With little fanfare last December, Lockheed Martin Space Systems launched a suborbital sounding rocket from a NASA pad in Virginia. Forty-four miles over the Atlantic, the five-story-tall, two-foot-diameter craft released an 800-pound payload. The package, containing aerodynamic reentry experiments, was nothing particularly special. The booster itself, however, was rather exceptional--it was the first launch of a rocket powered by a large-scale hybrid rocket motor.

Such rockets attempt to combine the best of solid and liquid propulsion, the traditional engine types. In a liquid-fuel rocket, the fuel and oxidizer, often liquid hydrogen and oxygen, are stored separately and then mixed to create combustion. Liquid-fuel rocket motors burn efficiently, provide high thrust and, critically, can be throttled and even stopped and restarted. Such control permits planners to tailor the rocket's trajectory. Complexity, though, is high, and so tends to be the price tag.

This article was originally published with the title Hybrids Take Off.

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