Space Exploration Stack Exchange is a question and answer site for spacecraft operators, scientists, engineers, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
I heard that Kessler Syndrome would essentially end space exploration, but how expensive would it be to get past it if Earth really wanted to?
To be more specific about the Syndrome, suppose all the satellites some time in the future, say in 2050, were destroyed.
It is worth reading http://webpages.charter.net/dkessler/files/KesSym.html and some of the linked articles in that article are also very informative reading, altough can be quite technical.
The first thing is that a cascade does not happen in a matter of days or even months. Instead what happens is increasing density of debris reduces the expected lifetime of a satellite.
Not all orbits are affected. The main problematic orbit is low earth orbit. Very low orbits, where atmospheric drag is significant, will not be badly affected because the atmosphere will quickly remove debris. Below around 800 km atmospheric drag will be reasonably effective as the orbits of debris will decay in the matter of decades.
Particularly problematic is low earth orbits in the range 800-2000km, at these altitudes it takes centuries for atmospheric drag to remove debris, the debris in those orbits stay. With nothing removing the debris, the density is free to build up from collisions. The low rate of orbital decay and the fact that they are below the van allen belts are factors which make these altitudes attractive for satellites.
Even in the worst case scenario, the low low earth orbit would remain reasonably hospitable because the atmosphere is quickly removing the debris and the very stability of the higher orbits means the debris flux from higher orbits would be reasonably low. During the worst of a kessler syndrome cascade there would be significant extra debris even at very low earth orbit, but it would improve in a matter of years.
In higher orbits, the orbit doesn't become unusable per se. Instead what you have is probabilities. With a desired mission lifetime in mind, a level of shielding is required for a certain probability of achieving that lifetime. Above a certain projectile mass (~100g) shielding becomes impractical. However, the same debris which are too large to shield against, are also large enough to track effectively, so active collision avoidance could be used. Both shielding and provision for active avoidance adds mass and complexity to the satellite.
Middle Earth Orbits will not be badly affected because the density of satellites is much lower. The density of satellites is much lower because these orbits are not as useful (also the van allen belts are found in MEO, and are problematic for satellites at certain altitudes). A satellite would still need to pass through the LEO debris belt, but it comes back down to probabilities, there is a probability of collision which damages the satellite, and you can add shielding to reduce the probability of damage to a level deemed acceptable. Also, a path can be plotted which avoids trackable debris.
In summary then, even in the case of a very bad kessler syndrome, very low earth orbits, where orbital decay measured on the matter of years, will remain quite usable. Collision avoidance and shielding can be used to reduce probability of satellite destruction to acceptable levels. It may be the case that certain altitude ranges become effectively unusable because the expense of making a satellite which can survive in the debris belt, would be greater than the expense of either having the satellite in a lower orbit (requiring frequent boosting) or a higher orbit (requiring a more powerful rocket and a dangerous pass through the worst of the debris). I think the impact of a kessler syndrome is sometimes exaggerated, although being deprived of the most useful altitudes and the destruction of nearly all existing LEO satellites would certainly be very harmful to humanity's ventures in space.
If you are talking about going through the debris, not staying in it (i.e. an escape trajectory or hohmann transfer to cleaner orbit) then the ship would only be in LEO for a few minutes to hours. Only the most severe Kessler Syndrome would cause a problem.
Kessler syndrome describes the cascade effect of debris to debris impacts. One catastrophic impact can cause many smaller object each capable of causing a further catastrophic impact, hence the cascade.
To be clear, if in 2050 all satellites are destroyed this isn't strictly Kessler syndrome. It also depends on how much all the satellites are destroyed. A good measure for this is the median cross sectional area of the resulting cloud of material. If the cross sectional area is very small, then the mass is even smaller! If you assume all objects are spheres then you can see through the area of a circle ($\pi r^2$) and the volume of a sphere ($\frac{4}{3} \pi r^3$) as you get 2 time smaller in radius you get 4 times smaller in area and 8 times smaller in volume (and hence mass). So very small particles actually deorbit pretty quickly because they have a much lower ballistic coefficient.
Now to your question:
If the object are small say 1mm or smaller we can handle the impact of them easily with existing technologies such as wipple shields. Anything larger and you're in more trouble. Assuming you don't want to first remedy the debris situation you're left with a few choices:
So in terms of expense you're looking at increasing cost the further you go down the list. Whether is be launch costs (at say \$10,000/kg) for extra mass or development costs for wormhole technology (at say \$1 Bazillion). Putting a accurate number is going to be difficult without a narrower question (spatial density of objects, median object size etc.)
I'm guessing that it would be cheaper to clean up the space debris than to build and launch a super strong shield for everything you send into space. I'm also not sure that we have the technology to build a shield like that at the moment.
As pointed out in another answer, orbits decay, so you can also just wait it out. Orbits tend to decay faster for objects in lower orbits, so it would probably be best to focus efforts on cleaning up higher orbit debris and larger debris items first.
What follows is a back-of-the-envelope calculation of what it would cost using small ion thruster "tug" satellites to deorbit all debris larger than 5cm in earth orbit at the moment (Note that this still leaves an enormous amount of debris smaller than 5cm that can still easily inflict a lot of damage as well):
The scenario outlined above is probably the least efficient way to do it, but it might give you an idea of the upper limit for cleanup operations.
The Kessler Syndrome does not end space exploration. At worst it delays it. The number of satellites in LEO is self correcting in a few decades see Space debris half life
If the amount of objects in LEO orbit gets high enough, they can become a fuel/reaction mass resource Can I get higher with Space Junk?
With sufficient technology it is not a concern, consider a star trek type shield, you would just turn it on and drive though same as debris in space. (I think we have a question/answer around this also, but not seeing it)
