The Pentagon files acquired by The Sun reveal a US PLAN for the biggest space spacecraft ever built, capable of transporting humans to Jupiter and back.

After a four-year Freedom of Information struggle, the Defense Intelligence Agency (DIA) – the Department of Defense’s intelligence arm – revealed the records addressing deep space research and colonisation.

They are among the 1,574 pages of real-life X-Files relating to the Pentagon’s covert UFO programme obtained by The Sun under the Freedom of Information Act.

One of the files contains blueprints and images for a spaceship called Fusion Ship II.

It depicts the blueprints for an enormously long and thin vehicle built around a tiny capsule and a succession of reactor arrays.

The deep space vessel driven by IEC fusion, a research method that harnesses electric fields to push a spacecraft forward.

According to the blueprints, the space ship will be 300 metres long, roughly three times the size of the Saturn V rocket that transported man to the Moon and nearly six times the size of the Space Shuttle.

However, the craft would be significantly lighter than earlier spacecraft, weighing little more than 500 metric tonnes.

The suggested architecture would be capable of transporting ten humans to Jupiter in 210 days there and 153 days return.

And in that timeframe, it may reach average speeds of up to 148,852mph, which is 10 times faster than the peak speed of the Saturn V rocket that launched man to the Moon.

The crew would be housed in a 12m circular room that could be utilised for sleep as well as exercise.

According to the papers, the spaceship will be one of the biggest ever built, weighing barely a fifth of the 2,000-ton Space Shuttle.

One of the most difficult aspects of space travel is the length of time it takes to traverse the emptiness.

Previously, probes travelling to the gas giant Jupiter, which lies between 365 and 601 million miles from Earth, had to journey for years.

Such long travel times make manned space flight problematic, but a ship travelling at Fusion II speeds would make things much easier.

“Human factors have not been fully evaluated in this design, but are thought to be acceptable with the short mission time achieved.