Given how expensive it is to lift anything into space from the surface of the Earth, the future of efficient and affordable space travel may be dependent on using the resources that are already up there. Space may seem big and empty, and it mostly is, but there's enough raw material floating around out there in the form of asteroids and comets to keep us going for eons. The trick is going to be rounding these asteroids up and bringing them somewhere they can be of use without spending so much fuel on the process that the effort is rendered pointless.
Made In Space is a company that develops technology for, you guessed it, making stuff in space. For example, they've got 3-D printers aboard the International Space Station that make tools, and they've experimented with turning simulated regolith (Moon dust) into a material that can be 3-D printed into useful things. With funding from NASA's Innovative Advanced Concept Program, Made in Space has been exploring a fairly wild idea: To gather the raw material for all of our making-in-space needs, Made in Space wants to send small “seed craft” to near-Earth asteroids with the aim of turning them into giant spacecraft that will fly themselves back to Earth to be mined.
The basic idea of grabbing asteroids and bringing them back to the Earth-Moon system to harvest their resources isn't a new one. In fact, it's such a not-new idea that NASA plans to send a robotic spacecraft to a near-Earth asteroid and bring a chunk of it back to lunar orbit for study sometime within the next decade. The problem: NASA can bring back only a very, very small portion of the space rock, because asteroids are very, very big, and moving big things in space takes a lot of fuel. (In the case of a big asteroid, an almost impossibly large amount of fuel, especially if you want things done in a timely manner.)
What Made in Space wants to do with Project RAMA*, short for Reconstituting Asteroids into Mechanical Automata, is to make asteroids into self-assembled, self-contained, self-propelled, fully autonomous spacecraft. If they can pull this off, it would mean that the small seed craft sent to an asteroid would be equipped to use materials on the asteroid itself to manufacture computers, guidance systems, engines, and enough energy to induce the asteroid to use its own mass to propel itself back to Earth’s immediate neighborhood. Then the seed craft would move on to the next asteroid to repeat the process.
According to Jason Dunn, co-founder and CTO of Made In Space, this is how the company framed the problem:
One of the big questions is, how do you take today's most intricate machines and make them replicate themselves? That seems really hard: how do you replicate electronics and processing units and so on. And that's when we had this concept that there are types of machines that could potentially be easy to self-replicate, and those would be very basic, analog type devices. The problem is if you have a small mechanical machine, it's not very useful. But what if the machine itself was the size of an asteroid? What could you do with a mechanical machine that large?
Right now, we don't have the technology to 3-D print, say, a digital guidance computer here on Earth. We certainly aren’t ready to do it using only the kind of materials that you'd find on an asteroid. What Made in Space has realized, though, is that it's not necessary to rely on digital electronics if you have an enormous amount of raw material and no constraints on volume or mass. Instead, you can build a purely mechanical analog computer, using things like gears and rods and levers linked by chain belts (perhaps with 3-D printed mechanical punchcards for data storage and mission execution instructions). This is all very old technology, but it's also well understood, reliable, and easy to build from simple parts.
With computing taken care of, what about everything else you'd need for a spacecraft? Well, you could 3-D print giant flywheel gyros for guidance and stabilization. For energy to run things, you could 3-D print springs and preload them with the seed craft, or you could 3D print tanks for storing volatiles, then heat them up using 3-D printed solar concentrators to generate mechanical power through the release of pressure. The engines are just as simple: catapults. Like, the kind that used to throw rocks at castles, medieval-style.
By throwing chunks of itself in one direction with catapult-like mass drivers, the asteroid can accelerate itself in the other direction. This is only about 10% as efficient as a chemical rocket engine, but the propellant is free, as long as you don't mind your spacecraft eating itself. Made in Space has estimated that it might take throwing away something on the order of 60 percent of a candidate near-Earth asteroid's mass in order to bring it in for mining. That sounds like a lot. But another way to look at it, though, is that if you're clever enough to throw away only the mass that you don't care about (leaving metals and volatiles behind), the asteroid could arrive at the mining station “pre-refined.”
The hardest part of all of this is going to be designing the seed craft. It'll have to be incredibly capable, with the ability to not just 3-D print things using whatever materials it finds, but also to 3-D print more (analog) 3-D printers to speed up the process. Fortunately, we know how to do this, too. You can imagine the seed craft setting down on an asteroid, scooping up some regolith, and then printing out an analog 3-D printer pre-programmed for self-replication. Eventually, it would switch over to printing gears and punchcards and catapult parts, and when it had everything it needed, the seed craft would become the assembler. Once everything is put together, the seed craft would do the equivalent of flipping the “on” switch, then leave the asteroid to pilot itself back to Earth.
As fantastical as it sounds, most of the fundamental technologies to make Project RAMA happen already exist, which is probably why NASA is funding it. The goal of this phase 1 study is understanding how the seed craft would have to work, defining requirements, and building a technological roadmap. If everything goes perfectly, a seed craft could potentially be sent to a near-Earth asteroid in the early 2030s.
*RAMA is an homage to Rendezvous with Rama, an excellent science fiction novel written by Arthur C. Clarke.