(The following information summary is from "Materials Processing in Space," publication PMS-026 (Hqs), distributed by NASA Headquarters, Washington, D.C.)
MATERIALS PROCESSING IN SPACE
Materials processing is the science by which ordinary and comparatively inexpensive raw materials are made into useful crystals, chemicals, metals, ceramics, and countless other manufactured products. With it, we can build modern computers and communications systems, turbines for aircraft, and electric power plants. Materials processing makes it possible for us to produce chemical and biological compounds for use in medicine, and high strength alloys and heat resistant ceramic tiles for use in the space program.
Materials processing on Earth took us into the Space Age and the near weightless environment of Earth orbit. There the extended benefits of working in weightlessness have opened new and unique opportunities for the science of materials processing. In the microgravity environment of an orbiting spacecraft, scientists can use procedures that are all but impossible on Earth.
In orbit, materials processing can be accomplished without the effects of gravity, which on Earth causes materials of different densities and temperatures to separate and deform under the influence of their own masses. However, when we refer to an object as "weightless," we do not strictly mean there is an absence of gravity. Rather we are referring to the absence of relative motion between objects in a freely falling environment.
For example, if a man standing in an elevator drops a coin, the coin falls to the floor. But if the elevator cable breaks and the elevator begins to fall, a dropped coin will literally float. The coin will float (relative to the man and the elevator) because the elevator and everything within it will be in a state of free fall. This principle of free-fall is used to obtain weightlessness on the ground (in drop towers and drop tubes), in the air (aboard research aircraft), and in orbit (aboard the Space Shuttle).
Drop towers and airplanes provide weightlessness for up to 40 seconds, but extended periods of weightlessness can only be achieved on an orbiting spacecraft, such as the Space Shuttle, the Space Station, or a privately owned free-flying platform. Moreover, the weightlessness that is achieved by a spacecraft is not caused by an absence of gravity, but by the effect the spacecraft's orbiting speed has in countering the effects of gravity. Without gravity, the spacecraft would not follow a circular orbit, but would shoot off like a stone from a slingshot.
Types of Experiment Payloads
At present, NASA's Space Shuttle is one of the principal means for conducting orbital research. Experiments aboard the Shuttle may be conducted in the middeck area of the crew cabin; in the cargo bay, using either the Materials Experiment Assembly (MEA) or the Materials Science Laboratory (MSL); and in the Spacelab module. Each Shuttle payload area offers certain special characteristics.
Middeck Payloads. Materials processing experiments can be carried in one or more of the 42 middeck storage lockers. These lockers are about .05 cubic meters (2 cu ft) in size and can hold experiments weighing up to 27 kilograms (60 lb). Shuttle crews can conduct the experiments inside the crew cabin.
Cargo Bay Payloads. Experiments carried in the cargo bay use either the Materials Experiment Assembly (MEA) or the Materials Science Laboratory (MSL). Payloads using the MEA are self-contained and operate independently of the Shuttle's power and other resources. Experiments on the MSL use the resources provided by the Orbiter, and on a single flight can be as large as .33 cubic meters (12 cu ft) and as heavy as 950 kilograms (2,100 lb).
Spacelab Payloads. Experiments conducted on Spacelab are similar to MSL experiments, except that the crew can be more involved. As Spacelab missions evolve, it is expected that each will be dedicated to a specific scientific discipline, such as life sciences, environmental observations, or materials processing. Such an arrangement will reduce flight costs and integration requirements, and will permit increased coordination among experimenters.
NASA's Commercial Use of Space program seeks to use the weightlessness achieved in space to better understand physical phenomena and to control materials processes. NASA's strategy in this program is to work upward from ground-based research (drop towers and drop tubes) to air and suborbital research (aircraft and sounding rockets) to orbital research (the Space Shuttle and Space Station). NASA also involves the academic and industrial communities in flight experiments aimed at understanding processes on Earth and at developing processes uniquely suited to the microgravity of space. Accomplishments have ranged from theoretical investigations to large experiments aboard the Space Shuttle.
Vapor growth of compound-type and alloy-type crystals. Crystals of compounds and alloys have been grown by chemical vapor transport. Practical applications of this experiment could improve semiconductor technology for the electronics industry.
Containerless processing of glass. Glass samples have been injected into a furnace, positioned by acoustic pressure, melted, and cooled. This containerless processing method can be used to better understand glass formation and to improve glass for optical and electrical applications.
Miscibility-gap materials. Immiscible metals have been alloyed with the desired distribution of constituents and studied. An immiscible alloy is a mixture that separates rapidly under the effects of gravity. Before the molten metals solidify, density differences cause the less dense metal to float on the denser metal. The miscibility problem for metals is very much like trying to mix oil and water. However, in the microgravity of space, the ability to mix such metals may lead to improved structural, electrical, and magnetic materials.
Continuous flow electrophoresis. NASA plans continued space-based research to refine and improve biological separation techniques for potential applications. A recent commercial experiment, the McDonnell Douglas continuous flow electrophoresis, is being watched closely by researchers. The experiment offers the potential for commercial production in space of biological materials, such as pharmaceuticals.
Growth of precision latex spheres. Experiments have demonstrated that weightless processing produces better formed and more uniformly sized microspheres. These small, uniform latex spheres are in demand on Earth for use in calibrating electron microscopes, particle counters, and aerosol monitoring devices. The National Bureau of Standards has made 10-micron sized spheres available as calibration standards in their Standard Reference Material Program. This makes the beads produced by these experiments the first product sold that was "made in space."
The Future of Microgravity Processing
Over the next 15 years, space-based research will stress both scientific and commercial goals. Products will include crystals, metals, ceramics, glasses, and biological materials. Processes will include containerless processing and fluid and chemical transport. As research in these areas develops, the benefits will become increasingly apparent on Earth: new materials, more efficient use of fuel resources, new pharmaceuticals, advanced computers and lasers, and better communications. Like space, the opportunities offered by microgravity science and applications are vast and are only beginning to be explored. The NASA program will evolve over the next decade to take maximum advantage of our planned Space Station capability.