View Full Version : Booster Rocket's Spray

04-15-2000, 08:19 PM
Whenever they show launch sequences of the space shuttle or other vehicles to space, they always zoom in on the rocket nozzles at the base of the units. As the guy starts to count down, and the camera zooms in for the ‘money shot’, something curious happens.

From the side of the launch assembly, from four stick/pipe like things there appears to be a spray of sparks in great quantity thrown in toward the centre of the rocket nozzles. These ‘pipes’ – for want of a better word – are almost always four in number and commence spraying before the rockets fire.

What are these things and what are they spraying? For one infantile moment I supposed that these were large and sophisticated ‘matchsticks’ lighting the rocket… but that can’t be .. or can it?
I look for these ‘spray things’ everytime there is a launch and I still can’t figure it out.

There is a video at NASA’s site here: http://spaceflight.nasa.gov/gallery/video/shuttle/sts-99/html/fd1.html

Watch closely as the guy begins the countdown.
Sorry, I can’t do codes yet.

the man with no sig.

04-15-2000, 10:55 PM
Last time I watched the launch live on CNN, they explained that it was for burning unburnt fuel. When the engine is first started, the combustion is uneven and a lot of hydrogen escape without burning. The sparklers burn the hydrogen as soon as it comes out of the engine. Otherwise it may accumulate and burn all at once - i.e. explode. I have no idea how exactly the device works, but I'd guess that it is just a cartridge of gunpowder-like substance. It's for the main engines, by the way, not the boosters which use solid fuel.

04-16-2000, 02:42 PM
Thanks much scr4,
Now I can sit back and actually enjoy ths show. This thing (not knowing) really irritated me.


04-16-2000, 11:51 PM
scr4 wrote:
It's for the main engines, by the way, not the boosters which use solid fuel.So which ones are you calling the main engines? The ones that I've always called "boosters" are the two tall, skinny, white rockets attached to the side of the fat external fuel tank. These are solid fuel, and a leak in the O-ring on one of these caused Challenger to malfunction.

I always thought the main engines were what they called the ones on the back of the shuttle itself. Those are liquid fuel, thus the need for an external fuel tank.

04-16-2000, 11:54 PM
I think you misread, Curt. Your description of main vs. booster engines, which is correct, is the same as scr's.

p.s. I think you know this but there is an internal fuel tank for the main engines as well.

"I'll tell him but I don't think he'll be very keen. He's already got one, you see!"

04-18-2000, 11:07 AM
I think you know this but there is an internal fuel tank for the main engines as well.

I don't think that is quite correct. IIRC the main engines (the three big bell engines at the back of the shuttle) are only supplied from the external tank.

The internal fuel tank on the shuttle runs the OMS engines (Orbital Manuvering System) engines which are located just above the main engines on either side of the tail (those bulges at the back of the shuttle).

I'll double check my Space Shuttle Operator's Manual when I get home, but I believe that is correct.

"Sometimes I think the web is just a big plot to keep people like me away from normal society." --- Dilbert

Sofa King
04-18-2000, 01:03 PM
In the late-80's it was discovered that acoustic vibration was causing progressive damage to the concrete structure of Pads 39A and B. A combination of sparks and high-pressure water jets are used to reduce the deterioration that the structure was experiencing. Here's NASA's bent on it:

A Sound Suppression Water System has been installed on the pads to protect the orbiter and its payloads from damage by acoustical energy and rocket exhaust reflected from the flame trench and Mobile Launcher Platform during launch. The Shuttle orbiter, with its payloads in the cargo hold, is much closer to the surface of the Mobile Launcher Platform than the Apollo spacecraft was at the top of a Saturn V or Saturn 1B vehicle.

The Sound Suppression System includes an elevated water tank with a capacity of 300,000 gallons (1,135,620 liters). The tank is 290 feet (88 meters) high and is located adjacent to each pad. The water releases just prior to the ignition of the Shuttle engines, and flows through 7-foot-diameter (2.1-meter) pipes for about 20 seconds. Water pours from 16 nozzles atop the flame deflectors and from outlets in the main engines exhaust hole in the Mobile Launcher Platform, starting at T minus 6.6 seconds. By the time the solid rocket boosters ignite, a torrent of water will be flowing onto the Mobile Launcher Platform from six large quench nozzles, or "rainbirds," mounted on its surface.

The rainbirds are 12 feet (3.7 meters) high. The two in the center are 42 inches (107 centimeters) in diameter; the other four have a 30-inch (76-centimeter) diameter.

The peak rate of flow from all sources is 900,000 gallons (3,406,860 liters) of water per minute at 9 seconds after liftoff.

Acoustical levels reach their peak when the Space Shuttle is about 300 feet (91 meters) above the Platform, and cease to be a problem at an altitude of about 1,000 feet (305 meters).

Solid Rocket Booster Overpressure Suppression System: This is part of the Sound Suppression Water System. It alleviates the effect of a reflected pressure pulse which occurs at booster ignition. Without the suppression system, this pressure would exert significant forces on the wings and control surfaces of the orbiter.

There are two primary components to this acoustic energy suppression system. A water spray system provides a cushion of water which is directed into the flame hole directly beneath each booster. A series of water bags stretched across the flame holes, providing a water mass to dampen the reflected pressure pulse, supplements this effort. Used together, this water barrier blocks the path of the reflected pressure wave from the boosters, greatly decreasing its intensity.

In the event of an aborted mission, a Post-Shutdown Engine Deluge System will cool the aft end of the orbiter. It also controls the burning of residual hydrogen gas after the Shuttle's main engines have been shut down with the vehicle on the pad. There are 22 nozzles around the exhaust hole for the main engines within the Mobile Launcher Platform. Fed by a 6-inch-diameter (15-centimeter) supply line, water flows at a rate up to 2,500 gallons (9,463.5 liters) per minute.

from http://www-pao.ksc.nasa.gov/kscpao/nasafact/count4.htm

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