The original Blade Runner film took place in an imagined Los Angeles of 2019, a futuristic city where acid rain fell from skies crowded with "skimmers": flying cars that zipped along aerial highways. Since the film’s 1982 debut, technology has advanced in ways that Hollywood might never have predicted – selfie sticks, murder drones, hashtag politics – yet hovercraft taxis still seem a far-off fantasy, reserved for science-fiction novels and theme park rides.

In fact, flying cars are real – and they could shape how we commute, work and live in the coming decades. Advances in battery energy density, materials science and computer simulation have spurred the development of a range of personal flying vehicles (and the navigation systems that will allow them to run), from electric gliders to fixed-wing craft and quadcopter drones.

These aircraft may not look exactly like Blade Runner’s imaginings. But they aren’t all that far off. Far smaller than a commercial plane, most are designed with rotors instead of wings, which allow for vertical takeoff and landing. Tilt rotors, for example, allow for efficiency in forward flight at longer distances, while multirotors are designed to reduce noise in hover flight. Most important, these vehicles are designed to offer faster commutes than traditional modes of transit for individuals, especially in traffic-clogged cities.

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At the moment, the autonomous urban aircraft market is still a bit of a Wild West. Dozens of start-up companies are competing to develop commercial jetpacks, flying motorbikes and personal air taxis. Venture capitalists, auto and aviation corporations (even rideshare company Uber, with its ambitious Uber Elevate) are staking claims on the burgeoning industry, which may be worth as much as $1.5tn (£1.1tn) by 2040. Meanwhile, aviation authorities hash out the policies and safety standards that will govern this new realm of transport.

Germany-based Volocopter, for instance, has marketed its VoloCity craft as the first commercially licensed electrically powered air taxi, a vehicle which will eventually run without a pilot. "It’s like an Uber Black or any other premium service," says Fabien Nestmann, vice president of public affairs at Volocopter.

With a few key differences, that is. Initially, the VoloCity will only have room for a single passenger. That will mean a higher cost per ride at first, but Volocopter hopes to build consumer confidence before transitioning to a full-autonomy model: an electric, wingless craft powered by nine batteries, which will transport passengers throughout a planned network of vertiports – airports for planes that take off and land vertically – across major cities. VoloCity’s first commercial flights are scheduled to take place in 2022.

These first flights will cost €300 ($350/£270) per ticket. But eventually, says Nestmann, the company’s goal is to make the cost competitive with, say, an Uber Black. "We don’t want this to be a toy for the wealthy, but part of a well-integrated journey for anyone in an urban area," he says. "Everyone should have the option to walk, be driven, cycle, or fly."

Other companies have partnered with existing car manufacturers to create models they plan to develop for eventual commercial use. Japanese startup SkyDrive, for example, recently teamed up with Toyota to conduct a test flight of its all-electric air taxi, said to be the world’s smallest electric vehicle that can take off and land from a vertical position. This summer, the company successfully flew its SD-03 craft for several minutes around an airfield with a pilot at the helm.

"Consumer demand has grown, but humans have not yet provided a clear solution to traffic, even through options like electric cars or speedy alternatives like [France’s intercity] TGV train," says SkyDrive representative Takako Wada. "You could say SkyDrive mobility has been nurtured by consumption demands as well as by advances in technology."

Indeed, those advances makes it possible for so many aircraft designers to clamour for airtime, as it were. Companies like Lillium, Wisk, Joby Aviation, Bell and countless others are capitalising on innovations like electric propulsion, which dramatically reduces noise emissions, and battery power, which enhances range. For an industry in its infancy, there are no shortage of Vertical Take Off and Landing (VTOL) designs, or the imaginary heights that might be reached with them.

Consider Gravity Industries, a UK-based aeronautical company that created a 1,050-horsepower wearable jetpack. "It’s a bit like a Formula One car," says Richard Browning, chief test pilot and founder of the company. "The Jetsuit is a specialist piece of equipment that only trade professionals and military fliers can ride, for now." Browning gestures to a metallic, Batman-esque contraption in his studio. "Someday, the jetpack might mean a hovering super hero paramedic can make decisions about where to go and what to do."

This is not as pie-in-the-sky a scheme as it sounds: the Great North Air Ambulance Service recently partnered with Gravity Industries to simulate a search and rescue mission. Browning flew in his jetpack from the craggy valley bottom of Langdale Pikes in England’s Lake District to a staged casualty site. By foot, it would have been a 25-minute arduous climb.

The flight took 90 seconds. The exercise illustrated the potential of jetpacks to deliver critical care services to remote locations.

"The dream of air transport has been around for a long time," says Parimal Kopardekar, director of Nasa’s Aeronautics Research Institute at the Ames Research Center in Silicon Valley, California. "There’s a powerful opportunity now to design vehicles that can transport goods and services where current aviation can’t reach."

Kopardekar is responsible for exploring aviation trends in autonomy and advanced air mobility, including VTOLs. Given the complexity of this undertaking, the team at Nasa must address and test an entire ecosystem of factors: aircraft, airspace, infrastructure, community integration, weather patterns, GPS, noise standards, maintenance, supply chain, parts acquisition… It’s a list that reveals numerous and not always obvious problems that must be resolved before aerial ridesharing at scale can become a reality.

Reimagining human flight requires vehicles that are "road legal" and safe to fly, but also a public willing to fly in them. Industry leaders need to convince riders that VTOLs aren’t compelling simply because the technology is possible, but because it is preferable to other modes of transport – and safe.

"You cannot offer commercial services without extremely vigorous testing regimes," says Nestmann, who oversees Volocopter’s public education initiatives. "Part of that is developing the infrastructure for these machines." That might mean hardware construction of vertiports and storage facilities equipped with electrical power, or software run behind the scenes: systems needed to run VTOLs will undoubtedly require near-full automation to properly coordinate the envisioned swarms of vehicles. While the commercial aircraft we travel on today are monitored by human controllers in a tower, the flying machines of tomorrow will rely on UTM: Unmanned Traffic Management. This digital tracking will ensure that all VTOLs have common awareness of other flights in their path.

Fully automated vertical transport with a proven track record may put the public at ease, but a vast network of flying objects creates a host of new challenges. VTOLs will obviate the need for runways or on-the-ground parking, but they will require dedicated air corridors and sky-harbours to store craft. Air taxis might reduce the number of cars on the ground and enhance arrival and departure time predictability, but the sheer number of objects in the sky – buildings, birds, delivery drones and airplanes – will require pilots (at least, while VTOLs are piloted) to practise a new kind of dynamic obstacle avoidance. The "Skyway", for want of a better term, will need its own set of laws.

Additionally, manufacturers and operators will have to show that no harm will come either to passengers or to people on the ground below. In concert with the US’s Federal Aviation Administration and other regulatory bodies, Kopardekar and the team at Nasa created an "Urban Air Mobility Maturity Levels Scale", which ranks craft, airspace and other systems on a scale of one to six based on complexity and urban density. They are devising ways to simplify cockpit operations, with a combination of automation and contingency management: guidelines for how a VTOL might respond to bad weather, bird strike, or sudden jetpack intruder, for example.

Already, incidents have shown the importance of these types of guidelines: in October 2020, crewmembers on a commercial airliner near LAX airport in Los Angeles spotted a jetpack at 6,000 feet (1,828m) – an altitude that presents serious risk of collision.

The European Aviation Safety Agency (EASA) has also created a set of technical specifications for VTOLS, though the agency hasn’t quite decided how to certify them. These specifications aim to address the unique characteristics of flying cars, and detail airworthiness standards like emergency exits, lightning protection, landing gear systems and pressurised cabins. "Despite having design characteristics of aeroplanes, rotorcraft or both," EASA’s statement reads, "in most cases EASA was not able to classify these new vehicles as being either a conventional aeroplane or a rotorcraft." In other words, EASA seems undecided about what, exactly, separates VTOLS from fixed-wing commercial jets or helicopters. Clearly, the successful operation of VTOLs will require coordinated efforts across sectors, including government, technology, transportation, urban planning and public outreach.

What accounts for the sudden proliferation of VTOL developers? Global trends like the rise of e-commerce, climate change, the gig economy and an integrated supply chain have accelerated interest in personal air travel, while failures in our current infrastructure and related industries underscore its necessity. As cities like New York, Hong Kong and Beijing reach capacity, urban living becomes less and less sustainable – yet our increasingly interconnected economy demands constant mobility.

The effects could transform commuting, and living, as we know it. "Right now, most people optimise living based on access to transportation," notes Kopardekar. "VTOLs and drones will make it possible to reach people wherever they are, to optimise transportation based on living." Businesses will no longer have to look to central business districts for their headquarters, while employees may choose to live anywhere within reach of an air taxi. Owning a VTOL could become as affordable and ubiquitous as owning a bicycle.

"On the macro level, ever-growing cities create a growing mobility need from the citizens in those cities," says Nestmann. "That leads to a rethinking of the city, because building everything around the car doesn’t improve life quality."

Traffic bottlenecks wear down our cities’ highways and the cars we drive on them, contributing to emissions that in turn threaten our planet’s delicate ecosystems and our own health. Meanwhile, eVTOLS (which are electric) will dramatically reduce emissions or reliance on diesel fuel.

Increasing numbers of flying cars will naturally give rise to a changing layout in the way our cities are structured as cities grow taller, rooftop landings expand and air highways connect super sky-scrapers, freeing up space below. Fewer cars on the ground will reduce congestion and may give rise to parks and green spaces. "In the long run – 2045 and onward – businesses and green spaces will become much more integrated," says Kopardekar. "While we may not ever eliminate metros and roads, we might be able to reduce their footprint with these machines."

VTOLs have vast implications for the future of transport, work-life, consumption, urban design, even healthcare and ecology. As soon as 2030, consumers might be able to press a button and order an air taxi straight to their cloud-tethered office. In the decades that follow, we may ultimately have fewer and fewer reasons to descend to the earth below, conducting our business and our lives atop a city in the sky.

"One mile of road can only take you one mile," says Kopardekar. "One mile of aviation can take you anywhere."

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Along a stretch of river in northern Belgium, a small ferry is running on a fuel that many hope could hold the key to decarbonising ships everywhere.

The fuel being tested on Hydroville, a 16-passenger shuttle moving between Kruibeke and Antwerp, is hydrogen. Hydroville launched three years ago as the world’s first hydrogen-powered passenger vessel. Its hybrid engine allows it to run on both hydrogen and diesel.

"We decided for ourselves, look, we have to start with it today, even though there is no demand yet," says Roy Campe, managing director at CMB.Tech, the R&D branch of CMB, Hydroville’s owner. "We have to start today to make certain that within 10 years we can already start producing all our ships on a low-emission level. It's not a light switch that you just flip over."

CMB is already building several other hydrogen-powered boats, including a larger, 80-person ferry in Japan set for launch in early 2021.

The small boat sector is a great "proving ground" to scale up clean tech solutions for large merchant vessels, according to Diane Gilpin, founder of the Smart Green Shipping Alliance. Ships currently emit 3% of all greenhouse gases, and emissions are projected to grow by up to 50% by 2050 if the industry continues on a business-as-usual path. Governments in 2018 pledged to cut shipping emissions in half by 2050, but industry has been slow so far to implement measures on the ground.

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It takes a lot of energy to haul a ship through the water – and there are an increasing number of ships to haul as world trade grows. To cut emissions, some of this energy could be reduced through ships using more efficient designs, installing technologies to harness wind, going a bit slower to conserve fuel, or simply transporting less things.

But ultimately, if shipping is going to fully decarbonise – and it will have to if the world is to stay within safe temperature limits – it needs to find a replacement for fossil fuels.

CMB’s hydrogen programme is one of several shipping projects across the world testing how hydrogen and other fuels made from it, such as ammonia and methanol, could be used to power a low-carbon maritime industry of the future. These fuels, together often called "synthetic" fuels, are seen as a particularly promising option because they can be made using clean electricity – such as solar or wind power – and burned without emitting any greenhouse gases.

Why hydrogen?

Hydrogen isn’t the only alternative fuel option, of course. Biofuels – fuels made from plant materials or animal waste – are another. But these have a large array of planned uses in other sectors while their sustainable production is limited, says Tristan Smith, a shipping emissions researcher at University College London.

Batteries charged using renewable electricity are another option. But there will likely be limits on the distance these can power; large ships crossing oceans would simply need too many batteries to run on these alone.

Which leaves hydrogen and other synthetic fuels made from clean electricity. The gas is already widely used in industrial processes across the globe – demand for it has increased three-fold since 1975. But nearly all hydrogen, which is already used heavily in industry, is produced using fossil fuels. In fact, 6% of global natural gas and 2% of coal currently goes to hydrogen production. While this kind of hydrogen could be used to power ships with zero emissions from the ship itself, obviously it is not low-carbon since fossil fuels are used to produce it.

But hydrogen also can be produced without fossil fuels, using renewable energy to split water in a process called electrolysis. This process is expensive, and currently just 0.1% of hydrogen is made using it, but this is where the main hope lies for a climate-friendly shipping fuel. "Green hydrogen can be really emission-free on a full lifecycle basis," says Marie Hubatova, a shipping emissions expert at the Environmental Defence Fund. "That means from the point of where the fuel is extracted, or produced, until the point of combustion."

The problem is that right now, the availability of green hydrogen is just not there, says Xiaoli Mao, a researcher on the marine team at the International Council on Clean Transportation (ICCT). "Fuel producers need to see some legitimate demand in order to invest into its production, so it’s sort of like a chicken/egg problem – whether the ship technology develops first or the fuel side develops first," she says.

CMB itself is already acting as an early mover by building its own maritime refuelling station for hydrogen cars, buses and ships in Antwerp port, which will produce its own hydrogen using an electrolyser. "We first need to show, look, we are customers and we are willing to pay that amount for hydrogen," says Campe. "And then you see, ‘Oh, there's a business case for the electrolysers’."

How it works

Once the hydrogen is produced, there are several ways it can be used to power ships.

It can be burnt in an internal combustion engine, as Hydroville is currently doing. One downside to this is that burning anything in air, which consists largely of nitrogen, inevitably produces some level of nitrogen oxides – which are major air pollutants.

These emissions could be tackled by fitting some kind of after-treatment device, says Mao. But hydrogen can also be used in a fuel cell – a device which chemically converts the fuel into electricity without the need to burn it, and the only emission is water. "The main challenges of making that work on a ship are just to make it big enough," says Smith, noting the huge expense of installing enough fuel cells to power a ship. "There's a real question as to whether or not that is an option that is going to work at the scales of vessels."

Further options may exist for hydrogen. One UK company, Steamology, is in the early stages of developing steam-powered hydrogen electricity. Here, steam created by burning hydrogen with pure oxygen from a tank is used to drive a turbine, generating electricity. The technology is currently being tested in trains but has strong potential to be used in the shipping sector, its founders say. "It's quite crude in many ways," says Matt Candy, CEO of Steamology. "So we believe that we've got both a steam-electric solution. We don't have any nitrogen oxides, we are genuinely zero emission. But we've got to go through the pain of burning hydrogen in an oxygen environment."

Despite these promising technologies, switching to hydrogen fuel does not come without major challenges.

For a start, it’s highly flammable. CMB runs training programmes for its crew and others, looking at everything from how to maintain a hydrogen system on board a ship to how to handle fire safety. It is also very expensive, although its costs are falling, and will require extra electricity capacity.

But the real challenge for using it in long-distance shipping is how tricky it is to store. Hydrogen cannot simply replace bunkering fuel in the current system. To store it on board a ship as a liquid, it needs to be frozen using cryogenic temperatures of -253C (-423F), says Hubatova. And even then, it takes up a lot of space – around eight times more than the amount of marine gas oil needed to give the same amount of energy, according to EDF analysis.

The extra space needed by hydrogen has caused concern in the industry that it might need to clear out cargo to make room for the fuel. But an analysis from the ICCT has found that this barrier could be overcome. It found that 43% of current voyages between China and the United States – one of the world’s busiest shipping lanes – could be made using hydrogen without the need for cargo space or to stop more times to refuel. Nearly all the voyages could be powered by hydrogen with only minor changes to fuel capacity or operations, it found.

Ammonia alternative

Hydrogen is often used as a catch-all term for synthetic fuels, but many experts believe another option is actually better: using the green hydrogen to make green ammonia, another fuel which can be either combusted or used in a fuel cell. Ammonia is far easier to store than hydrogen (it needs refrigeration but not cryogenic temperatures), and takes up around half the space since it is far denser. It can also be converted back to hydrogen onboard a ship, meaning it could be loaded and stored on the ship as ammonia but ultimately used in a hydrogen fuel cell.

"At the moment, the best bet is to just turn [hydrogen] into ammonia, which is this ‘Goldilocks fuel’," says Smith. "Ammonia is so much cheaper to store; you can store it at a pressurised tank, so you don't need to have any sort of cryogenics. It's only a small amount more expensive to make than hydrogen."

The caveats? First, ammonia is toxic to both humans and to aquatic life, so care will be needed. Second, the extra step to convert hydrogen to ammonia will use more renewable electricity, making ammonia that extra bit more expensive.

Still, ammonia is seen by many in the industry as the most viable option: a consortium of companies were recently granted EU funding to install the world’s first ammonia-powered fuel cell on a vessel in 2023.

Green hydrogen itself is already pricey, and for a long time many have doubted whether it could ever be cheap enough to see widespread use as a fuel. But the huge cost reductions in wind and solar over the past few years have helped to challenge this view, with some experts projecting the cost of green hydrogen to fall significantly more in the next decade.

Necessary change

After a lethargic start to climate action over the past decades, there are some signs the shipping industry is beginning to pay attention to risks posed to it by the climate crisis. According to Smith, large percentages of the industry now think they will need to get off fossil fuels, with hydrogen-derived fuels such as ammonia considered the most likely alternatives. "There are a million questions about how we get from where we are today to that end goal," he says. "But the idea that that's where we're heading, is now very, very, very, very mainstream."

This is backed up by groups like the Getting to Zero Coalition, a group of shipowners, ports and countries who have pledged to introduce zero-emission vessels on deep sea routes by 2030. Earlier this year the group compiled a list of 66 zero-emission pilots and demonstration projects for shipping around the world, many involving hydrogen fuels. "They will probably be the group which will really pioneer hydrogen and ammonia vessels on a larger scale than pilots," says Hubatova. "This bottom-up action is really important as it sends the right signal to the wider industry."

But in the absence of stronger regulation for the shipping industry’s emissions, the speed of decarbonisation will be limited. "The role of the top-down approach in the form of regulations is also crucial, as it will ensure everybody transforms to zero-carbon, not just the most progressive players," says Hubatova.

In fact, Smith argues that the main constraint for shipping emissions comes not from technological barriers but from the political process – most significantly, the International Maritime Organisation, the UN body responsible for addressing shipping’s climate impact. "We've got options: we can either essentially progressively ban fossil fuels on vessels, or we can try and incentivise the market for hydrogen-derived fuels," he says.

Smith himself foresees three stages over the next 15 years for hydrogen-derived fuels in shipping: an increase in trials and first-of-a-kinds from now to 2025; an uptake of hydrogen by early movers in the industry by 2030; then a wider scale roll out after 2030, as costs come down and the infrastructure for refuelling becomes more widespread. Already, shipping companies are talking about ordering "zero ready" ships that are ready to easily retrofit for ammonia, he adds. "Their mindset is, I know that in 10 years’ time I'm going to have to do something to run that vessel on ammonia," he says.

The result for shipping emissions depends on a whole range of factors, from regulations to the uptake of other technologies. But there is a growing body of evidence of how fast the shipping sector could decarbonise if it set its mind to it, with one major report finding it could almost completely decarbonise by 2035 using currently known technologies, including alternative green fuels such as hydrogen.

Gilpin thinks the sector could reduce emissions by half by 2030. "If we treated this climate emergency, like we've treated the Covid emergency, then absolutely we could," she says. "But we don't, we go 'Oh it's a bit difficult, let's have another meeting about it.'"

Mao agrees that to ensure widespread uptake of lower emissions shipping technology, stringent mandatory regulations are vital. Even though hydrogen fuels may not see widespread use for a decade or more, she says, "we really need to start now".

"There are many barriers, let's face it," she says. "We should devote our research money into making this a reality into the future."

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