Editing Rocket (section)

==Noise==
[[File:Sound suppression water system test at KSC Launch Pad 39A.jpg|thumb|upright=1.0|Workers and media witness the Sound Suppression Water System test at [[Launch Pad 39A]]]]
Rocket exhaust generates a significant amount of acoustic energy. As the [[supersonic]] exhaust collides with the ambient air, [[shock wave]]s are formed. The [[sound intensity]] from these shock waves depends on the size of the rocket as well as the exhaust velocity. The sound intensity of large, high performance rockets could potentially kill at close range.<ref name="CR566-3">{{Citation |last1=Potter |first1=R.C |last2=Crocker |first2=M.J |title=Acoustic Prediction Methods for Rocket Engines, Including the Effects of Clustered Engines and Deflected Exhaust Flow, CR-566 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660030602_1966030602.pdf |location=Washington, D.C. |publisher=NASA |year=1966 |oclc=37049198 |url-status=live |archive-url=https://web.archive.org/web/20131206122446/http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660030602_1966030602.pdf |archive-date=2013-12-06 }}{{Page needed|date=September 2010}}</ref>

The [[Space Shuttle]] generated 180&nbsp;dB of noise around its base.<ref>{{cite web |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20020094348.pdf |title=Launch Pad Vibroacoustics Research at NASA/KSC |archive-url=https://web.archive.org/web/20170302233823/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20020094348.pdf |archive-date=2017-03-02 |url-status=dead |access-date=30 April 2016}}</ref> To combat this, NASA developed a sound suppression system which can flow water at rates up to 900,000 gallons per minute (57&nbsp;m<sup>3</sup>/s) onto the launch pad. The water reduces the noise level from 180&nbsp;dB down to 142&nbsp;dB (the design requirement is 145&nbsp;dB).<ref>{{cite web |url=http://www.nasa.gov/mission_pages/shuttle/launch/sound-suppression-system.html |title=Sound Suppression System |archive-url=https://web.archive.org/web/20110629143632/http://www.nasa.gov/mission_pages/shuttle/launch/sound-suppression-system.html |archive-date=2011-06-29 |access-date=30 April 2016}}</ref> Without the sound suppression system, acoustic waves would reflect off of the launch pad towards the rocket, vibrating the sensitive payload and crew. These acoustic waves can be so severe as to damage or destroy the rocket.

Noise is generally most intense when a rocket is close to the ground, since the noise from the engines radiates up away from the jet, as well as reflecting off the ground. This noise can be reduced somewhat by flame trenches with roofs, by water injection around the jet and by deflecting the jet at an angle.<ref name="CR566-3"/>

For crewed rockets various methods are used to reduce the sound intensity for the passengers, and typically the placement of the astronauts far away from the rocket engines helps significantly. For the passengers and crew, when a vehicle goes [[supersonic]] the sound cuts off as the sound waves are no longer able to keep up with the vehicle.<ref name="CR566-3"/>