{{Short description|Water-based rocket launch noise control}} {{About|rocket launches|a method for reducing unwanted sound|Active noise control}} Sites for launching large rockets are often equipped with a '''sound suppression system''' to absorb or deflect [[Sound|acoustic energy]] generated during a rocket launch. As engine exhaust gasses exceed the [[speed of sound]], they collide with the ambient air and [[Shock wave|shockwaves]] are created, with noise levels approaching 200 db. This energy can be reflected by the [[Transporter erector launcher|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.<ref>Dougherty, N. S., &amp; Guest, S. H. (2012, August 17). A correlation of scale model and flight aeroacoustic data for the Space Shuttle Vehicle. ''Aeroacoustics Conferences''. Retrieved November 16, 2022, from https://arc.aiaa.org/doi/10.2514/6.1984-2351</ref> Sound is dissipated by huge volumes of water distributed across the launch pad and launch platform during liftoff.<ref name=":0">{{Cite journal|last=Lubert|first=Caroline Parsons|date=2017|title= Sixty years of launch vehicle acoustics|journal= The Journal of the Acoustical Society of America|volume=142|issue=4 |page=040004|doi=10.1121/1.5014084|bibcode=2017ASAJ..142.2489L|doi-access=free}}</ref><ref>{{Cite journal|last1=Walsh|first1=E. J.|last2=Hart|first2=P.M.|date=Nov 1982|title=Liftoff Ignition Overpressure-A Correlation|journal=Journal of Spacecraft and Rockets|language=en|volume=19|issue=6|pages=550–556|doi=10.2514/3.62300|bibcode=1982JSpRo..19..550W|issn=0022-4650}}</ref>

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 deflector|Flame deflectors]] or flame trenches are designed to channel rocket exhaust away from the launch pad but also redirect acoustic energy away.<ref name=":0" /><ref>{{Cite web|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710023719.pdf|title=Acoustic Loads Generated by the Propulsion System (NASA SP-8072)|last=|first=|date=June 1971|website=|access-date=}}</ref>

== Soviet Union/Russia == The launch pad built by the Soviet Union beginning in 1978 at the [[Baikonur Cosmodrome]] for launching the [[Energia (rocket)|Energiya]] rocket included an elaborate sound suppression system which delivered a peak flow of {{Convert|18|m3|USgal|abbr=}} per second fed by three ground level reservoirs totaling {{Convert|18000|m3|USgal|abbr=}}.<ref>{{Cite book|title=Energiya-Buran : the Soviet space shuttle|last=Hendrickx, Bart.|date=2007|publisher=Springer|others=Vis, Bert.|isbn=978-0-387-73984-7|location=Berlin|oclc=232363288}}</ref>

== NASA ==

=== Space Shuttle program === [[File:Sound_suppression_water_system_test_at_KSC_Launch_Pad_39A.jpg|thumb|Water is released onto an MLP at LC-39A at the start of a sound suppression system test in 2004. During launch, {{convert|300000|USgal|e6L|abbr=off}} of water are poured onto the pad in only 41 seconds.]] Data from the launch of [[STS-1]] found that 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 [[Space Shuttle thermal protection system|thermal protection tiles]], prompting modifications to the '''Sound Suppression Water System''' (SSWS) installed at both launch pads at [[Kennedy Space Center Launch Complex 39|Kennedy Space Center's Launch Complex 39]].<ref>{{Cite web|url=https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/archives/sts-1.html|title=NASA - STS-1|last=KSC|first=Lynda Warnock|website=www.nasa.gov|language=en|access-date=2020-02-02}}</ref><ref>{{Cite web|url=https://www.nas.nasa.gov/SC15/demos/demo10.html|title=NASA@SC15: Simulating the SLS Ignition Over-Pressure/Sound Suppression Water System|website=www.nas.nasa.gov|access-date=2020-02-02}}</ref>

The resulting gravity-fed system, used throughout the remainder of the program, began release from a {{convert|300000|USgal|e6L|adj=on|abbr=off}} [[water tower]] at the launch site 6.6 seconds before main engine start, fed through {{Convert|7|ft||abbr=}} diameter pipes connected to the [[Mobile launcher platform|mobile launch platform]]. Water flowed out of six {{convert|12|ft|m|-high|adj=mid}} towers (known as "rainbirds") onto the launch platform and into the flame trench below, emptying the system in 41 seconds<ref name="water-test">{{cite web|url=http://www.nasa.gov/missions/shuttle/f_watertest.html|title=Sound Suppression Test Unleashes a Flood|last1=Stuckey|first1=Jeff|last2=Heiney|first2=Anna|date=May 10, 2004|work=NASA.gov|url-status=live|archive-url=https://web.archive.org/web/20090215132833/http://www.nasa.gov/missions/shuttle/f_watertest.html|archive-date=February 15, 2009|access-date=March 6, 2009}}</ref> with a peak flow reducing acoustic energy levels at launch to approximately 142 [[Decibel|dB]].<ref>{{Cite web|url=https://www.nasa.gov/mission_pages/shuttle/launch/sound-suppression-system.html|title=Sound Suppression System|last=Warnock|first=Lynda|series=Space Shuttle|publisher=NASA|access-date=October 23, 2019}}</ref>

The massive white clouds that billowed around the shuttle components at each launch were therefore not smoke, but rather [[Steam#Types of steam and conversions|wet steam]] generated as the rocket exhaust boiled away huge quantities of water.<ref name="facts-sound">{{cite web|url=http://www-pao.ksc.nasa.gov/kscpao/nasafact/pdf/countdow.pdf|title=Countdown! NASA Launch Vehicles and Facilities|date=October 1991|publisher=NASA|pages=23–24|id=PMS 018-B, section 4|url-status=dead|archive-url=https://web.archive.org/web/20050127071338/http://www-pao.ksc.nasa.gov/kscpao/nasafact/pdf/countdow.pdf|archive-date=January 27, 2005|access-date=August 21, 2013}}</ref>

=== Antares === [[Mid-Atlantic Regional Spaceport Launch Pad 0|Launch pad 0 at the Mid-Atlantic Spaceport]] at [[Wallops Flight Facility|NASA's Wallops Flight Facility]] in Virginia is equipped with a {{Convert|950000|l|USgal|abbr=}} water tower {{Convert|307|ft||abbr=}} 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 {{Convert|4000|USgal|m3|abbr=}} per second.<ref>{{Cite web|url=https://twitter.com/nasa_wallops/status/677534473890697218|title=NASA Wallops|last=PAO|date=2015-12-17|website=@nasa_wallops|language=en|access-date=2020-02-02}}</ref><ref>{{Cite web|url=https://www.facebook.com/NASAWFF/photos/so-you-think-your-coldwaterchallenge-was-extremeour-water-tower-at-the-mid-atlan/829784687051634/|title=MARS Pad 0-A water deluge|last=PAO|date=|website=NASA's Wallops Flight Facility Facebook page|access-date=}}</ref> Additional storage tanks totaling {{Convert|100000|USgal||abbr=}} may be added for [[Launch vehicle system tests|static fire tests]]. Water not vaporized is held in a {{Convert|1200|m2||abbr=}} [[retention basin]] where it is tested before release.<ref>{{Cite web|url=https://code200-external.gsfc.nasa.gov/sites/code250-wffe/files/documents/expansion_ea/EWLR_FEA.pdf|title=Environmental Assessment for Expansion of the Wallops Flight Facility Launch Range|last=URS EG&G|date=August 2009|website=|url-status=live|archive-url=https://web.archive.org/web/20200202165936/https://code200-external.gsfc.nasa.gov/sites/code250-wffe/files/documents/expansion_ea/EWLR_FEA.pdf|archive-date=2020-02-02|access-date=}}</ref>

=== 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 {{Convert|250|miles}} of copper cables with {{Convert|57|mi}} of fiber optic cable. Capacity was upgraded to {{Convert|400000|USgal|L}} with a peak flow rate of {{Convert|1100000|USgal|L}} per minute. The upgraded system was tested in December 2018 with {{Convert|450000|USgal|L}}.<ref>{{Cite web|url=https://www.nasa.gov/sites/default/files/atoms/files/launchpad39b_factsheet_013018_508.pdf|title=Launch Complex 39B Fact Sheet|last=|first=|date=|website=|access-date=}}</ref>

== Japan Aerospace Exploration Agency (JAXA) == [[JAXA]] "seeks to achieve the world's quietest launch" from their [[Noshiro Rocket Testing Center]] in [[Akita Prefecture|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.<ref>{{Cite web|url=https://global.jaxa.jp/projects/rockets/h3/topics.html|title=JAXA {{!}} H3 Launch Vehicle|website=JAXA {{!}} Japan Aerospace Exploration Agency|language=en|access-date=2020-02-02}}</ref><ref>{{Cite web|url=http://www.parabolicarc.com/2019/10/30/renovation-of-launch-facilities-for-h3-launch-vehicle/|title=Renovation of Launch Facilities for H3 Launch Vehicle – Parabolic Arc|language=en-US|access-date=2020-02-02}}</ref>

== References == {{Reflist}}

[[Category:Acoustics]] [[Category:Rocketry]] [[Category:Rocket launch technologies]]