A Racket for a Rocket
Massive Speakers Simulate Supersonic Flight in Missile Tests
Take a giant speaker, connect it to an amplifier that could rock a stadium concert, and what do you get?
At Raytheon, you get missile music.
Deep inside the company's missile assembly and test facility in Andover, Massachusetts, 500-pound forward sections are being shaken and stirred by the biggest boom boxes you’ve ever seen. The idea is to ensure each missile will stand up to the blast of takeoff and the pounding turbulence of supersonic flight.
“We want to make sure that when we ship a missile out, it will perform to the technical requirements of the contract,” said Shaun Gehring, a Raytheon factory operations manager. “Most engagements are under 30 seconds. So there isn’t a lot of reaction time if it doesn’t work right.”
So what does music for a missile sound like?
It ain’t "Freebird." It’s a combination of rumble and whine, like the sound of flying saucers in old movies. The noise is based on telemetry data taken from actual flights.
The test is conducted on the forebody section of the missile, the part that includes the target seeker and circuit assemblies. Inside are circular slices of wiring that must be perfectly balanced before they’re put back into the missile.
The forebodies undergo various kinds of tests, like electronic checks and exposure to extremes of temperature and pressure. There’s even a drop test, which is just what it sounds like. And then there is the so-called “shock and vibe.”
“Shock simulates a missile launch, and Vertical/Trans Vibe simulates flight,” said Gehring. “The missile basically thinks it’s flying.”
SHAKE IT, DON'T BREAK IT
At the test station called Vibe 1, two handlers maneuvered a missile forebody on a rolling cradle toward the test machine, a T-4000 Electrodynamic Shaker Test System that can push with a force equivalent to more than 14 tons of weight.
“We’re making sure it can survive the 500-mile ride, that five-G turn a jet makes,” said principal test engineer Bill Christie, a 26-year Raytheon veteran.
The forebody is hoisted by crane into position. The giant speaker lies below, pointed up. An anechoic chamber is slid into position to shut out external radio frequencies. The missile’s target seeker will undergo signal tests, so there must be no interference.
Operators sit in a control room above the shaker. They start with a “tickle test;” low levels of vibration for 20 seconds, making sure the missile’s accelerometers are listening. “If they weren’t there, we couldn’t get a real reading,” said Gehring, “and we could over-shock or over-vibrate the missile.”
Then comes the real deal. The music plays for 10 to 15 minutes. Then the missile is lifted up, rotated 90 degrees, and tested again.
It’s not like a paint can mixer in a hardware store, shaking wildly back and forth. You barely see the missile move. Touch it, and all you feel is a smooth vibration. “It’s like you’re driving down the highway and you hit the rumble strip,” Christie said.
A QUESTION OF CONFIDENCE
Shock and vibe testing is used for equipment up to 1,600 pounds. The Andover facility tests assemblies from different missile types, including Standard Missile-2, SM-3, SM-6, TOW and Hawk. It also tests components from ground radars, including Patriot and AN/TPY-2. The “music” changes to test different real-world scenarios.
“We can recreate anything,” Christie said. “We can recreate [the vibration of] a tank going down a highway. We can recreate machine gun fire.”
The testing is designed to find any weaknesses. “In an upgrade, a lot of components that are left are original,” said Gehring. “The products may have reached their limits, so shaking them will reveal any problems; cold solder joints, cracked solder joints, loose cables.”
The end product is confidence. After these tests, Gehring and his team know the missiles they send out will hold up.
“We get to make and break things here, which is nice,” said Christie. “You don’t want it to break out there.”
Last Updated: 03/02/2015