Mechanical & Fluid Systems

Simulating Operation of a Planetary Rover

Simulating Operation of a Planetary Rover

Rover Analysis, Modeling, and Simulations (ROAMS) is a computer program that simulates the operation of a robotic vehicle (rover) engaged in exploration of a remote planet. ROAMS is a rover-specific extension of the DARTS and Dshell programs, described in prior NASA Tech Briefs articles, which afford capabilities for mathematical modeling of the dynamics of a spacecraft as a whole and of its instruments,actuators, and other subsystems. ROAMS incorporates mathematical models of kinematics and dynamics of rover mechanical subsystems, sensors, interactions with terrain, solar panels and batteries, and onboard navigation and locomotion-control software. ROAMS provides a modular simulation framework that can be used for analysis, design, development, testing,and operation of rovers. ROAMS can be used alone for system performance and trade studies. Alternatively, ROAMS can be used in an operator-in-the-loop or flight-software closed-loop environment. ROAMS can also be embedded within other software for use in analysis and development of algorithms,or for Monte Carlo studies, using a variety of terrain models, to generate performance statistics. Moreover, taking advantage of real-time features of the underlying DARTS/Dshell simulation software, ROAMS can also be used for real-time simulations.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Computer simulation, Computer software / hardware, Computer software and hardware, Computer software / hardware, Computer software and hardware, Robotics, Autonomous vehicles

Silicone-Rubber Microvalves Actuated by Paraffin

Relative to other microvalves, these would be simpler.

Microvalves containing silicone-rubber seals actuated by heating and cooling of paraffin have been proposed for development as integral components of microfluidic systems. In comparison with other microvalves actuated by various means (electrostatic, electro-magnetic, piezoelectric, pneumatic, and others), the proposed valves (1) would contain simpler structures that could be fabricated at lower cost and (2) could be actuated by simpler (and thus less expensive) control systems.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Elastomers, Valves

Flexible Shields for Protecting Spacecraft Against Debris

A report presents the concept of Flexshield —a class of versatile, light-weight, flexible shields for protecting spacecraft against impacts by small meteors and orbiting debris. The Flexshield concept incorporates elements of, but goes beyond, prior space-craft-shielding concepts, including those of Whipple shields and, more recently, multi-shock shields and multi-shock blankets. A shield of the Flexshield type includes multiple outer layers (called “bumpers” in the art) made, variously, of advanced ceramic and/or polymeric fibers spaced apart from each other by a lightweight foam.As in prior such shields, the bumpers serve to shock an impinging hypervelocity particle, causing it to disintegrate, vaporize, and spread out over a larger area so that it can be stopped by an innermost layer (back sheet). The flexibility of the fabric layers and compressibility of the foam make it possible to compress and fold the shield for transport,then deploy the shield for use. The shield can be attached to a spacecraft by use of snaps, hook-and-pile patches,or other devices. The shield can also contain multilayer insulation material, so that it provides some thermal protection in addition to mechanical protection.

Posted in: Briefs, Mechanical Components, Mechanics, Protective structures, Spacecraft

Controllable Curved Mirrors Made From Single-Layer EAP Films

A document proposes that light-weight, deployable, large- aperture, controllable curved mirrors made of reflectively coated thin electroactive-polymer (EAP) films be developed for use in spaceborne microwave and optical systems. In these mirrors, the EAP films would serve as both structures and actuators. EAPs that are potentially suit- able for such use include piezoelectric, electrostrictive, ferroelectric, and di-electric polymers. These materials exhibit strains proportional to the squares of applied electric fields. Utilizing this phenomenon,a curved mirror according to the proposal could be made from a flat film, upon which a nonuniform electrostatic potential (decreasing from the center toward the edge) would be imposed to obtain a required curvature. The effect would be analogous to that of an old-fashioned metalworking practice in which a flat metal sheet is made into a bowl by hammering it repeatedly, the frequency of hammer blows decreasing with distance from the center. In operation, the nonuniform electrostatic potential could be imposed by use of an electron gun. Calculations have shown that by use of a single-layer film made of a currently available EAP, it would be possible to control the focal length of a 2m-diameter mirror from infinity to 1.25 m.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Mirrors, Optics, Optics, Polymers

Centrifugal Adsorption System

Notable features include efficient collection of bioproducts and removal of bubbles.

The centrifugal adsorption cartridge system (CACS) is an apparatus that recovers one or more bioproduct(s) from a dilute aqueous solution or suspension flowing from a bioreactor. The CACS can be used both on Earth in unit gravity and in space in low gravity. The CACS can be connected downstream from the bioreactor; alternatively, it can be connected into a flow loop that includes the bioreactor so that the liquid can be recycled. A centrifugal adsorption cartridge in the CACS (see figure) includes two concentric cylinders with a spiral ramp between them. The volume between the inner and outer cylinders, and between the turns of the spiral ramp is packed with an adsorbent material. The inner cylinder is a sieve tube covered with a gas- permeable, hydrophobic membrane.

Posted in: Briefs, Mechanical Components, Mechanics, Containers, Biomaterials

Ultrasonic Apparatus for Pulverizing Brittle Material

Characteristics include light weight, low preload, and low power demand.

The figure depicts an apparatus that pulverizes brittle material by means of a combination of ultrasonic and sonic vibration, hammering, and abrasion. The basic design of the apparatus could be specialized to be a portable version for use by a geologist in collecting powdered rock samples for analysis in the field or in a laboratory. Alternatively, a larger benchtop version could be designed for milling and mixing of precursor powders for such purposes as synthesis of ceramic and other polycrystalline materials or preparing powder samples for x-ray diffraction or x-ray fluorescence measurements to determine crystalline structures and compositions. Among the most attractive characteristics of this apparatus are its light weight and the ability to function without need for a large preload or a large power supply: It has been estimated that a portable version could have a mass <0.5 kg, would consume less than 1 W·h of energy in milling a 1-cm 3 volume of rock, and could operate at a preload <10 N.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Particulate matter (PM), Manufacturing equipment and machinery, Milling, Composite materials, Acoustics, Acoustics, Test equipment and instrumentation

Liquid-Metal-Fed Pulsed Plasma Thrusters

A short document proposes liquid- metal- fed pulsed plasma thrusters for small spacecraft. The propellant liquid for such a thruster would be a low- melting- temperature metal that would be stored molten in an unpressurized, heated reservoir and would be pumped to the thruster by a magneto- hydrodynamic coupler. The liquid would enter the thruster via a metal tube inside an electrically insulating ceramic tube. A capacitor would be connected between the outlet of the metal tube and the outer electrode of the thruster. The pumping would cause a drop of liquid to form at the outlet, eventually growing large enough to make contact with the outer electrode. Contact would close the circuit through the capacitor, causing the capacitor to discharge through the drop. The capacitor would have been charged with enough energy that the discharge would vaporize, ionize, and electromagnetically accelerate the contents of the metal drop. The resulting plasma would be ejected at a speed of about 50 km/s. The vaporization of the drop would reopen the circuit through the capacitor, enabling recharging of the capacitor. As pumping continued, a new drop would grow and the process would repeat.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Capacitors, Capacitors, Spacecraft fuel, Ceramics, Metals, Liquid propellant rocket engines

Attitude Control for a Solar-Sail Spacecraft

A report describes the personal radiation protection system (PRPS), which has been invented for use on the International Space Station and other spacecraft. The PRPS comprises walls that can be erected inside spacecraft, where and when needed, to reduce the amount of radiation to which personnel are exposed. The basic structural modules of the PRPS are pairs of 1-in. (2.54-cm)-thick plates of high-density polyethylene equipped with fasteners. The plates of each module are assembled with a lap joint. The modules are denoted bricks. A report discusses the attitude-control system of a proposed spacecraft that would derive at least part of its propulsion from a solar sail. The spacecraft would include a bus module containing three or more reaction wheels, a boom attached at one end to the bus module and attached at its other end to a two-degree-of-freedom (DOF) gimbal at the nominal center of mass of a sail module. Each DOF of the gimbal could be independently locked against rotation or allowed to rotate freely. By using the reaction wheels to rotate the bus when at least one gimbal DOF was in the free state, the center of mass (CM) of the spacecraft could be shifted relative to the center of pressure (CP) on the solar sail. The resulting offset between the CM and CP would result in a solar torque, which could be used to change the attitude of the spacecraft. The report discusses numerous aspects of the dynamics and kinematics of the spacecraft, along with the relationships between these aspects and the designs of such attitude-control-system components as sensors, motors, brakes, clutches, and gimbals.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Attitude control, Attitude control, Sun and solar, Protective structures, Radiation protection, Spacecraft

Estimating Basic Preliminary Design Performances of Aerospace Vehicles

Aerodynamics and Performance Estimation Toolset is a collection of four software programs for rapidly estimating the preliminary design performance of aerospace vehicles represented by doing simplified calculations based on ballistic trajectories, the ideal rocket equation, and supersonic wedges through standard atmosphere. The program consists of a set of Microsoft Excel worksheet subprograms. The input and output data are presented in a user-friendly format, and calculations are performed rapidly enough that the user can iterate among different trajectories and/or shapes to perform "what-if " studies. Estimates that can be computed by these programs include:

Ballistic trajectories as a function of departure angles, initial velocities, initial positions, and target altitudes; assuming point masses and no atmosphere. The program plots the trajectory in two-dimensions and outputs the position, pitch, and velocity along the trajectory. The "Rocket Equation" program calculates and plots the trade space for a vehicle's propellant mass fraction over a range of specific impulse and mission velocity values, propellant mass fractions as functions of specific impulses and velocities. "Standard Atmosphere" will estimate the temperature, speed of sound, pressure, and air density as a function of altitude in a standard atmosphere, properties of a standard atmosphere as functions of altitude. "Supersonic Wedges" will calculate the free-stream, normal-shock, oblique-shock, and isentropic flow properties for a wedge-shaped body flying super-sonically through a standard atmosphere. It will also calculate the maximum angle for which a shock remains attached, and the minimum Mach number for which a shock becomes at-angle, altitude, and Mach number.
Posted in: Briefs, Mechanical Components, Mechanics, Design processes, Computer software / hardware, Computer software and hardware, Computer software / hardware, Computer software and hardware

Bubble Eliminator Based on Centifugal Flow

This device contains no moving parts.

The fluid bubble eliminator (FBE) is a device that removes gas bubbles from a flowing liquid. The FBE contains no moving parts and does not require any power input beyond that needed to pump the liquid. In the FBE, the buoyant force for separating the gas from the liquid is provided by a radial pressure gradient associated with a centrifugal flow of the liquid and any entrained bubbles. A device based on a similar principle is described in Centrifugal Adsorption Cartridge System (Nasa Tech Briefs August 2004, MSC-22863), which appears on page 48 of this issue. The FBE was originally intended for use in filtering bubbles out of a liquid flowing relatively slowly in a bioreactor system in microgravity. Versions that operate in normal Earth gravitation at greater flow speeds may also be feasible.

Posted in: Briefs, Mechanical Components, Mechanics, Gases, Test equipment and instrumentation

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