Kenneth R. Johnson

Development of segmented thermoelectric multicouple converter technology

The Jet Propulsion Laboratory (JPL), Pratt & Whitney Rocketdyne, and Teledyne Energy Systems, Inc., have teamed together under JPL leadership to develop the next generation of advanced thermoelectric space reactor power conversion systems. The program goals are to develop the technologies needed to achieve a space nuclear power system specific mass goal of less than 30 kg/kW at the 100 kW power level with a greater than 15 year lifetime. The technologies required for such a power system include liquid metal cooled reactors with outlet temperatures ranging from 1125 K up to 1325 K, segmented thermoelectric multicouple converter (STMC) arrays which can achieve greater than 8 percent system efficiency and carbon-carbon heat pipe radiator panels to reduce the radiator subsystem areal density to a goal of 5 kg/m . The STMC programs development efforts focused on a highly compact conductively coupled modular thermoelectric converter assembly (TCA) design. STMC design efforts were based on a multicouple design similar to the SP-100 Programs design but using segmented thermoelectric (TE) legs rather than the single alloy silicon-germanium legs. Efforts have addressed in parallel the selection and optimization of the most promising high temperature thermoelectric materials, the development of the various STMC components and sub-assemblies, design, analysis, fabrication and assembly of subscale STMC devices as well as scale-up plans to the 100 kW-class power level. The performance of the selected high temperature TE materials and initial thermal, electrical and mechanical test results on several STMC demonstration devices are reported

Segmented Thermoelectric Multicouple Converter Technology Development

The primary objectives of the segmented thermoelectric multicouple converter (STMC) technology development effort are: to define a conceptual design for a passive, low mass (3000 kg), long life (15 years) thermoelectric advanced Space Reactor Power System that provides 100kWe 400 Volt dc power for a 6000 volt dc electric propulsion system, to prepare a preliminary design of the power conversion system and to prepare technology development plan to advance power conversion system technology to TRL 6. The SRPS consists of a heat pipe cooled reactor radiatively couple to high efficiency solid‐state segmented thermoelectric multicouple converters which are conductively coupled to a low mass heat pipe radiator. The SRPS conceptual design as well as the Power Conversion System preliminary design is complete and their description reported in this paper.

Sublimation Extraction of Mars H 2 O for Future In-Situ Resource Utilization

H 2 O on Mars is an essential resource for future human exploration. H2O-based in-situ resource utilization (ISRU) on Mars will provide the necessary raw ingredients for propellant production and energy storage, oxygen and water for life support. The importance of H2O-based in-situ propellant production (ISPP) cannot be understated — there is no planned terrestrial launch vehicle in the near or longer term future that can deliver a fully fueled return launch vehicle to the surface of Mars. We provide a brief summary of trades considered when estimating mass requirements for H 2 O for a surface mission to Mars. A companion session paper (Accessible Water on Mars and The Moon by Rapp and others) describes the current understanding for the existence of H 2 O on Mars based on current orbital mapping missions and numerous existing corroborating models. Abundant, accessible Mars H 2 O likely exists in the form of near-subsurface ice-filled porous regolith, particularly at latitudes ∼50° and higher. The upcoming 2007 Phoenix mission will provide an additional datapoint to confirm or refute this expectation. In this paper, we describe a novel extraction mechanism for such an H 2 O resource based on enhancing the optical properties of the surface to improve the coupling of solar energy into the soil and induce forced sublimation down to > 0.5m within 150 sols (martian days). Development and results of a theoretical model for describing the sublimation process are presented.

The Mars Thermal Environment and Radiator Characterization (MTERC) Experiment

Radiators will be used on Mars to reject excess heat from various processes and surfaces and will help temper the climate of any future manned habitats. Radiator performance is a function of the radiator size (area), the emissivity, E, of the radiator surface, the radiator temperature, local environmental conditions, and the effective sky temperature to which it radiates. The ffective sky temperature of Mars is not known. Previous estimates have ranged between 80 K to 170 K. Also, it is not known how dust accumulation and other environmental effects act to change the performance of a radiator as a function of time. The MTERC Experiment is designed to gather data to address these unknowns. This paper will describe the operational theory and the configuration of the MTERC experiment hardware and will discuss results of MTERC performance testing.

Raman/CHAMP Instrument for Lunar In-situ Resource Prospecting I - Imager Design

Lunar ISRU precursor prospecting missions are being considered in order to characterize the lunar surface environment and to determine volatile and mineral content as well as mechanical and thermal properties of the lunar regolith for purposes of designing future excavation and In-Situ Resource Utilization (ISRU) processing equipment. The Raman/CHAMP instrument (RCI) is being developed as part of an instrument/experiment suite development project known as Regolith and Environment Science and Oxygen and Lunar Volatile Extraction (RESOLVE) being developed and sponsored under the NASA ISRU Project. The RCI supports the lunar surface characterization measurements by providing crucial field macroscopic and microscopic images coupled with Raman spectroscopy. The RCI provides the ability to collect high resolution, hand lens to field microscopy images and spectroscopic measurements from a robotic arm with the ability to resolve, characterize, and chemically differentiate >90% of lunar Apollo fines. The entire measurement process is highly adaptive and does not necessarily require any type of active sampling. In this paper we provide an overview of the RCI. We discuss the optical design optimization and analysis process for this particular type of instrument. We discuss recent results of integration tests of the Mars Microbeam Raman Spectrometer (MMRS) with the MIDP CHAMP instrument, fluorescence analysis, and individual glass fluorescence tests. Finally, we conclude with a summary of anticipated instrument measurement performance based on Zemax optical modeling of an RCI engineering model that is currently in development.