Adv. Space Res. zyxwvutsrqponmlkjihgfedcbaZYXWVUT Vol. 15, No. 3, pp. (3)423-(3)426, 1995 1994 cos PAR Printed in Great Britain. 0273-l 177195 $7.00 + 0.00 zyxwvutsrqpo COSMIC DUST ANALOG SIMULATION IN A MICROGRAVITY ENVIRONMENT: THE STARDUST PROGRAM F. Ferguson,’ L. U. Lilleleht,l J. Nuth,:! J. R. Stephens,3 E. Bussoletti,4y7, L. Carotenuto,5 L. Colangeli,6 P. Dell’Aversana,S F. Mele,5 V. Mennella7 and C. Mirra5 1 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA University of Virginia, Charlottesville, VA, U.S.A. 2 NASA Goddard Space Flight Center, Greenbelt, MD, U.S.A. 3 Matrix, Santa Fk, NM, U.S.A. 4 Istituto Universitario Navale, Naples, Italy 5 MARS Center, Naples, Italy 6 Universitri di Cassino, Cassino, Ital) 7 Osservatorio Astronomic0 di Capodimonte, Naples, Italy A Bmm We have undertaken a project called STARDUST which is a collaboration with Italian and American investigators. The goals of this program am to study the condensation and coagulation zyxwvutsrqponmlkjihgfedcba of refractory materialsfrom the vapor and to study the propertiesof the resulting grains as analogs to cosmic dust particles. To reduce thermalconvective currentsand to develop valuable experience in designing an experiment for the Gas-Grain Siiulation Facility aboard Space Station, Freedom we have built and flown a new chamber to study these processes under periods of microgravity available on NASA’s KC-135 Research Aimraft. Preliminary results from flights with magnesium and zinc are discussed. INTRODUCTION Small cosmic dust particles play an important role in several stages of stellar evolution. Major components of these interstellar grains are refractories such as silicates and catbides which condense in the outflows of red-giant stars. These refractory materials play a crucial role in the chemistry of the interstellar medium by serving as sites for chemical reactions and as regulators of the temperaturein denser clouds by absorbing and m-emitting light. Furthermore,the condensation and later coagulation of such grains will lead to insights into the formation of larger bodies such as planetesimals and planets. To understand how refractory particles form and grow we have undertaken a project called STARDUST as a collaboration between Italian and American investigators. The goals of this program are to study the processes of condensation and coagulation of nfractory materials from the vapor and to study the size. morphology, mechanical strength, and optical properties of the resulting gralns as analogs to the more complex cosmic dust pardcles. An Important fltst step in this project is the production of a quiescent suspension of monodisperse, refractory patticles. There is evidence that particles formed by nucleation and condensation of vapor am uniform in size with only a few, if any. aggregate clumps at the onset of formation. Although the nucleation of a few refractory systems has been investigated in terrestrial laboratories, accurate studies of the interaction between the fine-grained pardculates are greatly hampered by particle settling effects. Resuspension of smalI particles by a burst of gas or by other mechanical motion will result in fast-moving, shearing flows and the break-up of some particles, while other aggregates formed during the settling process may never break up. Thus uniform, quiescent suspensions of monodisperse particles in a low pressure gas am difticult, if not impossible to achieve by the injection or resuspension of previously characterized particulates. Yet such well-characterized suspensions are ideal starting points for many of the more interesting particle interaction experiments envisioned for the Gas-Grain Simulation Facility on Space Station Freedom. It should be possible, however, to produce such suspensions by the direct condensation of refractory vapors under controlled conditions in a micmgravity environment. The studies necessary to predict both the size distribution and characteristics of the particles produced by such a method may also yield high quality data on the vapor phase nucleation of refractory materials. Previous experiments on condensation of refractory material from the vapor have also been affected by thermal convective currents arising from the high temperatures needed to produce such vapors. As a result we have designed and built a new apparatus which can be operated aboard NASA’s KC- 135 Research Aircraft. This aircraft flies in a series of parabolic arches and may produce approximately 23 seconds of weightlessness per parabola, thereby reducing thermal convective currents. This microgravity environment is not expected to affect the condensation process itself; rather it should provide a quiescent environment for condensation and coagulation which is easier to model and mom suitable for producing uniform suspensions of condensed particles. These experiments also provide valuable information on the production of such refractory suspensions under sustained microgravity and are in fact crucial steps in the development of coagulation experiments for the Gas-Grain Simulation Facility for the investigation of the coagulation, JASR15:3-k% (3W3