标题: [其他] China Space Attack: Unstoppable zt [打印本页] 作者: 古堡游零 时间: 2007-1-20 10:30 标题: China Space Attack: Unstoppable zt
China has shown it can destroy a satellite in orbit. What could the U.S. do to stop Beijing, if it decided to attack an American orbiter next? Short answer: nothing.
It takes about 20 minutes to fire a ballistic missile into space, and have its "kill vehicle" strike a satellite at hypersonic speed -- over 15,000 miles per hour -- in low-earth orbit. That's far too quick for anything in the American arsenal to respond, in time. There's "no possibility of shielding" a relatively-fragile satellite against such a strike. "And it is impractical [for a satellite] to carry enough fuel to maneuver away even if you had specific and timely warning of an attack," Center for Defense Information analyst Theresea Hitchens notes.
The American military today counts on its satellites to relay orders, guide troops across battlefields, and spy on enemy hideouts. The U.S. Air Force's primer for war in space -- "Doctrine Document 2-2.1: Counterspace Operations" -- lists a number of measures that can be taken to protect American assets in orbit, including "deploying satellites into various orbital altitudes and planes" and "employing frequency-hopping techniques to complicate jamming." But those tactics are used to preserve the U.S. satellite constellation as a whole. None of them could save a single American orbiter against a direct attack. "Physical hardening of structures mitigates the impact of kinetic effects, but is generally more applicable to ground-based facilities than to space-based systems due to launch-weight considerations," the Air Force document notes. "Maneuver[ing] is limited by on-board fuel constraints, orbital mechanics, and advanced warning of an impending attack. Furthermore, repositioning satellites generally degrades or interrupts their mission."
With today's conventional defenses proving so impotent, expect a new push within the U.S. military for more exotic countermeasures. The Airborne Laser is a modified 747 that's being designed to blast missiles out of the sky, as soon as they leave they launch pad; the jet's first flight test in expected in 2009, after years and years of delays. The Kinetic Energy Interceptor is a long-range, non-explosive missile, meant for the same task. But the weapon "exists mostly on paper, and couldn't be operational before 2014," Defense Tech's David Axe noted recently.
The U.S. could also try to destroy an anti-satellite missile, before it took off. Over the last several years, momentum has been building in the Pentagon for the ability to conduct "Prompt Global Strikes," hitting anywhere on Earth, in an hour or less. But near-term PGS plans -- using modified Trident ballistic missiles -- have been put on hold, for fears that such an attack could start World War III, in the process. Destroying a satellite is as clear an act of war as there can be, however. Perhaps those Trident attacks will now be seen as worth the risk.
In the meantime, GlobalSecurity.org director John Pike figures the Chinese will continue to test their satellite-killing weapons. It takes a dozen or more trials before a strategic weapon like this is deemed reliable enough to be considered operational. "So expect one or two more tests like this every year, for a long time," he says.
The Chinese test, now confirmed by the National Security Council, would be the first successful anti-satellite weapons trial since 1985, when the United States used an F-15 and a kill vehicle to destroy the Solwind research satellite. And that trial was dangerous -- not just for its target, but for nearly everything orbiting in space, Hitchens notes. Even small pieces of space debris can be lethal to spacecraft. The '85 test "resulted in more than 250 pieces of debris, the last of which deorbited in 2002."
The Chinese trial could "lead to nearly 800 debris fragments of size 10 cm or larger, nearly 40,000 debris fragments with size between 1 and 10 cm, and roughly 2 million fragments of size 1 mm or larger," the Union of Concerned Scientists' David Wright notes on the Arms Control Wonk blog. "Roughly half of the debris fragments with size 1 cm or larger would stay in orbit for more than a decade."
"This raises an interesting public policy question because we are so much more dependent on commercial and military satellites that the ASAT [anti-satellite] options available to us are much more complicated than those available to the Chinese," adds Jeffrey Lewis. "This is a race that favors them, unfortunately."作者: 古堡游零 时间: 2007-1-20 10:31
WASHINGTON (CNN) -- China last week successfully used a missile to destroy an orbiting satellite, U.S. government officials told CNN on Thursday, in a test that could undermine relations with the West and pose a threat to satellites important to the U.S. military.
According to a spokesman for the National Security Council, the ground-based, medium-range ballistic missile knocked an old Chinese weather satellite from its orbit about 537 miles above Earth. The missile carried a "kill vehicle" and destroyed the satellite by ramming it.
The test took place on January 11. (Watch why the U.S. has protested the missile strike )
Aviation Week and Space Technology first reported the test: "Details emerging from space sources indicate that the Chinese Feng Yun 1C (FY-1C) polar orbit weather satellite launched in 1999 was attacked by an asat (anti-satellite) system launched from or near the Xichang Space Center."
A U.S. official, who would not agree to be identified, said the event was the first successful test of the missile after three failures.
The official said that U.S. "space tracking sensors" confirmed that the satellite is no longer in orbit and that the collision produced "hundreds of pieces of debris," that also are being tracked.
The United States logged a formal diplomatic protest.
"We are aware of it and we are concerned, and we made it known," White House spokesman Tony Snow said.
Several U.S. allies, including Canada and Australia, have also registered protests, and the Japanese government said it was worrisome.
"Naturally, we are concerned about it from the viewpoint of security as well as peaceful use of space," said Yashuhisa Shiozaki, chief cabinet secretary. He said Japan has asked the Chinese government for an explanation.
Britain has complained about lack of consultation before the test and potential damage from the debris it left behind, The Associated Press reported.
The United States has been able to bring down satellites with missiles since the mid-1980s, according to a history of ASAT programs posted on the Union of Concerned Scientists Web site. In its own test, the U.S. military knocked a satellite out of orbit in 1985.
Under a space policy authorized by President Bush in August, the United States asserts a right to "freedom of action in space" and says it will "deter others from either impeding those rights or developing capabilities intended to do so."
The policy includes the right to "deny, if necessary, adversaries the use of space capabilities hostile to U.S. national interests."
Low Earth-orbit satellites have become indispensable for U.S. military communications, GPS navigation for smart bombs and troops, and for real-time surveillance. The Chinese test highlights the satellites' vulnerability.
"If we, for instance, got into a conflict over Taiwan, one of the first things they'd probably do would be to shoot down all of our lower Earth-orbit spy satellites, putting out our eyes," said John Pike of globalsecurity.org, a Web site that compiles information on worldwide security issues.
"The thing that is surprising and disturbing is that [the Chinese] have chosen this moment to demonstrate a military capability that can only be aimed at the United States," he said.
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