Tech Briefs

Electrochemical Disposal of Hydrazines in Water

This method offers advantages of safety, economy, and scalability.

An electrochemical method of disposal of hydrazines dissolved in water has been devised. The method is applicable to hydrazine (N2H4), to monomethyl hydrazine [also denoted by MMH or by its chemical formula, (CH3)HNNH2], and to unsymmetrical dimethyl hydrazine [also denoted UDMH or by its chemical formula, (CH3)2NNH2]. The method involves a room-temperature process that converts the hydrazine to the harmless products N2, H2O, and, in some cases, CO2. In comparison with prior methods of disposing of hydrazines, the present method is safer and less expensive.

Posted in: Briefs, Physical Sciences, Water treatment, Hydrazines, Chemicals

Resistively Heated SiC Nozzle for Generating Molecular Beams

This nozzle is more durable and efficient relative to its predecessors.

An improved nozzle has been developed to replace nozzles used previously in an apparatus that generates a substantially unidirectional beam of molecules passing through a vacuum at speeds of several kilometers per second. The need to replace the previous nozzles arose from a complex set of causes that can be summarized as follows:

The previous nozzles had short operational lifetimes because it was necessary to fabricate them from components made of several different materials that, when used together, do not last long at the high operating temperatures needed to generate the requisite high molecular speeds and To protect the vacuum chamber from excessive heating, it was necessary to surround the operating nozzle with a cooling shroud that robbed the nozzle of reflected heater power and thereby contributed to energy inefficiency.
Posted in: Briefs, TSP, Physical Sciences, Nozzles

Modeling Evaporation of Drops of Different Kerosenes

One model applies to all three classes of hydrocarbon constituents.

A mathematical model describes the evaporation of drops of a hydrocarbon liquid composed of as many as hundreds of chemical species. The model is intended especially for application to any of several types of kerosenes commonly used as fuels. Like evaporating- multicomponent- fuel-drop models described in several previous NASA Tech Briefs articles, the present model invokes the concept of continuous thermodynamics, according to which the chemical composition of the evaporating multicomponent liquid is described by use of a probability distribution function (PDF). However, as described below, the present model is more generally applicable than is its immediate predecessor.

Posted in: Briefs, TSP, Information Sciences, Computational fluid dynamics, Mathematical models, Hydrocarbons, Thermodynamics, Gases

A Robustly Stabilizing Model Predictive Control Algorithm

The algorithm can be applied to industrial and automotive systems.

A model predictive control (MPC) algorithm that differs from prior MPC algorithms has been developed for controlling an uncertain nonlinear system. This algorithm guarantees the resolvability of an associated finite-horizon optimal-control problem in a recedinghorizon implementation. Given a feasible solution to the finite-horizon optimal control problem at an initial time, resolvability implies the ability to solve the optimal control problem at subsequent times.

Posted in: Briefs, TSP, Information Sciences, Mathematical models

Development of Vapor-Phase Catalytic Ammonia Removal System

A report describes recent accomplishments of a continuing effort to develop the vapor-phase catalytic ammonia removal (VPCAR) process for recycling wastewater for consumption by humans aboard a spacecraft in transit to Mars. The VPCAR process is implemented by a system of highly integrated design in which some power consumption is accepted as a cost of minimizing the volume and mass of a wastewater-processing system and eliminating the need to resupply water. The core of the system is a wiped-film rotating-disk (WFRD) evaporator, which removes inorganic salts and nonvolatile organic compounds from the wastewater stream and concentrates these contaminants into a recycle-and-bleed stream. The WFRD evaporator is also part of a subsystem that distills water from the wastewater stream. This subsystem operates in a vacuum-vapor/compression distillation configuration in the temperature range from 20 to 65 °C. Volatile organic compounds and ammonia, distilled along with water, are oxidized to CO2, H2O, and N2O in a packed-bed, hightemperature catalytic reactor placed at the outlet of the vapor-phase compressor of the distillation subsystem. A VPCAR engineering demonstration unit is expected to be included in a humanrated simulation of a mission to Mars.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Waste management, Water pollution, Water treatment, Spacecraft

Several Developments in Space Tethers

Five reports address different aspects of development of tethers to be deployed from spacecraft in orbit around the Earth. The first report discusses proposed optoelectronic tracking of retroreflective objects located at intervals or of retroreflective coats along the entire length of a tether to measure lateral motions. The second report describes digitally controlled spooling machinery that retracts or extends a tape tether at controlled speed and tension in the spool isolated from uncontrolled tension on the outside. The third report discusses part of this machinery that pivots to accommodate misalignments between the deployed and spooled portions of the tether and contains rollers used to exert tension and speed control. The fourth report discusses aspects of designs of proposed electrodynamic tethers, which would be electrically conductive and would interact with the magnetic field of the Earth to exert forces to modify orbits of deploying spacecraft. The fifth report discusses electrical aspects of designs of electrodynamic tape tethers, including the use of solar cells or motional electromagnetic force to generate currents in tethers and the use of electron emitters and electron and ion collectors at opposite ends of tethers to make electrical contact with the thin plasma in surrounding space.

Posted in: Briefs, Mechanical Components, Mechanics, Spacecraft

Design Concept for a Nuclear Reactor-Powered Mars Rover

A report presents a design concept for an instrumented robotic vehicle (rover) to be used on a future mission of exploration of the planet Mars. The design incorporates a nuclear fission power system to provide long range, long life, and high power capabilities unachievable through the use of alternative solar or radioisotope power systems. The concept described in the report draws on previous rover designs developed for the 2009 Mars Science laboratory (MSL) mission to minimize the need for new technology developments.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Design processes, Nuclear energy, Robotics, Autonomous vehicles

Formation-Initialization Algorithm for N Spacecraft

A paper presents an algorithm to initialize a formation of N distributed spacecraft in deep space. Such formations will enable variable-baseline interferometers in future NASA missions designed to study the structure and origin of the universe. The algorithm described in the paper reflects some basic assumptions:

Each spacecraft is capable of omnidirectional radio communication with any other spacecraft, Each spacecraft is equipped with a limited field-of-view sensor relative position sensor (RPS) to measure the relative positions and velocities of other formation members, and Spacecraft maneuvers must satisfy Sun-angle pointing constraints to shield sensitive optical equipment from direct sunlight.
Posted in: Briefs, TSP, Mechanical Components, Mechanics, Mathematical models, Test equipment and instrumentation, Spacecraft

DNSs of Multicomponent Gaseous and Drop-Laden Mixing Layers Achieving Transition to Turbulence

A paper describes direct numerical simulations (DNSs) of three-dimensional mixing-layer flows undergoing transition to turbulence; the mixing layers may or may not be laden with evaporating liquid drops. In contrast to most studies in this field, the general case is investigated here where both the gas and the liquid drops’ composition encompasses a very large number of species. The simulations were performed using a mathematical model discussed in several prior NASA Tech Briefs articles; the prior studies described a laminar mixing layer, whereas the present study describes a mixing layer that has all attributes of turbulence. The model includes governing equations in an Eulerian and a Lagrangian reference frame for the gas and drops, respectively. To mathematically describe the myriad of species, the model relies on continuous thermodynamics concepts. The paper succinctly reiterates the model and discusses results of the new numerical simulations. Comparisons are performed with previous single-species similar simulations and with the laminar simulations using the same model. The paper presents several conclusions, the main one being that differences between single- and multi-species turbulent flows having the same initial conditions are so significant that neither experiments on, nor theoretical studies of, single-species flows are adequate as surrogates for studies of multi-species flows.

Posted in: Briefs, TSP, Physical Sciences, Computer simulation, Mathematical models, Turbulence

Noise-Canceling Helmet Audio System

Voice communication is enhanced by digital processing to suppress noise.

A prototype helmet audio system has been developed to improve voice communication for the wearer in a noisy environment. The system was originally intended to be used in a space suit, wherein noise generated by airflow of the spacesuit life-support system can make it difficult for remote listeners to understand the astronaut’s speech and can interfere with the astronaut’s attempt to issue vocal commands to a voice-controlled robot. The system could be adapted to terrestrial use in helmets of protective suits that are typically worn in noisy settings: examples include biohazard, fire, rescue, and diving suits.

Posted in: Briefs, Electronics & Computers, Audio equipment, Wireless communication systems, Product development, Helmets, Protective equipment, Spacesuits

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