These days, engineering for space has a lot to do with packaging. Your biggest, most ambitious ideas have to be deliverable in small chunks that can be reassembled later, or blow up like a balloon, or even fold up like an origami crane. Everything you want to do in space, your super-telescopes and Mars colony ships, has to fit into the tip of a rocket, either once or over and over. To move space tech forward, you’ve got to design technology for zero gravity, but build it in single gravity — it’s annoying! But what if you could get around that problem by building tech in the same environment in which it’s designed to operate?
The idea of doing construction in space has existed for a long time, but like many long-lived ideas about What NASA Ought To Do, it’s always been far easier written than realized. Now, scientists are making increasingly serious propositions for increasingly detailed mission profiles, all aimed at giving mankind its first space-based shipyard. An incredibly detailed such mission was recently proposed in the Journal of Astronomical Telescopes, Instruments, and Systems, going through all the steps in building and assembling a modular 100-meter space telescope called the Robotically Assembled Modular Space Telescope, or RAMST.
The advantages of constructing space technology in space are obvious — if something is only ever going to have to function in zero gravity, building it there means it can be far more fragile than a machine that has to be able to support its own weight down on the surface. In space, you can build objects that are bigger and more convoluted without fear of internal collapse due to lack of significant tensile strength.
For the most part, building in space could realize the machines many astrophysicists have been imagining since they were children, and which your graduate education in physics told you would always be impossible. As long as there’s been a space program, there’s been a will to create a space construction program — the only question has been how to actually get it done.
The most obvious answer was to simply do construction in space. Get some astronauts, put them in space, give them building tools, and have them build things. The first problem with this is that space suits don’t lend themselves to physical labor, or precision work, or long-term use in general. You might get rid of some headaches in designing your next satellite, but those reduced costs and delays will likely be more than offset by the increased crew, food, equipment, and oxygen requirements, not to mention the increased chance of injury and crisis.
Designing a solution is no small feat. How do you build in orbit, where the near-zero pressure, absence of combustible gasses, and lack of an objective “down” all throw a wrench into the construction technologies we’ve developed over the past few thousand years? More to the point, how do you do it when human labor can’t even be used as part of the solution? Virtually any poured, hardening material won’t work right off the bat; all the sturdiest forms of welding are based on having oxygen available, and an atmosphere to quickly cool a molten welding material; even mechanically snapping pieces together often relies on the downward pull of gravity to keep everything stable and connected.
One possible way forward is 3D printing. As with welding, most 3D printing materials require the convection of air to cool the construction material and fuse it to the growing object — but not all. NASA has been working on a potential space-based 3D printing project called SpiderFab, aimed at creating “kilometer-scale” metal frameworks in space. SpiderFab would lay down the enormous skeleton of a space platform, for instance, and incorporate more complex components sent up from the surface. Not just tools and computer systems but objects with wider materials demands, like windows, would likely come up from traditional factories and fabs.
So, the quickly-oncoming James Webb telescope, with its segmented, folding mirror, might not look so out of date in the era of space-based construction; we probably won’t be vacuum-printing such high-precision objects as telescope mirrors any time soon.
But the basic ability to build in space will be important to develop if we’re ever to make sizable colonies on the Moon, or other worlds. Putting down roots in alien soil will require many of the same skills as printing in space — and space is closer. If we’re going to try building structures on Mars, we’ll need to start with less ambitious goals.
This is a theme the space world right now: modular, replaceable parts launched and assembled by robots. DARPA is still plugging away on Project Phoenix, which is aimed at undoing some of the incredible waste of mankind’s various space programs by scavenging old or aging satellites for parts, and assembling those parts into all-new space-based devices. Take a new central processing unit with newfangled sensing devices and send it up as part of a bulk shipment, then have Phoenix attach a scavenged solar panel or two, some thrusters that are in good condition, and anything else that can be found in Earth’s ever-more-crowded graveyard orbit.
Of course, unless we’re going to be making these scaffolds out of moon-dust, we’re still going to have to launch the raw materials the robot will use to print the basic skeleton of a structure, and attach pre-fabricated parts to that skeleton. In principle, you’re still launching the entire vehicle from Earth, but taking the packing efficiency to its logical conclusion — printer-ready cartridges or ingots of printing material packed nice and tightly, with no wasted volume on your launch vehicle.
Even with a vastly more affordable method of reaching space, like a space elevator with a large lift capacity, space-based construction will remain necessary. There’s enough profit potential in space to make full use of pretty much whatever launch capacity is available, so there’s always going to be an incentive to pack light.