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A general-purpose, multifunction light-scattering instrument has been developed at the NASA Lewis Research Center for Space Shuttle and Space Station colloid crystallization and other microgravity experiments. For a single sample, the instrument can measure two-dimensional Bragg scattering from 0.5 degrees to 60 degrees , dynamic and static light scattering from 10 degrees to 170 degrees , the shear modulus of samples before and after crystallization, and digital color images of the sample. A carousel positions any one of eight 3-ml samples into the test position for separate experiments. Program challenges and flight results from the STS-83 Space Shuttle mission are discussed.

We describe a new method for characterizing particles in turbid media by cross correlating the scattered intensity fluctuations at two nearby points in the far field. The cross-correlation function selectively emphasizes single scattering over multiple scattering. The usual dynamic light-scattering capability of inferring particle size from decay rate is thus extended to samples that are so turbid as to be visually opaque. The method relies on single-scattering speckle being physically larger than multiple-scattering speckle. With a suitable optical geometry to select nearby points in the far field or equivalently slightly different scattering wave vectors (of the same magnitude), the multiple-scattering contribution to the cross-correlation function may be reduced and in some cases rendered insignificant. Experimental results demonstrating the feasibility of this approach are presented.

Employing a differential optical mixing spectrometer, we have determined that the translational diffusion coefficient (DT) of aspartate transcarbamylase (AT-Case) decreases by (4.1 plus or minus 0.6)% in the presence of succinate and carbamyl phosphate. This result, combined with the change in the sedimentation coefficient determined by Gerhart and Schachman (1968) and repeated by us in the present work indicates that ATCase experiences an increase in frictional coefficient of approximately 4% due to succinate and carbamyl phosphate, and that any change in the enzyme's partial specific volume (v) under these conditions is less than about 0.3%. We have also measured (DT)20,w for ATCase as (3.75 plus of minus 0.11) x 10-7 cm2/sec. Combining this with our measured value of s20,2-o for ATCase of (11.7 plus or minus 0.2) x 10-13 sec and the calculated value of v of 0.738 cm3/g (Rosenbusch and Weber, 1971), we have determined the molecular weight of ATCase as (2.9 plus of minus 0.1) x 10-5. We have also observed the ATCase dimer and find that at a dimer concentration of 0.6 mg/ml the value of s20,w for the dimer is 15.8 x 10-13 sec and that this value decreases by (4.0 plus or minus 0.5)% upon the addition of succinate and carbamyl phosphate, a behavior essentially identical with that of the monomer.