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Local residents had a two-pronged reminder of our proximity to Edwards Air Force Base on Sunday, when double sonic booms shattered the peaceful, sunny afternoon. The space shuttle Endeavour was scheduled to land in Florida, but bad weather there diverted the shuttle and its seven astronauts to Edwards, where they landed safely at 1:25 p.m.

The astronauts had been gone for 16 days on a long-distance handyman call at the International Space Station. While in space, they expanded sleeping quarters, remodeled workout facilities and kitchen of the station, built a new bathroom and installed a water recovery system that converts crew members’ sweat and urine into drinkable water.

Why two sonic booms when the shuttle lands? Basically, it’s because both the front and back of the shuttle break the sound barrier a fraction of a second apart. Our closeness to the Air Force base – and the size of the shuttle -  allows us to hear both booms.

Here’s more on sonic booms, courtesy of NASA’s Dryden Flight Research Center:

A sonic boom is the thunder-like noise a person on the ground hears when an aircraft or other type of aerospace vehicle flies overhead faster than the speed of sound or supersonic.

The shock wave forms a cone of pressurized air molecules which move outward and rearward in all directions and extend to the ground. As the cone spreads across the landscape along the flight path, they create a continuous sonic boom along the full width of the cone's base. The sharp release of pressure, after the buildup by the shock wave, is heard as the sonic boom.

The change in air pressure associated with a sonic boom is only a few pounds per square foot -- about the same pressure change experienced riding an elevator down two or three floors. It is the rate of change, the sudden onset of the pressure change, that makes the sonic boom audible.

All aircraft generate two cones, at the nose and at the tail. They are usually of similar strength and the time interval between the two as they reach the ground is primarily dependent on the size of the aircraft and its altitude. Most people on the ground cannot distinguish between the two and they are usually heard as a single sonic boom. Sonic booms created by vehicles the size and mass of the space shuttle are very distinguishable and two distinct booms are easily heard.

This was the 126th space shuttle mission and the 22nd flight for Endeavour. The shuttle will be returned to Florida in seven to 10 days, piggybacked on a specially modified 727 jumbo jet. Its next mission is scheduled for May 2009.