First Shuttle launch: "sound suppression water." What is that?

[Leo_Bloom]

Just watched this birthday vid of first Shuttle launch. At 4:10, under a minute before takeoff, mission control voice says “the firing system for the sound suppression water will be armed.”

What is sound suppression water?

[beowulff]

They dump huge amounts of water into the exhaust stream to dampen the sound.

[Amateur_Barbarian]

Massive sprinkler system on the launch pad that dampens the acoustic shock and prevents it from damaging tiles and so forth.

[Joey_P]

Here’s a video of it.
And it’s not just the water that does the trick. A standing pool under the shuttle wouldn’t work since water is more or less incompressible that would bounce the sound waves back up just like the concrete and steel. It’s the air bubbles in the moving water that absorb the sound waves. I assume they could have a pool with a massive aerator, but doing it this way means they don’t need to reserve space for the water. Just dump the water on the platform and let it run off.

[Banquet_Bear]

@Joey_P

Here’s a video of it.
And it’s not just the water that does the trick. A standing pool under the shuttle wouldn’t work since water is more or less incompressible that would bounce the sound waves back up just like the concrete and steel. It’s the air bubbles in the moving water that absorb the sound waves. I assume they could have a pool with a massive aerator, but doing it this way means they don’t need to reserve space for the water. Just dump the water on the platform and let it run off.

…sorry to go off topic slightly, but I never cease to be amazed at how amazing the space programme is and even watching a video of water being sprayed over the launchpad is just amazing to me.

My favourite NASA footage:

Booster Camera Video of Atlantis Launch

Sorry for the non-GQ hijack.

[Heracles]

The deluge system had to be modified after STS-1 because it had not been as effective as expected and many tiles had been damaged as a result.

[Foggy]

@leo bloom

what is sound suppression water?

…what? :d

[Hail_Ants]

I believe the very first sound suppression water system was installed *after *the Saturn V’s very first, all-up flight (unmanned Apollo 4). This was the famous launch that Walter Cronkite narrated and mentioned that the ceiling tiles in his studio were falling down (because of the tremendous noise!)

[Machine_Elf]

@Joey_P

It’s the air bubbles in the moving water that absorb the sound waves.

You sure about that? The system looks like it will be very effective at generating a spray of airborne water droplets, rather than a bunch of waterborne air bubbles.

Here’s info straight from the horse’s mouth:

@NASA

SOUND SUPPRESSION WATER SYSTEM
A sound suppression water system is installed on the launch pads to protect the orbiter and its payloads from damage by acoustical energy reflected from the mobile launcher platform during launch. The system includes an elevated water tank with a capacity of 300,000 gallons. The tank is 290 feet high and stands on the northeast side of the pad. The water is released just before the ignition of the orbiter’s three main engines and twin solid rocket boosters and flows through parallel 7-foot-diameter pipes to the pad area.
Water pours from 16 nozzles atop the flame deflectors and from outlets in the space shuttle main engine exhaust hole in the mobile launcher platform at main engine ignition (T minus 6.6 seconds). When solid rocket booster ignition and lift-off follow at T minus zero, a torrent of water flows onto the mobile launcher from six large quench nozzles, or ‘‘rainbirds,’’ mounted on its surface.

Water is also sprayed into the primary solid rocket booster exhaust holes to provide overpressure protection to the orbiter at solid rocket booster ignition. The peak flow rate from the prelift-off and postlift-off systems is 900,000 gallons per minute nine seconds after lift-off.

The rainbirds are 12 feet high. Two of them, those in the center, are 42 inches in diameter. The other four are 30 inches in diameter. Acoustical levels reach their peak when the space shuttle is about 300 feet above the mobile launcher platform.

Below 300 feet, the rocket exhaust is channeled over the flame deflectors and into the flame trench. Above 300 feet, sound is reflected off the metal plates of the mobile launcher platform’s surface. In terms of time, the maximum sound reflection comes about five seconds after lift-off. The problem ends after the shuttle has been airborne for about 10 seconds and has reached an altitude of 1,000 feet.

Design specifications for space shuttle payloads require an ability to withstand acoustical loads of up to 145 decibels. The system reduces the acoustical levels within the orbiter’s payload bay to about 142 decibels, 3 decibels below the design requirement.

The solid rocket booster ignition overpressure suppression system was installed to alleviate the effect of the initial reflected pressure pulse when the solid rocket boosters ignite. This pressure pulse, without the overpressure suppression system, exerts a pressure on the wings and ailerons that approaches the design limit. The overpressure system is designed to reduce this pressure by a factor of 3. The system was designed and installed following STS-1 as a direct result of overpressures measured during the launch.

The system has two primary components. A water spray system fed from large headers provides a cushion of water directed down into and around the primary flame hole (directly beneath the stationary solid rocket booster). This barrier is supplemented by a series of water bags in the primary and secondary flame hole, which provides a water mass to dampen the blow-back pressure pulse. The water spray and the water barrier largely block the path of a reflected pressure wave and greatly decrease its intensity.

An engine deluge system consisting of 22 water nozzles spaced around the space shuttle main engine exhaust hole in the mobile launcher platform is designed to cool the aft end of the orbiter following flight readiness firing of the main engines and is also available in the event of an on-pad abort. After the engines are shut down, there can still be some residual hydrogen remaining in the vicinity of the main engines’ nozzles that can burn for an appreciable period of time. The system is fed by a 6-inch-diameter supply line and can provide a flow of up to 2,500 gallons per minute directed at the orbiter’s engine nozzle/boattail area to control hydrogen afterburning and provide cooling water.

What I got out of that writeup is that the mass of the water droplets absorbs acoustic energy: the airborne droplets shake back and forth as they are struck by the sound waves. This is something the droplets could not do if they were part of a contiguous pool of water below the launch pad. It’s a little bit like when a race car runs off the track and into a gravel-filled runout area: the gravel, like those airborne water droplets, gets pushed around and absorbs kinetic energy from whatever is hitting it.

[Joey_P]

@Machine_Elf

You sure about that? The system looks like it will be very effective at generating a spray of airborne water droplets, rather than a bunch of waterborne air bubbles.

Here’s info straight from the horse’s mouth:

What I got out of that writeup is that the mass of the water droplets absorbs acoustic energy: the airborne droplets shake back and forth as they are struck by the sound waves. This is something the droplets could not do if they were part of a contiguous pool of water below the launch pad. It’s a little bit like when a race car runs off the track and into a gravel-filled runout area: the gravel, like those airborne water droplets, gets pushed around and absorbs kinetic energy from whatever is hitting it.

I suppose that’s kinda what I meant. I didn’t really mean that the air itself was absorbing the sound (even though it’s what I said), I just meant it’s the air mixed in with the water that gives the water the ability to absorb the sound for the reasons you stated. As I mentioned somewhere, in theory, a highly aerated pool of water would probably work as well.