Air Force

Environmentally safe bipropellant fuel system decreases handling complexity

Businesses can improve energy density and decrease operational costs of rocket launches with the Air Force’s ionic liquid fuel system found to be hypergolic with hydrogen peroxide

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The high energy density and low environmental impact inherent in this new hypergolic bipropellant are ideal for applications that require high performance from limited volume systems. (Photo by Staff Sgt. Christopher Stoltz)

If launching rockets is your business, you’ll want to take notice of the Air Force’s new bipropellant fuel system, available for licensing: it’s truly clean and green, and it moves the needle on performance.

Today’s bipropellant rockets employ a hypergolic fuel system that must be storable, enable fast ignition and travel lightly. The conventional approach to this fuel system hinges on the use of the fuel component hydrazine, which is a known carcinogen with high vapor toxicity, rendering immense operational expenses and concerning environmental impacts. As propulsion scientists narrow in on effective and safe alternatives to hydrazines, the use of various ionic liquids has proven viable.

However, it has recently been discovered that the majority of hypergolic ionic liquids are only reactive with some form of nitric acid as the oxidizer. While oxidizers are inherently hazardous, the toxicity and corrosiveness of nitric acids, which have an even higher vapor pressure than hydrazine, make operability further complicated

In steps the Air Force Research Laboratory – Aerospace Systems Directorate, where scientists have developed and patented an environmentally responsible ionic liquid bi-propulsion system that addresses the toxicity of the oxidizer, diminishing the many operational constraints of state-of-the-art hypergolic fuel systems. The invention is an advanced bipropellant leveraging a fuel mixture of at least two ionic liquids, one of which must be metal-containing. This advancement is on the leading edge, as the scientific community has not realized hydrogen peroxide to be reactive with ionic liquids.

What makes the Air Force’s approach distinct and attractive is that the metal-containing ionic liquid functions as the catalyst for fast decomposition of hydrogen peroxide and does not have to be hypergolic with the hydrogen peroxide alone. It’s the mixture of the metal-containing ionic liquid with the other ionic liquid that enables fast ignition upon contact with the hydrogen peroxide. The development not only delivers a truly green bipropellant system whereby both the fuel and the oxidizer are environmentally safe, but the performance improvements are noteworthy.

The high energy density realized in this new hypergolic bipropellant system has the potential to replace bipropellants currently used in on-orbit spacecraft propulsion. Other applications may include liquid engines for boost and divert propulsion, and commercial applications like satellite deployment and space launch activities.

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