Bill Nesmith

A radioisotope powered cryobot for penetrating the Europan ice shell

The Cryobot team at JPL has been working on the design of a Cryo-Hydro Integrated Robotic Penetrator System (CHIRPS), which can be used to penetrate the Mars North Polar Cap or the thick sheet ice surrounding Jupiter’s moon, Europa. The science for either one of these missions is compelling. For both Mars and Europa the major scientific interest is to reach regions where there is a reservoir of water that may yield signs of past or extant life. Additionally, a Mars polar cap penetration would help us understand both climatic and depositional histories for perhaps as far back as 20 million years. Similarly, penetration of the Europa ice sheet would allow scientists to unravel the mysteries surrounding the thick ice crust, its chemical composition, and subsurface ocean properties. Extreme mass and power constraints make deep drilling/coring impractical. The best way to explore either one of these environments is a cryobot mole penetrator vehicle, which carries a suite of instruments suitable for sampling an...

Development of New High Temperature Power Generating Couples for the Advanced Thermoelectric Converter (ATEC)

Radioisotope Thermoelectric Generators (RTGs) have served as a reliable source of space power for decades, enabling robotic spacecraft to explore regions of the Solar System where photovoltaic systems are impractical. The increased power requirements for future missions, combined with the reduced availability of radioisotope fuel, has prompted the development of a higher specific power, higher efficiency converter system employing thermocouples with advanced thermoelectric materials. The challenges in incorporating these advanced materials into power generating thermocouples suitable for operation in a space-rated RTG are discussed herein.

Photovoltaic cell and array technology development for future unique NASA missions

A technology review committee from NASA, the U.S. Department of Energy (DOE), and the Air Force Research Lab (AFRL) was formed to assess solar cell and array technologies required for future NASA science missions. After consulting with mission planning offices, solar cell and array manufacturers, universities, and research laboratories, the committee assessed the state of the art of solar cells and arrays and made a comparison with projected needs. A technology development program was proposed in high-efficiency cells, electrostatically clean arrays, high-temperature solar arrays, high-power arrays for solar electric propulsion, low-intensity/low-temperature array conditions for deep-space mission, high-radiation missions, and Mars arrays that operate in dusty environments.

Miniaturized Radioisotope Solid State Power Sources

Electrical power requirements for the next generation of deep space missions cover a wide range from the kilowatt to the milliwatt. Several of these missions call for the development of compact, low weight, long life, rugged power sources capable of delivering a few milliwatts up to a couple of watts while operating in harsh environments. Advanced solid state thermoelectric microdevices combined with radioisotope heat sources and energy storage devices such as capacitors are ideally suited for these applications. By making use of macroscopic film technology, microgenrators operating across relatively small temperature differences can be conceptualized for a variety of high heat flux or low heat flux heat source configurations. Moreover, by shrinking the size of the thermoelements and increasing their number to several thousands in a single structure, these devices can generate high voltages even at low power outputs that are more compatible with electronic components. Because the miniaturization of state-...

Development and Prototype Testing of Low-Cost Lightweight Thin Film Solar Concentrator

A low-cost rigid foam-based concentrator technology development program was funded by the DOE SunShot Initiative to meet installed cost goals of

TEMPERATURE-STAGED THERMAL ENERGY STORAGE ENABLING LOW THERMAL EXERGY LOSS REFLUX BOILING IN FULL SPECTRUM SOLAR ENERGY SYSTEMS

75/m^2 vs. current costs of ∼

Milli-watt radioisotope power to enable small, long-term robotic “Probe” space exploration

200–250/m^2. Phase 1 of the project focused on design trades and cost analyses leading to a cost-optimized self-powered autonomous tracking heliostat concept with a mirror surface area in the 100m^2 range. In Phase 2 30-year accelerated testing of the mirror modules based on ReflecTec film with 94% specular reflectivity bonded on composite foam substrate were initiated and completed in Phase 3. The tests with 15 coupons showed optical performance degradation of less than 5% in specular reflectance following 30-year equivalent UV testing and other abuse testing such as acid rain, bird dropping, thermal cycling, etc. A small scale prototype (3m×2m) heliostat design based on modular truss elements with removable mirror modules was developed in detail. In this phase components such as the dual-axis actuators were sized and selected based on wind load requirements and pointing accuracy demands were completed. Finite Element analyses for the mechanical structure with mirror modules were performed using three separate commercial codes — ANSYS, COMSOL and SolidWorks to validate the optical errors induced by wind loads on the structure up to 35 mph. Results indicated that the RMS deflections contributed to less than 0.4 mrad pointing error. Dynamic response of the heliostat indicated that the first 5 eigenmodes were in the 17–20 Hz range. The individual structure elements such as the trusses and c-rails were fabricated locally and assembled with the mirror facets in the lab for initial fit check and testing. The nine mirror facet surface errors were characterized using photogrammetry and verified using Reverse Hartmann techniques and showed to be in the order of 1 mrad or less. A three-level controller (main, gateway and heliostat) was architected and built. Tracking of the sun is done using NREL’s Sun Tracking Algorithm implemented in the gateway controller. Target-pointing vectors are calculated for each heliostat and conveyed wirelessly to the individual heliostat controllers for actuating the azimuth and elevation motors. The power subsystem consisting of solar panels and a battery provide 24V for the actuators and controller boards. The system was sized to provide adequate power for a period of 5hrs of operation when power is not available. Initial calibration will be performed with on-site camera tracking the sun’s image on a target located approximately 52m from the heliostat. Testing of the heliostat pointing under calm and windy conditions will be done to demonstrate overall performance that meet DOE targets of 4 mrad under 27 mph winds. Commercialization efforts are underway to transition the design to the commercial sector. The project is well on its way to approaching overall cost targets and current estimates are approximately S90–110/m^2 and lower costs can be achieved with alternates to the film we have identified.

Full spectrum hybrid photovoltaics and thermal engine utilizing high concentration solar energy

The efficiency of solar power collection is increased by adding a thermal energy storage stage to a sunlight concentrator and thermodynamic power generator system. The thermal energy storage includes tubes or capsules made of a phase change material that stores thermal energy in different temperature stages through a working fluid. The stored thermal energy is directed to the thermodynamic generator during off-sun periods.

Development of Multi-Physics Dynamics Models for High-Frequency Large-Amplitude Structural Response Simulation

Milli-watt Radioisotope Power Systems (RPS) based on Radioisotope Heater Units (RHUs) could be an ideal power source for certain spacecraft that cannot use solar power due to large distances from the sun, or other environmental constraints, and where they enable or significantly enhance the ability of a mission to meet its scientific or operational goals. Various modular, compact RHU-based thermoelectric (TE) generator concepts developed or derived from current NASA Small Business Innovation Research (SBIR) projects satisfying this need have been investigated. These modular, compact and low mass power systems could support small, highly-mobile robotic exploration packages, and could be incorporated into different robotic package concepts, spacecraft or satellites. Current modular RPS design concepts with 40mW, 80mW and 120mW power levels use RHUs and Bi2Te3 TE converters. Skutterudites materials could be used in the future if new higher thermal energy output and higher temperature miniature heat sources were developed, for example, using technologies currently in the General Purpose Heat Source (GPHS) used in higher electric power output RTGs. Small (a.k.a., “mice-like”) robotic packages could effectively utilize these RHU-driven power levels to accommodate crawling, climbing, monitoring, taking measurements, and communicating during long-term planetary missions aimed at gathering environmental and geologic data (i.e., over multiple decades). Waste heat from the cold side of the TE converter could also be directed toward the electronics and / or energy storage (e.g. batteries) to keep them within design temperature ranges. In addition to power generation and electronics / battery heating, the RHU / TE configuration could be designed to survive an external 500°C bake out procedure for critical spacecraft sterilization, environmental certification and planetary protection. Analytical studies have been performed to optimize various design configurations for power, mass, volume and robotic mobility. Specific power (mW/kg) and volumetric specific power (mW/cm3) characteristics of various design configurations will be presented and key conceptual design tradeoffs will be discussed. Hot- and cold-side thermal interfaces required to meet power and mass goals and associated design sensitivities will also be discussed. RHU / TE systems must overcome critical design challenges to survive high-g loadings in some robotic applications and we will examine the mass impacts required to satisfy various dynamic loading environments up to 10,000 gs. Power can be generated for a minimum of 30 years or more using plutonium-238 dioxide heat sources (given that Pu-238 has an 87.7 year half-life) with some reduction in power as the heat source naturally degrades.

Solar cell measurements at high temperature

We describe a Hybrid full spectrum solar system (FSSS) that utilizes the full spectrum available from the sun. It is designed to convert the full solar spectrum into useful electrical energy by using both photovoltaics energy conversion and thermal energy conversion combined with thermal energy storage (TES) in order to operate around-the-clock even when solar energy is not available. It is composed of a parabolic dish concentrator and a hybrid high temperature photovoltaics and thermal engine. The target efficiency of the overall system is over 35% with the AM1.5D solar spectrum as a power input.