After stagnating following the end of the Cold War, interest in space travel and exploration is once again on the radar, providing engineering challenges on an incredible scale and in a tremendous diversity of conditions. And there are plenty of challenges right here on Earth as well, not least relating to how we might feed, clothe, house and support the largest population the planet has ever known.
If you’re a budding engineer, it can be motivating to think about the amazing projects you might one day have the chance to work on – projects like these:

1. Space elevator

One of the biggest challenges in exploring space is escaping the Earth’s atmosphere. It currently costs $10,000 to put less than half a kilo of payload into space, and much of that cost is contributed by the difficulty of getting anything through the atmosphere. The system we have right now – using rockets – is desperately inefficient, because rocket propellant is heavy in its own right (taking up most of the weight of the rocket) and dangerous to handle to boot. And launching a rocket requires incredible feats of mathematics to ensure the rocket ends up where you wanted it to be, not overshooting and not being dragged back to Earth by gravity.
Implausible as it sounds, a space elevator – if it could be built – would solve most of these problems at a stroke. For instance, it could be solar-powered, eliminating the need for expensive, heavy and dangerous fuel to get objects into orbit. There are huge challenges in terms of how it would be built, what materials it would be made of, and how it would avoid destruction from the debris in orbit around Earth, but as scientist, futurist and writer Arthur C Clarke said, a space elevator could well become a reality, “about 50 years after everybody quits laughing.”

2. Mars base

The idea of settling on Mars has been a science-fiction dream for generations. But it’s starting to look increasingly plausible. Space exploration is moving steadily from being a government/military pursuit to being a civil/corporate pursuit, powered by companies such as SpaceX – and that means that it’s limited not by government budgets and by foreign policy concerns, but by the ambitions of entrepreneurs, and the entrepreneurs in question are very ambitious indeed. For instance, Elon Musk, CEO of SpaceX, has announced his aim to retire on Mars as part of a colony of 80,000 people, and is working towards developing and building the technology to make this a reality.
That means that the engineering challenges of maintain human life on Mars will have to be solved. Transporting anything from Earth will come at a huge cost (even with that space elevator making it easier to get materials into space), so making the base self-sustainable will be of vital importance. With minimal atmosphere, no soil, lower gravity and extremes of temperature, developing housing and machinery suitable to work on Mars will be fascinating for the engineers of the future.

3. Transatlantic tunnel

The great engineering challenges of the future won’t just exist in space; some will be terrestrial too. In the past two hundred years, the speed of travel from cars to trains to aeroplanes has increased massively, but it still takes us the best part of a day of travel time to get from one side of the globe to the other, and it isn’t usually a pleasant or relaxing experience. As with launching rockets, the process of defying gravity to get from a to b uses up a lot of energy, making flight an expensive way to travel.
One solution is to go under the ocean instead of over it, by building a tunnel. A transatlantic tunnel would be incredibly expensive, with costs estimated at more than $100 billion (or roughly the lifetime cost of replacing the UK’s nuclear weapons system, Trident). But if new engineering techniques can bring these costs down, there could be considerable benefits in terms of ease of trade and travel.

4. Floating sphere cities

Buckminster Fuller was an architect and inventor who specialised in big ideas, and one of them was his plan for building cities even when land area was scarce: ‘Cloud Nine’. He theorised that a mile-wide geodesic sphere – a sphere constructed from triangular components – could be heated so that despite its mass, it would float. The principle is the same as a hot-air balloon, but on such a massive scale, Fuller believed that the air in the sphere would only have to be one degree warmer than the outside, which would make for a pleasant place to live. The sphere could be used as a floating mini-city, over land or over ocean. Thousands of people could live in one.
But despite how promising – and cool – floating sphere cities might sound, there are reasons why geodesic domes are seldom built on the ground, let alone floating spheres in the sky. We are used to building things with right angles; waterproofing spheres and creating fire escapes is a challenge; and you’d want to be very sure that your complicated, expensive sphere city would definitely float.

5. Underground megacities

Another solution to the shortage of space for our cities – especially with the threat of rising sea levels – is to build not up, but down. To a certain extent, this is already beginning to happen: from underground rail to underground shopping centres, cities, especially those based in climates that are inhospitable anyway, are moving underground. For instance, during the winter when daily average temperatures can be -10 degrees celsius, much of the city of Montreal moves into an extensive underground network of buildings and transport.
What may change in the future is that instead of happening piecemeal, driven by necessity, we may increasingly see planned underground cities, where all the necessities of life can be accessed underground. Engineers will be needed not only to figure out how to build these cities in a way that’s secure against natural disasters (underground cities are particularly vulnerable to earthquakes) but also how to make them pleasant places where people might choose to live. It’s easy to imagine how underground cities, without easy access to natural light, would seem like second-best, so a key challenge will be to make them not only tolerable, but desirable.

6. Asteroid mining

Asteroids are an incredible untapped source of raw materials, including elements that are rare on Earth such as palladium and ruthenium. But working out how best to extract these raw materials, not to mention getting them back to Earth in a cost-effective manner, represents a tremendous challenge. It’s likely to require advanced rocketry and robotics, as getting human workers out to the asteroid belt is unfeasible. Despite the difficulties, asteroid mining may prove not only lucrative, but necessary; the supply on Earth of some of the resources found in asteroids may be exhausted within the next few decades, and asteroids may then become the easiest source.
The challenges for engineers are manifold (as are the possible intellectual and financial rewards!). Getting equipment for extraction out to the asteroid belt is hard, to the extent that some engineers have suggested it may be easier to transport raw asteroid material nearer to Earth, for instance to an extraction plant that could be built on the Moon. Asteroid mining, unlike other space projects, is more about profit than about the achievement in its own right, so any innovations that can keep the costs down will be a priority.

7. Nanofactories

No matter how advanced our technology and manufacturing processes become, there are many areas in which nature seems to be unbeatable. One of those is manufacturing at incredible precision at a molecular or near-molecular level. The human body builds and rebuilds itself with a greater degree of accuracy, greater speed and lower energy usage than any machine can match. But with the advent of nanotechnology, that might change.
Nanofactories, building items at a molecular scale, could revolutionise manufacturing by producing items – even large-scale products – that are accurate down to an atomic level. The benefits would be vast, from the early stages where nanofactories might allow medicines to be created with much greater precision, to an advanced version of the technology that could conceivably allow almost anything to be created from basic starting materials given appropriate programming for the nanofactory.

8. Commuter rockets

One argument – the one that supports space elevators and transatlantic tunnels – is that rockets are complicated, expensive technology that will be avoided and replaced whenever possible in the future. But another view is that the difficulties and costs associated with rockets are temporary. In current space missions, rockets are typically single-use, which would be like scrapping a plane after a single flight, adding hugely to the cost. The company Space X is now developing reusable rockets, and it’s these that they propose could be used in the future, not to get to space but to get from anywhere on Earth to anywhere else in less than an hour. New York to London would take less than half an hour. And because the rockets would be following predictable routes from one place on Earth to another, the challenging calculations of using rockets to get into orbit would not be an issue.
The biggest challenge for engineers working on this grand idea would be passenger safety. We’re usually happy for astronauts, employed by the military, to take risks, but risks from air travel are not so easily tolerated. One such safety improvement might be finding ways to refine rocket fuel to make it less dangerous (not to mention less expensive).

9. Von Neumann probes

So far this article has focused on engineering projects on Earth and within our Solar System. But the engineers of the future will undoubtedly send their creations further afield as well. Von Neumann probes were the brainwave of mathematician and physicist John von Neumann; his concept was that machines could be built that would be self-replicating, using the raw materials found in the nearby environment to create new versions of themselves. Applied to space exploration, this would involve the launch of perhaps only a handful of probes, which would travel across the universe, landing on planets, asteroids or moons, replicating themselves and then spreading to cover an exponentially greater area of space.
The challenges for engineers trying to build von Neumann probes will be significant. The probes will be travelling through all the hazards of space, will need to be able to identify good locations for self-replication, find materials, replicate themselves, gather data and have a mechanism for returning the information found to Earth. That’s a lot to ask! But if we can find a way to conquer these challenges, then building and launching von Neumann probes could answer one of the biggest questions that humanity faces: whether Earth is the only home to intelligent life in the universe.

10. Dyson spheres

If everything else in this article has sounded achievable to you, then here’s an even greater challenge for the engineers of the future (possibly the far future). It’s a solution to an ongoing human problem: the production of energy. A Dyson sphere, or Dyson swarm, would be a collection of objects in orbit around a star, harvesting some of the massive quantities of energy that it emits. The swarm would be nowhere near large enough to block the light from the star, but instead might resemble a very thin ring. Even that would be sufficient to harvest incredible quantities of energy. Some futurists have imagined Dyson spheres and von Neumann probes working in tandem, with the probes harvesting energy from the spheres before travelling onwards to explore new places and establish Dyson spheres around new stars.
The idea of a Dyson sphere as a rigid structure is far beyond our engineering capabilities. But a loosely connected solar panel array orbiting the Sun is more feasible (though still at least decades, perhaps centuries away). Yet made to work, it would mean the end of energy scarcity, perhaps forever.
 
Images: space shuttle; Mars rover; Channel tunnel; slums; Montreal; asteroid; nanotechnology; Space X rocket; astronaut; sunrise; spaceship.