same type of engines used by Boeing 747s and is designed to take off at a maximum weight 589,676 kilograms.
It features twin fuselages — sort of the aeroplane equivalent of a catamaran — that span 72.5 meters long.
Stratolaunch originally touted this jet as the world's biggest aircraft, but toned down that statement this weekend referring to it as the "world's largest all-composite aircraft".
Other aeroplanes exceed it in length from nose to tail, including the six-engine Antonov AN 225 cargo plane, which is 84 meters long, and the Boeing 747-8, which is about 76.3 meters long.
The previous world wingspan record holder was Howard Hughes' World War II-era eight-engine H-4 Hercules flying boat — nicknamed the Spruce Goose.
Its wings stretch about 97.5-meters and can still be seen today at an aviation museum in Oregon.
With additional reporting from AP