Aerospace Industry Aims for Eco-Friendly Rocket Propulsion
In an era of unprecedented space exploration, the aerospace industry finds itself at a pivotal juncture, grappling with the need to harmonize efficiency and sustainability. Private players like SpaceX and Virgin Galactic have joined the fray, leading to a significant increase in rocket launches annually and raising concerns about the environmental impact of conventional propellants.
The stratospheric release of noxious gases, water vapor, nitrogen oxides, and soot particles from rocket exhaust is accelerating global warming. Kostas Tsigaridis, a researcher at Columbia University, emphasizes the urgency for a paradigm shift, noting the lack of stringent regulations allowing companies to freely determine the number of launches they conduct.
Kerosene: The Maligned Fuel
Since the 1950s, kerosene, specifically its highly refined variant, RP-1 (Refined Petroleum 1), has been the preferred propellant for rockets due to its cost-effectiveness and stability. However, its detrimental environmental impact has raised concerns about its future viability.
The combustion of kerosene in rocket engines not only produces carbon dioxide but also unoxidized carbon particles, known as "black carbon" or "soot." Tsigaridis explains that once released into the stratosphere, black carbon absorbs light and heat, exacerbating global warming. The increased number of rocket launches and continued use of kerosene have led to a worrying surge in black carbon emissions.
A 2022 study by the National Oceanic and Atmospheric Administration (NOAA) predicted that sustained black carbon emissions could warm the stratosphere by over 1.4°C, highlighting the need to phase out kerosene.
Exploring Cleaner Alternatives
Industry experts are actively exploring eco-friendly alternatives for future rockets. Methane emerges as a promising candidate due to its reduced black carbon production during combustion. However, methane-based propellants (liquefied natural gas, or LCH4, and its oxidizer, liquid oxygen, or LOX) still emit some black carbon.
Tsigaridis asserts that the only realistic way to create a rocket fuel without black carbon is to avoid using carbon altogether. Another option is liquid hydrogen (LH2), which, unlike kerosene, produces neither carbon dioxide nor black carbon during combustion. However, its production relies heavily on fossil fuels, posing limitations to its long-term viability.
Nevertheless, NASA is actively pursuing alternative solutions. The agency has partnered with Lockheed Martin to develop a nuclear fission-powered rocket engine, aiming to test a nuclear rocket by 2027. If successful, these engines could offer up to five times the efficiency of traditional engines, potentially facilitating crewed missions to Mars.
The aerospace sector faces the challenge of reconciling efficiency and sustainability. Jeff Gardner, senior writer at the Space Foundation, emphasizes that no new fuel has yet surpassed kerosene or hydrogen in terms of cost or development time. Despite this, efforts are underway to uncover the ideal fuel for eco-friendly rockets.