MICHELE NORRIS, Host:
The governments of Britain, Japan and Australia are voicing concern over China's apparent test of an anti-satellite missile. The U.S. says China shot down one of its own aging weather satellites last week, a kind of target practice in low Earth orbit. Scientist say hitting a satellite from the ground takes fairly sophisticated technology and it can create a real mess.
NPR's David Kestenbaum reports.
DAVID KESTENBAUM: At the time of the test, the U.S. Air Force was oddly enough having a conference on space policy. Hans Kristensen was there. Kristensen is a weapons expert at the Federation of American Scientist. He said there was no scramble of people talking on their cell phones. He only heard about the test later.
HANS KRISTENSEN: Well, I was surprised that they were able to do it because it's, you know, they've working on this for a long time but the assumption is always been that, yeah, they're working on it. They're working on it, but they're still quite sometime away from actually been able to hit a satellite.
KESTENBAUM: U.S. officials say the Chinese did hit the satellite with the help of a medium range ballistic missile.
KRISTENSEN: And China only has one medium range ballistic missile. It's called the DF-21.
KESTENBAUM: Kristensen said this missile can probably hit a spot on the ground with an accuracy of several hundred feet. But the satellite was small, close to the size of a refrigerator.
KRISTENSEN: Yes. The satellite is tiny for a ballistic missile flying at high speed, absolutely.
KESTENBAUM: So the assumption is that the Chinese device had some sort of advance guidance system, maybe a kind of telescope to pick out the satellite, then thrusters to steer it toward the target. The force of the collision would have destroyed the satellite. Kristensen says when the U.S. and Russia were developing anti-satellite missiles in the 1980s, hitting the target was the hard part.
KRISTENSEN: It was so much of an issue that the kind of the science we saw coming out with the science that have sort of big wings could spread out a fan of metal bars so that you could actually have a greater chance of really impacting small satellites.
KESTENBAUM: The U.S. successfully shut down one of its own satellites in 1985. So could a Chinese missile now take out the U.S. satellite? A rule of thumb is that a missile can go to a height about half its horizontal range. So this missile might be able to reach an altitude of 600 miles. The global positioning system satellites, for instance, are much higher, tens of thousands of miles. But Kristensen said there's plenty of stuff lower down.
KRISTENSEN: Spy satellites tend to go very low because you need to get close.
KESTENBAUM: So the Chinese could hit those low-flying U.S. spy satellites?
KRISTENSEN: Yes, in theory. And that's the worry. I mean, that's the concern.
KESTENBAUM: Another concern is the debris created by the collision. Laura Grego, with the Union of Concerned Scientists, has been looking at data released by NORAD, the North American Aerospace Defense Command. Before the collision, she could see the satellite chugging along in its orbit. There were about two tracking measurements a day.
LAURA GREGO: And then as we get closer to Thursday, the frequency of observations goes up.
KESTENBAUM: Suggesting that the U.S. military knew something about it.
GREGO: Yup. And was taking a closer look and anticipating something. And then on Tuesday, I believe, we start to see pieces of debris that were identified with that satellite.
KESTENBAUM: Those were probably just some of the big pieces. David Wright, a physicist also with the Union of Concerned Scientists, has been using computer models created by NASA to estimate debris from collisions. He said this smashup would have been the equivalent of a half ton of high explosives going off.
DAVID WRIGHT: This satellite was maybe three quarters of a ton in mass. And it would have thrown off about two million pieces that were bigger than a millimeter in size. And that sounds pretty small but at the speed these things are going, a millimeter object can be really deadly.
KESTENBAUM: For other satellites. The odds of debris hitting something look small he says, but this single event probably doubled the number of pieces of space junk at these altitudes.
David Kestenbaum, NPR News.
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