Mechanical & Fluid Systems

Synchronizing Attitudes and Maneuvers of Multiple Spacecraft

A report discusses the problem of controlling the maneuvers of multiple spacecraft flying in formation and, more specifically, making the entire formation rotate about a given axis and synchronizing the rotations of the individual spacecraft with the rotation of the formation. Such formation flying is contemplated for mission in which the spacecraft would serve as platforms for long-baseline-interferometer elements and the synchronized rotations would be needed for slewing of the interferometers. Starting from (1) a particle model of the dynamics of the spacecraft formation, (2) a rigid-body model of the spacecraft-attitude dynamics, and (3) an assumption that one spacecraft would serve as the reference for the positions and orientations of the other spacecraft, the report presents a mathematical derivation of control laws for formation flying in the absence of gravitation and disturbances. A simplified control law suitable for implementation is also derived. Results of a computer simulation for three spacecraft flying in a triangular formation are presented to show that the control laws are effective.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Attitude control, Flight control systems, Spacecraft

Mesoscopic Winch for Precise Extension and Retraction

A cable could be drawn in submicron steps over a range of ≈1 m.

A proposed lightweight, micromachined winch would have microscopic structural details and mesoscopic overall dimensions and would be capable of generating bidirectional macro- scopic motion (maximum cable extension or retraction ≈1 m) with submicron increments. Winches like this one could be useful for actuating small mechanisms in scientific instruments and robots: examples of such mechanisms include translation stages; slide shutters and filters for imaging photodetector arrays; pan, tilt, or zoom actuators for cameras; mechanisms for dragging sampling scoops; and steering mechanisms for small robotic vehicles.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Tools and equipment

Further Advances in Cooperative Transport by Mobile Robots

A gripping mechanism is presented for autonomous grasping/hoisting by two planetary rovers.

Hardware and decentralized-control algorithms have been developed during continued research on the sensors, the actuators, and the design and functional requirements for systems of multiple mobile robots cooperating in the performance of tightly coupled tasks — for example, grasping and lifting long objects on challenging terrain. [Different aspects of the hardware and algorithms were described in “Advances in Cooperative Transport by Two Mobile Robots” (NPO-30376) NASA Tech Briefs, Vol. 26, No. 8 (August 2002), page 60. Although this research is oriented toward developing robotic capabilities for exploration of Mars, these capabilities could also be utilized on Earth.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Mathematical models, Sensors and actuators, Materials handling, Robotics

Computational Test Cases for Oscillating Clipped Delta Wing

These data can be used to test computational simulations of aerodynamic behavior.

Computational test cases have been selected from archived sets of data acquired some years ago in wind-tunnel experiments on a clipped delta wing equipped with a hydraulically actuated trailing-edge control surface. In some of the experiments, the wing was subjected to pitching oscillations and control-surface oscillations. (The wing was stiff and thus did not undergo appreciable elastic oscillations; instead, it was mounted in such a way as to enable it to oscillate as a rigid torsionally sprung body.) The data obtained in the experiments included the static pressures and the real and imaginary parts of the first harmonics of dynamic pressures at a number of points on the upper and lower wing surfaces.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Wings, Computer simulation, Historical reference, Mountings, Hydraulic equipment, Wind tunnel tests

Control Derivatives of the F-18 Airplane

These derivatives will be used in designing an active-aeroelastic-wing control system.

Flight data gathered by use of the F-18 System Research Aircraft (SRA) based at Dryden Flight Research Center have been used to estimate stability and control derivatives for a baseline F-18 airplane. The data were obtained in the high-dynamic-pressure range of the F-18 flight envelope in an experiment performed in support of a future F-18 program to be devoted to the concept of the active aeroelastic wing (AAW). The AAW technology is intended to integrate aerodynamics, active controls, and aeroelasticity in such a way as to maximize the performance of the airplane. More specifically, the goal of the AAW project will be to maximize the contribution of a reduced-stiffness F-18 wing to roll-rate performance.

Posted in: Briefs, Mechanical Components, Mechanics, Wings, Stability control, Computer simulation, Mathematical models, Performance tests, Aerodynamics

Ultrasonically Induced Fountains and Fogs

Diverse visual effects could be produced in computer-controlled displays.

Experiments have demonstrated the feasibility of generating fountains and fogs over a body of water (see Figure 1) by utilizing high-intensity ultrasound to induce acoustic streaming, cavitation, and atomization. The transducer used in the experiments had a 10-cm diameter and a 10-cm focal length, was immersed in water at a depth approximately equal to its focal length, and was excited at various amplitudes and at various frequencies from 100 kHz to 2 MHz. It was observed in the experiments that the fountain and fog effects depend on the amplitude and frequency of excitation.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Computational fluid dynamics, Water, Acoustics, Test procedures

Fail-Safe, Continue-to-Operate Concept for Jackscrews

Redundant nut increases reliability and facilitates inspections.

A fail-safe, continue-to-operate design concept for machine jackscrews calls for the incorporation of a redundant follower nut that would assume the axial jack load upon failure of the primary nut. Heretofore, the way to design for increased reliability of jackscrews has been to provide for multiple jackscrews operating in unison. The present fail-safe, continue-to-operate design concept offers an alternative for preventing catastrophic failures in jackscrews, which are used widely in aeronautical, aerospace, and industrial applications.

Posted in: Briefs, Mechanical Components, Mechanics, Failure analysis, Product development, Wear, Fasteners, Reliability

Pulse-Tube Refrigerator for Liquid Hydrogen

An unusually high operating frequency enables reductions of size and weight.

An improved closed-loop, two-stage pulse-tube refrigerator provides 4 W of cooling power at a temperature of 15 K. The original intended application of this refrigerator is in preventing boiloff of liquid hydrogen from a propellant tank aboard a spacecraft. The basic refrigerator design can also be adapted to terrestrial applications like cooling superconducting electronic devices.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Liquid propellants, Thermal management, Spacecraft

Ultrasonic/Sonic Vibrating/Rotating Tool Bits

Teeth are made asymmetric to induce rotation without need for rotary actuators.

An easy-to-implement design concept shows promise for improving the performances of impact tool bits used in abrading surfaces, drilling, and coring of rock and rocklike materials. The concept is especially applicable to tools actuated with a combination of ultrasonic and sonic vibrations, as in the cases described in “Ultrasonic/Sonic Drill/Corers With Integrated Sensors (NPO- 20856), NASA Tech Briefs, Vol. 25, No. 1 (January 2001), page 38. Such tools were originally intended to be used in scientific drilling and coring of rock; they might also be useful for drilling, coring, and surface grinding of rock for art and construction.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Tools and equipment, Product development, Drilling, Vibration

Water-Jet Accelerator for Launching a Spacecraft

A proposed ground- based apparatus would accelerate a spacecraft to speed of about mach 1, thus making it possible to increase the payload and/or reduce the cost of launching the space- craft into orbit. The apparatus would include a track along which the spacecraft would ride on a sled. Hundreds of small water jets energized by compressed-air packs would be located under, and at small intervals along, the track. Each jet would be activated in turn as the sled passed by, aiming a high-speed (possibly supersonic) stream of water at baffles on the underside of the sled. The force of water impinging on the baffles would provide levitation and accelerate the sled along the track. Unlike a previously proposed launch-assisting linear electric motor, the water-jet apparatus would function without need for expensive electric-power-conditioning equipment. Unlike another launch-assist concept involving a piston driven along a pneumatic tube, the present concept does not present problems of how to (1) couple the piston to the sled and (2) exert fine control over acceleration. Another advantage of the water-jet concept is redundancy: even if several water jets were to malfunction, the remaining many functional water jets should suffice.

Posted in: Briefs, Mechanical Components, Mechanics

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