What weapon could the US have put into space?
The announcement by the United States that it has deployed a space weapon in Earth's orbit has raised questions about what weaponry is actually in space, and what role it could play in efforts by great powers to dominate that arena.
Washington has given away little in its announcement. Secretary of the Air Force Troy Meink said the "on orbit" weapon was necessary to safeguard US forces against hostile enemy action, but gave no details about the weapon's capabilities or when it was put into orbit.
So what could this weapon be, and what is wider picture like for military developments in space? Who else could have similar weaponry?
Advanced militaries already deploy satellites in space for range of purposes, from supplying secure communications to reconnaissance, and providing precise location information for targeted strikes and detecting missile launches.
As warfare become more technologically advanced, analysts expect the use of military hardware in space to increase.
Dr Bleddyn Bowen, an associate fellow in military sciences at the Royal United Services Institute and associate professor in astropolitics at Durham University, said he was only able to hazard a guess about the weapon announced by the US.
"I would expect there to be some kind of electronic warfare or radio-jamming platform, possibly, this would be a non-destructive kind of anti-satellite weapon," he told BBC Radio 4's Today programme.
Such weaponry already exists on Earth and can disrupt satellite communications, he said. "If you take out the radio links then your satellite is very useless."
Bowen also would not rule out some sort of more disruptive and riskier weaponry, which could create a lot of debris and destruction.
"Less likely would be a kinetic kill vehicle of some sort, so a vehicle that would release a projectile of some sort that could ram into a satellite and destroy it," he said.
"Possibly some sort of close inspection and grappling satellite would be another possibility as well."
But while the weapon placed in orbit appears to be a first, the US - and indeed its Russian and Chinese rivals - have had weapons that can be pointed and shot into space for some time.
In fact in the last 10 years, Russia and China have been doing a lot more manoeuvres in space, known as rendezvous and proximity operations (RPOs) - "buzzing" Western satellites.
"Theoretically, these RPO sats can become hunter-killer satellites by physically colliding with them or by nudging them out of orbit," Dr Rod Thornton, reader in Russian Defence and Security Studies at King's College, London, told the BBC.
Bowen adds that the Chinese have demonstrated "space tug capability", saying: "A vehicle can go up to a satellite, can grapple it and move it into a different orbit."
This, he says, can be a positive development - a way of removing space junk as well as knocking out working satellites.
Thornton says that what Russia lacks in space weaponry and satellites, it makes up for in missile capability.
"The Russians... have ground-based missiles which can be launched into space to strike sats in low Earth orbit. They also have ASAT missiles that can be launched from a great height by aircraft," he says.
"From the Russian point of view they see Nato as having much better and more sats than the Russian military can call up, therefore they have invested heavily in ASATs in order to 'level the battlefield' somewhat."
Thornton adds a sobering thought: "As a last resort, the Russians can also launch nuclear weapons into space and the EPM blast would 'fry' any unhardened sats over a wide expanse."
He says that, having so few satellites, Russia would be the "big winner" in any space war, which would involve "missiles fired up into space, manoeuvring sats designed to nudge/destroy them and ground-based lasers".
