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At least 145 records · Page 8

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NASA NTRS1992

Use of space ultra-vacuum for high quality semiconductor thin film growth

The utilization of space for materials processing is being expanded through a unique concept of epitaxial thin film growth in the ultra-vacuum of low earth orbit (LEO). This condition can be created in the wake of an orbiting space vehicle; and assuming that the vehicle itself does not pertub the environment, vacuum levels of better than 10 exp -14 torr can be attained. This vacuum environment has the capacity of greatly enhancing epitaxial thin film growth and will be the focus of experiments conducted aboard the Wake Shield Facility (WSF) currently being developed by the Space Vacuum Epitaxy Center (SVEC), Industry, and NASA.

Ignatiev, A.↗

NASA NTRS1993

Analysis of high vacuum systems using SINDA'85

The theory, algorithms, and test data correlation analysis of a math model developed to predict performance of the Space Station Freedom Vacuum Exhaust System are presented. The theory used to predict the flow characteristics of viscous, transition, and molecular flow is presented in detail. Development of user subroutines which predict the flow characteristics in conjunction with the SINDA'85/FLUINT analysis software are discussed. The resistance-capacitance network approach with application to vacuum system analysis is demonstrated and results from the model are correlated with test data. The model was developed to predict the performance of the Space Station Freedom Vacuum Exhaust System. However, the unique use of the user subroutines developed in this model and written into the SINDA'85/FLUINT thermal analysis model provides a powerful tool that can be used to predict the transient performance of vacuum systems and gas flow in tubes of virtually any geometry. This can be accomplished using a resistance-capacitance (R-C) method very similar to the methods used to perform thermal analyses.

Spivey, R. A.↗

NASA NTRS1994

New potentials of NIICHIMMASH's thermal vacuum facilities

The potentialities of existing test facilities as to simulating space environment governing factors for spacecraft successful development thermal vacuum testing are analyzed, ways of modernizing existing test facilities and specific proposals on their redesign are considered. The problem of spacecraft (S/C) ground development in simulated external environments, the solution of which started more than 30 years ago, has not lost its urgency today. Stringent requirements on S/C active lifetime under space conditions, module large dimensions, great number of extension elements and complicated mode of their interaction in long mission do not allow S/C designers to abandon ground tests. S/C thermal modes development is a combination of calculations, thermal vacuum tests and actions on improving S/C design and its thermal control system. Traditionally, tests are carried out by stages from component and end unit level verifications to complex tests of modules and S/C as a whole. In our opinion, sufficient correctness of calculated models and experience gained in organizations designing space systems allow to reduce cost and time of autonomous tests. Unfortunately, this is not true for complex (integrated) thermal vacuum tests. More than that, their recent programs include tasks of verifying other (than thermal control system) systems if S/C for operation under space simulated conditions. The outlined circumstances are the main reason for critical review of the potentialities of the existing test base, and of NIICHIMMASH's two large thermal vacuum chambers, first of all. The reasons for and ways of enlargement of these facilities potentially are analyzed and the results attained are described.

Afanassiev, N. A.↗

NASA NTRS1993

Effect of Long-Term 1093 K Exposure to Air or Vacuum on the Structure of Several Wrought Superalloys

Long-term 1093 K heat treatments of three commercial superalloy sheet materials were undertaken in air -IAI and vacuum. With either exposure, significant precipitation of second phases occurred in the Co-base Haynes(R) Alloy 188 (HA 188) and the Ni-base Haynes(R) Alloy 230 (HA 230); however, much less precipitation was found in the exposed Ni-base alloy Inconel(R) 617 (IN 617). Although some grain growth occurred in HA 198, no changes in the grain size of either HA 230 or IN 617 were observed after 22,500 h at temperature. Oxidation during air heat treatments led to weight gain due to the formation of chromia + spinel scales and surface-connected grain boundary pits/oxides in all three superalloys. Both the weight gain and depth of intergranular attack were dependent on the square root of time, which is indicative of diffusion-controlled phenomena. Because many alloy samples had neighbors in close proximity, most vacuum heat treated specimens did not suffer significant loss of volatile elements. However, some exposed samples were subjected to unrestricted vacuum heat treatments, allowing estimates of volatilization to be made. Based on the data for HA 188, the weight loss during 1093 K vacuum exposure was diffusion controlled once the inhibiting effects of surface films on the as-received alloys were broken down.

J.D. Whittenberger↗

NASA NTRS1998

Thermal Vacuum Testing of the Crew and Equipment Translation Aid for the International Space Station

The Crew and Equipment Translation Aid (CETA) is a human powered cart that will aid astronauts in conducting extra-vehicular activity (EVA) maintenance on the International Space Station (ISS). There are two critical EVA tasks relevant to the successful operation of the CETA. These are the removal of the launch restraint bolts during its initial deployment from the Space Shuttle payload bay and the manual deceleration of the cart, its two onboard astronauts, and a payload. To validate the launch restraint and braking system designs, the hardware engineers needed to verify their performance in an environment similar to that in which it will be used. This environment includes the vacuum of low earth orbit and temperatures as low as -11O F and as high as +200 F. The desire for quantitative data, as opposed to subjective information which could be provided by a suited astronaut, coupled with test scheduling conflicts resulted in an unmanned testing scenario. Accommodating these test objectives in an unmanned test required a solution that would provide remotely actuated thermal vacuum compatible torque sources of up to 25 ft-lbs at four horizontally oriented and four vertically oriented bolts, a variable input force of up to 125 lbs at the four brake actuators, and thermal vacuum compatible torque and force sensors. The test objectives were successfully met in both the thermal Chamber H and the thermal vacuum Chamber B at NASA's Johnson Space Center.

Blanco, Raul A.↗

NASA NTRS1999

Validation of Landsat-7 ETM+ MEM Thermal Improvement in Thermal Vacuum Tests and in Flight Due to Lower Louver Set Points

The Enhanced Thematic Mapper Plus (ETM+) Main Electronics Module (MEM) power supply heat sink temperature is critical to the Landsat-7 mission. It is strongly dependent on the thermal louver design. A lower power supply heat sink temperature increases the reliability of the MEM, and reduces the risk of over heating and thermal shut-down. After the power supply failures in ETM+ instrument thermal vacuum tests #1 and #2, the author performed detailed thermal analyses of the MEM, and proposed to reduce the louver set-points by 7C. At the 1998 Intersociety Energy Conversion Engineering Conference (IECEC), the author presented a paper that included results of thermal analysis of the MEM. It showed that a 70C reduction of the louver set points could reduce the maximum power supply heat sink temperature in thermal vacuum test and in flight to below 20"C in the cooler outgas mode and in the nominal imaging mode, and has no significant impact on the standby heater duty cycle. It also showed that the effect of Earth infrared and albedo on the power supply heat sink temperature is small. The louver set point reduction was implemented in June 1998, just prior to ETM+ thermal vacuum test #3. Results of the thermal vacuum tests, and temperature data in flight validate the MEM thermal performance improvement due to the 70C reduction of the louver set points.

Choi, Michael K.↗

NASA NTRS2000

Development of a Methodology for Conducting Hall Thruster EMI Tests in Metal Vacuum Chambers of Arbitrary Shape and Size

While the closed-drift Hall thruster (CDT) offers significant improvement in performance over conventional chemical rockets and other advanced propulsion systems such as the arcjet, its potential impact on spacecraft communication signals must be carefully assessed before widespread use of this device can take place. To this end, many of the potentially unique issues that are associated with these thrusters center on its plume plasma characteristics and the its interaction with electromagnetic waves. Although a great deal of experiments have been made in characterizing the electromagnetic interference (EMI) potential of these thrusters, the interpretation of the resulting data is difficult because most of these measurements have been made in vacuum chambers with metal walls which reflect radio waves emanating from the thruster. This project developed a means of assessing the impact of metal vacuum chambers of arbitrary size or shape on EMI experiments, thereby allowing for test results to be interpreted properly. Chamber calibration techniques were developed and initially tested at RIAME using their vacuum chamber. Calibration experiments were to have been made at Tank 5 of NASA GRC and the 6 m by 9 m vacuum chamber at the University of Michigan to test the new procedure, however the subcontract to RIAME was cancelled by NASA memorandum on Feb. 26. 1999.

Gallimore, Alec D.↗

NASA NTRS2000

Steady State Vacuum Ultraviolet Exposure Facility With Automated Calibration Capability

NASA Glenn Research Center at Lewis Field designed and developed a steady state vacuum ultraviolet automated (SSVUVa) facility with in situ VUV intensity calibration capability. The automated feature enables a constant accelerated VUV radiation exposure over long periods of testing without breaking vacuum. This test facility is designed to simultaneously accommodate four isolated radiation exposure tests within the SSVUVa vacuum chamber. Computer-control of the facility for long, term continuous operation also provides control and recording of thermocouple temperatures, periodic recording of VUV lamp intensity, and monitoring of vacuum facility status. This paper discusses the design and capabilities of the SSVUVa facility.

Stueber, Thomas J.↗

NASA NTRS2000

High-Speed Automated Tester for Vacuum Chamber Feedthrough Connectors and Cables

The Goddard Space Flight Center's thermal vacuum laboratory has developed a high-speed automated system for testing the integrity of 37-pin MIL-C-5015 cylindrical electrical feedthrough connectors used on penetration plates of thermal vacuum chambers. The system consists of a desktop PC driving a data acquisition front end. The latter measures the resistance through each pin of the connector and the resistance from each pin to all other pins and the connector shell. In addition to identifying unacceptable feedthroughs, the system is also used for testing cables. In the special case of Type T thermocouples (used almost exclusively at the lab), the difference in resistance between the copper and constantan wires provides positive proof of accidentally reversed connector wiring. Data acquisition time to completely test a cable or feedthrough connector is less than thirty seconds. The system provides a hardcopy printout of the resistance readings. Connectors or cables with fewer wires are tested using simple adapter cables. Initial tests indicate that the performance of a given feedthrough connector can be predicted on the basis of measured resistance readings, reducing ongoing cost of connector replacement. The opportunity to positively certify the integrity of cables, cable connectors and feedthroughs before the start of a thermal vacuum test minimizes the likelihood of a circuit problem that would require returning the chamber to ambient conditions for repair. This system has two principal advantages for the Goddard thermal vacuum laboratory. Its only significant cost was the labor to fabricate the test cable and shorting cable -- about 40 man-hours total. The system was built around a computer and data acquisition unit that were already on hand. The second advantage is that it very quickly tests both of the parameters that are essential.

Swope, Robert H.↗

NASA NTRS2001

Geoscience Laser Altimeter System (GLAS) Instrument: Flight Loop Heat Pipe (LHP) Acceptance Thermal Vacuum Test

Two loop heat pipes (LHPs) are to be used for tight thermal control of the Geoscience Laser Altimeter System (GLAS) instrument, planned for flight in late 2001. The LHPs are charged with Propylene as a working fluid. One LHP will be used to transport 110 W from a laser to a radiator, the other will transport 160 W from electronic boxes to a separate radiator. The application includes a large amount of thermal mass in each LHP system and low initial startup powers. The initial design had some non-ideal flight design compromises, resulted in a less than ideal charge level for this design concept with a symmetrical secondary wick. This less than ideal charge was identified as the source of inadequate performance of the flight LHPs during the flight thermal vacuum test in October of 2000. We modified the compensation chamber design, re-built and charged the LHPs for a final LHP acceptance thermal vacuum test. This test performed March of 2001 was 100% successful. This is the last testing to be performed on the LHPs prior to instrument thermal vacuum test. This sensitivity to charge level was shown through varying the charge on a Development Model Loop Heat Pipe (DM LHP) and evaluating performance at various fill levels. At lower fills similar to the original charge in the flight units, the same poor performance was observed. When the flight units were re-designed and filled to the levels similar to the initial successful DM LHP test, the flight units also successfully fulfilled all requirements. This final flight Acceptance test assessed performance with respect to startup, low power operation, conductance, and control heater power, and steady state control. The results of the testing showed that both LHPs operated within specification. Startup on one of the LHPs was better than the other LHP because of the starter heater placement and a difference in evaporator design. These differences resulted in a variation in the achieved superheat prior to startup. The LHP with the lower superheat was sensitive to the thermal environment around the compensation chamber, while the LHP with the higher superheat (similar in design to DM LHP) was not. In response to the test results the placement of the starter heater will be optimized for the flight instrument testing for higher achieved superheat. This presentation discusses startup behavior, overall conductance of a radiator system, low power operation, high power operation, temperature control stability, and control heater power requirements as measured during this acceptance thermal vacuum test. A brief summary of 'lessons learned' will be included.

Baker, Charles↗

NASA NTRS2002

Approximating Fluid Flow from Ambient to Very Low Pressures: Modeling ISS Experiments that Vent to Vacuum

Two ISS (International Space Station) experiment payloads will vent a volume of gas overboard via either the ISS Vacuum Exhaust System or the Vacuum Resource System. A system of ducts, valves and sensors, under design, will connect the experiments to the ISS systems. The following tasks are required: Create an analysis tool that will verify the rack vacuum system design with respect to design requirements, more specifically approximate pressure at given locations within the vacuum systems; Determine the vent duration required to achieve desired pressure within the experiment modules; Update the analysis as systems and operations definitions mature.

Minor, Robert↗

NASA NTRS2002

Fluid Dynamics of Small, Rugged Vacuum Pumps of Viscous-Drag Type

The need to identify spikes in the concentration of hazardous gases during countdowns to space shuttle launches has led Kennedy Space Center to acquire considerable expertise in the design, construction, and operation of special-purpose gas analyzers of mass-spectrometer type. If such devices could be miniaturized so as to fit in a small airborne package or backpack them their potential applications would include integrated vehicle health monitoring in later-generation space shuttles and in hazardous material detection in airports, to name two examples. The bulkiest components of such devices are vacuum pumps, particularly those that function in the low vacuum range. Now some pumps that operate in the high vacuum range (e.g. molecular-drag and turbomolecular pumps) are already small and rugged. The present work aims to determine whether, on physical grounds, one may or may not adopt the molecular-drag principle to the low-vacuum range (in which case viscous-drag principle is the appropriate term). The deliverable of the present effort is the derivation and justification of some key formulas and calculation methods for the preliminary design of a single-spool, spiral-channel viscous-drag pump.

Russell, John M.↗

NASA NTRS2004

Evaluation of Double-Vacuum-Bag Process For Composite Fabrication

A non-autoclave vacuum bag process using atmospheric pressure alone that eliminates the need for external pressure normally supplied by an autoclave or a press is an attractive method for composite fabrication. This type of process does not require large capital expenditures for tooling and processing equipment. In the molding cycle (temperature/pressure profile) for a given composite system, the vacuum application point has to be carefully selected to achieve the final consolidated laminate net shape and resin content without excessive resin squeeze-out. The traditional single-vacuum- bag (SVB) process is best suited for molding epoxy matrix based composites because of their superior flow and the absence of reaction by-products or other volatiles. Other classes of materials, such as polyimides and phenolics, generate water during cure. In addition, these materials are commonly synthesized as oligomers using solvents to facilitate processability. Volatiles (solvents and reaction byproducts) management therefore becomes a critical issue. SVB molding, without additional pressure, normally fails to yield void-free quality composites for these classes of resin systems. A double-vacuum- bag (DVB) process for volatile management was envisioned, designed and built at the NASA Langley Research Center. This experimental DVB process affords superior volatiles management compared to the traditional SVB process. Void-free composites are consistently fabricated as measured by C-scan and optical photomicroscopy for high performance polyimide and phenolic resins.

Hou, T. H.↗

NASA NTRS2004

Study of Vacuum Energy Physics for Breakthrough Propulsion

This report summarizes the accomplishments during a three year research project to investigate the use of surfaces, particularly in microelectromechanical systems (MEMS), to exploit quantum vacuum forces. During this project, we developed AFM instrumentation to repeatably measure Casimir forces in the nanoNewton range at 10 6 torr, designed an experiment to measure attractive and repulsive quantum vacuum forces, developed a QED based theory of Casimir forces that includes non-ideal material properties for rectangular cavities and for multilayer slabs, developed theoretical models for a variety of microdevices utilizing vacuum forces, applied vacuum physics to a gedanken spacecraft, and investigated a new material with a negative index of refraction.

Millis, Marc G.↗

NASA NTRS1996

Self-Lubricating, Wear-Resistant Diamond Films Developed for Use in Vacuum Environment

Diamond's outstanding properties--extreme hardness, chemical and thermal inertness, and high strength and rigidity--make it an ideal material for many tribological applications, such as the bearings, valves, and engine parts in the harsh environment found in internal-combustion engines, jet engines, and space propulsion systems. It has been demonstrated that chemical-vapor-deposited diamond films have low coefficients of friction (on the order of 0.01) and low wear rates (less than 10(sup -7) mm (sup 3/N-m)) both in humid air and dry nitrogen but that they have both high coefficients of friction (greater than 0.4) and high wear rates (on the order of 1(sup -4) mm sup 3/N-m)) in vacuum. It is clear that surface modifications that provide acceptable levels of friction and wear properties will be necessary before diamond films can be used for tribological applications in a space-like, vacuum environment. Previously, it was found that coatings of amorphous, non-diamond carbon can provide low friction in vacuum. Therefore, to reduce the friction and wear of diamond film in vacuum, carbon ions were implanted in an attempt to form a surface layer of amorphous carbon phases on the diamond films.

Source record↗

NASA NTRS2005

Solid Lubrication by Multiwalled Carbon Nanotubes in Air and in Vacuum for Space and Aeronautics Applications

To evaluate recently developed aligned multiwalled carbon nanotubes (MWNTs) and dispersed MWNTs for solid lubrication applications, unidirectional sliding friction experiments were conducted with 440 C stainless steel balls and hemispherical alumina-yttria stabilized zirconia pins in sliding contact with the MWNTs deposited on quartz disks in air and in vacuum. The results indicate that MWNTs have superior solid lubrication friction properties and endurance lives in air and vacuum under dry conditions. The coefficient of friction of the dispersed MWNTs is close to 0.05 and 0.009 in air and in vacuum, respectively, showing good dry lubricating ability. The wear life of MWNTs exceeds 1 million passes in both air and vacuum showing good durability. In general, the low coefficient of friction can be attributed to the combination of the transferred, agglomerated patches of MWNTs on the counterpart ball or pin surfaces and the presence of tubular MWNTs at interfaces.

Miyoshi, Kazuhisa↗

NASA NTRS2001

Effect of Air and Vacuum Storage on the Degradation of X-Ray-Exposed Aluminized-Teflon Investigated

Metalized Teflon FEP (fluorinated ethylene propylene, DuPont), a common thermal control material, has been found to degrade in the low-Earth-orbit space environment. The aluminized-FEP (Al-FEP) exterior layer on the Hubble Space Telescope has become extremely embrittled, with extensive cracking occurring on all sides of the telescope. This embrittlement has been primarily attributed to radiation exposure (x-rays from solar flares, electron/proton radiation, and possibly near-ultraviolet radiation) combined with thermal cycling. Limited samples of FEP tested after long-term exposure to low Earth orbit on the Hubble Space Telescope and on the Long Duration Exposure Facility indicated that there might be continued degradation in tensile properties over time. An investigation was conducted at the NASA Glenn Research Center to evaluate the effect of air and vacuum storage on the mechanical properties of x-ray-exposed FEP. Aluminized-FEP (5-mil-thick) tensile samples were x-ray exposed with 15.3-kV copper xrays for 2 hr, reducing the percent elongation to failure by approximately 50 percent in comparison to that for pristine Al-FEP. X-ray-exposed samples were stored in air or under vacuum for various time periods to see the effect of storage on tensile properties. Tensile results indicated that samples stored in air had larger decreases in tensile properties than samples stored under vacuum had, as seen in the graph. Samples stored under vacuum (for up to 400 hr) showed no further decrease in tensile properties over time, whereas samples stored in air (for up to 900 hr) appeared to show decreases in tensile properties over time. X-ray-exposed samples stored in air developed a hazy appearance in the exposed area, as seen in the photographs. When the source of the haziness was evaluated using scanning electron microscopy and atomic force microscopy, it was found to reside at the Al/FEP interface as witnessed by an increased surface roughness of the aluminized side of the material and a dramatic decrease in the adhesion between the Al and FEP. Optical properties of air-stored irradiated samples showed an increase in the diffuse reflectance, which is consistent with observed roughening that was characterized by AFM. These findings indicate that air exposure helps degrade x-ray-irradiated FEP. These results indicate that proper sample handling and storage is necessary with space-retrieved materials and with those exposed to ground-based irradiation simulation exposures.

deGroh, Kim K.↗

NASA NTRS2007

Vacuum Pyrolysis and Related ISRU Techniques

A number of ISRU-related techniques have been developed at NASA Goddard Space Flight Center. The focus of the team has been on development of the vacuum pyrolysis technique for the production of oxygen from the lunar regolith. However, a number of related techniques have also been developed, including solar concentration, solar heating of regolith, resistive heating of regolith, sintering, regolith boiling, process modeling, parts manufacturing, and instrumentation development. An initial prototype system was developed to vaporize regolith simulants using a approx. l square meter Fresnel lens. This system was successfully used to vaporize quantities of approx. lg, and both mass spectroscopy of the gasses produced and Scanning Electron Microscopy (SEM) of the slag were done to show that oxygen was produced. Subsequent tests have demonstrated the use of a larger system With a 3.8m diameter reflective mirror to vaporize the regolith. These results and modeling of the vacuum pyrolysis reaction have indicated that the vaporization of the oxides in the regolith will occur at lower temperature for stronger vacuums. The chemical modeling was validated by testing of a resistive heating system that vaporized quantities of approx. 10g of MLS-1A. This system was also used to demonstrate the sintering of regolith simulants at reduced temperatures in high vacuum. This reduction in the required temperature prompted the development of a small-scale resistive heating system for application as a scientific instrument as well as a proof-of principle experiment for oxygen production.

Cardiff, Eric H.↗