Taking Out the Trash, NASA-Style

Spinoff is NASA’s annual publication featuring successfully commercialized NASA technology. This commercialization has contributed to the development of products and services in the fields of health and medicine, consumer goods, transportation, public safety, computer technology, and environmental resources.

Astronauts pack several thousand pounds of trash into expendable cargo resupply spacecraft. When it is time to “take out” the trash, the filled cargo spacecraft undocks from the International Space Station and falls into Earth’s atmosphere at about 17,500 mph; the spacecraft and its contents are vaporized.

Objects entering the atmosphere experience significant friction created by the drag of compressing atmospheric gases. As the spacecraft plunges deeper into the atmosphere where the air is denser, a tremendous amount of energy is released as heat, forcing the gas molecules to dissociate. A spacecraft without a heat shield, like these expendable cargo vehicles, experiences the same heating, vaporizing the solid material. Replicating this high-temperature trash processing on Earth is precisely what InEnTec is doing, with some help from NASA arc jet research and technology.

NASA learned how to recreate the extreme temperatures and speeds of atmospheric entry decades ago as a way to test heat shields. InEnTec (Richland, WA) looked to the power source modifications NASA used to generate high-temperature plasma and incorporated them into its technology design to create its Plasma Enhanced Melter (PEM) that transforms waste material into synthetic gas and other products.

Incinerators that rely on combustion produce toxic pollutants but plasma-enabled gasification does not. It heats the waste, called feedstock, to extremely high temperatures. At 1,800 to 27,000 °F, carbonaceous material breaks down into basic molecules — carbon, hydrogen, and oxygen. By controlling the combination of heat and pressure, it’s possible to regulate the chemical activity that leads up to gasification.

The Arc Jet Complex at Ames Research Center tests thermal protection material with plasma like that generated during atmospheric reentry to make sure it will work effectively. (Credit: NASA)

The molecules are separated and then converted into products that can be used to create anything from jet fuel to clothing. Any inorganic material that’s left over, called slag, is added to superheated glass. The resulting nontoxic substance is safe for a number of industrial uses including building materials. The entire system generates no air pollution or toxic waste.

The key to this efficiency is the heat. The temperature is boosted with the same kind of plasma that NASA created to test the first heat shields used on spacecraft.

Replicating the conditions of reentry on Earth wasn’t possible with 1950s technology when NASA began testing heat shields. An oxy-acetylene torch was used early on but the torch could only reach a maximum of around 6,290 °F. Arc heaters used in the chemical industry were an ideal alternative.

The plasma arc heaters NASA uses now consist of a tube about 3' in diameter and up to 16' long that contains hundreds of 3/8"-thick copper discs, each cooled with water. Two electrodes at either end of the tube provide the points for each end of the electrical arc to attach. At the end of the tube is a supersonic nozzle designed to generate supersonic speeds from Mach 3 to Mach 5, creating the environment in the test chamber where the samples of heat shield material are placed to simulate entry conditions.

The design breakthrough was the use of the individual copper discs to control the arc inside the tube, dramatically increasing the temperature. Cooling the heater while in use prevents the components from melting. In 1965, NASA patented the segment-constricted arc heater. InEnTec used the NASA information while developing its power supply, designing its own patented plasma arc gasification technology.

InEnTec’s gasification facility in Oregon converts medical and other waste into hydrogen for vehicles powered by hydrogen fuel cells. In addition to dramatically reducing vehicle pollution — hydrogen cars emit only water vapor — these systems could replace high-cost toxic waste disposal by incineration and specialized landfill.

Read this article and other NASA Spin-Offs at NASA.gov .