Sites for launching large rockets are often equipped with a sound suppression system to absorb or deflect acoustic energy generated during a rocket launch. As engine exhaust gasses exceed the speed of sound, they collide with the ambient air and shockwaves are created, with noise levels approaching 200 db. This energy can be reflected by the launch platform and pad surfaces, and could potentially cause damage to the launch vehicle, payload, and crew. Sound is dissipated by huge volumes of water distributed across the launch pad and launch platform during liftoff. Water based acoustic suppression systems are common on launch pads. They aid in reducing acoustic energy by injecting large quantities of water below the launch pad into the exhaust plume and in the area above the pad. Flame deflectors or flame trenches are designed to channel rocket exhaust away from the launch pad but also redirect acoustic energy away.
Soviet Union/Russia
The launch pad built by the Soviet Union beginning in 1978 at the Baikonur Cosmodrome for launching the Energiya rocket included an elaborate sound suppression system which delivered a peak flow of per second fed by three ground level reservoirs totaling.
Data from the launch of STS-1 found an overpressure wave created by the shuttle's three RS-25 liquid fueled rocket engines and the three segment solid rocket boosters contributed to the loss of sixteen and damage to an additional 148 thermal protection tiles prompting modifications to the Sound Suppression Water System installed at both launch pads at Kennedy Space Center's Launch Complex 39. The resulting gravity fed system, used through the remainder of the program, began release from a water tower at the launch site 6.6 seconds before main engine start through diameter pipes connected to the mobile launch platform. Water flowed out six towers known as "rainbirds" onto the launch platform and flame trench below, emptying the system in 41 seconds with a peak flow of reducing acoustic energy levels to approximately 142 dB. The massive white clouds that billowed around the shuttle at each launch were not smoke, but wet steam generated as the rocket exhaust boiled away huge quantities of water.
Antares
at NASA's Wallops Flight Facility in Virginia is equipped with a water tower above the ground, among the tallest in the world. Engine exhaust exits through ring of water jets in the launch platform, directly beneath engine nozzles. The system is capable of delivering per second. Additional storage tanks totaling may be added for static fire tests. Water not vaporized is held in a retention basin where it is tested before release.
Following the retirement of the Space Shuttle program, pad B at launch complex 39 was upgraded for launches of the Space Launch System. SLS features an additional RS-25 liquid fueled rocket engine along with an additional segment in each of its solid rocket boosters over the Space Shuttle program prompting upgrades to the system creating the Ignition Over-Pressure/Sound Suppression Water System. The control system was upgraded including replacement of nearly of copper cables with of fiber optic cable. Capacity was upgrade to with a peak flow rate of. The upgrade system was tested in December 2018 with.
The Japanese Space Agency "seeks to achieve the world's quietest launch" from their Noshiro Rocket Test Center in Akita with the installation of a sound suppression water system as well as sound absorbing walls. The H3 Scaled Acoustic Reduction Experiment completed in 2017 provided additional data about the noise generated during liftoff.
