Taking sustainability to soaring heights

7,434 rockets have been launched into space since the launch of the V2 missile in 1942, the first ever successful launch of a spacecraft. 

Ever since then, space travel has yielded many impressive scientific results. 

At USC, in October 2024, USC’s Rocket Propulsion Team launched a rocket 470,000 feet into the air, setting a new world record for amateur rocketry. Named Aftershock II, the rocket flew through the Kármán line that separates Earth’s atmosphere and outer space.

However, the team utilizes solid propellant, making reusable rocket casing and fuel cells very difficult. Sustainable rocket materials are important for sustainability and efficiency reasons, as reusable cells can help reduce the rocket’s overall environmental impact and reduce costs for the team itself. 

Now, more companies in the industry have begun to focus on reusable models for rocketry. Namely, the Falcon 9, created by the company SpaceX, revolutionized orbital travel, exceeding 160 relaunches in 2025, following a period where retrieving — let alone reusing —- rockets seemed implausible. Reusability seems to be becoming a main industry priority nowadays.

“Reusability is a huge tenant of space travel currently. It would suck to have single use rockets and have to rebuild it from scratch every day. That's both inefficient operationally and inefficient in terms of resource consumption,” said Sana Hamid, a junior mechanical engineering major and lab lead of Liquid Propulsion Laboratory. “There's a lot of development being done in the area of how to make different vehicles reusable and the performance lifespan of said vehicles, so that they can be reliably used over and over again.”

However, amongst these astonishing achievements are also environmental issues.

“Devils venom,” as Soviet scientists dubbed it, scientifically named unsymmetrical dimethylhydrazine (UDMH), is a unique liquid propellant that doesn’t require an ignition nor much energy. It earned its antagonistic name because of its carcinogenic property that turned the world’s oldest spaceport, the Kazakh Steppe, into an “ecological disaster” according to  BBC. 

Whether from accidental spills or rocket crashes, the soil in this region suffered from the kerosene poisoning. As a result, the cellulolytic activity of the soil decreases, weakening the ability for microorganisms like fungi and bacteria to break down the cellulose in the soil for plants to consume and grow. Thankfully, the contamination was reversible, but it took a surfeit amount of months for the microorganisms to complete the task, qualifying how unfortunate this devastating environmental zone was.

In 2009 the US Environmental Protection Agency (EPA) established the Greenhouse Gas Reporting Program (GHGRP), requiring those working with emission sources like kerosene to report their amount of emissions. They have regulations in place setting boundaries for the proper handling and storage of flammable, combustible liquids like kerosene as well as other regulations that pressure companies to burn them before it’s released in order to avoid consequences such as fines. These can be found both in the EPA’s Clean Air Act or the Bureau of Land Management’s Waste Prevention Rule.

Additionally, rocketry and aviation companies that use kerosene and other harmful liquid propellants are mandated to have an oil spill response plan for kerosene spills under 33 U.S.C. 1321 in the Code of Federal Regulations. 

These rules apply both to rockets and commercial aircrafts alike as airplanes usually rely on jet fuel composed of kerosene, making the latter an additional contributor to carbon emissions. However, the difficulty with unenforced mandates — opting for financial pressures — is that the amount of space airplanes could potentially have for an alternative fuel source like electric batteries is scarce because of passengers and cargo, so it’s not worth it to conform to said fuel alternatives.

Inherently, however, rocketry does produce a large amount of emissions due to propellant combustion. 

Rockets rely on strong, high-energy propellants to reach the heights that they do. These propellants are composed by combining fuel, which burns for propulsion when in contact with oxygen, and an oxidizer, which releases said oxygen. The majority of orbital rockets opt for liquid propellant because they have higher specific impulse, meaning that they have better efficiency — similar to miles per gallon in a car.

Petroleum fuels in particular are among the most common, specifically a kind called Rocket Propellant 1. RP-1 is a form of highly refined kerosene.

Kerosene is extremely dangerous for the environment. According to the National Library of Medicine, “The combustion of each gallon of kerosene would directly release 9.98 kg of CO2.” Some estimates have SpaceX’s Falcon 9 launch — which uses RP-1 — releasing as much as 116 tonnes of CO2 into the atmosphere in the 165 seconds of the first part of the launch. 

Additionally, according to Eloise Marais, an associate professor in physical geography at University College London, RP-1 launches can affect the atmosphere more than other aviation flights, as rockets expel propellant from the surface of the Earth to the top layers of the atmosphere. “When pollution is released into those upper layers it lasts for a longer time than earthbound sources." Marais said, in an interview with BBC. 

“Another harmful impact that might go underlooked is the material sourcing,” Hamid said. “A lot of the materials that are required to survive in the very extreme conditions that are seen during like, like when you're leaving the atmosphere, tend to be ones that are either difficult to find or aren't ethically sourced.”

While using highly-polluting fuel in rockets may seem oxymoronic, as it can harm the Earth in the name of bettering our knowledge, rocketry can be both efficient and sustainable, making it worthwhile, according to Hamid. 

“You could use something that's very carbon heavy like kerosene, or you could see something that's a simpler compound and can be naturally or sustainably sourced, like methane,” said Hamid. “This area of green propellants is something that's definitely expanding also because they're super high energy and mutually beneficial towards both sustainability and the success of the project.”

Methane — another combustible liquid bound to the same legal safety pressures — is a promising and more environmentally conscious orbital rocket propellant. Not only is it naturally sourced as a leftover from industrial and agricultural processes, but has the potential for extremely high energy output.

The byproduct of methane combustion is the release of carbon dioxide and water, but this is better than the current alternative of a more complex hydrocarbon excrement from kerosene, which remains in the atmosphere longer. 

Hamid also went on to explain that space travel can continue to revolutionize scientific understanding, without losing sight of sustainability initiatives. 

“Research might hit dead ends, but then you always just end up having somebody with a different perspective on the problem, and that leads to breakthroughs,” she said. “It's possible to be in a very fast paced environment where the primary objective is to advance the frontier of technology and space travel, while simultaneously being sustainable…..I don't see the two as mutually exclusive, and I don't see one as better than the other.”

For Hamid, the fact that federal regulations such as the ones placed on kerosene already is “already a huge step in making sure that it's safe — that we're taking preventative measures to make it safe.” Prohibitions and mandates affirm that the government recognizes the potential environmental fallbacks and isn’t turning a blind eye to the risks associated with rocketry.

While the current reality isn’t ideal, as put by Hamid, “there [isn’t] necessarily a worst case scenario.” Legislative discourse — like the potential carbon tax presently being debated —  and advocacy are steps in the right direction. The more research conducted on improving the functionality of green rocket material and propellant sourcing, the brighter the future of sustainable orbital travel appears.

This article was edited for accuracy and more information has been added on up-to-date rocketry regulations.