I was reading entry #4 of this Cracked article, which says that the events of the film Gravity would basically end the space age, and I wondered: Does anyone know, or have a guess or a link, to how much junk it would take chucked into orbit either from below (launched from the surface), or above (alien attack) to render it impossible (or at least prohibitively risky) for an Earthlike planet to maintain a space (weather, communication, and spy satellites, missions to other planets) program? Say the aliens chuck Ceres into a really big blender and render it down to, uh, BB size? And then inject it into a whole bunch of crisscrossing orbits around the Earth. No more space program? Overkill? Underkill? Without further intervention, how long would such a quarantine last?
This is the so-called Kessler Syndrome, suggested by Donald J. Kessler of NASA in 1978. http://en.wikipedia.org/wiki/Kessler_syndrome
yep, it is possible; it could happen by accident, or be triggered by a well-deployed anti-satellite missile ( or several). You wouldn’t need to grind up Ceres, or even Comet 69P.
I think the Kessler Syndrome is a little overstated. Not that we should be blowing up satellites with missiles willy-nilly, but it’s not quite the civilization-ending event it’s usually presented as.
Anything with a perigee below a few hundred kilometers will deorbit on its own in a few months to years due to air drag. This includes the orbit the ISS occupies, for instance, and other interesting stuff.
So space won’t be cut off completely. It’s not in fact true that “We couldn’t even send missions to fix it, because the debris would shred anything else we sent up”, as the article says–a laser-based cleaning satellite could start at lower altitudes and progressively move upward.
Another thing is that the debris cloud will tend to organize itself over time. Early on, debris will be moving every which way. So any orbit at a given altitude will be dangerous. But the debris will collide with itself, and those pieces which are moving relative to the majority of debris will tend to either turn into even smaller debris, or get sent into another orbit altogether (hopefully one that intersects Earth’s atmosphere). Eventually, most of the debris will be mostly moving in the same direction, and at that point a satellite could be put there with little danger. Collisions aren’t so bad when you have the same velocity.
Well, there’s one thing the movie got wrong (not that this should be a surprise to anyone). There’s no way you’re going to have orbital collisions at 50,000 mph. Orbital velocities are basically an inverse function of the distance from the center of the Earth and low Earth orbits have velocities about 17,000 mph. Since it’s an inverse function, the higher the orbit, the slower it moves, so that’s about as fast as anything in Earth orbit can go. Even allowing for prograde-retrograde collisions, that’s a maximum of 34,000 mph.
However the Cracked article has problems as well. It says cell phones are useless without satellite communications. Ditto for the internet, and by implication, telecommunication in general. Wrong on all counts. Cell phones only talk to the nearest cell tower, not to comm satellites. And there’s lots of telecommunication that goes on without using satellites at all. Far more than that which uses them, in fact. There’s lots and lots of fibre-optic cables all around the world that carry the bulk of the world’s telecomunication. At most there’ll be some islands that aren’t connected by undersea cable that will be cut off.
That’s not to say that things will be just peachy without any functioning satellites. As they note GPS will be out, and there seems to be more and more things we are doing with GPS every day. Weather satellites will also be out so weather predictions will take a major hit. There’s various other satellites that observe the Earth or the Universe in various ways, but those generally don’t affect people on a daily basis.
The higher you go the longer it takes. Below about 500 km, though, we’re talking just a few years. The ISS is at ~400 km and it would deorbit within a year or two if it weren’t for the periodic reboosts.
Only once you get to roughly the 800 km range does it start taking many decades. These are definitely useful orbits but if we really had to, we could make do with lower ones. Satellites can be equipped with electric drives so that they can have a useful lifetime in these orbits. I know of a guy who wants to build really low-altitude imaging satellites using an electric drive to keep it aloft; for equivalent resolution, the optics on a satellite at 250 km are 1/8 the size as they are at 500 km.
As far as the debris field cleaning itself out through collisions… it’s really hard to say since it depends on so many factors. It’s definitely a secondary factor compared to the air drag, though.
You don’t need satellites for a positioning system similar to GPS. Space is convenient but it’s not the only method. You can put up tall towers and broadcast line of sight positioning signals from there. It’s going to take a huge number of towers, though, to get coverage comparable to GPS.
You can also use a smaller number of towers and use shortwave radio frequencies. The signals bounce off the ionosphere so you can receive a signal without line of sight. This method introduces inaccuracies, though.
If we had to get by without GPS satellites being practical, you’d use a system similar to LORAN for long distance, approximate positioning. Then, when airplanes come in for a landing, you’d send line of sight radio beams to the aircraft from fixed locations at the airport or aircraft carrier. For car navigation, you could paint 2d barcodes (QR codes) onto the street or street signs so that automated vehicles would know their position.
You could also use high altitude balloons instead of satellites for communication (the balloons would probably drift too much for positioning)
There’s actually been quite a bit of work done on this over the years. Kessler himself, after whom the “syndrome” is named, has written about it quite a bit (as you’d expect). As you wouldn’t expect, perhaps, he’s not unduly alarmed about it. It will take some time to clean up, of course. The time depends upon how intense the effort is, but runs a couple of decades. He assumes we will be starting sometime soon.
That is the problem – as far as I know, no one has an active program for cleaning up space, or even an active effort that will result in a program. It’s an easy thing to put off – a very expensive program with no immediate obvious results, and therefore a hard sell. There have been a number of exotic suggestions for getting the stuff down, including space-based lasers and sending up “chewing gum” satellites to which debris will cling, but Kessler and others advocate essentially going up there and rendezvousing with the junk and bringing it back.
You also have to realize that the issue is one of altitude, or distance from the earth. The reason that “space” got so cluttered so fast isn’t that we’re filling up not the vast empty void between the planets, but only relatively narrow spheres centered on the earth in relatively well-defined orbits. Stuff in Low Earth Orbit will eventually slow down due to atmospheric friction and come down on its own. Stuff in Geosynchronous orbit is a lot rarer – we don’t put a lot of stuff up that high (it costs more in fuel and effort. And, being farther away, doesn’t see as well or communicate as easily as stuff lower down. Plus, being bigger, you have to fill a lot more space in order to get the likelihood of collisions).
It’s the stuff between these regimes that’s in trouble. The time for atmospheric drag to pull it down is a lot longer, so it’s effectively up there forever, and it’s close enough so that a lot of things were put there, leading to the likelihood of collision. This is the regime that needs to be cleaned out. Not doing so means risking your communications satellites, weather satellites, and other such relay points. Plus, if you get that “chain reaction”, this filled layer could make sending anything up problematic, since in order to get to higher orbits you still have to pass through this layer.
I’m being vague because I’m not at home right now. I have a collection of papers on this at home, and I can link to them later tonight.
First, everything is pretty much going in the same directions. Everyone launches in the direction of earth’s rotation to add that velocity to a launch, it’s free momentum. There are some polar orbit satellites and associated debris (IIRC, there was actually a collision about a decade ago) and the Iridium constellation was in a number of weird orbits to provide full coverage, but the vast majority of stuff out there is going in the same direction; the only difference being the angle, the Russians needing a larger angle vs. equator than the KSC launches or Guyana. Even more so, stationary satellites in geosynch orbit are all going the same direction, nobody puts satellites up there to go the wrong way…
(Of course, even a collision with debris doing a few hundred kph different from you is a serious matter. I recall one discussion in the media about a paint chip collision that left a small pit on a shuttle window).
Second, decay - Skylab lasted what, about 6 years before it de-orbited? Ditto for Mir. Mind you, these were basically “sails”, lots of area for wind resistance vs. weight, but not a lot of debris is made to be heavy. It’s thin metal aerospace bits, generally - exploding bolts, pieces of launch vehicles left over from separation, etc.
NASA tried to track this. I read one article they were tracking about 40,000 pieces in orbit. Nations try to limit this, now, being aware of the issue. China got a lot of grief a few years ago when it tested a satellite killer, cleverly filling the orbit with pieces of killer and target.
As for wild scenarios, IIRC the shape of Saturn’s rings is determined by “shepherd moons” at the edges of some rings. These are tiny moons that “herd” the pieces of ice that make up the rings. Anything slows to get close to the moon, the moon “speeds” it up to get back into place; same for anything that collides and starts going to fast out of the ring - the outer shepherd’s gravity slows it down. Anything that departs the plane is pulled back down… and so on.
You could make it work. The balloons would know their own position by using fixed ground stations. Mobile stations would figure out their position relative to the balloons, and then their absolute position by querying the balloon positions. The real problem is coverage; there’s no practical way to make it global. Would work in densely populated areas, though.
It would almost certainly do a good job, but getting it up there would be a problem. The payloads on rockets are limited in dimension. You could, in principle, make the rocket look like a lollipop (thin stick with giant ball on top); it would experience more drag in getting into space but if the payload were light enough it might be all right. Even so, I doubt you could launch anything bigger than a few tens of meters.
I’m thinking a large balloon made not of a strong material but rather weak, like thin plastic. Fill it with a dense gas, and colliding debris will shed much of their velocity on impact; hopefully enough to lower their perigee into the atmosphere. Of course the bag will become riddled with holes over time and thus leaky. Maybe there’s a way to make it self-sealing, but if not one could just keep a large supply of bags on hand and periodically replace them.
Yeah, you’d pretty much have to manufacture it in orbit. I’m envisioning a payload of the condensed starter material launched into orbit and then somehow “puffed out” by some automatic chemical reaction- if any aerogels can be made that way, and in the volumes required.
I think there would still be some issues in the lower altitudes with objects coming down from above and polluting the space. The question becomes a matter of the distribution of debris amongst the different altitudes and how quickly debris would enter the “usable” space at lower altitudes. Isn’t it possible that the lower altitude would take much longer to really clear out?