The world's biggest plane is set to take off early next year in its groundbreaking first test flight.
The aircraft, named the Stratolaunch Carrier, is currently under construction at Mojave Air and Spaceport in California, and will eventually have a wingspan of 385 feet (117 metres).
It will be so huge that if the plane sat in the centre of a football field, it would be wide enough for its wings to reach 12.5 feet (3.8 metres) beyond each goalpost.
The idea is for the aircraft to act as a giant air pad in the sky, allowing payloads to reach space faster and at a lower cost than existing technologies.
The craft is the brainchild of Microsoft co-founder Paul Allen and Burt Rutan, founder of Scaled Composites - the same company blamed by Virgin for the SpaceShipTwo crash in October.
Last week, Virgin said the flight breakup of SpaceShipTwo was down to: 'Scaled Composite’s failure to consider and protect against human error and the co-pilot’s premature unlocking of the spaceship’s feather system.'
But the tragedy- which killed one pilot, Michael Alsbury, and left his co-pilot Peter Seibold, suffering major injuries - has not slowed down work in the Mojave Desert, according to a report in Kern Golden Empire.
The company today confirmed to DailyMail.com that construction is going ahead as planned.
When its complete, the Stratolaunch Carrier aircraft will be powered by six 747-class engines.
Its 385 feet (117 metres) wingspan compares to 320 feet (97 metres) wingspan for the Hughes H-4 Hercules and 225 feet (68 metres) for the Boeing 747-8.
The plane will climb to 30,000 feet and launch a rocket at high altitude, avoiding the huge fuel costs of launching from Earth.
Initially, the system is intended to deliver satellites weighing up to about 13,500lbs (6,124 kg) into orbits between 112 miles and 1,243 miles (180 km and 2000 km) above Earth.
THE STRATOLAUNCH CARRIER AIRCRAFT: KEY FACTS
Wingspan: 385 feet (117 metres)
Engines: Six 747-class engines
Fuselage length: 238 feet (72 metres)
Weight: 1,200,000 lb (544,311 kg)
Maximum speed: 460 knots, 530 mph (850 km/h)
Maiden launch: Flight testing will begin in 2016. The first launch of the space launch vehicle is likely to take place in 2018.
Satellite delivery: Initially, the system is intended to deliver satellites weighing up to about 13,500lbs (6,124 kg) into orbits between 112 miles and 1,243 miles (180 km and 2000 km) above Earth.
Launch sites: Several sites are under consideration, including Kennedy Space Center, Wallops Island and Vandenberg AFB.
Instead of a satellite, the Stratolaunch airplane could also launch a Dream Chaser spaceship, which would be outfitted with an as-yet-unspecified upper-stage rocket motor.
'Dream Chaser seemed to be the logical way to go,' Stratolaunch Executive Director Charles Beames said in October.
'It could provide a highly responsive capability with the potential to reach a variety of LEO destinations and return astronauts or payloads to a U.S. runway within 24 hours,' Chuck Beames, president of Allen's Vulcan Aerospace added.
In April, billionaire Allen revealed that he had created a new company, 'Vulcan Aerospace', to oversee construction of the ambitious project.
The company will 'shift how the world conceptualises space travel through cost reduction and on‐demand access,' according to Vulcan Aerospace president Chuck Beames who made a presentation in Colorado Springs this week.
The Stratolaunch Systems project was inspired by SpaceShipOne which won the $10 million Ansari X Prize in 2004 for becoming the first privately funded manned vehicle to reach space.
'Stratolaunch's ability to launch from variable locations will enable satellites and humans to be efficiently inserted into their most optimal orbit at a time of the customer's choosing,' Beames wrote.
'Launching far away from populated areas (i.e. middle of the ocean) also significantly reduces public safety risk.
The rocket is being developed by Orbital ATK, and the designs uses solid-fuel lower stages and an upper stage powered by RL-10 engines.
But according to SpaceNews, Beames indicated that the company is also looking at other launch vehicle options.
'What we really want to do is focus on a lower-cost propulsion system that is evolvable in some fashion,' he said.
'We're still looking at Orbital as a potential option,' he said. 'We're widening our aperture to see if this is the right path forward.'
Stratolaunch could someday support several launch vehicles, he said.
As a result, Stratolaunch said it is temporarily halting work on a crewed vehicle that would launch on the Orbital ATK booster.
That company added that it is deferring work on a crewed vehicle that would launch on the Orbital ATK booster to focus more heavily on getting the Stratolaunch Carrier aircraft off the ground.
In February, the world received its first glimpse of a gigantic airplane.
Rare stills taken from footage shot for a recent news story by KGET 17, a Bakersfield TV station, show its huge size, according to a report by Guy Norris in Aviation Week.
The images show one of the two twin fuselage sections under assembly.
In the news report, Scaled Composites president Kevin Mickey says the company has so far built 'roughly 200,000lbs of composite structure' for the vehicle.
Each of the twin fuselages of the Stratolaunch Carrier aircraft is 238 feet (72 metres) long and, when complete, will be supported by 12 main landing gear wheels and two nose gear wheels.
Stratolaunch has produced computer-generated images and videos of the aircraft, but the TV footage was the first time images of the real vehicle have been shown.
Allen has previously said his project would 'keep America at the forefront of space exploration and give a new generation of children something to dream about'.
Several companies are competing to develop spacecraft to deliver cargo and astronauts to the International Space Station.
The Microsoft billionaire criticised the fact that government-sponsored space programmes are waning.
Nasa is paying Boeing and SpaceX to build the capsules and fly them from Cape Canaveral, which hasn't seen a manned launch since the shuttles retired in 2011.
From Scotland to space: Europe & UK’s first spaceport by 2018
The government will convert an existing airfield to handle space travel within the next four years
The UK will build a spaceport by 2018, with eight locations under consideration - many of which are in Scotland.
That's right: a spaceport. Like an airport, but destination space.
The Department of Transport is evaluating existing airfields for their suitability to become a spaceport, examining factors such as the weather - strong winds are a problem - and how it will affect the local environment and economy.
In more practical considerations, the spaceport will require a runway that's 3,000m long, the ability to segregate airspace so there's a dedicated area for space vehicles, and it will have to be away from densely populated areas "to minimise impact on the uninvolved general public".
In its report, the government noted that commercial sub-orbital spaceflights for paying passengers will kick off in the US by the end of this year via Virgin Galactic. It wants the UK to get in on the space-tourist action by becoming the centre for such activity in Europe.
Aside from the sheer joy that having a spaceport would bring, it would also result in boosting scientific research by attracting space firms, and spur the economy by creating jobs.
Since spaceplanes - spaceplanes! - are more dangerous than existing aircraft, they don't meet current regulatory requirements to carry paying passengers. The government is therefore considering changing laws to allow such "experimental" aircraft to take tourists.
"In the longer term, it is possible that spaceplanes will enable intercontinental travel at very high speeds," the report added. "There have been suggestions that by travelling on a sub-orbital trajectory, journey times from the UK to Australia could be cut from the current duration of around 20 hours to as little as two hours."
Aside from space tourism and weekend getaways to Brisbane, the spaceport will also allow satellite launches as well as delivery of cargo and scientific payloads into orbit. If all goes well, the government predicted the first sub-orbital flights will take place by 2018, followed by satellite launches in 2020, and orbital flights by 2030.
Here's a selection of the firms working on spaceplanes and how they work.
Airbus Defence and Space
This firm is working on a spaceplane the size of a business jet for tourism. It takes off in the same way as a standard plane using jet engines, and has a rocket engine to get into the sub-orbital trajectory. The flights will last an hour – but don't expect any gin and tonics: there's no in-flight service. Flights are hoped to start by the beginning of next decade.
This UK firm was founded in 1991. It's working on a plane called Spacecab, which hopes to be the first orbital spaceplane. Until then, it's working on a sub-orbital plane called the Ascender, which would carry one paid tourist and a crew member.
"It would take off from an ordinary airfield and climb to 8km at subsonic speed, before starting the rocket engine," the report noted. "It would then accelerate to a speed of around Mach 3 on a near-vertical climb and then follow an unpowered trajectory to reach a height of 100km."
This UK firm's SKYLON is an unmanned spaceplane, designed to carry satellites and cargo to the International Space Station (ISS). However, it could be used to carry space tourists or astronauts to the ISS too. Testing will begin in 2020 and, if all goes well, it will be operational by 2022.
It uses a specialised engine that hits Mach 5 before accelerating to Mach 25 "for orbital insertion".