Mechanical & Fluid Systems

Large Deployable Reflectarray Antenna

A report discusses a 7-meter-diameter reflectarray antenna that has been conceived in a continuing effort to develop large reflectarray antennas to be deployed in outer space. Major underlying concepts were reported in three prior NASA Tech Briefs articles: "Inflatable Reflectarray Antennas" (NPO-20433), Vol. 23, No. 10 (October 1999), page 50; "Tape-Spring Reinforcements for Inflatable Structural Tubes" (NPO- 20615), Vol. 24, No. 7 (July 2000), page 58; and "Self-Inflatable/Self-Rigidizable Reflectarray Antenna" (NPO-30662), Vol. 28, No. 1 (January 2004), page 61. Like previous antennas in the series, the antenna now proposed would include a reflectarray membrane stretched flat on a frame of multiple inflatable booms. The membrane and booms would be rolled up and folded for compact stowage during transport. Deployment in outer space would be effected by inflating the booms to unroll and then to unfold the membrane, thereby stretching the membrane out flat to its full size. The membrane would achieve the flatness for a Ka-band application. The report gives considerable emphasis to designing the booms to rigidify themselves upon deployment: for this purpose, the booms could be made as spring-tape-reinforced aluminum laminate tubes like those described in two of the cited prior articles.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Antennas

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Periodically Discharging, Gas-Coalescing Filter

In effect, small bubbles would be made to coalesce into very large ones. A proposed device would remove bubbles of gas from a stream of liquid (typically water), accumulate the gas, and periodically release the gas, in bulk, back into the stream. The device is intended for use in a flow system (1) in which there is a requirement to supply bubble-free water to a downstream subsystem and (2) that includes a sensor and valves, just upstream of the subsystem, for sensing bubbles and diverting the flow from the subsystem until the water stream is again free of bubbles. By coalescing the gas bubbles and then periodically releasing the accumulated gas, the proposed device would not contribute to net removal of gas from the liquid stream; nevertheless, it would afford an advantage by reducing the frequency with which the diverter valves would have to be activated.

Posted in: Briefs, Mechanical Components, Mechanics

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System Would Detect Foreign-Object Damage in Turbofan Engine

Vibration-sensor and gas-path-analysis data would be fused. A proposed data-fusion system, to be implemented mostly in software, would further process the digitized and preprocessed outputs of sensors in a turbofan engine to detect foreign-object damage (FOD) [more precisely, damage caused by impingement of such foreign objects as birds, pieces of ice, and runway debris]. The proposed system could help a flight crew to decide what, if any, response is necessary to complete a flight safely, and could aid mechanics in deciding what post-flight maintenance action might be needed.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Recovering Residual Xenon Propellant for an Ion Propulsion System

Most of the otherwise unusable xenon is recovered. Future nuclear-powered Ion-Propulsion- System-propelled spacecraft such as Jupiter Icy Moon Orbiter (JIMO) will carry more than 10,000 kg of xenon propellant. Typically, a small percentage of this propellant cannot be used towards the end of the mission because of the pressure drop requirements for maintaining flow. For large missions such as JIMO, this could easily translate to over 250 kg of unusable xenon.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Predicting Tail Buffet Loads of a Fighter Airplane

Airframes can be designed to be more robust. Buffet loads on aft aerodynamic surfaces pose a recurring problem on most twin-tailed fighter airplanes: During maneuvers at high angles of attack, vortices emanating from various surfaces on the forward parts of such an airplane engine inlets, wings, or other fuselage appendages) often burst, immersing the tails in their wakes. Although these vortices increase lift, the frequency contents of the burst vortices become so low as to cause the aft surfaces to vibrate destructively.

Posted in: Briefs, Mechanical Components, Mechanics, Aerodynamics, Military aircraft

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System Finds Horizontal Location of Center of Gravity

Mass and center-of-mass data are updated at a rate of = 267 Hz. An instrumentation system rapidly and repeatedly determines the horizontal location of the center of gravity of a laboratory vehicle that slides horizontally on three air bearings (see Figure 1). Typically, knowledge of the horizontal center-of- mass location of such a vehicle is needed in order to balance the vehicle properly for an experiment and/or to assess the dynamic behavior of the vehicle.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Bearings, Test equipment and instrumentation, Vehicle dynamics

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Water Containment Systems for Testing High-Speed Flywheels

Water-filled containers are stacked like bricks. Water-filled containers are used as building blocks in a new generation of containment systems for testing high-speed flywheels. Such containment systems are needed to ensure safety by trapping high-speed debris in the event of centrifugal breakup or bearing failure. Traditional containment systems for testing flywheels consist mainly of thick steel rings. While steel rings are effective for protecting against fragments from conventional and relatively simple metal flywheels, they are also expensive. Moreover, it is difficult and expensive to configure steel-ring containment systems for testing of advanced flywheel systems that can include flywheels made of composite materials, counter-rotating flywheels, and/or multiple flywheels rotating about different axes. In contrast, one can quickly, easily, and inexpensively stack waterfilled containers like bricks to build walls, (and, if needed, floors, and ceilings) of sufficient thickness to trap debris traveling in any debris traveling in any possible direction at the maximum possible kinetic energy that could be encountered in testing a given flywheel system.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Containers, Flywheels, Test procedures

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