Mechanical & Fluid Systems

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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Variable-Specific-Impulse Magnetoplasma Rocket

This rocket is expected to enable long-term human exploration of outer space. Johnson Space Center has been leading the development of a high-power, electrothermal plasma rocket — the variable- specific-impulse magnetoplasma rocket (VASIMR) — that is capable of exhaust modulation at constant power. An electrodeless design enables the rocket to operate at power densities much greater than those of more conventional magnetoplasma or ion engines. An aspect of the engine design that affords a capability to achieve both high and variable specific impulse (Isp) places the VASIMR far ahead of anything available today. Inasmuch as this rocket can utilize hydrogen as its propellant, it can be operated at relatively low cost.

Posted in: Mechanics, Briefs

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Carbon Nanotube Bimorph Actuators and Force Sensors

These devices would make possible novel microelectromechanical systems, possibly even microscopic robots. A proposal has been made to develop bimorph actuators and force sensors based on carbon nanotubes. The proposed devices could make it possible to generate, sense, and control displacements and forces on a molecular scale, and could readily be integrated with conventional electronic circuits. These devices could also enable the development of a variety of novel microelectromechanical systems, including low-power mechanical signal processors, nanoscale actuators and force sensors, and even microscopic robots.

Posted in: Mechanics, Briefs, TSP

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Robot for Positioning Sensors in a Plant-Growth Chamber

The Advanced Life Support Automated Remote Manipulator (ALSARM) is a three-degree-of-freedom robotic system that positions an array of sensors inside a closed-system hydroponic chamber used in research on the production of biomass and the use of hydroponic subsystems of life-support systems. The array includes sensors to measure the light intensity, air temperature, infrared temperature, relative humidity, and airflow. The ALSARM operates under either automatic control by a personal computer or manual control through a teaching pendant (essentially, a hand-held box that contains switches and indicators wired to a plug for connection to the rest of the ALSARM control circuitry). The motivation for developing the ALSARM was the need to eliminate the leakage of the chamber atmosphere and the potential for contamination associated with the prior practice of opening the chamber so that technicians could enter to take environmental measurements. One especially notable feature of the ALSARM is a horizontal telescoping arm, through which power and signal cables for the sensors are routed. The cables are extended and retracted with the motion of the telescoping sections by use of a servomotor and gravitation, respectively.

Posted in: Mechanics, Briefs, TSP

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Magnetic/Extendible Boom Mechanism for Docking of Spacecraft

Docking loads can be smaller than those of prior mechanisms. The magnetic/extendible boom docking aid is an improved mechanism that enables two spacecraft to capture and structurally mate with each other without inducing the large (and frequently excessive) loads encountered in docking by use of prior docking mechanisms. The capability afforded by this mechanism should prove invaluable when applied to the International Space Station. This mechanism is relatively simple to construct, easily integrable into pre-existing docking hardware, and highly reliable.

Posted in: Mechanics, Briefs

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Vapor-Compression Solar Refrigerator Without Batteries

Practical refrigeration is powered by an environmentally benign source. A solar-powered vapor-compression refrigeration system developed for Johnson Space Center operates without batteries. The design of this system will make the cost of solar-powered refrigeration systems competitive and enable the use of such systems in long-distance spaceflights, military field operations, and other situations in which electric power for conventional refrigerators and freezers is unavailable.

Posted in: Mechanics, Briefs

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Airlocks for Pressurized Rovers

A report presents a survey of the design engineering and scientific literature on airlocks and on planetary-exploration vehicles ("rovers"), from the perspective of evaluating existing and potential design concepts for airlocks for pressurized rovers. The airlocks are the key to designing a pressurized rover that is useful and productive for the full range of activities and operational requirements. The report presents a representative embodiment of each of these three airlock types through illustrations of a "simplified rover." The report concludes with a cogent set of design recommendations and characteristics for the three types of airlocks that would be particularly relevant to the design of a highly capable pressurized planetary rover.

Posted in: Mechanics, Briefs, TSP

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