The document outlines US military and commercial ambitions in space

As the White House unveils a tough new policy aimed at protecting its interests in space - and denying access to hostile "adversaries" - the BBC's Matthew Davis considers the timing of and reaction to the move.

The United States is economically and militarily more dependent on space than it has ever been.

Take the current crisis over North Korea, where spy satellites are giving observers an almost-real-time view of what is happening on the ground.

Or the concern last month when China allegedly used a ground-based laser to "paint" a "US intelligence asset" orbiting above its territory.

The United States will preserve its rights, capabilities, and freedom of action in space... and deny, if necessary, adversaries the use of space capabilities hostile to US national interests US National Space Policy in full (44K) Most computers will open PDF documents automatically, but you may need to download Adobe Acrobat Reader. Download the reader here

Not to mention services like ATMs, personal navigation, package tracking and cell phones.

No surprise then that protecting space - for civil and military reasons - has been rapidly evolving as a US priority.

Space expert Leo Enright, head of Ireland's science awareness programme, told the BBC: "The world economy has become very very dependant on satellites in orbit for a whole range of services.

"I suppose the most dramatic example of this so far was about 10 years ago when an American satellite went out of control, it was hit by a piece of space junk and went out of commission.

"Ninety per cent of America's 45 million pagers went dead for over a day and it brought home very starkly to American strategic planners that they had become very dependent upon these systems."

'Proprietorial attitude'

This latest strategic document places America's emphasis squarely on making use of space for defensive purposes, linking this to protecting US national security.

Much military intelligence is linked to space-based technology

It says the US will develop "capabilities, plans and options to ensure freedom of action in space", and if directed, will "deny such freedom of action to adversaries".

Baker Spring, of the conservative think-tank the Heritage Foundation, says the administration is right to be worried.

"If you can't protect your territory against somebody's who's going to use the space domain for that purpose then I think you're not serving the national interest very effectively," he says.

But what will worry some countries and experts is the document's uncompromising language, and what is being seen as a proprietorial attitude towards the heavens.

One commentator said this first revision of US space policy for 10 years seemed to suggest that the final frontier was now "the 51st state of America".

Space weapons

The White House insists that this is not about putting weapons in space, but about protecting assets vital to US strategic interests.

... others will similarly weaponise and then we'll have another place where we can cause havoc Jonathan Granoff Global Security Institute

Yet there have been previous reports of the Pentagon trying to develop space weapons.

Some that have been discussed by commentators include manoeuvrable satellites that could be used as rams, lasers that could "blind" other satellites, or even space-based weapons firing 100kg tungsten bolts.

Last year the US rejected a call from 160 other United Nations countries to have talks on banning weapons in space.

Experts say that because many space initiatives are classified it is hard to know just what developments are being worked on.

Jonathan Granoff, President of the Global Security Institute - which campaigns for the elimination of nuclear weapons - says weapons in space would be "crossing the threshold".

"The same weapons that are used for alleged defensive purposes can also be used for offensive purposes and its for that reason that virtually every nation in the world except for the United States, and our ally in this matter, Guam, have voted for preventing the weaponisation of space.

"If we claim the prerogative of making anti-satellite weapons then we would be constrained to deny others the same capacity, so you end up having another arms race.

"That is the myopia or short-sightedness of a policy that says 'We're ahead today and let's go as far ahead militarily as we possibly can', forgetting the fact that science and technology don't know national borders, and others will similarly weaponise - and then we'll have another place where we can cause havoc."

It is also unclear as to where the US thinks threats to space operations will come from.

Some 40 countries have national space associations, the giants among them China and Russia.

Even Iran has its own satellite which it plans to launch soon.

But as technology advances and the use of space increases, the US clearly feels it has to robustly defend its position at the forefront of the final frontier.