Special Coverage

Technique Provides Security for Multi-Robot Systems
Bringing New Vision to Laser Material Processing Systems
NASA Tests Lasers’ Ability to Transmit Data from Space
Converting from Hydraulic Cylinders to Electric Actuators
Automating Optimization and Design Tasks Across Disciplines
Vibration Tables Shake Up Aerospace and Car Testing
Supercomputer Cooling System Uses Refrigerant to Replace Water
Computer Chips Calculate and Store in an Integrated Unit
Electron-to-Photon Communication for Quantum Computing

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: Briefs, TSP, Mechanical Components, Mechanics, Downsizing, Spacecraft fuel, Rocket engines, Spacecraft

Using Photosynthetic Bacteria To Make Oxygen on Mars

A report presents a proposal to harness photosynthetic bacteria to generate essential materials needed during human and robotic exploration on the surface of Mars. Utilizing an extremely small amount of H2O and an ample amount of CO2 (and N2 and/or other elements and compounds) already present in the Martian environment, along with sunlight as the source of energy, the bacteria would produce O2 and carbon-containing compounds (and nitrogen-containing compounds). The O2 could be used to support human respiration and to burn fuels; the other compounds could be used, variously, to produce food and fuel or to grow green plants other than bacteria to produce food and fuel. The proposal would exploit the inherent capability of bacteria to reproduce and to adapt to changing environmental conditions. Bacteria to implement the proposal would be bred selectively and/or be genetically engineered for the intended applications, starting from candidate strains of natural terrestrial purple and green bacteria and cyanobacteria that can withstand harsh environments.

Posted in: Briefs, TSP, Bio-Medical, Medical, Bacteria, Life support systems, Oxygen

DNS of a Transitional Supercritical C7H16/N2 Mixing Layer

This report discusses direct numerical simulations (DNS) of a mixing layer, between a nitrogen stream and a heptane stream initially flowing at different velocities, under supercritical conditions and undergoing a transition to turbulence. Thermodynamically, supercritical conditions prevail when either the temperature or the pressure exceeds its critical value; the critical regime is in particular characterized by the existence of a single phase. The governing conservation equations were formulated according to fluctuation-dissipation (FD) theory, in which the low-pressure typical transport properties (viscosity, diffusivity, and thermal conductivity) are complemented, at high pressure, by a thermal-diffusion factor.

Posted in: Briefs, Physical Sciences, Computer simulation, Mathematical analysis, Thermodynamics

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: Briefs, Mechanical Components, Mechanics, Hydrogen fuel, Product development, Electro-thermal engines, Rocket engines

Current-Signature Sensor for Diagnosing Solenoid Valves

Changes in current signatures are indicators of electrical and mechanical deterioration.

The "smart" current-signature sensor is an instrument that noninvasively measures and analyzes steady-state and transient components of the magnetic field of (and, thus, indirectly, the electric current in) a solenoid valve during normal operation. The instrument is being developed to enable continuous monitoring of integrity and operational status of solenoid valves without need for interrupting operation to conduct frequent inspections. The instrument is expected to be capable of warning of imminent solenoid-valve failures so that preventive repairs can be performed. The basic instrument concept should also be adaptable to similar monitoring of electromechanical devices, other than solenoid valves, that are required to be highly reliable.

Posted in: Briefs, Electronics & Computers, Sensors and actuators, Valves, Test equipment and instrumentation

Si Microsensor Baseplates With Low Parasitic Capacitances

An improved design also reduces thermal-expansion mismatches.

An improved design for baseplates in silicon microsensors reduces parasitic capacitances between adjacent coplanar electrodes. It also reduces thermal-expansion mismatches, which are present in baseplates of older design.

Posted in: Briefs, TSP, Electronics & Computers, Sensors and actuators, Performance upgrades, Silicon alloys, Parts

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: Briefs, TSP, Mechanical Components, Mechanics, Sensors and actuators, Nanomaterials

Built-in "Health Check" for Pressure Transducers

Calibrations could be verified approximately, without removing transducers to calibration laboratories.

"Health check" would be built into pressure transducers, according to a proposal, to enable occasional, rapid, in situ testing of the transducers between normal pressure-measurement operations. The health check would include relatively simple devices that, upon command, would provide known stimuli to the transducers. The responses of the pressure transducers to these stimuli would be analyzed to quantify (at least approximately) deviations from the responses expected from previous rigorous calibrations. On the basis of such an analysis, a given pressure transducer could be removed from service, rigorously recalibrated, or continued in use with corrections applied for calibration drift. The use of the health check could provide timely warnings of pressure-transducer malfunctions and make it possible to retain confidence in the calibrations of pressure transducers while reducing the frequency with which they are replaced or subjected to full laboratory recalibration.

Posted in: Briefs, TSP, Physical Sciences, Test equipment and instrumentation

Improvements in a Fast Transient-Voltage Recorder

The instrument is now more readily adjustable and reconfigurable.

Some improvements have been made in an instrument designed expressly for recording lightning-induced transient voltages on power and signal cables. The instrument as it existed prior to the improvements was described in "Fast Transient-Voltage Recorder" (KSC-11991), NASA Tech Briefs, Vol. 23, No. 10 (October 1999), page 6a.

Posted in: Briefs, Electronics & Computers, Electric cables, Performance upgrades, Lightning, Test equipment and instrumentation

Improved Field-Emission Cathodes

Arrays of microscopic cathodes would resist poisoning and sputtering.

Microscopic cathodes based on field emission (in contradistinction to thermionic emission) are undergoing development with a view toward using them as miniature or scalable sources of electrons in diverse applications that could include spacecraft thrusters, semiconductor-fabrication equipment, flat-panel display devices, miniature x-ray sources, and electrodynamic tethers and mass spectrometers. Increasing current levels can be accomplished by increasing the number of tips in an array. The basic concepts of utilizing field-emission cathodes for such applications and of scaling up by enlarging arrays are not new; the novel aspect of the present developmental cold cathodes lies in a microfabricated cathode lens and ion repeller (CLAIR) similar to an Einzel lens which will enable the integration of field-emission cathodes with electric propulsion systems, electrodynamic tethers, and instruments while meeting performance and lifetime requirements.

Posted in: Briefs, TSP, Electronics & Computers, Electrical systems

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