ELISSA NADWORNY, HOST:
A rocket the size of a 10-story building tumbled out of the sky on Friday and splashed into the Pacific Ocean. The debris didn't cause any casualties, but the rocket's uncontrolled descent was no accident. The Chinese rocket booster was designed to fall to Earth after propelling a piece of China's space station into orbit. NASA administrator Bill Nelson said in a statement Friday that China was taking, quote, "unnecessary risks." Here to talk more about this is Jonathan McDowell with Harvard's Center for Astrophysics. Hey there.
JONATHAN MCDOWELL: Hello.
NADWORNY: So this is the fourth time that debris from a Chinese rocket has cascaded down to Earth. Several years ago, chunks hit villages in West Africa, causing property damage but no casualties. Is there any way to know where this stuff is going to fall?
MCDOWELL: No, there really isn't. The problem is that the rocket booster is tumbling along at the edge of the atmosphere at 17,000 miles an hour. So if you estimate wrong when it's going to break up by an hour, you're 17,000 miles off.
NADWORNY: Wow.
MCDOWELL: And so it's that lack of predictability that makes this particularly worrying.
NADWORNY: What are the odds that a piece of rocket debris would actually hurt someone?
MCDOWELL: The chance of it hurting someone is not that high. It's maybe one in a thousand, but that's still a lot higher than the criterion that most countries use for going, eh, probably too high a risk to take. If you're doing a lot of these, even a one in a thousand risk, eventually you're going to get unlucky.
NADWORNY: Is there a way to make sure that large pieces of debris like this won't cause loss of life or property?
MCDOWELL: Well, there are various things that people do. If you have a smaller rocket stage, you can make it a restartable (ph) engine and slam it deliberately down into the atmosphere at a specific place in time. For a big booster like this, the usual way people will take care of it is not to put it in orbit in the first place, make it do most of the work of getting your satellite into orbit but shut it down just a little early so that it falls immediately in the ocean at a predictable place and then make little engines on the satellite do the last little puff of getting it into space.
NADWORNY: Why hasn't China designed its rockets that way?
MCDOWELL: That's a great question. I think fundamentally the answer is that they have a different attitude to risk than, say, the United States. They see that one in a thousand, and they go, no problem; we'll take those odds, whereas in the U.S., we're like, oh, no, you better do some redesign.
NADWORNY: But even despite kind of that risk calculation difference, the Chinese government has said it's just doing what every other country does when it sends stuff up into space. I mean, for example, debris from SpaceX rockets has crashed into farms in Australia and even Washington state. Do you think critics of China's space program are just being unfair?
MCDOWELL: No, I think the Chinese are being a little disingenuous here. There's a big difference between a 20-ton rocket stage and the one-ton or two-ton objects that the U.S. lets reenter. But it is a bit nuanced. So I would say these four Long March 5B core stages are the biggest uncontrolled reentries - all four of them - in 30, 40 years. So they're clear outliers. Other countries don't let things that big reenter.
NADWORNY: Is there talk or discussion about creating stricter rules about these uncontrolled reentry rocket debris?
MCDOWELL: There's a lot of discussion right now about the general governance of space and how the rules aren't really keeping up with the rapid commercialization of outer space. The specific issue with the uncontrolled reentries, I think, hasn't made it really to the top of the agenda yet, although there is a recent change that you're meant to at least make sure that your junk reenters within five years, whereas the previous recommendation was within 25 years. So that's an improvement, but that's still letting it reenter uncontrolled. And I think that as our space activities increase, that's just not going to be acceptable anymore.
NADWORNY: Astrophysicist Jonathan McDowell of Harvard, thank you so much for joining us.
MCDOWELL: Thank you. Transcript provided by NPR, Copyright NPR.
