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Public Radio's Environmental News Magazine (follow us on Google News)

Space Junk

Air Date: Week of

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Spent rocket stages and broken lens caps are just some of the junk littering Earth’s orbit, posing serious environmental and safety hazards. Host Steve Curwood talks with Jonathan McDowell, an astrophysicist at the Smithsonian Observatory and contributing editor for Sky and Telescope magazine, about the dangers of littering in the final frontier.


CURWOOD: Welcome to an encore edition Living on Earth. I’m Steve Curwood. For decades, probes, satellites and other spacecraft have paved a path for space exploration, orbiting and collecting data from the far reaches of the universe. But in recent years that path has become littered with the trash and other remnants of these missions, posing a serious environmental and safety hazard. Joining me now is Jonathan McDowell, an astrophysicist at the Smithsonian Observatory and contributing editor for Sky and Telescope Magazine. Welcome.

MCDOWELL: Thank you.

CURWOOD: How much junk is there out in space?

MCDOWELL: Well, there's about 9000 objects that the radars track right now, we know their orbits and so on. But that's only the tip of the iceberg, because there's a lot of smaller stuff that the radars can't see. So we really don't know.

CURWOOD: And how big does it have to be to be dangerous to something like a spacecraft or a satellite?

MCDOWELL: Well, it's quite surprising. Even a rather small piece of junk a few inches across can be nasty. If you imagine that you have something that's only a few ounces, but it's traveling with a head-on collision of 20,000 miles an hour, that's the equivalent energy to being hit on the interstate by a two-ton truck.

CURWOOD: Now, where does all this junk come from?

MCDOWELL: Typically, when people throw things away on space walks, when they lose lens caps off of their camera, stuff like that, when they're on the space station, that reenters pretty quickly. The big problem is from rocket stages that blow up after they've been in orbit for some time. They have a little fuel leftover, they have some fuel and some oxygen, and it's in separate tanks. And after a few years the tanks crack, and the fuel and the oxygen go out on a date together, and so suddenly you have 100 new pieces of space debris. And that's the major contribution. There's also some military weapons tests that have left a bunch of shrapnel in orbit, which contributes to the population.

CURWOOD: Now, what kind of damage can this space debris cause?

MCDOWELL: Well, there was one satellite that we know of so far that's been damaged by space debris. It has its antennae broken off, it stopped working. But you can imagine that if you have a big satellite, like the Hubble telescope, like a space station that's in orbit for a lot of years, its chances of getting a nasty hit are quite large.

The thing that people are most scared of is up in geostationary orbit, where all the television satellites live. And there, even though it's a huge area of space, there are so many satellites that if you destroyed one in a collision you could get a chain reaction, and turn this area of space into a new ring around the earth, like Saturn's rings, but made up of lots of tiny pieces of very expensive television satellite.

CURWOOD: So far we've been talking about remnants of bodies of spacecraft, and accidental releases from operations, but what about plain, old-fashioned trash? How much stuff did people just dump out there from the shuttles, and the space stations, and the earlier trips to space?

MCDOWELL: Well, there's all kinds of trash. And, indeed, on the Mir space station, every few weeks we would see five or six new space debris objects be catalogued, and we eventually discovered that they were putting their trash in plastic bags and shoving them out the airlock. And so, that's happened all through the space program. On the Shuttle to the present day, they don't throw trash overboard, but they do jettison water. But in general, all of that stuff is in low orbit. It doesn't stay up very long, and so it's not a huge problem compared to the exploding rocket stages higher up.

CURWOOD: Now, who is keeping track of all this junk?

MCDOWELL: Well, the US Air Force, and also the Russians, have radars that track the bigger stuff. And they started off because they were worried, in the early days of the Cold War, that you saw things on your radar that might be nuclear missiles attacking the U.S., and so you wanted to make sure that you knew what was space junk and what was missiles. In fact, in the early days in the Cuban Missile Crisis, a Russian Mars probe blew up and the U.S. radar operators saw 20 pieces come on their radar screens. And very quickly the computers figured out that, yes, this was in orbit and it was a piece of space junk that had blown up.

CURWOOD: How much does our design of spacecraft, space systems, contribute to all this junk? Do we just think trash? Are we designing for trash?

MCDOWELL: Well, that certainly used to be the case, and that was the mindset of people in the Cold War, particularly. The space program grew out of the military missile programs, to some extent. And when you first went into space, as for the first time that humans have gone anywhere, you think, wow, this is big, there's no way we can fill this up. And it's true, the distance between your average piece of space junk is about 1000 miles to the next one. But, nevertheless, you're traveling so fast you sweep out a large area, and pretty soon it starts to be a problem.

CURWOOD: So how are we doing, then, with understanding that hey, space is not infinite, that we can't just leave our trash behind.

MCDOWELL: I think there's been huge progress in the past 10 years. The United States and Europe have really taken the lead on this. There's been a number of international conferences deciding what are the sources of space debris, how do we stop making more of them. They began to take counter measures, in particular using up all your rocket fuel and making sure that rocket stages go into lower orbits where they'll reenter quickly, not throwing away your lens cap, putting it on a hinge instead of just jettisoning it.

There's also starting to be ecological concerns about the effects of space rockets during launch, when lower stages of the rockets fall downrange. Now, America launches eastward over the ocean, and our trash from the launch falls in the sea, where it's actually a pretty small effect compared to all the other ways that we foul up our oceans. But in Russia, they've been falling in the desert, and contaminating the water table, and causing health problems in villages. And so there's a move, for instance, to change the design of which fuels you use, so that you don't use nasty stuff like nitrogen tetroxide but clean stuff like hydrogen and oxygen.

But mother nature does give us a hand. The friction with the upper atmosphere – space isn't completely empty, there's a very thin outer atmosphere that brings the satellites down over a period of decades and centuries. And what we have to do is make sure that the rate at which we dirty up things is slow compared to that natural cleaning time scale.

CURWOOD: Jonathan McDowell is an astrophysicist at the Smithsonian Observatory and contributing editor for Sky and Telescope Magazine. Thanks for taking this time with me today.

MCDOWELL: Thanks for having me.



California Academy of Sciences


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