May 7, 2013
NASA Adopts Greener Rocket Fuel For 2015 Mission
Brett Smith for redOrbit.com - Your Universe Online
NASA has announced that it will stop using the rocket fuel that has been an aeronautics mainstay since the 1940s and switch to a greener, environmentally-benign propellant. The space agency says that the first space flight powered with this new fuel will take place in 2015.
Hydrazine was used to power the first rocket-powered fighter plane in World War II, the Viking Missions of the 1970s, and more recently the Curiosity mission on its trip to Mars. The new propellant is an energetic ionic liquid (EIL), a class of liquids known for the thermal stability and extremely low vapor pressure that make them a prime candidate for rocket fuel.
At first, hydrazine was prized as a propellant for the extremely exothermic reaction that it produces, releasing a massive amount of heat in a very short time. Additionally, it is capable of producing large amounts of energy and hot gas from a relatively small volume of liquid.
However, hydrazine has several significant drawbacks, including its high toxicity, high volatility, and limited capacity as a propellant.
The effort to refine an EIL for rocket fuel was spearheaded by Tom Hawkins of the Air Force Research Laboratory (AFRL). Hawkins first became interested in the potential of EILs while working on Strategic Defense Initiative (SDI) in the 1980s. Derided as “Star Wars” by the media at the time, President Regan envisioned SDI as a ground- and space-based system designed to protect the United States from attack by strategic“¯nuclear ballistic missiles.
By 2002, Hawkins said "[we] thought we were on the right track when we produced an ionic liquid monopropellant that incorporated an EIL that was investigated under our AFOSR program. This propellant class, known as AF-M315, has an energy density close to twice that of the state-of-the-art spacecraft monopropellant, hydrazine."
After testing the potential new propellant for safety and hazardous properties, Hawkins said the fuel was "absolutely outstanding; we found the oral toxicity of AF-M315E to be less than that of caffeine, and its vapor toxicity to be negligible.”
“The vapor flammability of AF-M315E was essentially nil, and this made it difficult to unexpectedly ignite and sustain combustion of AF-M315E — one could even put out small fires with the propellant,” he said.
In 2005 NASA-sponsored efforts aimed at further refining the fuel until 2012 when the Green Propellant Infusion Mission began producing new AF-M315E-based thrusters for the space agency´s 2015 spacecraft mission.
In his statement, Hawkins also noted the support of the Air Force Office of Scientific Research (AFOSR) in his quest to produce a low-toxicity fuel.
"The AFOSR-funded program provided the synthesis and characterization work for an EIL that enabled the experimental USAF fuel, AF-M315E, to act as a high-energy density, environmentally benign, easy-to-handle replacement for spacecraft hydrazine fuel," he said.
The propulsion expert noted that 20 years is a significant time period for producing such a revolutionary propulsion system in light of the fact that the EIL approach is completely different than that of hydrazine. He noted specifically that the change was not due to small incremental improvements and as EIL-based propellants are refined, they will bring lower costs and safer propulsion systems, along with greater mission flexibility and faster response times.