Problem: Collisions

First, it is important to understand what space debris collisions actually are. Everything that stays in space is in orbit, and most of those orbits are not orchestrated with each other. Satellites have been placed in orbit for more than 50 years, by inaccurate rockets. The vast majority are derelict, unresponsive, and out of fuel. A significant fraction are rocket upper stages. They are subject to drag, light pressure, gravitational non-linearity, and other orbit modifiers. And most are tracked by a few ground based radars, with limited visibility and atmospheric path distortion. Thus, it is not clear what is up there, and typical prediction errors are on the order of a kilometer.

Still active satellites have limited reaction fuel. Near misses - satellites coming within the 1 kilometer error range - are frequent. Collisions - coming within a couple of meters - are rare, but occur every few years. That creates more debris and more collisions. The frequency of collisions goes up as the square of the density of satellites - much higher in the thin shell of Low Earth Orbit, below altitudes of 500 kilometers or so. The collision frequency also goes up with velocity (higher in lower orbit) and average inclination - highly inclined orbits are more likely to cross paths with high closing velocity.

A few collisions have been intentional - Anti-Satellite Warfare tests, most recently by China. Typically, the collisions that make the news are between valuable satellites and old derelicts. One such collision occurred in 2009, between one of the 78 Iridium communications satellites and a derelict Soviet Cosmos military satellite. This collision occurred over the north polar region, where there are no tracking radars, and orbits are inaccurately modeled.

Server Sky Collisions

Server Sky arrays will eventually fill large regions of space. They will all be traveling in the same large pattern, in allocated orbits with the same period, all surrounding a central equatorial orbit. Nearby server-sats will be moving at nearly identical velocities. A constellation of server-sky arrays will never be in self-intersecting orbits. They can only - potentially - collide with other objects that cross their orbit.

Most objects are in low earth orbit, a few are in GPS and Geosynchronous orbits. In between, there are a few objects in elliptical transfer orbits - mostly spent rocket boosters and failed satellites. Since most of these transfer orbits are inclined, they only cross the equatorial plane in two places. If those crossing places are at higher or lower altitudes (99% are) they will not intersect a server-sky satellite until their orbit changes significantly.

Because server-sats use light pressure for maneuvering, they do not run out of fuel, and will remain in position as long as at least a portion of the redundant control circuitry is still operable. If a server-sat fails completely, another server-sat can slowly push it towards a disposal area. Unlike traditional big-iron satellites, a server sky array will never go dead and out of control - when obsolete, an array will gather in one place and wait for disposal.

Server satellites can act as orbiting phased array radar illuminators. In combination with sensitive dish receivers, they can locate and track orbiting objects, even small ones, that might eventually pass through an array and possibly cause damage. In a day or two, an array can reposition itself away from the path of the collider. This is another advantage of an "infinite fuel supply". If the server sky data is good enough, it can be used to accurately predict collisions between other satellites. Server sky technology can potentially greatly reduce satellite collision rates.

Carefully positioned gaps in the clouds can be allocated to provide safe passage for objects passing through, such as high orbit launches.

Even if an array completely loses control, and server-sat light pressure shifts the orbit so that perigee is in the densely occupied low earth orbit region (where all collisions to date have occurred), the server-satellites are soon cleared out of that orbit by atmospheric drag. The "ballistic coefficient" is so very small that even the residual gas at 1000 kilometers altitude is enough to decay the orbit in a few years. At the 300 kilometer altitude of the international space station, the drag is enough to bring down a server satellite in hours.

In the distant future, we may launching billions of server satellites into orbit per day. We will be launching much thinner satellites to much higher orbits, well above geosynchronous orbit. From there, the delta-V to earth escape is smaller than the delta-V to earth reentry. If we lose control of all of them, only a few will return to earth, and they will do so over a very long time. Meanwhile, perhaps a thousand tons of meteoric material falls to earth every day, and a lot more passes by the earth. So the additional effect on orbital assets will be small, and if we have lost control of server sky, we have probably lost control of those assets, too.

It is hard to imagine a scenario where server sky adds to the existing space collision problem. Different altitudes, different orbital planes, better control, and active collision warning and avoidance, along with an aggressive program to remove obsolete server satellites, will make server sky an essential part of the solution.

Kessler Syndrome estimates of "critical mass" are relevant at some density of occupation.

Space Elevators

If space elevators ever come to pass ( launch loops are more likely ) they will pass through the orbital plane of the serversats twice a day. Gaps must be created for them. However, a failing space elevator cable will likely sweep through areas without gaps. In a densely populated server cloud, this may smash many server-sats, and the flying debris from those might damage more. Eventually, the non-synchronous debris will slow down to cloud velocity, but not before it bumps into a lot of server-sats. Cleanup after a space elevator failure will be expensive.

MORE LATER