Exploring Planets with Directed Aerial Robot Explorers

Global Aerospace Corporation (GAC) is developing a revolutionary system architecture for exploration of planetary atmospheres and surfaces from atmospheric altitudes. The work is supported by the NASA Institute for Advanced Concepts (NIAC). The innovative system architecture relies upon the use of Directed Aerial Robot Explorers (DAREs), which essentially are long-duration-flight autonomous balloons with trajectory control capabilities that can deploy swarms of miniature probes over multiple target areas. Balloon guidance capabilities will offer unprecedented opportunities in high-resolution, targeted observations of both atmospheric and surface phenomena. Multifunctional microprobes will be deployed from the balloons once over the target areas, and perform a multitude of functions, such as atmospheric profiling or surface exploration, relaying data back to the balloons or an orbiter. This architecture will enable low-cost, low-energy, long-term global exploration of planetary atmospheres and surfaces. This paper focuses on a conceptual analysis of the DARE architecture capabilities and science applications for Venus, Titan and Jupiter. Preliminary simulations with simplified atmospheric models show that a relatively small trajectory control wing can enable global coverage of the atmospheres of Venus and Titan by a single balloon over a 100-day mission. This presents unique opportunities for global in situ sampling of the atmospheric composition and dynamics, atmospheric profiling over multiple sites with small dropsondes and targeted deployment of surface microprobes. At Jupiter, path guidance capabilities of the DARE platforms permits targeting localized regions of interest, such as "hot spots" or the Great Red Spot. A single DARE platform at Jupiter can sample major types of the atmospheric flows (zones and belts) over a 100-day mission. Observations by deployable probes would reveal if the differences exist in radiative, dynamic and compositional environments at these sites

Mars Exploration with Directed Aerial Robot Explorers

Global Aerospace Corporation (GAC) is developing a revolutionary system architecture for exploration of planetary atmospheres and surfaces from atmospheric altitudes. The work is supported by the NASA Institute for Advanced Concepts (NIAC). The innovative system architecture relies upon the use of Directed Aerial Robot Explorers (DAREs), which essentially are long‐duration‐flight autonomous balloons with trajectory control capabilities that can deploy swarms of miniature probes over multiple target areas. Balloon guidance capabilities will offer unprecedented opportunities in high‐resolution, targeted observations of both atmospheric and surface phenomena. Multifunctional microprobes will be deployed from the balloons when over the target areas, and perform a multitude of functions, such as atmospheric profiling or surface exploration, relaying data back to the balloons or an orbiter. This architecture will enable low‐cost, low‐energy, long‐term global exploration of planetary atmospheres and surfaces. A conceptual analysis of DARE capabilities and science applications for Mars is presented. Initial results of simulations indicate that a relatively small trajectory control wing can significantly change planetary balloon flight paths, especially during summer seasons in Polar Regions. This opens new possibilities for high‐resolution observations of crustal magnetic anomalies, polar layered terrain, polar clouds, dust storms at the edges of the Polar caps and of seasonal variability of volatiles in the atmosphere

Observing Mars from Areostationary Orbit: Benefits and Applications

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Toward More Realistic Simulation and Prediction of Dust Storms on Mars

Global dust storms have major implications for the past and present climate, geologic history, habitability, and future exploration of Mars. Yet their mysterious origins mean we remain unable to realistically simulate or predict them. We identify four key Knowledge Gaps and make four Recommendations to make progress in the next decade

Low order model of Martian circulation and interannual variability of global dust storms

The main theme of this work is the development of a simplified model of the martian circulation suitable for conducting computationally fast long term simulations of the martian climate system. In particular, we are looking for causes of the irregular occurrence of the martian global dust storms (GDSs). The low-order model (LOM) is constructed by Galerkin projection of a 2D (zonally averaged) general circulation model (GCM) onto a truncated set of basis functions. The resulting low-order model consists of twelve coupled nonlinear ordinary differential equations (ODEs). The forcing of the model is described by simplified physics based on Newtonian cooling and Rayleigh friction. The atmosphere and surface are coupled: atmospheric heating depends on the dustiness of the atmosphere, and the surface dust source depends on the strength of the atmospheric winds. Parameters of the model are tuned to fit output of the NASA Ames GCM. The model performance is examined for different seasons and dust opacities and it is found that the simulated mean meridional circulation and temperature fields compare well with the more sophisticated GCM. The time of occurence and duration of the global dust storms produced by the model compare well with observations by Viking Landers (VLs). The intensity of the meridional circulation as simulated by the LOM during northern summer is stronger than that predicted by the GCM. The situation can be improved if the Rayleigh friction varies seasonally. The LOM uncoupled from the dust source can be further simplified to form the Lorenz system with forcing. The model is applied to the problem of interannual variability of martian global dust storms. Basic hypotheses of the intrinsic and of the extrinsic irregularity of the martian climate system are tested. The intrinsic irregularity hypothesis implies that the system under consideration is chaotic, so that small variations in initial conditions make the behavior of the system essentially unpredictable. Different paths taken by the system in state space would correspond to years with and without a GDS. The extrinsic irregularity hypothesis, on the other hand, implies that without noise the system behaves periodically, but stochastic forcing of the system causes it to behave irregularly. It is concluded that the observed variability of GDSs is more easily explained by extrinsic irregularity. The stochastic forcing (``noise') could be provided by transient weather systems or some surface process, like size sorting or redistribution of the sand particles in the ``active' (i.e., storm generating) zones on the surface. The results are very sensitive to the value of the saltation threshold, which hints at the possible feedback between saltation threshold and dust storm activity. According to this hypothesis, the saltation threshold has adjusted its value so that dust storms are barely able to occur.</p

Subsurface heat transfer on Enceladus: Conditions under which melting occurs

Given the heat that is reaching the surface from the interior of Enceladus, we ask whether liquid water is likely and at what depth it might occur. The heat may be carried by thermal conduction through the solid ice, by the vapor as it diffuses through a porous matrix, or by the vapor flowing upward through open cracks. The vapor carries latent heat, which it acquires when ice or liquid evaporates. As the vapor nears the surface it may condense onto the cold ice, or it may exit the vent without condensing, carrying its latent heat with it. The ice at the surface loses its heat by infrared radiation. An important physical principle, which has been overlooked so far, is that the partial pressure of the vapor in the pores and in the open cracks is nearly equal to the saturation vapor pressure of the ice around it. This severely limits the ability of ice to deliver the observed heat to the surface without melting at depth. Another principle is that viscosity limits the speed of the flow, both the diffusive flow in the matrix and the hydrodynamic flow in open cracks. We present hydrodynamic models that take these effects into account. We find that there is no simple answer to the question of whether the ice melts or not. Vapor diffusion in a porous matrix can deliver the heat to the surface without melting if the particle size is greater than ~1 cm and the porosity is greater than ~0.1, in other words, if the matrix is a rubble pile. Whether such an open matrix can exist under its own hydrostatic load is unclear. Flow in open cracks can deliver the heat without melting if the width of the crack is greater than ~10 cm, but the heat source must be in contact with the crack. Frictional heating on the walls due to tidal stresses is one such possibility. The lifetime of the crack is a puzzle, since condensation on the walls in the upper few meters could seal the crack off in a year, and it takes many years for the heat source to warm the walls if the crack extends down to km depths. The 10:1 ratio of radiated heat to latent heat carried with the vapor is another puzzle. The models tend to give a lower ratio. The resolution might be that each tiger stripe has multiple cracks that share the heat, which tends to lower the ratio. The main conclusion is that melting depends on the size of the pores and the width of the cracks, and these are unknown at present

Interannual variability of Mars global dust storms: an example of self-organized criticality?

Previous simulations of martian global dust storms with a simple low-order model showed the desired interannual variability of storms if one of the model parameters—the threshold wind speed for starting saltation and lifting dust from the surface—was finely tuned. In this paper we show that the fine-tuning of this parameter could be the result of negative feedback in which processes associated with global dust storms raise the threshold and small-scale processes like dust devils, which are active in years between the storms, lower the threshold

Ejecta Pattern of the Impact of Comet Shoemaker–Levy 9

The collision of Comet Shoemaker–Levy 9 (SL 9) with Jupiter created crescent-shaped ejecta patterns around impact sites. Although the observed impact plumes rose through a similar height of ∼3000 km, the radii of the created ejecta patterns differ from impact to impact and generally are larger for larger impacts. The azimuthal angle of the symmetry axis of the ejecta pattern is larger than that predicted by the models of oblique impacts, due to the action of the Coriolis force that rotates ejecta patterns counterclockwise from the south. We study the formation of ejecta patterns using a simple model of ballistic plume above a rotating plane. The ejected particles follow ballistic trajectories and slide horizontally for about an hour after reentry into the jovian atmosphere. The lateral expansion of the plume is stopped by the friction force, which is assumed to be proportional to the square of the horizontal velocity. Two different mass–velocity distributions used in the simulations produce qualitatively similar results. The simulated ejecta patterns fit very well the “crescents” observed at the impact sites. The sizes and azimuthal angles of symmetry axis of ejecta patterns depend on a parameterL, which has dimension of length and is related to the mass of the fragment. Thus more massive impacts produce larger ejecta patterns that are rotated through a wider angle

A Multiannual Record of Convective Instability in Mars’s Middle Atmosphere from the Mars Climate Sounder

Gravity waves (GW) transfer energy and momentum from the lower to the middle and upper atmospheres of Earth and Mars. Momentum transfer can occur through the wave dissipative process of saturation associated with convective or shear instability. GW saturation both impacts the atmospheric circulation where saturation occurs and also mediates the GW flux above the level of saturation. It was previously demonstrated that convective instabilities are observable in Mars’s middle atmosphere. Here we characterize the seasonal, interannual, and dust event-driven variability in convective instability in Mars’s atmosphere using retrieved temperature profiles from more than 7 Martian yr of observations by the Mars Climate Sounder on board the Mars Reconnaissance Orbiter. The mean probability of convective instability in the middle atmosphere is <1%, except in the upper portions of the winter westerly jets (≈70 km altitude, 60°–75° N/S), near 30°–40° S and ≈60 km altitude on the dayside in southern summer, and in the tropics at 40–50 km altitude around northern fall equinox. Probabilities of convective instability in or near these three regions can increase by an order of magnitude during planetary-scale dust events and some regional-scale dust events. GW-driven drag on both the equatorial easterly jet and winter westerly jet therefore could increase by an order of magnitude during these dust events, as long as changes in GW properties and the local winds do not provide a compensating reduction of the drag