Few people are talking about settling asteroids. However, there was a brief time when asteroid mining was a hot topic. NASA’s official “next step” was missions to asteroids (as part of the road to Mars). Several companies were formed expressly to mine asteroids and return the material back to Earth to sell. Unfortunately, by 2020 almost all of this activity has ended and asteroid missions are back to being strictly robotic and exploratory. No crewed mining and certainly no settlements.
NASA had a plan to redirect a very small (4-meter) asteroid into Lunar orbit called the Asteroid Redirect Mission. The main purpose of the program was to develop deep space exploration capabilities for future Mars missions. The secondary objectives were to develop asteroid capture and planetary defense tech. The program was officially cancelled in 2017, with only the solar electric propulsion system still being researched.
The private sector was busy as well, for a while. Several asteroid mining companies gained a measure of fame, if not success, before being bought out by non-asteroid mining companies. Planetary Resources, Inc. and Deep Space Industries to name two. Some just disappeared. As of 2020 there are still a few small companies working on asteroid mining but the focus for everyone else has shifted to Luna and Mars.
Mining (and perhaps settling) asteroids isn’t a medium-term dead-end like Mars. Resources from asteroids can easily and cheaply (if slowly) be sent to cis-Lunar markets. But it sure isn’t as easy (relatively speaking) as building settlements on Luna. And why would we settle an asteroid anyway?
There are three main reasons why asteroid mining operations are going to require people on-site, regardless of the dangers and expense. First, the name “near-Earth asteroids” is deceptive. They are only “near” in relation to other asteroids. Most of these asteroids can be pretty far away depending on where they are in their orbit. Remote control of mining robots and equipment will be difficult, at best. Second, stuff will break. And third, humans are substantially better than machines at dealing with the unexpected. We need people at the asteroid to effectively control and maintain the equipment.
Some, perhaps most, asteroids are resource rich. Gold, platinum, and silver are thought to be abundant in some asteroids. Iron and other construction metals should be common and easy to find in large amounts in most asteroids. More importantly, some asteroids contain large amounts of water and critical elements, such as nitrogen and carbon. All of these resources would have value in a cis-Lunar marketplace, and some could be sold directly to Earth. A settlement could be very successful with the right asteroid and technology.
There are four basic ways we could gain access to asteroid resources.
- Asteroid mining operations could simply send the raw material to cis-Lunar space for processing. This would be the simplest and cheapest option because it would require the least amount of equipment and people. Raw materials will include a lot of stuff that is common in cis-Lunar space (rock, iron, aluminum, etc.) so this would be the least efficient method.
- Raw materials could be processed on-site and the finished materials could be sent to cis-Lunar space. This would require more equipment and people to be on site. That means more people at risk unless they are adequately sheltered.
- We can also move the asteroid (if it’s small enough) to a stable orbit in cis-Lunar space. We can then mine and process it there. This would allow for the least amount of waste but comes at a higher risk. Even a small asteroid could cause a lot of damage if it hits the wrong spot on Earth (or Luna once we have settlements there). Humans have a great track record for making mistakes.
- The best method, in my opinion, would be for a self-reliant orbital settlement (an orbital Homestead, if you will) to park itself next to an asteroid and mine it until there is nothing left. The orbital Homestead is home for the miners (and everyone else) and provides for all their needs. The Homestead uses the resources it needs from the asteroid and ships the rest to cis-Lunar space (method to be determined). When the asteroid is depleted the Homestead moves on to the next. See the section on Asteroid Homesteads for more details.
If asteroid mining is so great then why aren’t we doing it already. It turns out that there are some significant difficulties we need to overcome first. Asteroids, and comets, share many of the Martian drawbacks.
The distance and lack of a protective magnetic field and atmosphere problems are the same for asteroids as they are for Mars, only worse. Martian crews, and settlers, can live in shielded habitats underground once they get to their destination. Their exposure to deep space hazards (radiation being the worse) is more limited than asteroid crews/settlers. Asteroid crews aren’t going to be able to burrow under the ground unless the asteroid is pretty big. So, the crew is going to have to bring their 24/7 protection with them. More mass, more/larger vehicles, more cost, more risk.
Gravity is also a big challenge, just like Mars. Only for different reasons. Even large asteroids have very little gravity. They just don’t have enough mass (excluding Ceres which is really a dwarf planet). We know from long-duration missions onboard the International Space Station that the human body reacts poorly to extended exposure of micro-gravity. I’m not going to get into the details here as there are books written on this topic. The point is that crewed long-term visits to asteroids are going to require some form of artificial gravity. And we only know of two ways to do it, sustained high (almost 1 meter per second per second just to simulate 1/10 G) thrust and spinning.
Continual fast acceleration of spacecraft over long periods of time is beyond our technology at this time. Electric propulsion can operate a long time but the acceleration is very small. And sustained acceleration only works for the trip to and from the asteroid. So, spinning the habitat is the only way to protect the crew/settlers from the effects of micro-gravity. This is a problem as humans have no practical experience in generating artificial gravity in space. No one has spun up a habitat in space and tracked how people do in it. Developing this new technology, and then using it on spacecraft, is going to take a substantial amount of time and money.
The other major challenges come from the mining process. We’ve only visited a small number of asteroids and collected samples for just a few. We actually don’t know much about asteroids in general and almost nothing about specific asteroids. At least one robotic prospecting mission will have to visit each potential asteroid mine just so we’ll know what’s there and in what form. More missions equal more time and money.
We also don’t have the technology or techniques needed to extract the resources we find. Asteroid mining will require specialized equipment that won’t work for Earth, Lunar, or Martian mining. Micro-gravity, radiation, and vacuum are going to be difficult challenges to engineer for. We don’t even have field-proven tech that will allow us to “dock” our mining equipment with the asteroid. Again, more money and time will be needed.
- Billions to trillions of taxpayer dollars. A lot less if private corporations develop the tech and fund the missions. The only way this is going to happen is if there are cis-Lunar, and Lunar, markets willing to pay for asteroid resources.
- Years of effort, probably at the expense of Lunar settlements.
- As with Mars, asteroid missions are going to need some luck. And for the same reasons. High risk and high reward. Hopefully. I doubt we’ll gain any kind of permanent settlement from government or corporate sponsored asteroid missions. We will end up with some useful tech and experience though. And maybe some resources to help defray the cost.
- If we’re really lucky we’ll start establishing long-term asteroid resource supply lines for cis-Lunar markets. This kind of infrastructure is going to require a level of vision, commitment, and long-term thinking that we just haven’t seen yet. I’m not saying it couldn’t happen, just that it’s a long shot.
A cis-Lunar economy is going to need people out in the dark mining asteroids. Those resources are what’s going to make our expansion into the rest of the Solar system possible. However, we shouldn’t get ahead of ourselves. We need Lunar settlements first so they can establish the markets necessary for asteroid mines to thrive. Lunar settlements will also develop the tech needed to keep asteroid miners alive and well. In short, we need Lunar settlements before we need asteroid mining.