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NASA NTRS2017

Thermal Design for Extra-Terrestrial Regenerative Fuel Cell System

The Advanced Exploration Systems (AES) Advanced Modular Power Systems (AMPS) Project is investigating different power systems for various lunar and Martian mission concepts. The AMPS Fuel Cell (FC) team has created two system-level models to evaluate the performance of regenerative fuel cell (RFC) systems employing different fuel cell chemistries. Proton Exchange Membrane fuel cells PEMFCs contain a polymer electrolyte membrane that separates the hydrogen and oxygen cavities and conducts hydrogen cations (protons) across the cell. Solid Oxide fuel cells (SOFCs) operate at high temperatures, using a zirconia-based solid ceramic electrolyte to conduct oxygen anions across the cell. The purpose of the modeling effort is to down select one fuel cell chemistry for a more detailed design effort. Figures of merit include the system mass, volume, round trip efficiency, and electrolyzer charge power required. PEMFCs operate at around 60 C versus SOFCs which operate at temperatures greater than 700 C. Due to the drastically different operating temperatures of the two chemistries the thermal control systems (TCS) differ. The PEM TCS is less complex and is characterized by a single pump cooling loop that uses deionized water coolant and rejects heat generated by the system to the environment via a radiator. The solid oxide TCS has its own unique challenges including the requirement to reject high quality heat and to condense the steam produced in the reaction. This paper discusses the modeling of thermal control systems for an extraterrestrial RFC that utilizes either a PEM or solid oxide fuel cell.

thermal modeling↗
NASA NTRS2019

The Lunar Geophysical Network Mission

Overarching Principles: Must be better than Apollo (coverage, duration, instrument performance); Learn from the Apollo experience. Lunar Geophysical Network (LGN) New Frontiers (NF)-class mission, as part of the NF-5 call. “This mission consists of several identical landers distributed across the lunar surface, each carrying geophysical instrumentation. The primary science objectives are to characterize the Moon’s internal structure, seismic activity, global heat flow budget, bulk composition, & magnetic field.” Global distribution of multiple stations. Each station should contain a seismometer, heat flow probe, electromagnetic sounder, laser retroreflector (lunar nearside). Each station must be long-lived (e.g., approximately10 years)to allow other stations (from other countries?) to be integrated with the anchor nodes to form the International Lunar Network. Why LGN? Planetary Science: Moon represents an end-member in planetary evolution (large small body, small rocky planet); Primary planetary differentiation preserved; Key to understanding terrestrial planet initial differentiation. Lunar Science: Heat flow probes yield crustal heat budget estimates; Combined with EMS (ElectroMagnetic Sounding), the temperature profile of the deep interior can be modeled along with mineralogy; Seismic and LLR (Lunar Laser Ranging) data also yield structure and compositional information of the lunar interior; High fidelity data from LGN would enhance the usefulness of the GRAIL (Gravity Recovery and Interior Laboratory) and SELENE (Selenological and Engineering Explorer) gravity data. Human Exploration: LGN must be established prior to renewed human lunar activity - we do not know the exact locations or causes of the shallow moonquakes (SMQs) - the largest magnitude seismic events recorded by Apollo (1 event per year of magnitude greater than or equal to 5); Establishing surface infrastructure near SMQ epicenters must be avoided.

Neal, C. R.↗
NASA NTRSDate not supplied

Cryogenic Flow Boiling Parabolic Flight Experiment and Universal Correlations for Cryogens

Cryogenic fluids are employed in many industries and play crucial roles in space applications, including nuclear thermal propulsion systems, LOX/LCH4 ascent and descent stage feedlines, LOX/LH2 transfer lines for in-space fuel depots, and LHe transfer lines that cool space experiments. Due to the ultra-low boiling point of cryogens, phase change is inevitable in these systems, which leads to complex boiling behavior in reduced gravity. For cost-effective design and sizing of the aforementioned systems, accurate knowledge of two-phase parameters such as pressure drop, heat transfer coefficient (HTC), and critical heat flux (CHF) is desired. Since 2018, researchers from Purdue University and NASA Glenn Research Center (GRC) have been collaborating to investigate the effects of reduced gravity on cryogenic pool boiling, flow boiling ins tubes, and spray cooling. Using a variety of both terrestrial and parabolic flight experimental rigs, extensive LN2 data have been amassed and combined with cryogenic data from World literature to develop both ‘universal’ empirical correlations and CFD models, which are expected to serve as foundation for design of future space systems involving cryogenic fluids. This presentation will provide an overview of both the experimental work and predictive tools that have resulted from the joined Purdue-Glenn studies.

Flow Boiling↗
NASA NTRS2024

Automatic Detection of Large-scale Flux Ropes and Their Geoeffectiveness with a Machine-learning Approach

Detecting large-scale flux ropes (FRs) embedded in interplanetary coronal mass ejections (ICMEs) and assessing their geoeffectiveness are essential, since they can drive severe space weather. At 1 au, these FRs have an average duration of 1 day. Their most common magnetic features are large, smoothly rotating magnetic fields. Their manual detection has become a relatively common practice over decades, although visual detection can be time-consuming and subject to observer bias. Our study proposes a pipeline that utilizes two supervised binary classification machine-learning models trained with solar wind magnetic properties to automatically detect large-scale FRs and additionally determine their geoeffectiveness. The first model is used to generate a list of autodetected FRs. Using the properties of the southward magnetic field, the second model determines the geoeffectiveness of FRs. Our method identifies 88.6% and 80% of large-scale ICMEs (duration 1day) observed at 1au by the Wind and the Solar TErrestrial RElations Observatory missions, respectively. While testing with continuous solar wind data obtained from Wind, our pipeline detected 56 of the 64 large-scale ICMEs during the 2008–2014 period (recall = 0.875), but also many false positives (precision = 0.56), as we do not take into account any additional solar wind properties other than the magnetic properties. We find an accuracy of 0.88 when estimating the geoeffectiveness of the autodetected FRs using our method. Thus, in space-weather nowcasting and forecasting at L1 or any planetary missions, our pipeline can be utilized to offer a first-order detection of large-scale FRs and their geoeffectiveness.

Sanchita Pal↗
NASA NTRS1994

Modulating terrestrial impacts from Oort cloud comets by the adiabatically changing galactic tides

Time modulation of the flux of new Jupiter-dominated Oort cloud comets is the subject of interest here. The major perturbation of these comets during the present epoch is due to the tidal field of the relatively smooth distribution of matter in the galactic disk. A secondary source of the near-parabolic comet flux are stars penetrating the inner Oort cloud and providing impulses that create brief comet showers. Substantial stellar-induced showers occur approximately every 100 m.y. Less frequent (but stronger) impulses due to giant molecular clouds can also perturb comets from the inner cloud. These occur on timescales of approximately equal to 500 m.y. In contrast to these infrequent stochastic shower phenomena is the continuously varying tidal-induced flux due to the galaxy. As the Sun orbits the galactic center it undergoes quasiharmonic motion about the galactic midplane, which is superimposed on the small eccentricity, near-Keplerian motion in the plane having epicycle period approximately equal to 150 m.y. In the process the galactic tidal field on the Sun/cloud system will vary causing a modulation of the observable Oort cloud flux. We have created a model of the galactic matter distribution as it affects the solar motion over a time interval ranging from 300 m.y. in the past to 100 m.y. into the future. As constraints on the disk's compact dark matter component we require consistency with the following: (1) the observed galactic rotation curve, (2) today's flux distribution of new comets, (3) the studies of K-giant distributions, and (4) the periodicity found in the terrestrial cratering record. The adiabatically varying galactic tidal torque is then determined and used to predict the time dependence of the flux. We find that a model in which approximately half the disk matter is compact is consistent with these constraints. Under such circumstances the peak-to-trough flux variation will be approx. equal to 5:1 with a full width of 9 m.y. This variability will manifest in the terrestrial cratering record and is consistent with the observed cratering periodicity, if over half of the impacts on Earth are caused by comets or asteroids that originate in the outer Oort cloud.

Matese, J. J.↗
NASA NTRS2022

A Process-Model Perspective on Recent Changes in the Carbon Cycle of North America

Continental North America has been found to be a carbon (C) sink over recent decades by multiple studies employing a variety of estimation approaches. However, several key questions and uncertainties remain with these assessments. Here we used results from an ensemble of 19 state-of-the-art dynamic global vegetation models from the TRENDYv9 project to improve these estimates and study the drivers of its interannual variability. Our results show that North America has been a C sink with a magnitude of 0.37 ± 0.38 (mean and one standard deviation) PgC year−1 for the period 2000–2019 (0.31 and 0.44 PgC year−1 in each decade); split into 0.18 ± 0.12 PgC year−1 in Canada (0.15 and 0.20), 0.16 ± 0.17 in the United States (0.14 and 0.17), 0.02 ± 0.05 PgC year−1 in Mexico (0.02 and 0.02) and 0.01 ± 0.02 in Central America and the Caribbean (0.01 and 0.01). About 57% of the new C assimilated by terrestrial ecosystems is allocated into vegetation, 30% into soils, and 13% into litter. Losses of C due to fire account for 41% of the interannual variability of the mean net biome productivity for all North America in the model ensemble. Finally, we show that drought years (e.g., 2002) have the potential to shift the region to a small net C source in the simulations (−0.02 ± 0.46 PgC year−1). Our results highlight the importance of identifying the major drivers of the interannual variability of the continental-scale land C cycle along with the spatial distribution of local sink-source dynamics.

Guillermo Murray-Tortarolo↗
NASA NTRS2009

Controls on Highly Siderophile Element Concentrations in Martian Basalt: Sulfide Saturation and Under-Saturation

Highly siderophile elements (HSE; Re, Au and the platinum group elements) in shergottites exhibit a wide range from very high, similar to the terrestrial mantle, to very low, similar to sulfide saturated mid ocean ridge basalt (e.g., [1]). This large range has been difficult to explain without good constraints on sulfide saturation or under-saturation [2]. A new model for prediction of sulfide saturation places new constraints on this problem [3]. Shergottite data: For primitive shergottites, pressure and temperature estimates are between 1.2-1.5 GPa, and 1350-1470 C [4]. The range of oxygen fugacities is from FMQ-2 to IW, where the amount of Fe2O3 is low and thus does not have a significant effect on the S saturation values. Finally, the bulk compositions of shergottites have been reported in many recent studies (e.g., [5]). All of this information will be used to test whether shergottites are sulfide saturated [3]. Modeling values and results: The database for HSE partition coefficients has been growing with many new data for silicates and oxides [6-8] to complement a large sulfide database [9- 11]. Combining these data with simple batch melting models allows HSE contents of mantle melts to be estimated for sulfide-bearing vs. sulfide-free mantle. Combining such models with fractional crystallization modeling (e.g., [12]) allows HSE contents of more evolved liquids to be modeled. Most primitive shergottites have high HSE contents (and low S contents) that can be explained by sulfide under-saturated melting of the mantle. An exception is Dhofar 019 which has high S contents and very low HSE contents suggesting sulfide saturation. Most evolved basaltic shergottites have lower S contents than saturation, and intermediate HSE contents that can be explained by olivine, pyroxene, and chromite fractionation. An exception is EET A79001 lithology B, which has very low HSE contents and S contents higher than sulfide saturation values . evidence for sulfide saturation during late fractional crystallization. These results show that shergottite HSE contents are controlled by silicates, oxides, and sulfides. In addition, the mantle producing the most primitive shergottites did not contain near chondritic relative ratios of the HSEs like the terrestrial mantle, and did not experience a late chondritic veneer.

Righter, Kevin↗
NASA NTRS1991

Exploration of relationships between low-Ti and high-Ti pristine lunar glasses using an armalcolite assimilation model

The pristine glasses of Delano are the most primitive lunar basaltic magma compositions discovered to date. They are grouped into two (and possibly three) arrays: a low-alumina array and a high alumina array. These glasses are very olivine normative and are multiply saturated at pressures of approximately 20 kbar, implying a depth of origin of 400 to 500 km in the Moon. Thus, these glasses appear to be the best candidates for primitive partial melts of the upper lunar mantle. One of the most perplexing characteristics of the pristine glasses is a positive correlation between Ni and SiO2 within each array. This is contrary to the terrestrial experience, where Ni is observed to positively correlate with MgO and negatively correlate with SiO2. These systematics are believed to be due to the depletion of Ni by olivine fractionation. The difference between the lunar and terrestrial Ni vs. SiO2 trends may be partially ascribed to the Ti-rich component. In the case of the pristine glasses, SiO2 increases not because of olivine fractionation, but because they contain less of the high-Ti component. An attempt was made to model this variation in Ni and SiO2 with a simple assimilation-fractional crystallization (AFC) model. Silica and Ni both decreased dramatically as the AFC process proceeded. Only 15 to 20 percent AFC was necessary to produce the observed variation, and the SiO2 vs. Ni variation was modeled quite well. The D(Ni) for olivine/liquid in this model was taken to be 10 and the olivine was assumed to be Fe sub 80. However, the results of this model for Ti and Mg were less than satisfactory. It seemed difficult to achieve the high TiO2 contents of some glasses (16 to 17 wt. percent) by this method. Continual addition of ilmenite by AFC could indeed raise the titania concentrations to the necessary levels, but only by enriching the magma in FeO and greatly depleting the magma in MgO. An attempt was made to circumvent this problem by using armalcolite, (Fe, Mg)Ti2O5, in the AFC model, and the results are presented.

Jones, John H.↗
NASA NTRS2020

Oxygen and carbon stable isotope composition of the weathering Mg-carbonates on the surface of the LEW 85320 ordinary chondrite: Revisited

New δ13C and δ18O values were measured to constrain the formation mechanisms of two previously identified generations (Antarctica and Houston) of terrestrial weathering carbonates, nesquehonite, which formed on the surface of the Lewis Cliff 85320 ordinary chondrite. These two nesquehonite generations exhibit a characteristic carbon and oxygen isotopic trend which starts with a linear δ13C-δ18O covariation followed by a continuous increase in δ18O with little to no change in δ13C. Based upon the newly developed nesquehonite-water oxygen isotope thermometry and the measured δ18O value of melted ice from Antarctica, the formation temperature of the Antarctic nesquehonite generation was estimated to be -1.9 ± 3℃. Houston nesquehonite generation was most likely formed from an evaporative residue of the melted Antarctic ice at 30 ± 4℃. Modeling the isotopic trend of the two generations suggests that evaporation created large δ18O variations in the nesquehonite while carbon isotopes were stabilized by exchange between the parent liquid and atmospheric CO2. Thus, we suggest that carbonates formed by terrestrial weathering in Antarctica should possess a widespread in δ18O values and a narrow range in δ13C values under dry and cold conditions. Finally, the observed wide spread of δ18O in Martian carbonates (e.g., Allan Hills 84001 and Nakhla) can be explained by evaporation near 0℃ and may have formed by a similar mechanism to that of the nesquehonite in the LEW 85320. Meanwhile, the wide spread of δ13C suggests that two carbon reservoirs with distinct isotope compositions on Mars (e.g., the atmospheric carbon and magmatic carbon) may be actively participating in the formation process.

weathering↗
NASA NTRSDate not supplied

Heat-death by volcano - how Venus went rogue?

The idea of a habitable Venus epoch has gained traction in recent years via 1-D and 3-D General Circulation Modeling (GCM) efforts [1,2,3]. Although recent work has supported an alternative permanent hot and dry scenario [4]. However, the habitable scenario presents us with a conundrum - how does a terrestrial planet transform from temperate to hot-house? For decades it was proposed that the gradual brightening of the sun was the probable cause [5]. Yet 4 billion years ago Venus was receiving nearly 1.4 times the insolation that Earth receives today, and many studies have put Earth at the inner boundary of the habitable zone today [6]. The newer 3-D GCM efforts have demonstrated that if Venus had an early habitable period, that the cloud-albedo feedback responsible for maintaining temperate surface conditions [7] could still be in operation today. From this perspective increasing insolation through time cannot be an answer to the transition from habitable to hot-house. We propose that the 'Great Climate Transition' (GCT) was trigged by simultaneous large igneous provinces (LIPs) akin to those like the Siberian Traps responsible for the End Permian [8]. We have taken the most up to date LIP database for Earth [9] and characterized their distribution through time as random or nearly random. Next we initiate a large suite of Monte Carlo simulations based on this record and generate the likelihood for simultaneous, or environmentally overlapping events in this hypothetical setup. We find the probability of such events to be quite high, a probable cause for Venus' GCT, and a possible harbinger of things to come for Earth.

Venus↗
NASA NTRS2019

Remote Sensing of Solar-Induced Chlorophyll Fluorescence (SIF) in Vegetation: 50 Years of Progress

Remote sensing of solar-induced chlorophyll fluorescence (SIF) is a rapidly advancing front in terrestrial vegetation science, with emerging capability in space-based methodologies and diverse application prospects. Although remote sensing of SIF – especially from space – is seen as a contemporary new specialty for terrestrial plants, it is founded upon a multi-decadal history of research, applications, and sensor developments in active and passive sensing of chlorophyll fluorescence. Current technical capabilities allow SIF to be measured across a range of biological, spatial, and temporal scales. As an optical signal, SIF may be assessed remotely using highly-resolved spectral sensors and state-of-the-art algorithms to distinguish the emission from reflected and/or scattered ambient light. Because the red to far-red SIF emission is detectable non-invasively, it may be sampled repeatedly to acquire spatio-temporally explicit information about photosynthetic light responses and steady-state behaviour in vegetation. Progress in this field is accelerating with innovative sensor developments, retrieval methods, and modelling advances. This review distills the historical and current developments spanning the last several decades. It highlights SIF heritage and complementarity within the broader field of fluorescence science, the maturation of physiological and radiative transfer modelling, SIF signal retrieval strategies, techniques for field and airborne sensing, advances in satellite-based systems, and applications of these capabilities in evaluation of photosynthesis and stress effects. Progress, challenges, and future directions are considered for this unique avenue of remote sensing.

Review↗
NASA NTRS1995

Cogenetic Rock Fragments from a Lunar Soil: Evidence of a Ferroan Noritic-Anorthosite Pluton on the Moon

The impact that produced North Ray Crater, Apollo 16 landing site, exhumed rocks that include relatively mafic members of the lunar ferroan anorthositic suite. Bulk and mineral compositions indicate that a majority of 2-4 mm lithic fragments from sample 67513, including impact breccias and monomict igneous rocks, are related to a common noritic-anorthosite precursor. Compositions and geochemical trends of these lithic fragments and of related samples collected along the rim of North Ray Crater suggest that these rocks derived from a single igneous body. This body developed as an orthocumulate from a mixture of cumulus plagioclase and mafic intercumulus melt, after the plagioclase had separated from any cogenetic mafic minerals and had become concentrated into a crystal mush (approximately 70 wt% plagioclase, 30 wt% intercumulus melt). We present a model for the crystallization of the igneous system wherein "system" is defined as cumulus plagioclase and intercumulus melt. The initial accumulation of plagioclase is analogous to the formation of thick anorthosites of the terrestrial Stillwater Complex; however, a second stage of formation is indicated, involving migration of the cumulus-plagioclase-intercumulus-melt system to a higher crustal level, analogous to the emplacement of terrestrial massif anorthosites. Compositional variations of the lithic fragments from sample 67513 are consistent with dominantly equilibrium crystallization of intercumulus melt. The highly calcic nature of orthocumulus pyroxene and plagioclase suggests some reaction between the intercumulus melt and cumulus plagioclase, perhaps facilitated by some recrystallization of cumulus plagioclase. Bulk compositions and mineral assemblages of individual rock fragments also require that most of the mafic minerals fortned in close contact with cumulus plagioclase, not as separate layers. The distribution of compositions (and by inference, modes) has a narrow peak at anorthosite and a broader, larger peak at noritic anoilhosite. Characteristics of the samples and their geochemical trends imply an origin in a system that was large relative to the (unknown) size of the impact that produced the breccias of ferroan noritic-anorthosite composition that were excavated later by the formation of North Ray Crater, and they appear to be consistent with an origin of the suite within a perched plagioclase cumulate. If the Moon's crust formed by accumulation of plagioclase in a magma ocean, ferroan noritic anothosite, formed as an orthocumulate, is an alternative to extensive adcumulus formation of ferroan anorthosite (greater than 90 vol% plagiclase). This provides a relatively mafic ferroan anorthositic component (approximately 15 vol% mafics), which is required by mass-balance models of compositions of polymict lunar-crustal materials. The inferred bulk composition of the system of cumulus plagioclase and intercumulus melt is similar to that of ferroan regolith breccia MacAlpine Hills 88104/5, a lunar-highland meteorite, and may represent a common and widespread component of the Moon's early highland crust.

Jolliff, B. L.↗
NASA NTRSDate not supplied

Demonstration of Fluid Dynamics for Plant Growing Systems in Varied Gravity Environments Through Scaled Capillary Models

The development of reliable and bioregenerative crop growth production systems is vital for human exploration into deep space. As humans prepare for space travel beyond LEO, scientists need to find a way to provide reliable and adequate water delivery for all stages of the plant's life cycle. Past production systems struggled with this and often led to overwatering in the system. To better understand this issue, NASA's Plant Water Management (PWM) experiments were able to model fluid flow through granular substrates, specifically a clay-based material arcilite, in 0-G. The PWM study can help researchers to predict fluid flow through the systems, however their model only works for an arcilite based system and was unable to account for different stages of plant growth. For future missions, payload requirements to support crop production system will need to be limited, leading to the use of in situ resources. This project aims to validate the PWM experiments as well as incorporate various materials into the design for growth systems. To meet these objectives, a series of terrestrial experiments will be deployed to mimic all gravities. By modifying the material, fluid, and size of the test subjects, the effect of Earth's gravity can be minimized. This project will aid researchers in the design of future crop production systems for surface missions by creating a refined model that can be used at all stages of plant growth and utilize in situ resources.

Plant Biology↗
NASA NTRS2008

Terrestrial Environment (Climatic) Criteria Guidelines for use in Aerospace Vehicle Development

This document provides guidelines for the terrestrial environment that are specifically applicable in the development of design requirements/specifications for NASA aerospace vehicles, payloads, and associated ground support equipment. The primary geographic areas encompassed are the John F. Kennedy Space Center, FL; Vandenberg AFB, CA; Edwards AFB, CA; Michoud Assembly Facility, New Orleans, LA; John C. Stennis Space Center, MS; Lyndon B. Johnson Space Center, Houston, TX; George C. Marshall Space Flight Center, Huntsville, AL; and the White Sands Missile Range, NM. This document presents the latest available information on the terrestrial environment applicable to the design and operations of aerospace vehicles and supersedes information presented in NASA-HDBK-1001 and TM X-64589, TM X-64757, TM-78118, TM-82473, and TM-4511. Information is included on winds, atmospheric thermodynamic models, radiation, humidity, precipitation, severe weather, sea state, lightning, atmospheric chemistry, seismic criteria, and a model to predict atmospheric dispersion of aerospace engine exhaust cloud rise and growth. In addition, a section has been included to provide information on the general distribution of natural environmental extremes in the conterminous United States, and world-wide, that may be needed to specify design criteria in the transportation of space vehicle subsystems and components. A section on atmospheric attenuation has been added since measurements by sensors on certain Earth orbital experiment missions are influenced by the Earth s atmosphere. There is also a section on mission analysis, prelaunch monitoring, and flight evaluation as related to the terrestrial environment inputs. The information in these guidelines is recommended for use in the development of aerospace vehicle and related equipment design and associated operational criteria, unless otherwise stated in contract work specifications. The terrestrial environmental data in these guidelines are primarily limited to information below 90 km altitude.

D L Johnson↗
NASA NTRS1978

Light element geochemistry of the Apollo 12 site

Analytical techniques of improved sensitivity have revealed details of the concentrations and isotopic compositions of light elements for a comprehensive suite of samples from the Apollo 12 regolith. These samples show a wide spread in maturity, although maximum contents observed for solar wind elements are less than observed at other sites, possibly reflecting relative recency of craters at the Apollo 12 site. Isotopic composition of nitrogen is consistent with the idea that N-15/N-14 in the solar wind has increased with time, at least a major part of this increase having occurred in the past 3.1 Gyr. Sulfur isotope systematics support a model in which sulfur is both added to the regolith, by meteoritic influx, and lost, by an isotopically selective process. Most soils from this site are heavily contaminated with terrestrial carbon.

Kerridge, J. F.↗
NASA NTRS1980

The role of volatiles and lithology in the impact cratering process

A survey of published descriptions of 32 of the largest, least eroded terrestrial impact structures shows that the amount of melt at craters in crystalline rocks is approximately two orders of magnitude greater than that at craters in sedimentary rocks. A model is proposed for the impact process, and it is examined whether the difference in melt abundance is due to differences in the amount of melt generated in various target materials or due to differences in the fate of the melt during late stages of the impact. The model accounts semiquantitatively for the effects of porosity and water and volatile content on the cratering process. Important features of the model are noted. Even if the recondensation of released volatiles is very efficient, the cumulative effect of repeated impacts on accreting planets would be to continually transfer volatiles toward the outer surface. By this process, volatiles might be enriched toward the outer layer of a growing planet.

Kieffer, S. W.↗
NASA NTRS1980

The influence of solar UV variations on climate

The effects on the terrestrial ozone abundance and temperature (and hence on the earth's climate) of periodic variations in the solar spectrum are investigated. Temporal variations of the solar UV spectrum are modeled in accordance with the measurements of Heath and Thekaekara (1977), and the spectrum at wavelengths greater than 2900 A is altered uniformly by small amounts so that the total luminosity remains constant with time. One-dimensional photochemical-radiative-convective models are used to predict the response of the earth's surface to the solar spectral changes. Results show that the data interpreted by Heath and Thekaekara to indicate that the solar UV flux varies by a factor of 2.5 at 1750 A from solar minimum to solar maximum are inconsistent with the historical records of ozone abundance. It is concluded, however, that if the amplitude of solar UV variations increases with increasing period, and if the spectral characteristics variations are similar to the well established solar UV variations over a solar rotation period, these variations could have a significant impact on the earth's climate and the biosphere.

Borucki, W. J.↗
NASA NTRS1981

Overview

The creation of a spherical model in cylindrical geometry is discussed. The model requires a radial body force to simulate gravity. This force is achieved by dielectric effects on a liquid in the presence of a large voltage, but in the terrestrial laboratory it cannot be made large enough to overwhelm gravity. However, in an orbiting vehicle like Spacelab, this dielectric force will dominate. The behavior of a stripped down general circulation system (GCS) is a salient omission of GCM. It is suggested that the system will contribute to global weather and climate studies.

Fowlis, W. W.↗