The US government's decision to shoot down its errant spy satellite has met with concern.
A plan by the US government to shoot down an out-of-control spy satellite has been described as a cynical tit-for-tat move in response to China doing the same last year. Scientists and arms-control experts fear that the operation will create damaging debris and weaken international efforts to ban space weaponry.
On 14 February, officials from the Pentagon, White House and NASA announced plans to use a ship-based missile to strike the satellite as it passes roughly 240 kilometres overhead. The satellite, which belongs to the National Reconnaissance Office in Virginia, dropped out of control after its launch in December 2006, and would re-enter Earth’s atmosphere around early March if no action were taken.
The strike is necessary to prevent the dispersal of around 450 kilograms of hazardous hydrazine thruster fuel onboard, according to James Jeffrey, assistant to the president and deputy national security adviser. If the fuel survived re-entry, it could be dispersed over an area of roughly 20,000 square metres, although “the likelihood of the satellite falling in a populated area is small,” he says. “Nevertheless, if the satellite did fall in a populated area, there was the possibility of death or injury to human beings.” The Pentagon denies that the shoot-down is to protect classified technologies on the satellite.
But scientists familiar with both satellite re-entry and the US missile defence system question the decision. The chances that the tank, which is 1 metre in diameter, will survive and strike land are extremely small, says Geoffrey Forden, a physicist at the Massachusetts Institute of Technology in Cambridge. “Most likely it will land in the ocean,” he says. The reasons given for the plan “don’t sound too credible to me”, he adds. “I think they’re doing it mainly to tell the Chinese that we can blow up a satellite too,” says Jonathan McDowell, an astronomer at the Harvard–Smithsonian Center for Astrophysics in Cambridge, Massachusetts. “This gives the US cover to carry out a test.”
The firing will probably take place in the coming weeks, although not before the return of the space shuttle Atlantis, which is expected back from the International Space Station on 20 February. David Wright, a physicist at the Union of Concerned Scientists, a non-profit organization in Cambridge, Massachusetts, says that he believes the station could be vulnerable to debris. But NASA administrator Michael Griffin says he is “very comfortable” with the decision.
Hitting the satellite could have serious consequences. In January last year, when China used an interceptor to destroy one of its own, obsolete weather satellites, the test littered more than 100,000 debris fragments throughout low-Earth orbit. Much of this hazardous debris will remain there for decades, posing a risk to other satellites.
The errant US satellite is at a much lower orbit than the Chinese one was, and therefore debris would be shorter lived and less likely to cross the path of other spacecraft. But it is also at least 2.5 times larger than the Chinese one, so it will create more debris. Furthermore, the cloud could behave unpredictably, says Wright.
The government plans to destroy the satellite using a ship-launched Standard Missile 3, or SM-3. The missile is designed to use a kinetic kill vehicle to ram incoming ballistic missiles, destroying them before they damage US targets. It is a smaller and slower device than the ground-based interceptors located at Fort Greeley in Alaska and Vandenberg Air Force Base in California. But it is better at intercepting targets, according to Forden. “They have had quite a bit of success with the SM-3,” he says.
Travelling at 3–4 kilometres per second, the device would smash into the 2,250-kilogram satellite, which itself will be moving at roughly 8 kilometres per second. “At these speeds it is like setting off a huge amount of high explosive at the satellite,” Wright says. Even without carrying explosives, the energy of the collision could boost fragments of the satellite into a higher orbit, creating hazards for other craft. “It sounds like a bad idea to me,” he says.
The announcement came just two days after Russia proposed a treaty, backed by China, to ban the use of space weapons — including those used to destroy a country’s own satellite — at an international conference on disarmament in Geneva, Switzerland.
The proposed US shoot-down would have far-reaching diplomatic implications. “If you do this,” says McDowell, “you have converted your missile-defence system into a missile-defence and anti-satellite system.”
“It would reinforce people’s sense of the United States as being irresponsible,” says Rebecca Johnson, executive director of the Acronym Institute for Disarmament Diplomacy in London. The United States has blocked a ban on space weapons for more than a decade on the grounds that it would interfere with its right to develop a missile-defence programme. Using that system to destroy an orbiting satellite would probably anger countries such as Russia.
McDowell says he thinks the shoot-down, following in the wake of China’s test last year, will dramatically weaken already floundering efforts for a ban on space weapons. That in turn could be hazardous for satellites everywhere. “Just because the Chinese were idiots, doesn’t mean that we have to be bigger idiots,” he says.
Additional reporting by Rachel Courtland.