I saw the opening of *Gravity* and it was pretty terrifying, but to quote Billy Bob Thornton in *Armageddon*, it’s a big-ass sky.
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Yes, the space junk will eventually deorbit. But “eventually” is a long time and, before it does, it will take out most of our satellites.
It’s so dangerous because it’s an expontential growth problem…the likelyhood of a collision depends on how many bits of junk there already are, and each collision creates more junk. You can reach a tipping point where the frequency of collisions goes up very abruptly and the probability of any particular thing getting hit goes from effectively zero (“big-ass sky”) to something meaningfully high. j
It’s taken decades and tens to hundreds of billions of dollars (possibly trillions) to build our existing space infrastructure. A runaway Kessler effect could wipe all that out in months, far faster than we can replace it, and it would render low-earth orbit effectively unusable for years/decades. It would ruin our ability to do a lot of stuff that we currently take for granted without *tons* of effort and money.
You are right, eventually all of those object’s orbits will decay and come back to earth. The problem is that the rate of increase of number of objects will become enormous as more and more objects collide, creating more and more objects, until our navigable space is no longer sustainable. And what is there will take generations for them to naturally decay and burn up. One burns up, but we create 100 or 1000 more.
It’s a real problem, and until we come to grips with it and create technologies that can start to capture and eliminate the threat, it will continue to get worse. And China and Russia do an occasional test kinetic attack on a satellite and create thousands more.
It will fall back *eventually* but can cripple very important systems for tens to hundreds of years
NASA has estimates for how long it takes for debris to come down at various heights. At 600 km (50% higher than the space station) it takes a few years, at 800 km its decades, and 1000 km and up you’re looking at centuries. An incident in Geostationary orbit could remove all the communication satellites there until we can figure out a way to clean up the debris, they all exist in a narrow ring around the equator and are not impacted by atmospheric drag.
Centuries with no chance of a space station or GPS or satellite communication networks would severely disrupt global logistics for a longgg time
*Gravity*’s physics is not the best out there, but the premise of a kessler cascade is sound.
It’s a big sky, but it only takes a little bit of debris to destroy a satellite and one destroyed satellite produces a *lot* of debris.
And yeah, after a few years most of it will be gone, but not all of it.
Higher orbits will last much longer, so depending on how high our satellites are that have the issue, it could go on a *very* long time.
Orbital debris cannot just “drift off into space”. An object’s kinetic energy defines its orbit. Without a means of propulsion, an object’s kinetic energy cannot increase (unless during a collision, another object transfer’s some of its kinetic energy).
Over time, friction with molecular gases (the remnants of Earth’s atmosphere that extend many thousands of kilometers above the planet) and collissions with dust and other debris gradually robs an object of its kinetic energy, reducing its orbital height until it reaches thicker parts of the atmosphere and its rate of deceleration increases sharply, initiating re-entry.
Between 100 km and 500 km in altitude, an unboosted satellite will re-enter in anywhere between a matter of hours to a couple of years, depending on the satellite’s size and density. Beyond 1000km in altitude, a satellite will remain in orbit for many thousands of years.
Should a Kessler event produce a cloud of debris above 1000 km in altitude, safe space flight through that region becomes impossible.
Things don’t drift off into space when they are in orbit. It requires energy to do that.
It’s like expecting a ball to roll up a mountain.
It will eventually deorbit or maybe get captured by the moon if it is high enough, but it will take a long time to deorbit, and until it does, there is a much bigger chance of hitting stuff in orbit, which is not good if you want functioning satellites.
Simply that there are enough items in low Earth orbit that collision becomes a factor to consider when putting anything into orbit. That and an object the size of a grain of sand can be moving fast enough to poke a decent hole into something important before it gets pulverized into smaller dust.
A few years ago, China launched a rocket/missile at a satellite, blowing up the satellite and creating an even bigger cloud of really fast moving debris. Imaging floating bits of metal that are going really fast in a direction opposite to your satellite but in its flight path. It’s basically a bullet aimed at your satellite. You need to hope it hits a part that’s not crucial.
Imagine when a satellite gets hit. If it gets hit badly enough, then pieces of that satellite can fly off and create more flying debris, creating even more of a problem, and so on and so on and so on.
Well space junk does end up falling back into the lower atmosphere. Its called orbital decay. Basically there is still enough atmosphere a few hundred kilometres up that is slows down spacecraft slowly. So space junk does erode. But the rate of humans putting junk into orbit is greater than its natural erosion.
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