Acta Astronautica Vol. 7, pp. 685-698 Pergamon Press Ltd., 1980. Printed in Great Britain Joining methods in space: a theoretical model for diffusion bonding B. DERBY AND E. R. WALLACH Department of Metallurgy & Materials Science, University of Cambridge, Pembroke Street, Cambridge, England (Received 9 January 1980) Abstract--In the near future it will be necessary to join metal components in space, for either construction or repair purposes. Potential joining techniques are briefly considered in terms of their suitability for bonding the likely materials to be used, aluminium and/or titanium alloys. One technique, diffusion bonding, is of considerable promise but the bonding mechanisms are not fully understood. Thus the paper describes a computer model which is being developed to gain sufficient understanding that diffusion bonding can be more fully and efficiently developed and thus exploited. Introduction IF A very large structure such as a large manned laboratory or a space solar power station is to be placed in Earth orbit, the volume and mass of the structure will make it difficult to launch as a single unit. Instead the structure probably will have to be assembled in space from separate prefabricated units originally constructed on Earth. At first, only simple connections and joining methods might be used to construct these units in space. However, eventually many more of existing terrestial joining techniques will be required and/or new methods developed. This is for several reasons. Firstly, when a structure currently is sent into orbit it must be fabricated so as to fit into a certain volume which imposes a constraint on size and complexity of design. Clearly, it would be more efficient if, instead, the materials were launched into orbit and then were subsequently assembled; this approach also would remove the constraints on size and complexity. Secondly, welded structures are generally stronger than bolted sub-units. Thirdly, and perhaps most important, it would permit major repairs and/or alterations to be carried out in orbit, this not being easy to accomplish at present, In this article, constructional materials suitable for space applications and available joining techniques are briefly reviewed. It is evident that one process, diffusion bonding, may be very suitable for the construction of large structures. However, the process suffers in that the mechanisms by which joining is achieved are poorly understood. Thus, the article includes a description of some current research into the establishment of a theoretical model for diffusion bonding. It is hoped this approach will not only lead to understanding of the dominant bonding mechanisms but also more widespread use of the process. Materials for space structures Many aspects must be taken into account when selecting materials suitable 685