For the obvious reasons, I invariably get too busy to blog exactly when things get interesting...
Orbital Debris
As explained before, when preparing the games, we need to coordinate our lasing activities with the Laser Clearinghouse, so we know that we don’t accidentally illuminate a satellite. By the time our laser beam reaches orbital altitudes (let’s say 200 km) it is very dispersed – about 200 meters across – but it can still pose a risk to sensitive downwards looking optical equipment (wink wink nudge nudge). The Laser Clearinghouse is a Department of Defense service whose purpose is to coordinate lasing activities above the horizon, so that commercial lasing activity is not impeded. In military parlance, this is called “Deconfliction”. Sounds more like a psychiatric term to me.
When the real Space Elevator is built, laser-satellite deconfliction will have to be undertaken on a constant basis, but we’re also going to be faced with a more difficult problem: tether-satellite deconfliction. The tether, unlike the laser beam, cannot be turned off when an impending collision is predicted. Instead, it has to be physically moved out of the way, which is done by moving the ship-borne anchor point, since the rest of the tether will follow the anchor. The risk we’re mitigating is actually greater than in the case of optical satellites – the risk here is of actually breaking the tether, causing the portion that is below the cut point to fall back down to earth.
The same deconfliction technology – projecting satellite orbits far enough in advance and looking for collisions threats – also comes into play today when looking at multiple satellite and other metal fragments (known as orbital debris, or “space junk”). Remember that all low-orbit objects are moving at a speed of about 5 miles per second, but they all move in different directions! Not too recently, a commercial communication satellite was destroyed by such a collision with an inactive satellite. It is interesting to note that each collision creates a large number of additional fragments, and so if there are enough satellites in orbit, the increase in fragment density will cause additional collisions, and so we will end up with a cascade effect, a chain reaction, and lot of dead satellites. We’re not there yet, but the problem of orbital debris is an important one to keep track of, especially in the context of a Space Elevator.
The good news is that the orbits of small orbital debris objects decay faster, especially at the low orbital altitudes where they are prevalent. If we stop producing space junk, a large fraction of it will disappear after 5-10 years. This is a lot cheaper than going after the pieces afterwards. The problem is that it is human nature to save money at the present, even if it means incurring large expenses in the future, since the future is someone else’s problem.
Which brings us back to Spaceward’s motto – “The future is closer than it appears” – if we keep polluting low earth orbit at the current rate, it will become our problem very soon. Yet even today, satellites are not equipped with de-orbiting devices that will prevent them from becoming orbital debris sources.