 On an upcoming shuttle flight, an experiment will be conducted to study fire in the microgravity environment of Earth orbit. The solid surface combustion experiment, or SSCE, was built at the NASA Lewis Research Center in Cleveland, Ohio to study the details of a fire spreading over a small solid fuel sample. On Earth, gravity causes the hot gases in a plane to rise. This air motion, called buoyant convection, brings fresh oxygen to the flame and affects the heat carried forward to ignite the fuel ahead of the flame. Buoyant convection is one of the more difficult aspects of fire for scientists to understand. In microgravity, buoyant convection all but disappears. Without convection, the flame's oxygen supply and forward heat transfer depend upon different physical mechanisms. These other mechanisms are present in normal gravity but are overwhelmed by buoyant convection. By performing the SSCE experiment in microgravity, scientists will be able to observe these simpler flame-spread mechanisms directly. With the inside gain from this experiment, scientists will better understand how the complex system of physical and chemical mechanisms interact in fires on Earth. Several years ago, NASA began investigating the possibility of doing experiments in the shuttle on combustion topics, one being droplet combustion, another flame spreading over solids, and a third being premixed combustion. At that time, I was doing flame-spreading experiments and had proposed to NASA an experiment to be conducted on the shuttle and describe the key features of the experiment, and that experiment was ultimately designed by people at NASA Lewis. Technicians at Lewis built the hardware and performed a series of exhaustive tests to show it would work once it was launched in the shuttle. Scientists and engineers utilized special ground-based facilities for testing experiments in microgravity. Drop towers at the NASA Lewis Research Center in Cleveland, Ohio and special aircraft at Lewis and the Johnson Space Center in Houston, Texas provide a few seconds of microgravity at a time to obtain a hint of how the experiment will work in orbit. At the heart of the SSCE, a sealed vessel filled with an atmosphere of oxygen and nitrogen houses a single sample of solid fuel. The test samples are materials like paper that burn easily in air. The flight specimens are mounted in a special holder that keeps them secured during the rigors of a shuttle launch. The sample holder is bolted into the test chamber and the chamber is sealed and filled with a test atmosphere before the hardware is placed in the shuttle. In flight, the experiment is started by a simple computer igniting the sample. Two movie cameras are activated by the computer to photograph the flame through the windows in the chamber. The SSCE is scheduled to fly aboard the shuttle eight times. Since October 1990, five flights have been completed. In the first three tests, an ashless filter paper was burned in 50% oxygen at three different pressures. This is an edge view of the burning paper. At higher test pressures, the flame produces more soot and is therefore brighter. The flame is photographed from both the top and the side to gather detailed information about the flame's shape. At two times normal atmospheric pressure, the flame is very sooty. The soot particles glow providing the familiar bright orange flame. Before each flight, shuttle astronauts are trained in both the scientific objectives of the experiment and how it is to be operated. In July 1992 aboard the shuttle in the United States Microgravity Laboratory, USML-1, the SSCE experiment burned another ashless filter paper sample in an atmosphere of 35% oxygen and normal atmospheric pressure. During the STS-47 mission, mission specialist Jay Abbott performed the SSCE experiment under 35% oxygen and one and a half times normal atmospheric pressure. The final three flights of the solid surface combustion experiment will be used to test the flame spreading characteristics of a thick fuel. This fuel, PMMA, is more commonly known as plexiglass. Variations of atmospheric pressure and oxygen content will be similar to those for paper tests. The experiments being conducted to gather information that will ultimately allow us to improve the fire safety aspects of space travel from the point of view of material selection and also extinguisher development. In addition, flame spreading is a fundamental scientific problem that has been investigated for a number of years. By doing experiments in reduced gravity, we hope to be able to answer some of the questions that remain about that scientific phenomenon.