Control and dynamics of a flexible spacecraft during stationkeeping maneuvers

A case study of a spacecraft having flexible solar arrays is presented. A stationkeeping attitude control mode using both earth and rate gyro reference signals and a flexible vehicle dynamics modeling and implementation is discussed. The control system is designed to achieve both pointing accuracy and structural mode stability during stationkeeping maneuvers. Reduction of structural mode interactions over the entire mode duration is presented. The control mode using a discrete time observer structure is described to show the convergence of the spacecraft attitude transients during Delta-V thrusting maneuvers without preloading thrusting bias to the onboard control processor. The simulation performance using the three axis, body stabilized nonlinear dynamics is provided. The details of a five body dynamics model are discussed. The spacecraft is modeled as a central rigid body having cantilevered flexible antennas, a pair of flexible articulated solar arrays, and to gimballed momentum wheels. The vehicle is free to undergo unrestricted rotations and translations relative to inertial space. A direct implementation of the equations of motion is compared to an indirect implementation that uses a symbolic manipulation software to generate rigid body equations

Ultrastructural Studies On Stomata Development In Internodes Of Avena Sativa

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141606/1/ajb209789.pd

Heat Transfer and Pressure Drop in Concentric Annular Flows of Binary Inert Gas Mixtures

Studies of heat transfer and pressure drop of binary inert gas mixtures flowing through smooth concentric circular annuli, tubes with fully developed velocity profiles, and constant heating rate are described. There is a general lack of agreement among the constant property heat transfer correlations for such mixtures. No inert gas mixture data exist for annular channels. The intent of this study was to develop highly accurate and benchmarked pressure drop and heat transfer correlations that can be used to size heat exchangers and cores for direct gas Brayton nuclear power plants. The inside surface of the annular channel is heated while the outer surface of the channel is insulated. Annulus ratios range 0.5 < r* < 0.83. These smooth tube data may serve as a reference to the heat transfer and pressure drop performance in annuli, tubes, and channels having helixes or spacer ribs, or other surfaces

Steady-state measurements of respiration rate with an oxygen electrode

An oxygen electrode was developed which measures steady-state respiration rates in a volume of 0.25 ml and at oxygen concentrations as low as 0.1 [mu]. The steady state was achieved by pumping air-equilibrated buffer into the respirometer at various rates. The method is most suitable for tissue slices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22139/1/0000568.pd

Measurement of oxygen partial pressure within soybean nodules by oxygen microelectrodes

The internal pO 2 of soybean ( Glycine max Merr.) nodules was measured with oxygen microelectrodes. For nodules in air at 23°, the pO 2 decreased sharply across the nodule cortex, and was too low to measure in the central tissue. At 1° in 1.0 atm O 2 , the pO 2 in the central tissue was measurable, and was approximately uniform from the center to the edge of the central tissue. This uniformity was probably due to the intercellular air spaces of the central tissue, since infiltrating the spaces with water substantially decreased the pO 2 in the central tissue. The results strongly suggest that most of the resistance to O 2 diffusion into the nodule occurs within the cortex.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47462/1/425_2004_Article_BF00388335.pd