http://www.designfax.net/cms/dfx/opens/article-view-dfx.php?nid=4&bid=940&aid=8935&et=featurearticle&pn=01

That airplane is NASA's X-59 QueSST (short for Quiet SuperSonic
Technology), an experimental piloted aircraft designed to fly faster than sound
without producing the annoying -- if not sometimes alarming -- sonic booms of
previous supersonic aircraft.

During the 1960s, as both the United States and Europe were developing a
civilian supersonic transport -- the SST and Concorde, respectively -- the
general public made it known they did not want to endure the constant annoyance
of sonic booms from airplanes flying over their work and homes.

So, in 1973, after several years of research and due process, the Federal
Aviation Administration (FAA) banned aircraft from flying over land faster than
Mach 1 -- the speed of sound, which can vary based on temperature and
atmospheric conditions. That would prevent the loud sonic booms.

Although the SST program was cancelled in 1971, the Concorde went on to fly for
British Airways and Air France from 1976 to 2003, its supersonic cruising near
the United States limited to only over the Atlantic Ocean.

Still, the demand for commercial supersonic air travel continued, which prompted
this question: What if you could fly a supersonic airplane that didn't produce
loud sonic booms? What if, for those on the ground below, those sonic booms were
quiet enough not to be an annoyance, or perhaps not heard at all?

That's what the X-59 project aims to help find out.