BREVARD COUNTY, Fla. -- Something invisible could be putting some space shuttles at risk during launches. NASA engineers spent Monday installing extra microphones at the launch pad to listen for something very important when Atlantis lifts-off next week.

More than 125 space shuttle missions have taken off from the space center, but never quite like the one NASA is planning next week.

Technicians don't want a closer look they want a closer listen to figure out why the sound waves coming from launches recently are not what engineers have anticipated.

"It's a little more severe than we thought it was,"

So they are installing microphones and more sensors to measure the vibrations coming from the sound itself.

Since the beginning of the shuttle program, engineers have been aware the engine's roar could damage the orbiters. That's why just before lift-off, the launch team releases thousands of gallons of water into the flame trench below the pad.

"It's there to dampen the sound,"

Engineers don't believe the sound pressure or vibrations are responsible for recent foam debris falling off the external tank. NASA doesn't believe there is any more risk with this mission than any previous one. But engineers know if the sound concussions are too severe it could damage critical equipment.

"This is not because we've had any problems, but we are trying to preemptively look for the remaining six flights we have of the shuttle program, if there's something we can do to help lessen that sound,"

Extra microphones and sensors may give them an earful on what kind of forces are at work.

A shuttle at lift-off is 180 decibels, by some estimates that is the same as the blast you would feel from one pound of dynamite at 15 feet away.