Made in Space

History characterizes the various eras of civilization in terms of available materials technology, leading to the recognition of such eras as the Stone Age, Bronze Age, Steel Age, and Silicon Age. One of the areas of intense research in the present era has been the processing of materials in the space environment to develop new or improved products for use on Earth. In the 1960s, during the early phase of this effort, the advent of a new industry was predicted based on the promising initial results obtained, and it was anticipated that by the 1980s "made in space" would be a common label on a large number of products.

That new manufacturing industry based in space is still in the future, primarily because of the high cost of placing the carrier vehicles into orbit—$35,000 per pound at the beginning of the twenty-first century. Advances in propulsion technology, however, will reduce the cost of transportation to space in the future. Currently the emphasis is on making better products here on Earth based on the knowledge and processes discovered through space research. To understand the great potential of space we must examine what it is that makes the space environment so unique in the processing of materials.

The Advantages of Space-Based Manufacturing

There are two primary effects on Earth that can be reduced to almost zero in the microgravity environment (nominally one-thousandth to one-millionth of Earth's gravitation) present in orbiting vehicles: sedimentation and thermal convection . Sedimentation makes heavier liquids or particles settle at the bottom of a container, as when sugar added to coffee settles at the bottom of the cup. Thermal convection establishes currents where cooler fluids fall to the bottom and warmer ones rise to the top.

Because many chemical, fluid-physics, biological, and phase-change (e.g., changing from a liquid to a solid state) processes are affected by the effects of sedimentation and thermal convection, the form and size properties of materials formed under these influences are different in space compared to those formed under the influence of Earth's gravitation. A close examination of the accompanying images shows the impact of things made in space.

A study conducted for the National Aeronautics and Space Administration (NASA) in the early 1970s identified seventy-seven representative unique products or applications that can be obtained in space. Since that early study, the list of potential applications has at least doubled. Most of the items have been the subject of many investigations conducted on rockets, the space shuttle, and the Mir space station by scientists and engineering teams from many countries, particularly the United States, Germany, Russia, France, Italy, Canada, and Japan (see table on page 141 for a representative subset of the space applications that have been investigated or are in the process of being investigated). The following two examples in the medical area serve to illustrate the current research.

Protein Crystal Growth

Growing crystals in microgravity has the advantage of virtually eliminating the thermal convection that produces poor crystal quality and increases the time required to grow a useful crystal. This advantage of microgravity is particularly important in obtaining crystals that have the size and high degree of structural perfection necessary to determine, through X-ray analysis, the three-dimensional structure of those complex organic molecules. For instance, long before the space era the structure of DNA was determined using crystallography , but there are many protein crystals that are difficult to grow under the influence of gravitational forces. Urokinase, a significant protein in cancer research, is an example of a protein that is difficult to grow on Earth and that benefits from microgravity. Complete three-dimensional characterization, that is, determining the relative location of the approximately 55,000 atoms in this molecule, would permit pharmaceutical scientists to design drugs to counteract the harmful effects of urokinase in promoting the spread of cancer throughout the body, particularly in the case of cancerous breast tumors. Research being conducted in the space shuttle is seeking to grow urokinase crystals in space for subsequent X-ray analysis in Earth-based laboratories.

Microcapsules for Medical Applications

Experiments conducted in space have shown more spherical perfection and uniformity of size distribution in microcapsules, which are capsules with diameters of 1 to 300 micrometers (0.00004 to 0.012 inches). The size and shape of microcapsules are key factors in how effective they are at delivering medicinal drugs directly to the affected organs by means of injections or nasal inhalations. The feasibility of newly developed processes for producing multilayered microcapsules has been limited because of the effects of density differences in the presence of gravity. In order to circumvent this, a series of experiments has been performed onboard the space shuttle to produce superior microcapsules in space. If these experiments prove successful, large-scale demand for these types of microcapsules may require future development of ground manufacturing equipment that counteracts the effects of gravity.

Student Experiments in Space-Based Material Processing

Since the initial activity in materials processing in space, student participation has been an important part of the effort. Since the early space shuttle

flights, the NASA-sponsored Getaway Special program has provided experiment containers in the shuttle cargo bay capable of accommodating 50 to 200 payloads of 23 to 90 kilograms (50 to 200 pounds), with the primary focus on student experiments. Industry also plays an important role in student education. One U.S. space company pioneered a hands-on student experiment program for microgravity experiments onboard the space shuttle. Several industrial concerns have since donated space accommodations in scientific equipment on the shuttle and on rockets, as well as engineering and scientific manpower during integration of the experiments in the spacecraft.

The Role of the International Space Station

The advent of the International Space Station during the first decade of the twenty-first century will be an important milestone in the growth and maturing of the research phase of the materials processing in space program. The International Space Station will provide continuing, long-duration microgravity capability to conduct experiments with the participation of astronauts and cosmonauts. This is an international endeavor the scope of which reaffirms the important role that our society places on materials development. Our rapid technological advancement continues to place great demands on the development of new materials; space is an important tool in meeting those challenges.

see also Crystal Growth (volume 3); International Space Station (volumes 1 and 3); Microgravity (volume 2); Zero Gravity (volume 3).

John M. Cassanto and Ulises R. Alvarado

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