Design evolution of the orbiter reaction control subsystem

The challenges of space shuttle orbiter reaction control subsystem development began with selection of the propellant for the subsystem. Various concepts were evaluated before the current Earth storable, bipropellant combination was selected. Once that task was accomplished, additional challenges of designing the system to satisfy the wide range of requirements dictated by operating environments, reusability, and long life were met. Verification of system adequacy was achieved by means of a combination of analysis and test. The studies, the design efforts, and the test and analysis techniques employed in meeting the challenges are described

Towards the noise reduction of piezoelectrical-driven synthetic jet actuators

This paper details an experimental investigation aimed at reducing the noise output of piezoelectrical-driven synthetic jet actuators without compromising peak jet velocity. Specifically, the study considers double-chamber ('back-to-back') actuators for anti-phase noise suppression and corrugated-lobed orifices as a method to enhance turbulent mixing of the jets to suppress jet noise. The study involved the design, manufacture and bench test of interchangeable actuator hardware. Hot-wire anemometry and microphone recordings were employed to acquire velocity and noise measurements respectively for each chamber configuration and orifice plate across a range of excitation frequencies and for a fixed input voltage. The data analysis indicated a 32% noise reduction (20 dBA) from operating a singlechamber, circular orifice SJA to a double-chamber, corrugated-lobed orifice SJA at the Helmholtz resonant frequency. Results also showed there was a small reduction in peak jet velocity of 7% (~3 m/s) between these two cases based on orifices of the same discharge area. Finally, the electrical-to-fluidic power conversion efficiency of the double-chamber actuator was found to be 15% across all orifice designs at the resonant frequency; approximately double the efficiency of a single-chamber actuator. This work has thus demonstrated feasible gains in noise reduction and power efficiency through synthetic jet actuator design

Terrestrial carbon pools in grasslands and agricultural soils: preliminary data from the Corn Belt and Great Plains regions

Soil organic matter is recognized as an important component of soil quality through its influence on soil physical properties and the cycling of nutrients. Interest in soil organic matter has expanded to include its role in the worldwide carbon (C) budget and climate change. This chapter develops reliable data sets to assess the potential for C sequestration in agroecosystems of the Great Plains and Corn Belt. It represents the spring sampling of six sites within the network of 41 sites, three from the Corn Belt and three from the Great Plains. For the Corn Belt sites, C mineralization and particulate organic matter (POM)-C were the most sensitive indicators of management effects on soil organic matter. No-till generally showed increased amounts of POM and mineralized C in the top 20 cm, suggesting increases in labile C fractions compared with conventional tillage