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One of NASA priorities is the in-situ exploration of ocean worlds in the solar system where potentially there might be life under the ice shell. This requires reaching the ocean below extremely cold through significant deep ice. Jupiter’s moon, Europa, is such a challenging body, where it is estimated to have a 40 km thick ice shell. An approach for reaching the ocean has been conceived using a melting probe Cryobot concept that has been studied for a potential future mission. A lander is assumed to be the platform from which the Cryobot would be deployed. The ice penetrating vehicle concept consists of a cylindrical, narrow-body probe that encases a radioisotope heat/power source that would be used to do the penetration by melting through the icy crust. The baseline design of the probe includes a suite of science instruments to analyze the ice during descent and the liquid ocean underneath. For communication, a set of fiber optic wire as well as wireless RF in the very cold porous top layer is assumed, and then acoustic modules would be used for the communication in warmer denser ice over distance of 25 km between the modules. In addition to the acoustic communication modules, a sonar is part of the concept, for obstacle avoidance. The focus of this paper is on the use of elastic waves in the 1kHz range.

Melting probes as vehicles to explore terrestrial ice sheets have been designed and applied successfully since the early 1960’s. Later on, in the 1990’s, various proposals were made to apply such probes also as a means to explore ice sheets on other bodies of the solar system, e.g. Jupiter’s icy satellite Europa or the ice caps of Mars. For this type of subsurface probes the name cryobot has become common. We review both early developments and more recent efforts to develop probes for application in planetary environments, i.e. under low pressures and low temperatures. The current state of art as well as the pros and cons of the different concepts hitherto considered are described. While many tests with various probes have been done in terrestrial environments, experiments under low surface pressure conditions are rare. Therefore, we report here on lab tests with a simple melting probe under the range of pressure and temperature conditions that would be encountered on the surface of Mars and compare them with corresponding tests under a much lower gas pressure, possibly representative for icy satellites. The contribution of evaporation during the melting and its variation with surface pressure is also considered. All surface pressure measurements that have been performed on Mars up to now indicate a surface pressure above the water triple point pressure (612 Pa). This means that water ice always transforms into the liquid phase when warmed up to 0°C, before it evaporates into the ambient atmosphere. The temporary existence of the liquid phase around the heated tip of the cryobot allows good thermal conductance between probe and surrounding ice, which is an important pre-requisite for efficient melt penetration. Our experiments indicate that under all possible Mars surface pressures the liquid phase is present when the probe is heated up. This finding confirms experimentally that a probe as it was proposed by Paige (1992) for in situ exploration of the Mars north polar layers would work in the expected way, although the penetration velocity must be expected be lower than under Earth pressure conditions. A test with the same probe, but under an almost two orders of magnitude lower gas pressure than on Mars, still indicates the temporary existence of the liquid phase in the contact region between the probe and the surrounding ice.

The development of algorithms for agile science and autonomous exploration has been pursued in contexts ranging from spacecraft to planetary rovers to unmanned aerial vehicles to autonomous underwater vehicles. In situations where time, mission resources and communications are limited and the future state of the operating environment is unknown, the capability of a vehicle to dynamically respond to changing circumstances without human guidance can substantially improve science return. Such capabilities are difficult to achieve in practice, however, because they require intelligent reasoning to utilize limited resources in an inherently uncertain environment. Here we discuss the development, characterization and field performance of two algorithms for autonomously collecting water samples on VALKYRIE (Very deep Autonomous Laser-powered Kilowatt-class Yo-yoing Robotic Ice Explorer), a glacier-penetrating cryobot deployed to the Matanuska Glacier, Alaska (Mission Control location: 61°42′09.3″N 147°37′23.2″W). We show performance on par with human performance across a wide range of mission morphologies using simulated mission data, and demonstrate the effectiveness of the algorithms at autonomously collecting samples with high relative cell concentration during field operation. The development of such algorithms will help enable autonomous science operations in environments where constant real-time human supervision is impractical, such as penetration of ice sheets on Earth and high-priority planetary science targets like Europa.

There currently is significant interest within NASA and the scientific community to explore outer planetary ocean worlds, including Jupiter's moon Europa. Since the Galileo spacecraft magnetometer data indicated that an ocean of liquid water/slush might exist 10-15Km below Europa's icy shell, ocean access became of particular interest for future missions in view of the possibility of finding signs of life or life itself. In this study, both passive and active melt probes (cryobots) have been theoretically analyzed to determine heating power requirements and rates of descent. It is based in part on earlier experimental JPL cryobot studies, as well as more recent system engineering studies, and provides an analytical estimation adapted to the unique cryogenic Europan environment. The Cryobot probe will descend though Europa's ice core until it reaches liquid water at about 10km depth. This analysis corresponds to the melting and descent rate starting at a 3 km location where water jets are used instead of a mechanical drill. The Computational Fluid Dynamics (CFD) analysis was performed using Transient Multiphase Static model in StarCCM+, but was validated with experimental empirical data performed by Honeybee Robotics, obtained from small-scale probe passive melt data in both cryogenic and warm ice, as well as modeling data from CFX and FLUENT performed by U Pittsburg. The first step of the analysis was focused on the heating power required to form a melt a layer around the probe. Based on earlier passive thermal melt models developed by Stone Aerospace for the conceptual probe developed for this trade study, it was determined that a minimum of 7KWt would be required to meet a 2yr transit through cryogenic ice. Analysis showed that the water jets at the tip of the probe will significantly increase the melt rate over purely conductive, passive heating. A purely conductive melting probe will descend at a rate of approximate 9cm/hr, while using water jetting the probe will increase this rate to approx. 50 cm/hr. The rate of descent also increases as the probe travels through warmer ice, so case studies at 180K, 200K, 230K and 250K were used to calculate an approximate melt rate through the 10kn of ice. The water jet locations and spacing are also a significant factor in the rate of descent, since if they too close together, it could create freeze zones that would slow the probe. The paper will show results of water jet optimization for their location and mass flow rate to improve the probe's descent rate.

In this paper a forward looking (end fire) synthetic aperture radar (SAR) system is described for the Very deep Autonomous Laser-powered Kilowatt-class Yo-yoing Robotic Ice explorer (VALKYRIE) project. Design and analysis of novel conformal log periodic antennas for the radar and the forward looking SAR ambuguity function is presented. Fabrication and laboratory characterization of the antennas system design and in situ testing of the SAR system are discussed in detail.

VALKYRIE (Very-deep Autonomous Laser-powered Kilowatt-class Yo-yoing Robotic Ice Explorer) is a NASA-funded project to develop key technologies for an autonomous ice penetrator, or cryobot, capable of delivering science payloads through outer planet ice caps and terrestrial glaciers. This 4 year effort will produce a cylindrical cryobot prototype 280 cm in length and 25 cm in diameter. One novel element of VALKYRIE’s design is the use of a high-energy laser as the primary power source. 1070 nm laser light is transmitted at 5 kW from a surface-based laser and injected into a custom-designed optical waveguide that is spooled out from the descending cryobot. Light exits the downstream end of the fiber, travels through diverging optics, and strikes an anodized aluminum beam dump, which channels thermal power to hot-water jets that melt the descent hole. Some beam energy is converted to electricity via photovoltaic cells, for running on-board electronics and jet pumps. Since the vehicle can be sterilized prior to deployment, and forward contamination is minimized as the melt path refreezes behind the cryobot, expansions on VALKYRIE concepts may enable cleaner access to deep subglacial lakes. This paper focuses on laser delivery and beam dump thermal design.

In this paper a log periodic folded slot antenna array is described for a forward-looking synthetic aperture radar (IceSAR) system for the ‘Very deep Autonomous Laser-powered Kilowatt-class Yo-yoing Robotic Ice explorer’ (VALKYRIE) cryobot project. Design and performance characterization of the log periodic antennas is presented along with a first light radar imagery obtained during in situ operation to prove the feasibility of this design for use in a cryobot obstacle avoidance and mapping system.

Europa is an incredibly enticing target for exploration – the nearest reaches of what may be a vast new "habitable zone" of interior oceans warmed and stirred by tidal forces. Decades of NASA and National Academy studies including the most recent planetary science decadal survey have affirmed the preeminence of Europa as a destination for astrobiology research. This report provides a comprehensive technology roadmap and an assessment of current state of the art and future technologies to enable an under-ice mission to Europa. In this study, the authors provide an overview of key mission objectives, a profile of Europa, and a mission overview. The authors then delve into a discussion of the key fundamental science objectives and design tradeoffs to arrive at a comprehensive science traceability matrix and value system for design of a multi-vehicle, under-ice mission to Europa. The current state of the art is assessed and design alternatives discussed. The report culminates in a concept of operations for the mission and a recommended mission architecture utilizing three surface units, each deploying a single cryobot, with each cryobot carrying three biologically inspired, gliding under-ice hydrobots equipped with sensor packages that will characterize the physical and chemical state of Europa’s ocean over its entire depth. NASA Innovative Advanced Concepts (NIAC) Grant No. NNX12AR07G

The mathematical modeling results of the simultaneous processes of heat and mass transfer under the conditions of intense phase changes (melting of ice) during the movement of cryobot have been given. The spatial unevenness of the melting rate of ice has been taken into account. It has been established that the rate of passage of the cryobot depends essentially on its temperature. According to the results of the numerical simulation, considerable cooling of the cryobot sheath has been established. The latter is due to the high endothermic effect of melting ice.

The HADES Europa mission concept aims to provide a framework for an astrobiological in-depth investigation of the Jupiter moon Europa, relying on existing technologies and feasibility. This mission study proposes a system consisting of an orbiter, lander and cryobot as a platform for detailed exploration of Europa. While the orbiter will investigate the presence of a liquid ocean and characterize Europa's internal structure, the lander will survey local dynamics of the ice layer and the surface environment. The lander releases a cryobot, that melts into the ice, will sample the pristine subsurface and is expected to provide data on organic and gaseous content and putative bio-signatures. In summary, we present the scientific objectives for an astrobiological investigation of Europa, resulting in a mission concept with a detailed evaluation of scientific instrumentation, mission sequences, basic design of the spacecraft, technology needs and cost estimations.

The opportunity for direct examination of the Europan surface and sub-surface calls for a systematic and deductive approach to experimental design. To avoid the limitations of our inherent Earth-centric definition of life (Nealson et al., 2002), we would be forced to examine a wide range of potential bio-signatures to guide more specific biological experiments (Chela-Flores, 2003). It is also important to look for recurring features that are important from the evolutionary history of our own biosphere (Zakon, 2003). Of the many candidate molecules, the structurally heterologous superfamily of voltage-gated cation channels is an evolutionary sensitive group of molecular structures, the single varieties of which can be easily distinguished. Implementation of the analytical aspects of this experiment would require remote control of miniaturized robotic systems. These mechanisms are under constant evolution since their uses are strongly tied to commercial, scientific and military interests. One paradigm for feasibility studies could come from data inferring the reprocessing of ice covering a Europan ocean. Reprocessing could be inducing life forms extant in the liquid water subsurface towards the ice covering, as it has already been demonstrated at the frozen surfaces of Antarctic lakes (Bhattacherjee and Chela-Flores, 2004), and as it has been suggested by geophysical analysis of the Galileo images of the icy surface of Europa (Greenberg et al., 2002). The proposed series of experiments can be carried out in situ either within a submersible in the ocean beneath the ice layer (carried and launched from a cryobot), or even on the surface ice itself. Results from a preliminary examination of the environment would be used to determine the conditions necessary for sampling and pre-processing of any material of possible biological origin. Many techniques are currently available for identifying targets according to their molecular structure and their chemical-physical characteristics: novel sampling and isolation methods, specific antibodies or diabodies engineered as molecular probes, micro-arrays based on site-specific immobilization of complementary molecules, microscopy and micro-sensors for visualization/digital sampling of positive results.

A 2007 Mars North Polar Cap penetration mission is being proposed under the Mars Scout Discovery Program. The Cryobot robotic mole vehicle being developed by a team of JPL engineers would penetrate 200 meters below the polar ice cap in the only known accessible reservoir of water on the planet. The probe would be manifested with a suite of science instruments which will (1) examine the climatic history of Mars as reflected in the layers of ice-the Mars Surveyor Orbiter Camera (MOC) has revealed exciting images of the polar ice cap indicating the layers to be of the order of 1 to 100 meters thick; (2) look for organics and bio-signatures potentially transported via wind and trapped in the ice; (3) examine trapped minerals and understand the chemical make-up of soluble constituents; and (4) provide the first-ever polar cap surface images as well as characterize the polar cap meteorology. Although radioisotope power is baselined for the Mars '07 version of the Cryobot, no decision on the final design of the Cryobot will be made until the environmental review process is complete. Any use of the Cryobot for Mars will conform to all environmental and planetary protection requirements.

Several studies have been conducted to design robotic exploration vehicles for investigating a sub-surface water ocean within Jupiter's moon Europa. The current data from the Galileo spacecraft indicates a possible sub-surface ocean of undetermined depth covered by a water ice crust on the order of 10 kilometres thick. The ice crust also flexes several tens of metres every Europan day due to tidal forces. This presents several design challenges, especially for the communications link back to the science team on Earth. This paper presents the modeling and analysis for a communications system that uses transceivers embedded within the ice crust. The work was done for a design study that examined using ice-embedded transceivers to communicate between a deep ice penetration "cryobot" at the liquid water ocean and a communications package on the Europan surface. This paper focuses on the microwave properties of ice and the communications link margin analysis.

Recently, a team from JPL and the DOE carried out a study to investigate the utility of a 3 kWe surface fission power system for Mars landed missions. In the course of the study it became clear that the application of such a power system was enabling to a wide variety of potential missions. Of these, two concepts were developed, one for a stationary lander and one for a reactor‐powered rover. This paper discusses the design of the lander mission, which was developed around the concept of landing a cryobot on the Mars north polar ice cap. The cryobot is designed to bore through the entire 2–3 km thickness of the ice cap, providing a picture of the Martian climate spanning more than a million years of Martian history. The high sustained power available from the reactor system proves to be an ideal match for this mission design, enabling a level of science return unavailable from any alternative power sources. The lander design is based on a minimum extrapolation of technology, drawing heavily on the existin...

NASA's desire to study and characterize the solar system will be done by in-situ robotic systems in the near term. Specific interest is focused towards finding water on Mars and understanding both the climatic and depositional history of the planet. In the case of Europa, scientists desire to unravel the mysteries surrounding the thick ice crust, its chemical properties, and subsurface ocean properties. For both Mars and Europa, the major scientific interest is whether there are signs of past or extant life in either the Mars polar ice, or the sub-ice ocean of Europa. The best way to explore either of these environments is a cryobot mole vehicle, which carries a suite of instruments suitable for sampling and analyzing the ice or ocean environments. JPL is currently developing a unique robotic vehicle, which utilizes gravity, and both passive and active heating systems to drive ice to a melt state, in order to facilitate mobility. This paper describes the science driven requirements for such a vehicle, a description of the cryobot design, and results of recent performance tests in both clean and dust laden ice. Although a radioisotope power system for a flight version of the cryobot is currently baselined, no decision on the final design of the flight cryobot will be made until the environmental review process is complete. Any use of the cryobot for Mars or Europa will conform to all environmental and planetary protection requirements.

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 and analyzing the ice or ocean environments. This paper concentrates on a Europa deep ice (i.e., kilometers thick) application of the CHIRPS, and introduces the reader to the vehicle design with focus on the use of radioisotope thermoelectric generator (RTG) technology as the primary heat (1 kW total) and power source for the robotic vehicle. Radioisotope heater unit (RHU) milli-watt power systems (120 mW total) are also employed to power the mini-radiowave ice transceivers, which are used to relay data through the ice up to the surface lander. The results of modeling and design work for both of these areas are discussed in this paper. Although radioisotope power is baselined for the Europa flight version of the cyrobot, no decision on the final design of the cryobot will be made until the environmental review process is complete. Any use of the cryobot for Mars or Europa will conform to all environmental and planetary protection requirements.

This paper examines the heat transfer characteristics of a probe (cryobot) penetrating through the ice layer of Europa. Initially, simple 1D calculations are used to predict the ideal (no heat losses or temperature limitations) penetration rates for various size cryobots. Next, a detailed 2D model is used to more realistically model penetration rates. It is found that for small, low power density systems, conductive losses can cause the penetration rate to be significantly lower than the ideal rate. The results of these calculations are meant to establish rough limits on the size of cryobot that can be powered by an RHU (Radioisotope Heater Unit), and at what sizes a reactor becomes enabling. It is concluded that if an RHU system (that delivers almost all power to the bit) can be developed with an overall, fully-engineered power density of ∼1 W/cm3, then an RHU system may be suitable for some mission scenarios, although slow penetration times (which increase mission risk) and/or high Pu-238 requirements (cost and availability) may still make a reactor a more optimal choice. If there is a requirement for a large payload and/or a rapid penetration time (∼months), then a reactor will probably be required. The final portion of the paper examines potential reactor designs that could be used to power a cryobot. Two potential reactor designs are discussed—a near-term, low-cost heatpipe cooled system and a conductively-cooled metal-fueled reactor.

The present work is concerned with the search for life in the outer Solar System. We devote our attention to the determination of the likely degree of evolution of such biota (Chela-Flores, 1996; 1997a,b,c), and the determination of the Europan environments that should be probed. Archaebacteria-like organisms are the most likely biota to exist on Europa (Delaney et al., 1996). We have argued that evolution should have occurred in Europa and that the experimental test of this conjecture is feasible through a Cryobot/Hydrobot type of space mission (Horvath et al., 1997). Although difficult instrumentation issues are involved in the preparation of a package to search for life in Europa, we have initiated the discussion of what would seem to be a reasonable biological experiment.

One of the more likely places in the solar system for the existence of extraterrestrial life forms is the Jovian moon Europa. It has been postulated that a volcanically-heated ocean is likely to exist underneath Europa's icy surface. If a detailed remote-sensing reconnaissance of Europa determines that an ocean does exist under the ice, then in- situ measurements will be needed to directly explore the Europan ocean and the ice that lies above it. In order to make quantitative measurements of the Europan environment, a lander spacecraft capable of penetrating the surface ice layer by melting through it is proposed. This vehicle, dubbed a `Cryobot', will be designed to carry a small deployable submersible (a `Hydrobot') equipped with a complement of instruments. The design of an instrument package to search for life across the wide range of thermal and pressure environments expected on Europa, the issues in sample handling, and long-term reliability for a potential multi-year transit through the ice all present difficult design issues. Opportunities for performing investigations of deep, submerged Antarctic lakes on Earth are described which would test the Cryobot/Hydrobot system while collecting intrinsically valuable terrestrial science data.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.