Tibor S. Balint

Thermal Analysis of a Small‐RPS Concept for the Mars NetLander Network Mission

The NetLander Network mission concept was designed with up to 10 small landers to perform environmental monitoring on the surface of Mars over a long duty cycle. Each lander would utilize a small Radioisotope Power System (RPS) to generate about 20 to 25 We of electric power. Each small‐RPS would use a single General Purpose Heat Source (GPHS) module to generate about 250 Wt of thermal power (BOL), which must be dissipated throughout all phases of the mission. This paper describes a custom concept for a small‐RPS, specifically suited for the NetLander, and discusses an analysis of the thermal environment for five phases of the mission. On Earth and on Mars the small‐RPS would operate in planetary atmospheres and the waste heat would be removed through a passive radiator. During the cruise phase, including the launch, a fluid loop would provide active cooling to the radiator of the small‐RPS and would reject the excess heat through an external radiator. For the entry, descent and landing (EDL) phase the la...

Instability of a Cantilevered Flexible Plate in Viscous Channel Flow Driven by Constant Pressure Drop

A new approach for studying the stability of a cantilevered flexible plate positioned within a 2-D viscous channel flow is presented as a representation of the human upper airway. Previous work has used constant inlet velocity conditions, an unrealistic assumption when modelling inhalation. Here we model a constant pressure drop that reflects inspiratory effort. Positioning of the flexible plate within the channel can also be varied. The constant pressure drop is imposed for each time step by computing appropriate inlet velocities. The Navier-Stokes equations are solved using an explicit finite-element method written specifically for the channel geometry within which the fully coupled plate moves. The motion of the plate, driven by the pressure field, is modelled using classical thin-plate mechanics with the addition of a shear-stress induced tension term. The investigation focuses on the motion of the flexible plate (soft palate) as one of the contributors to airway blockage during sleep. It is found that the tension induced by the fluid shear-stress can be significant when the plate is sufficiently flexible. We also demonstrate that imposing constant inlet velocity generates over-predictions of energy transfer between flow and flexible plate. Finally, we show that offsetting the flexible plate within the channel leads to changes in oscillation frequency and significant change to its energy interaction with the fluid flow.Copyright

Nuclear systems for Mars exploration

This paper identifies breakpoints for various power and propulsion technologies, with a special focus on fission-based sources in support of NASAs Mars exploration program. Transportation, orbital, and surface missions are addressed through an assessment architecture developed for this study. This architecture is based on three key considerations; decomposition of generic Mars missions into phases, a lumped parameter approach, and a bounding case analysis. With these simplifications breakpoints are identified beyond which new technologies, such as nuclear fission power, are required to achieve mission objectives. It is found that in-space propulsion and power generation are sized by launch vehicle delivery limits and trajectory options. Similarly, power levels for surface-based reactors are affected by transportation system and EDL limits imposed by current technologies. After summarizing the breakpoints for todays state of the art, development targets are identified to enable space-based nuclear power and propulsion systems to perform at their full potential.

Small-RPS Enabled Mars Rover Concept

Both the MER and the Mars Pathfinder rovers operated on Mars in an energy‐limited mode, since the solar panels generated power during daylight hours only. At other times the rovers relied on power stored in batteries. In comparison, Radioisotope Power Systems (RPS) offer a power‐enabled paradigm, where power can be generated for long mission durations (measured in years), independently from the Sun, and on a continuous basis. A study was performed at JPL to assess the feasibility of a small‐RPS enabled MER‐class rover concept and any associated advantages of its mission on Mars, The rover concept relied on design heritage from MER with two significant changes. First, the solar panels were replaced with two single GPHS module based small‐RPSs. Second, the Mossbauer spectroscope was substituted with a laser Raman spectroscope, in order to move towards MEPAG defined astrobiology driven science goals. The highest power requirements were contributed to mobility and telecommunication type operating modes, hence...

Technology Perspectives in the Future Exploration of Venus

Science goals to understand the origin, history and environment of Venus have been driving international space exploration missions for over 40 years. Today, Venus is still identified as a high priority science target in NASAs Solar System Exploration Roadmap, and clearly fits scientific objectives of ESAs Cosmic Vision Program in addition to the ongoing Venus Express mission, while JAXA is planning to launch its own Venus Climate Orbiter. Technology readiness has often been the pivotal factor in mission prioritization. Missions in all classes-small, medium or large-could be designed as orbiters with remote sensing capabilities, however, the desire for scientific advancements beyond our current knowledge point to in-situ exploration of Venus at the surface and lower atmosphere, involving probes, landers, and aerial platforms. High altitude balloons could circumnavigate Venus repeatedly; deep probes could operate for extended periods utilizing thermal protection technologies, pressure vessel designs and advancements in high temperature electronics. In situ missions lasting for over an Earth day could employ a specially designed dynamic Stirling Radioisotope Generator (SRG) power system, that could provide both electric power and active thermal control to the spacecraft. An air mobility platform, possibly employing metallic bellows, could allow for all axis control, long traversing and surface access at multiple desired locations, thus providing an advantage over static lander or rover based architectures. Sample return missions are also featured in all planetary roadmaps. The Venus exploration plans over the next three decades are anticipated to greatly contribute to our understanding of this planet, which subsequently would advance our overall knowledge about Solar System history and habitability.

Venus Mobile Explorer with RPS for active cooling: A feasibility study

This paper presents the findings from a study to evaluate the feasibility of a radioisotope power system (RPS) combined with active cooling to enable a long-duration Venus surface mission. On-board power with active cooling technology featured prominently in both the National Research Councils Decadal Survey and in the 2006 NASA Solar System Exploration Roadmap as mission enabling for the exploration of Venus. Power and cooling system options were reviewed and the most promising concepts were modeled to develop an assessment tool for Venus mission planners considering a variety of future potential missions to Venus, including a Venus Mobile Explorer (either a balloon or rover concept), a long-lived Venus static lander, or a Venus Geophysical Network. The concepts modeled were based on the integration of General Purpose Heat Source (GPHS) modules with different types of Stirling cycle heat engines for power conversion and cooling. Unlike prior investigations which reported on single point design concepts, this assessment tool allows the user to generate either a point design or parametric curves of approximate power and cooling system mass, power level, and number of GPHS modules needed for a “black box” payload housed in a spherical pressure vessel. Input variables include altitude, pressure vessel diameter, payload temperature, and payload power on Venus. Users may also specify the number and type of pressure vessel windows, use of phase-change material for additional (time-dependent) payload cooling, and amount of (rechargeable) battery power for peak power demand operations. Parameter sets that would enable a Venus surface mission with fewer than 16 GPHS modules were identified. Thus, the study provides guidance for design practices that might enable a long-duration Venus surface mission with an attainable quantity of 238Pu, and with achievable operating parameters.

Design Reference Mission Set for RPS Enabled Missions in Support of NASA's SSE Roadmap

NASAs 2006 Solar System Exploration (SSE) Strategic Roadmap identified a set of small, medium and large missions, to address exploration targets, set out by the National Research Council (NRC) in the SSE Decadal Survey. Large size Flagship class missions are proposed to target Europa, Titan / Enceladus, Venus, and the Neptune system. Under the current candidate architectures, all of these Flagship class missions would require Radioisotope Power Systems (RPSs), as enabling technologies. Medium size New Frontiers (NF) class missions could also consider RPSs, although the ones targeting the 3rd NF opportunity would not likely utilize them. To constrain costs, small size Discovery class missions are not allowed to use RPSs. The proposed SSE Roadmap missions represent the highest priority subset of a broader collection of mission concepts, called NASAs SSE Design Reference Mission (DRM) set. In line with the SSE DRM set, the RPS DRM set includes a collection of potential future missions, which could be enabled or enhanced by the use of RPS technologies. Currently, NASA has proposed the development of the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), with static power conversion; and the Stirling Radioisotope Generator (SRG), with dynamic conversion. Advanced RPSs under consideration for possible development target increased specific power levels, consequently increasing electric power generation for the same amount of fuel, or reducing fuel requirements for the same power output, compared to the proposed MMRTG or SRG. It is expected that the RPSs will need modifications to operate in the extreme environments of Titan or Venus. An RPS on the proposed Titan Explorer would use smaller fins to minimize heat rejection in the extreme cold environment; while the Venus Mobile Explorer long-lived in situ mission would require the development of a new RPS, in order to tolerate the extreme hot environment, and to provide active cooling to the payload and other electric components. This paper discusses NASAs SSE RPS DRM set in line with the SSE DRM set, and gives a qualitative assessment of the impact of various RPS options on the potential mission architectures. The assessment could aid NASA with RPS technology development planning, and with the understanding of fuel needs over the next three decades.

Thermal Analysis and Testing of a Small Radioisotope Power System Concept

Oregon State University (OSU) is conducting an experimental study into the thermal behavior of a GPHS based small RPS concept. The subject RPS configuration is applicable for a number of Mars surface missions, such as using them to power small rovers and small static landers. Each module will use a single GPHS module to generate about 20–25W of electric power. Initial designs for similar RPS concepts have been completed and initial numerical analysis models have been developed by NASA’s JPL. The primary purpose of this research project is to develop an experimental model of the GPHS module based small RPS concept and generate operational data that can be used to validate the thermal analysis codes and methodologies. The validation of codes and methodologies is to be completed by JPL. Five mission phases have been identified for the subject RPS concept. This experimental program focuses on one of these mission phases, earth storage. This paper addresses model design, construction, and testing.

Technology Challenges for Planetary Probes to Dense Atmospheres

Both the 2003 Solar System Exploration Decadal Survey, by the National Research Council, and NASAs 2006 Solar System Exploration Roadmap identified Saturn, Jupiter, and Venus, as high priority scientific targets and recommended missions to explore them. Specifically, potential probe missions to these two gas giants and a proposed Venus In-Situ Explorer (VISE) mission were listed under the New Frontiers mission class. Deep probe missions to these destinations have much in common. In particular, key technologies must address: environmental protection to provide isolation from the extreme environments; environmental tolerance for exposed components or systems; and operations in these harsh environments. While these proposed missions could be designed with current technologies, advanced technologies could significantly enhance their performance and consequently the science return. Therefore, in this paper we will discuss state-of-practice technologies to mitigate conditions faced by the probes, followed by an assessment of possible mission impacts and benefits resulting from targeted technology developments. It is expected that the findings of this assessment should help NASA plan its technology investments.

Overview of NASA's 2006 SSE Strategic Roadmap

In the 2003 solar system exploration (SSE) decadal survey, the national research council (NRC) prioritized scientific targets and recommended missions to explore them. Taking these into account, NASAs 2006 solar system exploration (SSE) strategic roadmap (SRM) identified a set of large flagship, medium new frontiers (NF) and small discovery class missions, addressing key exploration objectives. Discovery and NF missions are competed, and due to their lower cost caps, address fewer science objectives than the large missions, while mostly utilizing existing technologies. Directed flagship class missions are considered necessary to answer some of the most important questions on solar system formation and habitability. They also provide drivers for technology development, which in turn would benefit all mission classes. Additionally, this SSE SRM offers a comprehensive discussion on science objectives for solar system exploration, and technologies enabling these missions. It outlines research and analysis (R&A), which is required to maintain the proposed program, and to post process scientific data. Education and public outreach (E/PO) communicates NASAs activities to the public of all ages, and as discussed, is considered an important part of the agencys programs. These elements are connected through interdependencies and links to other programmatic activities, including the mars and new millennium programs. The roadmap also explores potential implementation trades, suggesting multiple ways to execute a balanced program that consist of all mission classes and supported by technology development, R&A, and E/PO, while staying within a projected budget allocation for SSE. In this paper we outline this proposed SSE strategic roadmap, representing NASAs exploration plans for the next three decades.