Before you can design a supersonic aircraft with lower sonic boom, you have to be able to measure the boom - outdoors and indoors. To get the precise information it needs when it begins testing a low-boom research aircraft, the Japan Aerospace Exploration Agency (JAXA) is developing a measurement system that uses a tethered balloon.
A protoype of the Airborne Blimp Boom Acquisition (ABBA) system has been tested in Sweden, with air force Saab Gripen fighters providing the sonic booms. The system is designed to measure the sonic boom waveform, which with a conventional supersonic aircraft is an N-wave that produces the classic "double-bang".
Because the boom waveform is distorted by atmospheric turbulence near the ground, the tethered blimp is designed to take measurements at an altitude of 3,000ft. Measurements will also be made on the ground, both outside and inside a wooden building, to see how much vibration the boom causes.
JAXA plans to use the ABBA system during flight tests of its Silent Supersonic Technology Demonstrator (S3TD) - a subscale unmanned aircraft designed to prove sonic boom can be reduced by shaping the airframe. JAXA says it has developed concepts that could cut the boom in half compared with Concorde.
The S3TD will be tested initially by dropping it from a balloon at 30km altitude, the unpowered model reaching Mach 1.4 on its way down. The first drop test, D-SEND 1, is planned for 2011 and will use two 5m- and 10m-long "darts" to generate baseline data. The second test, D-SEND 2, is set for 2012 and will use a 5-6.5m-long model of the S3TD. Powered flight tests may come later.