Mechanical Components

The Future of Space Propulsion

A paper presents an overview of state of the art of space propulsion, oriented toward attempting to understand recent history in order to make some predictions about future developments. As used here, "space propulsion" refers generally to what are now called "spacelift" and "spacecraft propulsion." Further, as used here, "spacelift" refers generally to large rockets, associated equipment, and other resources for launching spacecraft into outer space, while "spacecraft propulsion" refers generally only to systems for propelling spacecraft once they are in outer space. The paper includes a summary of recent history of spacecraft propulsion, with greatest emphasis on spacelift systems, from the perspective of striving to maintain the military superiority and economic competitiveness of the United States in the face of the rapid international evolution of space technology. Advantages and disadvantages of various engine designs and propellant substances, and considerations of cost and development time, are discussed. Trends in spacelift (and, to a lesser extent, trends in spacecraft propulsion) are discussed. An attempt is made to predict the general nature of future developments by extrapolating the trends into the foreseeable future.

This work was done by John F. Remen and Glenn Liston of the Air Force Research Laboratory.

Posted in: Briefs, Mechanical Components, Technical reference, Rocket engines, Launch vehicles, Spacecraft
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Miniature Wheel-Leg Mobile Robots

Mini-Whegs™ are small mobile robots, designed according to abstracted cockroach locomotion principles, that can run and can climb obstacles taller than themselves. Mini-Whegs are derived from larger mobile robots denoted Whegs™, with modifications to reduce size, reduce the number of mechanisms, and increase relative mobility. The name "Whegs" originated as a contraction of "wheel-legs," referring to three-spoke appendages by means of which these robots move, as described below.

Posted in: Briefs, Mechanical Components, Wheels, Downsizing, Robotics
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Simulations of Brush Contacts of Homopolar Motor/Generators

A computational- simulation study of distributions of electric current and temperature in brushes and slip rings in two model homopolar- motor/generator configurations was performed in support of the development, by the U.S. Navy, of a superconducting homopolar motor/generator (SCHPMG) machine for ship propulsion. Electrical-contact performance (more specifically, brush/slip-ring contact performance) is a limiting factor in the performance of an SCHPMG machine. The present study and similar studies are needed to gain understanding of brush/slip-ring contact performance in order to enable optimal design of brushes for homopolar machines.

Posted in: Briefs, Mechanical Components
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Generic Miniature Airplane for Research and Development

The Air Force Research Laboratory has promulgated the geometrical design of a miniature airplane denoted the Generic Micro Aerial Vehicle (GENMAV). This design is intended to serve as a baseline for analyses of geometrical designs of other micro aerial vehicles (MAVs). As such, the GENMAV design is meant to be distributed openly among organizations engaged in research and development pertaining to MAVs. The need for the GENMAV or a similar standard of comparison has become more acute in recent years because of the increasing interest in the use of MAVs [a subset of uninhabited aerial vehicles (UAVs)] for diverse purposes, especially in military, law-enforcement, and rescue activities.

Posted in: Briefs, Mechanical Components
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Establishment of a Center for Defense Robotics

A document presents an overview of the recently established Joint Center for Unmanned Ground Vehicles (JC-UGV), located at the Army's Detroit Arsenal in Warren, Michigan. The JC-UGV is intended to become the central facility for managing all phases of the life cycles of military robotic ground vehicles: from concept; through research and development, acquisition, and sustainment; to the end of life. The JC-UGV is also intended to facilitate the move of the Robotic Systems Joint Program Office (RS-JPO) from Huntsville, Alabama to the Detroit Arsenal as part of a consolidation of military development and acquisition of all ground vehicles. An important part of the mission of the JC-UGV is to provide a system- integration laboratory that will include both robotic hardware and a distributed computational-simulation environment that will enable researchers and developers in the RS-JPO, industry, and academia to collaborate to solve complex problems. In addition to describing the aforementioned developments in detail, the document describes the organizational structure of the JC-UGV, discusses the role of the JC-UGV as one of several military organizations oriented toward lifecycle management, and summarizes JC-UGV university outreach, industry outreach, and pilot programs.

Posted in: Briefs, Mechanical Components
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Hybrid Three-Axis Vibration Reducers

Hybrid (passive/active) devices have been developed to reduce the magnitudes of possibly threedimensional vibrations coupled from vibrating equipment on platforms to bases that support the platforms. These hybrid devices are three-axis generalizations of singleaxis hybrid vibration reducers developed and reported previously. Each hybrid device includes rubber passive vibration-isolator pads, piezoelectric actuators, optional piezoelectric force sensors, and accelerometers. Each device operates in conjunction with a computer and control-and-actuation circuitry, which process accelerometer readings using feedforward and/or feedback control laws to excite the piezoelectric actuators with signals having amplitudes and phases chosen to minimize acceleration of the base.

Posted in: Briefs, Mechanical Components, Vibration
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Some Advances in Reducing Drag and Suppressing Convection

Theoretical and computational research has yielded some advances in the art of designing active feedforward and feedback controllers to suppress thermal convection and reduce drag (by suppressing turbulence) in boundary-layer flows. The advances include (1) improved means for designing reduced-order (and, hence, computationally more efficient) controllers and (2) discovery of a previously unknown phenomenon that could be exploited for feedforward control to reduce drag.

Posted in: Briefs, Mechanical Components, Electronic control systems, Drag
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Simulations of Stall and Stall Control in Turbocompressors

Anumerical-simulation study of stall and stall control in radial and axial compressor stages of gas turbine engines has been performed. This and other similar studies are needed because even though the adverse consequences of stall are well known and rudimentary stall-warning and stall-control systems are in use, the scientific basis for predicting and mitigating stall is not yet established.

Posted in: Briefs, Mechanical Components, Simulation and modeling, Compressors, Gas turbines
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Thrust-Augmented Nozzles for Rocket Engines

The thrust-augmented nozzle (TAN) has been invented as a means of obtaining high performance from a rocket engine both during liftoff at sea-level atmospheric pressure and later during flight under near-vacuum conditions. In effect, the TAN rocket engine amounts to a booster rocket engine contained entirely within a sustainer rocket engine, and very little weight is associated with the incorporation of the TAN portion. Heretofore, it has been difficult or impossible to design the same rocket engine to perform well at both extremes of ambient pressure.

Posted in: Briefs, Mechanical Components, Performance upgrades, Nozzles, Booster rocket engines, Reliability
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Thermal Design and Analysis of a Rocket-Engine TAN Injector

A subscale thrust - augmented - nozzle (TAN) rocket engine was designed, built, and hot-fire tested to demonstrate the validity of the TAN concept. As described in more detail in the immediately preceding article, in a TAN, during operation at sea level, thrust is augmented through injection and burning of secondary propellants (a fuel and an oxidizer) within the nozzle, downstream of the nozzle throat. The secondary propellants can be the same as, or different from, the primary propellants (the fuel and oxidizer burned during operation, in a near vacuum, in the absence of thrust augmentation).

Posted in: Briefs, Mechanical Components, Propellants, Nozzles, Booster rocket engines, Fuel injection
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