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Wake Up and Smell the Rocket Fuel

The underlying principle of rocketry is a simple equation from high-school physics classes: Force equals mass times acceleration.

That is, to lift that 70-ton (mass) vehicle high enough to put your satellite into orbit, you’ve got to keep it going faster and faster (acceleration) all the way up by burning fuel in an engine (force).

And you don’t want it to blow up.

That may be the hardest part--getting highly flammable fuel to burn like Baby Bear’s porridge: Not too hot, not too cold, but just right.

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Some young scientists recently brought Werner Dahm a design that sends engine exhaust directly out the bottom of a rocket.

Such ignorance of the past bemuses Dahm, chief of the Aerophysics Division in the Structures and Dynamics Laboratory at the NASA Marshall Space Flight Center in Huntsville, Ala. “We learned in the mid-'50s not to discharge combustible turbine exhaust from the rear of the vehicle,” he says.

Hot rocket exhaust plus air equals kaboom !

To keep the temperature low inside a rocket engine, designers use less air in the air-fuel mixture, Dahm says, which means the exhaust gases are still combustible: “We discharge the gases through nozzles or into the ambient flow (the air around the vehicle). But not out the rear of the vehicle.”

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Apparently, not even rocket scientists know everything about rocket science.


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