Boom Technology Inc. is trying to revive supersonic travel, but the most ambitious part of its plan might be to run its aircraft on 100% sustainable fuels.
Running conventional flights on so-called sustainable aviation fuel, or SAF, is already a challenge due to a dearth of supply and high costs. Adding more supersonic jets to the mix would make the challenge even tougher, experts say, because they use more fuel than conventional planes.
“It’ll be challenging enough to ramp [SAF production] up to meet subsonic [demand] without making it even more challenging by needing to ramp up production to meet both subsonic and supersonic,” said Andrew Murphy, aviation director at Transport & Environment, a Brussels-based nonprofit group that advocates for low-carbon transport.
But Boom founder and Chief Executive Blake Scholl said the company’s Overture jets will be able to do things that weren’t possible for less advanced planes. For instance, he said its turbofan engine will allow the plant to break the sound barrier without making more noise than the latest subsonic aircraft. The ambition extends to the plane’s environmental impact.
“Overture will be the first airplane designed from the ground up to run on 100% SAF,” Mr. Scholl said. Only being able to run on SAF will make the jets “net-zero carbon from day one,” he said.
Boom hopes to fly a prototype of the Overture, which it says would nearly halve the journey time from New York to London to three-and-a-half hours, this year or early in 2022, and begin commercial operation in 2029. United Airlines Holdings Inc., which announced this month that it plans to buy 15 of the jets, said the deal will be contingent on the plane meeting the airline’s safety, operational and sustainability standards. United aims to reach net-zero greenhouse-gas emissions by 2050.
But sustainability experts say going supersonic would make it harder for the airline industry to reduce its emissions.
Supersonic aircraft are estimated to burn five to seven times as much fuel per passenger as a regular aircraft, according to the nonprofit International Council on Clean Transportation.
Roughly 300,000 flights used SAF between 2016 and 2020, according to the International Air Transport Association—less than 0.2% of the 188 million flights world-wide. SAF costs up to 3½ times as much as regular fuel, according to S&P Global Platts, a provider of benchmark prices for commodities and energy markets.
There are constraints to the production of the most commonly used SAF, biofuel, which can be made from animal fats, crops or waste. Growing more crops for fuel will take up more land as demand increases, which would have its own environmental toll, Mr. Murphy said.
As for waste, there are around 340 million tons of biomass—material from plants and animals that can be used as fuel—available in the U.S. annually, according to a 2016 Energy Department estimate. The expected growth of jet-fuel demand means the U.S. airline industry alone would need an estimated 700 million tons a year by 2050 if it were to rely on biomass, a spokesman for the department said. And airlines will be competing for that supply with shipping and other industries trying to shift to green fuels.
United started dabbling in biofuels in 2009 but began using them regularly beginning in 2016 at its Los Angeles hub. SAF accounts for a tiny fraction of its fuel, the company said.
In recent years, United has spent tens of millions of dollars on a string of investments aimed at increasing the supply of sustainable fuel and developing technologies for removing carbon dioxide from the air and storing it underground.
The most scalable form of sustainable fuel will be power-to-liquid fuels, Mr. Scholl said. Also known as e-fuels, or synthetic fuels, they use renewable energy such as solar and wind power to split water into hydrogen and oxygen. The hydrogen is then combined with carbon monoxide created from captured carbon dioxide.
In theory, the supply of synthetic fuels is only constrained by the availability of water and electricity to split it. But the technology is still being developed, and would require a large amount of land for solar or wind projects, according to a report by engineering group Ricardo PLC for Transport & Environment.
“You could address the carbon dioxide climate impact of supersonics with synthetic fuels if you had unlimited dollars and a lot of renewable, excess electricity,” said Dan Rutherford, an aviation program director at the ICCT. “Will it be achievable in the next 20 years? I think the answer is very unlikely.”
Mr. Scholl said Boom’s supersonic jets would require more fuel to carry the same number of passengers as a regular jet, but said they would have other efficiency benefits. Flying supersonic means each plane would be able to make more flights over its lifespan than a regular plane, he said.
“The faster you fly, the more you can do with a limited resource,” he said.
Boom will partner with multiple companies to ensure there is enough SAF to provide all the fuel needed for its aircraft, Mr. Scholl said.
In 2019, the company formed a partnership with Prometheus Fuels, a company that supplies carbon-neutral fuels by removing carbon dioxide from the air and using clean electricity to turn it into jet fuel.
United will also work with Boom to increase the supply of sustainable fuels, the carrier said this month.
Mr. Murphy at Transport & Environment said he doubted that enough sustainable fuel would become available in time for Boom’s goal to get commercial flights running by 2029.
“That’s good for them to say that, but where actually is the SAF?” he said.
The amount of sustainable fuel needed to run supersonic jets isn’t their only potential environmental drawback. The ICCT said the current configuration of supersonic aircraft was likely to exceed globally agreed limits for pollutants called nitrogen oxides by 40% and 70% for carbon dioxide.
Boom said it is working with engine maker Rolls Royce Holdings PLC to develop propulsion systems for the aircraft that will help the engines match the same standards as subsonic aircraft, as well as running on clean fuel.