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NASA NTRS2019

Maximum Carbon Uptake Rate Dominates the Interannual Variability of Global Net Ecosystem Exchange

Terrestrial ecosystems contribute most of the interannual variability (IAV) in atmospheric carbon dioxide (CO2) concentrations, but processes driving the IAV of net ecosystem CO2 exchange (NEE) remain elusive. For a predictive understanding of the global C cycle, it is imperative to identify indicators associated with ecological processes that determine the IAV of NEE. Here, we decompose the annual NEE of global terrestrial ecosystems into their phenological and physiological components, namely maximum carbon uptake (MCU) and release (MCR), the carbon uptake period (CUP), and two parameters, α and β, that describe the ratio between actual versus hypothetical maximum C sink and source, respectively. Using long‐term observed NEE from 66 eddy covariance sites and global products derived from FLUXNET observations, we found that the IAV of NEE is determined predominately by MCU at the global scale, which explains 48% of the IAV of NEE on average while α, CUP, β, and MCR explain 14%, 25%, 2%, and 8%, respectively. These patterns differ in water‐limited ecosystems versus temperature‐ and radiation‐limited ecosystems; 31% of the IAV of NEE is determined by the IAV of CUP in water‐limited ecosystems, and 60% of the IAV of NEE is determined by the IAV of MCU in temperature‐ and radiation‐limited ecosystems. The Lund‐Potsdam‐Jena (LPJ) model and the Multi‐scale Synthesis and Terrestrial Model Inter‐comparison Project (MsTMIP) models underestimate the contribution of MCU to the IAV of NEE by about 18% on average, and overestimate the contribution of CUP by about 25%. This study provides a new perspective on the proximate causes of the IAV of NEE, which suggest that capturing the variability of MCU is critical for modeling the IAV of NEE across most of the global land surface.

Fu, Zheng↗

NASA NTRS2010

Does Aerosol Weaken or Strengthen the South Asian Monsoon?

Aerosols are known to have the ability to block off solar radiation reaching the earth surface, causing it to cool - the so-called solar dimming (SDM) effect. In the Asian monsoon region, the SDM effect by aerosol can produce differential cooling at the surface reducing the meridional thermal contrast between land and ocean, leading to a weakening of the monsoon. On the other hand, absorbing aerosols such as black carbon and dust, when forced up against the steep slopes of the southern Tibetan Plateau can produce upper tropospheric heating, and induce convection-dynamic feedback leading to an advance of the rainy season over northern India and an enhancement of the South Asian monsoon through the "Elevated Heat Pump" (EHP) effect. In this paper, we present modeling results showing that in a coupled ocean-atmosphere-land system in which concentrations of greenhouse gases are kept constant, the response of the South Asian monsoon to dust and black carbon forcing is the net result of the two opposing effects of SDM and EHP. For the South Asian monsoon, if the increasing upper tropospheric thermal contrast between the Tibetan Plateau and region to the south spurred by the EHP overwhelms the reduction in surface temperature contrast due to SDM, the monsoon strengthens. Otherwise, the monsoon weakens. Preliminary observations are consistent with the above findings. We find that the two effects are strongly scale dependent. On interannual and shorter time scales, the EHP effect appears to dominate in the early summer season (May-June). On decadal or longer time scales, the SDM dominates for the mature monsoon (July-August). Better understanding the physical mechanisms underlying the SDM and the EHP effects, the local emission and transport of aerosols from surrounding deserts and arid-regions, and their interaction with monsoon water cycle dynamics are important in providing better prediction and assessment of climate change impacts on precipitation of the Asian monsoon land regions.

Lau, William K.↗

NASA NTRS2015

Loop Heat Pipe Temperature Oscillation Induced by Gravity Assist and Reservoir Heating

The Laser Thermal Control System (LCTS) for the Advanced Topographic Laser Altimeter System (ATLAS) to be installed on NASA's Ice, Cloud, and Land Elevation Satellite (ICESat-2) consists of a constant conductance heat pipe and a loop heat pipe (LHP) with an associated radiator. During the recent thermal vacuum testing of the LTCS where the LHP condenser/radiator was placed in a vertical position above the evaporator and reservoir, it was found that the LHP reservoir control heater power requirement was much higher than the analytical model had predicted. Even with the control heater turned on continuously at its full power, the reservoir could not be maintained at its desired set point temperature. An investigation of the LHP behaviors found that the root cause of the problem was fluid flow and reservoir temperature oscillations, which led to persistent alternate forward and reversed flow along the liquid line and an imbalance between the vapor mass flow rate in the vapor line and liquid mass flow rate in the liquid line. The flow and temperature oscillations were caused by an interaction between gravity and reservoir heating, and were exacerbated by the large thermal mass of the instrument simulator which modulated the net heat load to the evaporator, and the vertical radiator/condenser which induced a variable gravitational pressure head. Furthermore, causes and effects of the contributing factors to flow and temperature oscillations intermingled.

Thermal Control Systems↗

NASA NTRS2015

Loop Heat Pipe Temperature Oscillation Induced by Gravity Assist and Reservoir Heating

0000↗

NASA NTRS2001

Laminarization of Turbulent Boundary Layer on Flexible and Rigid Surfaces

An investigation of the control of turbulent boundary layer flow over flexible and rigid surfaces downstream of a concave-convex geometry has been made. The concave-convex curvature induces centrifugal forces and a pressure gradient on the growth of the turbulent boundary layer. The favorable gradient is not sufficient to overcome the unfavorable; thus, the net effect is a destabilizing, of the flow into Gortler instabilities. This study shows that control of the turbulent boundary layer and structural loading can be successfully achieved by using localized surface heating because the subsequent cooling and geometrical shaping downstream over a favorable pressure gradient is effective in laminarization of the turbulence. Wires embedded in a thermally insulated substrate provide surface heating. The laminarized velocity profile adjusts to a lower Reynolds number, and the structure responds to a lower loading. In the laminarization, the turbulent energy is dissipated by molecular transport by both viscous and conductivity mechanisms. Laminarization reduces spanwise vorticity because of the longitudinal cooling gradient of the sublayer profile. The results demonstrate that the curvature-induced mean pressure gradient enhances the receptivity of the flow to localized surface heating, a potentially viable mechanism to laminarize turbulent boundary layer flow; thus, the flow reduces the response of the flexible structure and the resultant sound radiation.

Maestrello, Lucio↗

NASA NTRS1994

Thermal and albedo mapping of the polar regions of Mars using Viking thermal mapper observations: 2. South polar region

We present the first maps of the apparent thermal inertia and albedo of the south polar region of Mars. The observations used to create these maps were acquired by the infrared thermal mapper (IRTM) instruments on the two Viking Orbiters over a 30-day period in 1977 during the Martian late southern summer season. The maps cover the region from 60 deg S to the south pole at a spatial resolution of 1 deg of latitude, thus completing the initial thermal mapping of the entire planet. The analysis and interpretation of these maps is aided by the results of a one-dimensional radiative convective model, which is used to calculate diurnal variations in surface and atmospheric temperatures, and brightness temperatures at the top of the atmosphere for a range of assumptions concerning dust optical properties and dust optical depths. The maps show that apparent thermal inertias of bare ground regions decrease systematically from 60 deg S to the south pole. In unfrosted regions close to the south pole, apparent thermal inertias are among the lowest observed anywhere on the planet. On the south residual cap, apparent thermal inertias are very high due to the presence of CO2 frost. In most other regions of Mars, best fit apparent albedos based on thermal emission measurements are generally in good agreement with actual surface albedos based on broadband solar reflectance measurements. The one-dimensional atmospheric model calculations also predict anomalously cold brightness temperatures close to the pole during late summer, and after considering a number of alternatives, it is concluded that the net surface cooling due to atmospheric dust is the best explanation for this phenomenon. The region of lowest apparent thermal inertia close to the pole, which includes the south polar layered deposits, is interpreted to be mantled by a continuous layer of aeolian material that must be at least a few millimeters thick. The low thermal inertias mapped in the south polar region imply an absence of surface water ice deposits, which is consistent with Viking Mars atmospheric water detector (MAWD) measurements which show low atmospheric water vapor abundances throughout the summer season.

Paige, David A.↗

NASA NTRS2007

Anomalies in the South American Monsoon Induced by Aerosols

We have investigated the direct effects of aerosols on the water cycle of the South American monsoon using the NASA finite-volume general circulation model (fvGCM). Global aerosol forcings are computed from radiative transfer functions derived from global distributions of five species of aerosols, i.e., dust, black carbon, organic carbon, sulphate and sea salt from the Goddard Chemistry Aerosol Radiation Transport (GOCART) model. Comparing fvGCM experiments without aerosol forcing, and with different combinations of aerosol forcing, we evaluate the impacts of aerosol direct heating on the onset, maintenance and evolution of the South American summer monsoon. We find that during the pre-monsoon season (September-October-November) Saharan dust contribute to heating of the atmosphere over the central and eastern equatorial Atlantic/Africa region through the elevated heat pump mechanism. The heating generates an anomalous Walker circulation with sinking motion, and low level northeasterlies over the Caribbean and northwestern South America. The low level flow is blocked by the Andes, and turn south and southeastward, increasing the low level jet (LLJ) along the eastern slope of the Andes. The increased LLJ transports more moisture from the Atlantic and the Amazon, enhancing the moisture convergence over subtropical land regions of South America. The moisture convergence was further accelerated by atmospheric heating by biomass burning over the Amazon. The net results of the dust and biomass heating are: a) an advance of the monsoon rainy season, b) an enhanced LLJ and c) a shifting the South America monsoon land precipitation equatorward, with increased rain over southern Brazil and reduced rain over the La Plata basin. ramifications of this elevated heating heat pump mechanism in aerosol monsoon water cycle on climate variability and change will be discussed. The ramifications of this "elevated heating heat pump" mechanism in aerosol monsoom water cycle on climate variability and change will be discussed.

Lau, K. M. William↗

NASA NTRS2002

Airborne Sunphotometer Measurements of Aerosol Optical Depth and Columnar Water Vapor During the Puerto Rico Dust Experiment, and Comparison with Land, Aircraft, and Satellite Measurements

Analyses of aerosol optical depth (AOD) and columnar water vapor (CWV) measurements obtained with the six-channel NASA Ames Airborne Tracking Sunphotometer (AATS-6) mounted on a twin-engine aircraft during the summer 2000 Puerto Rico Dust Experiment are presented. In general, aerosol extinction values calculated from AATS-6 AOD measurements acquired during aircraft profiles up to 5 km ASL reproduce the vertical structure measured by coincident aircraft in-situ measurements of total aerosol number and surface area concentration. Calculations show that the spectral dependence of AOD was small (mean Angstrom wavelength exponents of approximately 0.20) within three atmospheric layers defined as the total column beneath the top of each aircraft profile, the region beneath the trade wind inversion, and the region within the Saharan Air Layer (SAL) above the trade inversion. This spectral behavior is consistent with attenuation of incoming solar radiation by large dust particles or by dust plus sea salt. Values of CWV calculated from profile measurements by AATS-6 at 941.9 nm and from aircraft in-situ measurements by a chilled mirror dewpoint hygrometer agree to within approximately 4% (0.13 g/sq cm). AATS-6 AOD values measured on the ground at Roosevelt Roads Naval Air Station and during low altitude aircraft runs over the adjacent Cabras Island aerosol/radiation ground site agree to within 0.004 to 0.030 with coincident data obtained with an AERONET Sun/sky Cimel radiometer located at Cabras Island. For the same observation times, AERONET retrievals of CWV exceed AATS-6 values by a mean of 0.74 g/sq cm (approximately 21 %) for the 2.9-3.9 g/sq cm measured by AATS-6. Comparison of AATS-6 aerosol extinction values obtained during four aircraft ascents over Cabras Island with corresponding values calculated from coincident aerosol backscatter measurements by a ground-based micro-pulse lidar (MPL-Net) located at Cabras yields a similar vertical structure above the trade inversion. Finally, AATS-6 AOD values measured during low altitude aircraft traverses over the ocean are compared with corresponding AOD values retrieved over water from upwelling radiance measurements by the MODIS, TOMS, and GOES-8 Imager satellite sensors, with mixed results. These exercises highlight the need for continued satellite sensor comparison/validation studies to improve satellite AOD retrieval algorithms, and the usefulness of airborne sunphotometer measurements in the validation process.

Livingston, John M.↗

NASA NTRS2007

Does Aerosol Weaken or Strengthen the South Asian Monsoon?

Aerosols are known to have the ability to block off solar radiation reaching the earth surface, causing it to cool - the so-called solar dimming (SDM) effect. In the Asian monsoon region, the SDM effect by aerosol can produce differential cooling at the surface reducing the meridional thermal contrast between land and ocean, leading to a weakening of the monsoon (Ramanathan et al. 2005). On the other hand, absorbing aerosols such as black carbon and dust, when forced up against the steep slopes of the southern Tibetan Plateau can produce upper tropospheric heating, and induce convection-dynamic feedback leading to an advance of the rainy season over northern India and an enhancement of the South Asian monsoon through the "Elevated Heat Pump" (EHP) effect (Lau et al. 2006). In this paper, we present modeling results showing that in a coupled ocean-atmosphere-land system in which concentrations of greenhouse gases are kept constant, the response of the South Asian monsoon to dust and black carbon forcing is the net result of the two opposing effects of SDM and EHP. For the South Asian monsoon, if the increasing upper tropospheric thermal contrast between the Tibetan Plateau and region to the south spurred by the EHP overwhelms the reduction in surface temperature contrast due to SDM, the monsoon strengthens. Otherwise, the monsoon weakens. Preliminary observations are consistent with the above findings. We find that the two effects are strongly scale dependent. On interannual and shorter time scales, the EHP effect appears to dominate in the early summer season (May-June). On decadal or longer time scales, the SDM dominates for the mature monsoon (July-August). Better understanding the physical mechanisms underlying the SDM and the EHP effects, the local emission and transport of aerosols from surrounding deserts and arid-regions, and their interaction with monsoon water cycle dynamics are important in providing better prediction and assessment of climate change impacts on precipitation of the Asian monsoon land regions.

Lau, William K. M.↗

NASA NTRS2001

Analytical Models for Variable Density Multilayer Insulation Used in Cryogenic Storage

A unique multilayer insulation concept for orbital cryogenic storage was experimentally evaluated at NASA Marshall Space Flight Center (MSFC) using the Multipurpose Hydrogen Test Bed (MHTB). A combination of foam/Multi layer Insulation (MLI) was used. The MLI (45 layers of Double Aluminized Mylar (DAM) with Dacron net spacers) was designed for an on-orbit storage period of 45 days and included several unique features such as: a variable layer density and larger but fewer DAM perforations for venting during ascent to orbit. The focus of this paper is on analytical modeling of the variable density MLI performance during orbital coast periods. The foam/MLI combination model is considered to have five segments. The first segment represents the foam layer. The second, third, and fourth segments represent the three layers of MLI with different layer densities and number of shields. Finally, the last segment is considered to be a shroud that surrounds the last MLI layer. The hot boundary temperature is allowed to vary from 164 K to 305 K. To simulate MLI performance, two approaches are considered. In the first approach, the variable density MLI is modeled layer by layer while in the second approach, a semi-empirical model is applied. Both models account for thermal radiation between shields, gas conduction, and solid conduction through the separator materials. The heat flux values predicted by each approach are compared for different boundary temperatures and MLI systems with 30, 45, 60, and 75 layers.

Hedayat, A.↗

NASA NTRS1997

Automated Fabrication of High Performance Composites: An Overview of Research at the Langley Research Center

Automated heated placement of consolidated fiber reinforced polymer ribbon/tape is a rapid, cost effective technique for net shape fabrication of high performance composites. Several research efforts in the United States are developing the heated head robotic hardware and associated software needed to bring this technology into widespread use for building aircraft parts. These efforts emphasize the use of pre-consolidated thermoplastic ribbon or tape which is thermally welded on-the-fly . The approach provides in-situ consolidation and obviates the need for autoclave processing and massive debulking, thereby reducing costs. Addressed in this paper are some key issues being pursued at NASA Langley related to this technology. These include: (a) preparation of high quality intermediate materials forms such as thermoplastic powders, powder-coated towpreg and consolidated ribbon/tape and (b) achievement of precise control of the following: robot head positioning on the tool; material placement; heat delivery to the lay-down zone; and cut/add, start/stop capability. Heated head development has dealt with the use of hot gases alone and in combination with focused infrared radiation as heat sources.

Johnston, N. J.↗

NASA NTRS2004

Probing me Reverse Shock in an Oxygen-Rich Supernova Remnant

The aim of this project is to examine the O VI emission at three positions around the X- ray bright ring of the remnant in order to investigate the relation between the O VI emission, the X-ray O VII and O VIII emission, and the optical [OIII} emission, and how these vary around the rim of the remnant. All three pointings and the background pointing have now been observed; the archive notification for the most recent dataset was Oct 30, 2003. After reprocessing and screening, the net exposure time for the SE exposure is only 54 percent of the approved time (15 kilosec). for the SE exposure, the available statistics are not good enough for analysis. A request for reobservation to make up for the lost time in the SE pointing has been approved. Broad O VI 1032 and O VI 1038 emission is detected with velocity width of at least 800 km/s, and possibly exceeding 1000 km/s. The Flanagan et al. analysis of the Chandra grating data show bulk velocities in the X-ray gas of order +/- 1000 km/s. In the region of the FUSE E0lO2-SE pointing, the Chandra data indicate both blue-shifted and red-shifted emission. Analysis of the velocity structure of the O VI emission will provide additional constraints on the kinematics of the gas: is it emission from a tilted expanding barrel, or a more symmetric expansion? The O VI fluxes are also needed to assess whether the O VI is radiation from recombining O VII or instead fiom cooler gas ionizing toward O VII. The emission is faint, however, which complicates the analysis. Because the lines are so broad, absorption by intervening H2, CII, and foreground OVI must be considered. A number of stars in the SMC have been observed which provide information on foreground OVI absorption. The initial analyses have concentrated on the Li1F channel since the guidance is based on that channel. The Li2F channel is being examined exposure by exposure to see if any of the data can be used to improve the signal to noise in the Li1F data.

Gaetz, Terrance↗

NASA NTRS1995

Validation of clear-sky fluxes for tropical oceans from the Earth Radiation Budget Experiment

The existence and magnitude of a systematic bias in the clear-sky longwave fluxes from the Earth Radiation Budget Experiment (ERBE) is investigated. The bias is apparently introduced because the ERBE method for scene identification does not account for large zonal gradients in longwave absorption by water vapor. The ERBE fluxes are compared to fluxes calculated with a radiative transfer model from ship radiosonde measurements. The comparison is based upon an analysis of 5 yr of coincident satellite and radiosonde observations for equatorial ocean regions. The differences between the ERBE and model fluxes are examined as functions of sea surface temperature (SST) and relative humidity. The authors use height-mean relative humidity bar-RH as an index of atmospheric moisture. The average offset between and model ERBE fluxes ranges between +2 and +6 W/sq m for SSTs above 295 K, and the gradients with respect to SST are nearly identical. However, the difference between the model and ERBE depends significantly on the tropospheric relative humidity. ERBE fluxes exceed model fluxes for bar-RH above 70%, and the maximum offset of +9 to +12 W/sq m is consistent with previous estimates. There are also indications that the clear-sky fluxes for bar-RH below 25% may be underestimated by about 10-15 W/sq m. Since extreme values of height-mean humidity are relatively infrequent, the net bias introduced in the ERBE monthly mean clear-sky fluxes is generally less than the systematic error in estimates introduced in the ERBE monthly mean clear-sky fluxes is generally less than the systematic error in estimates of the instantaneous fluxes. These findings support earlier work on the coupling between SST and the atmospheric greenhouse effect, in particular the existence of a super greenhouse effect for oceans warmer than 300 K. Recent reports of much larger systematic differences are not supported by this analysis. The results indicate that comparison of general circulation model (GCM) and ERBE clear-sky longwave fluxes will depend explicitly on atmospheric humidity.

Collins, W. D.↗

NASA NTRS2001

Arctic Stratus Cloud Properties and Their Effect on the Surface Radiation Budget: Selected Cases from FIRE ACE

To study Arctic stratus cloud properties and their effect on the surface radiation balance during the spring transition season, analyses are performed using data taken during three cloudy and two clear days in May 1998 as part of the First ISCCP Regional Experiment (FIRE) Arctic Cloud Experiment (ACE). Radiative transfer models are used in conjunction with surface- and satellite-based measurements to retrieve the layer-averaged microphysical and shortwave radiative properties. The surface-retrieved cloud properties in Cases 1 and 2 agree well with the in situ and satellite retrievals. Discrepancies in Case 3 are due to spatial mismatches between the aircraft and the surface measurements in a highly variable cloud field. Also, the vertical structure in the cloud layer is not fully characterized by the aircraft measurements. Satellite data are critical for understanding some of the observed discrepancies. The satellite-derived particle sizes agree well with the coincident surface retrievals and with the aircraft data when they were collocated. Optical depths derived from visible-channel data over snow backgrounds were overestimated in all three cases, suggesting that methods currently used in satellite cloud climatologies derive optical depths that are too large. Use of a near-infrared channel with a solar infrared channel to simultaneously derive optical depth and particle size appears to alleviate this overestimation problem. Further study of the optical depth retrieval is needed. The surface-based radiometer data reveal that the Arctic stratus clouds produce a net warming of 20 W m(exp -2) in the surface layer during the transition season suggesting that these clouds may accelerate the spring time melting of the ice pack. This surface warming contrasts with the net cooling at the top of the atmosphere (TOA) during the same period. All analysis of the complete FIRE ACE data sets will be valuable for understanding the role of clouds during the entire melting and refreezing process that occurs annually in the Arctic.

Doug, Xiquan↗

NASA NTRS2014

Revised (Mixed-Effects) Estimation for Forest Burning Emissions of Gases and Smoke, Fire/Emission Factor Typology, and Potential Remote Sensing Classification of Types for Ozone and Black-Carbon Simulation

We summarize recent progress (a) in correcting biomass burning emissions factors deduced from airborne sampling of forest fire plumes, (b) in understanding the variability in reactivity of the fresh plumes sampled in ARCTAS (2008), DC3 (2012), and SEAC4RS (2013) airborne missions, and (c) in a consequent search for remotely sensed quantities that help classify forest-fire plumes. Particle properties, chemical speciation, and smoke radiative properties are related and mutually informative, as pictures below suggest (slopes of lines of same color are similar). (a) Mixed-effects (random-effects) statistical modeling provides estimates of both emission factors and a reasonable description of carbon-burned simultaneously. Different fire plumes will have very different contributions to volatile organic carbon reactivity; this may help explain differences of free NOx(both gas- and particle-phase), and also of ozone production, that have been noted for forest-fire plumes in California. Our evaluations check or correct emission factors based on sequential measurements (e.g., the Normalized Ratio Enhancement and similar methods). We stress the dangers of methods relying on emission-ratios to CO. (b) This work confirms and extends many reports of great situational variability in emissions factors. VOCs vary in OH reactivity and NOx-binding. Reasons for variability are not only fuel composition, fuel condition, etc., but are confused somewhat by rapid transformation and mixing of emissions. We use "unmixing" (distinct from mixed-effects) statistics and compare briefly to approaches like neural nets. We focus on one particularly intense fire the notorious Yosemite Rim Fire of 2013. In some samples, NOx activity was not so suppressed by binding into nitrates as in other fires. While our fire-typing is evolving and subject to debate, the carbon-burned delta(CO2+CO) estimates that arise from mixed effects models, free of confusion by background-CO2 variation, should provide a solid base for discussion. (c) We report progress using promising links we find between emissions-related "fire types" and promising features deducible from remote observations of plumes, e.g., single scatter albedo, Angstrom exponent of scattering, Angstrom exponent of absorption, (CO column density)/(aerosol optical depth).

Remote sensing↗

NASA NTRS1991

Conceptual studies on the integration of a nuclear reactor system to a manned rover for Mars missions

Multiyear civilian manned missions to explore the surface of Mars are thought by NASA to be possible early in the next century. Expeditions to Mars, as well as permanent bases, are envisioned to require enhanced piloted vehicles to conduct science and exploration activities. Piloted rovers, with 30 kWe user net power (for drilling, sampling and sample analysis, onboard computer and computer instrumentation, vehicle thermal management, and astronaut life support systems) in addition to mobility are being considered. The rover design, for this study, included a four car train type vehicle complete with a hybrid solar photovoltaic/regenerative fuel cell auxiliary power system (APS). This system was designed to power the primary control vehicle. The APS supplies life support power for four astronauts and a limited degree of mobility allowing the primary control vehicle to limp back to either a permanent base or an accent vehicle. The results showed that the APS described above, with a mass of 667 kg, was sufficient to provide live support power and a top speed of five km/h for 6 hours per day. It was also seen that the factors that had the largest effect on the APS mass were the life support power, the number of astronauts, and the PV cell efficiency. The topics covered include: (1) power system options; (2) rover layout and design; (3) parametric analysis of total mass and power requirements for a manned Mars rover; (4) radiation shield design; and (5) energy conversion systems.

El-Genk, Mohamed S.↗

NASA NTRS2003

Modeling Variability of Plasma Conditions in the Io Torus

Telescopic observations an in situ measurements of the Io plasma torus show the density, temperature and composition to vary over time, sometimes up to a factor of 2. While previous models of the physical and chemical processes in the Io plasma torus have reasonably modeled the conditions of the Voyager 1 era, their authors have not addressed the observed variability nor explored the sensitivity of torus conditions to input parameters. In this paper we present a homogeneous torus model parameterized by five variables (transport timescale, neutral source strength, ratio of oxygen sulfur to atoms in the source, fraction of superthermal electrons, temperature of these hot electrons). The model incorporates the most recent data for ionization, recombination, charge exchange and radiative energy losses for the major torus species (S, S(sup +), S(sup ++), S(sup +++), O, O(sup +), O(sup ++). We solve equations of conservation of mass and energy to find equilibrium conditions for a set of input parameters. We compare model plasma conditions with those observed by Voyager 1 Voyager 2, and Cassini. Furthermore, we explore the sensitivity of torus conditions to each parameter. We find that (1) torus conditions are distinctly different for the Voyager 1, Voyager 2 and Cassini eras, (2) unique torus input parameters for any given era are poorly constrained given the wide range of solution space that is consistent with the range of observed torus conditions, (3) ion composition is highly sensitive to the specification of a non-thermal electron distribution, (4) neutral O/S source ratio is highly variable with model values ranging between 1.7 for Cassini to 4.0 for Voyager 1 conditions, (5) transport times range between 23 days for Voyager 2 to 50 days for Voyager 1 and Cassini, (6) neutral source strengths range between 7 to 30 x 10(sup -4) cm (sup -3) s(sup -1) which corresponds to a net production of 0.4 to 1.3 tons/s for a torus volume of 1.4 x 10(sup 31) cm(sup 3), or 38 R(sub j)(sup 3).

Delamere, P. A.↗

NASA NTRSDate not supplied

Composite Technologies for Science Missions

ASTROLAB, Lunar Geophysical Network, Mars Icebreaker and Mars PLACER Net missions propose use of various types of vehicles – such as rovers, landers and flying probes - to accomplish their scientific objectives. Although designs for such vehicles are myriad, many structural components can be made using composite manufacturing technologies. Composite materials are also myriad, by nature, but carbon fiber reinforced polymers (CFRP) in particular are sought after for their high specific strength and specific stiffness. CFRP components could be especially beneficial in vehicle designs for Moon or Mars missions due to their nearly negligible coefficient of thermal expansion (CTE). CTE is a critical design characteristics in environments where significant thermal swings are prevalent, such as those of atmosphere-less Moon and Mars.MSFC/EM42 houses several relevant composites technologies. Strong and rigid struts can be filament-wound. Shells and platforms can be laid-up using automated fiber placement (for repeatability) or by hand (for small features). Monolithic structures can even be designed to reduce part count and therefore reduce the risk of joint failures. Composites are also tailorable, allowing the incorporation of different material types or formats through the thickness of a part. This includes materials which shield from radiation or electrostatic discharge. Finally, the rigidity of composite parts minimizes overall vibration and compliance within a design.Additionally, missions such as Triton Ocean World Surveyor anticipate use of traditional, metallic fuel tanks. Composite overwrapped pressure vessels (COPVs) are suitable for use in this application as well. The Triton mission even cites a concern for heat retention, for which CFRP also offers improved characteristics over traditional metallic tanks.

Lightweight↗