294 research outputs found
Electron beam charging of Space Shuttle thermal protection system tiles
Six space shuttle reusable surface insulation tiles were tested in the NASA Lewis Research Center's electron bombardment test facility. The 30-cm-square specimens were assembled by using the same materials and techniques used to apply the tiles to the space shuttle and were composed to 15-cm- and 20-cm-square tiles and pieces on 0.6-cm-thick aluminum substrates. There were two specimens of each of three thicknesses. One specimen of each thickness had gaps of less than 0.1 cm between tiles, and the other had gaps of approximately 0.15 cm. The specimens were exposed to monoenergetic electron beams (2 to 25 keV) with nominal fluxes of 0.1 and 1 nA/sq. cm. Tests were conducted with both grounded and floating substrates. The data presented include charging rates, equilibrium potentials, and substrate currents. There is evidence that discharging occurred
Testing of a spacecraft model in a combined environment simulator
A scale model of a satellite was tested in a large vacuum facility under electron bombardment and vacuum ultraviolet radiation to investigate the charging of dielectric materials on curved surfaces. The model was tested both stationary and rotating relative to the electron sources as well as grounded through one megohm and floating relative to the chamber. Surface potential measurements are presented and compared with the predictions of computer modelling of the stationary tests. Discharge activity observed during the stationary tests is discussed and signals from sensing devices located inside and outside of the model are presented
Charging of flexible solar array substrates in kilovolt electron beams
A series of survey tests were conducted to evaluate samples of flexible solar arrays. The samples used woven carbon fibers and/or coatings to increase the surface conductivity of the KAPTON substrate and thereby reduce surface charging. Four different samples were evaluated by exposing them to monoenergetic electron beams of 2 to 20 KeV at a current density of 1 nA sq cm. Simulated eclipse tests were also conducted. The results were as expected; the more continuous the conductive pattern, the lower the surface charging
Test program for transmitter experiment package and heat pipe system for the communications technology satellite
The test program is described for the 200 watt transmitter experiment package and the variable conductance heat pipe system which are components of the high-power transponder aboard the Communications Technology Satellite. The program includes qualification tests to demonstrate design adequacy, acceptance tests to expose latent defects in flight hardware, and development tests to integrate the components into the transponder system and to demonstrate compatibility
The Space Station Photovoltaic Panels Plasma Interaction Test Program: Test plan and results
The Plasma Interaction Test performed on two space station solar array panels is addressed. This includes a discussion of the test requirements, test plan, experimental set-up, and test results. It was found that parasitic current collection was insignificant (0.3 percent of the solar array delivered power). The measured arcing threshold ranged from -210 to -457 V with respect to the plasma potential. Furthermore, the dynamic response of the panels showed the panel time constant to range between 1 and 5 microsec, and the panel capacitance to be between .01 and .02 microF
Testing of typical spacecraft materials in a simulated substorm environment
The test specimens were spacecraft paints, silvered Teflon, thermal blankets, and solar array segments. The samples, ranging in size from 300 to 1000 sq cm were exposed to monoenergetic electron energies from 2 to 20 keV at a current density of 1 NA/sq cm. The samples generally behaved as capacitors with strong voltage gradient at their edges. The charging characteristics of the silvered Teflon, Kapton, and solar cell covers were controlled by the secondary emission characteristics. Insulators that did not discharge were the spacecraft paints and the quartz fiber cloth thermal blanket sample. All other samples did experience discharges when the surface voltage reached -8 to -16kV. The discharges were photographed. The breakdown voltage for each sample was determined and the average energy lost in the discharge was computed
Robotic Hand Controlled by Myoelectric Signals
In this project we developed a prosthetic hand that is controlled by myoelectric signals from the forearm. The forearm signals were filtered and amplified to be easier read by a microcontroller. The microcontroller then generated signals to control the mechanical hand based on these myoelectric input signals. This is done by the microcontroller increasing the pulse width sent to several servos making up the hand. The larger the pulse width the more flexed the hand becomes until it reaches the maximum programmed into it. In order to open the hand the high input to the microcontroller must be deactivated and then reactivated for the pulse width to begin decreasing.
Several designs and products are currently available online as complicated limbs and hands for amputees, however many of these can be costly and heavy. This project has taken inspiration from these designs with the goal of reducing cost and weight without sacrificing functionality. One major advantage of our project is the dry reusable electrodes used to capture the myoelectric signals in the forearm. The silver coated cloth functions as an electrode with the help of a pushbutton from a tarp making kit. This electrode is reusable and remains in the same place in the sleeve it is sewn into for ease of use
Investigation of high voltage spacecraft system interactions with plasma environments
An experimental investigation was undertaken for insulator and conductor test surfaces biased up to + or - 1kV in a simulated low earth orbit charged particle environment. It was found that these interactions are controlled by the insulator surfaces surrounding the biased conductors. For positive applied voltages the electron current collection can be enhanced by the insulators. For negative applied voltages the insulator surface confines the voltage to the conductor region. Understanding these interactions and the technology to control their impact on system operation is essential to the design of solar cell arrays for ion drive propulsion applications that use direct drive power processing
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A double-stranded secondary structure for hyaluronic acid in aqueous-organic solvent as revealed by vacuum ultraviolet circular dichroism
The association of hyaluronic acid (HA) into a double stranded
structure has been investigated by circular dichroism (CD)
spectroscopy into the vacuum ultraviolet region. The CD of HA changes
dramatically, monitoring a cooperative transition as the dielectric
constant of an aqueous solution is reduced by adding organic solvents.
This structural transition results in a high intensity CD band at 190
nm, indicating an ordered structure in the mixed solvent. Heating
hyaluronic acid in the mixed solvent also causes a cooperative
transition reducing the CD to that found for the polymer in aqueous
solution. The CD for the polymer in aqueous solution is not very
different from some of the CD's for the constituent monomers, and the
CD of the monomers is similar in both aqueous solution and mixed
solvent. Furthermore, heating HA in aqueous solution results in
small, noncooperative changes in the CD spectrum. The CD as
dielectric constant is reduced exhibits isodichroic points, showing
that there are two states. Singular value decomposition of the CD as
a function of organic solvent has only two principal components,
confirming that there are only two states.
Oligomers of HA show a chain length effect with approximately nine
disaccharides required for the structural transition as a function of
organic solvent. This proves that the transition is indeed
cooperative. The concentration dependence for the transition was
investigated in detail for the 12 mer and 16 mer, and it was possible
to prevent completely the transition in mixed solvent with sufficient
dilution of the oligomer. The CD data in mixed solvent as a function
of oligomer concentration were fit with various models for association
of two and more strands. Simplex directed search methods were used to
investigate the vector space of unknown model parameters, and two
strand models were shown to consistently give a better fit. A
cooperative two-strand zipper model which allows relative sliding of
the chains gave the smallest error and produced the following
thermodynamic parameters for the ordered structure: enthalpy of
growth, -1000 ± 300 cal/mole; entropy of growth, -2.25 ± 1.30 eu/mole:
enthalpy of initiation, -20,000 ± 3000 cal/mole; entropy of
initiation, -71 ± 15 eu/mole. These results are consistent with a
double-stranded and helical structure for hyaluronic acid in solutions
of reduced dielectric constant
First results of material charging in the space environment
A satellite experiment, designed to measure potential charging of typical thermal control materials at near geosynchronous altitude, was flown as part of the SCATHA program. Direct observations of charging of typical satellite materials in a natural charging event ( 5 keV) are presented. The results show some features which differ significantly from previous laboratory simulations of the environment
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