Sound suppression system

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. For instance, the maximum admissible overall sound power level (OASPL) for payload integrity is approximately 145 db. 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 18 m3 per second fed by three ground level reservoirs totaling 18000 m3.

Space Shuttle program
Data from the launch of STS-1 found an overpressure wave created by the shuttle's three SSME (now designated RS-25) liquid-fueled rocket engines and the four-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 (SSWS) 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 300000 USgal water tower at the launch site 6.6 seconds before main engine start through 7 ft diameter pipes connected to the mobile launch platform. Water flowed out six 12 ft 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
Launch pad 0 at the Mid-Atlantic Spaceport at NASA's Wallops Flight Facility in Virginia is equipped with a 950000 l water tower 307 ft 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 4000 USgal per second. Additional storage tanks totaling 100000 USgal may be added for static fire tests. Water not vaporized is held in a 1200 m2 retention basin where it is tested before release.

Space Launch System
Following the retirement of the Space Shuttle program, pad B at launch complex 39 was upgraded for launches of the Space Launch System (SLS). 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 (IOP/SS).

The control system was upgraded including replacement of nearly 250 miles of copper cables with 57 mi of fiber optic cable. Capacity was upgraded to 400000 USgal with a peak flow rate of 1100000 USgal per minute. The upgrade system was tested in December 2018 with 450000 USgal.

Japan Aerospace Exploration Agency (JAXA)
JAXA "seeks to achieve the world's quietest launch" from their Noshiro Rocket Testing 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.