Results for “Mechanical Power” — Page 10

NASA NTRS1991

AlGaAs top solar cell for mechanical attachment in a multi-junction tandem concentrator solar cell stack

The AstroPower self-supporting, transparent AlGaAs top solar cell can be stacked upon any well-developed bottom solar cell for improved system performance. This is an approach to improve the performance and scale of space photovoltaic power systems. Mechanically stacked tandem solar cell concentrator systems based on the AlGaAs top concentrator solar cell can provide near term efficiencies of 36 percent (AMO, 100x). Possible tandem stack efficiencies greater than 38 percent (100x, AMO) are feasible with a careful selection of materials. In a three solar cell stack, system efficiencies exceed 41 percent (100x, AMO). These device results demonstrate a practical solution for a state-of-the-art top solar cell for attachment to an existing, well-developed solar cell.

Dinetta, L. C.↗

NASA NTRSDate not supplied

Dust Mitigation Technology to Enable Survive the Night Capabilities

Introduction: As we return to the Moon, the lunar regolith (i.e. lunar dust) covering the surface will be an obstacle to nominal operations. Accounts from Apollo astronauts and analysis of hardware returned from the surface illustrate just how deleterious the dust can be [1]. During Apollo missions, the lunar dust adhered to hardware mechanically and electrostatically [2]. Surviving the Night: Mitigating the lunar dust will be critical to surviving the night. Going hand-in-hand with other extreme environment considerations, dust mitigation is critical to mission success. Dust Impacts on Other Systems: The lunar dust can have negative implications for power, thermal, mechanisms, and several other systems or sub-systems. For example, Apollo encountered marked degradation of performance in heat rejection systems for the lunar roving vehicle, science packages, and other components because of the lunar dust [1]. For power alone, dust can cause internal clogging for power connectors, heat rejection issues, excessive dust on reflective surfaces, reduced power output for solar arrays, and so on. Dust Mitigation Strategy: In addition to considering technology solutions, it is important for hardware, systems, and or components to have a dust mitigation strategy. At a high level, hardware that will encounter the lunar dust should consider these things when defining a dust mitigation strategy: • Understand Natural Environment • Understand Induced Environment • Understand Tolerance to Dust • Write Dust Requirements • Select Dust Mitigation Solutions • Test Hardware in Dusty Environment More information on each of these can be provided to hardware owners. Dust Mitigation Technology Development: NASA has a series of technologies that may be available for hardware that needs to survive the lunar night. Many of these solutions are leveraging dust mitigation technology development efforts from NASA’s Space Technology Mission Directorate (STMD), as well as efforts from ESDMD programs, industry, and academia. Through a series of STMD programs (both internal to NASA and through partnerships), there are several technologies in development as considerations as dust mitigation solutions for hardware. Within STMD, the Game Changing Development Program (GCD) has funded several internal dust mitigation projects including low to mid TRL development, demonstrations on CLPS landers of high TRL solutions, and creating standards and best practices for dust mitigation. STMD dust mitigation efforts also include a series of partnerships for developing technologies and advancing the state of dust mitigation at NASA. This includes the Lunar Surface Innovation Consortium (LSIC), Small Business Innovation Research, Early Stage Innovations (ESI), Space Technology Research Grants (STRG), Announcement of Collaboration Opportunities (ACOs) and Tipping Points (TPs), and Challenges and Crowdsourcing, among others. There are also a series of dust mitigation solutions that have been widely used terrestrially, or during Apollo. In recent years, several studies have produced more data on the efficacy of these potential solutions in the lunar environment. Dust Mitigation Solutions: Dust mitigation solutions generally fall into four categories: • Dust Tolerant Mechanisms • Passive Dust Mitigation Capabilities • Active Dust Mitigation Capabilities • Dust Measurement Capabilities There are a series of solutions that may prove beneficial for hardware that needs to survive the lunar night, including new technology development as well as proven, terrestrial solutions. This presentation will discuss in more detail what some of these solutions are for payloads going to the surface. References: [1] J. R. Gaier, NASA/TM—2005-213610, The Effects of Lunar Dust on EVA Systems During the Apollo Missions [2] T. J. Stubbs, et al. Impact of Dust on Lunar Exploration, 2005

dust mitigation↗

NASA NTRSDate not supplied

Survive the Dust: Dust Mitigation Technology to Enable Survive the Night Capabilities

Introduction: As we return to the Moon, the lunar regolith (i.e. lunar dust) covering the surface will be an obstacle to nominal operations. Accounts from Apollo astronauts and analysis of hardware returned from the surface illustrate just how deleterious the dust can be [1]. During Apollo missions, the lunar dust adhered to hardware mechanically and electrostatically [2]. Surviving the Night: Mitigating the lunar dust will be critical to surviving the night. Going hand-in-hand with other extreme environment considerations, dust mitigation is critical to mission success. Dust Impacts on Other Systems: The lunar dust can have negative implications for power, thermal, mechanisms, and several other systems or sub-systems. For example, Apollo encountered marked degradation of performance in heat rejection systems for the lunar roving vehicle, science packages, and other components because of the lunar dust [1]. For power alone, dust can cause internal clogging for power connectors, heat rejection issues, excessive dust on reflective surfaces, reduced power output for solar arrays, and so on. Dust Mitigation Strategy: In addition to considering technology solutions, it is important for hardware, systems, and or components to have a dust mitigation strategy. At a high level, hardware that will encounter the lunar dust should consider these things when defining a dust mitigation strategy: • Understand Natural Environment • Understand Induced Environment • Understand Tolerance to Dust • Write Dust Requirements • Select Dust Mitigation Solutions • Test Hardware in Dusty Environment More information on each of these can be provided to hardware owners. Dust Mitigation Technology Development: NASA has a series of technologies that may be available for hardware that needs to survive the lunar night. Many of these solutions are leveraging dust mitigation technology development efforts from NASA’s Space Technology Mission Directorate (STMD), as well as efforts from ESDMD programs, industry, and academia. Through a series of STMD programs (both internal to NASA and through partnerships), there are several technologies in development as considerations as dust mitigation solutions for hardware. Within STMD, the Game Changing Development Program (GCD) has funded several internal dust mitigation projects including low to mid TRL development, demonstrations on CLPS landers of high TRL solutions, and creating standards and best practices for dust mitigation. STMD dust mitigation efforts also include a series of partnerships for developing technologies and advancing the state of dust mitigation at NASA. This includes the Lunar Surface Innovation Consortium (LSIC), Small Business Innovation Research, Early Stage Innovations (ESI), Space Technology Research Grants (STRG), Announcement of Collaboration Opportunities (ACOs) and Tipping Points (TPs), and Challenges and Crowdsourcing, among others. There are also a series of dust mitigation solutions that have been widely used terrestrially, or during Apollo. In recent years, several studies have produced more data on the efficacy of these potential solutions in the lunar environment. Dust Mitigation Solutions: Dust mitigation solutions generally fall into four categories: • Dust Tolerant Mechanisms • Passive Dust Mitigation Capabilities • Active Dust Mitigation Capabilities • Dust Measurement Capabilities There are a series of solutions that may prove beneficial for hardware that needs to survive the lunar night, including new technology development as well as proven, terrestrial solutions. This presentation will discuss in more detail what some of these solutions are for payloads going to the surface. References: [1] J. R. Gaier, NASA/TM—2005-213610, The Effects of Lunar Dust on EVA Systems During the Apollo Missions [2] T. J. Stubbs, et al. Impact of Dust on Lunar Exploration, 2005

dust mitigation↗

NASA NTRS1997

A Thermal and Electrical Analysis of Power Semiconductor Devices

The state-of-art power semiconductor devices require a thorough understanding of the thermal behavior for these devices. Traditional thermal analysis have (1) failed to account for the thermo-electrical interaction which is significant for power semiconductor devices operating at high temperature, and (2) failed to account for the thermal interactions among all the levels involved in, from the entire device to the gate micro-structure. Furthermore there is a lack of quantitative studies of the thermal breakdown phenomenon which is one of the major failure mechanisms for power electronics. This research work is directed towards addressing. Using a coupled thermal and electrical simulation, in which the drift-diffusion equations for the semiconductor and the energy equation for temperature are solved simultaneously, the thermo-electrical interactions at the micron scale of various junction structures are thoroughly investigated. The optimization of gate structure designs and doping designs is then addressed. An iterative numerical procedure which incorporates the thermal analysis at the device, chip and junction levels of the power device is proposed for the first time and utilized in a BJT power semiconductor device. In this procedure, interactions of different levels are fully considered. The thermal stability issue is studied both analytically and numerically in this research work in order to understand the mechanism for thermal breakdown.

Vafai, Kambiz↗

DOE OSTI2022

Designing, synthesizing, and modeling active fluids

We review recent advances in the design, synthesis, and modeling of active fluids. Active fluids have been at the center of many technological innovations and theoretical advances over the past two decades. Research on this new class of fluids has been inspired by the fascinating and remarkably efficient strategies that biological systems employ, leading to the development of biomimetic nano- and micro-machines and swimmers. The review encompasses active fluids on both the nano- and micro-scale. We start with examples of biological active systems before we discuss how experimentalists leverage novel propulsion mechanisms to power nano- and micro-machines. Furthermore, we then examine how the study of these far-from-equilibrium systems has prompted the development of new simulation methods and theoretical models in nonequilibrium physics to account for their mechanical, thermodynamic, and emergent properties. Recent advances in the field have paved the way for the design, synthesis, and modeling of autonomous systems at the nano- and micro-scale and opened the door to the development of soft matter robotics.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Characterization and Optimization of the Fitting of Quantum Correlation Functions

This case study presents a characterization and optimization of an application code for extracting parton distribution functions from high energy electron-proton scattering data. Profiling this application code reveals that the phase-space density computation accounts for 93% of the overall execution time for a single iteration on a single core. When executing multiple iterations in parallel on a multicore system, the application spends 78% of its overall execution time idling due to load imbalance. We address these issues by first transforming the application code from Python to C++ and then tackling the application load imbalance via a hybrid scheduling strategy that combines dynamic and static scheduling. These techniques result in a 62% reduction in CPU idle time and a 2.46x speedup in overall execution time per node. In addition, the typically enabled power-management mechanisms in supercomputers (e.g., AMD Turbo Core, Intel Turbo Boost, and RAPL) can significantly impact intra-node scalability when more than 50% of the CPU cores are used. This finding underscores the importance of understanding system interactions with power management, as they can adversely impact application performance, and highlights the necessity of intra-node scaling tests to identify performance degradation that inter-node scaling tests might otherwise overlook.

Chuang, Pi-Yueh [Virginia Tech,Dept. of Computer S↗

NASA NTRS2011

Integrated Software Health Management for Aircraft GN and C

Modern aircraft rely heavily on dependable operation of many safety-critical software components. Despite careful design, verification and validation (V&V), on-board software can fail with disastrous consequences if it encounters problematic software/hardware interaction or must operate in an unexpected environment. We are using a Bayesian approach to monitor the software and its behavior during operation and provide up-to-date information about the health of the software and its components. The powerful reasoning mechanism provided by our model-based Bayesian approach makes reliable diagnosis of the root causes possible and minimizes the number of false alarms. Compilation of the Bayesian model into compact arithmetic circuits makes SWHM feasible even on platforms with limited CPU power. We show initial results of SWHM on a small simulator of an embedded aircraft software system, where software and sensor faults can be injected.

Schumann, Johann↗

NASA NTRS1989

The space station tethered elevator system

The optimized conceptual engineering design of a space station tethered elevator is presented. The elevator is an unmanned mobile structure which operates on a ten kilometer tether spanning the distance between the Space Station and a tethered platform. Elevator capabilities include providing access to residual gravity levels, remote servicing, and transportation to any point along a tether. The potential uses, parameters, and evolution of the spacecraft design are discussed. Engineering development of the tethered elevator is the result of work conducted in the following areas: structural configurations; robotics, drive mechanisms; and power generation and transmission systems. The structural configuration of the elevator is presented. The structure supports, houses, and protects all systems on board the elevator. The implementation of robotics on board the elevator is discussed. Elevator robotics allow for the deployment, retrieval, and manipulation of tethered objects. Robotic manipulators also aid in hooking the elevator on a tether. Critical to the operation of the tethered elevator is the design of its drive mechanisms, which are discussed. Two drivers, located internal to the elevator, propel the vehicle along a tether. These modular components consist of endless toothed belts, shunt-wound motors, regenerative power braking, and computer controlled linear actuators. The designs of self-sufficient power generation and transmission systems are reviewed. Thorough research indicates all components of the elevator will operate under power provided by fuel cells. The fuel cell systems will power the vehicle at seven kilowatts continuously and twelve kilowatts maximally. A set of secondary fuel cells provides redundancy in the unlikely event of a primary system failure. Power storage exists in the form of Nickel-Hydrogen batteries capable of powering the elevator under maximum loads.

Anderson, Loren A.↗

DOE OSTI2022

Polarization-dependent conversion efficiency of carbon nanotube-Si heterojunction solar cells based on aligned carbon nanotube films

We have fabricated solar cells that implement heterojunctions of Si and aligned carbon nanotube (CNT) films. Polarization-dependent optical absorption of highly aligned CNTs led to polarization-dependent conversion efficiencies, which in turn provided insight into the role of the CNT layer in the power generation mechanism in these heterojunction solar cells. When the incident light polarization was parallel to the CNT alignment direction so that the light absorption in the CNT layer was maximized, the short circuit photocurrent decreased by ~25%. This indicates that electron–hole pair generation in the CNT layer does not directly lead to power generation and that the CNT-Si heterojunctions in our devices are Schottky junctions rather than p–n junctions.

Physics↗

DOE OSTI2022

BISON validation of FeCrAl cladding mechanical failure during simulated reactivity-initiated accident conditions*

Here, a reactivity-initiated accident (RIA) is a postulated design basis accident in light water reactors (LWRs) in which a rapid reactivity insertion induces a fission rate increase and a fuel pellet temperature rise. During RIA, the fuel pellet thermally expands and may cause pellet-cladding mechanical interaction (PCMI). Separate effects PCMI tests were performed on C26M FeCrAl cladding tube samples, introducing biaxial stress via a well understood modified burst test (MBT) system. A high-speed camera in the MBT system captured the projections, covering a 360° view of the cladding deformation and enabling a digital image correlation (DIC) method to quantify the surface strains with high fidelity. Representative hot zero-power RIA mechanical loading conditions were applied to the sample, and the test duration ranged from 20 to 500 ms at an average temperature of 573 K. BISON finite element–based fuel performance code modeling was performed against the high-fidelity DIC data produced from the MBTs. Validation calculations were conducted with 2D models and systematically compared with test data of the burst time, burst pressure, burst hoop strains, and hoop strain rates. Based on the behaviors from the separate effects test, BISON calculations satisfactorily predicted the cladding deformation behaviors. Sensitivity analysis was conducted to identify highly influential mechanical properties responsible for the cladding failure behavior during the MBT experiments. The results highlight the significance of the cladding's mechanical strength in governing cladding strain, followed by the significance of the mechanical interactions between the pellet and the cladding.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

NASA NTRS1992

Approximation methods for stochastic petri nets

Stochastic Marked Graphs are a concurrent decision free formalism provided with a powerful synchronization mechanism generalizing conventional Fork Join Queueing Networks. In some particular cases the analysis of the throughput can be done analytically. Otherwise the analysis suffers from the classical state explosion problem. Embedded in the divide and conquer paradigm, approximation techniques are introduced for the analysis of stochastic marked graphs and Macroplace/Macrotransition-nets (MPMT-nets), a new subclass introduced herein. MPMT-nets are a subclass of Petri nets that allow limited choice, concurrency and sharing of resources. The modeling power of MPMT is much larger than that of marked graphs, e.g., MPMT-nets can model manufacturing flow lines with unreliable machines and dataflow graphs where choice and synchronization occur. The basic idea leads to the notion of a cut to split the original net system into two subnets. The cuts lead to two aggregated net systems where one of the subnets is reduced to a single transition. A further reduction leads to a basic skeleton. The generalization of the idea leads to multiple cuts, where single cuts can be applied recursively leading to a hierarchical decomposition. Based on the decomposition, a response time approximation technique for the performance analysis is introduced. Also, delay equivalence, which has previously been introduced in the context of marked graphs by Woodside et al., Marie's method and flow equivalent aggregation are applied to the aggregated net systems. The experimental results show that response time approximation converges quickly and shows reasonable accuracy in most cases. The convergence of Marie's method and flow equivalent aggregation are applied to the aggregated net systems. The experimental results show that response time approximation converges quickly and shows reasonable accuracy in most cases. The convergence of Marie's is slower, but the accuracy is generally better. Delay equivalence often fails to converge, while flow equivalent aggregation can lead to potentially bad results if a strong dependence of the mean completion time on the interarrival process exists.

Jungnitz, Hauke Joerg↗

DOE OSTI2024

Co-existence of Heterogeneous Wireless Networks in 2.4 GHz and 5 GHz Spectrum

To achieve automation across different applications, next-generation nuclear power plants are beginning to leverage advanced wireless technologies. The deployment of these wireless technologies is a salient need for modernizing the existing nuclear plants. A “one-size-fits-all” solution cannot be adopted since wireless technologies are selected according to specific application needs, quality of service, and economic restrictions. To balance the trade-off between technical and economic requirements, a multi-band heterogeneous wireless network architecture is needed. However, the co-existence of these multi-band wireless technologies poses numerous challenges. Due to factors including dissimilarity in channel access mechanisms, transmit power levels, distance between nodes, and interference among co-existing solutions, performance can be seriously degraded, leading to very low signal-to-noise ratio. This report builds on our previous study, "Experimental Evaluation of Interference in 2.4 GHz Wireless Network," which analyzed the performance of wireless communication technologies such as Wi-Fi, Zigbee, and Bluetooth co-existing within the 2.4 GHz band. We now extend this study by developing a new upper-layer approach that uses rate control to create temporary opportunities for signal transmission while using the shared band. Unlike existing work in the literature, our approach does not require modifications at the link or physical layers of the network. Further, we extend our work to explore the co-existence of Wi-Fi and fifth-generation (5G) in the 5 GHz unlicensed spectrum, using both experiments and simulations. This report provides a technical foundation for understanding the operational designs of Wi-Fi and 5G in the unlicensed band and evaluates their performance when these networks co-exist. Our findings show that the performance of 5G can be improved by controlling the Wi-Fi’s packet rate at the upper layer.

42 ENGINEERING↗

DOE OSTI2022

Numerical analysis of dynamic load following response in a natural circulation molten salt power reactor system

The Molten Salt Reactor (MSR) concept is a rapidly evolving Generation IV design that has recently attracted favorable attention due to the potential for reducing waste generation, realizing passive safety features, and seizing on the opportunity for cost effective economics. An investigation into the power transient behavior of an autonomous load-following, closed-loop, natural circulation MSR system is important to quantifying operational and safety performance under dynamic conditions. This paper presents the results of a STAR-CCM+ and a comparatively simple asymmetric, one-dimensional, numerical model to solve the compound dynamic MSR power behavior subject to flow and temperature reactivity feedback only. Results show that reactor power is affected by fuel salt flow velocity (global) and temperatures (local bulk volume averages) in a coupled, time-delayed manner that results in a unique compound dynamic, closed-loop power feedback mechanism. The 1-D simulation approach opens the possibility of performing inexpensive computations to evaluate time-dependent reactor performance relative to thermo-physical fuel salt limitations. Results also potentially motivate a convincing conclusion that natural circulation MSRs provide a leap in safety and reliability.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

NASA NTRSDate not supplied

Modeling and Trade Space for Fuel Cell Powered Aircraft

Hydrogen has gained significant traction in research as a potential carbon-neutral fuel for future aircraft propulsion. The focus of this paper is on the hydrogen-electric aircraft (HEA) propulsion system which is a highly integrated network of high-power electrical, mechanical, fluidic, cryogenic, and thermal management components. These systems require careful analysis to determine the most efficient and light-weight design that ultimately reduces carbon emissions and operating cost. Fuel cell and energy storage sizing and optimization will be major factors that contribute to the aircraft feasibility independent of hydrogen storage. This paper describes the framework and modeling approach for the analysis of hydrogen-electric aircraft (HEA) propulsion systems for a under the National Aeronautics and Space Administration (NASA) Commercially-viable Hydrogen Aircraft for Reduction of Greenhouse Emissions (CH 2 ARGE) Project. For the first time, the Electrical Power System – Sizing and Analysis Tool (EPS-SAT) is used to conduct the sizing and trade studies on the hydrogen-electric aircraft propulsion system.

Hydrogen Electric Aircraft↗

NASA NTRS2019

Mechanisms of Heavy Ion-Induced Single Event Burnout in 4H-SiC Power MOSFETs

This describes the mechanisms behind the failure of 4H-SiC Power MOSFETs when struck by a heavy ion. The modeled device is designed to simulate a commercially available 1200 V power MOSFET and the ion simulated is a silver ion with a Linear Energy Transfer of 46 MeV-cm2/mg commonly used in single event effect (SEE) testing. The device is shown in simulation to fail near 500 V, which is in close agreement to experiments. These simulations go to show that the failure of SiC MOSFET occurs near the interface between the epi and substrate layers due to the rapid increase of the electric field in that region and destruction of the device from impact ionization. From this, two designs were proposed and investigated that would help to mitigate the electric field in these regions and improve the device's tolerance to single-event burnout (SEB). The new designs increased the voltage at which SEB occurs from 500 V to over 900 V and increased the Ron,sp by only 5%.

Mcpherson, Joseph A.↗

NASA NTRS1999

Nonlinear Effects in Single-Pass ICRF Heating

The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) concept employs Ion Cyclotron Resonant Frequency (ICRF) heating as the main power deposition mechanism. Since the ions accelerate to the full energy in a single pass through the cyclotron resonance, their response to the RF-field will be essentially nonlinear - hence the motivation to amend the commonly used linear approach to the problem. In a collisionless plasma, the energy gain of an accelerated ion is limited by the time the particle spends at the resonance. This time is affected by: (1) incident flow velocity, (2) longitudinal grad B force, (3) ambipolar electric field, and (4) ponderomotive force of the RF-field. Our analysis shows that the grad B force is the dominant factor at low to moderate levels of RF-power. We present nonlinear scaling for the energy gain and the absorption efficiency with RF-power and plasma parameters. We also demonstrate that the nonlinear regime exhibits a steep decrease in the plasma density at the resonance.

Arefiev, A. V.↗

DOE OSTI2025

Lessons learned from the design and operation of a small-scale cross-flow tidal turbine

In 2023, a first-generation prototype of a small-scale marine current turbine was operated in Sequim Bay, Washington (USA) for 141 days. The system, referred to as the Turbine Lander, was the product of a laboratory-to-field effort to develop a system that enables enhanced ocean sensing or vehicle recharge in remote, energetic settings. The turbine consists of a vertical-axis, cantilevered rotor (1.19 m x 0.85 m) with four foils installed on a gravity foundation. A broader range of constraints including the deployment strategy, site characteristics, and estimated loads, drove the system’s design. This work presents the design, characterization, operation, and post-recovery engineering assessment of the Turbine Lander. Pre-deployment characterization efforts yielded a peak power coefficient of approximately 0.3 for the rotor, although system losses resulted in much lower water-to-wire efficiencies under most operating conditions. The results demonstrate the importance of co-design among key components of the powertrain and control systems to achieve acceptable system efficiency across operating conditions.

Co-design↗

NASA NTRS2009

Enceladus: An Active Cryovolcanic Satellite

Enceladus is one of the most remarkable satellites in the solar system, as revealed by Cassini's detection of active plumes erupting from warm fractures near its south pole. This discovery makes Enceladus the only icy satellite known to exhibit ongoing internally driven geological activity. The activity is presumably powered by tidal heating maintained by Enceladus 2:1 mean-motion resonance with Dione, but many questions remain. For instance, it appears difficult or impossible to maintain the currently observed radiated power (probably at least 6 GW) in steady state. It is also not clear how Enceladus first entered its current self-maintaining warm and dissipative state initial heating from non-tidal sources is probably required. There are also many unanswered questions about Enceladus interior. The silicate fraction inferred from its density of 1.68 g per cubic centimeter is probably differentiated into a core, though we have only indirect evidence for differentiation. Above the core there is probably a global or regional water layer, inferred from several models of tidal heating, and an ice shell thick enough to support the ~1 kilometer amplitude topography seen on Enceladus. It is possible that dissipation is largely localized beneath the south polar region. Enceladus surface geology, ranging from moderately cratered terrain to the virtually crater-free active south polar region, is highly diverse, tectonically complex, and remarkably symmetrical about the rotation axis and the direction to Saturn. South polar activity is concentrated along the four tiger stripe fractures, which radiate heat at temperatures up to at least 167 K and are the source of multiple plumes ejecting ~200 kilograms per second of H2O vapor along with significant N2 (or C2H4), CO2, CH4, NH3, and higher-mass hydrocarbons. The escaping gas maintains Saturn's neutral gas torus, and the plumes also eject a large number of micron-sized H2O ice grains that populate Saturn's E-ring. The mechanism that powers the plumes is not well understood, and whether liquid water is involved is a subject of active debate (but likely nonetheless). Enceladus provides a promising potential habitat for life in the outer solar system, and the active plumes allow the unique opportunity for direct sampling of that zone. Enceladus is thus a prime target for Cassini's continued exploration of the Saturn system, and will be a tempting target for future missions.

Spencer, J. R.↗