Mechanical & Fluid Systems

Code Assesses Risks Posed by Meteoroids and Orbital Debris

BUMPER II version 1.92e is a computer code for assessing the risk of damage from impacts of micrometeoroids and orbital debris on the International Space Station (ISS), including those parts of the ISS covered by shielding that affords partial protection against such impacts. (Other versions of BUMPER II have been written for other spacecraft.) Bumper II quantifies the probability of penetration of shielding and the damage to spacecraft equipment as functions of the size, shape, and orientation of the spacecraft; the parameters of its orbit; failure criteria that quantify impact damage at the threshold of failure for each spacecraft surface; and the impact-damage resistance of each spacecraft surface as defined by “ballistic limit equations” that return the size of a failure causing particle as a function of target parameters (including materials, configurations, thicknesses, and gap distances) and impact conditions (impact velocity and the density and shape of the impactor). BUMPER II version 1.92e contains several dozen ballistic limit equations that are based on results from thousands of hypervelocity impact tests conducted by NASA on ISS shielding and other hardware, and on results from numerical simulations of impacts.

Posted in: Briefs, Mechanical Components, Mechanics, Computer software and hardware, Risk assessments, Spacecraft


Self-Regulating Water-Separator System for Fuel Cells

This system would not depend on hydrophobic or hydrophilic surfaces. A proposed system would perform multiple coordinated functions in regulating the pressure of the oxidant gas (usually, pure oxygen) flowing to a fuel-cell stack and in removing excess product water that is generated in the normal fuel-cell operation. The system could function in the presence or absence of gravitation, and in any orientation in a gravitational field.

Posted in: Briefs, Mechanical Components, Mechanics, Fuel cells


Staggering Inflation To Stabilize Attitude of a Solar Sail

A document presents computational simulation studies of a concept for stabilizing the attitude of a spacecraft during deployment of such structures as a solar sail or other structures supported by inflatable booms. Specifically, the solar sail considered in this paper is a square sail with inflatable booms and attitude control vanes at the corners. The sail inflates from its stowed configuration into a square sail with four segments and four vanes at the tips. Basically, the concept is one of controlling the rates of inflation of the booms to utilize in mass distribution properties to effect changes in the system’s angular momentum.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Simulation and modeling, Solar energy, Spacecraft


Bare Conductive Tether for Decelerating a Spacecraft

A document describes a prototype of electrically conductive tethers to be used primarily to decelerate spacecraft and/or generate electric power for the spacecraft. Like prior such tethers, this tether is designed so that when it is deployed from a spacecraft in orbit, its motion across the terrestrial magnetic field induces an electric current. The Lorentz force on the current decelerates the spacecraft. Optionally, the current can be exploited to convert some orbital kinetic energy to electric energy for spacecraft systems. Whereas the conductive portions of prior such tethers are covered with electrical insulation except for end electrodes that make contact with the ionosphere, this tether includes a conductive portion that is insulated along part of its length but deliberately left bare along a substantial remaining portion of its length to make contact with the ionosphere. The conductive portions of the tether are made of coated thin aluminum wires wrapped around strong, lightweight aromatic polyamide braids. The main advantages of the present partly-bare-tether design over the prior all-insulated-tether design include greater resistance to degradation by the impact of monatomic oxygen at orbital altitude and speed and greater efficiency in collecting electrons from the ionosphere.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Electric power, Conductivity, Spacecraft


Inferring Gear Damage From Oil-Debris and Vibration Data

Data fusion increases the reliability and reduces the difficulty of gear-damage diagnosis. system for real-time detection of surface- fatigue-pitting damage to gears for use in a helicopter transmission is based on fuzzy-logic used to fuse data from sensors that measure oil-borne debris, referred to as “oil debris” in the article, and vibration signatures. A system to detect helicopter-transmission gear damage is beneficial because the power train of a helicopter is essential for propulsion, lift, and maneuvering, hence, the integrity of the transmission is critical to helicopter safety. To enable detection of an impending transmission failure, an ideal diagnostic system should provide real-time monitoring of the “health” of the transmission, be capable of a high level of reliable detection (with minimization of false alarms), and provide human users with clear information on the health of the system without making it necessary for them to interpret large amounts of sensor data.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, On-board diagnostics, On-board diagnostics (OBD), Fatigue, Vibration, Gears, Transmission gears, Rotary-wing aircraft


Nuclear Reactor Cooling Valve Design Optimized With FEA

Finite element analysis simulated the valve’s condition following an earthquake. Atomic Energy of Canada, Ltd., a subcontractor of Societatea Nationala Nucleoelectrica S.A. (SNN) of Romania, contracted Badger Meter to model, test, and produce a set of precision valves for Cernavoda Unit 2, the second nuclear power plant in Cernavoda, Romania. The main concern for the construction and operation of the valves was their survivability and continued functioning after enduring an earthquake. In nuclear power plants, such valves control the cooling of the nuclear reactors where continued flow of water around the nuclear core is essential for safety. After the earthquake that precipitated the eruption of Mt. Saint Helens in 1980, testing criteria for valves routinely has included their capability to ensure the safe functioning of the reactor after seismic events, at least in terms of cooling capacity.

Posted in: Briefs, Mechanical Components, Mechanics, Finite element analysis, Water, Nuclear energy, Cooling, Valves


Graphite Composite Booms With Integral Hinges

A document discusses lightweight instrument booms under development for use aboard spacecraft. A boom of this type comprises a thin-walled graphite-fiber/matrix composite tube with an integral hinge that can be bent for stowage and later allowed to spring back to straighten the boom for deployment in outer space. The boom design takes advantage of both the stiffness of the composite in tubular geometry and the flexibility of thin sections of the composite. The hinge is formed by machining windows in the tube at diametrically opposite locations so that there remain two opposing cylindrical strips resembling measuring tapes. Essential to the design is a proprietary composite layup that renders the hinge tough yet flexible enough to be bendable as much as 90° in either of two opposite directions. When the boom is released for deployment, the torque exerted by the bent hinge suffices to overcome parasitic resistance from harnesses and other equipment, so that the two sections of the hinge snap to a straight, rigid condition in the same manner as that of measuring tapes. Issues addressed in development thus far include selection of materials, out-of-plane bending, edge cracking, and separation of plies.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Composite materials, Graphite, Lightweight materials, Materials properties, Spacecraft


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