Mechanical & Fluid Systems

Modular, Highly Maintainable, and Flexible Control Software

This software also lends itself to multitasking and distributed processing. Model Rocket Engine Software System (MRECS) is a system of control software that was originally intended for use in controlling rocket engines but is also applicable to almost any real-time, closed- loop process-control system — for example, the feedback control system of a robot. MRECS affords the capabilities necessary for feedback control, actuation of valves and other devices by use of discrete and/or analog commands, processing of sensor readings, and generation of alarms by comparison of various quantities with limiting values. MRECS is capable of real-time multitasking and is amenable to distributed processing. It is designed, from the outset, to be highly maintainable and to be flexible in the sense that, in response to changing requirements, it can be quickly and reliably modified and tested.

Posted in: Machinery & Automation, Briefs

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Water-Jet Accelerator for Launching a Spacecraft

A proposed ground- based apparatus would accelerate a spacecraft to speed of about mach 1, thus making it possible to increase the payload and/or reduce the cost of launching the space- craft into orbit. The apparatus would include a track along which the spacecraft would ride on a sled. Hundreds of small water jets energized by compressed-air packs would be located under, and at small intervals along, the track. Each jet would be activated in turn as the sled passed by, aiming a high-speed (possibly supersonic) stream of water at baffles on the underside of the sled. The force of water impinging on the baffles would provide levitation and accelerate the sled along the track. Unlike a previously proposed launch-assisting linear electric motor, the water-jet apparatus would function without need for expensive electric-power-conditioning equipment. Unlike another launch-assist concept involving a piston driven along a pneumatic tube, the present concept does not present problems of how to (1) couple the piston to the sled and (2) exert fine control over acceleration. Another advantage of the water-jet concept is redundancy: even if several water jets were to malfunction, the remaining many functional water jets should suffice.

Posted in: Machinery & Automation, Briefs

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Electroactive-Polymer Actuators With Selectable Deformations

There are numerous options for selecting materials, config- urations, and modes of operation. Efforts are underway to develop compact, lightweight electro- mechanical actuators based on electroactive polymers (EAPs). An actuator of this type is denoted an electroactive-polymer actuator with selectable deformation (EAPAS). The basic building blocks of these actuators are sandwichlike composite-material strips, containing EAP layers plus electrode layers, that bend when electric potentials are applied to the electrodes. Prior NASA Tech Briefs articles that have described such building blocks as parts of actuators for specific purposes include “Robot Hands With Electroactive-Polymer Fingers” (NPO-20103), Vol. 22, No. 10, (October 1998), page 78; “Robot Arm Actuated by Electroactive Polymers” (NPO-20393), Vol. 23, No. 6 (June 1999), page 12b; “Wipers Based on Electroactive Polymeric Actuators” (NPO-20371), Vol. 23, No. 2 (February 1999), page 7b; and “Miniature Electroactive-Polymer Rakes” (NPO-20613), Vol. 25, No. 10 (October 2001), page 6b.

Posted in: Mechanics, Briefs, TSP

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Optimization of Synthetic Jet Actuators

A report presents a study oriented toward optimization of synthetic jet actuators. [A syn- thetic jet actuator is a fluidic control device that partly resembles a loudspeaker. It typically comprises a piezo- electric actuator/ diaphragm situated in a cavity, facing an orifice or nozzle at the opposite end of the cavity.] The instant report describes an experimental synthetic jet actuator equipped for tuning through variation of some of its cavity dimensions and its excitation frequency and for selection of either (1) clamping of the edge of the diaphragm between flat surfaces or (2) pinning of the edge of the diaphragm between steel O rings. The report goes on to discuss the effects of the cavity and nozzle geometry, diaphragm design, excitation frequency, and other design features on the vibrational resonance of the diaphragm, the acoustic resonance of the cavity, the coupling (or lack thereof) of these resonances, and the overall performance as characterized by the displacement at the center of the diaphragm or the speed of the jet at a specified distance from the orifice. Conclusions reached in this study are that (1) the pinning configuration results in better performance than does the clamping configuration and (2) the maximum performance is achieved by matching the resonant frequencies of the diaphragm and the cavity.

Posted in: Mechanics, Briefs, TSP

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Sonic-Boom Tests of Model of a Supersonic Business Jet Plane

A report discusses wind-tunnel tests of a scale model of a con- ceptual two-engine jet airplane designed to carry 10 passengers, have a range of 4,000 miles (≈6,400 km), cruise at a mach number of 2.0, and generate a low sonic boom [char- acterized by a shock overpressure of ≤ 0.5 lb/ft2 (≤24 Pa)]. The model could optionally include either of two differently sized nacelle submodels representing alternative engine designs. In each test, the pressure was measured at intervals along a horizontal line at a specified height below the model. One conclusion drawn from predicted and measured pressure values is that it is more difficult to tailor the geometry of this airplane for low sonic boom than it is to do so for a larger supersonic airplane capable of carrying 300 passengers and for which the allowable shock overpressure is 1.0 lb/ft2 (48 Pa). It was found that decreasing the allowable overpressure intensifies the conflicts between the design choices for reducing sonic boom and those for increasing aerodynamic efficiency. It was also found that due to the nacelles’ aft location, their contribution to the shock overpressures could be expected to be small enough to be unnoticeable by an observer on the ground.

Posted in: Mechanics, Briefs, TSP

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Automated System for Fluid and Electrical Connections

The Smart Umbilical Mating System (SUMS) is an automated, three-degreeof- freedom, scalable system for quickly mating, demating, and/or remating ganged umbilicals. SUMS connects electrical and fluid paths between spacecraft and ground support equipment whether liftoff or side mount for NON T-0 umbilicals. SUMS prevents electrical arcing and leakage of fluids by providing for automated alignment of mating connectors and verification of mating. SUMS could readily be adapted to such other applications as servicing of aircraft, orbiting spacecraft, or ground vehicles. Major elements of SUMS include mating cones equipped with force sensors with integral latches; computer control; robotic vision with tracking aided by laser beams; actuation by a compliant pneumatic motor; and a secondary mate plate, which holds the ground-side fluid electrical connectors in proper alignment, is pneumatically actuated to complete mating once the cones have been latched, and is the only part of the system that one must change to adapt SUMS to different applications. A commercial version plumbed with electrical power, communications, fuel, lubricants, and coolant fluids could be installed at a central location for servicing land vehicles. SUMS could be utilized between moving vehicles. Automated functions could include electronic identification of vehicles to prevent errors; recording of data about the vehicle; its consumption of fluids; sampling for wear analysis; maintenance scheduling; distance traveled; and topping off or changing of all fluids in the correct amounts.

Posted in: Machinery & Automation, Briefs, TSP

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Apparatus for Friction Stir Welding of Pipes

FSW heads would move circum- ferentially and pipes would be supported against FSW loads. A proposed apparatus would effect friction stir welding (FSW) along a circumferential path to join two pipes. The apparatus is denoted an “orbital FSW system” because the circum- ferential motion of the FSW head would be similar to the motions of welding heads in commercial orbital fusion welding systems.

Posted in: Mechanics, Briefs

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