26,578 research outputs found
Behavior of Combined Dielectric-Metallic Systems in a Charged Particle Environment
The charging and discharging characteristics of an electrically isolated solar array segment were studied in order to simulate discharges seen during geomagnetic substorms. A solar array segment was floated while bombarded with monoenergetic electrons at various angles of incidence. The potentials of the array surface and of the interconnects were monitored using Trek voltage probes to maintain electrical isolation. A back plate was capacitively coupled to the array to provide information on the characteristics of the transients accompanying the discharges. Several modes of discharging of the array were observed at relatively low differential and absolute potentials (a few kilovolts). A relatively slow discharge response in the array was observed, discharging over one second with currents of nanoamps. Two types of faster discharges were also seen which lasted a few hundredths of a millisecond and with currents on the order of microamps. Some results indicate an electron emission process associated with the arcs
Degradation mechanisms of materials for large space systems in low Earth orbit
Degradation was explored of various materials used in aerospace vehicles after severe loss of polymeric material coatings (Kapton) was observed on an early shuttle flight in low Earth orbit. Since atomic oxygen is the major component of the atmosphere at 300 km, and the shuttle's orbital velocity produced relative motion corresponding to approx. 5 eV of oxygen energy, it was natural to attribute much of this degradation to oxygen interaction. This assumption was tested using large volume vacuum systems and ion beam sources, in an exploratory effort to produce atomic oxygen of the appropriate energy, and to observe mass loss from various samples as well as optical radiation. Several investigations were initiated and the results of these investigations are presented in four papers. These papers are summarized. They are entitled: (1) The Space Shuttle Glow; (2) Laboratory Degradation of Kapton in a Low Energy Oxygen Ion Beam; (3) The Energy Dependence and Surface Morphology of Kapton Degradation Under Atomic Oxygen Bombardment; and (4) Surface Analysis of STS 8 Samples
Electron yields from spacecraft materials
Photoyields and secondary electron emission (SEE) characteristics were determined under UHV conditions for a group of insulating materials used in spacecraft applications. The SEE studies were carried out with a pulsed primary beam while photoyields were obtained with a chopped photon beam from a Kr resonance source with major emission at 123.6 nm. This provides a photon flux close to that of the Lyman alpha in the space environment. Yields per incident photon are obtained relative to those from a freshly evaporated and air oxidized Al surface. Results are presented for Kapton, FEP Teflon, the borosilicate glass covering of a shuttle tile, and spacesuit outer fabric
Phase-dependent X-ray observations of the beta Lyrae system: No eclipse in the soft band
We report on observations of the eclipsing and interacting binary beta Lyrae
from the Suzaku X-ray telescope. This system involves an early B star embedded
in an optically and geometrically thick disk that is siphoning atmospheric
gases from a less massive late B II companion. Motivated by an unpublished
X-ray spectrum from the Einstein X-ray telescope suggesting unusually hard
emission, we obtained time with Suzaku for pointings at three different phases
within a single orbit. From the XIS detectors, the softer X-ray emission
appears typical of an early-type star. What is surprising is the remarkably
unchanging character of this emission, both in luminosity and in spectral
shape, despite the highly asymmetric geometry of the system. We see no eclipse
effect below 10 keV. The constancy of the soft emission is plausibly related to
the wind of the embedded B star and Thomson scattering of X-rays in the system,
although it might be due to extended shock structures arising near the
accretion disk as a result of the unusually high mass-transfer rate. There is
some evidence from the PIN instrument for hard emission in the 10-60 keV range.
Follow-up observations with the RXTE satellite will confirm this preliminary
detection.Comment: to appear in A&A Letter
Display/control requirements for automated VTOL aircraft
A systematic design methodology for pilot displays in advanced commercial VTOL aircraft was developed and refined. The analyst is provided with a step-by-step procedure for conducting conceptual display/control configurations evaluations for simultaneous monitoring and control pilot tasks. The approach consists of three phases: formulation of information requirements, configuration evaluation, and system selection. Both the monitoring and control performance models are based upon the optimal control model of the human operator. Extensions to the conventional optimal control model required in the display design methodology include explicit optimization of control/monitoring attention; simultaneous monitoring and control performance predictions; and indifference threshold effects. The methodology was applied to NASA's experimental CH-47 helicopter in support of the VALT program. The CH-47 application examined the system performance of six flight conditions. Four candidate configurations are suggested for evaluation in pilot-in-the-loop simulations and eventual flight tests
Development of a cobalt-tungsten ferromagnetic, high-temperature, structural alloy
Cobalt-tungsten ferromagnetic, high temperature structural alloy for rotor applications in space power generator
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