If anyone knows how to build a megastructure, it would be China.
With the Great Wall of China being an early example of a megastructure, when Chinese government officials say they have their hearts set on building a mile-long spaceship in orbit around the Earth, we should probably take such a proposal seriously.
What exactly is China proposing, though? How close are they to actually building such a ship? Is such a thing even possible and why would we want to build such a colossal spacecraft?
While the proposal at the moment isn't a substantial commitment on the part of the Chinese government, it does reflect a growing ambition in space exploration for the country. How serious is the proposal and is this something China is seriously pursuing?
What China is Proposing
To start with, we should look at what the National Natural Science Foundation of China (NNSFC) is actually asking for in its official call for research proposals.
According to the South China Morning Post, the NNSFC proposal says the spacecraft "is a major strategic aerospace equipment for the future use of space resources, exploration of the mysteries of the universe and staying in long-term orbit.”
The proposal only includes a grant for $2.3 million dollars, however, which clearly isn't enough to actually build, or even develop, such a spacecraft.
Instead, the proposal is calling for preliminary studies on what it would take to build such a spacecraft. This is a very different proposition than saying they actually want to start building a ship.
For good reason. Getting a spacecraft, any spacecraft, into space is a major endeavor that only a few nations have managed to successfully pull off. And all of those efforts have been incredibly expensive.
What the NNSFC, a research funding agency under China's Ministry of Science and Technology, lays out in its call for research proposals is the feasibility of carrying material and even entire sections of a miles-long vessel piecemeal into orbit, where it would then be assembled into a completed ship.
Whether those proposals will end up providing the foundation for building a miles-long vessel in orbit remains to be seen and is, in fact, the entire point of the exercise. But how far-fetched is it to attempt to build that kind of vessel in space? Not as outlandish as it might seem.
We're Not That Far Off from a Mile-long Spacecraft As It Is
Let's just start with a mile-long vessel as the milestone we want to hit, which in itself would qualify as a megastructure in engineering terms.
What would it take to build a mile-long spacecraft? Doing what we've already done with the International Space Station another nine times over.
The International Space Station is already about 357 feet long and 246 feet wide (109 meters long and 75 meters wide). This is just about the size of an American football field, and took 10 years and more than 30 missions to assemble, involving the efforts of five different space agencies representing 15 countries. It cost about $100 billion to construct and costs about $4 billion a year to operate.
This is a titanic sum of money, to be sure, even spread out over 10 years, and the effort to build 1/10th of a kilometer-long space station has been considerable. Extrapolating from this, sending material equivalent to the entire International Space Station into space 10 times over, in order to create a mile-long spacecraft, would take more than 300 missions and around $1 trillion dollars.
That is a tall order, but it isn't the tallest of orders. After all, humanity went from a point in time where we had never put an artificial satellite into space to putting a person on the Moon in just 12 years. And that was the kind of challenge that had never been done before and where no one was certain that it could even be done.
Building large structures in orbit around the Earth? We've done that several times already.
Building a mile-long spacecraft then isn't so much an issue of scope as it is of scale. Apollo 11 had to invent new technology and come up with entirely new systems and processes for every step of how to put a human on the Moon and return them safely back to Earth.
China would just have to do what we've already done before and do it much more efficiently, which is an easier challenge in many ways, or is at least a more simple problem than trying to plan a Moon landing without knowing what the conditions of the lunar surface would be like.
"I think it's entirely feasible," Mason Peck, a professor of aerospace engineering at Cornell University and a former NASA chief technologist, told Live Science in September. "I would describe the problems here not as insurmountable impediments, but rather problems of scale."
Unique Engineering Challenges Do Need to Be Overcome
While microgravity does wonders for relieving stress on a structure, it does not eliminate it. And the longer the vessel, the more stresses can be amplified or ripple through a structure, requiring more consideration of the forces that any mile-long ship would be subjected to.
One example Peck gives is the vibrations caused in the structure from maneuvering, which it will likely have to do to avoid the growing shooting gallery of space debris, the way the International Space Station now has to routinely do.
Shock absorbers and active control might be needed to counter the stress from vibrations on the structure, all of which would undoubtedly add to the overall cost.
Another consideration would be how high in orbit the ship would operate, as solar radiation becomes more intense the higher you move away from the Earth.
This would obviously pose a substantial risk to human crew members, and the kind of materials that could insulate against radiation, like lead, are extremely heavy, so are not in any way practical for hauling up into orbit.
Another issue that Peck raises is drag from the Earth's atmosphere. Any orbiting structure is going to be slowed and dragged down by skimming through the faint wisps of the atmosphere in low Earth orbit. Countering this drag requires occasionally firing thrusters to maintain an orbital trajectory.
Even in space though, physics still applies when dealing with mass, and a mile-long structure is will have an incredible amount of mass for those thrusters to move which will require a lot of fuel just to maintain a stable orbit.
Possible Is Not the Same As Feasible
All of this is to say that the engineering challenges of building a mile-long spacecraft aren't actually difficult in the conceptual sense. But like a space elevator, knowing how to do something and being able to do something are two very different things.
"It's kind of like us talking about building the Starship Enterprise," Michael Lembeck, professor of aerospace engineering at the University of Illinois at Urbana-Champaign told Live Science. "It's fantastical, not feasible, and fun to think about, but not very realistic for our level of technology."
Determining if such a project is possible would also depend very much on what the spaceship would be doing. If China was only interested in effectively building a mile-long space station rather than an actual ship in the traditional sense, things would be more feasible.
If China wanted that ship to actually travel beyond low Earth orbit under thrust, then that makes puts its construction even more out of reach.
The forces exerted on a structure under thrust propulsion can be considerable, and that becomes even more of a challenge when what you're trying to move is a mile long.
There is also just the ultimate resource challenge for something like this. Constructing a mile-long ship requires assembling a mile-long ship's worth of minerals, metals, electronics, and other components.
These will need to come from somewhere, and material used for a spaceship can't be used elsewhere. A mile-long spaceship could end up being a very hard sell, politically. Even for a centrally-controlled government like China's.
What Could a Mile-Long Spaceship Do?
Given the cost and effort involved, you really have to want this in order to get it built, so the reward would have to be something substantial enough to justify its expense.
What could we do with a mile-long spaceship, assuming one could be built? Interstellar travel isn't really on the table, since accelerating a mile's worth of mass to the reasonable fraction of the speed of light that you'd need for interstellar travel is going to be exponentially more expensive than doing so with a smaller craft.
Interplanetary travel isn't out of the question though, since the long voyage to the moons of Jupiter or Saturn would require a fair amount of living space for travelers, along with systems such as hydroponics. Though, again, a smaller craft would be much more cost-effective for initial missions of this kind.
There could be other scientific uses for a megastructure of this size, though, even if it wouldn't really be a spaceship in the way many are imagining it.
Possibly the most intriguing use for a mile-long structure of this kind would be as a platform for a space telescope, Peck said, which at this size could be powerful enough to see surface details on exoplanets in our galactic neighborhood.
"That could be transformative for our understanding of extrasolar planets and potentially life in the universe."