Mechanical & Fluid Systems

Actuated Ball-and-Socket Joints

These joints would be relatively compact, lightweight, simple, and inexpensive. The term "actuated ball-and-socket" (ABS) characterizes a proposed class of ball-and-socket joints that would incorporate ultrasonic motors and other piezoelectric actuators to generate multidimensional actuation. In some applications, ABS joints could supplant traditional joint-and-actuator assemblies that include passive rotary joints actuated by electromagnetic motors via gears. In comparison with such assemblies, ABS joints offer potential advantages of compactness, relative mechanical simplicity, higher torque-to-weight ratios, no backlash, self-braking with power turned off, and lower cost. ABS joints are expected to be particularly attractive for use as robot joints and as general low-power orienting actuators for diverse applications that could include robot hands, tools, and mechanisms for aiming scientific instruments.

Posted in: Briefs, TSP

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Flex Wedges

Brakes and clutches could perform more reliably and predictably. Flex wedges have been proposed for use in brakes and clutches like those in which, heretofore, basic wedges have been used. Flex wedges (see Figure 1) offer advantages of superior braking and clutching performance and less weight, relative to basic wedges.

Posted in: Mechanics, Briefs, TSP

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Heat-Shield Panels in a 2D Shingling Arrangement

Adjacent panels are slid aside to make room for insertion or removal. Figure 1 depicts mockups of lightweight metal heat-shield panels that have been proposed for use on spacecraft of the reusable-launch-vehicle type. These panels are designed for simplicity of insertion and removal. The design could also be adapted to both insulating and noninsulating panels in nonspacecraft applications.

Posted in: Mechanics, Briefs, TSP

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Modular Propulsion Clusters

A report proposes the development of modular propulsion clusters (MPCs) — small, self-contained propulsion systems that would be standardized, mass-produced, and readily installed on a variety of miniature future spacecraft. The MPCs would be inexpensive, "turn-key" alternatives to expensive conventional propulsion systems that are designed and built integrally with other spacecraft systems and structures. Each MPC would contain its own propellant tank, isolation valve, gas plenum, and valve/nozzle thruster assemblies. Each MPC would be delivered fully loaded; installation on a spacecraft would involve only mounting and electrical connections. The propellant would be a liquid that, by electrical actuation of valves, would be metered into the plenum as needed to vaporize and generate thrust. An important advantage of using a vaporizing propellant liquid (as opposed to a propellant gas) is that stopping a liquid leak is orders of magnitude easier than is preventing a gas leak.

Posted in: Mechanics, Briefs, TSP

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Positioning System for a Human Habitat in a Large Centrifuge

A report describes the system for controlling the radial position and tilt of a spacecraftlike habitat for humans in NASA's Space Flight Environmental Simulator (SFES) — a 16-m-diameter centrifuge used previously to evaluate effects of hypergravitational acceleration on animals. The habitat-positioning system was installed as an upgrade of the SFES to enable similar testing on humans to obtain guidance for designing centrifugal artificial-gravitation systems for future spacecraft.

Posted in: Mechanics, Briefs, TSP

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Launch-on-Demand Servicing Microsatellites

A report describes an emerging class of miniature, highly capable, relatively inexpensive satellites that could be launched rapidly by nontraditional methods. Of particular interest is a subclass of proposed launch-on-demand microsatellites for inspecting and servicing other satellites (targets) already in orbit. A satellite of this subclass would have a mass of ≤30 kg and could be launched, by use of a modified missile system, from a fighter airplane in flight.

Posted in: Mechanics, Briefs, TSP

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Miniature Electrothermal Thruster

A report proposes a miniature electrothermal spacecraft engine. The engine would include a chamber with an inside length of ≈1.5 cm and inside diameter of ≈0.25 cm, with a dielectric (ideally diamond) sidewall lining, a metal-coated expansion nozzle at one end, and a metal electrode at the other end. A propellant liquid (ammonia) would be vaporized into the cavity. To heat the NH3 vapor and dissociate it to a nitrogen/hydrogen plasma, the cavity would be excited with an electromagnetic field at a cavity resonance frequency of about 25 GHz (also the frequency of a dielectric resonance of NH3). The expansion of the plasma through the nozzle would generate thrust. The electric field would be of such a strength and configuration as to prevent contact between the plasma and the inner surface of the chamber. The plasma skin depth would be great enough that the plasma could absorb a large proportion of the electromagnetic energy. By use of refractory electrode and dielectric materials, pulsed operation, and, preferably, evaporative cooling of the chamber wall by the propellant liquid, it should be possible to achieve high plasma temperature and pressure and, thus, high thrust.

Posted in: Mechanics, Briefs, TSP

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