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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Catastrophic volcanism as a cause of shocked features found at the K/T boundary and in cryptoexplosion structures

The presence of quartz grains containing shock lamellae at the Cretaceous/Tertiary (K/T) boundary is viewed by many as the single most compelling evidence of meteoritic or cometary impact because there is no known endogenous mechanism for producing these features. Similarly the presence of shocked quartz, shatter cones, coesite and stishovite at cryptoexplosion structures is comonly taken as conclusive evidence of impact. However, several recent studies have cast doubt on this interpretation. It is argued that basaltic volcanism, although not normally explosive, can under exceptional circumstances produce overpressures sufficiently high to produce shock features. The exceptional circumstances include a high content of volatiles, usually CO2, and no preestablished pathway to the surface. Rapid cooling of the saturated basaltic magma can occur if it underlies a cooler more evolved magma in a chamber. Initial slow cooling and partial exsolution of the volatiles will cause the density of the basaltic magma to become less than that of the overlying magma, leading to overturning and mixing. Gas will escape the magma chamber along planar cracks once the pressure becomes sufficiently high. In the vicinity of the crack tip there is a smallscale deviatoric stress pattern which is thought to be sufficiently high to produce transient cracks along secondary axes in the quartz crystals, causing the planar features. The CO2-rich fluid inclusions which have been found along planar elements of quartz in basement rocks of the Vredefort Dome were likely to have been emplaced by such a process. If the mechanism described is capable of producing shocked features as above, it would require a reassessment of the origin of many cryptoexplosion structures as well as seriously weakening the case for an impact origin of the K/T event.

Loper, D. E.↗
NASA NTRSDate not supplied

In-Orbit Selection of Cryocooler Drive Frequencies for XRISM/Resolve

The XRISM/Resolve instrument cooling system uses adiabatic demagnetization refrigerators (ADRs) to cool the detectors to 50 mK and two types of cryocoolers to reduce heat load on the He tank, Joule-Thomson and Stirling cryocoolers. Resolve was designed with tunable cryocooler frequencies so that any mechanical interference and its effect on performance could be minimized. Measurements at different cryocooler drive frequencies were used to quantify the interference and narrow the acceptable range of frequency options. For Resolve the choice of cryocooler drive frequencies dramatically influences the instrument performance. Poor choices have been shown to degrade ADR cooling power and degrade the spectroscopic performance of the instrument. However, good choices have been shown to be free of undesirable features, allowing the instrument to satisfy its performance requirements with significant margin. Thus, the choice of drive frequencies is a critical factor for overall instrument performance. The drive frequencies of the Joule-Thomson cooler operating near 52 Hz, and the Stirling coolers operating near 15 Hz were adjusted in three distinct scan sequences to efficiently narrow the candidate frequency options. The frequency choices were based on stability of the 50 mK control thermometer, changes in the ADR demagnetization rate, and changes in detector noise. Scans across the drive frequency range of each cryocooler were performed multiple times during ground testing. Surprisingly, the results were not repeatable across test campaigns and did not conform to any discernable trend, but they were repeatable when remeasured within a single cool-down cycle. The conclusion was that the good/bad drive frequencies changed during Dewar warmup/cooldown, and possibly after mechanical vibration tests. Therefore, the settings could not be finalized before launch, and scans during instrument commissioning were necessary. This paper describes the cryocooler frequency scan measurements and compares the results during instrument commissioning to those performed during ground tests.

Gary A. Sneiderman↗
NASA NTRSDate not supplied

In-Orbit Selection of Cryocooler Drive Frequencies for XRISM/Resolve

The XRISM/Resolve instrument cooling system uses adiabatic demagnetization refrigerators (ADRs) to cool the detectors to 50 mK and two types of cryocoolers to reduce heat load on the He tank, Joule-Thomson and Stirling cryocoolers. Resolve was designed with tunable cryocooler frequencies so that any mechanical interference and its effect on performance could be minimized. Measurements at different cryocooler drive frequencies were used to quantify the interference and narrow the acceptable range of frequency options. For Resolve the choice of cryocooler drive frequencies dramatically influences the instrument performance. Poor choices have been shown to degrade ADR cooling power and degrade the spectroscopic performance of the instrument. However, good choices have been shown to be free of undesirable features, allowing the instrument to satisfy its performance requirements with significant margin. Thus, the choice of drive frequencies is a critical factor for overall instrument performance. The drive frequencies of the Joule-Thomson cooler operating near 52 Hz, and the Stirling coolers operating near 15 Hz were adjusted in three distinct scan sequences to efficiently narrow the candidate frequency options. The frequency choices were based on stability of the 50 mK control thermometer, changes in the ADR demagnetization rate, and changes in detector noise. Scans across the drive frequency range of each cryocooler were performed multiple times during ground testing. Surprisingly, the results were not repeatable across test campaigns and did not conform to any discernable trend, but they were repeatable when remeasured within a single cool-down cycle. The conclusion was that the good/bad drive frequencies changed during Dewar warmup/cooldown, and possibly after mechanical vibration tests. Therefore, the settings could not be finalized before launch, and scans during instrument commissioning were necessary. This paper describes the cryocooler frequency scan measurements and compares the results during instrument commissioning to those performed during ground tests.

XRISM↗
NASA NTRS2017

Cooling the Origins Space Telescope

The NASA Astrophysics Division has commissioned 4 studies for consideration by the 2020 Decadal Survey to be the next flagship mission following WFIRST (Wide Field Infrared Survey Telescope). One of the four studies is the Origins Space Telescope (OST), which will cover wavelengths from 6 microns to 600 microns. To perform at the level of the zodiacal, galactic, and cosmic background, the telescope must be cooled to 4 degrees Kelvin. 4 degrees Kelvin multi-stage mechanical cryocoolers will be employed along with a multilayer sunshield/thermal shield to achieve this temperature with a manageable parasitic heat load. Current state-of-the-art cryocoolers can achieve close to 4 degrees Kelvin, providing about 50 megawatts of cooling at 4 degrees Kelvin with an input power of 500 watts. Multiple coolers at this power level will be used in parallel. These coolers also provide extra cooling power at intermediate temperature stages of 15-20 degrees Kelvin and 50-70 degrees Kelvin . This upper stage cooling will be used to limit the heat conducted to 4 degrees Kelvin . The multi-layer sunshield will limit the radiated thermal energy to the 4 degrees Kelvin volume. This paper will describe the architecture of the cryogenic system for OST along with preliminary thermal models.

cryogenics↗
NASA NTRS1999

Hybrid Thermal Control Testing of a Cryogenic Propellant Tank

This report presents the experimental results of a hybrid thermal control system, one that integrates a passive system (multi-layer insulation) with an active system (a mechanical cyrocooler) applied to cryogenic propellant storage. These experiments were performed on a 1.39 m diameter spherical propellant tank filled with LH2 while installed in an evacuated chamber. The tank heat transfer to the cryocooler was accomplished with a condenser installed in the ullage of the tank and mated to the second stage of the cooler, and by conduction, through copper leaves mated to the first stage of the cooler. The first hybrid system test was performed with both the condenser and the leaves, a configuration that had excess capacity to remove the heat entering the tank; the second test was performed with only the condenser, with a capacity closely matched to the tank heating rate. In both of these tests, the goal of zero boil-off was achieved.

Plachta, David W.↗
NASA NTRS1988

The origin of broad emission line clouds in active galactic nuclei

Numerous arguments suggest that the broad emission lines characteristic of many types of active galactic nuclei are formed in comparatively cool clouds embedded in a much hotter medium of roughly equal pressure. Here it is shown that a cycle exists in which cooler condensations form within the hot medium via a finite-amplitude thermal instability, drop to temperatures characteristic of photoionization equilibrium, are destroyed by hydrodynamic processes, and then return their material to the hot medium. Clouds of characteristic pressure about 10 to the 14th K/cu cm and thickness about 10 to the 23rd/sq cm are produced by this mechanism, in agreement with the pressure and thickness inferred from photoionization model analysis of observed emission-line ratios. Only a fraction of the hot medium's mass must encounter a finite-amplitude perturbation in order to produce the observed mass in clouds.

Krolik, Julian H.↗
NASA NTRS1993

Extrapolation of space weathering processes to other small solar system bodies

A diverse range of processes were invoked as the dominant factor or as important contributory factors in the modification of the optical surface and regolith of the moon. These include impact vitrification by large and small projectiles, solar wind implantation and the reduction of oxidized iron during energetic events, sputtering and crystal lattice damage by energetic cosmic rays, shock metamorphism of minerals, mixing of diverse lithologies by impacts, and contamination by external materials. These processes are also potentially important on the rocky surfaces of other small solar system bodies. For icy bodies, several additional processes are also possible, including formation of complex organic compounds from methane and ammonia-bearing ices by ultraviolet irradiation and the condensation of vapor species to form frost layers in the polar or cooler regions of objects at appropriate heliocentric distances. The lunar case, even when completely understood, will not extend in a simple linear fashion to other small rocky objects, nor will the optical surfaces of those objects all be affected to the same degree by each process. The major factors that will control the relative efficacy of a possible mechanism include the efficiency of ejecta retention and the degree to which the regolith materials experience multiple events (primarily a function of body size, escape velocity, and impactor velocities); the mean duration of typical regolith particle exposure at the optical surface and within reach of the micrometeorite, cosmic ray, solar wind, or UV fluxes (a function of the rate and scale of regolith mixing, production, and removal processes); the incident flux of solar (low energy) cosmic rays, solar wind, or UV radiation (inverse square of heliocentric distance) or of galactic (high energy) cosmic rays (slowly increasing flux with heliocentric distance); and the compositional and mineralogical nature of the surface being affected. In general, those processes that depend upon either the retention of impact ejecta or on the presence of multigenerational regoliths should be substantially less effective on smaller bodies with lower escape velocities. However, there are important exceptions to this generalization. For example, a process that involves the hypervelocity impact of small particles into a fine-grained regolith may be able to effectively retain highly shocked or melted material due to the nature of shock wave propagation in such a heterogeneous material.

Gaffey, M. J.↗
NASA NTRS2000

Growth of Matrix Cracks During Intermediate Temperature Stress Rupture of a SiC/SiC Composite in Air

The crack density of woven Hi-Nicalon(sup TM) (Nippon Carbon, Japan) fiber, BN interphase, melt-infiltrated SiC matrix composites was determined for specimens subjected to tensile stress rupture at 815 C. A significant amount of matrix cracking occurs due to the growth of fiber-bridged microcracks even at stresses below the run-out condition. This increased cracking corresponded to time dependent strain accumulation and acoustic emission activity during the constant load test. However, the portion of the rupture specimens subjected to cooler temperatures (< 600 C than the hot section had significantly lower crack densities compared to the hotter regions. From the acoustic emission and time dependent strain data it can be inferred that most of the matrix crack growth occurred within the first few hours of the tensile rupture experiment. The crack growth was attributed to an interphase recession mechanism that is enhanced by the presence of a thin carbon layer between the fiber and the matrix as a result of the composite fabrication process. One important consequence of matrix crack growth at the lower stresses is poor retained strength at room temperature for specimens that did not fail.

Morscher, Gregory N.↗
NASA NTRS1974

Effect of volatile removal during molding on the properties of two phenolic-fiber composites

A comparison has been made of the effect of three volatile-removing techniques during molding on the properties of phenolic-fiber composites. The first technique involved heating the molding compound from one side, initiating the volatile-producing reactions, and driving these volatiles through the compound toward the cooler side. The second technique involved the application of a vacuum to the molding cavity before and during the cure cycle. The third technique was a combination of the first two. These techniques were used in the compression molding of phenolic-asbestos and phenolic-glass composites. The effects of both the individual and combined techniques on the mechanical, thermal, and sorption properties of the composites are reported.

Price, H. L.↗
NASA NTRS1981

Comparative aspects of Venus and terrestrial meteorology

The observations and measurements made by Pioneer Venus orbiters are presented in terms of comparison of Venus and terrestrial meteorology. Although the temperature-pressure profiles of the two planets differ at lower altitudes, the temperatures are similar over their common range of pressures except for a much cooler mesosphere on Venus. The additional similarities between the earth and Venus relate to the warm polar stratospheres and the zonally-averaged energy budgets of the two planets. A difference in the mean radiation budgets for Venus is the relative smallness of the upward and downward thermal flux components. It is noted that the observed similarities reflect common mechanisms despite the difference in the dynamical regimes of the two planets.

Taylor, F. W.↗
NASA NTRS2000

Hot HB Stars in Globular Clusters: Physical Parameters and Consequences for Theory: Radiative Levitation Versus Helium Mixing - 5

Atmospheric parameters (T(sub eff), log g), masses and helium abundances are derived for 42 hot horizontal branch (HB) stars in the globular cluster NGC6752. For 19 stars we derive magnesium and iron abundances as well and find that iron is enriched by a factor of 50 on average with respect to the cluster abundance whereas the magnesium abundances are consistent with the cluster abundance. Radiation pressure may levitate heavy elements like iron to the surface of the star in a diffusive process. Taking into account the enrichment of heavy elements in our spectroscopic analyses we find that high iron abundances can explain part, but not all, of the problem of anomalously low gravities along the blue HB. The blue HB stars cooler than about 15,100 K and the sdB stars (T(sub eff) greater than or = 20,000 K) agree well with canonical theory when analysed with metal-rich ([M/H] = +0.5) model atmospheres, but the stars in between these two groups remain offset towards lower gravities and masses. Deep Mixing in the red giant progenitor phase is discussed as another mechanism that may influence the position of the blue HB stars in the (T(sub eff), log g)-plane but not their masses.

Moehler, S.↗
NASA NTRS2003

Coronal Structures in Cool Stars: XMM-NEWTON Hybrid Stars and Coronal Evolution

This program addresses the evolution of stellar coronas by comparing a solar-like corona in the supergiant Beta Dra (G2 Ib-IIa) to the corona in the allegedly more evolved state of a hybrid star, alpha TrA (K2 II-III). Because the hybrid star has a massive wind, it appears likely that the corona will be cooler and less dense as the magnetic loop structures are no longer closed. By analogy with solar coronal holes, when the topology of the magnetic field is configured with open magnetic structures, both the coronal temperature and density are lower than in atmospheres dominated by closed loops. The hybrid stars assume a pivotal role in the definition of coronal evolution, atmospheric heating processes and mechanisms to drive winds of cool stars. We are attempting to determine if this model of coronal evolution is correct by using XMM-NEWTON RGS spectra for the 2 targets we were allocated through the Guest Observer program.

Dupree, Andrea K.↗
NASA NTRS2004

Hybrid Stars and Coronal Evolution

This program addresses the evolution of stellar coronas by comparing a solar-like corona in the supergiant Dra (G2 Ib-IIa) to the corona in the allegedly more evolved state of a hybrid star, TrA (K2 11-111). Because the hybrid star has a massive wind, it appears likely that the corona will be cooler and less dense as the magnetic loop structures are no longer closed. By analogy with solar coronal holes, when the topology of the magnetic field is configured with open magnetic structures, both the coronal temperature and density are lower than in atmospheres dominated by closed loops. The hybrid stars assume a pivotal role in the definition of coronal evolution, atmospheric heating processes and mechanisms to drive winds of cool stars.

Mushotzky, Richard↗
NASA NTRS2006

An Overview of NASA Space Cryocooler Programs--2006

Mechanical cryocoolers represent a significant enabling technology for NASA's Earth and Space Science Enterprises. Many of NASA's space instruments require cryogenic refrigeration to improve dynamic range, extend wavelength coverage, or enable the use of advanced detectors to observe a wide range of phenomena--from crop dynamics to stellar birth. Reflecting the relative maturity of the technology at these temperatures, the largest utilization of coolers over the last fifteen years has been for instruments operating at medium to high cryogenic temperatures (55 to 150K). For the future, important new developments are focusing on the lower temperature range, from 6 to 20 K, in support of studies of the origin of the Universe and the search for planets around distant stars. NASA's development of a 20K cryocooler for the European Planck spacecraft and a 6 K cryocooler for the MIRI instrument on the James Webb Space Telescope (JWST) are examples of the thrust to provide low-temperature cooling for this class of future missions.

cryogenics↗
NASA NTRS1975

S192 multispectral scanner channel 13 electromechanical noise investigation ECP-166

A review is presented of all data on the multispectral scanner having to do with low frequency noise. The noise is component-induced, either mechanical or electrical or a combination of both. To assist in understanding the source of the noise, several dynamic analyses both structural and electrical were made and are reported. A review is presented of structural resonance test data obtained with the use of an accelerometer and strain gage sensors. Results of an analysis of the natural frequencies of the Dewar leads is included along with an analysis of the S192 cooler and its supporting structure. Other topics discussed include electronic stability of the forward signal, automatic gain control, and the offset control feedback loops as well as the preamplifier which utilized on integrator feedback circuit.

Koumjian, H.↗
NASA NTRS1992

Ultra-high temperature stability Joule-Thomson cooler with capability to accomodate pressure variations

A Joule-Thomson cryogenic refrigeration system capable of achieving high temperature stabilities in the presence of varying temperature, atmospheric pressure, and heat load is provided. The Joule-Thomson cryogenic refrigeration system includes a demand flow Joule-Thomson expansion valve disposed in a cryostat of the refrigeration system. The expansion valve has an adjustable orifice that controls the flow of compressed gas therethrough and induces cooling and partial liquefaction of the gas. A recuperative heat exchanger is disposed in the cryostat and coupled to the expansion valve. A thermostatically self-regulating mechanism is disposed in the cryostat and coupled to the J-T expansion valve. The thermostatically self-regulating mechanism automatically adjusts the cross sectional area of the adjustable valve orifice in response to environmental temperature changes and changes in power dissipated at a cold head. A temperature sensing and adjusting mechanism is coupled to a cold head for adjusting the temperature of the cold head in response to the change in heat flow in the cold head. The temperature sensing and adjusting mechanism comprises a temperature sensitive diode, a wound wire heater, and an electrical feedback control circuit coupling the diode to the heater. An absolute pressure relief valve is interposed between the output of the cryostat and an exhaust port for maintaining a constant exhaust temperature in the refrigerating system, independent of the changes in atmospheric pressure.

Bard, Steven↗
NASA NTRS1996

On the Anticorrelation Between High Accretion Luminosity and Radio Jet Ejection in Gro J1655-40 and Other Objects

A model is described in which radio jet formation in accreting objects is suppressed by processes which occur when the accretion rate approaches the Eddington limit. This was motivated by GRO J1655-40 and other objects which show an anticorrelation between high luminosity and the onset of a radio jet. The jet production mechanism employed is the Blandford-Payne MHD acceleration process, seeded by an e'e- pair wind. Observations indicate that all key ingredients of this mechanism are, or should be, present in these sources. Observed jet velocities and total powers are consistent with theoretical and numerical predictions of this model. The primary jet suppression mechanism proposed is the Papaloizou-Pringle compressible shear instability, which should disrupt the jet-producing region of the disk when the accretion rate approaches about one-third Eddington. The turn-on of the jet in GRO J 1 655 - 40 is consistent with this estimate. When super-Eddington, the disk should also drive an optically thick, subrelativistic wind, which may be a secondary jet suppression mechanism. The possible presence of such a wind is seen in the early spectral evolution of GRO J1655-40 and in the broad absorption lines of certain quasi-stellar objects (QSOs). Important tests of the model would be independent measurements of the compact object masses in these sources, a comparison of normal and broad absorption line (BAL) QSO X-ray spectra to see if the latter objects are significantly cooler, and a low-frequency search around BAL QSOs to see if at least some have fossil radio sources.

Meier, D.↗
NASA NTRS2014

New Aspects of a Lid-Removal Mechanism in the Onset of a SEP-Producing Eruption Sequence

We examine a sequence of two ejective eruptions from a single active region on 2012 January 23, using magnetograms and EUV images from SDO/HMI and SDO/AIA, and EUV images from STEREO. Cheng et al. (2013) showed that the first eruption's ("Eruption 1'') flux rope was apparent only in "hotter'' AIA channels, and that it removed overlying field that allowed the second eruption (``Eruption 2'') to begin via ideal MHD instability; here we say Eruption 2 began via a ``lid removal'' mechanism. We show that during Eruption-1's onset, its flux rope underwent ``tether weakening'' (TW) reconnection with the field of an adjacent active region. Standard flare loops from Eruption 1 developed over Eruption-2's flux rope and enclosed filament, but these overarching new loops were unable to confine that flux rope/filament. Eruption-1's flare loops, from both TW reconnection and standard-flare-model internal reconnection, were much cooler than Eruption-2's flare loops (GOES thermal temperatures of approx. 9 MK compared to approx. 14 MK). This eruption sequence produced a strong solar energetic particle (SEP) event (10 MeV protons, >10(exp 3) pfu for 43 hrs), apparently starting when Eruption-2's CME blasted through Eruption-1's CME at 5-10 R_s. This occurred because the two CMEs originated in close proximity and in close time sequence: Eruption-1's fast rise started soon after the TW reconnection; the lid removal by Eruption-1's ejection triggered the slow onset of Eruption 2; and Eruption-2's CME, which started approx. 1 hr later, was three times faster than Eruption-1's CME.

Sterling, Alphonse C.↗