THE WALL OF A TRILLION STONES
Nukes, lasers, orbital bombardment, and planet-destructing superstations are often found tropes regarding space warfare in fiction — but none calls more my attention more than the orbital blockades, because at first, they sound very stupid, bordering the level of logic of ground invasions.
We've seen before in comics and movies that space blockades often consist on the control of local spacestations and the equatorial region of the planet.
At first, it sounds silly to just plant a ring or partial section of reinforcements around the planet's equator, while the defenders can just launch from other places. Let's look at the Earth spinning for a moment, the poles experience a minimum rotation speed because the polar circles have a small circunference rotating over the course of a day, but this circunference gets larger towards the equator and the time it takes to rotate does not change, which means that the velocity must and does increase to a maximum value around the planet's equator — and this greatly benefits space launches because it reduces the necessary delta-V to leave the planet's surface, and thus reduces the costs of launches, because the rockets get a little kick from the Earth's surface.
Launching from the poles grants you no extra delta-V, and so all the work must be done by the rocket, while launching straight from the Earth's equator gets you a boost of ~1600 km/h.
So any blocks around tropical regions will drastically increase the launch costs and risks of spacetravel, depending on how efficient it is.
BLOCKADE ARCHITECTURE
Not gonna lie, it gets frustrating to discuss this with people because everyone assumes maximum efficiency or focus towards solving a problem, which is just impractical, sure the world has thousands of nukes at bay, but your average country simply does not, so guys, shut up — we're talking about multi-billion or trillion dollar projects to take down these blockades in the first case, when we can get to barely spend a few millions domestic food-supply or healthcare.
TECHNOLOGICAL
Pretty straightforward, disabling a considerable part or all of their stationed network of stations and satellites — ideally with an electromagnetic pulse like that of a small nuclear device (up to 300 kt) which can have an effective radius of some few thousand kilometers in space for temporary damage, or a moderately sized one for permanent disruption of all surface and air devices, the element of surprise is essential because countermeasures to EMP's exist for extreme solar activity incidents. This would essentially send their comms back to short-range analogical technology, imagine sending a future humanity all the way back to early 60s or 70s communication tech with only a handful of sturdy satellites online, the crash in economy this would cause. Even a small detonation at ISS height could affect an area the size of North America.
PHYSICAL CONTROL
This is about going to the blockade with an array of warships under your command, and taking down any ship with fire.
You won't want to take over the orbital infraestructure of the attacked planet because they might as well destruct it themselves in order to affect you, so taking them down is one step into trapping them at home. Unless those stations serve of critical strategic importance for you blockade and movements within enemy territory, a well placed explosive charge is the approach you want to take.
This can be particularly hard to execute depending on how practical are your defesive and offensive technology, and actually, way harder than the nuke approach because you're putting your own infraestructure at risk in this.
KESSLER SYNDROME or COLLISIONAL CASCADING
Along with the nuke EMP, this is the second if not best model for a space blockade, because if well executed, it will be a nightmare to clean and rebuild from it. Kessler Syndrome is the condition in which the lower orbits of the planet become so littered with debris or space junk that traveling through this layer of objects is impossible or really difficult.
Here's a few things from BRUTE FORCE MODELING OF THE KESSLER SYNDROME by Sergei Nikolaev et al.
For Low Earth Orbit or LEO zone (orbiting less than 2000km from the surface), there are about 15 thousand manmade objects greater than 10cm in size — this includes dead and active satellites, boosters, paint flakes, bolts, and all sorts of broken equipment and slag from launches and previous satellite collisions, with some studies pointing the instability of orbits between 700 and 1000km from the surface due the presence of such junk. Nowadays the type of close encounters between objects in LEO occurs at some 10km or less scale, and our objective in this post is to dramatically increase the closeness and occurence of these.
If we continue to do launches as frequently as we do today, the number of objects may increase to four times or some 65 thousand objects until 2100. This results in nearly 3 encounters a year, with 2 of them involving intact objects meeting fragments. This occurs because large assets such as large satellites and space stations have larger surface areas exposed to impacts, as it increases to the square of the radius, whereas whole object encounters are much more rare.
In the case that we continue to launch as often as we do today, the number of encounters at less than 100 meters will have increased to 50 per day by 2100. So 1.0~1.5 collisions per decade with debris, and 1 whole satellite collision every two decades.
Now let's talk why this condition is also called collisional cascading: imagine a car, it is composed of some 30 thousand small parts with every bolt and nut, and some 1800 parts accounting for mounted components. Put this car in space, it is one single object, but any considerably catastrophic impact will make this one car into a cloud of some few hundred up to thousands of small parts in divergent orbits, which in case can and will cause more assets to be shredded into more parts, thus initiating a cascading reaction of collisions. Again, for the purposes of our blockade we will, on purpose find a way to potentiallize this phenomenon, which only works with mid/high tier technological societies like us.
My attempts at a mathematical regression relating the number of objects to the number of encounter and collisions rendered the following:
THE OBJECT OF CHOICE
There are several things we can use for these objects, from literal junk, to pebbles, to nuts, or satellite parts... A single 1/2" nut weighs about 30 grams. So 10 billion nuts would cost us nearly 300 million kilograms of carbon-steel, and at 7 american cents a unit retail cost, this is a raw cost of 700 million american dollars as of 2022.
We can conserve the mass of our blockade and decrease the object mass anywhere between 1 and 30 grams, which puts our object count in the range of 10 to 300 billion — this would increase our impacts per decade from 1250 to 7130. Such count of objects would render between 0.009 and 0.26 nuts per cubic kilometer if evenly distributed in a shell between 400 and 2000km from the Earth's surface, if we limit ourselves to orbits between 400 and 1000 km however, we can pack close to 1 nut per cubic kilometer.
Another way to increase the virtual object count is to limit ourselves to fill out a torus around the Earth instead of a shell, this way, blocking the tropical zone. Giving between 0.06 and 8 nuts/km³, but with the total height of the torus approaching 1000 km, this isnt very efficient, unless you're determined to litter the LEO in several batches of objects.
Of course, our objects don't have to be nut-shaped but it could also take the form of nails, spheres, amorphic rocks, or caltrops. The shape is important because the atmosphere swells with increasing solar activity, increasing the atmospheric drag and thus the number of reentries, achieving less than 10 reentries during minimum, up to an average of 100 reentries during solar maximums. So caltrops or nail-shaped objects sound appropriate to avoid much atmospheric drag and thus extends the halflife of our blockade, this also increases the effective impact radius of our objects.
Alternatively, we can use rocky pebbles from milling down a small asteroid, if we want to keep our cloud of 10 billion 30g objects, then the asteroid we are looking for is precisely between 60 and 64 meters in diameter, for a total mass of 300 million kg.
As of the 2020s, the technology required for asteroid mining is still crawling, the OSIRIS-REx in a sample and study mission only returned only about 60 grams of material costed 184 million dollars for the equipment only and 800 million for the Atlas V rocket — which is pretty salty — let's say that a dedicated mission could carry between 10 and 100 kg of material per shipment, for the same cost, we would still need to make 3 million travels at a grand total of 3000 trillion dollars to mine that rock to the last grain. Not to speak that it takes around 7 years for a trip to and back from NEO's, what to say of asteroids in the asteroid belt. Mining from Mars however could cut the trip time to half or less of that time, since Mars orbits much closer to the asteroid belt, being smaller than Earth and at a higher orbit, the delta-V required for missions is much smaller, making the economics of the launches much cheaper.
THE LOGISTICS OF MINING A HUGE ROCK IN SPACE (kinda?)
It takes around 11 months of travel between Earth and the asteroid belt, plus a few weeks to approach, land, mine and take off from your target asteroid, then flying back for another 11 months, the whole trip this way took little over 2 years and you got a few hundred kilograms of mineral, costing about 2 billion dollars, and with nearly 11km/s of delta-V. That's what mining the asteroid belt in the 2040s or 2050s might look like.
Now, doing these same calculations for a mission departing from Mars, it requires less delta-V (about to 7km/s) but little more time, about 1 year and 3 months to reach the belt, add few weeks for all the work, and another 1.24 years back, and your mission took about 3 years, BUT despite the longer time, we compensate by saving fuel or being able to bring more stuff in the next payload. In the case we want to take this material from Mars to Earth instead, it takes about those 11 months on the trip back (2.1 years total).
It is kind of nasty how it is easier to explore Mars as a waypoint to mine the asteroid belt, even though the time is practically the same, there is quite some savings in fuel which can be used to toll more material back to Earth at the same cost of an Earth-Belt trip. This same ease can also be used to deliver our cloud of pebbles, nukes, or even whole rocks towards Earth.
Based on the Apollo mission spendings on Delta-V, our Mars-Belt-Earth trip would consume around 20,000 ft/s of delta-V (14.5 km/s), we would need about 91 thousand kilograms of rocket fuel for the whole endeavor. A thrust plataform with the similar capabilities of an Atlas V rocket is more than capable of executing such a mission, which puts our base cost at least 800 million dollars.
Let's say a small permanent mining station weighs about the same as the MIR station, on the range of 100-200 tons, at current prices per kilogram of payload, the price of putting such station in orbit is about 20-40 million dollars — give it some 500 million dollars for development, launch and initial operation costs, and the price of such a mission to fetch 300 million kilograms of being 22 dollars per ton (little over the price of iron per ton), total cost of our mission (minus dispersion) is.... between 1.3 and 2.0 billion dollars! Maybe even as little as 4 billion dollars with more material or a more robust station.
THE DISPERSION METHOD
There isn't any good dispersion methods I can think of for deploying this many objects, assuming you can actually pack billions of little caltrops in a spaceship or several spaceships — the most efficient thing that comes to my mind is to build a rotor which can spread them out through centrifugal force in all directions, Mark Rober style. As this would ensure nearly even spread of objects filling orbits at all orbital inclinations.
- M.O. Valent, 05/12/2022
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