Special Coverage

Home

Brush-Wheel Samplers for Planetary Exploration

A report proposes brush-wheel mechanisms for acquiring samples of soils from remote planets. In simplest terms, such a mechanism would contain brush wheels that would be counter-rotated at relatively high speed. The mechanism would be lowered to the ground from a spacecraft or other exploratory vehicle. Upon contact with the ground, the counterrotating brush wheels would kick soil up into a collection chamber. Thus, in form and function, the mechanism would partly resemble traditional street and carpet sweepers. The main advantage of using of brush wheels (in contradistinction to cutting wheels or other, more complex mechanisms) is that upon encountering soil harder than expected, the brushes could simply deflect and the motor(s) could continue to turn. That is, sufficiently flexible brushes would afford resistance to jamming and to overloading of the motors used to rotate the brushes, and so the motors could be made correspondingly lighter and less power hungry. Of course, one could select the brush stiffnesses and motor torques and speeds for greatest effectiveness in sampling soil of a specific anticipated degree of hardness.

Posted in: Briefs, TSP

Read More >>

Lightweight Energy Absorbers for Blast Containers

Aluminum foam liners tested for possible replacement of solid lead liners. Kinetic-energy- absorbing liners made of aluminum foam have been developed to replace solid lead liners in blast containers on the aft skirt of the solid rocket booster of the space shuttle. The blast containers are used to safely trap the debris from small explosions that are initiated at liftoff to sever frangible nuts on hold-down studs that secure the spacecraft to a mobile launch platform until liftoff.

Posted in: Briefs, TSP

Read More >>

Tilt-Sensitivity Analysis for Space Telescopes

A report discusses a computational- simulation study of phase- front propagation in the Laser Interferometer Space Antenna (LISA), in which space telescopes would transmit and receive metrological laser beams along 5-Gm interferometer arms. The main objective of the study was to determine the sensitivity of the average phase of a beam with respect to fluctuations in pointing of the beam. The simulations account for the effects of obscurations by a secondary mirror and its supporting struts in a telescope, and for the effects of optical imperfections (especially tilt) of a telescope. A significant innovation introduced in this study is a methodology, applicable to space telescopes in general, for predicting the effects of optical imperfections. This methodology involves a Monte Carlo simulation in which one generates many random wavefront distortions and studies their effects through computational simulations of propagation. Then one performs a statistical analysis of the results of the simulations and computes the functional relations among such important design parameters as the sizes of distortions and the mean value and the variance of the loss of performance. These functional relations provide information regarding position and orientation tolerances relevant to design and operation.

Posted in: Briefs, TSP

Read More >>

Study of Dislocation-Ordered InxGa1–xAs/GaAs Quantum Dots

A report describes an experimental study of dislocation-induced spatial ordering of quantum dots (QDs) comprising nanometer-sized InxGa1–xAs islands surrounded by GaAs. Metastable hetero-epitaxial structures were grown by molecular-beam epitaxy of InxGa1–xAs onto n+ GaAs and semi-insulating GaAs substrates. Then the structures were relaxed during a post-growth annealing/self-organizing process leading to the formation of surface undulations that acted as preferential sites for the nucleation of QDs. Structural effects of annealing times and temperatures on the strain-relaxed InxGa1–xAs/GaAs and the subsequent spatial ordering of the QDs were analyzed by atomic-force microscopy and transmission electron microscopy. Continuous-wave spectral and time-resolved photoluminescence (PL) measurements were performed to study the effects, upon optical properties, of increased QD positional ordering, increased QD uniformity, and proximity of QDs to arrays of dislocations. PL spectral peaks of ordered QD structures formed on strain-relaxed InxGa1–xAs/GaAs layers were found to be narrower than those of structures not so formed and ordered. Rise and decay times of time-resolved PL were found to be lower at lower temperatures — apparently as a consequence of decreased carrier-transport times within the barriers surrounding the QDs.

Posted in: Briefs, TSP

Read More >>

Alternative Electrochemical Systems for Ozonation of Water

Hydrogen gas, ozone gas, and ozonated water can be delivered under pressure. Electrochemical systems that are especially well suited for the small-scale generation of ozone and ozonated water for local use have been invented. These systems can operate with very little maintenance, and the only inputs needed during operation are electric power and water. These systems are closely related to the ones described in "Electrochemical Systems Generate Ozone and Ozonated Water" (MSC-23046), NASA Tech Briefs, Vol. 26, No. 3 (March 2002), page 68. Ozonated water produced by these systems can be used in diverse industrial applications: A few examples include sterilization in the brewing industry, general disinfection, and treatment of sewage and recycled water.

Posted in: Briefs

Read More >>

Magnetic Field Would Reduce Electron Backstreaming in Ion Thrusters

Erosion of accelerator grid could also be reduced. The imposition of a magnetic field has been proposed as a means of reducing the electron backstreaming problem in ion thrusters. Electron backstreaming refers to the backflow of electrons into the ion thruster. Back- streaming electrons are accelerated by the large potential difference that exists between the ion- thruster acceleration electrodes, which otherwise accelerates positive ions out of the engine to develop thrust. The energetic beam formed by the backstreaming electrons can damage the discharge cathode, as well as other discharge surfaces upstream of the acceleration electrodes. The electron-backstreaming condition occurs when the center potential of the ion accelerator grid is no longer sufficiently negative to prevent electron diffusion back into the ion thruster. This typically occurs over extended periods of operation as accelerator-grid apertures enlarge due to erosion. As a result, ion thrusters are required to operate at increasingly negative accelerator-grid voltages in order to prevent electron backstreaming. These larger negative voltages give rise to higher accelerator-grid erosion rates, which in turn accelerates aperture enlargement. Electron backstreaming due to accelerator-grid-hole enlargement has been identified as a failure mechanism that will limit ion-thruster service lifetime.

Posted in: Briefs, TSP

Read More >>

Software for Improved Extraction of Data From Tape Storage

A computer program has been written to replace the original software of Racal Storeplex Delta tape recorders, which are used at Stennis Space Center. The original software could be activated by a command- line interface only; the present software offers the option of a command-line or graphical user interface. The present software also offers the option of batchfile operation (activation by a file that contains command lines for operations performed consecutively).

Posted in: Briefs

Read More >>

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