Aerojet Rocketdyne to develop ‘greener’ next generation propellants
On a recent flight, the commercial aircraft’s intercom chirped with an announcement: “Please return unwanted newspapers to help further our commitment to environmental sustainability.” While the sentiment was admirable, the request was laced with heavy irony given the immense carbon footprint individual passengers bear whenever they board a flight. In rocketry as in air travel, it is easy to overlook the environmental implications of the aerospace industry. One company has begun work on a propellant which might help to alleviate that.
To be sure, spaceflight is not a major factor in climate change. Low numbers of launches, compared to the use of cars or airplanes, keeps their impact limited. In 2009, researches estimated that as much as five percent of the world’s total CO2 emissions were derived from air traffic. Rocket launches, by contrast, only contributed to approximately one percent of ozone depletion in that year. While launches have since increased, and the use of certain ozone depleting particles curtailed, the percentage of climate change associated with rocket launces remains negligible.
Nevertheless, in an industry often at the forefront of climate change research, there remains the continued awkward use of less-than-clean propellants. As Slate noted, rockets pour reactive agents directly into the stratosphere, which combine with venting soot and aluminum particles in the upper atmosphere.
Solid-fuel rockets are particularly studied and thus known to be destructive. Burning solid-fuel, as National Geographic has written, emits chlorine gas in the stratosphere. When combined with oxygen, the result is a fast-acting ozone depletion.
In a Quora forum, NASA engineer Robert Frost compares some of the most common types of propellant and their environmental impacts. The Space Shuttle offers a good primer because it used various types of fuel for a single launch. “The main engines,” Frost explains, “were powered by that enormous orange tank behind the Orbiter. That fuel was cryogenic hydrogen and oxygen. The waste product was water vapor – so there was no real environmental impact from the main engines.”
The Solid Rocket Boosters, however, “used a solid fuel made from powdered aluminum and ammonium perchlorate. When that burns, the significant waste product is hydrochloric acid. About 34,000 kg of HCl was deposited within a 1km circle of the launch pad. That resulted in a pH change to any water in that area that lasted up to 3 days. NASA…has carefully studied the launch site area for the last 30 years. They have noted a reduction in plant species in that immediate area and observed some fish death in that immediate area.”
According to Frost, “NASA studied their contribution [to ozone depletion] and found that each Space Shuttle launch was responsible for 0.016 percent of the halocarbons released worldwide, annually. [Their] report determined that a Space Shuttle launch had no significant impact on the ozone layer. NASA did make changes in other ways to decrease the amount of chlorofluorocarbons they used, though. The original foam covering of the external tank was made using CFCs. Even though NASA had an exemption, it had the contractor develop the foam a different way, without using CFCs.”
Hypergolics are also commonly used, which are “substances that are so reactive that when they come into contact with each other, they combust. A common combination is hydrazine and nitrogen tetroxide,” the waste product of which is nitrogen oxide, which mixes with atmospheric water to form nitric acid.
Finally, perhaps the least environmentally friendly rocket propellant is kerosene, which produces CO2 and soot as waste just as any other petroleum-based fuel. As Frost illustrates, “Kerosene is similar to diesel, so if you’ve ever been behind a dirty semi-truck on the highway, belching black smoke, that’s essentially the waste product of a kerosene fueled rocket.”
And the concern is not merely theoretical. In a 2009 paper in Astropolitics, the authors caution that increased launches and the possibility of a space tourism industry create the potential for spaceflight to become a greatly enhanced contributor to greenhouse gas emissions. In the words of one of the articles coauthors, Darin Toohey of the University of Colorado at Boulder, “This isn’t urgent, but if we wait 30 years, it will be.”
That is why Aerojet Rocketdyne was recently awarded a contract to begin exploring greener propellants for rocketry. The effort comes in partnership with the U.S. Army Aviation and Missile Research, Development and Engineering Center; the U.S. Air Force Research Laboratory at Edwards Air Force Base; and the U.S. Army Medical Command. The contract is funded through the Strategic Environmental Research and Development Program within the Department of Defense.
The three-year contract will be executed in experimental phases. First, Aerojet’s research arm in Washington State will begin with small-batch testing of various monopropellants. Monopropellants do not require oxidizers, and while not always as effective pound-for-pound, can be more environmentally friendly as a result.
Candidates which the team determines to be promising leads will then be scaled-up at the Sacramento Chemical Synthesis Laboratory, and finally thruster testing of selected propellants will provide greater detail on thrust and environmental impact.
Aerojet has already begun experimenting with next-generation propellants. The company notes that it has already completed designs for the 2016 NASA program Green Propellant Infusion Mission, which will use the Air Force’s greener AF-M315E.
In a statement from the company, Julie Van Kleeck, vice president of Space Advanced Programs at Aerojet, expressed optimism at the firm’s qualifications to tackle next-generation propellants. “Aerojet Rocketdyne has decades of experience researching next-generation propellants for space and defense applications. That research has covered many different types of technologies and resulted in maturing propellant and propulsion system technologies from early lab research and development to fielding flight systems,” she noted. “We are excited to capitalize on our past accomplishments and are looking forward to helping develop the next generation of advanced green propellants – enhancing the capabilities of future systems while making the world we work in safer.”
Since 2011 Joshua Tallis has served as the manager for research and analysis at an intelligence and security services provider in Washington, DC. Josh has co-authored several articles in the Journal of Counterterrorism and Homeland Security International with colleagues from the defense community. Previous work experience includes internships at the U.S. Congress and the Foundation for Defense of Democracies. Josh is also a PhD student in International Relations at the University of St Andrews' Centre for the Study of Terrorism and Political Violence. He is a Summa Cum Laude, Phi Beta Kappa and Special Honors graduate of The George Washington University where he received a BA in Middle East Studies from the Elliott School of International Affairs.