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Interface Between STAR-CCM+ and 42 for Enhanced Fuel Slosh Analysis

Fuel slosh is excited during spacecraft maneuvers. The forces and torques exerted on the spacecraft by the slosh must be controlled by the attitude control system to maintain correct pointing and spacecraft orbit. In some rare cases, the attitude control system may excite the slosh and cause a loss of control of the spacecraft, or the expected spacecraft motion from a certain control command will be different enough from the control command to adversely affect the mission. By linking the computational fluid dynamics (CFD) and the flight simulation software, the fuel slosh can be modeled at high fidelity by the CFD software, while receiving and passing information to and from the flight simulation software, thus increasing the fidelity of both models. In the past, fuel slosh has either been modeled with an equivalent mechanical model, such as a pendulum, or with a standalone CFD simulation.

Posted in: Briefs, Mechanical Components, Mechanics, Fluid Handling

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Mechanisms for Achieving Non-Sinusoidal Waveforms on Stirling Engines

The current state-of-the-art Stirling engines use sinusoidal piston and displacer motion to drive the thermodynamic cycle and produce power. Research performed at NASA Glenn has shown that non-sinusoidal waveforms have the potential to increase Stirling engine power density, and could possibly be used to tailor engine performance to the needs of a specific application. However, the state-of-the-art Stirling engine design uses gas springs or planar springs that are very nearly linear, resulting in a system that resonates at a single frequency. This means that imposing non-sinusoidal waveforms, consisting of multiple frequencies, requires large forces from the drive mechanism (either the alternator or the crank shaft). These large forces increase losses, and increase the size and requirements of the control system. This innovation aims to reduce the external forcing requirements by introducing internal mechanical components that provide the forces necessary to achieve the desired waveforms.

Posted in: Briefs, Mechanical Components, Mechanics, Motion Control

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RFID Cavity

Potential applications include inventory tracking for containers such as waste receptacles or storage containers.This technology provides a method for interrogating collections of items with radio-frequency identification (RFID) tags. It increases the read accuracy, meaning that more of the item tags will be successfully read. It also permits smaller tag antennas than would otherwise be necessary.

Posted in: Briefs, Mechanical Components, Mechanics, Fluid Handling

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Method for Asteroid Volatile Extraction in Space

The method would support human missions to Mars or other distant objects.Some meteorites representative of certain classes of asteroids are 25% or more water by weight. This is consistent with infrared spectra of some asteroids, indicating hydrated minerals are abundant in some varieties of carbonaceous chondrite asteroids. Since water is very valuable in space, it would be desirable to be able to process asteroids to recover this water and other volatiles. The Asteroid Redirect Mission concept has formulated a method for returning asteroids of 1,000-ton mass into the Earth-Moon system orbit using only ~10 tons of propellant. If ~25% of that returned asteroid mass were recovered as volatiles and solar power used to make those volatiles into propellant, then the overall system would generate approximately 25 times as much propellant as it uses. This could be used to make sustainable human missions to Mars or otherwise spread humanity into the solar system.

Posted in: Briefs, Aerospace, Mechanical Components, Mechanics, Fluid Handling

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Improving Stirling Engine Performance Through Optimized Piston and Displacer Motion

Stirling engines typically achieve high efficiency, but lack power density. Low power density prevents them from being used in many applications where internal combustion engines are viable competitors, and increases system costs in applications that require Stirling engines. This limits their operating envelope in both terrestrial and space applications. Sinusoidal piston and displacer motion is one of the causes of low power density. Previous work proposed solving this problem by replacing sinusoidal waveforms with waveforms that more closely approximate those of the ideal Stirling cycle. However, when working with real engines, imposing ideal waveforms has been shown to reduce power density and efficiency due to increased pressure drop through the regenerator and heat exchangers.

Posted in: Briefs, Mechanical Components, Mechanics, Fluid Handling, Motors & Drives

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Prototype Capture System Simulates Asteroid Mission

A prototype of the robotic capture module system is tested with a mock asteroid boulder in its clutches at NASA’s Goddard Space Flight Center. A robotic capture module system prototype was built to help NASA engineers understand the operations required to collect a multi-ton boulder from an asteroid’s surface. The hardware includes three space frame legs with foot pads, and two seven-degrees-of-freedom arms with microspine gripper “hands” to grasp onto the boulder.

Posted in: News, Motion Control, Robotics

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Dike Inspection Robot is Energy-Autonomous

The robot's drive train, including the dual-hemisphere system. (Image: University of Twente) Inspecting the condition of dikes and other sea defense structures is typically a task for robots, working in a team and in a highly autonomous way. But if they move around across the dikes, perform tests, and communicate the results for six hours a day, they use a lot of energy.

Posted in: News, Motion Control, Motors & Drives, Power Transmission

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