Acoustic Shaping: Application to Space Based Construction

Previous work has shown the formation of solid particles into thin walls of specified shape using a resonant acoustic field in microgravity. Here these results are summarized, and extended to study the qualitative effects of liquid addition and melting/ solidification in the acoustic field. Pure liquid forms into sheets, even in the 1-g environment, due to the static pressure differences in the resonant chamber; however these sheets exhibit instabilities, and shatter into droplets. Stable thin walls are formed from liquid with suspended powder in 1-g. With some adjustment of the frequency, the use of processes involving heating, cooling and phase changes are seen to be feasible. The implications of these findings to non-contact manufacturing and construction in space are discussed. INTRODUCTION The focus of this effort is on constructing complex shapes from raw materials using an acoustic field. A long-term goal is to develop construction technology, where materials obtained from lowgravity environments such as the moon or asteroids are used to provide the bulk of construction material for space operations. Non-contact, flexible fabrication of components, in this context, would provide an enabling technology for the human exploration and habitation in space. Today the cost of launching payloads into low Earth orbit ranges from $6000 to $25000 per kilogram. Even if this cost comes down to $4000 per kilogram, as projected today, most concepts for developing industry in Space remain infeasible. Space-based manufacturing techniques, using materials derived from low-gravity environments and supplying space-based markets, would provide a long-term solution to this problem. Acoustic shaping deals with the issue of manufacturing components in microgravity with minimal requirements for heavy machinery. Experiments to-date by our group have demonstrated that stable walls of specified shape can be formed, along or parallel to nodal surfaces of a resonant acoustic field, in micro-gravity. Results from flight tests and ground tests show that Copyright 1999 by the authors. Published by the American Institute of Aeronautics and Astronautics Inc. with permission. the concept of acoustic shaping can be applied to various types of materials, including solid spheres, low-density foam particles, porous organic particles, micron-scale powder, hollow aluminum spheres, and hollow aluminum oxide spheres. Most recently, experiments mixing liquids into the process have shown encouraging results.