Figure 1: Innovations from NASA will help the US meet its sustainable aviation goals
Aerospace is one of the fastest growing markets. While both the size of the market and its growth rate are both large, so is its carbon footprint. While electric vehicles are already replacing conventional automobiles, no electric aircraft is ready for large scale commercial production that can usher in a sustainable revolution in aerospace. There are smaller scale changes that can be made, however. These include offsetting greenhouse gas production by purchasing carbon credits, investing in more efficient gas turbine engines, using sustainable aviation fuel, and manufacturing with novel materials and 3D printing methods.
1. The Aviation Market
Ever since the Wright Brother’s famous first flight in 1903, the aviation market has gone nowhere but up. This includes not only commercial airlines, but also cargo planes and military aircraft. By 2026, the global market for commercial aircraft is projected to reach around $70 billion, up from $55 billion in 2019. The market for freighter aircraft is projected to grow by around 4.5% per year over the same period.
When it comes to understanding the carbon footprint of these aircraft, the primary culprit is the engine. The turbo and jet engine market are dominated by three major players: GE Aviation, Rolls-Royce (not the car), and Pratt & Whitney. Most commercial airlines contain two engines, while cargo planes and some military craft generally require four or more (common engines for these large-scale aerospace vehicles include PW JT9D-7R4G2 engines, GE CF6-80C2B1, or RR RB211-524D4 engines).
Aircraft engines produce carbon dioxide, so much so that the global aviation market accounts for 2% of all human-created CO2 emissions. There are a few ways that airlines are attempting to reduce emissions, from decarbonization to electrification. Some of these changes will require advancements in technology while others will require societal change.
Figure 2: Aviation Industry CO2 Emissions
A critical decision point is coming. If the aviation industry continues down the path of high CO2 emissions, what will happen when new aerospace markets open: sub-orbital travel, supersonic flight, and space hotels? Sub-orbital travel, popularized in 2021 by Jeff Bezos, Richard Branson, and Elon Musk, is projected to become a $3.5 Billion industry by 2027. If civilian aviation is not carbon neutral, how can aircraft traveling up to the edge of our atmosphere be expected to achieve this goal?
2. Aviation Industry Trends & Uncertainties
2.1 Policy Incentives
The US Transportation Secretary Pete Buttigieg recently pledged that America will achieve carbon neutrality for its aviation sector by 2050. Other countries that attended COP26 in Glasgow committed to similar goals. For example, Sustainable Aviation in the UK provided a roadmap for achieving net zero carbon emissions (see Figure 3 below).
Figure 3: Sustainable Aviation’s Carbon Roadmap from the United Kingdom
The impact of governmental policy on sustainable aviation can be seen in the above plot. Governments should incentivize and reward carbon neutral or carbon offset initiatives, such as purchasing carbon credits or switching to sustainable fuels. Additional initiatives that will be needed include investing in carbon capture technologies and biological methods of CO2 removal.
2.2 Carbon Credits
Another frequent proposal to achieve sustainable aviation is carbon credits. Companies which require regular travel for business (e.g. management consulting firms) produce high levels of carbon dioxide emissions that cannot otherwise be reduced. A thousand miles of air travel generates nearly 500 pounds of carbon emissions per passenger. One solution for consulting firms is to purchase carbon credits which certify that they have offset their emissions.
Firms and individuals can visit websites such as Terrapass to calculate their carbon footprint and purchase offsets. The funds from these credits go towards financing various sustainability projects. For example, Terrapass donates to a range of projects including landfill gas capture, farm power, wind farms, and abandoned coal mine methane capture projects.
2.3 Technology Advancement
Policy changes and carbon offsets are short term solutions to achievable sustainability in aviation. However, to achieve substantial long run changes, greater technological improvements need to be made. Since most aircraft use gas turbine engines, completely replacing them with electric motors would offer the potential to eliminate carbon dioxide emissions.
The chief problem is that electric aircraft are not here yet. In 2021, Rolls-Royce debuted an all-electric aircraft that smashed the airspeed record with a top speed of 387 MPH. Although this represents great progress, electrification still has the Achilles’ heel that current batteries are 50 times less energy dense than jet fuel. This means that significant advancements are required in areas such as energy storage to pave the way for long distance electric aviation.
Although complete electrification of aircraft engines is not possible yet, there are some near term solutions. Companies such as GE Aviation and Safran are working on improving engine efficiency in order to reduce emissions. For example, they have developed a new Open Fan Design that will reduce carbon emissions by more than 20%.
Figure 4: GE Aviation and Safran’s Open Fan Design
2.4 Chemical Innovations
In addition to changing the mechanical component, another innovation supporting the pursuit of carbon neutrality is Sustainable Aviation Fuel (SAF). Shell aims to produce around 2 million tons of SAF per year by 2025. And by 2030, it aims to have SAF account for at least 10% of its global aviation fuel sales. Typically produced from feedstock, as well as fats, sugar crops, trees, and grasses, SAF is on track to become a main source of jet fuel by mixing it with up to 50% traditional jet fuel. BP estimates that SAF could offer an 80% reduction in carbon dioxide emissions over the life cycle of the fuel.
One current road bump is the high cost of SAF compared with traditional jet fuel; it is up to 4 times more expensive. The expectation is that SAF will become less costly over time as production processes become more efficient and technology improves.
While SAF is currently used as a mixture in jet fuel, United Airlines has run a test flight using 100% SAF in December 2021. One engine used pure SAF while the other used traditional jet fuel. The test showed no observable operational difference between the two. While this was just an experimental step, this could open the door to more permanent SAF usage.
Figure 5: Breakdown of relative expected contributions towards IATA’s net zero plan (Source: International Air Transport Association)
2.5 Other Trends
There are many other options for making aviation more sustainable. Interest in hydrogen powered engines is growing, although projections indicate that large scale production of hydrogen turbines will not be possible before 2027 (according to the Doosan Group). Artificial intelligence and machine learning might also be employed to optimize routes and reduce unnecessary miles traveled. Many airplane manufacturers are also turning towards cheaper, lighter, and more sustainable materials for aircrafts and engines, and 3D printing is also becoming more attractive as a manufacturing technique that has the potential to improve the durability of aircraft components.
3. Business Opportunities
While turning away from fossil fuels may seem like closing a door, sustainable aviation provides plenty of opportunity for research and development and solving complex global problems. Many new startups already have million dollar or billion dollar valuations.
3.1 Vertical Take-Off and Landing
Have you ever ordered an Uber, and due to rush hour traffic it takes forever to arrive? Don’t you just wish it could take flight and get to you instantly? Well, that dream might soon be a reality with the introduction of vertical take-off and landing vehicles (VTOLs). Startups such as Joby Aviation are working on these novel aircraft to one day serve as flying taxis.
3.2 3D Printed Rockets
Other companies are focused on the sustainability of aircraft parts. For example, Relativity Space is building 3D printed rocket pieces and autonomous rockets that can be built and deployed in as little as 60 days.
3.3 Reusable Parts
SpaceX, Elon Musk’s space travel company, focuses on building reusable rockets and launch vehicles so that new ones do not need to be built every time. This approach contrasts with NASA’s efforts from the 1960’s onwards where they built new modules for every launch. SpaceX’s approach is clearly successful, and today the company is valued at over $6 billion.
3.4 Supersonic Flight
To cut down on emissions, why not just fly faster? Traditionally this has been a challenge since planes flying at a speed of 767 MPH, Mach 1, are travelling at the speed of sound. Flying at this speed creates of a shock wave, which can negatively affect the performance of the aircraft. Some companies are attempting overcome this barrier by designing new aircraft models that can handle the shock wave. For example, Boom Supersonic is building narrow body supersonic aircraft that can travel up to twice the typical airspeed, cutting commutes in half.
3.5 Sustainable Aviation Fuel
Sustainable aviation is not exclusively a US goal; many European countries are also making policy changes to decarbonize the aviation industry. Two of these changes are carbon pricing and blending mandates. Blending traditional fuel with biofuel is a method previously used in Brazil to combat rising gasoline prices. However, blending can also help to reduce the quantity of carbon dioxide produced by jet fuel. Multiple countries, including France, Holland, Denmark, Finland, and Sweden, are focused on increasing the use of SAF blends. Portugal has even decided to decarbonize its entire transportation sector.
Figure 6: European policies on sustainable aviation fuel
3.6 Start Ups
While the aviation sector seems to be dominated by major players at first glance, aerospace is also filled with many startups. According to Exploding Topics, the top ten aerospace startups to work for are:
- ABL Space Systems
- Joby Aviation
- Relativity Space
- Voyager Space Holdings
- SpaceX
- Accion Systems
- CesiumAstro
- Iris Automation
- Astranis
- Skydio
Conclusion
The aviation sector produces huge amounts of carbon dioxide and electrification is not an immediate solution. As a result, other decarbonization methods are required to reduce greenhouse gas emissions, including blending and replacing fuel with sustainable alternatives, manufacturing more efficient gas turbine engines, and introducing novel materials and manufacturing methods (such as 3D printing) in order to reduce weight and increase aircraft durability.
Ricky Hollenbach is a third year Ph.D. student at Duke University in Mechanical Engineering, studying unsteady aerodynamics and mechanical vibrations in jet engines and turbomachinery. He aspires to become a management consultant in the aerospace and defense fields.
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