Could Biodiesel Power Future Rockets?

Could future trips to space be powered by vegetable oil? In a test firing earlier this month, the California-based engineering firm Flometrics announced that commercially available biodiesel produced almost the same amount of thrust as conventional rocket fuel.

The find may not come as much of a surprise. After all, biodiesel is already being tested by the airline industry, which gobbles up billions of gallons of jet fuel each year.

But despite fluctuating petroleum prices, interest in alternative fuels among rocket builders has been slow to grow.

Flometrics leader Steve Harrington hopes the test will stoke interest in biodiesel-powered rocketry. "Most rocket scientists are knee-jerk anti-environmentalists," Harrington says. "But we're going to run out of rocket fuel at some point, so what are we going to run our rockets on after that?"

Could biodiesel be the answer? New Scientist takes a closer look at its potential for fuelling the space age.

How well does biodiesel work in rockets?

It may be too early to tell. Flometrics's test rocket contained a modest RocketDyne LR-101 engine, the same type used to control the attitude of the rockets that launched NASA's Mercury capsules. In a bolted-down test-firing, the biofuel produced 820 pounds of thrust, which compared well with the 840 pounds of thrust generated by the conventional rocket fuel RP-1, a form of highly refined kerosene.

And the team suspects biodiesel could perform even better with slight modifications to the rocket setup. The fuel contains more oxygen than kerosene does, so lowering the amount of liquid oxygen in the mix might be able to increase its lifting power.

Will powering rockets with biodiesel put a dent in greenhouse-gas emission levels?

Perhaps not. The environmental benefits of biofuel are still being debated. Some say clearing forests to accommodate the demand for biofuel crops like corn will release more greenhouse gases into the atmosphere than petrol. But others hope algae and decomposing plant waste could throw the carbon balance in favor of biofuel.

Burning biodiesel will also leave behind many of the same byproducts as kerosene: namely carbon dioxide and water vapour, both of which act as greenhouse gases.

Why bother then? Is there any advantage to using biodiesel?

There are some engineering benefits. Biodiesel is somewhat denser than kerosene, allowing rockets to pack more power in the same size fuel tank. The fuel is also less flammable, making it easier to store.

Harrington envisions biodiesel could also have a wider reach, eventually replacing noxious propellants like nitrogen tetroxide or hydrazine. In February 2008, the Pentagon shot down a defunct spy satellite, reportedly to avoid the possibility of a hydrazine spill.

But even if biodiesel rocket fuel becomes widespread, chances are that such traditional propellants will still be used for some applications. The fuels, which do not require a separate oxidiser to burn, are a simple way to power spacecraft thrusters.

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