Student Features

Preventing Fires on the Launch Pad
08.12.04
Photograph of a shuttle during launch
Whether it's at home, school, or work, many people create a plan of prevention and response if a fire should break out. Fire prevention is important everywhere, but when you think of the launch pads at Kennedy Space Center, where hundreds of thousands of gallons of highly combustible materials are handled, fire prevention takes on even greater significance.

Image to right: Fire safety is especially important during a shuttle launch because the Space Shuttle is surrounded by hundreds of thousands of gallons of highly combustible materials. Credit: NASA

NASA stores 900,000 pounds each of liquid oxygen (LOX) and hydrogen at the launch area. Hydrogen is the fuel for the rockets that propel the Shuttle, and LOX is the oxidizer -- the substance that makes the combustion occur. If these two substances should combine too soon, a major explosion would take place. The LOX and hydrogen are kept far apart on opposite ends of the launch area, and are pumped to the external tank just prior to launch. The external tank is actually two tanks in one, separating the LOX and hydrogen until the very last moment. When the fuel and oxidizer are combined, the result is a controlled explosion that launches the spacecraft.

Water, Water, Everywhere

Thousands of gallons of water flood the launch area at the crucial moments surrounding ignition, serving two purposes. Water keeps flames from spreading and prevents damage caused by sound waves. Sound waves can cause pipes to burst, walls to crack, and joints to loosen. Damaged systems could lead to more fires because of those leaks and breaks. Water floods the launch area to muffle the sound energy.

The Sound Suppression System protects the orbiter and its payloads from being damaged by muffling acoustical energy -- sound waves -- that could crack and damage surfaces during liftoff. Water stored in a 300,000-gallon elevated tank is released just prior to main engine ignition and flows to the launch platform outlets.

There are six 12-foot high nozzles, called rainbirds. At main engine ignition, a torrent of water flows onto the mobile launcher. Nine seconds after liftoff, 900,000 gallons of water per minute are spraying through the area to reduce the acoustical levels in the payload bay area to about 180 decibels (db). (As a frame of reference, a quiet home emits about 40 decibels of noise, amplified rock and roll music is about 120 db at 100 feet, and a jet plane gives off 130 db at 100 feet.)

The Solid Rocket Booster Ignition Overpressure Suppression System reduces the effect of pressure caused when the solid rocket boosters ignite. A water spray system provides a cushion of water directed down into and around the primary flame hole beneath the solid rocket boosters, and a secondary water spray blocks the path of pressure waves to decrease the intensity of pressure at the launch site.

When you view a Space Shuttle launch on television, the white smoke filling the air is really steam from those millions of gallons of water evaporating. The actual exhaust smoke from the solid rocket motors goes out the other end of the launch pad through the Flame Deflector System.

The Flame Deflector System

Photograph of the flame trench located under the launch pad
The Flame Deflector System protects the vehicle and launch pad structures from the intense heat of launch. It's located in the flame trench, as seen in the photograph to the left, and is built of concrete and refractory brick. Flames are directed through twin troughs coming from the openings in the Mobile Launcher Platform and horizontally down the flame trench, rather than bouncing back to envelope the vehicle. The entire flame trench is as long as 1 1/2 football fields!

Image to left: The Flame Deflector System deflects flames away from the Space Shuttle so the flames don't come back up and envelop the vehicle. Credit: NASA

The deflector for the Space Shuttle is actually a two-in-one device, where one side receives the flames from the orbiter's main engines, and the other side gets the flames from the two solid rocket boosters, minimizing the intensity of the blast in any one given spot. The orbiter and booster deflectors are built of steel and covered with 5 inches of concrete material that flakes off to shed heat. Each deflector weighs over 453,600 kilograms (1 million pounds).

Just In Case...

If a fire should ever occur at the launch area, Kennedy Space Center has a 152-person fire department with special teams and various specialties standing ready, led by Mike Stevens, KSC's Authority Having Jurisdiction for Fire Protection.

"We have several modes to respond to, should the need arise," Stevens says. "In Mode One, astronauts can evacuate unaided, using slide wire baskets from the 195-foot level of the launch pad, down to the ground, and jump into armored personnel carriers to exit the launch area quickly. If the situation evolves up to Mode Four, the pad rescue team would remove the crewmembers. We've practiced the various safety drills often, but have never had to use them."

Excerpted from NASAexplores
Find this article at:
http://www.nasa.gov/audience/forstudents/9-12/features/F_Preventing_Fires_on_the_Launchpad.html