by Adam Manning
One of the regular conference calls took place last week for the space colonies' study group for the British Interplanetary Society and we had an in depth discussion about some of the fundamental components of the classic concept for space colonies as set out in the works of Dr Gerard O’Neill and others.
In particular, we discussed the use of mass drivers on the lunar surface as a way of propelling material from the Moon to the point where the colony is to be constructed. This is typically given as L5, which here is used to refer to a point in the Moon’s orbit around the Earth that lies sixty degrees behind the Moon.
If a space colony were put in orbit around the L5 point it is expected to remain there almost indefinitely due to its gravitational equilibrium. In the concept of space colonies put forward by the studies in the 1970s, the space colony is largely made from material mined from the lunar surface. This material is then propelled to L5 using a mass driver.
|A mass driver on the lunar surface|
A mass driver uses a long series of electromagnets to accelerate a payload so that the payload is moving fast enough to launch off the surface of the Moon into space. Dr O’Neill and his colleagues were able to achieve quite remarkable results using prototypes they developed. Whilst as a technology the mass driver has seemingly rather languished in obscurity since that time, the similar rail gun concept has received more attention and the US Navy recently revealed the advanced stage that their development of the rail gun as a weapon of war had reached.
In considering the rail gun, we noted the very large energy requirements involved and considered the implications for the proposed mass driver on the Moon. Whilst the energy requirements for a mass driver would presumably be less on the Moon than on Earth due to the much lower gravity and virtual lack of an atmosphere, there can be no doubt that this would still be an intensive operation and the original plans, such as set out in Colonies in Space by Thomas Heppenheimer, call for a nuclear power station to be installed on the Moon for this purpose. This of course would entail practical problems by itself, not least of which would be the general hostility and caution that launching nuclear materials from Earth involves.
Thinking through these issues lead to a reconsideration of the plan as a whole. Perhaps one of the most substantial change in outlook since the seventies when the original plans were drawn up is the much greater awareness of Near-Earth Objects (NEOs) and in particular the asteroids that make up a large contingent of NEOs. It was suggested that the construction of a colony could be simplified by use of the resources of NEOs.
NASA is currently working on a mission to capture an asteroid and then move it to lunar orbit. This striking plan, known as the Asteroid Retrieval and Utilisation mission (ARU), was considered by us as a possible precursor for the sort of activity that might form the basis for an alternative method of colony construction. ARU proposes using essentially a net to capture an asteroid and then transfer it to lunar orbit using an unmanned spacecraft.
|Illustration of astronauts during an ARU mission|
Here, an asteroidal NEO could be retrieved in a similar way and then transferred to L5. Once in position, it could then directly be fashioned into the structure that was needed to form a space colony. The material of the asteroid could be fashioned into the main structure itself along with perhaps the shielding that is needed to protect the inhabitants of the colony from cosmic rays.
Ostensibly the advantages here are a simplification and shortening of the mode of construction of the space colony. Rather than having to construct a lunar base and its attendant mass driver and then propel the construction material to L5, then build what Heppenheimer refers to as the construction shacks and then build the colony itself, instead the colony is simply fashioned out of the body of the asteroid with the colony then in place once it is completed. One particular advantage of this asteroid utilization would be an incremental approach. A smaller asteroid could be used at first to construct a small habitat, such as the construction shack itself. As larger asteroids are captured, larger habitats could be built until a full colony was established.
Objections to this approach include a certain lack of knowledge of the structure of asteroids, particular NEO ones. For example, it may be that they are simply not dense enough to be used in this way. Indeed it is speculated that some smaller asteroids are actually bundles of rubble kept together by gravity rather than a solid mass. The ARU mission, which NASA hopes to complete by 2025, may hold the answers to this. Similarly, a large asteroid may have fault lines running through it or sections that have a different density from others. In this case, the operation may involve processing the asteroid material into a suitable condition rather than just effectively carving the colony out of it. A combination of both methods might also be employed.
This brings to mind another method of using NEO material not considered during our discussion. This plan has been proposed by, amongst others, Al Globus, a much respected advocate of space colonization. In brief the plan, called AsterAnts, involves launching solar sail powered spacecraft from the International Space Station to retrieve small NEOs (between 50 cm and 1 metre in diameter) and returning them to the ISS for the material to be processed. At that point, the new material can then be used for new spacecraft, the extension of the ISS, rocket propellant and so forth.
This discussion bought home to me the realization that this was a striking difference in how the original plans by Dr O’Neill might be if drawn up today based on asteroid material rather than construction based on lunar soil. We also discussed how the introduction of these extraterrestrial resources could affect the global economy and how this would be regulated by a legal system.
I’m looking forward to further discussions with the other participants from the British Interplanetary Society’s study group and hoping we have another of our meetings at their headquarters as well.