NASA amps up sonic booms to learn how to quiet them

NASA ”superboom” group looking for ways to develop supersonic jets that can safely fly over land

NASA this week said it was embarking on a project that creates produce amped-up, super-loud sonic booms in an effort to understand how to minimize their impact and improve future supersonic aircraft.

"The ultimate goal is to allow supersonic transportation over land," said Edward Haering, principal investigator for the Superboom Caustic Analysis and Measurement Program, or SCAMP, at NASA's Dryden Flight Research Center in California.

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For SCAMP,  NASA researchers built a two-mile long string of microphones that consisted of a straight row of 81 microphones set 125 feet apart along an east-west dirt road to record the thunder made by an accelerating F/A-18 jet. 

Airborne microphones were mounted on a Dryden TG-14 motorized glider with sound recording equipment that flew between the booming F/A-18 jet and the ground at altitudes from 4,000 feet to 10,000 feet to record the SCAMP booms. Additionally, a 35-foot-long blimp was tethered at 3,500 feet above ground with two microphones along its tether, NASA said.

"When a supersonic aircraft accelerates to its cruise speed, a focusing effect occurs that makes the sonic boom five to 10 times louder than its normal cruise sonic boom over a small region," said Haering in a release. "This effect is similar to how light rays are focused by a lens."

The flights were flown in the remote Black Mountain Supersonic Corridor north of Boron, Calif., in restricted military testing airspace near Edwards in which supersonic flight is allowed. The research team recorded 70 sonic booms from 13 flights.

In the end the measurements will be used to validate computer prediction tools that will be used in the design of future quiet supersonic aircraft, NASA said.

NASA has a long history of supersonic flight and sonic boom testing. In 2007  it noted that researchers had spent some 200,000 processor-hours on the Columbia supercomputer, screening various new control concepts for a tailless supersonic aircraft. Exploration of non-conventional controls today may someday translate to better fuel economy, increased flight range, and sonic boom reduction.  In 2008 it teamed with the Japan Aerospace Exploration Agency (JAXA) to jointly research sonic booms. NASA said sonic boom modeling is one of the key technologies needed to let a next generation supersonic aircraft quiet enough that it can fly supersonically over land without significant disturbance to the people or damage to property under such noise.

According to NASA, an aircraft, flying supersonic at 50,000 feet can produce a sonic boom about 50 miles wide. The sonic boom, however, would not be uniform. Maximum intensity is directly beneath the aircraft, and decreases as the lateral distance from the flight path increases until it ceases to exist because the shock waves refract away from the ground. The lateral spreading of the sonic boom depends only upon altitude, speed and the atmosphere -- and is independent of the vehicle's shape, size, and weight, NASA said.

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