Lewis, Derek | Search NASA

NASA NTRS2017

A sub-arcsecond Pointing stability fine stage for a high altitude balloon platform

High-altitude balloons (HABs) are platforms for collecting astrophysical and planetary science data that offer a number of advantages compared to conventional groundbased or space-based systems. However, they also pose a set of new environmental challenges that must be addressed in order to offer a viable alternative to ground- or space- based assets. In particular, maintaining science-quality pointing stability is a critical challenge for HAB platforms. For these missions, dynamic errors must be limited to a fraction of the observation wavelength, so as the wavelength becomes smaller, it becomes more difficult to meet the needed performance. As a result, there are very few existing pointing stabilization solutions that use visible-spectrum guide stars, despite their relatively wide distribution across the sky. This paper describes the results achieved with the STABLE (Subarcsecond Telescope And BaLloon Experiment) project whose goal is to provide the fine pointing stage for a balloonborne platform observing in the visible wavelength.

Porter, Michael↗

NASA NTRS2016

Digital Valve for High Pressure High Flow Applications

To address the challenges, which are involved with the development of flow control valves that can meet the requirements of deep oil wells such as high pressure, high flow rate, limited power and limited space, the authors have conceived a novel design configuration [1]. This design consists of a digitalized flow control valve with multipath and multistage pressure reduction structures. Specifically, the valve is configured as a set of parallel flow paths from the inlet to the outlet. A choke valve controls the total flow rate by digitally opening different paths or different combination of the paths. Each path is controlled by a poppet cap valve basically operated in on-off states. The number of flow states is 2N where N is the number of flow paths. To avoid erosion from sand in the oil and high speed flow, the seal area of the poppet cap valve is located at a distance from the flow inlet away from the high speed flow and the speed is controlled to stay below a predefined erosion safe limit. The path is a multistage structure composed of a set of serial nozzles-expansion chambers that equally distribute the total pressure drop to each stage. The pressure drop of each stage and, therefore, the flow speed at the nozzles and expansion chambers is controlled by the number of stages. The paths have relatively small cross section and could be relatively long for large number of stages and still fit in the strict annular space limit of a typical downhole region of an oil well. The paper will present the design configuration, analysis and preliminary test results.

downhole↗