I have been reading “Spaceflight, A Smithsonian Guide,” which includes a special little feature called Hazards of Space Debris:
“Thousands of pieces of debris – many of them microscopic – are already in orbit. Traveling at speeds up to 17,500 mph, they can seriously damage spacecraft and threaten the safety of the astronauts. If traveling at high speed, a speck of paint an inch or two in diameter could damage a spacecraft and endanger its crew.”
And then the book goes blithely on. I know space suits are supposed to be puncture proof, but there is so much junk in orbit, and whenever it collides with other junk, it makes more junk. Is it a matter of time before someone’s helmet is smashed? Or a hull is breached?
Someone in NASA or otherwise in the know please respond.
Astronauts are my heroes.
How much danger are they in up there?
Anything large enough to cause serious damage to the shuttle is being tracked by, IIRC, NORAD. One or two shuttle missions ago, they had to shift the shuttle’s orbit, because a little chuck of metal was expected to come within a couple of miles of it.
I’m not sure if they’re able to track everything large enough to puncture a suit. But they don’t spend all that much time outside the ship.
Can they track such small objects, though?. A fleck of paint (Yes, PAINT) took a gouge out of one of the reinforced windows of one of the shuttle missions (Don’t remember which). A single steel BB traveling in an opposite orbit would be able to punch clean through the shuttle and destroy just about anything in its path. Might not kill the shuttle, but it’d definatly make it hard to do ANYTHING (No way you’re re-entering with a hole in your heat shield, even after you patch the holes (Entry and exit) to stop the pressure-loss).
From what I understood, such small objects were not tracked by location, but by “knowledge” of their location; If an object leaves debris in orbit, its location and velocity is recorded and tracked that way. Or can they actually find something that small?
I’ve been following this for quite a while. There was an article on it in Scientific American IIRC. Last week there was an hour-long show on it on Discovery or THe Learning Channel. The problem has gotten worse, aspparently, with recent launches of private industry satellites (which apparently have an appallingly high failure rate). As they pointed out on the show, one French satellite failure can reliably be credited to a debris collision, and there’s good reason to think that a 1960s satellite failure might be. According to the show, they attempt to shield astronauts by positioning them in the “lee” of the space shuttle and by limiting their time outside. According to the show, the standard suits offer a lot of protection to paint-chip-sized objects.
It seems to me that this is a serious problem for future space missions. Orbital debris is clearly a man-made pollution problem. The show sugested that there is no way to clean it up, but IIRC some SDI proponents have been working on just such proposals. I know that Arthur C. Clarke talked about such cleanups as an essential prelude to building a “Sace Elevator” in The Fountains of Paradise.
Just another good reason not to go shooting off projectiles and “Brilliant Pebbles” in orbit.
Objects smaller than tens of centimeters are extremely hard to pick up on radar.
According to Table 1 from the UN Technical Report on Space Debris the most sensitive radar currently in operation can detect a bit of debris 6 mm in diameter at 1000 km. The Radar has a field of view of 0.1 square degrees, so it’s not practical to use it to survey the entire sky for space junk.
A bit of calculation shows that this sort of resolution leaves some dangerous objects undetected:
A 40g bullet moving at 1500 fps = .02 kg at 609m/s (rifle bullets typically 40 g, speed 1200-2200 fps)
has an energy of 4172 kg/m^2 S^2 An object traveling in low earth orbit at 6 km/sec would have to mass ~83 milligrams to match the energy of the bullet. If the object were a bit of ice, that would make it about 4.5 mm in diameter; which is below detection by even the best radar.
Fortunately, there is a LOT of space even in low earth orbit. A quick and dirty calculation shows that it’d take ~1.1E12 particles to sweep all the orbits between 100-200 km with a 1 meter resolution in ~90 minutes. (The calculation is based on the area of an annulus/2. It ignores all sorts of restrictions required by orbital mechanics). That’s quite a few more particles than the thousands to millions of bits of junk that are up there now.
It seems to me that astronauts in orbit would not be in much danger from space debris that is also in orbit, because if they were in the same orbit, their speeds would have to be the same, so the relative speed of the junk would be close to zero. Of course, if the orbit of the junk was highly eccentric, then there could be a speed differential, but in that case the junk would be more likely to hit the atmosphere and burn up. So it looks to me as if the main danger to spaceships and astronauts would be during take-off and re-entry, when their motion would be (more or less) perpendicular to the motion of the debris.
I don’t question the fact that it would be extremely difficult to track all the little pieces of debris floating around up there, but is the reason really due to the size?
I read the book Skunk Works (so that is my only authority on this subject) and the author said that radar signatures are due to the shape of an object, not the size. In other words, on radar, a B-52 (actual size) and a 12 inch identical model of a B-52 are going to look like two identical B-52’s. As if it were the way the radar is reflected and not the amount of radar beams (or whatever) that bounce back.
So, I guess it comes down to the initial identification, input into the computers and tracking of said debris. The radar doesn’t follow it because it wasn’t identified in the first place, not because it is “too small” for the radar.
I did some work on the preliminary space station studies.
Yes, it is only a matter of time before an astronaut dies due to space debris.
If it makes you feel any better, I doubt very much that the danger would stop the astronauts from doing what they love. Those are some tough cookies, make no mistake. Even so, the day after Challenger we were talking at NASA Ames, and all the engineer folks there agreed we’d go up in the next shuttle, regardless of the risk.
Hulls have already been breached. I could dig out the specifics of a Russian situation, if need be. The Russians, quite cleverly, built their equipment away from the side of the MIR, so they could get to a leak quickly and seal it. I can’t remember all the details, but it was reasonably ugly. They patched it, and in the end, no one was hurt.
By the way, Richard wondered whether there was really any danger, since both the astronaut and the debris were “in orbit”. The information you’re missing on this point, Richard, is that orbits can be in any direction, including exactly opposite one another. The collisions worried about are not the 100 mph ones, but the 10,000+ mph ones.
I just saw a special on this a couple of days ago on The Learning Channel.
Couple of facts I thought I would share from the show:
There are radar stations around the world that actively monitor 1,000s of pieces of debris in space. Some of it is only a few cm across. (As a side note, the radars are so powerful that they would cook in minutes any animal that walked in front of the transmitter).
When a small object hits an armored metal panel at 8000mph, it punches a hole through it. The force of the impact also liquidates the object. So there is a danger that a small object wouldn’t drive through the entire shuttle, it would breach the first wall and spray the interior with hot molten metal. Scientists can armor the leading edges of space stations with multiple layers spaced apart so that the object will be vaporized before it reaches the inner hull. This doesn’t work with big objects.
One concern is that a chain reaction could be created in orbit. The theory is that if we put enough satellites and space stations in orbit, a major collission could create so many particles that other satellites would be destroyed, creating more debris, and so on. The result would be a semi-permenant ring of space junk that would make orbital flight suicidal. This seems kind of an exreame case though.
Other than that, it seems pretty straightforward. There’s some debris in space but not that much (space is, after all, pretty big) and a lot of it eventually gets pulled down to Earth (another concern is where it lands). If a small piece were to hit the anything at 10,000mph, it would be like shooting it with a cannon, only worse.
Richard has a good point, that a piece of space debris isn’t likely to be in an orbit opposite the Space Shuttle: It’s cheaper to put things in a west-to-east orbit than an east-to-west one. Even if the orbits are not exactly opposite, though, you can get some pretty high relative speeds. For instance, the standard Space Shuttle orbit has an inclination of about 30[sup]o[/sup] (whatever the latitude of Cape Canaveral is; I’m too lazy to look it up at the moment). This means that if the Space Shuttle is crossing the Equator southwards, and a bit of debris from a previous shuttle mission is crossing northwards, then the relative speed could be as high as the Shuttle’s orbital speed. You could get speeds even higher if, for instance, the Shuttle is on a mission to the ISS (inclination fifty-something degrees), or the debris is in, say, a polar orbit.
Objects smaller than the wavelength of the radar do not reflect the beam nearly as well as objects that are many times the wavelength. The increased resolution available at short wavelengths is why radar gas progressed from the multi-meter long forms used in the 40’s and 50’s to the centemeter length waveforms used today. Look at the wavelength column in table 1 of the link I provided, the radars are running at these wavelengths in order to increase their ability to detect small objects. The author of “Skunk Works” is correctin stating that the shape of an object affects its’ reflectivity, but I’m sure he did not mean to imply that radar could as easily be used to track beachballs and atoms at a distance of hundreds of kilometers.
If its the same show I saw on TLC awhile back I remember it having this ridiculous, enviromentalist “man is evil” attitude to it. It kept treating space like it was the rain forest or the oceans, that it was a limited resource that short-sighted man was ‘polluting’.
It never pointed out the obvious fact that the mass of all the junk man has ever put into space is so small that, even in terms of just low Earth orbit, calling it ‘pollution’ is nonsense.
Actually it would be fairly inexpensive to “pollute” low earth orbit to the point where nothing but well shielded spacecraft could survive. All you’d have to do would be boost ~2300 tons of water, or similar substance, into low orbit, and then blow up the rocket. If you did it right, you’d end up with ~2.3E12 droplets with a mass of ~ 1mg each, all in different orbits…
That’d be enough to seriously mess with anyones plans for low flying satellites, and at $1000 per pound to launch could be done for under 5 billion dollars. (For quicker destruction, or faster interdiction, just increase the number or mass of the particles)
Geostationary orbits could be made untenable with a similar technique.
next time i unpack that old Saturn V i have somewhere in the basement i will be sure to try that out!
lemme add the essentials to my shopping list.
[ul]
[li]pay water bill in advance[/li][li]buy plastic explosive (remember! use shaped charges!)[/li][li]1000 cases trash bags[/li][li]more hydrogen![/li][li]eggs[/li][/ul]
i think i will go and get that ol’ Saturn V out of the basement right now.
Putting 2300 tons of anything into an orbit 23,000 miles high would be a tad more pricey than low Earth.
Sure, if everyone in the country were suddenly struck insane we could do it. My point was that show was implying that we were already past the point of no return.
If you used fresh water, wouldn’t the droplets or ice crystals sublime fairly quickly and eliminate the problem? All that would remain in orbit are any previously dissolved minerals.
They sure would, and that’d be a real plus if all you wanted to do was wreck your enemies satellites, missiles etc. Water would be a good choice for clearing out geosync orbits because it would get the job done and then sublime, leaving leaving you with nothing to worry about except debris from all the satellites you’ve wrecked. It wouldn’t matter so much in low orbits 100-200 km as anything you put up would come back down in a few years anyway.
Hail Ants, I think the “point of no return” argument refers to some recent calculations on what would happen if one of the satellites already up there blows up into X million pieces and one of those pieces hits another satellite and causes it to explode etc. etc. There’s a density at which the reaction becomes self sustaining. I have no idea how they calculated it, but apparently some folks at least think we have already achieved the critical density.