Mechanical & Fluid Systems

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

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Compact, Precise Inertial Rotation Sensors for Spacecraft

A document describes a concept for an inertial sensor for measuring the rotation of an inertially stable spacecraft around its center of gravity to within 100 microarc- seconds or possibly even higher precision. Whereas a current proposal for a spacecraft-rotation sensor of this accuracy requires one spacecraft dimension on the order of ten meters, a sensor according to this proposal could fit within a package smaller than 1 meter and would have less than a tenth of the mass. According to the concept, an inertial mass and an apparatus for monitoring the mass would be placed at some known distance from the center of gravity so that any rotation of the spacecraft would cause relative motion between the mass and the spacecraft. The relative motion would be measured and, once the displacement of the mass exceeded a prescribed range, a precisely monitored restoring force would be applied to return the mass to a predetermined position. Measurements of the relative motion and restoring force would provide information on changes in the attitude of the spacecraft. A history of relative- motion and restoring-force measurements could be kept, enabling determination of the cumulative change in attitude during the observation time.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Cargo-Positioning System for Next-Generation Spacecraft

A report discusses a proposed system for mounting loaded pallets in the cargo bay of a next-generation space-shuttle-like spacecraft, such that the center of mass of the cargo would lie within a 1-in. (2.54- cm) cube that would also contain the center of mass of the spacecraft. The system would include (1) an algorithm for planning the locations of the pallets, given the geometric and weight properties of the pallets, and the geometric restrictions of the cargo bay; (2) quick-connect/ quick-disconnect mounting mechanisms similar to those now used on air hoses; (3) other mounting mechanisms, comprising mostly spring-loaded pins, in a locking subsystem that would prevent shifting of the pallets under load; and (4) mechanisms for performing fine position adjustments to satisfy the center-of-mass requirement. The position-adjusting mechanisms would be motor-driven lead-screw mechanisms in groups of three — one for positioning each pin of the locking subsystem along each of three mutually perpendicular coordinate axes. The system also would include a triple threaded screw that would provide compensation for thermal expansion or contraction of the spacecraft.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Buckling and Fracture Analysis of Composite Skin-Stringer Panel Using VCCT and FEA Software

New finite element analysis simulation capabilities predict crack propagation in composites. In the continuing goal of developing products with better performance at a lower cost, composites are becoming increasingly prevalent in the aerospace industry. Composite structures offer exceptional performance due to their high strength at a low weight. Additionally, one large integrated composite component can replace ten or more traditional metal parts, dramatically reducing manufacturing costs. For the first time in the aviation industry, companies are beginning to use composites for primary load-bearing components. Boeing announced that the new 787 aircraft will be the first airliner to use composite materials in the majority of the aircraft construction.

Posted in: Briefs, Mechanical Components, Mechanics

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Large Deployable Reflectarray Antenna

A report discusses a 7-meter-diameter reflectarray antenna that has been conceived in a continuing effort to develop large reflectarray antennas to be deployed in outer space. Major underlying concepts were reported in three prior NASA Tech Briefs articles: “Inflatable Reflectarray Antennas” (NPO-20433), Vol. 23, No. 10 (October 1999), page 50; “Tape-Spring Reinforcements for Inflatable Structural Tubes” (NPO- 20615), Vol. 24, No. 7 (July 2000), page 58; and “Self-Inflatable/Self-Rigidizable Reflectarray Antenna” (NPO-30662), Vol. 28, No. 1 (January 2004), page 61. Like previous antennas in the series, the antenna now proposed would include a reflectarray membrane stretched flat on a frame of multiple inflatable booms. The membrane and booms would be rolled up and folded for compact stowage during transport. Deployment in outer space would be effected by inflating the booms to unroll and then to unfold the membrane, thereby stretching the membrane out flat to its full size. The membrane would achieve the flatness for a Ka-band application. The report gives considerable emphasis to designing the booms to rigidify themselves upon deployment: for this purpose, the booms could be made as spring-tape-reinforced aluminum laminate tubes like those described in two of the cited prior articles.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Periodically Discharging, Gas-Coalescing Filter

In effect, small bubbles would be made to coalesce into very large ones. A proposed device would remove bubbles of gas from a stream of liquid (typically water), accumulate the gas, and periodically release the gas, in bulk, back into the stream. The device is intended for use in a flow system (1) in which there is a requirement to supply bubble-free water to a downstream subsystem and (2) that includes a sensor and valves, just upstream of the subsystem, for sensing bubbles and diverting the flow from the subsystem until the water stream is again free of bubbles. By coalescing the gas bubbles and then periodically releasing the accumulated gas, the proposed device would not contribute to net removal of gas from the liquid stream; nevertheless, it would afford an advantage by reducing the frequency with which the diverter valves would have to be activated.

Posted in: Briefs, Mechanical Components, Mechanics

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System Would Detect Foreign-Object Damage in Turbofan Engine

Vibration-sensor and gas-path-analysis data would be fused. A proposed data-fusion system, to be implemented mostly in software, would further process the digitized and preprocessed outputs of sensors in a turbofan engine to detect foreign-object damage (FOD) [more precisely, damage caused by impingement of such foreign objects as birds, pieces of ice, and runway debris]. The proposed system could help a flight crew to decide what, if any, response is necessary to complete a flight safely, and could aid mechanics in deciding what post-flight maintenance action might be needed.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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