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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

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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

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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, TSP

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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

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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

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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

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Protective Sleeve for a Pyrotechnic Reefing Line

The sleeve provides improved operation of a parachute reefing system. A metallic sleeve provides protection and guidance for the actuating lanyard pull of a parachute system reefing line cutter. This device ensures that the reefing line cutter is not damaged during packing or deployment. In addition, the device ensures that the actuating lanyard that initiates the cutter is pulled within the device’s specification cone angle. Combined, these features increase the durability of the reefing line cutter used in parachute reefing systems, and significantly increases the reliability of the underlying reefing cutter. Protecting such a critical element of the controlled deployment of parachutes significantly improves the operation of the parachute reefing system.

Posted in: Mechanical Components, Machinery & Automation, Briefs

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