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A control scheme is described for slewing exible spacecraft with both suppression of de ection during the slew and elimination of residual oscillations. The method minimizes the maneuver time subject to constraints on residual vibration magnitude, sensitivity to modeling errors, rest-to-rest slew distance, and the transient de ection amplitude. Furthermore, a solution is sought that provides inherent fuel ef ciency. The feasibility of the approach is demonstrated with linear and nonlinear computer simulations.

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We present experimental results demonstrating that, relative to continuous illumination, an increase of a factor of 3-10 in the photon efficiency of algal photosynthesis is attainable via the judicious application of pulsed light for light intensities of practical interest (e.g., average-to-peak solar irradiance). We also propose a simple model that can account for all the measurements. The model (1) reflects the essential rate-limiting elements in bioproductivity, (2) incorporates the impact of photon arrival-time statistics, and (3) accounts for how the enhancement in photon efficiency depends on the timescales of light pulsing and photon flux density. The key is avoiding ''clogging'' of the photosynthetic pathway by properly timing the light-dark cycles experienced by algal cells. We show how this can be realized with pulsed light sources, or by producing pulsed-light effects from continuous illumination via turbulent mixing in dense algal cultures in thin photobioreactors.

A recent review of all ivory from excavations in Chalcolithic and