As high-speed commercial air travel gathers momentum, how can high-speed aircraft be made sustainable?
Commercial high-speed air travel is picking up speed. The US government has embedded speed of air travel in its strategic priorities and NASA and the European Union are investing in research into high-speed vehicle design. Products like Boom Supersonic’s commercial aircraft, Overture, are progressing towards doubling the speed of existing air transportation.
The benefits of air travel are clear – it connects the world, links people and ultimately enables global economies to prosper. High-speed air travel has the potential to make the world even more accessible, unlocking new travel destinations and possibilities.
Yet, this renewed interest in high-speed flight (defined here as supersonic speeds) comes as the aviation industry aims to abate its climate impact. The aviation industry accounts for ~2% of global greenhouse gas emissions and has prioritized reducing its environmental impact. In this context, can speed and sustainability co-exist
Sustainability and high-speed travel are not mutually exclusive concepts, as products like Boom’s Overture – optimized for speed, safety, and sustainability – and others show. Furthermore, advances in aerospace technology provide modern high-speed aircraft with a head start towards sustainable flight. Low-emission technologies and fuels are critical to continue this momentum. When implemented, they will ensure that faster travel is safe, sustainable and a net good for society.
Sustainable aviation fuel: integral to decarbonizing high-speed flight
Sustainable aviation fuel (SAF) is recognized as an immediate and scalable solution to decarbonizing the aviation industry. Instead of fossil-based sources, SAF relies on carbon atoms from organic and waste materials already part of the carbon cycle, lowering CO2 emissions by up to 100% compared to fossil jet fuels. While current international standards cap the blending of SAF with fossil jet fuels at 50%, new standards are being developed for 100% SAF.
It is essential that high-speed aircraft manufacturers design their vehicles to accommodate 100% SAF – notably, non drop-in SAF (fuel with enhanced specifications that deliver greater performance and emission benefits but which could require existing equipment to be modified to make it compatible).
High-speed flight has energy requirements two to three times greater than comparable subsonic travel, emphasizing the importance of designing to accommodate SAF. By optimizing aircraft designs for 100% SAF, modern supersonic airliners such as Overture and engine Symphony will be able to achieve net-zero carbon operation upon entry into service without extensive and time-consuming retrofits. To follow through on those commitments, Boom has procured 10 million gallons per year of SAF for flight testing and delivery operations; other industry players have similarly followed suit.
Across the industry, demand for SAF continues to be strong. Presently, more than 100 airlines, manufacturers and airports have expressed interest in SAF procurement, with multi-year agreements between fuel users and producers exceeding 11.2 billion gallons – more than 5.7 billion gallons were signed in 2022 alone.
SAF production needs to scale rapidly to meet this strong and increasing demand, requiring concerted efforts now from industry and governments alike. Drawing parallels to the successful exponential growth of renewable energy industries such as wind and solar, four core measures are critical to scaling the SAF industry: early adoption, sustained R&D funding, a strong government incentive model and consistent SAF policies. Through these measures, SAF will be poised to deliver carbon reductions, not just for high-speed travel, but across the entire global aviation industry.
Technological innovation to improve efficiency
Sustained innovation and improvement in aircraft technology plays a pivotal role in faster flight’s enduring sustainability. Reassuringly, a review of the aviation industry’s evolution affirms a deep-rooted desire for continual technological improvement.
The advent of the jet engine doubled the speed of commercial air transport relative to piston-engine airliners in the 1960s. However, initial jet aircraft were approximately three times as energy intensive as the technologically-mature, piston-engine airliners of the time (on a per-seat-kilometre basis). Research and development and improvement of aircraft and engine technology increased the energy efficiency of jet aircraft over the ensuing 30-year period to meet and even surpass those of piston airliners.
As modern high-speed vehicles enter airline fleets, they are well positioned to capitalize on advancements in subsonic aircraft and engine technology to achieve greater efficiencies (for example, lighter composite materials and higher fidelity modelling). Coupled with the anticipated efficiency improvements to high-speed aircraft gained through innovation, this will enable the benefits of faster flight to be delivered sustainably.
Further R&D needed to understand and address non-CO2 climate impacts
Aircraft engine emissions beyond CO2 affect the climate as well, though with varying magnitudes depending on altitude. According to recent research, contrails may be the largest contributor to aviation-attributable climate change, though contrail formation is greatly reduced at cruising altitudes typical of supersonic aircraft. Conversely, nitrogen oxides and water vapour emissions in the stratosphere could have greater climate impacts than emissions at lower altitudes.
The exact magnitude of stratospheric emissions impacts remains under debate. Further climate science research is required to better understand the holistic impacts of high-speed flight. This will enable evaluation of potential mitigation strategies, such as optimal aircraft routing to avoid contrails and climate-optimal cruise altitudes.
Notable engine emission reduction technologies include lean burn combustion, idle cycle manipulation and plasma combustion, aimed at lowering nitrogen oxides and other pollutants which have an effect on climate and local air quality. Next-generation SAF shows great potential for reducing the soot emissions that contribute to contrail formation, in addition to their enhanced fuel performance.
Speed and sustainability can co-exist
The reintroduction of high-speed flight brings with it a novel opportunity to integrate sustainability from the start as a pillar of modern aircraft design. New entrants are well positioned as they can optimize aircraft for sustainability from the start. Our collective focus on sustainability must be matched by collaboration across the public and private sector to scale SAF and research efforts to understand and mitigate non-CO2 effects. This will ensure speed is never at the expense of sustainability, making faster travel safe, sustainable and good for society.
This article was first published by World Economic Forum and is being republished under the Creative Commons Licence.
