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Topics addressed include: Mars' volatile budget; climatic implications of martian channels; bulk composition of Mars; accreted water inventory; evolution of CO2; dust storms; nonlinear frost albedo feedback on Mars; martian atmospheric evolution; effects of asteroidal and cometary impacts; and water exchange between the regolith and the atmosphere/cap system over obliquity timescales.
Vertical distribution and reflectance properties of aerosols in the Martian atmosphere are presented, based on Viking Orbiter images containing the planetary limb. Profiles of scattered light above the limb are used to constrain the temporal and spatial behavior of the aerosols. The data cover a wide range of seasons, locations, and viewing geometries. The typical atmospheric column contains one or more discrete, optically thin, ice-like haze layers between 30 and 90 km elevation, depending on the season, whose composition is inferred to be water ice. Below the detached hazes there is a continuous haze extending to the surface. The continuous haze is rarely above 50 km and is much redder in color than the detached hazes above, implying a composition that has a strong dust component. The aerosol distribution exhibits solid seasonal control inferred to be driven by the variable solar flux around the orbit of Mars.
Estimates of the mass of dust suspended in the Martian atmosphere are derived from global and regional 9-micrometer opacity maps produced from Viking Infrared Thermal Mapper data. During the peak of the 1977b storm, a total dust mass of approximately 4.3 x 10(exp 14) g was suspended, equivalent to 4.3 x 10(exp -4) g/sq cm, or a layer 1.4 micrometers thick. During a local dust storm near Solis Planum at L(sub s) 227 deg, approximately 1.3 x 10(exp 13) g of dust were lofted, equal to about a 6-micrometer layer in that vicinity.
Studies currently underway for Mars missions often envision the use of aerobraking for orbital capture at Mars. These missions generally involve blunt-nosed vehicles to dissipate the excess energy of the interplanetary transfer. Radiative heating may be of importance in these blunt-body flows because of the highly energetic shock layer around the blunt nose. In addition, the Martian atmosphere contains CO2, whose dissociation products are known to include strong radiators. An inviscid, equilibrium, stagnation point, radiation-coupled flow-field code has been developed for investigating blunt-body atmospheric entry. The method has been compared with ground-based and flight data for air, and reasonable agreement has been found. In the present work, the method was applied to a matrix of conditions in the Martian atmosphere. These conditions encompass most trajectories of interest for Mars exploration spacecraft. The predicted equilibrium radiative heating to the stagnation point of the vehicle is presented.
A mechanical process was designed for direct extraction of molecular oxygen from the martian atmosphere based on liquefaction of the majority component, CO2, followed by separation of the lower-boiling components. The atmospheric gases are compressed from about 0.007 bar to 13 bar and then cooled to liquefy most of the CO2. The uncondensed gases are further compressed to 30 bar or more, and then cooled again to recover water as ice and to remove much of the remaining CO2. The final gaseous products consisting mostly of nitrogen, oxygen, and carbon monoxide are liquefied and purified by cryogenic distillation. The liquefied CO2 is expanded back to the low-pressure atmosphere with the addition of heat to recover a majority of the compression energy and to produce the needed mechanical work. Energy for the process is needed primarily as heat to drive the CO2-based expansion power system. When properly configured, the extraction process can be a net producer of electricity. The conceptual design, termed 'MARRS' for Mars Atmosphere Resource Recovery System, was based on the NASA/JSC Mars Reference Mission (MRM) requirement for oxygen. This mission requires both liquid oxygen for propellant, and gaseous oxygen as a component of air for the mission crew. With single redundancy both for propellant and crew air, the oxygen requirement for the MRM is estimated at 5.8 kg/hr. The process thermal power needed is about 120 kW, which can be provided at 300-500 C. A lower-cost nuclear reactor made largely of stainless steel could serve as the heat source. The chief development needed for MARRS is an efficient atmospheric compression technology, all other steps being derived from conventional chemical engineering separations. The conceptual design describes an exceptionally low-mass compression system that can be made from ultra-lightweight and deployable structures. This system adapts to the rapidly changing martian environment to supply the atmospheric resource to MARRS at constant conditions.
Radiative and convective heat transfer effects on temperature variation in martian atmosphere
Surface pressure and carbon dioxide content of Martian atmosphere, comparing polarimetric, photometric and spectroscopic methods
A detailed chemical dynamic model is presented for a moist Martian atmosphere. Recombination of CO2 is catalyzed by trace amount of H2O. The abundances of CO and O2 should vary in response to changes in atmospheric H2O and atmospheric mixing.
Information has been collected on Martian atmospheric scale heights derived from observations of the occultation of Epsilon Gem by Mars on Apr. 8, 1976; the observations give data in the altitude range of approximately 50-80 km. A rough, unweighted average of results so far available yields a temperature of approximately 165 K. Excursions of plus or minus 40 K about this mean may be present as a function of both altitude and areographic coordinates.
The CO2 seasonal cycle of the Martian atmosphere and surface is simulated with a hybrid energy balance model that incorporates dynamical and radiation information from a large number of general circulation model runs. This information includes: heating due to atmospheric heat advection, the seasonally varying ratio of the surface pressure at the two Viking landing sites to the globally averaged pressure, the rate of CO2 condensation in the atmosphere, and solar heating of the atmosphere and surface. The predictions of the energy balance model are compared with the seasonal pressure variations measured at the two Viking landing sites and the springtime retreat of the seasonal polar cap boundaries. The following quantities are found to have a strong influence on the seasonal pressures at the Viking landing sites: albedo of the seasonal CO2 ice deposits, emissivity of this deposit, atmospheric heat advection, and the pressure ratio.
Human exploration of Mars will require the optimal utilization of planetary resources. One of its abundant resources is the Martian atmosphere that can be harvested through filtration and chemical processes that purify and separate it into its gaseous and elemental constituents. Effective filtration needs to be part of the suite of resource utilization technologies. A unique testing platform is being used which provides the relevant operational and instrumental capabilities to test articles under the proper simulated Martian conditions. A series of tests were conducted to assess the performance of filter media. Light sheet imaging of the particle flow provided a means of detecting and quantifying particle concentrations to determine capturing efficiencies. The media's efficiency was also evaluated by gravimetric means through a by-layer filter media configuration. These tests will help to establish techniques and methods for measuring capturing efficiency and arrestance of conventional fibrous filter media. This paper will describe initial test results on different filter media.
The National Weather Service (NWS) releases approximately 75,000 radiosondes each year to measure pressure, altitude, temperature, relative humidity, wind and cosmic radiation [1]. The data obtained from these measurements have led to a more thorough understanding of the Earth s lower atmosphere. On the contrary, there have been only six fully successful landings on Mars, and there is much less known about the variations in winds, density, etc., in the mid-regions of the Martian atmosphere (see Fig. 1). This data is vital to understanding Martian weather and the development of Mars landers for larger payloads [2,3,4]. Mars has too much atmosphere to land like is done on the moon, and too little atmosphere to land like is done on Earth. It is suggested that radiosondes could be added as secondary payloads on Mars missions and used to map physical properties in the different regions of the Martian atmosphere.
Simulation of transportation and deposition of dust and sand by Martian atmospheric processes
On-line parameter updating for relationship between Martian atmospheric density and height above surface during spacecraft descent based on least squares approach
Martian atmospheric temperature and pressure and temperature gradient determination by least squares differential correction of satellite photometric solar eclipse data
Computations are conducted for the periods of free modes in the Martian atmosphere with a view to the short atmospheric radiative damping time and the seasonal and interannual variation of globally representative temperatures, both of which differ from their terrestrial counterparts by an order of magnitude. Attention is given to the possibility of atmospheric resonance and the efficient excitation (or even the resonant amplification) of forced modes. A thermally-forced diurnal Kelvin wave is recommended as the most reasonable of several alternative explanations of the short-period transient mode that occurs just before, or during, Mars' great episodic dust storms.
A summary of calculations describing the Martian atmosphere water vapor content based on data from the Mars Atmospheric Water Detectors carried by the Viking landers is presented. The water column has been observed to vary with season, time of day, and locality. Over 5 yr of continuous data collection has permitted modeling of the Martian year into 24 seasonal periods of planetocentric solar longitude, with gaps in the model due to the presence of dust storms. The vapor content is asymmetric pole-to-pole, but symmetric latitudinally with respect to the equator. Low elevation areas display a higher vapor content, especially with rapid height changes in nearby terrain. Dust storms reduced the total atmospheric vapor, with concentration shifts tending toward the north, from where it is expected renewed balances will be reinstated. Consideration is also given to diurnal variations, and variations due to temperature, composition, and wind velocity.
In order to provide in-situ heat rejection to the thin Martian atmosphere, approaches relying on forced convection and buoyancy flow are conceptualized. A convective radiator concept utilizing a fan to draw local atmosphere through an expanded metal foam heat exchanger panel is developed. To provide a pumped fluid loop interface, flow tubes are embedded in the heat exchanger panel and heat is transferred from the tubes to the foam via conduction and subsequently convectively to the environment. To forgo the use of a specialized high throughput fan, a concept utilizing a buoyant chimney tower to draw atmospheric flow through a low pressure drop heat exchanger is also considered. Both concepts may best align with moderate- to high-temperature heat loads that provide a significant delta temperature relative to the ambient atmosphere temperature. While eliminating dust accumulation on radiator surfaces, some type of serviceable filtration or screening may be required to prevent accumulation of dust inside the expanded metal foam heat exchanger for both concepts.