Orbit All the Things

To get to a higher version number in the Space 2.x. series, we will need to go beyond simply (!) reusing rocket first stages, as SpaceX does with their Falcon 9 rocket (Space 2.0). A few other rocket companies are working towards partial reusability as well, but the approaching implementation of the very large and fully reusable rockets known as Starship and New Glenn is likely to so re-structure space launch that these smaller efforts (Ariane, Soyuz, Vulcan) will become inconsequential. Let us call this outcome Space 2.1.

Space 2.1, with its unprecedented reduction in launch costs, will likely exacerbate the orbital debris problem by triggering an exponential increase in the number of satellites. In early days of space exploration, little thought was given to the fate of spent upper stages and expired satellites. Today is different. These hulks occasionally collide, at high velocities, shattering into multitudes of fragments, each of which becomes a potential participant in future collisions. This situation leads eventually to Kessler Syndrome, analogous to criticality in a nuclear reactor. As we increase the number of expired objects in orbit, the collision rate increases to the point that a chain reaction occurs and an exponentially increasing number of flying shards reduces the expected lifetime of a launched payload to an interval far too short to justify launching it, essentially cutting off access to space, possibly for centuries.

Today, if you launch a satellite, you need to responsibly deal with the spent upper stage, and with the satellite itself once it expires. The main benefit from this regulation is to simply postpone Kessler Syndrome, as the number of orbiting objects still increases, all the more with Space 2.1. What is needed is an active program to remove expired objects from orbit. This is just as expensive, if not more so, as putting them there: you have to match orbits with your target, attach to it, and then burn propellant to give it Earth escape velocity or force re-entry. Fortunately, with Space 2.1, this becomes a lot cheaper, and realistic projects for actively preventing Kessler Syndrome can now be imagined, leading to a situation we might call Space 2.2.

Another consequence of the formerly prohibitive expense of space launch is that exploring the Solar System has mostly been a series of one-off probes, whether flybys or orbital missions. Orbiters give the best return, typically lasting a long time and providing a continuous stream of data about the conditions and dynamics of the body of interest rather than a snapshot. But orbiters are really tough to pull off. You need to pack enough propellant just to slow down and enter orbit – half or more of the total mass of the probe, mass that won’t be instruments. With Space 2.1 that is still the case, but at least the costs of all that extra mass are now much lower. An expanded series of Solar System orbiters can now be envisioned. Coincidentally, to pull off Space 2.2 (anti-Kessler) successfully, we will probably need to supersede the one-off mission concept, at least in Earth orbit. Once your anti-Kessler craft attaches to its target and burns propellant to de-orbit it, will also de-orbit, unless it does another burn to prevent re-entry. This additional burn requires having enough propellant left over from the original mission. With Space 2.1 it becomes conceivable to envision a refueling network, so that your very expensive anti-Kessler craft can, through frequent servicing by tankers, de-orbit dozens of hulks. It doesn’t take much imagination (although it would take a lot more engineering!) to extend this concept to maintaining a network of orbiters around all the planets and moons of interest, Space 2.3, if you will. Orbit All the Things!

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