The Big Bangs : Sonic Booms From Space Shuttle Startle Quake-Rattled Southland

A returning space shuttle set off twin sonic booms over Los Angeles early Monday, jolting residents whose nerves have been frayed by the Northridge earthquake and countless aftershocks this year.

The safe touchdown by Atlantis and its six-member crew was the third Southern California shuttle landing in three months, but the first two descents approached Edwards Air Force Base from the west and north, so that the booms were barely heard in Los Angeles.

On Monday, Atlantis hurtled back to Earth from the south, passing over the heavily populated Los Angeles Basin on its way to Edwards. It set off the twin booms about 7:30 a.m., while many residents were still swallowing their coffee and cornflakes--or sleeping.

Many were caught off guard by the thunder-like blasts because NASA officials, watching storm conditions in Florida, did not officially move the landing site to California until about 2 a.m. Monday. Some residents contacted Edwards to inquire about the noise or to express irritation.

“I have an idea that people are more sensitive to something like this because of the earthquake,” NASA spokesman Don Haley said.

During a short news conference Monday afternoon, the six astronauts chuckled when informed that some residents mistook their man-made booms for fresh Earth tremors.

Air Force Lt. Col. Curtis Brown, the mission’s pilot, said the shuttle was traveling at three or four times the speed of sound--or up to 2,800 m.p.h.--when it passed over Los Angeles.

Sonic booms are created when a speeding aircraft pushes aside air molecules in its path, forming shock waves. The sharp release of pressure from these shock waves causes the noise.

*

All supersonic aircraft set off twin sonic booms, one at the nose and one at the tail. But when small military jets break the sound barrier, the booms follow one another so quickly that people usually hear it as one sound.

The space shuttles, at 122 feet long, produce a gap of about half a second between the nose and tail sounds, resulting in the distinctive double booms familiar to High Desert residents.

NASA officials said sonic booms sound louder in canyon areas, where the noise reverberates, and are more intense on days like Monday, when few clouds are present to muffle the sound.

Atlantis pilot Brown said he was paying more attention to the sights outside his window than the sounds that his descent was creating. “I had a perfect view of the L.A. area,” he said.

Last year, NASA designated the Kennedy Space Center in Florida as the primary landing site for its shuttles, with Edwards as the backup. But bad weather in Florida forced the agency to divert Discovery to Edwards on Sept. 20 and Endeavour to Edwards on Oct. 11.

Landings at Edwards add about $1 million to the cost of each mission, NASA officials say, largely because the vessel must be ferried back to Florida atop a jet.