Mechanical & Fluid Systems

Stable Satellite Orbits for Global Coverage of the Moon

A document proposes a constellation of spacecraft to be placed in orbit around the Moon to provide navigation and communication services with global coverage required for exploration of the Moon. There would be six spacecraft in inclined elliptical orbits: three in each of two orthogonal orbital planes, suggestive of a linked-chain configuration. The orbits have been chosen to (1) provide 99.999-percent global coverage for ten years and (2) to be stable under perturbation by Earth gravitation and solar-radiation pressure, so that no deterministic firing of thrusters would be needed to maintain the orbits. However, a minor amount of orbit control might be needed to correct for such unmodeled effects as outgassing of the spacecraft.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Architecture, Attitude control, Satellite communications, Architecture, Attitude control, Satellite communications
Read More >>

Oil Recycling System Controls Contamination

OilTrac™ fluid maintenance program/oil recycling system
COMO Filtration Systems
Janesville, WI
608-756-3838
www.como.biz
Posted in: Application Briefs, Green Design & Manufacturing, Recycling Technologies, Fluid Handling, Recycling, Lubricating oils
Read More >>

Improved Gear Shapes for Face Worm Gear Drives

These shapes offer potential for increasing precision and reducing vibration and noise.

Shapes different from the traditional ones have been proposed for face worm gears and for conical and cylindrical worms that mesh with them. The proposed shapes are based on the concept of generating a face worm gear surface by use of a tilted head cutter instead of by the traditional use of a hob. (As used here, “head cutter” is also meant to signify, alternatively, a head grinding tool.)The gear-surface-generation equipment would be similar to that used for generation of spiral bevel and hypoid gears. In comparison with the corresponding traditional hob, a tilted head cutter according to the proposal would be larger, could be fabricated with greater precision, and would enable the generation of gear surfaces with greater precision and greater productivity.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Computer simulation, Fabrication, Gears
Read More >>

Two High-Temperature Foil Journal Bearings

These are prototypes of foil bearings for aircraft gas turbine engines.

An enlarged, high-temperature -compliant foil bearing has been built and tested to demonstrate the feasibility of such bearings for use in aircraft gas turbine engines. At 150 mm in diameter, this is the largest foil bearing known to date. This bearing is a scaled-up version of a patented 100-mm-diameter foil bearing, augmented by coating the foil with a proprietary high-temperature material. In a companion development, a foil bearing as described above has been combined with a 150-mm-diameter active magnetic bearing to make a hybrid foil magnetic bearing.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Bearings, Gas turbines
Read More >>

Using Plates To Represent Fillets in Finite-Element Modeling

Structural deflections are approximated by use of simplified computational submodels of fillets

A method that involves the use of fictitious plate elements denoted bridge plates has been developed for representing the stiffnesses of fillets in finiteelement calculations of deflections, stresses, and strains in structures. In the absence of this method, it would be necessary to either neglect the effects of fillets to minimize the computational burden or else incur a large computational burden by using complex computational models to represent the fillets accurately. In effect, the bridge plates of the present method are reduced-order models of fillets that do not yield accurate stresses within fillets but do make it possible to accurately calculate the dynamic characteristics of the structure and to approximate the effects of fillets on stresses and strains elsewhere in a structure that contains the fillets. Such approximations are accurate enough for final modal analysis and preliminary stress analyses.

Posted in: Briefs, Mechanical Components, Mechanics, Aircraft structures, Finite element analysis
Read More >>

Stochastic Representation of Chaos Using Terminal Attractors

Fictitious control forces stabilize what would otherwise be unstable computed trajectories.

A nonlinear version of the Liouville equation based on terminal attractors is part of a mathematical formalism for describing postinstability motions of dynamical systems characterized by exponential divergences of trajectories leading to chaos (including turbulence as a form of chaos). The formalism can be applied to both conservative systems (e.g., multibody systems in celestial mechanics) and dissipative systems (e.g., viscous fluids).

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Trajectory control, Mathematical models, Turbulence
Read More >>

Lunar Constellation of Frozen Elliptical Inclined Orbits

A document discusses the design of orbits of spacecraft for relaying communications between Earth stations and robotic and human explorers in craters in one of the polar regions on the Moon. In simplest terms, the basic problem is to design a constellation of orbits to provide continuous and preferably redundant communication coverage of one of the poles with a minimal number of spacecraft and little or no controlled maneuvering of the spacecraft to maintain the orbits. The design method involves the use of analytical techniques for initial selection of orbits, followed by a numerical procedure for tuning the coverage of the constellation to obtain a design. In an example application, the method leads to a constellation of three spacecraft having elliptical, inclined orbits, the apoapsides of which would remain in the hemisphere (North or South) containing the pole of interest. The orbits would be stable and would maintain the required spacecraft formation for at least 10 years, without need for controlled maneuvering if gravitation is the only force considered to affect the orbits. A small amount of controlled maneuvering would be needed to counteract effects of solar-radiation pressure and other perturbations.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Telecommunications, Telecommunications, Spacecraft
Read More >>

Custom-Built Machining Centers Create Telescope Mirrors

Custom horizontal machining centers
Mitsui Seiki USA
Franklin Lakes, NJ
201-337-1300
www.mitsuiseiki.com
Posted in: Application Briefs, Mechanical Components, Mirrors, Machining processes, Manufacturing equipment and machinery
Read More >>

Modification of a Limbed Robot to Favor Climbing

A kinematically simplified design affords several benefits.

The figure shows the LEMUR IIb, which is a modified version of the LEMUR II — the second generation of the Limbed Excursion Mechanical Utility Robot (LEMUR). Except as described below, the LEMUR IIb hardware is mostly the same as that of the LEMUR II. The IIb and II versions differ in their kinematic configurations and characteristics associated with their kinematic configurations. The differences are such that relative to the LEMUR II, the LEMUR IIb is simpler and is better suited to climbing on inclined surfaces.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Kinematics, Performance upgrades, Product development, Robotics
Read More >>

Controlling Herds of Cooperative Robots

A document poses, and suggests a program of research for answering, questions of how to achieve autonomous operation of herds of cooperative robots to be used in exploration and/or colonization of remote planets. In a typical scenario, a flock of mobile sensory robots would be deployed in a previously unexplored region, one of the robots would be designated the leader, and the leader would issue commands to move the robots to different locations or aim sensors at different targets to maximize scientific return. It would be necessary to provide for this hierarchical, cooperative behavior even in the face of such unpredictable factors as terrain obstacles. A potential-fields approach is proposed as a theoretical basis for developing methods of autonomous command and guidance of a herd. A survival-of-the-fittest approach is suggested as a theoretical basis for selection, mutation, and adaptation of a description of (1) the body, joints, sensors, actuators, and control computer of each robot, and (2) the connectivity of each robot with the rest of the herd, such that the herd could be regarded as consisting of a set of artificial creatures that evolve to adapt to a previously unknown environment. A distributed simulation environment has been developed to test the proposed approaches in the Titan environment. One blimp guides three surface sondes via a potential field approach. The results of the simulation demonstrate that the method used for control is feasible, even if significant uncertainty exists in the dynamics and environmental models, and that the control architecture provides the autonomy needed to enable surface science data collection.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Computer simulation, Architecture, Electronic control systems, Architecture, Electronic control systems, Fleet management, Robotics, Autonomous vehicles
Read More >>

The U.S. Government does not endorse any commercial product, process, or activity identified on this web site.