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Full list of authors: Blanc, Michel; Prieto-Ballesteros, Olga; André, Nicolas; Gomez-Elvira, Javier; Jones, Geraint; Sterken, Veerle; Desprats, William; Gurvits, Leonid I.; Khurana, Krishan; Balmino, Georges; Blöcker, Aljona; Broquet, Renaud; Bunce, Emma; Cavel, Cyril; Choblet, Gaël; Colins, Geoffrey; Coradini, Marcello; Cooper, John; Dirkx, Dominic; Fontaine, Dominique; Garnier, Philippe; Gaudin, David; Hartogh, Paul; Hussmann, Hauke; Genova, Antonio; Iess, Luciano; Jäggi, Adrian; Kempf, Sascha; Krupp, Norbert; Lara, Luisa; Lasue, Jérémie; Lainey, Valéry; Leblanc, François; Lebreton, Jean-Pierre; Longobardo, Andrea; Lorenz, Ralph; Martins, Philippe; Martins, Zita; Marty, Jean-Charles; Masters, Adam; Mimoun, David; Palumba, Ernesto; Parro, Victor; Regnier, Pascal; Saur, Joachim; Schutte, Adriaan; Sittler, Edward C.; Spohn, Tilman; Srama, Ralf; Stephan, Katrin; Szegő, Károly; Tosi, Federico; Vance, Steve; Wagner, Roland; Van Hoolst, Tim; Volwerk, Martin; Wahlund, Jan-Erik; Westall, Frances; Wurz, Peter, Europa is the closest and probably the most promising target to search for extant life in the Solar System, based on complementary evidence that it may fulfil the key criteria for habitability: the Galileo discovery of a sub-surface ocean; the many indications that the ice shell is active and may be partly permeable to transfer of chemical species, biomolecules and elementary forms of life; the identification of candidate thermal and chemical energy sources necessary to drive a metabolic activity near the ocean floor. In this article we are proposing that ESA collaborates with NASA to design and fly jointly an ambitious and exciting planetary mission, which we call the Joint Europa Mission (JEM), to reach two objectives: perform a full characterization of Europa's habitability with the capabilities of a Europa orbiter, and search for bio-signatures in the environment of Europa (surface, subsurface and exosphere) by the combination of an orbiter and a lander. JEM can build on the advanced understanding of this system which the missions preceding JEM will provide: Juno, JUICE and Europa Clipper, and on the Europa lander concept currently designed by NASA (Maize, report to OPAG, 2019). We propose the following overarching goals for our Joint Europa Mission (JEM): Understand Europa as a complex system responding to Jupiter system forcing, characterize the habitability of its potential biosphere, and search for life at its surface and in its sub-surface and exosphere. We address these goals by a combination of five Priority Scientific Objectives, each with focused measurement objectives providing detailed constraints on the science payloads and on the platforms used by the mission. The JEM observation strategy will combine three types of scientific measurement sequences: measurements on a high-latitude, low-altitude Europan orbit; in-situ measurements to be performed at the surface, using a soft lander; and measurements during the final descent to Europa's surface. The implementation of these three observation sequences will rest on the combination of two science platforms: a soft lander to perform all scientific measurements at the surface and sub-surface at a selected landing site, and an orbiter to perform the orbital survey and descent sequences. We describe a science payload for the lander and orbiter that will meet our science objectives. We propose an innovative distribution of roles for NASA and ESA; while NASA would provide an SLS launcher, the lander stack and most of the mission operations, ESA would provide the carrier-orbiter-relay platform and a stand-alone astrobiology module for the characterization of life at Europa's surface: the Astrobiology Wet Laboratory (AWL). Following this approach, JEM will be a major exciting joint venture to the outer Solar System of NASA and ESA, working together toward one of the most exciting scientific endeavours of the 21st century: to search for life beyond our own planet. © 2020, The authors received support from the sponsors of their home institutions during the development of their projects, particularly at the two institutes leading this effort: at IRAP, Toulouse, MB and NA acknowledge the support of CNRS, University Toulouse III - Paul Sabatier and CNES. At CAB, Madrid, OPB and JGE acknowledge the support of INTA and Spanish MINECO project ESP2014-55811-C2-1-P and ESP2017-89053-C2-1-P and the AEI project MDM-2017-0737 Unidad de Excelencia "Maria de Maeztu". We would also like to extend special thanks to the PASO of CNES for its precious assistance and expertise in the design of the mission scenario.

Low-energy transfers (LET) for lunar and interplanetary missions has received immense attention of the scientific community during the last few decades as its importance was understood by the success of JAXA’s Hiten, ESA’s SMART-1, NASA’s GRAIL and ARTHEMIS missions, and several proposals, like the BepiColombo, Multi-Moon Orbiter and Europa Orbiter. In this paper the developments in the area of LET and low-thrust trajectories are reviewed. Starting with the basics of the restricted three-body problem and its use in finding invariant manifolds in phase space, the design of LET trajectories and optimisation methods used to find optimal LET and low-thrust transfers is discussed.

A versatile relay communications system has been implemented on the highly capable low size, weight, and power (SWaP) space-grade Frontier Radio platform for use on the NASA Europa Clipper mission and other possible future missions. The Frontier Radio, developed by JHU/APL, has been used for traditional Earth-to-spacecraft communication links and has now been enhanced to implement relay communications between two Frontier Radios for use on Europa missions. NASA has been studying a future Europa Lander mission, one variation of which required relay links to a Carrier and Relay Stage (CRS) as well as to the Europa Clipper spacecraft. The relay communications are at X-band, using the same Frontier Radio already in use for direct-to-Earth (DTE) communications. By exploiting the software-defined nature of the Frontier Radio, a new software protocol “relay personality” was created for relay communications. The process of relay-session establishment, loss of lock actions, and emergency communications contingencies are discussed here. The radios each perform self-acquisition by internally sweeping their receivers to lock onto the incoming signal and has a feature to implement Doppler predicts instead of relying on a ground station to sweep the uplink signal frequency as in DTE links. The protocol leverages the existing flight computer/ command and data handling (C&DH) similar to the DTE links. The concept of operations (CONOPS) for the Europa relay links nominally uses scheduled passes preloaded from contact parameter tables, but unscheduled passes are also supported where either node can initiate. These protocols and processes were implemented in flight software running on a Microprocessor without Interlocked Pipeline Stages (MIPS) core located in the radio's field programmable gate array (FPGA). The constraints imposed on the design of the relay communications and the current implementation of this relay protocol is covered in this paper.

In 1995, the Galileo spacecraft arrived at Jupiter to conduct follow-up experiments on pathfinder Pioneer and key Voyager discoveries especially at Io, Europa, Ganymede and Callisto. These new observations helped expand our scientific knowledge of the prominent Galilean satellites; studies revealed diversity with respect to their geology, internal structure, evolution and degree of past and present activity. Jupiter's diverse Galilean satellites, of which three are believed to harbor internal oceans, are central to understanding the habitability of icy worlds. Galileo provided for the first time compelling evidence of a near-surface global ocean on Europa. Furthermore, by understanding the Jupiter system and unraveling the history of its evolution from initial formation to the emergence of possible habitats and life, gives insight into how giant planets and their satellite systems form and evolve. Most important, new light is shed on the potential for the emergence and existence of life in icy satellite oceans. In 2009, NASA released a detailed Jupiter Europa Mission Study (EJSM) that proposed an ambitious Flagship Mission to understand more fully the satellites Europa and Ganymede within the context of the Jovian system. Key to EJSM is the NASA led Jupiter Europa Orbiter (JEO) and the ESA led Jupiter Ganymede Orbiter (JGO). JEO and JGO would execute a choreographed exploration of the Jovian system before settling into orbit around Europa and Ganymede, respectively. The National Academies Planetary Decadal Survey, 2011 has listed the NASA-led JEO as the second highest priority mission for the decade 2013-2022, and if chosen it would be launched in 2020 with arrival at Jupiter in 2025. If the JEO mission is not chosen it is anticipated that there will be opportunities in future decadal cycles. Jupiter Orbit Insertion (JOI) begins a 30-month Jovian system tour followed by nine months of science mapping after Europa Orbit Insertion (EOI) in July 2028. The orbiter will ultimately impact the surface of Europa after the mission is completed. The current JEO mission concept includes a range of instruments on the payload, to monitor dynamic phenomena (such as Io's volcanoes and Jupiters atmosphere), map the Jovian magnetosphere and its interactions with the Galilean satellites, and characterize water oceans beneath the ice shells of Europa and Ganymede. The payload includes a low mass (3.7 Kg) and low power (< 5 W) Thermal Instrument (TI) concept for measuring possible warm thermal anomalies on Europa s cold surface caused by recent (< 10,000 years) eruptive activity. Regions of anomalously high heat flow will be identified by thermal mapping using a nadir pointing, push-broom filter radiometer that provides far-IR imagery in two broad band spectral wavelength regions, 8-20 m and 20-100 m, for surface temperature measurements with better than a 2 K accuracy and a spatial resolution of 250 m/pixel obtained from a 100 Km orbit. The temperature accuracy permits a search for elevated temperatures when combined with albedo information. The spatial resolution is sufficient to resolve Europa's larger cracks and ridge axial valleys. In order to accomplish the thermal mapping, the TI uses sensitive thermopile arrays that are readout by a custom designed low-noise Multi-Channel Digitizer (MCD) ASIC that resides very close to the thermopile linear array outputs. Both the thermopile array and the MCD ASIC will need to show full functionality within the harsh Jovian radiation environment, operating at cryogenic temperatures, typically 150 K to 170 K. In the following, a radiation mitigation strategy together with a low risk Radiation-Hardened-By-Design (RHBD) methodology using commercial foundry processes is given for the design and manufacture of a MCD ASIC that will meet this challenge.

Resonant orbits have been widely employed in mission design for planetary flyby trajectories (Jupiter Europa Orbiter) and, more recently, as a source of long-term stability (Interstellar Boundary Explorer). Yet, resonant orbits have not been explored extensively as transfer mechanisms between nonresonant orbits in multibody systems. To highlight the benefit of employing resonant orbits for transfers and given the increased interest in employing libration-point orbits for a variety of purposes, planar and three-dimensional transfers from a low Earth orbit to the vicinity of the Earth–moon libration points via resonant arcs are constructed. Solutions are efficiently generated in the circular restricted three-body model, and transitioned to a higher-fidelity model for validation. Direct optimization techniques are applied to further reduce the propellant requirements, and a system translation process is defined to allow for the quick translation of Earth–moon transfers to other three-body systems.

A recent study by Schmidt et al. (2011) suggests that Thera Macula, one of the “chaos regions” on Europa, may be actively forming over a large liquid water lens. Such a process could conceivably produce a thermal anomaly detectable by a future Europa orbiter or flyby mission, allowing for a direct verification of this finding. Here, we present a set of models that quantitatively assess the surface and subsurface temperatures associated with an actively resurfacing chaos region using constraints from Thera Macula. The results of this numerical study suggest that the surface temperature over an active chaos region can be as high as ∼ 200 K . However, low-resolution Galileo Photo-Polarimeter Radiometer (PPR) observations indicate temperatures below 120 K over Thera Macula. This suggests that Thera Macula is not currently active unless an insulating layer of at least a few centimeters in thickness is present, or activity is confined to small regions, reducing the overall intensity of the thermal signature. Alternatively, Thera may have been cooling for at least 10–100 yr and still contain a subsurface lake, which can take ∼300,000 yr to crystallize. According to the present study, a more sensitive instrument capable of detecting anomalies ∼5 K above ambient could detect activity at Thera Macula even if an insulating layer of ∼50 cm is present.

Orbital remote sensing provides a powerful way to efficiently survey targets such as the Earth and other planets and moons for features of interest. One such feature of astrobiological relevance is the presence of surface sulfur deposits. These deposits have been observed to be associated with microbial activity at the Borup Fiord glacial springs in Canada, a location that may provide an analogue to other icy environments such as Europa. This article evaluates automated classifiers for detecting sulfur in remote sensing observations by the hyperion spectrometer on the EO-1 spacecraft. We determined that a data-driven machine learning solution was needed because the sulfur could not be detected by simply matching observations to sulfur lab spectra. We also evaluated several methods (manual and automated) for identifying the most relevant attributes (spectral wavelengths) needed for successful sulfur detection. Our findings include (1) the Borup Fiord sulfur deposits were best modeled as containing two sub-populations: sulfur on ice and sulfur on rock; (2) as expected, classifiers using Gaussian kernels outperformed those based on linear kernels, and should be adopted when onboard computational constraints permit; and (3) Recursive Feature Elimination selected sensible and effective features for use in the computationally constrained environment onboard EO-1. This study helped guide the selection of algorithm parameters and configuration for the classification system currently operational on EO-1. Finally, we discuss implications for a similar onboard classification system for a future Europa orbiter.

Missions to explore Europa have been imagined ever since the Voyager mission first suggested that Europa was geologically very young. Subsequently, the Galileo spacecraft supplied fascinating new insights into this satellite of Jupiter. Now, an international team is proposing a return to the Jupiter system and Europa with the Europa Jupiter System Mission (EJSM). Currently, NASA and ESA are designing two orbiters that would explore the Jovian system and then each would settle into orbit around one of Jupiter’s icy satellites, Europa and Ganymede. In addition, the Japanese Aerospace eXploration Agency (JAXA) is considering a Jupiter magnetospheric orbiter and the Russian Space Agency is investigating a Europa lander. The Jupiter Europa Orbiter (JEO) would be the NASA-led portion of the EJSM; JEO would address a very important subset of the complete EJSM science objectives and is designed to function alone or in conjunction with ESA’s Jupiter Ganymede Orbiter (JGO). The JEO mission concept uses a single orbiter flight system that would travel to Jupiter by means of a multiple-gravity-assist trajectory and then perform a multi-year study of Europa and the Jupiter system, including 30 months of Jupiter system science and a comprehensive Europa orbit phase of 9 months. The JEO mission would investigate various options for future surface landings. The JEO mission science objectives, as defined by the international EJSM Science Definition Team, include: A. Europa’s ocean: Characterize the extent of the ocean and its relation to the deeper interior. B. Europa’s ice shell: Characterize the ice shell and any subsurface water, including their heterogeneity, and the nature of surface–ice–ocean exchange. C. Europa’s chemistry: Determine global surface compositions and chemistry, especially as related to habitability. D. Europa’s geology: Understand the formation of surface features, including sites of recent or current activity, and identify and characterize candidate sites for future in situ exploration. E. Jupiter system: Understand Europa in the context of the Jupiter system. The JEO orbital mission would provide critical measurements to support the scientific and technical selection of future landed options. The primary challenge of a Europa mission is to perform in Jupiter’s radiation environment, radiation damage being the life-limiting parameter for the flight system. Instilling a system-level radiation-hardened-by-design approach very early in the mission concept would mitigate the pervasive mission and system-level impacts (including trajectory, configuration, fault protection, operational scenarios, and circuit design) that can otherwise result in runaway growth of cost and mass. This paper addresses the JEO mission concept developed by a joint team from JPL and the Applied Physics Laboratory to address the science objectives defined by an international science definition team formed in 2008, while designing for the Jupiter environment.

For a Europa Orbiter mission, the strategy for designing Jovian System tours that include Io flybys differs significantly from schemes developed for previous versions of the mission. Assuming that the closest approach distance of the incoming hyperbola at Jupiter is below the orbit of Io, then an Io gravity assist gives the greatest energy pump-down for the least decrease in perijove radius. Using Io to help capture the spacecraft can increase the savings in Jupiter orbit insertion Δ V over a Ganymede-aided capture. The tour design is guided by Tisserand graphs overlaid with a simple and accurate radiation model so that tours including Io flybys can maintain an acceptable radiation dosage. While Io flybys increase the duration of tours that are ultimately bound for Europa, they offer Δ V savings and greater scientific return, including the possibility of flying through the plume of one of Io's volcanoes.

In this analysis, the relationship between a planar Europa Orbiter trajectory and the invariant manifolds of resonant periodic orbits is studied. An understanding of this trajectory with its large impulsive maneuvers should provide basic tools that can be extended to cases that approximate low thrust with many small maneuvers. This study therefore represents a step in understanding low-thrust trajectories. Unstable resonant orbits are computed along with their invariant manifolds in order to examine the resonance transitions that the planar Europa Orbiter trajectory travels through. The stable manifold of a Lyapunov orbit at the L 2 libration point is used to show why a 5:6 resonance is necessary at this energy for capture around Europa.

Satellite-aided capture is a mission design concept used to reduce the delta-v required to capture into a planetary orbit. The technique employs close flybys of a massive moon to reduce the energy of the planet-centered orbit. A sequence of close flybys of two or more of the Galilean moons of Jupiter may further decrease the delta-v cost of Jupiter orbit insertion. A Ganymede-Io sequence can save 207 m/s of delta-v over a single Io flyby. A phase angle analysis based on the Laplace resonance is used to find triple-satellite-aided capture sequences involving Io, Europa, and Ganymede. Additionally, the near-resonance of Callisto and Ganymede is used to find triple-satellite-aided capture sequences involving Callisto, Ganymede, and another moon. A combination of these techniques is used to find quadruple-satellite-aided capture sequences that involve gravity-assists of all four Galilean moons. These sequences can save a significant amount of delta-v and have the potential to benefit both NASA’s Jupiter Europa orbiter mission and ESA’s Jupiter Ganymede orbiter mission.

For planetary satellite orbiters (such as the Europa Orbiter Mission) and planet orbiters (such as the Mercury Messenger Mission), third-body forces can induce large changes in orbital elements over one orbit. As a result, transfers involving an ellipse cannot be considered without taking these forces into account, and two- and three-impulse transfers must model these effects at larger distances from the central body. A new use of third-body perturbations is presented to effect plane changes. It is shown, in particular, that large plane changes can be obtained by using only two impulsive maneuvers and a proper timing of the first burn. The resulting plane change maneuvers are shown to be optimal over classical one-impulse maneuvers for large enough inclination change values, replacing the classical optimality of bielliptic transfers (as compared to one-impulse plane changes) in the case of environments perturbed by a large, third body. The investigation is performed by solving an optimization problem with constraints and using the Hill three-body problem to describe the underlying dynamics. Savings on the order of 25% are obtained when compared to the one-impulse transfers for plane changes of ∼60 deg, and plane changes of ′180 deg are shown to be possible without escaping.

This paper describes the results of OSC's department of energy (DOE)-sponsored alkali metal thermal-to-electric conversion (AMTEC) generator studies. The paper was prepared in response to an invitation from the International Astronautic Federation for the presentation of a 1-h keynote lecture on our AMTEC studies at the Space Nuclear Power and Propulsion Systems session of the 48th International Astronautical Congress. The paper covers a broad range of topics, which explains its unusual length. After presenting the background of those studies and the operational principles of the AMTEC converters, it describes a novel methodology for the coupled solution of the interdependent thermal, electrical, and fluid flow differential and integral equations governing their performance, and the application of that procedure to OSC's recommended cell design. As explained in the paper, that design was the result of parametric analyses of 35 cell design variations to determine the individual effects of 27 design parameters and various operating parameters on the cell's power output, efficiency, and critical temperatures. The analysis revealed a method of substantially improving the cell's performance by enhancing the internal reflectivity of the cell wall, and identified a specific cell wall composition and coating to achieve that goal. The paper presents a set of OSC-recommended cell design parameters for the ultimate long-service flight generators, as well as a set of parameters for an interim cell design for planned short-term ground tests. The primary difference between them is that the ultimate design employs refractory metal components to enhance compatibility with high-temperature sodium vapor, while the interim design is based on stainless steel, nickel, and Haynes-25, which are expected to be adequate for initial short-term tests, but not for long-duration missions at high operating temperatures. The paper also presents a detailed fabrication sequence for the recommended interim cell design, which is being implemented by AMPS, Inc., for a DOE-sponsored technology development program. It then describes the extension of that analytical procedure to a variety of OSC-designed radioisotope-heated generators employing the recommended cell design, with particular attention to the thermal insulation between the outside of the 16 cells and the inside of the generator housing. The studies found that the performance of the generator is optimized by employing a hybrid insulation system, in which the space between the cells is filled with fibrous Min-K insulation, and the generator walls are lined with tapered (i.e., graded-length) multifoil insulation. The paper then examines the performance of the OSC generator designs for various fuel loadings, output voltages, and mission phases, and assesses their ability to meet the stipulated temperature constraints and power demands of the Europa Orbiter and Pluto Express missions under consideration by NASA. Finally, it presents an OSC-recommended design and fabrication procedure of an electrically heated four-cell test assembly with hybrid insulation to simulate the prototypic 16-cell generator. That test assembly will be analyzed by OSC, built by AMPS, and tested by the Air Force Phillips Laboratory (AFPL), to check the validity of the analytical predictions. The reason for basing the recommended test assembly on the interim rather than the ultimate refractory metal cell design is to avoid the delays required to develop the new technology for the latter.

Thestability oforbit dynamicsaround a planetary satelliteisstudied using analyticaland numerical techniques. The Europa orbiter mission is used to motivate our analysis and to provide specie c numerical data for verie cation of our analytical results. After verie cation, the results are applied to a large number of planetary satellites in the solar system. The motivation is that numerically integrated, low-altitude spacecraft orbits about Europa often impacton thatmoon’ ssurfaceafterashortperiod ofafewdaystoweeks.Numericalintegrationsindicatethatthese impact orbits only occurfor inclinations within » 45 deg of a polarorbit. An analytical study of this problem using averaging theory, which resultsin an approximate, closed-form solution fortheorbiterdynamics, is described. The solution includes the effect of theplanetgravity and theplanetary satellite oblateness, with theassumption that the eccentricity of the nominal orbit is small. This solution is used to compute limits for impacting and nonimpacting orbits at Europa and provides good agreement with numerical computations of these limits performed with highprecision numerical integrations of the motion. The analytical result predicts a set of initial conditions that can postpone impact with the planetary surface for considerable lengths of time.

The modern space era can greatly benefit from the rapidly growing microelectronics technologies in order to enable the ambitious exploratory and commercial space endeavors of the new millennium. A smart sensor, analog/digital, integrated circuit, suitable for spacecraft avionics data acquisition and control is presented. The Remote Input/Output (RIO) device is developed by The Johns Hopkins University/Applied Physics Laboratory, for NASA's Jet Propulsion Laboratory, to support many oncoming new millennium space missions. TRIO—the first version of RIO—is designed to interface to temperature, pressure, total radiation dose sensors, and generally to voltage/current transducers. The microchip includes front-end conditioning circuitry, an ADC, memory, serial and CPU interface, and a digital port. Furthermore the device is developed to meet extreme space qualification specifications such as radiation effects. This versatile system-on-a-chip device is becoming a key enabling technology for new-generation NASA and Commercial spacecraft systems. Missions that are intended to use the TRIO device are the: Europa Orbiter, Deep Space 4, Solar Probe, Pluto Express, Mars Sample Return, Stereo, Contour, etc.

Radioisotope thermoelectric generators (RTGs) have been used by the United States to provide electrical power for spacecraft since 1961. All RTGs that have been launched by the U.S. have used heat sources fueled with the plutonium-238 isotope. Low-power (1 W thermal ) Light Weight Radioisotope Heater Units have also been used to maintain spacecraft equipment within their normal operating temperature range. Los Alamos National Laboratory is responsible for fabricating heat sources for current and future space missions. The 238 PuO 2 is purified by aqueous processing, fabricated into hot pressed pellets, encapsulated into precious metal cladding material, then the fueled clads are nondestructively tested. NASA currently plans for the potential use of radioisotope power systems for the Europa Orbiter and the Solar Probe missions, which are all scheduled for launch this decade. In addition several Mars Exploration missions over the next decade will employ radioisotope heater units.

The Galileo spacecraft arrived at Jupiter in December of 1995 to begin an orbital tour of the Jovian system. The objective of the tour was up close study of the planet, its satellites, and its magnetosphere. The spacecraft completed its 11 orbit prime mission in November of 1997 having had 16 successful close encounters with the Galilean satellites (including two prior to Jupiter orbit insertion). Galileo continues to operate and will have made an additional 10 orbits of Jupiter by the date of this Conference. Earlier papers discuss the determination of the spacecraft orbit in support of mission operations from arrival at Jupiter through the first 9 orbits. In this paper we re-examine those earlier orbits and extend the analysis through orbit 12, the first orbit of the Galileo Europa Mission (GEM). The objective of our work is the reconstruction of the spacecraft trajectory together with the development of a consistent set of ephemerides for the Galilean satellites. As a necessary byproduct of the reconstruction we determine improved values for the Jovian system gravitational parameters and for the Jupiter pole orientation angles. Our preliminary analyses have already led to many of the results reported in the scientific literature. Unlike the Galileo Navigation Team which operates in the EME-1950 coordinate system, we elected to work in the (J2000) International Celestial Reference Frame (ICRF), the reference frame of the current JPL planetary and satellite ephemerides as well as the standard frame of the international astronomical and planetary science community. Use of this frame permits more precise modelling of the spacecraft and satellite observations. Moreover, it is the frame of choice for all other operational JPL missions and will probably be the frame for future missions for some time. Consequently, our adoption of the ICRF will facilitate the combination of our results with any obtained from future missions (e.g. the proposed Europa Orbiter mission). In addition, our results may be used by the science community, without need of a reference frame conversion.

Three radii from the surface of the Sun… more natural radiation around Jupiter than would be encountered immediately following a nuclear war… to the farthest planet and beyond… these challenges are faced by the three “Ice & Fire” missions: Solar Probe, Europa Orbiter, and PlutoKuiper Express. These three missions will be beneficiaries of the X2000 and related advanced technology development programs. Technology developments now in progress make these missions achievable at costs recently thought adequate only for missions of relatively short durations to “nearby” destinations. The next mission to Europa after Galileo will determine whether a global subsurface liquid water ocean is currently present, and will identify locations where the ocean, if it exists, may be most accessible to future missions. Pluto-Kuiper Express will complete the reconnaissance of the known planets in our Solar System with geological, compositional, and atmospheric mapping of Pluto and Charon while Pluto remains relatively near the Sun during its 248 year orbit. An extended mission to a Kuiper Disk object may be possible, depending on remaining sciencecraft resources. Using a unique combination of Sun shield/high gain antenna and quadrature encounter geometry, Solar Probe will deeply penetrate our nearest star's atmosphere to make local measurements of the birth of solar wind, and to remotely image features as small as 60 kilometers across on the Sun's surface. Avionics technology, leading to integration of functions among a set of multichip modules with standard interfaces, will enable lower production costs, lower power and mass, and the ability to package with modest shielding to enable survival in orbit around Europa inside Jupiter's intense radiation belts. The same avionics and software can be utilized on the other Ice & Fire missions. Each mission is characterized by a long cruise to its destination, facilitated by planetary flybys. The flight systems will represent a unique early integration of science “payload” and “spacecraft,” becoming a more integrated “sciencecraft.” To reduce operations and tracking costs, sciencecraft will be more autonomous. They will self-monitor and self-command, while sending a continuous beacon alerting ground receivers to general sciencecraft health and any need for immediate attention. Where solar power proves impractical for achieving mission goals, an advanced radioisotope power source may be utilized with a much smaller amount of fuel than on prior missions. The three missions described are to begin the Outer Planets/Solar Probe exploration program, as first proposed in the FY1998 Federal Budget. Sciencecraft, launch systems and mission operations must all fit within a single program, encouraging system- and program-wide tradeoffs to minimize costs. Some of the system and technological solutions utilized by these missions may find application in a variety of other science-driven missions.

This paper presents the findings of a series of planetary mission studies which supported development of the Space Science Strategic Plan. The studies evaluated the feasibility, science return, and cost of missions that were candidates for inclusion in the Strategic Plan and also assessed the effects of advanced technology on these parameters. The mission set covered includes high priority missions to planets and/or comets and asteroids subsequent to Pluto Express and Europa Orbiter (i.e., launching after 2004) except for missions to Mars (handled by a different office at JPL). A wide range missions were studied with emphasis on nine mission targets in two priority groups identified in the Strategic Plan. The first group are leading candidates for launch slots in the middle of the next decade: a comet nucleus sample return mission, a Jupiter deep multi-probe mission, and a Mercury Orbiter/solar physics mission. These are feasible today but can use advanced technology to enhance performance and/or reduce cost. The second group are future technology drivers, high priority science missions that require technology breakthroughs prior to implementation. These include comet deep coring and advanced sampling, Europa Lander, Io Volcano Observer, Neptune Orbiter, and investigations of the atmospheres and surfaces of Titan and Venus by aerobots or other means. The paper describes the mission concepts and the enabling and enhancing technologies developments identified for each mission. The current trend toward miniaturization of avionics will benefit all of the missions. Several were found to be enabled or strongly enhanced by advances in low thrust propulsion, either solar electric or solar sail. Another critical area is in-situ technologies, including precision approach; landing; surface mobility; sample collection, analyses and packaging; and sample return to Earth.

This paper describes the authors' approach to using commercial-off-the-shelf (COTS) products in highly reliable systems. The methodology calls for multilevel fault-protection. The methodology realizes that COTS products are often not developed with high reliability in mind. Nevertheless, by using multi-level fault protection, the same level of reliability as the traditional full-custom fault tolerance approach can be achieved. This methodology allows more freedom for design trade-offs among the fault-protection levels, which can result in less complicated designs than the traditional strictly-enforced fault-containment policy. This paper covers the authors' experiences and findings on the design of a fault-tolerant avionics bus architecture comprised of two COTS buses, the IEEE 1394, and the I/sup 2/C, for the avionics system of X2000 program at the Jet Propulsion Laboratory. The X2000 design is judicious about ensuring the fault-tolerance provisions do not cause the bus design to deviate from commercial standard specifications, so that the economic attractiveness of using COTS is preserved. The hardware and software designs of the X2000 fault-tolerant bus are being implemented, and flight hardware will be delivered to the Europa Orbiter missions. This work provides an example of how to construct a highly reliable system with low-cost COTS interfaces.

The Advanced Deep Space System Development Program is managed by the Jet Propulsion Laboratory for NASA and is also called X2000. X2000 is organized to create advanced flight and ground systems for the exploration of the outer planets and beyond; it has been created to develop the engineering elements of flight and ground systems. Payloads will be developed by another team. Each X2000 delivery gets its requirements from a set of planned missions, or “mission customers”. The X2000 First Delivery Project supports missions to the Sun (to 4 solar radii), Europa (looking for a liquid ocean), Mars (in support of several Mars missions including a sample return), a comet (including a sample return), and Pluto followed by a trip into the Kuiper belt. This set of missions leads to some outstanding requirements: 1. 1. Long-life (10–12 years) 2. 2. Total Ionizing Dose of 4 Mrad (for a Europa Orbiter) 3. 3. Average power consumption less than or equal to 150 Watts 4. 4. Autonomous operations that result in an extreme reduction in operations costs This paper describes the X2000 first delivery and its technologies following a brief overview of the program.

Recent cuts to NASA's planetary exploration budget have precipitated a debate in the community on whether large flagship missions to planetary bodies in the outer solar system or sequences of smaller missions as part of a long-term exploration program would be more beneficial. The work presented explores the trade between these two approaches as applied to the exploration of Europa and concentrates on identifying combinations of flyby, orbiter and/or lander missions that achieve high value at a lower cost than the Jupiter Europa Orbiter (JEO) flagship mission concept. The effects of the value attributed to the four main science objectives for Europa, which can be broadly classified as investigating the ocean, ice-shell, composition and geology, are demonstrated. The current approach proposed to complete the ocean exploration objective is shown to have conflicting requirements with the other three objectives. For missions that fully address all the science objectives, such as JEO, the ocean goal is therefore found to be the main cost driver. Instrument combinations for low-cost flyby missions are also presented, and simple lander designs able to achieve a wide range of objectives at a low additional cost are identified. Finally, the current designs for the Europa Habitability Mission (EHM) are compared to others in the trade space, based on the prioritization given to the science goals for the exploration of Europa. The current EHM flyby mission (Clipper) is found to be highly promising in terms of providing very high potential science value at a low cost.

At the start of 2011, the proposed Jupiter Europa Orbiter (JEO) mission was staffing up in expectation of becoming an official project later in the year for a launch in 2020. A unique aspect of the pre-project work was a strong emphasis and investment on the foundations of Model-Based Systems Engineering (MBSE). As so often happens in this business, plans changed: NASA's budget and science priorities were released and together fundamentally changed the course of JEO. As a result, it returned to being a study task whose objective is to propose more affordable ways to accomplish the science. As part of this transition, the question arose as to whether it could continue to afford the investment in MBSE. In short, the MBSE infusion has survived and is providing clear value to the study effort. In the process, the need to remain relevant in the new environment has brought about a wave of innovation and progress. By leveraging the existing infrastructure and a modest additional investment, striking advances in the capture and analysis of designs using MBSE were achieved. The effort has reaffirmed the importance of architecting. It has successfully harnessed the synergistic relationship of architecting to system modeling. We have found that MBSE can provide greater agility than traditional methods. We have also found that a diverse ‘ecosystem’ of modeling tools and languages (SysML, Mathematica, even Excel) is not only viable, but an important enabler of agility and adaptability. This paper will describe the successful application of MBSE in the dynamic environment of early mission formulation, the significant results produced and lessons learned in the process.

One of the major challenges for a mission to the Jovian system is the radiation tolerance of the spacecraft (S/C) and the payload. Moreover, being able to achieve science observations with high signal to noise ratios (SNR), while passing through the high flux radiation zones, requires additional ingenuity on the part of the instrument provider. Consequently, the radiation mitigation is closely intertwined with the payload, spacecraft and trajectory design, and requires a systems-level approach. This paper presents a design for the Io Volcano Observer (IVO), a Discovery mission concept that makes multiple close encounters with Io while orbiting Jupiter. The mission aims to answer key outstanding questions about Io, especially the nature of its intense active volcanism and the internal processes that drive it. The payload includes narrow-angle and wide-angle cameras (NAC and WAC), dual fluxgate magnetometers (FGM), a thermal mapper (ThM), dual ion and neutral mass spectrometers (INMS), and dual plasma ion analyzers (PIA). The radiation mitigation is implemented by drawing upon experiences from designs and studies for missions such as the Radiation Belt Storm Probes (RBSP) and Jupiter Europa Orbiter (JEO). At the core of the radiation mitigation is IVO's inclined and highly elliptical orbit, which leads to rapid passes through the most intense radiation near Io, minimizing the total ionizing dose (177 krads behind 100 mils of Aluminum with radiation design margin (RDM) of 2 after 7 encounters). The payload and the spacecraft are designed specifically to accommodate the fast flyby velocities (e.g. the spacecraft is radioisotope powered, remaining small and agile without any flexible appendages). The science instruments, which collect the majority of the high-priority data when close to Io and thus near the peak flux, also have to mitigate transient noise in their detectors. The cameras use a combination of shielding and CMOS detectors with extremely fast readout to minimize noise. INMS microchannel plate detectors and PIA channel electron multipliers require additional shielding. The FGM is not sensitive to noise induced by energetic particles and the ThM microbolometer detector is nearly insensitive. Detailed SNR calculations are presented. To facilitate targeting agility, all of the spacecraft components are shielded separately since this approach is more mass efficient than using a radiation vault. IVO uses proven radiation-hardened parts (rated at 100 krad behind equivalent shielding of 280 mils of Aluminum with RDM of 2) and is expected to have ample mass margin to increase shielding if needed.

Radar instruments are part of the core payload of the two Europa Jupiter System Mission (EJSM) spacecraft: NASA-led Jupiter Europa Orbiter (JEO) and ESA-led Jupiter Ganymede Orbiter (JGO). At this point of the project, several frequency bands are under study for radar, which ranges between 5 and 50 MHz. Part of this frequency range overlaps with that of the natural jovian radio emissions, which are very intense in the decametric range, below 40 MHz. Radio observations above 40 MHz are free of interferences, whereas below this threshold, careful observation strategies have to be investigated. We present a review of spectral intensity, variability and sources of these radio emissions. As the radio emissions are strongly beamed, it is possible to model the visibility of the radio emissions, as seen from the vicinity of Europa or Ganymede. We have investigated Io-related radio emissions as well as radio emissions related to the auroral oval. We also review the radiation belts synchrotron emission characteristics. We present radio sources visibility products (dynamic spectra and radio source location maps, on still frames or movies), which can be used for operation planning. This study clearly shows that a deep understanding of the natural radio emissions at Jupiter is necessary to prepare the future EJSM radar instrumentation. We show that this radio noise has to be taken into account very early in the observation planning and strategies for both JGO and JEO. We also point out possible synergies with RPW (Radio and Plasma Waves) instrumentations.

Solar system exploration as an international enterprise has entered a new era of activity and multinational cooperation. A number of the currently envisaged missions are targeted to bodies (e.g., Mars, Europa) that have significant interest with respect to the origin of life and chemical evolution, and the potential for biological studies. COSPAR has an important role as the standard-setting international organization in the area of planetary protection—a required reference for international missions to such bodies. Recently, COSPAR has formed a Panel on Planetary Protection that is concerned with the development, maintenance, and promulgation of planetary protection knowledge, policy, and plans to prevent the harmful effects of biological contamination—and through symposia, workshops, and topical meetings at COSPAR Assemblies to provide an international forum for exchange of information in this area. Through COSPAR the Panel will inform the international community, e.g., the Committee on the Peaceful Uses of Outer Space (COPUOS) of the United Nations, as well as various other bilateral and multilateral organizations. This Panel will work to ensure that its deliberations are based on the best current knowledge of the nature of the extraterrestrial bodies involved and to appreciate the potential biological implications of that knowledge. The nature of the deliberations of the body should serve both science and policy development requirements. Example missions for which a consensus agreement on requirements will be sought include Mars sample return missions, Europa Orbiter, and missions to other small bodies of the solar system (MUSES-C and Stardust). Mission planning and implementation efforts need a scientifically appropriate standard, developed as a consensus within the Panel, on which to base their efforts.

The Jupiter Europa Orbiter (JEO) is NASA's element of the joint Europa Jupiter System Mission (EJSM). Based on current trajectories, the spacecraft will spend a significant amount of time in the Jovian radiation belts. Therefore, research endeavors are underway to study the radiation effects on the various parts and components needed to implement the instruments. Data from these studies will be used for component selection and system design to ensure reliable operation throughout the mission duration. The radiation environment en route to Jupiter is nothing new for NASA designed systems, however, the long durations orbiting Jupiter and Europa present new challenges for radiation exposure. High-energy trapped electrons and protons at Jupiter dominate the expected radiation environment. Therefore, most of the initial component level radiation testing is being conducted with proton exposure. In this paper we will present in-situ monitoring of the optical transmission of various laser optical components during proton irradiation. Radiation induced optical attenuation of some components is less than would be expected, based on the authors experiences, and is attributed to the interaction of the protons with the materials. The results are an encouraging first step in screening these optical materials for spaceflight in a high radiation environment.

Tradition Radio Science techniques utilizing microwave links between spacecraft and ground stations have successfully lead to numerous discoveries. However, limitations on the received Signal-Noise-Ratio or geometrical coverage necessitate alternate observation configurations and new instrumentation. Spacecraft-to-spacecraft observations have significant SNR advantage over the traditional technique and can yield considerably improved geometrical coverage. These observations have been rarely carried out before because a special receiver is required onboard the spacecraft. One type of such open-loop receiver has been utilized on GRACE and will be utilized on GRAIL for precision measurements of the gravitational fields of the Earth and the Moon, respectively. A Different receiver type is onboard the New Horizons mission for an uplink occultation of Plutos atmosphere. Yet another prototype instrument onboard the Mars Reconnaissance Orbiter and has been used to demonstrate spacecraft-to-spacecraft radio science experiments with the Odyssey spacecraft. A new digital open-loop receiver specifically designed to meet the requirements of an occultation experiment has been prototyped for flight on the Europa Jupiter System Missions to the Jovian system, i.e., a Europa orbiter and a Ganymede orbiter. This instrument can be used to achieve multiple scientific including occultations of the atmosphere and ionosphere of Jupiter, occultations of the tenuous atmospheres and ionospheres of the Jovian satellites, occultations of the tenuous Jovian rings, and bistatic scattering from surfaces of the satellites. This paper will discuss the functional instrumentation under development as well as the potential achievable scientific investigations.

The proposed Jupiter Europa Orbiter (JEO) mission to explore the Jovian moon Europa poses a number of challenges. The spacecraft must operate for about seven years during the transit time to the vicinity of Jupiter, and then endure unusually high radiation levels during exploration and orbiting phases. The ability to withstand usually high total dose levels is critical for the mission, along with meeting the high reliability standards for flagship NASA missions. Reliability of new microelectronic components must be sufficiently understood to meet overall mission requirements.

Study of the Outer Planets is considered as a high priority activity by the Planetary Science community. One candidate for the next Outer Planets Flagship Mission (OPFM –missions in the $2B–$4B range) is the Jupiter Europa Orbiter (JEO) concept. In this work, we address the interplay of various types of uncertainties to probe the possibility of characterizing the reliability of a proposed mission concept. By combining the aleatory characterization of spacecraft subsystems and the epistemic uncertainties of the Jovian environment we describe an approach for quantifying possible ranges of mission durations for a potential JEO concept. The work here illustrates the potential for probabilistic representations of epistemic uncertainties by introducing temporal correlations. In addition the effects of failure correlations among similar components in a spacecraft are incorporated to assess their impact on the failure likelihood.

The NASA Jupiter Europa Orbiter (JEO) conceptual payload contains a thermal instrument with six different spectral bands ranging from 8µm to 100 m. The thermal instrument is based on multiple linear arrays of thermopile detectors that are intrinsically radiation hard; however, the thermopile CMOS readout needs to be hardened to tolerate the radiation sources of the JEO mission. Black Forest Engineerin g is developing a thermopile readout to tolerate the JEO mission radiation sources. The thermal instrument and ROIC process/design techniques are described to meet the JEO mission requirements. Keywords: CMOS, NASA, Jupiter Europa Orbiter, thermopile, RHBD, ROIC, ASIC 1.0 INTRODUCTION The Europa Jupiter System Mission (EJSM) launch planned in year 2020 will provide a better understanding as to how gas giant planets and their satellites form and evolve. The Jupiter Europa Orbiter (JEO) is the NASA element of the EJSM. JEO will be built to withstand the intense radiation in Europa orbit, and will consist of an orbiter with different science instruments designed for extensive mapping of Europa. On the way to Europa, JEO will tour the Jovian system and make observations of Jupiter, its satellites and its environment. The JEO conceptual payload includes a thermal instrument (TI) based on thermopile detectors that are intrinsically radiation hard to at least 10 Mrad; however the thermopile readout IC needs to be hardened to tolerate the radiation sources of the JEO mission. Black Forest Engineering (BFE) on a NASA sponsored SBIR effort is developing a thermopile readout application specific integrated circuit (ASIC) using radiation hardened by design techniques (RHBD) to tolerate the JEO mission radiation sources. The readout ASIC when developed on Phase II of the SBIR effort and combined with JPL thermopiles will meet the thermal instrument requirements of the JEO. The thermal instrument designed and developed for the JEO mission will be subjected to four major radiation sources: (1) solar energetic particles (protons, electrons, and heavy ions ) during the interplanetary cruise; (2) galactic cosmic rays (protons and heavy ions) during the interplanetary cruise; (3) trapped charged particles (electrons, protons, and heavy ions) in the Jovian magnetosphere during Jovian Tour and the orbits at Europa; and (4) particles (neutrons and gammas) from the Multi-Mission Radioisotope Generator (MMRTG). Among the four radiation sources, the high energy trapped electrons and protons at Jupiter are the dominating contributors to the “life-limiting” effects. Both total ionizing dose (TID) and displacement damage dose (DDD) effects produce long-term permanent degradation in the thermal instrument performance characteristics. Thermopile signal readout is planned through 128 channel CMOS ICs on the focal plane very close to the detector arrays. Thus radiation hardness will depend on the hardness of both the thermopile arrays and the readout IC. Thermopiles have been tested for TID by JPL with excellent harness to 10 Mrad. The instruments on the JEO will be new designs in order to meet the radiation challenges for electronics and materials. Radiation hardened mixed-signal ASICs will be a key instrume nt technology. BFE is using RHBD techniques to create a new thermopile readout ASIC to meet the JEO radiation challenges. BFE is developing the readout ASIC using 180 nm CMOS. On-readout analog-to-digital conversion is used to improve instrument performance (especially dynamic range) and provide system noise immunity.

Multiple-satellite-aided capture employs sequential gravity-assist flybys of more than one of Jupiter’s Galilean moons. These flybys substantially reduce the amount of propellant required for a spacecraft to capture into orbit around Jupiter. The “average” plane of the Galilean satellites constrains the arrival V-infinity vector, which in turn constrains the interplanetary trajectories from Earth to Jupiter. The solution space of interplanetary trajectories that permit multiple-satellite-aided capture is explored, and trajectories that start from Earth and end at Jupiter capture are integrated. I. Introduction Satellite-aided capture is a mission design technique that is used to decrease the V required to capture a spacecraft into orbit around a planetary body. The technique employs gravity-assist flybys of massive satellites of a planetary body, so only missions to planets with large moons can benefit from this technique. Hence, satellite-aided capture is only available to Earth-return missions and missions to Jupiter, Saturn, Uranus, or Neptune. Jupiter, in particular, has four massive Galilean moons that can be used for satellite-aided capture. These satellite-aided capture trajectories were first proposed for missions to Jupiter by Longman 1 and by Longman and Schneider. 2 Cline 3 determined the best use of a Ganymede gravity-assist to minimize the Jupiter insertion maneuver (JOI) V required for capture into Jupiter orbit. Nock and Uphoff 4 performed a tour-de-force of satellite-aided capture trajectories for the entire Solar System by varying several trajectory parameters, including perijove radius after flyby, flyby altitude, declination of the incoming satellite-centered hyperbola, and the distribution of V between powered satellite flybys and the JOI maneuver. They also briefly investigated double-satellite-aided capture by determining the phasing and transfer orbit parameters necessary to achieve capture. Malcolm and McInnes 5 employ a vectorial targeting approach to solve the satellite-aided capture problem. Yam 6 and Okutsu et al. 7 present a central-body-changing algorithm that can model a satellite-aided capture using a patched-conic method. The algorithm accepts a planet-centeredV1 vector and a moon’s radius vector as input and outputs the phase angle between the incoming Jupiter-centered asymptote and the flyby. Landau et al. 8 proposed using solar electric propulsion (SEP) to reduce the Jupiter arrivalV1 of interplanetary trajectories in order to ballistically capture an SEP spacecraft into orbit about Jupiter with gravity assists of one or two of Jupiter’s Galilean moons. The first implementation of a single-satellite-aided capture occurred during the Galileo mission to Jupiter. 9 Two proposed NASA missions to Jupiter (the Europa Orbiter Mission 10‐12 and the Jupiter Icy Moons Orbiter 13 ) had designed single-satellite-aided capture trajectories using Ganymede and Callisto, respectively. The planned Jupiter Europa Orbiter mission has a nominal trajectory that includes an Io-aided capture. 14 Lynam et al. 15 proposed the use of double-, triple-, or quadruple-satellite-aided capture as another method of capturing a spacecraft into orbit around Jupiter with still lower V cost. That study focuses on the Jupiter capture phase of these trajectories and only briefly discusses the interplanetary trajectory phase of these missions. In this paper, we connect several of the multiplesatellite-aided capture sequences designed by Lynam et al. with interplanetary trajectories to form complete trajectories from Earth launch to Jupiter capture. Figure 1 shows a complete trajectory that begins at Earth launch and then performs gravity-assist flybys of Ganymede and Io as it approaches Jupiter. We also determine how often some of these capture trajectories are available for use in a future mission and how much total mission V can be saved. As in Lynam et al., we assume that the (non-trivial) navigational challenges associated with these trajectories can be surmounted.

The Sub-Surface Radar (SSR) instrument is a core payload for the Jupiter Ganymede Orbiter (JGO) of the EJSM, which is complementary to the Ice Penetrating Radar on board the Jupiter Europa Orbiter (JEO). These instruments work at low frequency (HF/VHF band) and are designed to penetrate the surfaces of icy moons of Jupiter. The paper will present a preliminary performance model aimed to assess the penetration capability of the instrument in different operative conditions and planet's surface characteristics.

The Europa Jupiter System Mission (EJSM) has been prioritized as the next Outer Planets Flagship Mission that would be devoted to exploring the emergence of habitable worlds around gas giants. This joint NASA and ESA endeavor would focus on the Galilean moons Europa and Ganymede but would also investigate Io, Callisto, and the Jupiter system as a whole. The NASA-contributed Jupiter Europa Orbiter (JEO) and the ESA-contributed Jupiter Ganymede Orbiter (JGO) would be launched on separate launch vehicles in 2020. Here we focus on JEO. 12

A brief overview of the Jupiter Europa Orbiter (JEO) mission is presented along with a discussion of the challenges associated with the harsh radiation environment anticipated for the mission. The shielding approach for such harsh environment is discussed.

A summary of the radiation environment and requirements of a Europa Orbiter mission as well as a system-level design for a radiation monitoring facility instrument is presented. The current understanding of the various species of ionizing radiation present at Europa is compiled, offering insight into the aspects relevant for instrument engineering. We argue that the unique and complex nature of the Europa radiation environment both precipitates a need for its further understanding and presents a challenge for its quantification. A review of the use of RadFET sensors is presented for the purpose of highlighting its suitability for a Europa radiation monitor and providing context for the utilization of a radiation monitor on a Europa Orbiter. Finally, new designs are presented for a RadFET facility instrument which utilizes existing scientific instrument interfaces to achieve total dose quantification with a mass and power allocation that does not significantly impact the spacecraft.

Missions to explore Europa have been imagined ever since the Voyager mission first suggested that Europa was geologically very young. Subsequently, Galileo supplied fascinating new insights into that satellite's secrets. The Jupiter Europa Orbiter (JEO) would be the NASA-led portion of the Europa Jupiter System Mission (EJSM), an international mission with orbiters developed by NASA, ESA and possibly JAXA. JEO would address a very important subset of the complete EJSM science objectives and is designed to function alone or in conjunction with ESA's Jupiter Ganymede Orbiter (JGO).

International audience; The sodium and potassium exospheres of Europa are described as well as the variations of the Na/K ratio from Europa's surface up to about 20 Europa radii. Observations carried out by M. E. Brown (2001) are used to constrain the Na and K source terms. We find that an average source rates ratio of 17 ± 2 at the surface and loss rates ratio of 26 ± 2 reproduce well the observations. These values are consistent with the conclusions by R. E. Johnson et al. (2002) on its most probable origin. Moreover, we here show that a local increase of the surface Na/K ratio by a factor 2 in a 20° × 30° wide region should induce an observable exospheric signature between 80 and 300 km above the surface. Therefore simultaneous observations of sodium and potassium from an Europa orbiter would allow one to derive important properties of the surface and subsurface of the Galilean moon.

Concept studies for deep space missions are typically time-consuming and costly, given the variety of missions and uniqueness of each design. Yet, in an increasingly cost-constrained environment, it is critical to identify the most scientifically valuable and cost-effective designs early in the design process. Modeling is an integral part in helping to identify the most desirable design option. While some spacecraft design models currently exist for Earth-orbiting spacecraft, there has been less success with deep space missions. Instead, these missions require a modified design and modeling approach to enable the same construction of a comprehensive, yet credible, mission tradespace. This paper presents an approach for efficiently constructing such a mission tradespace. In addition to a proposed design and modeling approach, three case study missions are presented including a solar orbiter, a Europa orbiter, and a near-Earth asteroid (NEA) sample return mission.

The Galileo mission has indicated the possibility of the existence of a subsurface ocean on Europa. The measurement of the surface deformation in response to the tidal forcing and the measurement of the amplitude and frequency of the librations of Europa around a 1:1 spin-orbit resonant state is considered as the best indirect verification of both the existence and approximate depth of such an ocean. Previous studies have separately dealt with the detection of a global liquid ocean beneath the icy crust of Europa with altimeter measurements, and through the detection of the libration amplitudes from Earth-based radio tracking. The purpose of the present study is to simulate the combined detection of bodily tides and librations with the use of altimeter data from a low-altitude Europa orbiter and radio tracking from the Earth. The analysis thus provides some insight into the sensitivity of the orbit geometry to the direct altimetric measurement and the indirect sensing through the analysis of the orbit perturbations due to the tidal mass displacement and the Europan librations. The results indicate that orbits of at least 70 inclination are required, although polar orbits are not necessary. A formal error propagation also indicates that the Love numbers of Europa can be determined with an error of a few percent from measurement arcs spanning just a few days. This information can be of value for the preliminary planning phase of future Europa exploration missions, like the LAPLACE mission recently considered by the ESA Cosmic Vision program and similar missions under study by NASA and other space agencies.

A detailed; mission-level systems study has been performed to show the benefit resulting from engine performance gains that will result from NASA's In-Space Propulsion ROSS Cycle 3A NRA, Advanced Chemical Technology sub-topic. The technology development roadmap to accomplish the NRA goals are also detailed in this paper. NASA-Marshall and NASA-JPL have conducted mission-level studies to define engine requirements, operating conditions, and interfaces. Five reference missions have been chosen for this analysis based on scientific interest, current launch vehicle capability and trends in space craft size: a) GTO to GEO, 4800 kg, delta-V for GEO insertion only approx.1830 m/s; b) Titan Orbiter with aerocapture, 6620 kg, total delta V approx.210 m/s, mostly for periapsis raise after aerocapture; c) Enceladus Orbiter (Titan aerocapture) 6620 kg, delta V approx.2400 m/s; d) Europa Orbiter, 2170 kg, total delta V approx.2600 m/s; and e) Mars Orbiter, 2250 kg, total delta V approx.1860 m/s. The figures of merit used to define the benefit of increased propulsion efficiency at the spacecraft level include propulsion subsystem wet mass, volume and overall cost. The objective of the NRA is to increase the specific impulse of pressure-fed earth storable bipropellant rocket engines to greater than 330 seconds with nitrogen tetroxide and monomothylhydrazine propellants and greater than 335 , seconds with nitrogen tetroxide and hydrazine. Achievement of the NRA goals will significantly benefit NASA interplanetary missions and other government and commercial opportunities by enabling reduced launch weight and/or increased payload. The study also constitutes a crucial stepping stone to future development, such as pump-fed storable engines.

A mission to Europa has been identified as a high priority by the science community for several years. The difficulty of an orbital mission - due primarily to the propulsive requirements and Jupiter's trapped radiation - led to many studies that investigated various approaches to meeting the science goals. The Europa Orbiter Mission studied in the late 1990s only met the most fundamental science objectives. The science objectives have evolved with the discoveries from the Galileo mission. JPL studied one concept-Europa Explorer - for a Europa orbiting mission that could meet a much - expanded set of science objectives. A study science group was formed to verify that the science objectives and goals were being adequately met by the resulting mission design concept. The Europa Explorer design emerged primarily from two key self-imposed constraints: (1) Meet the full set of identified non-lander science objectives. (2) Use only existing technology. Though other design concepts are viable for alternate program constraint sets, this paper will only discuss the results of this concept study. The Europa Explorer conducts a multi-year study of the Jupiter system, relies on existing technologies, and returns considerably more science data than previously examined conventional-propulsion mission concepts. In this mission concept, a single orbiter would traverse to Jupiter by means of a gravity assist trajectory and reach Jupiter ~6 years after launch, followed by an ~1frac12 year tour of the Galilean satellites, before entering Europa orbit. The Europa Prime Mission would be 90 days, with the expectation of being operational for upwards of a year. The flight system would return approximately three year's worth of Cassini data (~3 Tbit) during the first 90 days in Europa orbit. During this Europa Prime Mission, the flight system would orbit Europa more than 1000 times and provide three orders of magnitude more close (

The National Research Council's solar system exploration decadal survey identified Jupiter's moon Europa as its highest-priority destination for near-term exploration. Voyager and Galileo missions to the Jupiter system provided evidence consistent with a subsurface ocean on Europa, which is of great interest as a potential abode for extraterrestrial life. This paper describes a conceptual flagship-class Europa orbiter concept that was assumed to launch as early as 2012, arriving at Europa approximately 8 years later using inner solar system gravity assists to reach Jupiter. Jupiter's intense radiation environment limits the mission duration at Europa to 30 days for this study, though the duration is a result of multiple trades and is by no means fixed. The Europa subgroup of the outer planets assessment group identified six primary science objectives for this concept. An /spl sim/150-kg instrument suite selected for the study addresses those objectives. Large heliocentric distances, high power levels required, and especially the harsh Jovian radiation environment drove the selection of radioisotope thermoelectric generators (RTGs) for all onboard electrical power, with the excess heat aiding spacecraft thermal control. Mass and architecture trades were performed using different spacecraft trajectories, launch vehicle types, radioisotope power systems, and mission durations. The study shows that new mission constraints allow a scientifically compelling Europa orbiter mission that might also deliver a Europa lander.

This study analyses a single Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) unit, and two Stirling Radioisotope Generator (SRG) units for powering Jupiter Europa Orbiter. The RTG power system will independently produce an uninterrupted power supply, as opposed to a solar powered orbiter, as studied by Astrium for ESA, which depends on distance from Sun, eclipse and Jupiter’s occultation. The orbiter’s thermal control system uses excess heat from the RTG to maintain the spacecraft’s temperature using a heat transfer loop. The additional heat loads received by the spacecraft during Venus and Earth flybys are removed with this heat transfer loop through the RTG radiators. The MMRTG provides a continuous power output of 110 W with a 13% reduction in mass compared to a solar powered equivalent. The total radiation dose from the MMRTG is about 5 krad behind 10 mm aluminium shielding, which is much lower than the expected mission natural radiation dose. The electromagnetic interference produced by the MMRTG magnetic field strength is only 17 nT which is less than the NASA standard requirement of 25 nT at one meter distance. The power system with two SRG units has an overall mass saving of 9% compared to the solar cell equivalent and requires only four General Purpose Heat Sources (GPHS) to produce 220 W of electrical power. It emits less radiation and has a weaker magnetic field than the MMRTG. Results show that a Jupiter Europa Orbiter spacecraft designed with single MMRTG unit or with two SRG units as power source would be the best choice for the proposed ESA Jovian Minisat Exploration mission.

Due to their unique construction, Super NiCd cells are resistant to degradation by radiation expected from a mission to Europa and other high radiation environments present in interplanetary space. In place of conventional nylon separators the Super NiCd uses a zirconium oxide fabric (Zircar) impregnated with polybenzimidazole (PBI), a fire retardant polymer developed after the fire on Apollo 1. The Super NiCd cells were fabricated at Eagle Picher Power Systems Department (now, Electro Energy, Mobile Products Inc.) and furnished to NASA for the Mars Observer program in 1990. After storage for 10 years the cells were reconditioned then subjected to radiation testing for the Europa Orbiter Program in 2000. The 37 Ah name plate cells yielded capacities greater than 50 Ah both before and after controlled radiation testing. Cells were DPAed after radiation testing with no visible evidence of damage.

In August 2000, an independent assessment of the Europa Orbiter baseline mission was performed to evaluate the planned implementation. As part of this activity, multiple alternative mission concepts were investigated that could meet the full science objectives as well as concepts that could meet a reduced set of science objectives. The results of the study validated the estimated costs of the mission, while recommending a modified mission approach that reduced'the overall risk of the mission.

Hill’s equations can be used for approximating the dynamic behavior around many celestial bodies. When considering also the perturbation due to the non-sphericity of the central body, the model closely reproduces the real dynamics of an orbiter around planetary satellites. Classically, the long-term behavior of this problem is studied by averaging techniques. The double averaged problem is integrable, but it presents a symmetry of direct and retrograde inclination orbits that does not exist in the original problem. We use Lie transforms to reduce the problem to an integrable one, performing the transformations up to third order where the inclination symmetry is broken. Then, the proper use of the double reduced space, which is a sphere, allows us to make a full description of families of frozen orbits and their bifurcations. We identify saddle-center and pitchfork bifurcations related to stable, frozen orbits. Finally, for the specific case of a Europa orbiter, we relate the equilibria of the reduced problem with periodic solutions of the non-averaged problem in a synodic frame.

The Europa Orbiter mission, currently baselined for launch in 2008, is intended to follow up on tantalizing results from the Galileo spacecraft, data from which suggests that there may be a global ocean underneath the Jovian satellite Europa's water ice crust. Europa orbit is propulsively one of the most difficult destinations to reach in the Solar System, making mass a major driver of mission cost. The combination of high radiation and the need for low-mass and -power electronics led to the X2000 avionics development activity, which is now at the core of the Europa Orbiter project. At the heart of the X2000 development are rad-hard, high performance application specific integrated circuits (ASICs), which may be utilized either on the avionics "slices" for which they are being designed, or separately if that is beneficial to a user. The Europa mission provides a challenge in terms of extreme environmental requirements. The key driving requirements are the one mega-rad total ionizing dose and the fourteen-year life. The X2000 power system electronics (PSE) must reduce its power, mass and volume envelope by incorporating new technology developed by industry partners.