The trapping and behavior of gas bubbles were studied during low gravity solidification of carbon tetrabromide. The flight experiments were performed during two sounding rocket flights (SPAR 1 and SPAR 3) and involved gradient freeze solidification of gas saturated melts. Gas bubbles were evolved at the solid-liquid interfaces during the low gravity intervals. No large-scale thermal migration of bubbles, bubble pushing by the solid-liquid interface, or bubble detachment from the interface were observed during the low gravity experiments. During the SPAR 3 experiment, a unique bubble motion-fluid flow event occurred in one specimen: a large bubble moved downward and caused some circulation of the melt. The gas bubbles that were trapped by the solid in commercial purity material formed voids that had a cyclindrical shape in SPAR 3, in contrast to the spherical shape that had been observed in SPAR 1. These shapes were not influenced by the gravity level, but were dependent upon the initial temperature gradient. In higher purity material the shape of the voids changed from cylindrical in one-g to spherical in low-g. Papazian, J. M. and Wilcox, W. R. Unspecified Center NASA-CR-161159, RM-680 NAS8-31529

The peaceful use of space flight systems for research and technological devel opments in the context of promoting European and international cooperation represents the essential motivation for the programmes of the European Space Agency (ESA). One of ESA's programmes is dedicated to microgravity research, which is now an established discipline in Europe, with a dedicated group of scientists participating. The Challenger disaster has resulted in a serious dis continuity of flight opportunities in the next few years but the forthcoming International Space Station, new launchers and reentry vehicles are expected to provide ample opportunities for microgravity research in the long term. Meanwhile parabolic aircraft flights, sounding rockets as well as the delayed Shuttle-dependent missions, Spacelab D-2, the IML-missions and EURECA I, will be employed to keep microgravity experimenters reasonably busy in the interim period. To prepare the ground for these activities, both regarding research and experiment facilities, an in-depth analysis of the state of the art is an essential requirement at this time. Such an analysis is presented in this volume. It ad dresses all of the topics that have been identified to be of relevance. Besides a presentation of the fundamental aspects justifying microgravity research, the results of experiments already performed are reviewed and recommendations for future activities are made. Close to fifty European scientists have cooper ated in the preparation of this volume and their dedicated and concerted effort is greatly appreciated.