Multi-Mission Radioisotope Thermoelectric Generator Research Articles

Bayesian Reliability Analysis of the Enhanced Multimission Radioisotope Thermoelectric Generator

Radioisotope thermoelectric generators (RTGs) have been used as power sources for several space missions, including the multimission RTG (MMRTG) in NASA’s recent Mars Curiosity and Perseverance rovers. The enhanced MMRTG (eMMRTG) design is an MMRTG retrofitted with advanced skutterudite thermoelectric couples to improve efficiency and power output over time. The eMMRTG’s predicted reliability over the mission duration is influenced by the uncertainty in the physics parameters governing its performance. We use a Bayesian approach to account for two types of uncertainty: epistemic and aleatory. The reliability analysis has two steps: 1) uncertainty quantification from experimental data for key physics parameters, and 2) uncertainty propagation through a computational RTG life performance prediction. In particular, we use hierarchical models to separate specimen-to-specimen uncertainty and also to model the separate manufacturing batches of thermoelectric couples loaded into the eMMRTG. We use a secondary probability method to predict reliability with epistemic uncertainty intervals for the eMMRTG system at 10,000 h for which recent data are available. We show how reliability and uncertainty intervals depend on hypothetical power requirements at 10,000 h. The approach is generally applicable when experimental data and computer simulation are used to predict the reliability of a new technology.

A Micro-Nuclear Power Generator for Space Missions

The significance of reliable energy storage systems in spacecraft applications cannot be overstated, since they play a vital role in ensuring continuous power supply and prolonged mission durations. This research deals with the modeling of a hybrid multi-mission radioisotope thermoelectric generator (MMRTG)-lithium-ion (Li-ion) battery integrated energy storage system for spacecraft applications to combine the RTGs’ long lifespan and reliability benefits alongside the Li-ion battery’s rechargeability and high energy density to achieve a single energy unit. The investigation’s main problem was exploring a power unit that improves the limitations of MMRTG and Li-ion batteries to achieve a highly efficient and reliable power supply for autonomous systems, such as a spacecraft. The proposed hybrid system comprises a 110 W/32 V RTG and a 3.6 V/43 Ah Li-ion battery connected to a DC motor through power converters. Results demonstrate the potential of the adopted hybrid energy system in improving the efficiency, reliability, and mission duration of spacecraft missions. The assessment of the hybrid energy system under various load conditions shows that the highest power peak of 3500 W was achieved at a load resistance of 1 Ω. Furthermore, the results show that the hybrid energy system output voltage at temperatures of 253 °K and 293 °K are relatively equal. However, the power cycle was wider and required a long time before dropping.

Comprehensive modeling and parametric analysis of Multi-Mission Radioisotope Thermoelectric Generator

Radioisotope thermoelectric generators (RTGs) have been widely used as a promising power source for space mission, in which the Multi-Mission RTG (MMRTG) is the state of the art type. However, due to the scarcity of the 238 P u fuel and associated cost concerns, there exists an imperative need to increase the efficiency of RTGs. This requires intuitive, detailed and accurate system property predictions of the RTG system. In this work, a comprehensive finite element model of the MMRTG has been developed, by using a commercial software, COMSOL Multiphysics, including a full-size three-dimensional geometry model, temperature dependent materials and the thermoelectric and radiation heat transfer multiphysics fields involved. The calculation results agree well with reported experimental and simulated values. Through the obtained detailed temperature and voltage distribution, thermal and power properties of the MMRTG are characterized and the effects of non-uniform distributions of temperature and power generated in each TE couple are revealed. At last, the parametric analyses of operation conditions, thermal environment and key design factors are performed and several salient findings have been obtained. Through the analysis results, the design parameters and working mechanisms of the MMRTG are clarified, which can help the design and optimization of the future hundred-watt RTG. • The comprehensive FEM method is first implemented in the MMRTG modeling and analysis. • The non-uniform distributions of temperature and power in TE modules are revealed. • Suitable load and sufficient thermal inventory ensure adequate power output. • The insensitivity of performance to ambient temperature expands MMRTG’s application.

Multi-Mission Thermoelectric Generator Fueling Testing and Integration Operations for Mars 2020

The Space Nuclear Power and Isotope Technologies (SNPIT) Division at Idaho National Laboratory fuels, performs acceptance testing, and provides spacecraft integration support of radioisotope power systems in support of National Aeronautics and Space Administration missions. Recently, the SNPIT team completed fueling, testing, and launch support of the Multi-Mission Radioisotope Thermoelectric Generator for the Mars 2020 Perseverance Rover mission.

Modeling of Am-241 as an alternative fuel source in a radioisotope thermoelectric generator

Radioisotope thermoelectric generators (RTGs) have been utilized in the USA to power satellites and space exploration equipment for over half a century. In our preceding paper, Dustin and Borrelli (2021), we assessed the performance of 241Am as an alternative to 238Pu by modeling the specific decay-heat and gamma spectra of several potential radioisotopes in SCALE-ORIGEN, and comparing these with 238Pu An analysis of heat output, heat stability, safety, availability and required mass showed that of the isotopes reviewed, 241Am had the greatest potential for replacing 238Pu, with additional design considerations. In our current work, we have assessed radiation transport for two configurations of an 241Am powered Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), due to the potential health effects for operators, fabricators, and others with the potential to be exposed to neutrons and lower energy gamma rays. We have modeled the use of americium as a fuel source replacement for plutonium in current MMRTG designs. The assessment has been performed using MCNP6, in terms of neutron and gamma emissions that might interfere with sensitive equipment and power system production. The radiation transport behavior in terms of dose rate of the 241Am fueled models is compared with that of a 238Pu fueled model. Additional work was performed to validate modeling simplifications with regards to thermocouple material configurations.

Empirical Analysis of the Multi-Mission Radioisotope Thermoelectric Generator Qualification Unit Operated at a Low Thermal Inventory with Potential for Improved End-of-Life Power

Performance predictions for the first multi-mission radioisotope thermoelectric generator (MMRTG) flight unit and engineering unit were recently reported. Both units were produced and operated/tested within specifications [i.e., nominal thermal inventory = 2000 W(thermal)]. In an attempt to study the effect of a deep space cruise on an MMRTG that has been operational for 6.25 years (2.25 years storage + 4 years cruise), the qualification unit (QU) was placed on life test with a below-specification thermal inventory of 1904 W(thermal). Analysis indicates that loading an MMRTG with a lower thermal inventory may result in less power at the beginning-of-life but more power at the end-of-design-life (EODL). The lower thermal inventory in the QU produces a lower operating temperature, which appears to cause a significant reduction in the degradation rate of the thermoelectric couples. Preliminary calculations indicate that a thermal inventory of 1904 W(thermal) could result in a 9 W(electric) power boost at EODL [i.e., 84 W(electric)], which is a 12% improvement over the first MMRTG flight unit and engineering unit predictions. Preliminary degradation analysis suggests that a 1904 W(thermal) unit will begin to produce more power than a 2027 W(thermal) unit approximately 4 years after fueling. This suggests that missions with a primary power requirement more than 4 years after fueling would benefit from a lower thermal inventory. In addition, using a lower thermal inventory has significant benefits for 238Pu stockpile management and may allow for additional MMRTGs to be fueled from our current reserves. Conclusions and hypotheses presented here should be considered preliminary because the QU data set is very small and there are some uncertainties regarding how early-life QU data will translate into later-life performance. More QU testing at a thermal inventory of 1904 W(thermal) is needed to prove that the preliminary conclusions presented here are valid.

Enhancing NASA's Multi-Mission Radioisotope Thermoelectric Generator Using Highly Efficient Thermoelectric Materials

This project proposal aims to enhance NASA’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) by identifying and analyzing new material technologies that have been researched for their excellent thermoelectric properties at higher temperatures. By choosing the most efficient thermoelectric material available, the MMRTG’s energy conversion efficiency will be greatly improved as thermoelectric generator efficiencies are largely determined by the properties of the materials within the thermocouple devices used to convert the heat into energy. A project that focuses on enhancing the MMRTG is imperative for the future of space exploration as there is global shortage of plutonium fuel production, limiting future missions to available supplies. A more efficient generator will minimize the use of this fuel while maximizing power output, allowing for increased mission capabilities and better conservation of the scarce plutonium fuel. In this report, lanthanum telluride, Yb14MnSb14, and a multiple-filled skutterudite (SKD) compound are analyzed for their excellent thermoelectric performance. The multiple filled SKD compound is chosen as the ideal material to enhance the MMRTG based on the low cost and low risks associated with the material while producing a nearly identical efficiency relative to the other candidates. Keywords: eMMRTG, MMRTG, thermoelectric materials, thermoelectric generator, efficiency

Assessment of water content in martian subsurface along the traverse of the Curiosity rover based on passive measurements of the DAN instrument

This paper presents the method of estimating water-equivalent hydrogen (WEH) content from neutron sensing data that were measured by the Dynamic Albedo of Neutron (DAN) instrument onboard the Curiosity rover. Analyzed data are derived from the DAN passive operations, when the instrument measures the flux of neutron albedo from the surface, which is produced by bombardment by Galactic Cosmic Rays (GCR) and irradiation from Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) installed onboard the rover. The suggested Method of Referencing by Active Data (MRAD) for the analysis of DAN passive data is compared with the previously suggested Method of Numerical Simulation (MNS, see Tate et al. 2015, 2018 and 2019) for the analysis of DAN passive data: the qualitative agreement between them is shown with some systematic increase of WEH for the second one. The possible reason for that is explained in Section 6. Results for the DAN passive data analysis by MRAD are presented obtained for almost 20 km of the rover's traverse (until November 2, 2018 or sol 2218). The range of WEH average concentration of (2.6 ± 0.7) wt% is found for this part of the traverse, which is consistent with a method of active neutron sensing (Mitrofanov et al., 2014, 2016; Lisov et al., 2018).

Analysis of Raw Materials Sourcing and the Implications for the Performance of Skutterudite Couples in Multi-Mission Radioisotope Thermoelectric Generators

The NASA enhanced MMRTG (eMMRTG) project seeks to enhance the performance of the Multi-Mission Radioisotope Thermoelectric Generator by exchanging the heritage thermoelectric couple materials and design with that of more efficient skutterudite (SKD)-based thermoelectric (TE) couples. Both at the Jet Propulsion Lab—where the SKD materials were developed—and at Teledyne Energy Systems, Inc.—where the technology is being matured and optimized for fabrication under the Skutterudite Technology Maturation (SKD Tech Mat) Project—many SKD material batches have been produced. A strong correlation has been observed between the TE performance of the materials and the particular lot numbers (same producer and supplier) of various raw materials used to produce the SKD materials. An analysis of the differences between lots, their effects on performance, and the current plan to mitigate the risk posed by these results is discussed.

Observed diurnal variations in Mars Science Laboratory Dynamic Albedo of Neutrons passive mode data

The Mars Science Laboratory Dynamic Albedo of Neutrons (DAN) experiment measures the martian neutron leakage flux in order to estimate the amount of water equivalent hydrogen present in the shallow regolith. When DAN is operating in passive mode, it is sensitive to neutrons produced through the interactions of galactic cosmic rays (GCR) with the regolith and atmosphere and neutrons produced by the rover’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG). During the mission, DAN passive mode data were collected over the full diurnal cycle at the locations known as Rocknest (sols 60–100) and John Klein (sols 166–272). A weak, but unexpected, diurnal variation was observed in the neutron count rates reported at these locations. We investigate different hypotheses that could be causing these observed variations. These hypotheses are variations in subsurface temperature, atmospheric pressure, the exchange of water vapor between the atmosphere and regolith, and instrumental effects on the neutron count rates. Our investigation suggests the most likely factors contributing to the observed diurnal variations in DAN passive data are instrumental effects and time-variable preferential shielding of alpha particles, with other environmental effects only having small contributions.

Advanced Skutterudite-Based Unicouples for a Proposed Enhanced Multi-Mission Radioisotope Thermoelectric Generator: An Update

Radioisotope Thermoelectric Generators (RTG’s) have been used on several NASA missions when they enable or significantly enhance the ability of a mission to meet its objectives. The current state-of-the-art RTG power source, Curiosity rover’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has operated for more than one Martian year (687 earth days) on the red planet. In order to increase the power and conversion efficiency of future MMRTG systems and extend the lifetime of future rover missions, an effort was started in 2013 to mature advanced thermoelectric technology for use in a proposed Enhanced Multi-Mission Radioisotope Thermoelectric Generator (eMMRTG). The conceptual design approach of the eMMRTG is to replace the heritage MMRTG couples in the thermoelectric module assembly with more advanced skutterudite (SKD)-based couples without any significant design changes to the generator. The new SKD thermoelectric materials not only can provide higher thermoelectric performance, but also can operate at higher maximum operating temperature than MMRTG thermoelectric materials. As a result, the proposed eMMRTG would preserve all the MMRTG’s multi-mission capability while offering an expected enhancement in power, relative to MMRTG, of about 25 % at beginning-of-life and potentially lower power degradation rates leading to a ≥ 50% increase in power at end-of-design life (17 years) with an 80W power output goal at 17 years. Here, we will report on the progress for demonstrating manufacturability and validating performance of these advanced SKD unicouples jointly developed and tested by Jet Propulsion Laboratory (JPL) and Teledyne Energy Systems, Inc. (TESI).

Skutterudite-Based Thermoelectric Technology for Integration into a Proposed Emmrtg for Space Power Applications

The overall objective of the Skutterudite Technology Maturation (STM) project at NASA’s Jet Propulsion Laboratory (JPL) is to advance JPL-developed skutterudite (SKD) technology to a point where it can be considered for use in a proposed enhanced Multi-Mission Radioisotope Thermoelectric Generator (eMMRTG). The goal is to be prepared for potential flight unit development readiness by end of FY2018. Conversion efficiency values on the order of 9% have been demonstrated for SKD-based un-segmented couples when operating at a hot junction of 600C and a cold junction of 200C. This represents ~ a 25% improvement over the conversion efficiency of PbTe/TAGS MMRTG couples at beginning-of-life (BOL). The STM project entered its third year at the beginning of FY2016. This talk will highlight the material and device challenges associated with the maturation of this technology. During the first two years of the project, JPL and Teledyne Energy Systems Inc. (TESI) have collaborated to complete the initial technical technology transfer to TESI. Manufacturing capabilities for SKD TE materials have been established at TESI. TESI has also established the manufacturing capabilities for couples and module thermal insulation. First iteration SKD couples have been fabricated and tested at TESI. Key findings from this initial Phase of the technology maturation project will be summarized. TESI and JPL are currently developing a second iteration of couples and module thermal insulation, incorporating lessons learned from the development and testing of the first iteration of couples and insulation. Progress to date on the development of this second iteration of couples will be presented and discussed. The eMMRTG life performance prediction approach and development status will also be presented.

Results from the dynamic albedo of neutrons (DAN) passive mode experiment: Yellowknife Bay to Amargosa Valley (Sols 201–753)

The Mars Science Laboratory (Curiosity rover) Dynamic Albedo of Neutrons (DAN) experiment detects neutrons for the purpose of searching for hydrogen in the shallow subsurface of Mars. DAN has two modes of operation, active and passive. In passive mode, the instrument detects neutrons produced by Galactic Cosmic Ray interactions in the atmosphere and regolith and by the rover's Multi-Mission Radioisotope Thermoelectric Generator. DAN passive data from Yellowknife Bay to Amargosa Valley (sols 201 through 753) are presented and analyzed here. Water equivalent hydrogen (WEH) estimates from this portion of Curiosity's traverse range from 0.0 wt. % up to 15.3 wt. %. Typical uncertainties on these WEH estimates are ∼0.5 wt. % but in some cases can be as high as ∼4.0 wt. % depending on the specific circumstances of a given measurement. Here we also present a new way of reporting results from the passive mode of the experiment, the DAN passive geochemical index (DPGI). This index is sensitive to some key geochemical variations, but it does not require assumptions about the abundances of high thermal neutron absorption cross section elements, which are needed to estimate WEH. DPGI variations in this section of the traverse indicate that the shallow regolith composition is changing on both the local (∼meters) and regional (∼100 s of meters) scales. This variability is thought to be representative of the diverse composition of source regions for sediments within the crater floor. Kolmogorov-Smirnov Tests on the populations of WEH estimates and DPGI values demonstrate there are statistically significant differences between nearly all of the geologic units investigated along the rover's traverse. We also present updated previous DAN passive results from Bradbury Landing to John Klein that make use of revised DAN active mode results for calibration, however, no qualitative changes in the interpretations made in Tate et al. (2015b) are incurred.

Erratum to: Increasing the Efficiency of the Multi-mission Radioisotope Thermoelectric Generator

Erratum to: Increasing the Efficiency of the Multi-mission Radioisotope Thermoelectric Generator

Water equivalent hydrogen estimates from the first 200 sols of Curiosity’s traverse (Bradbury Landing to Yellowknife Bay): Results from the Dynamic Albedo of Neutrons (DAN) passive mode experiment

The Dynamic Albedo of Neutrons (DAN) experiment on the Mars Science Laboratory (MSL) rover Curiosity is designed to detect neutrons to determine hydrogen abundance within the subsurface of Mars (Mitrofanov, I.G. et al. [2012]. Space Sci. Rev. 170, 559–582. http://dx.doi.org/10.1007/s11214-012-9924-y; Litvak, M.L. et al. [2008]. Astrobiology 8, 605–613. http://dx.doi.org/10.1089/ast.2007.0157). While DAN has a pulsed neutron generator for active measurements, in passive mode it only measures the leakage spectrum of neutrons produced by the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) and Galactic Cosmic Rays (GCR). DAN passive measurements provide better spatial coverage than the active measurements because they can be acquired while the rover is moving. Here we compare DAN passive-mode data to models of the instrument’s response to compositional differences in a homogeneous regolith in order to estimate the water equivalent hydrogen (WEH) content along the first 200 sols of Curiosity’s traverse in Gale Crater, Mars. WEH content is shown to vary greatly along the traverse. These estimates range from 0.5±0.1wt.% to 3.9±0.2wt.% for fixed locations (usually overnight stops) investigated by the rover and 0.6±0.2wt.% to 7.6±1.3wt.% for areas that the rover has traversed while continuously acquiring DAN passive data between fixed locations. Estimates of WEH abundances at fixed locations based on passive mode data are in broad agreement with those estimated at the same locations using active mode data. Localized (meter-scale) anomalies in estimated WEH values from traverse measurements have no particular surface expression observable in co-located images. However at a much larger scale, the hummocky plains and bedded fractured units are shown to be distinct compositional units based on the hydrogen content derived from DAN passive measurements. DAN passive WEH estimates are also shown to be consistent with geologic models inferred from other MSL instruments, which indicate that fluvial/lacustrine activity occurred at certain locations (e.g., Yellowknife Bay).

A Progress Report on the eMMRTG

A multimission radioisotope thermoelectric generator (MMRTG), developed by the US Department of Energy for the National Aeronautics and Space Administration, powers the Mars Science Laboratory Curiosity rover on Mars. New thermoelectric couples (TECs) have been developed in recent years that offer significant improvements over the TECs used in the MMRTG. The maturity of the new TECs and the design flexibility of the MMRTG enable a low-risk system upgrade that is predicted to substantially enhance the MMRTG’s performance. System design trades are looking at changing the TECs and increasing the hot-side temperature to find the best combination of performance and program cost in this enhanced MMRTG (eMMRTG). Initial studies indicated that a low-risk enhancement would be to use skutterudite (SKD) materials developed at JPL to form TECs for the eMMRTG. Simply replacing the PbTe/TAGS TECs with SKD TECs and making a few low-risk modifications to the MMRTG design could potentially provide a 25% increase in power output at beginning of life (BOL). More important than the BOL power output increase is the end of design life (EODL) power output increase. With the anticipated lower degradation rate of the SKD materials, it is anticipated that the EODL power output will be more than 50% higher than for the MMRTG (with EODL defined as 17 years from fueling). This paper presents an overview of the results of the initial trades leading to the pursuit of the eMMRTG and the progress made since those were concluded.

Increasing the Efficiency of the Multi-mission Radioisotope Thermoelectric Generator

The National Aeronautics and Space Administration’s Mars Science Laboratory terrestrial rover, Curiosity, has recently completed its first Martian year (687 Earth days) during which it has provided a wealth of information and insight into the red planet’s atmosphere and geology. The success of this mission was made possible in part by the reliable electrical power provided by its onboard thermoelectric power source—the multi-mission radioisotope thermoelectric generator (MMRTG). In an effort to increase the output power and efficiency of these generators, a newly designed enhanced MMRTG (eMMRTG) that will utilize the more efficient skutterudite-based thermoelectric materials has been conceptualized and modeled, and is now being developed. A discussion of the motivations, modeling results and key design factors are presented and discussed.

Neutron background environment measured by the Mars Science Laboratory's Dynamic Albedo of Neutrons instrument during the first 100 sols

AbstractThe Dynamic Albedo of Neutrons (DAN) instrument on board Mars Science Laboratory has been operating successfully since the landing and has been making measurements regularly along Curiosity's traverse at the surface. DAN measures thermal (E < 0.4 eV) and epithermal neutrons (0.4 eV < E < ~1 keV) while operating in two different modes: active and passive. The active mode uses a pulsed neutron generator (PNG) to study the geological characteristics of the subsurface. In the passive mode, DAN measures the background neutron environment. This paper presents results of measurements in the passive mode from landing through to sol 100 and provides an interpretation of the data based on extensive Monte Carlo simulations. The main observations are summarized as follows: (1) the thermal neutron counts vary strongly along the rover traverse while the epithermal counts do not show much variation; (2) the neutrons from the Multi‐Mission Radioisotope Thermoelectric Generator (MMRTG) are a larger contributor to the DAN passive data than the Galactic Cosmic Ray (GCR)‐induced neutrons; (3) for the MMRTG neutrons, both the thermal and the epithermal counts increase as a function of the subsurface water content; (4) on the other hand, for the GCR‐induced neutrons, the thermal counts increase but the epithermal counts decrease as a function of the subsurface water content; and (5) relative contributions by the MMRTG and GCR to the DAN thermal neutron counts at the Rocknest site, where the rover was stationed from sol 59 to sol 100, are estimated to be ~60% and ~40%, respectively.

Mars Science Laboratory Mission and Science Investigation

Scheduled to land in August of 2012, the Mars Science Laboratory (MSL) Mission was initiated to explore the habitability of Mars. This includes both modern environments as well as ancient environments recorded by the stratigraphic rock record preserved at the Gale crater landing site. The Curiosity rover has a designed lifetime of at least one Mars year (∼23 months), and drive capability of at least 20 km. Curiosity’s science payload was specifically assembled to assess habitability and includes a gas chromatograph-mass spectrometer and gas analyzer that will search for organic carbon in rocks, regolith fines, and the atmosphere (SAM instrument); an x-ray diffractometer that will determine mineralogical diversity (CheMin instrument); focusable cameras that can image landscapes and rock/regolith textures in natural color (MAHLI, MARDI, and Mastcam instruments); an alpha-particle x-ray spectrometer for in situ determination of rock and soil chemistry (APXS instrument); a laser-induced breakdown spectrometer to remotely sense the chemical composition of rocks and minerals (ChemCam instrument); an active neutron spectrometer designed to search for water in rocks/regolith (DAN instrument); a weather station to measure modern-day environmental variables (REMS instrument); and a sensor designed for continuous monitoring of background solar and cosmic radiation (RAD instrument). The various payload elements will work together to detect and study potential sampling targets with remote and in situ measurements; to acquire samples of rock, soil, and atmosphere and analyze them in onboard analytical instruments; and to observe the environment around the rover. The 155-km diameter Gale crater was chosen as Curiosity’s field site based on several attributes: an interior mountain of ancient flat-lying strata extending almost 5 km above the elevation of the landing site; the lower few hundred meters of the mountain show a progression with relative age from clay-bearing to sulfate-bearing strata, separated by an unconformity from overlying likely anhydrous strata; the landing ellipse is characterized by a mixture of alluvial fan and high thermal inertia/high albedo stratified deposits; and a number of stratigraphically/geomorphically distinct fluvial features. Samples of the crater wall and rim rock, and more recent to currently active surface materials also may be studied. Gale has a well-defined regional context and strong evidence for a progression through multiple potentially habitable environments. These environments are represented by a stratigraphic record of extraordinary extent, and insure preservation of a rich record of the environmental history of early Mars. The interior mountain of Gale Crater has been informally designated at Mount Sharp, in honor of the pioneering planetary scientist Robert Sharp. The major subsystems of the MSL Project consist of a single rover (with science payload), a Multi-Mission Radioisotope Thermoelectric Generator, an Earth-Mars cruise stage, an entry, descent, and landing system, a launch vehicle, and the mission operations and ground data systems. The primary communication path for downlink is relay through the Mars Reconnaissance Orbiter. The primary path for uplink to the rover is Direct-from-Earth. The secondary paths for downlink are Direct-to-Earth and relay through the Mars Odyssey orbiter. Curiosity is a scaled version of the 6-wheel drive, 4-wheel steering, rocker bogie system from the Mars Exploration Rovers (MER) Spirit and Opportunity and the Mars Pathfinder Sojourner. Like Spirit and Opportunity, Curiosity offers three primary modes of navigation: blind-drive, visual odometry, and visual odometry with hazard avoidance. Creation of terrain maps based on HiRISE (High Resolution Imaging Science Experiment) and other remote sensing data were used to conduct simulated driving with Curiosity in these various modes, and allowed selection of the Gale crater landing site which requires climbing the base of a mountain to achieve its primary science goals. The Sample Acquisition, Processing, and Handling (SA/SPaH) subsystem is responsible for the acquisition of rock and soil samples from the Martian surface and the processing of these samples into fine particles that are then distributed to the analytical science instruments. The SA/SPaH subsystem is also responsible for the placement of the two contact instruments (APXS, MAHLI) on rock and soil targets. SA/SPaH consists of a robotic arm and turret-mounted devices on the end of the arm, which include a drill, brush, soil scoop, sample processing device, and the mechanical and electrical interfaces to the two contact science instruments. SA/SPaH also includes drill bit boxes, the organic check material, and an observation tray, which are all mounted on the front of the rover, and inlet cover mechanisms that are placed over the SAM and CheMin solid sample inlet tubes on the rover top deck.

RPS strategies to enable NASA's next decade robotic Mars missions

NASA's proposed roadmap for robotic Mars exploration over the next decade is influenced by science goals, technology needs and budgetary considerations. These requirements could introduce potential changes to the succession of missions, resulting in both technology feed forward and heritage. For long duration robotic surface missions at locations, where solar power generation is not feasible or limited, Radioisotope Power Systems (RPS) could be considered. Thus, RPSs could provide enabling power technologies for some of these missions, covering a power range from 10s of milliwatts to potentially a kilowatt or even higher. Currently, NASA and DoE with their industry partners are developing two RPSs, both generating about 110 W(e) at BOL. These systems will be made available as early as 2009. The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG)—with static power conversion—was down-selected as a potential power source for the MSL mission. Development of small-RPSs is in a planning stage by NASA and DoE; potentially targeting both the 10s of milliwatts and 10s of watts power ranges. If developed, Radioisotope Heat Unit (RHU) based systems—generating 10s to 100s of milliwatts—could power small adjunct elements on larger missions, while the GPHS module-based systems—each generating 10s of watts—could be stacked to provide the required power levels on MER class surface assets. MMRTGs and Stirling Radioisotope Generators (SRGs) could power MSL class or larger missions. Advanced Radioisotope Power Systems (ARPS) with higher specific powers and increased power conversion efficiencies could enhance or even enable missions towards the second half of the next decade. This study examines the available power system options and power selection strategies in line with the proposed mission lineup, and identifies the benefits and utility of the various options for each of the next decade launch opportunities.