IT STARTS with a handful of missiles taking out orbiting satellites. The shrapnel destroys more satellites and triggers a chain reaction, generating yet more high-speed debris. Before long, we鈥檙e trapped on Earth in the nightmare scenario: space is a no-go zone, made too dangerous to use for generations by countless chunks of junk.
That is the risk of 鈥渟pace war鈥� that the US White House seeks to avoid with its , released on 28 June. The policy reopens the door to international arms-control measures against space weapons, reversing the 2006 policy of George W. Bush鈥檚 administration, which ruled out such talks.
Crafting such an agreement is easier said than done, thanks to issues created by technologies that are dual-use, in that they can be used for peaceful or defensive purposes as well as for attacking other countries鈥� satellites.
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鈥淒ual-use technology will hugely complicate the issue of agreements,鈥� says Joan Johnson-Freese of the US Naval War College in Newport, Rhode Island. For example, missiles that can shoot down other missiles to shield a country from attack could also be used to destroy a satellite in space.Indeed, there is 鈥渘o fundamental difference鈥� between the missiles used in each application, says Ray Williamson of the Secure World Foundation (SWF) in Washington DC.
The US demonstrated this in 2008 when it shot down one of its own defunct satellites, called USA 193, using an interceptor fired from a ship equipped with the US鈥檚 . Officials said this was to prevent the satellite, which was on a decaying orbit, from falling to Earth in a populated area and causing harm by releasing its toxic hydrazine fuel.
Some analysts speculated that it was in fact intended to demonstrate the US鈥檚 anti-satellite capabilities, in response to a 2007 test in which China destroyed one of its own satellites with a missile.
USA 193 was destroyed in an orbit low enough that the debris quickly entered the atmosphere and burned up, but the Chinese test created thousands of pieces of long-lived debris, many of which remain in orbit.
Russia, too, has tested anti-satellite weapons, though not since the cold war. It also has a missile defence system that could in theory be used to knock out satellites, though this has not been put to the test. India may soon have the ability to wage space war too, having recently announced that it is developing anti-satellite and missile-defence interceptors.
Eliminating all missiles that can hit satellites would require getting rid of these missile-defence systems, something countries that have them will almost certainly refuse to do, particularly the US. Any treaty that attempts to ban such missile defence would 鈥渟tir up a hornet鈥檚 nest on Capitol Hill鈥�, says Michael Krepon of the in Washington DC.
On top of that, the technology is still spreading. The US has sold or is selling the Aegis system (pictured, below) to countries including Norway, Spain, South Korea and Japan. Though the current system uses relatively short-range missiles with limited ability to reach the altitudes where satellites orbit 鈥� USA 193 was exceptionally low, on the verge of re-entering the atmosphere 鈥� a planned system upgrade 鈥渨ould have much longer range and would be able to reach probably nearly all low-Earth orbiting satellites, should one want to use it that way鈥�, says Laura Grego of the Union of Concerned 快猫短视频s in Cambridge, Massachusetts.
Other double-edged swords are satellites designed to autonomously navigate their way to the vicinity of another satellite in space, a technology that the US demonstrated by flying a mission called XSS-11 in 2005.
A country could use such technology to inspect and repair one of its own malfunctioning satellites or to grab it and drag it into the atmosphere to dispose of it without adding to space junk. But the technology could also be used to interfere with or damage another country鈥檚 satellite, says Brian Weeden of SWF. 鈥淚f you can remove a piece of debris from orbit, then if you really wanted to you could probably remove an active satellite maliciously,鈥� he says. 鈥淭he rendezvous technology is spreading to a lot of places, because people are seeing economic incentive in on-orbit servicing.鈥�
鈥淚f you can remove a piece of debris from orbit, you can maliciously remove an active satellite鈥�
On 16 June, for example, the Swedish Space Corporation launched a couple of satellites called Mango and Tango to demonstrate rendezvous technology in a joint project called , with the German Aerospace Center, France鈥檚 National Centre for Space Studies and the Technical University of Denmark. Even as early as the cold war, a Soviet satellite was designed to closely approach a target satellite, then release pellets to act like a shotgun blast, colliding with the satellite at high speed and destroying it.
So given how difficult it is to separate offensive technology from the peaceful or defensive stuff, is there any way to keep space from becoming a littered battleground?
鈥淚 think the key is in trying to constrain behaviours rather than capabilities, because the capabilities are not going to be constrained,鈥� says Krepon. So even if missile interceptors themselves remain legal, an agreement could outlaw their use in tests that destroy satellites.
To deal with the issue of malicious satellites with autonomous rendezvous technology, spacefaring nations might agree to a code of conduct requiring a country to provide advance notice if it expects one of its satellites to closely approach one belonging to another country.
This would be similar to agreements between countries to by land, naval and air forces, Krepon says. 鈥淭he only domain in which such a code of conduct is lacking is space,鈥� he points out.
For such agreements to work, though, there must be ways to detect cheaters. 鈥淎ctors are much less likely to commit nefarious acts if they know they鈥檙e being watched,鈥� says Johnson-Freese.
In its new space policy, Barack Obama鈥檚 administration says the US will only consider agreements that meet this criterion 鈥� in its words, they must be 鈥渆ffectively verifiable鈥�.
The US has telescopes, radar facilities and satellites that can help in this regard. Its space-surveillance system is capable of detecting missile launches and observing the clouds of debris that result from an anti-satellite test. But the US does not have the ability to see everywhere at all times, Johnson-Freese admits.
Some other countries, such as Russia, also have space-surveillance capabilities, though none can match the US鈥檚. In order to sign up to space arms control, countries lacking in surveillance infrastructure may at the very least request access to a system operated jointly by the various signatories, says Weeden. Developing international 鈥渟pace situational awareness鈥� capabilities may be key, he adds.
No one knows how many destroyed satellites could trigger a runaway reaction (快猫短视频, 13 September 2008, p 24). 鈥淎re we talking about having five major collisions in space?鈥� asks Williamson. 鈥淚s it 10? Is it one?鈥�
Johnson-Freese argues that preventing further testing of missiles on satellites will reduce various militaries鈥� inclination to use them, even in a conflict. After all, she says, countries have a shared interest in keeping space a battle-free zone: 鈥淭he more we can work together on identifying that it is in the common interest to keep these assets safe and agree to working together towards that, the better off everybody will be.鈥�
