Electrically Conductive, Failure-Resistant Tethers

Fine wires are loosely woven into a load-bearing netlike structure. Marshall Space Flight Center, Alabama Special electrically conductive, failure-resistant rope/wire combinations are being developed for use as electrodynamic spacecraft tethers. These or similar combinations could also prove useful on Earth in applications in which there are requirements for strong, reliable, lightweight tethers that can conduct electric currents of moderate size: such applications might include tethering of aerostats and of wind-powered electric generators.

Posted in: Mechanics, Mechanical Components, Briefs

Read More >>

ATHLETE Low-Gravity Testbed

NASA’s Jet Propulsion Laboratory, Pasadena, California A six-degrees-of-freedom (DOF) testbed was developed for evaluating microgravity and low-gravity proximity and contact operations, e.g. in the vicinity of a near Earth orbit, for simulation of proximity operations for a human mission to an asteroid. This is accomplished using an “inverted Stewart platform” where the vehicle under test — in this case, the ATHLETE (All-Terrain Hex-Limbed Extra-Terrestrial Explorer) — is suspended by six computer-controlled cable winches so that it can be maneuvered in all six degrees of freedom. Position feedback is provided by both the encoders at the winch motor, and a motion capture system installed on the testbed structural frame. The payload is attached to the work platform at the end of the six cables.

Posted in: Mechanics, Mechanical Components, Briefs

Read More >>

Acoustic Mechanical Feedthroughs for Producing Work Across a Structure

This technology is applicable wherever an actuator needs to be isolated from another environment. Electromagnetic motors can have problems when operating in extreme environments. In addition, if one needs to do mechanical work outside a structure, electrical feedthroughs are required to transport the electric power to drive the motor. Piezoelectric motors can be designed directly with high torques and lower speeds without the need for gears. One can also actuate piezoelectric, electrostrictive, or magnetostrictive materials in a benign environment and transmit the power in acoustic form as a stress wave and actuate external to the benign environment. This technology removes the need to perforate a structure and allows work to be done directly on the other side of a structure without the use of electrical feedthroughs, which can weaken the structure, pipe, or vessel.

Posted in: Mechanics, Mechanical Components, Briefs

Read More >>

Advanced Symbolic and Numeric Techniques for Machine Vibration Analysis

The operational reliability of a rotary equipment train is dependent on the vibration of its components. Often, the only evidence of this vibration is gear noise or coupling wear. However, these early indicators might eventually develop into high-amplitude vibration, resulting in gear wear, gear tooth failures, or broken shafts. The torsional response characteristics of rotating and reciprocating equipment should therefore be analyzed and evaluated to ensure system reliability.

Posted in: Mechanical Components, White Papers

Read More >>

Simplify designs with 4-point contact ball bearings

Four-point contact ball bearings can handle radial, thrust and moment loads simultaneously, saving space, weight and cost by eliminating the need for a second bearing. They are generally used for slow to moderate-speed applications, or where oscillatory movement is sufficient to cause the balls to make one or more revolutions. A new white paper from Kaydon Bearings explains how four-point contact bearings work, their advantages, and design considerations when using them.

Posted in: Mechanical Components, White Papers

Read More >>

Re-entry Vehicle Shape for Enhanced Performance

A convex structure is used with a continuous slope. A vehicle entering the atmosphere of a planet will do so at hypersonic speeds and will need to decelerate and maneuver through that atmosphere while protecting its payload from excessive heating. As a consequence, the vehicle shape must be designed to provide optimal aerodynamic lift and drag properties, while minimizing convective and radiative heating to the vehicle outer surfaces.

Posted in: Mechanical Components, Machinery & Automation, Briefs

Read More >>

CubeSat Deployable Log Periodic Dipole Array

Any small satellite with a need for a VHF antenna might benefit from this design, in addition to communications and military applications. The antenna is composed of two main deployable structural components that help it achieve the large packing factor necessary to fit within the small volume of the CubeSat. The primary component of the antenna array is a tension stiffened truss, which is preloaded using a large tape spring. The truss bays are formed from solid discs connected by thin Kevlar thread. The Kevlar threads are set up in a hexapod configuration, and are fully tensioned and preloaded from the force of the tape spring, which runs through the center of the truss. The truss gets its overall stiffness from the properties and configuration of these Kevlar wires.

Posted in: Mechanical Components, Machinery & Automation, Briefs

Read More >>