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IRA FLATOW, host:

You're listening to Science Friday from NPR News. I'm Ira Flatow. The mission to repair the Hubble Space Telescope, now scheduled for May, may be delayed due to the collision last week of two satellites in orbit. The dangerous debris - perhaps a thousand pieces - increases the risk to the space shuttle and its crew that would service the Hubble. But why did no one see this crash coming? And is there any way to clean up the Earth's orbital environment? And what other satellites may be in jeopardy? All of this caught us all by surprise. And here to talk about it with us is Mark Matney. He's an orbital debris scientist - that's a nice job - at the Johnson Space Center in Houston. Our number, 1-800-989-8255. Welcome to Science Friday.

Dr. MARK MATNEY (Orbital Debris Scientist, Johnson Space Center, Houston, Texas): Thank you, sir.

FLATOW: What kind of evaluation are you making about the repair mission?

Dr. MATNEY: Well, there are a number of different aspects that go into risk from any kind of orbital debris. There's the normal - we call it the normal background environment of orbital debris. We've been doing activities in space now for 50 years, and we've built up quite a bit of space junk up there.

FLATOW: Mm hmm.

Dr. MATNEY: And then we also look at - when there's been some sort of recent unusual event, like the Chinese anti-satellite test two years ago.

FLATOW: Right.

Dr. MATNEY: We try to see if there's some extra risk from that. And then of course, we had the event that happened last week.

FLATOW: And so, when should we know whether the Hubble mission is going to be delayed or any trouble with it?

Dr. MATNEY: Well, it looks like what we'll be doing is accumulating information - maybe a little later we can talk how we do that - accumulating information on the size of this cloud. And about mid-March would be about the time scale when we're really starting looking at what the risk is and what sort of things we can do to try and mitigate that risk. And a final decision will be made in April.

FLATOW: Well, let's talk right about that - talk about accumulating the information.

Dr. MATNEY: OK, it turns out that when you hear about a break up, the news will talk about so many pieces that have been - that are being tracked. And those are objects that are big enough to be seen by what we call the Space Surveillance Network, which is run by the Department of Defense - the old NORAD system and sensors like that - that can actually track the objects, figure out where it's going to be in the future. Those are objects generally larger than about 10 centimeters, which is about 4 inches in diameter. And those are pretty small, if you consider you're measuring those at…

FLATOW: Like a baseball.

Dr. MATNEY: Yeah, baseball size at a thousand kilometers or several hundred miles, that's a pretty impressive achievement. But the problem is there are debris smaller than that that can still do a lot of damage to our spacecraft. We know that objects even 1 centimeter in size, which is about the size of a Tylenol tablet, at orbital velocities can really do a lot of damage to a spacecraft. And of course, the space station, the space shuttle have very, very valuable cargos on board.

FLATOW: Yeah, yeah. If you say you can track something larger than a baseball, why didn't we know that these collisions between two big objects was going to happen?

Dr. MATNEY: Well, the problem is there are a lot of objects up there. Right now, we track something - the Space Surveillance Network tracks something like 18,000 objects in space. So, it's very, very busy. And the other thing is, even if something's going to have a close approach, we don't know for sure if it's actually going to collide or not. All we can do, because of limitations in measurement and limitations in propagation - propagating those orbits forward in time - and limitations on what the atmosphere is exactly going to do in terms of drag, we can only give a probability of collision. So, even if you knew that two objects were going to be coming close to each other, you could only give the odds on a collision.

FLATOW: And the fact that these are not military threats or, you know, they're tracked by a government organization - does the fact that these are civilians satellites mean that you don't track them, you don't warn anybody?

Dr. MATNEY: Well, the situation on how information is done about collision avoidance, that's a really a Department of Defense job. I don't know exactly who gets warned and so forth, things like that. But I do know that the Department of Defense does collision avoidance on our manned assets for NASA - the ISS and the shuttle - and for certain other government assets. But there's been a lot of discussion through the years about doing collision avoidance about other things. But the Department of Defense is - part of the problem is it's not their job to do, you know, the…

FLATOW: Yeah.

Dr. MATNEY: Policing low Earth orbit, so…

FLATOW: I've got enough to do. If you want to police your satellites do it yourself.

(Soundbite of laughter)

FLATOW: Well, that makes sense if you got - how many ten of thousands you have up there?

Dr. MATNEY: Eighteen thousand that are being tracked.

FLATOW: Eighteen thousand?

Dr. MATNEY: Eighteen thousand.

FLATOW: So - and this was a huge collision, wasn't it?

Dr. MATNEY: It was a pretty big - pretty big collision. These were two rather large spacecraft, both of them were little less than a ton, but they were pretty good sized spacecraft. And the latest numbers I've heard is something on the order of 600 tracked debris. And right now, I believe 132 have been catalogued, which means you can go online and look up the information on the orbits on those objects.

FLATOW: And we should expect more of these in the future as…

Dr. MATNEY: More collisions or more debris?

FLATOW: Yeah, more - both I guess.

(Soundbite of laughter)

Dr. MATNEY: Yes. We've been looking for this for a long time because space is...

FLATOW: You mean expecting a collision like this?

Dr. MATNEY: Yes, eventually. Space is a finite environment. It's big, but we actually launch things into space quicker than they come down. So, you don't have to be a rocket scientist to know that if you keep putting objects into a finite space, it's going to get crowded after a little while.

FLATOW: Yeah, let's go to Bryan in Grand Rapids. Hi, Bryan.

BRYAN (Caller): Good afternoon, Ira. I'm wondering - I know they got treaties about space and stuff like that, but in cleaning up some of that debris, can they take a net up there and just kind of swoop some of that up and send it back to burn up in the atmosphere?

FLATOW: Big fishing there, right?

Dr. MATNEY: That would be a nice thing we could do. The problem is is things orbiting in space are traveling at very high velocities - 7 kilometers a second is a typical velocity. That's about four and a half miles per second or about 16,000 miles per hour. And the problem is things are going in different directions. And so, in order to catch up with one thing, it takes a tremendous amount of energy to do that. It's a little bit like trying to catch bullets from guns with a net. It's - and these things are traveling much, much faster than a bullet.

FLATOW: Wow. So, there's no way to actually - once they're up there, they're up there, and they're coming down whenever they want to?

Dr. MATNEY: Well, there's some - yes, that's - for the small things especially.

FLATOW: Yeah.

Dr. MATNEY: Now, for big things you have some control over them, especially if it's an operational spacecraft. Some spacecraft have rocket engines aboard and can try to lower their orbit if you want to deorbit them. And there is a little bit of atmosphere up there, and it causes things to drag down. It just takes a while to do that.

FLATOW: What is the biggest source of junk of up there?

Dr. MATNEY: Well, up until recently, the biggest source of junk was actually explosions in space. It turns out that when people use space, they typically use an upper stage to put a satellite into orbit. And that stage - when they've deployed the satellite, that stage becomes a piece of space junk. And oftentimes, there's a little bit of fuel leftover. And if you know - as you know, rocket fuel is very explosive stuff, and usually there's an oxidizer in there. And sometimes, if engineers leave fuel onboard, at some time in the future, that fuel can explode, maybe a decade or a year down the road. So, one of the things we've been trying to educate people on - satellite users - for a long time is when you're done with something, get rid of that onboard energy source. Clean up after yourself. And that helps avoid explosions.

FLATOW: Well, why not use that little rocket and the rocket fuel there to put it in some safe place when you're done with it?

Dr. MATNEY: Well, people are looking into those sorts of things. And we've done some experiments with that, and it is possible in some situations. But - and one of the things is you can try to burn your rocket to try and drop it into a lower orbit that will decay quicker and burn up in the atmosphere.

FLATOW: So, in the near term then, we're just going to have to put up with what's going on. And is there one orbital pattern in space that's more crowded than the rest of them?

Dr. MATNEY: Well, in terms of altitude - the problem is all the orbit planes cross each other. But in terms of altitude, from about 700 up to about 1000 kilometers is very, very busy. That's about, oh, about 500 miles - 400, 500 miles up to a little higher than that - 600 miles, something like that - is very, very crowded. Now, it turns out the ISS and the shuttle fly well below those altitudes. So, they're actually in a relatively benign environment compared to those high altitudes. Unfortunately, that's also where a lot of operational satellites operate - robotic space craft.

FLATOW: Yeah. You mean the communication satellite?

Dr. MATNEY: Well, the communication ones like Iridium and OrbComm operate - OrbComm may be higher, but Iridium operates in that altitude - but a lot of scientific satellites, a lot of military satellites - just a lot of different types of useful things. Now, the satellites you're thinking of - the communications satellites are - the ones you should think about are the ones that geosynchronous orbit, which is quite a bit higher.

FLATOW: Yeah, they're at 40,000 miles or something.

Dr. MATNEY: Yeah, 22,000.

FLATOW: 22,000.

Dr. MATNEY: Yeah.

FLATOW: Yeah. I knew there was a four in there.

(Soundbite of laughter)

FLATOW: But there are a lot of ones below - the lower ones - that you can move them around, right?

Dr. MATNEY: If they have fuel on board, you can move them around. For instance, a Hubble Space Telescope does not have rocket engines on board. So, it can't move around. It's basically orbiting happily uncontrolled.

FLATOW: So, there's no short term solution to this?

Dr. MATNEY: Well, there are - it turns out the thing you can do today to help the long term is to clean up after yourself. Like I said, remove - get rid of your spacecraft out of Earth orbit in a reasonable length of time. And the number we've talked about with our international colleagues is 25 years. When you're done with your spacecraft, get it out of orbit, out of the crowded region in about 25 years. And if you could do that, it turns out it helps a lot down the road.

FLATOW: Is it - could it get too crowded up there that it gets too dangerous to put any more satellites up?

Dr. MATNEY: Well, there's - it's always a probability. I mean, could it? Maybe in a hundred years, it might get that bad. I don't know. The problem depends on how many collisions we have and so forth, and it tends to be certain altitudes are more crowded than others. But the problem is, again, as you put more objects, more mass, big objects in space, we're going to have more collisions, and collisions create lots and lots of little debris, which is what everybody's worried about.

FLATOW: And that - and some of those pieces come raining down on our heads after a while?

Dr. MATNEY: Well, the little pieces aren't too bad. They usually burn up in the atmosphere. It's the big things that we worry about raining down on our heads, like Skylabs and Mirs and things like that.

FLATOW: It was that debris that came flaming over - I saw it on the news the other day - that was possibly from that collision, right?

Dr. MATNEY: No, no. It definitely was meteorites. Scientists - some researchers on the ground have already picked up pieces of the meteorite. It was a natural event.

FLATOW: Yeah, so every time somebody sees something like this, they say, there goes some more space junk,and you have to go out…

Dr. MATNEY: Right. Guilt by association in this case.

(Soundbite of laughter)

FLATOW: So, what is your life like there? You have a very interesting job title.

Dr. MATNEY: Yes, it is. It's very interesting. I tell my daughter, every time I come to work, I know I'm going to learn something new every day.

FLATOW: And how many - so, you're involved in the orbital debris?

Dr. MATNEY. Yes.

FLATOW: Exclusively?

Dr. MATNEY: Yes. Well, we do a little bit of other things. For instance, there's natural debris in space, that's meteoroids. Sometimes - we have our colleagues at Marshall Space Flight Center. We work with them sometimes on meteoroids. But most of the things we do is manmade debris - how it's made, how much stuff is up there, what can we do to try and prevent it in the future, and what can we do about it today.

FLATOW: Well, you have a job I don't think that you'll be out of for a while.

Dr. MATNEY: Well, things have been busy lately.

FLATOW: Yeah. (Laughing) Thank you very much for taking time to be with us.

Dr. MATNEY: You're welcome.

FLATOW: Mark Matney is an orbital debris scientist - now, there's something you can major in when - if you want to get into something - at the Johnson Space Center in Houston. We're going to take a short break and come back. We're going to talk about all these great new 3-D animated features coming up. We have some of the biggest names and scientists and a gentleman who's credited with the modern invention - invention of modern 3-D technology. 1-800-989-8255. Also, you can Twitter us, @scifri, and talk about 3-D technology and also in Second Life. So, stay with us. We'll be right back after this short break.

(Soundbite of Talk of the Nation theme) FLATOW: I'm Ira Flatow. This is Science Friday from NPR News.

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