Mechanical & Fluid Systems

Ice-Melting Probe Using Steam and Jets of Hot Water

This probe would overcome some of the deficiencies of prior ice-melting probes. An improved probe has been proposed for burrowing vertically into ice for scientific exploration of polar icecaps, glaciers, and the like. The predecessor of the improved probe is a Philbert probe, which contains an electric heater to melt the ice in contact with it and thereby make it descend through the ice under its own weight. A Philbert probe also contains a mechanism from which the wires for the electric heater and any sensors in the probe are paid out behind the probe; these wires become sealed into the overlying ice as the probe descends. The two major drawbacks of a Philbert probe are that (1) it tends not to go straight down and (2) a plug of dust, sand, rock, and/or other debris tends to build up in the meltwater ahead of the probe, eventually becoming large enough to halt the descent by interrupting the heat-transfer interface between the vehicle nose and the ice. The improved probe is designed to eliminate these drawbacks.

Posted in: Mechanics, Briefs, TSP

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Pneumatic Accelerator for Launching a Spacecraft

A report proposes the development of a ground-based launch-assist apparatus that would accelerate a spacecraft to a speed of about 270 m/s. The apparatus would include a track along which the spacecraft would ride on a sled coupled to a large piston driven by compressed air along a tube (more precisely, a concrete tunnel lined with stainless-steel sheet) below the track. The connection between the sled and the piston would be made via a coupling plate that would slide along a slot on top of the tube. The slot would seal after passage of the coupling plate. As described thus far, the apparatus could be characterized as a modern, high-acceleration, high-speed version of pneumatic drives with slot connections to rail cars that were used in Europe during the 1840s.

Posted in: Mechanics, Briefs, TSP

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"Smart" Actuators for Alleviating Buffet of Aircraft

Peak stresses could be reduced without sacrificing control authority. An active-control surface modal (ACSM) device has been developed as an improved means of alleviating buffet of an aircraft. The ACSM device is a "smart" actuator system that includes an array of antagonistic piezoelectric actuators installed within a rudder or other aircraft control surface (see Figure 1). These actuators are used to deform the control surface in what amounts to controlled vibration modes (see Figure 2), the frequencies and mode shapes being chosen to affect unsteady aerodynamic damping to suppress the dynamic effects of buffet.

Posted in: Mechanics, Briefs, TSP

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Improved Lightweight Freeze-Tolerant Tubes

Improved designs have been conceived for lightweight tubes that can withstand the large (as much as 8 or 9 volume percent) freeze/thaw expansions and contractions of typical heat-transfer fluids like water and ammonia. Intended originally for radiators for rejecting waste heat from spacecraft, these designs may also be suitable for such terrestrial applications as freeze-tolerant water pipes in houses and sprinkler systems. Typical prior freeze-tolerant-tube designs are characterized by short operating lives because they rely on compressible polymeric inserts that are degraded by permeability and by embrittlement at low temperatures. The improved designs call for thin tube walls with noncircular (typically oval) cross sections and solid or hollow metal inserts of various shapes, all selected together to obtain specific combinations of limited volume expansion and mechanical advantage such that the stresses in the tube walls remain sufficiently low under all anticipated freeze/thaw conditions.

Posted in: Mechanics, Briefs, TSP

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Mechanisms Facilitate Blowdown of Large Diesel Engines

Blowdown can be performed faster, more easily, and more safely. Simple mechanisms have been devised to facilitate the blowdown of large diesel engines. As explained below, these mechanisms reduce the amount of time and effort that must be expended to test engines before operating them.

Posted in: Mechanics, Briefs, TSP

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Uncertainty Models From Ground Vibration Testing

Test data indicate least conservative errors in model. Structural dynamics are often an important consideration when evaluating system characteristics. A concern related to structural dynamics is the analysis of flutter for a flight vehicle. The instability associated with flutter can be quite sensitive to the structural dynamics; therefore, analysis of robustness with respect to error, or uncertainty, is becoming increasingly important for the flight test community. In particular, uncertainty models are needed for μ-method analysis as described in "Characterizing Worst-Case Flutter Margins From Flight Data'' (DRC-97-03), NASA Tech Briefs, Vol. 21, No. 4 (April 1997), page 62.

Posted in: Mechanics, Briefs

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Spacecraft Nuclear Reactor Would Be Fueled in Orbit

Two reports summarize progress thus far in the continuing development of a spacecraft nuclear reactor, some or all of the fuel rods of which would not be loaded until the spacecraft was in orbit. (Keeping the fuel rods out of the reactor core before and during launch is intended to minimize the risk of release of radioactive material in the event of a launch accident.) The report describes the design and operation of the fueling mechanism, and problems in the design and fabrication of the core. The fuel rods include uranium oxide in rhenium sleeves. The core includes niobium star-cross-section inserts and molybdenum tubes, into which the fuel rods are to be inserted.

Posted in: Mechanics, Briefs

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