Mechanical & Fluid Systems

Simulation and Testing of Maneuvering of a Planetary Rover

A report discusses the development of a computational model of a Mars Explorer Rover maneuvering across terrain under varying conditions. The model is used to increase understanding of the rover dynamics. Increased understanding is helpful in planning further tests and in extending the operational range of the rover to terrain conditions that would otherwise have to be avoided in a conservative approach. The model is implemented within MSC.ADAMS®, a commercial suite of computer programs for simulating a variety of automotive and aeronautical mechanical systems. Following its initial formulation, the model has been successively refined in an iterative process of simulation, testing on simulated terrain, correlation of simulation results with test results, and adjustment of model parameters to increase degrees of matching between simulation and test results. In particular, three aspects of the model have been refined, as follows:

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Simulation and modeling, Terrain, Autonomous vehicles
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Retaining Rings for Industrial Fastening Applications

Retaining rings are selected based on material, finish, and a variety of application parameters.

A discussion of retaining rings inevitably must begin with a debunking of myths; namely, that one style of retaining ring will function better than all other types in all instances. No one retaining ring style is better than another. Rather, the parameters of an application actually determine which retaining ring is best to use, and this can vary from assembly to assembly. Selecting the correct type of retaining ring based on variables such as installation/removal requirements, anticipated thrust load, and end-play take-up can ensure the retaining ring chosen will perform reliably, while significantly reducing fastener costs.

Posted in: Briefs, Mechanical Components, Mechanics, Fastening, Parts
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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
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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
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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
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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
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Six-Message Electromechanical Display System

This system would overcome the three-message limit of prior such systems.

A proposed electromechanical display system would be capable of presenting as many as six distinct messages. This system would be a more capable and more complex successor to the proposed system reported in “Four-Message Electromechanical Display System” (MFS-31368), NASA Tech Briefs, Vol. 24, No. 4 (April 2000), page 32. In contrast to the now-proposed six-message system and the previously proposed four-message system, a typical conventional electromechanical display system is limited to three messages.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Displays, Displays
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Motorcycle Design Optimized With Finite-Element Software

Sierra Design Engineering, Mount Aukum, California
BUB Enterprises, Grass Valley, California;

and

ALGOR, Inc., Pittsburgh, Pennsylvania

FEA software was used to analyze key components of a racing streamliner.

A streamliner motorcycle designed and built by Sierra Design Engineering and BUB Enterprises achieved a new world-record speed of 350.884 miles per hour last year at the Bonneville Salt Flats in Utah. In 1989, the original engine and transmission were designed by Joe Harralson of Sierra Design Engineering, with the rest of the streamliner being designed and built by BUB Enterprises.

Posted in: Briefs, Mechanical Components, Mechanics, Design processes, Finite element analysis, Two or three wheeled vehicles
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Low-Friction, High-Stiffness Joint for Uniaxial Load Cell

Friction and hysteresis are minimized.

A universal-joint assembly has been devised for transferring axial tension or compression to a load cell. To maximize measurement accuracy, the assembly is required to minimize any moments and non-axial forces on the load cell and to exhibit little or no hysteresis. The requirement to minimize hysteresis translates to a requirement to maximize axial stiffness (including minimizing backlash) and a simultaneous requirement to minimize friction. In practice, these are competing requirements, encountered repeatedly in efforts to design universal joints. Often, universal-joint designs represent compromises between these requirements.

Posted in: Briefs, Mechanical Components, Mechanics, Design processes, Measurements, Universal joints
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Magnet-Based System for Docking of Miniature Spacecraft

The capture envelope for this system is approximated by a 5-in. (12.7-cm) cube.

A prototype system for docking a miniature spacecraft with a larger spacecraft has been developed by engineers at the Johnson Space Center. Engineers working on Mini AERCam, a free-flying robotic camera, needed to find a way to successfully dock and undock their miniature spacecraft to refuel the propulsion and recharge the batteries. The subsystems developed (see figure) include (1) a docking port, designed for the larger spacecraft, which contains an electromagnet, a ball lock mechanism, and a service probe; and (2) a docking cluster, designed for the smaller spacecraft, which contains either a permanent magnet or an electromagnet.

Posted in: Briefs, Mechanical Components, Mechanics, Attitude control, Electromagnetic compatibility, Attitude control, Electromagnetic compatibility, Robotics, Magnetic materials, Refueling, Spacecraft
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