* Photo: Brent Humphreys * What it is: Vertical Friction Stir Welder

What it's used for: Joining pieces of spacecraft with friction instead of blowtorches.

Gas metal arc welding is fine if you just want a truck's bumper to stay put for a few hundred thousand miles. But if you're building an Ares I rocket—the craft that will shuttle astronauts to the moon and beyond starting in 2020—you'll need a more sophisticated technique: stir welding. Ares I will be made from aluminum-lithium 2195, an ultralight, ultrastrong alloy that's nearly impossible to weld using traditional fusion methods, because melting can create small pores that weaken the metal. Stir welding plunges a rapidly rotating pin about the size of a pencil into the joint between two panels with more than 5,000 pounds of force per square inch; the friction makes the alloy pliable, and the rotation forces grains of metal to mingle behind the pin as it crawls up the joint. The resulting welds are strong, defect-free, and actually shave material (and weight) from the craft rather than leaving a bulky seam. NASA's vertical spaceship-fusing welder stands 35 feet high, weighs 60 tons, and typically requires up to six operators. Luckily, the space agency has a pretty big workshop.

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