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EXPLOSIVE RESULTS A Safer Liftoff An innovative rocket-fuel system taps a novel source of power and breakthrough engineering to deliver high-energy thrust with improved safety. On a broad mesquite plain in central New Mexico, a small crew fits a metal cylinder into a rocket the size of a baseball bat, then slips the rocket onto guide rods on a platform. A “Los Alamos” logo on the fuselage certifies this launch as official science by the world-famous national laboratory, not a weekend outing with the kids. Bryce Tappan and a handful of scientists, engineers, and students from Los Alamos National Laboratory and New Mexico Tech stand back as another crew member handles a control box set on a folding table. He counts down, “Three, two, one, zero!” The rocket issues a loud pssshhhhhewwwweeee! and whisks into the cobalt sky, the cylinder trailing a stream of gases and tilting toward horizontal as it soars to its apogee. The small group cheers, perhaps a little more vigorously than one might expect, but that’s because this 41-inch rocket just proved that a novel fuel invented by Tappan and others at the Lab actually works. Powerful, safe, and potentially powerful enough to launch a full-sized spacecraft, the breakthrough segregated-fuel- oxidizer system, called IsoFOX, enables a new era in propellants. For rockets, missiles, and satellites the fuel is a “humongous safety improvement,” according to Dan Hooks, director of the Los Alamos Explosives Center. Hooks explains that missiles carry “a huge tonnage of propellant,” which multiplies the risk of their detonable fuels exploding accidentally, “so any safety improvement is tremendous.” materials,” Tappan explains. “High nitrogen content is interesting in explosives because it can reduce the amount of oxygen needed to burn the fuel atoms in the molecule, making an oxygen balance easier to achieve.” Managing the amount of oxygen in a fuel helps tune its safety characteristics. The nitrogen makes for a higher-energy-density system that works much like an automobile efficiently burning gasoline. Tappan was experimenting with these high-nitrogen/high- hydrogen materials, which contain little or no oxygen, for their applications to explosives. In his first large-scale test with TAGzT, the material didn’t detonate. “I thought, this sucks,” Tappan recalls with a laugh. “Then I thought, wow, this could be an important discovery as a propellant ingredient. Non-detonable materials that combust well are good for propellants and bad for explosives.” TAGzT—and the novel fuel that Tappan would later develop from it—“doesn’t detonate at all. It just burns.” That property opened up the potential for a new kind of rocket fuel several years later, when a collaborator from Penn State University came to Tappan for oxidizer pellets to use with a liquid fuel. Tappan had a better idea, based on his research: use a high- nitrogen/high-hydrogen energetic material. “There was nothing else out there like it in the research literature,” he says. Actually, It Is Rocket Science In a slow-motion video of the test showing the simultaneous launch of Tappan’s rocket beside a conventionally fueled twin, Tappan’s rocket ignites and vanishes from the frame as the other lumbers up. It’s a jackrabbit leaving a tortoise in the dust. From Failure to Breakthrough Ironically, Tappan, who came to the Lab first as an undergraduate in 1996, then returned as a postdoctoral researcher in 2003, stumbled onto this propellant in the wake of a disappointment. He was studying an energetic material called TAGzT (triaminoguanidinium azotetrazolate) and related compounds. (Energetic materials store chemical energy, which is a useful characteristic for making explosives, propellants, or fuels.) It had failed miserably as an explosive. “For more than 20 years, Los Alamos had been experimenting with synthesizing high-nitrogen materials for use in energetic The next-generation rocket? Los Alamos scientists recently tested a powerful new rocket fuel and motor that are safer because the fuel is kept separate from its oxidizer. The new rocket motor and fuel outperformed commercial rockets in thrust with at least twice the velocity. (Photo: Los Alamos ) 18 Los Alamos National Laboratory