This is Talk of the Nation, Science Friday. I'm Ira Flatow. A bit later in the hour, we'll be talking with Temple Grandin. But first, when a New Horizon space probe blasted off to Pluto yesterday, it had to steer through a maze of orbiting space junk. Rocket scientists had to make sure the craft did not have an unhappy close encounter with some of the more than 9,000 separate pieces of manmade debris orbiting the Earth. The celestial litter includes everything from fragments of an exploded launch vehicle to a 31-year-old rocket, and experts say the amount of space junk will only go up as more satellites are launched and more countries man missions to space.

Scientists can track the bigger pieces and have successfully steered the international space station out of the way of orbiting junk, but is there a better way to manager what ends up in orbit? What kind of risk does the debris pose to spaceflight and space commerce? Joining me now to talk about it is my guest Nicholas Johnson, program manager and chief of the NASA Orbital Debris Program at Johnson Space Center in Houston. Welcome to the program, Mr. Johnson.

Mr. NICHOLAS JOHNSON (Program Manger and Chief, NASA Orbital Debris Program): Thank you very much.

FLATOW: Would it be fair to say that you're in charge of tracking all that junk?

Mr. JOHNSON: Well, actually, our colleagues at the Department of Defense do the tracking, so we rely on them quite a bit for the larger objects. We try to characterize the smaller objects.

FLATOW: Do they, does a little red phone go on if they find an imminent collision of something happening?

Mr. JOHNSON: Well, actually, there is a direct line from Cheyenne Mountain here to the Johnson Space Center in Houston to advise us just for that situation.

FLATOW: Mm hmm. I said there were 9,000 objects. I mentioned a few of them. Give us a range, an idea of the kinds of objects that are out there.

Mr. JOHNSON: Well, they go back all the way to 1958. One of the very first US satellites is still in orbit, obviously, it hasn't been functional for many decades, obviously, up to the international space station which is the largest object currently in orbit.

FLATOW: What's that one from '58 left over?

Mr. JOHNSON: It's a Vanguard satellite.

FLATOW: Oh, no kidding.

Mr. JOHNSON: Yes, sir.

FLATOW: It's still up there?

Mr. JOHNSON: Yeah, it will be for at least 100 years or more.

FLATOW: No kidding. How much does, do these objects pose as a risk, you know, to when we launch? I mentioned yesterday the mission to Pluto. I imagine every rocket that goes up there has to find, you know, find its way through that stuff.

Mr. JOHNSON: Actually, that's not too difficult, but we still go through the exercise, you know, even weird events can happen.

FLATOW: Mm hmm.

Mr. JOHNSON: But it's not a very great risk, but we do make sure that the way is clear for every trajectory out into space.

FLATOW: Has there ever been any real collision out there that has affected the health of any of the orbiting satellites or rockets or space missions?

Mr. JOHNSON: Well, we've identified three different accidental collisions which have occurred in Earth orbit over the last 15 years.

FLATOW: Mm hmm.

Mr. JOHNSON: And one of them did involve an operational French spacecraft. Fortunately, it was damaged but not sufficiently enough that it couldn't continue its mission.

FLATOW: Mm hmm. Anything within the last few months or year?

Mr. JOHNSON: The last collision occurred about a year ago in January of last year. It was an old U.S. rocket body and a fragment from a Chinese launch vehicle which had exploded a few years earlier.

FLATOW: Mm hmm. Is there any way to send up, for lack of a better word, a garbage truck or something to collect this stuff?

Mr. JOHNSON: Well, we certainly looked at that for quite a long period of time, and some ideas are technically feasible, but they're just not economically viable. The cost of removing an old rocket body or spacecraft right now is simply astronomical.

FLATOW: So to speak.

Mr. JOHNSON: So to speak.

FLATOW: 1-800-989-8255 is our number. What about putting something on a rocket that is being launched, knowing that someday you want to nudge it back down and burn up in the atmosphere?

Mr. JOHNSON: Well, actually, we have that pretty much in hand now. In the United States and internationally, we have what's called a 25-year rule which says that once you've completed the use of a particular spacecraft or a rocket body that you ensure that it comes down back to Earth within 25 years, and so that policy is gaining in its worldwide acceptance, and we're making good progress in that area.

FLATOW: Mm hmm. And as far as the other stuff, we just have to dodge around it now.

Mr. JOHNSON: That's right. In fact, what our recent study said that even if we were to launch no more objects from this point on that collisions will start to occur, and after about 50 years, the population will actually start to grow.

FLATOW: It'll get more.

Mr. JOHNSON: It will get more, more than there is today because things will start running into each other and creating more debris.

FLATOW: Is there a band in space, you know, an altitude where most of this stuff is located?

Mr. JOHNSON: The worst area is about 800 to 1,000 kilometers above the surface of the Earth.

FLATOW: Mm hmm.

Mr. JOHNSON: And that's simply because we put more things there over the years, and we've had quite a number of explosions in those areas, so the number of objects simply is greater there.

FLATOW: And where would the space station be in relationship to that?

Mr. JOHNSON: It's about halfway down. It's up, down to about 400 kilometers, so well removed from those particular areas, thankfully.

FLATOW: I imagine, and there must be somebody or something assigned to continually watching to see that the space station doesn't get hit or hit something.

Mr. JOHNSON: Yeah, we actually do those calculations three times a day. Yeah, we're always.

FLATOW: Really?

Mr. JOHNSON: We're always looking about three days into the future, so we're always updating and making sure we have the most accurate information.

FLATOW: Could there be things that are too small for you to see?

Mr. JOHNSON: Absolutely. We can only see things down to about four inches in diameter, so smaller things can pose a hazard. The space station, however, is the most heavily protected vehicle in space, and it can withstand impact from things as large as about half an inch in diameter.

FLATOW: Hm. 1-800-989-8255 is our number. Talking with Nicholas Johnson. So what is the solution? Do you have a solution to any of this accumulation of space junk?

Mr. JOHNSON: Well, to be honest with you, we don't yet. The United Nations looked at this issue several years ago, and we simply came to the conclusion that current technology doesn't allow us to go up and remove significant numbers of these objects. Fortunately, it's not a near-term problem. It's more of a problem that will arise later in this century, so that if, you know, we gain better technology, cheaper space transportation costs, maybe someone will come up with a good idea and we'll be able to start remediating (sic) the environment.

FLATOW: So you're saying, basically, there's no cheap fix to this.

Mr. JOHNSON: Unfortunately not.

FLATOW: Mm hmm. And it has not been built into the old junk that's up there, to get rid of it.

Mr. JOHNSON: No, but we are building it into the new things we launch, so that's the good news.

FLATOW: Mm hmm. Is it the stuff is just into so heavy and indestructible that it stays up forever almost?

Mr. JOHNSON: Well, the rate at which things fall back to Earth is really a function of their altitude, and if you're only, say, up where the international space station is today, things normally fall back within a few years or even sooner. But if you go up about twice that high, up to about 800 kilometers, then things will naturally stay up there for decades or hundreds of years.

FLATOW: Mm hmm. Let's see if I can get phone call or two. 1-800-989-8255. Rich in Rochester. Hi, Rich.

RICH (Caller): Yeah, I think you just touched on one of my questions. I was gonna ask at what point, at what altitude does the Earth's gravitational pull come into play? And also does the space station have any built-in protection against projectile junk in space?

FLATOW: Yeah. Good question.

Mr. JOHNSON: Well, the first question, actually, it's not the gravitational pull. It's the drag of the atmosphere. The atmosphere is very tenuous at high altitudes where the station is and other satellites, but it does exist, and that's what pulls things back. And if you're above 600 kilometers, then you're gonna be up there for, you know, typically, over 25 years or thousands of years.

FLATOW: Any, but the atmosphere doesn't it swell and contract?

Mr. JOHNSON: It does, and as you may know, the sun goes through a cycle every 11 years where it's active and less active.

FLATOW: Mm hmm.

Mr. JOHNSON: And we see a direct affect on atmospheric density. So during periods of high solar activity, we have an increase in the number of objects falling back to Earth, and during periods of low solar activity, the reentry rate goes down.

FLATOW: Mm hmm. And he also asked about if there's any protection on the space station.

Mr. JOHNSON: Again, it is highly protected. Over 200 different types of shields all around the space station, and we, again, dodge the larger thing. So we go to a great extent to protect those group that are up there.

FLATOW: I know I remember, I'm trying to remember what space mission it was and going back it was finding, something that was there in orbit for 20 years. And they brought it back and was just astounded by the amount of micro pits they found in it.

Mr. JOHNSON: Yeah, we brought back several articles, you may be referring to NASA's Long Duration Exposure Facility.

FLATOW: Yeah, I think that's…

Mr. JOHNSON: Was up there for several years.


Mr. JOHNSON: And brought back several things. In fact that's one of the ways that we understand how many very small particles there are. And these are particles typically less than five millimeters.

FLATOW: Mm hmm.

Mr. JOHNSON: And by counting the number of craters and figuring out what particle would have caused that size crater we can determine how many particles are out there statistically.

FLATOW: Do you also have to worry about meteorites coming in also, that might knock things off course and change the orbit of some these, the space junk?

Mr. JOHNSON: Fortunately, most meteorites are relatively small. So they will do minor damage. They certainly won't change the course of a satellite. But they could impact it. We've had a couple of satellites, which have been hit by meteoroids and they're still in space.

FLATOW: Mm hmm.

Mr. JOHNSON: And they actually have caused some operational problems, but typically this is not serious.

FLATOW: I remember when Sky Lab was taken down. Did it come down on its own? I know it was maneuvered to try to make it a safe reentry?

Mr. JOHNSON: It was…

FLATOW: When it first went down.

Mr. JOHNSON: It was basically falling back to earth on its own. We were able to in the very last part of an orbit to nudge it just a little bit. But most things fall back to earth completely uncontrolled.

FLATOW: Mm hmm.

Mr. JOHNSON: The good news is that most of those objects don't survive reentry. And the components that do survive reentry typically fall into the water or some poorly populated area.

FLATOW: What is the largest object that is still up there?

Mr. JOHNSON: Well now it's by far the International Space Station.

FLATOW: Well I don't want to, you called it junk not me.

Mr. JOHNSON: Oh, you said junk. Oh, the administrator will have my hide for that. There are some rocket bodies up there, which are in the order of six tons or more.

FLATOW: You mean old rocket boosters or?

Mr. JOHNSON: Yeah, the upper stages of launch vehicles.

FLATOW: We still have any Saturn Five stuff that's orbiting up there?

Mr. JOHNSON: Actually there are a few upper stages of Saturn's but they're not in earth orbit. They're in solar orbit and they come by the earth every now and then. And they'll come by typically, you know about the distance of the moon or farther. But close enough actually a couple years ago we saw one again after several decades.

FLATOW: And you can still track that sort of stuff?

Mr. JOHNSON: No we normally don't track that, it was sort of happenstance that we found it. Our tracking or DOD's tracking capabilities normally don't go out that far.

FLATOW: What a shock it must have been. What is that thing?

Mr. JOHNSON: That's right. We thought at first it was an asteroid, then by looking at it and taking readings for its spectral characters, what kind of materials it was made out of. And then going back and looking at its orbit we decided in fact it probably was one of the Saturn upper stages that had gone near the moon.

FLATOW: Wow. Nicholas Johnson, fabulous, thank you for taking time to talk with us.

Mr. JOHNSON: My pleasure.

FLATOW: And good luck on your tracking of the space junk.

Mr. JOHNSON: Well, thank you, sir.

FLATOW: You're welcome and have a good weekend. Nicholas Johnson is program manager and chief of the NASA, Orbital Debris Program at the Johnson Space Center in Houston.

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