Kessler syndrome is a theoretical scenario in which the density of objects in low Earth orbit (LEO) due to space pollution is high enough that collisions between objects could cause a cascade in which each collision generates space debris that increases the likelihood of further collisions.
The density can be greatly increased deliberately by deliberate collision with other satellites. This could be an early act in a war, reducing the value of space to the enemy by killing or disabling communications, positioning, observation or military satellites.
Satellites use many different orbits. Some use geostationary orbit, so that they can stay in the same direction in the sky. Polluting that orbit with debris clouds would disable satellite TV for example but that orbit is very high and it would take a lot more debris to cause a problem. Also, many channels available via satellite are also available via terrestrial or internet channels, so although it would be inconvenient for some people, it would not be catastrophic.
On the other hand, low orbits are easier to knock out and are more densely populated, so are a much more attractive target.
With such vulnerabilities, it is obviously useful if we can have alternative mechanisms. For satellite-type functions, one obvious mechanism is a high altitude platform. If a platform is high enough, it won’t cause any problems for aviation, and unless it is enormous, wouldn’t be visually obvious from the ground. Aviation mostly stays below 20km, so a platform that could remain in the sky, higher than say 25km, would be very useful.
In 2013, I invented a foam that would be less dense than helium.
It would use tiny spheres of graphene with a vacuum inside. If those spheres were bigger than 14 microns, the foam density would fall below helium. Since then, such foams have been made and are strong enough to withstand many atmospheres of pressure. That means they could be made into strong platforms that would simply float indefinitely in the high atmosphere, 30km up. I then illustrated how they could be used as launch platforms for space rockets or spy planes, or to use as an aerial anchor in my Pythagoras Sling space launch system. A large platform at 30km height could also be strong and light enough to act as a base for military surveillance, comms, positioning, fuel supplies, weaponry or solar power harvesting. It could also be made extendable, so that it could be part of a future geoengineering solution if climate change ever becomes a problem. Compared to a low orbit satellite it would be much closer to the ground, so offer lower latency for comms, but also much slower moving, so much less useful as a reconnaissance tool. So it wouldn’t be a perfect substitute for every kind of satellites, but would offer a good fallback for many.
It would seem prudent to include high altitude platforms as part of future defence systems. Once graphene foam is cheap enough, perhaps such platforms could house many commercial satellite alternatives too.