NIST/Space Shuttle Tests Could Enhance Space Station Safety

A NIST experiment aboard the space shuttle Columbia launched today could help keep tomorrow's space station and its astronauts safe from fire. The experiment, called the Radiation Ignition and Transition to Spread Investigation, or RITSI, will look at flame behavior in low gravity situations. Scientists hope to use the data to learn how to keep a spark from growing into a life-threatening fire aboard a spacecraft.

Takashi Kashiwagi, NIST materials research engineer who is a principal investigator for RITSI along with Sandra Olson of NASA's Lewis Research Center, said NASA recognizes that someday a momentary ignition due to electrical shorts or overheating could grow into a large-scale fire. Such a spacecraft fire could be disastrous. Toxic products could quickly poison the atmosphere and be difficult to remove. Production of gases at high temperatures also could lead to rapid over-pressurization and rupture of the spacecraft. Even fire suppression systems might damage critical electrical hardware.

"The trick is to contain the momentary ignition, avoiding any possibility of flame spread," said Kashiwagi. "The microgravity situation of an orbiting spacecraft, however, requires us to first do some basic research into how the unique environment affects the transition from ignition to flame spread. We hope to be able to compare computer predictions with actual experimental results and remedy deficiencies in our calculations and understanding."

European Space Agency astronaut Maurizio Cheli is conducting three days of RITSI tests during the STS-75 mission. To protect the crew from fumes, he ignites ashless filter paper inside an air-proof "glove box." Video and 35 mm cameras record the ignition and flame development process.

RITSI glove box engineering hardware built to provide the scientific data specified by Kashiwagi and Olson, consists of a flow duct with screens at both ends and a fan that pulls air through the duct. The transparent lid of the duct opens for access to the sample holder for a change of samples. Some samples are rectangular to allow for two-dimensional flame spread, and some are square to allow for three-dimensional flame spread. A near-infrared radiant heater is used to ignite the samples and is recessed into the back wall of the duct to minimize disturbances to the flow.

Thin metal sample holders contain a cellulose sample. Some samples are treated to study smoldering rather than flaming combustion. Six thermocouples and an ignitor wire are pre-installed on each sample holder. The thermocouple data are recorded along with radiant heater power, ignitor power and flow velocity.

Astronaut experiment controls on the small external control box include fan on/off and variable speed control, ignitor wire activation, radiant heater activation and variable power adjustment, and chamber light on/off.

Kashiwagi and Olson are monitoring the experiments during operations from NASA's Marshall Space Flight Center, Huntsville, Ala. Between tests, they are analyzing the down-linked data to determine the conditions for subsequent tests. Kashiwagi also served as a microgravity co-investigator four years ago during a previous Columbia flight. Kashiwagi currently serves as a group leader in NIST's Building and Fire Research Laboratory.

Another NIST colleague soon will share the distinction of actively assisting the U.S. space program. Last month, NASA announced that Gregory T. Linteris, a mechanical engineer in the Building and Fire Research Laboratory, has been selected to fly as one of two payload specialists on the space shuttle Columbia's spring 1997 Microgravity Science Laboratory mission. Linteris, along with NASA's Roger K. Crouch, will conduct more than 25 investigations in microgravity sciences, such as fluid physics, combustion science and materials science. Linteris currently is responsible for a NIST research program on advanced fire suppressants.

A non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.