“Will we ever live amongst the stars?”

This is Rachel Armstrong’s big question — and one she’s determined to answer. A professor of experimental architecture at Newcastle University in the UK, Armstrong has been thinking about zero-g construction for her whole career and especially since joining Icarus Interstellar, an international project designed to promote and facilitate interstellar flight in the 21st century. “It has to do with going beyond our limits and being more than what we are right now,” she says. “The starship question really is about the nature of humanity. And that’s different from asking whether we can build a starship.”

The can or cannot is subject to change, but the would or would not is a product of humanity itself — our reasoning, our priorities. The context of the starship question is population growth, environmental deterioration, scientific research, and the impulse to explore. Compared to all that, defining the subject of inquiry is easy: A starship, according to Armstrong, is a vessel that can be used to transport organic life to worlds beyond our solar system. There are two major characteristics that separate a starship from other kinds of spacecraft: The ability to sustain life onboard for a lengthy amount of time and the ability to carry that life over to other moons and planets.

'Skyscraper In Space 3' Teodor Petrov

Life in space is a thing we can do. That’s what the ISS offers. What the ISS can’t do is move over galactic distances. Propulsion is, when it comes to starships, the rub. Scientists estimate that in order to get to another star system within 100 years, a spacecraft would have to be traveling at about 10 percent the speed of light. Without a warp drive, things are tricky.

Of all the current or proposed technologies, Armstrong thinks that solar sails are the most realistic. A solar sail basically uses the radiation pressure emitted from stars as a propelling force. The radiation pressure in this case would push against large ultra-thin mirrors attached to the spacecraft like a sail, moving it forward at very high speeds. This is a (comparatively) affordable type of propulsion. In fact, it’s so cheap that it’s the basis for The Planetary Society’s citizen-funded LightSail project, which held a test flight in June 2015. There’s no need to carry and store any kind of propellant onboard.

“We can actually start to build that,” says Armstrong.

But there are drawbacks. If unexpected chunks of space dust and debris hit the sail’s thin material, the whole thing can be irreparably damaged in seconds. Armstrong says a robotic probe scanning for such space junk could help provide some early warning, but the sail would still need to execute evasive maneuvers. If there are no backup propulsion systems onboard, astronauts would be at the complete mercy of radiation pressures and solar winds, which are less than predictable.

There are other, more radical propulsion technologies that would probably make more sense for bigger types of starships. Nuclear power makes the most sense. We can already do nuclear fission (it’s how we power nuclear reactors here on Earth), but nuclear fusion would be much more efficient. Many other kinds of conceptual technologies build off of fusion technology, like using lasers and electron beams to propel a ship forward. Sadly, we don’t seem to be any closer to making fusion a reality than we were a decade ago.

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The other big obstacle to starship design is habitability. It’s one thing to send people into space and another to keep them alive. Armstrong claims the latter can be done, but only with soil.

“If we’re going to survive, we’re going to need soil,” she says. “That’s where organic matter is.”

Soil is necessary for plant growth, which is necessary to produce oxygen, fruits, and vegetables. Different kinds of plants could also provide a ton of different organic materials helpful in a wide variety of circumstances. Unfortunately, this research is hard to pursue. The 1967 international Outer Space Treaty limits experiments on microorganisms in extreme environment. Assuming that the treaty were modified, scientists would have to figure out a way to use dynamic chemical processes to terraform highly localized zones. This would require “super soils.”

“We can design complex life-baring fabrics that go beyond the idea of water and air mixed in certain ratios,” says Armstrong. “If we strategically introduced different kinds of organisms and maybe even technological fabrics, we might find that soils can do an awful lot more than they naturalistically do.”

Synthetic biology could even help us bioengineer plants that could play a critical role in a starship environment. These plants could be made to produce oxygen in bigger quantities, live off of less resources, filter aquatic systems to recycle potable water, produce fruits and vegetables at faster rates, etc.

But a sustainable habitat doesn’t just mean providing the resources to help grow life. Armstrong has spent a lot of time exploring ‘living technologies’ — in which metabolic materials act as “a chemical interface or language through which artificial structures such as, architecture, can connect with natural systems.” These materials basically possess metabolic traits that allow them to transform into different states through energy processes. Armstrong is most interested in understanding how metabolic materials could participate in the creation of an ecological landscape alongside more conventional structural materials.

One example is “protocell oil droplets” that can move around an environment and undergo complex behaviors based on changing conditions. This might mean becoming more and less light-sensitive; responding to vibrations and shakes; altering changing air compositions by shedding different kinds of waste products; or even self-repairing after being damaged. That last ability could be especially useful for creating a layer of spacecraft hull that helps minimize damage inflicted by other unseen objects hurting around space, like small rocks or bits of ice.

'Skyscraper In Space 4' Teodor Petrov

These obstacles make it unlikely that we’ll meet Armstrong’s self-imposed 2100 starship deadline. Even if the technological constraints weren’t an issue, economic and political forces would undoubtedly slow the process. Still, Armstrong is hopeful that with increased interest in going back to the Moon and getting humans to Mars, we might soon establish a research station dedicated solely to considering how to build a starship.

“We’re pretty serious about creating an interplanetary civilization,” says Armstrong.

“Although it sounds like science fiction, thinking about starships invites us to think strategically about the way we go about making things in the longterm, for generations to come. We don’t know what’s going to happen next, yet we must go into the unknown.”