The first two posts in this series have focused on the pros and cons of using rockets and mass drivers to collect raw materials in orbit. This post will discuss the merits of capturing an asteroid using what I’m calling the Planetary Resources (PR) method. As far as I can tell, PR will capture whole asteroids (small ones) and somehow drag them back to more convenient orbits closer to Earth for processing (as opposed to strip-mining them or processing the ore on-site).
Let’s start with the advantages:
- Easier transportation to destination – The more accurate way to state this is that it takes less of a change in velocity (delta-v) to move asteroids around the Earth-Moon system than it does to haul materials up from the Moon or Earth. This is because asteroids are already at the top of the cislunar gravity well. In other words, one should expend less fuel moving a typical asteroid from its orbit into, say, geosynchronous orbit, than one would on moving an equivalent mass from the lunar surface to geosynchronous orbit.
This is a HUGE advantage. Perhaps an Earth-bound analogy will drive home the point. Consider two mines on Earth. In one, the ore is laying on the surface and just has to be picked up and trucked to the processing facility. This is the PR method – snagging an asteroid and sliding it to where it needs to go. Now, consider another mine where the ore is buried deep underground. First one digs up the ore and hauls it to the surface and then it has to be trucked to the processing facility. Obviously it’s a lot more work to move all that heavy stuff around but this is what happens when ore is collected from the Earth or the Moon and then transported into orbit. By eliminating the need to haul the material up out of a gravity well, Planetary Resources has a great advantage over the other methods.
- Provides massive infusions of raw material – Thousands of tons of material will be delivered immediately upon the arrival of a near-earth asteroid at the destination. No other technology known today has the capacity to deliver thousands of tons in one delivery. Rockets can, at most, deliver tens of tons of material. Space elevators and mass drivers provide a continuous trickle of material that, over time, can add up to thousands (even millions) of tons –but it requires patience. If you need a lot of space rocks and you need them right away, asteroid capture may be the way to go.
- Provides goodies – Asteroids could more easily provide resources that are not known to exist in great quantities on the Moon and are difficult to haul up from Earth e.g. rare platinum group metals, volatiles or even hydrocarbons.
But what about those disadvantages:
- Lots of unknowns – No one has ever captured, or barely even landed on an asteroid. Pristine asteroidal material has never been examined on Earth. The composition of different classes of asteroids is essentially unknown and manipulating asteroids is, at this point, a best guess. Can a rubble pile asteroid be de-spun without it falling apart? Can a volatile-rich asteroid be “bagged” without all the water and oxygen boiling off and popping the containment unit? Mastering the capture and processing of asteroids will take many years, as well as the coordination of the swarms of robots it will take to accomplish these tasks. It may be decades before these techniques are commercially viable, especially when compared to the more familiar technologies required to exploit lunar resources.
“A mine is just a hole in the ground owned by a liar”
– Mark Twain
- Long delays between deliveries – While a mass driver or space elevator provides a steady continuous trickle of material to orbit, asteroid capture provides huge shipments once every two or three years. This time lag will complicate processing as facilities will have to be designed to store or digest a huge amount of material when the asteroid arrives but will then lay fallow while they wait for the next shipment. It could lead to inefficiencies.
- Potential public relations problem – I’m not going to spill too much e-ink on this topic but it is possible that the same Luddites who oppose nuclear-powered space probes could oppose and potentially derail or delay asteroid mining because they fear “killer space rocks” being positioned closer to the Earth. Even though putting them into a more convenient orbit makes it easier for them to be deflected and diverted should something go wrong.
So, lots of pros and cons for this item. Stay tuned for the final installment regarding lunar space elevators.