The Grain Impact Analyser and Dust Accumulator (GIADA) Experiment for the Rosetta Mission: Design, Performances and First Results

The Grain Impact Analyser and Dust Accumulator (GIADA) onboard the ROSETTA mission to comet 67P/Churyumov–Gerasimenko is devoted to study the cometary dust environment. Thanks to the rendezvous configuration of the mission, GIADA will be plunged in the dust environment of the coma and will be able to explore dust flux evolution and grain dynamic properties with position and time. This will represent a unique opportunity to perform measurements on key parameters that no ground-based observation or fly-by mission is able to obtain and that no tail or coma model elaborated so far has been able to properly simulate. The coma and nucleus properties shall be, then, clarified with consequent improvement of models describing inner and outer coma evolution, but also of models about nucleus emission during different phases of its evolution. GIADA shall be capable to measure mass/size of single particles larger than about 15 μm together with momentum in the range 6.5 × 10⁻¹⁰ ÷ 4.0 × 10⁻⁴ kg m s⁻¹ for velocities up to about 300 m s⁻¹. For micron/submicron particles the cumulative mass shall be detected with sensitivity 10⁻¹⁰ g. These performances are suitable to provide a statistically relevant set of data about dust physical and dynamic properties in the dust environment expected for the target comet 67P/Churyumov–Gerasimenko. Pre-flight measurements and post-launch checkouts demonstrate that GIADA is behaving as expected according to the design specifications. The International GIADA Consortium (I, E, UK, F, D, USA).     

Top-level modeling of an ALS system utilizing object-oriented techniques.

The possible configuration of an Advanced Life Support (ALS) System capable of supporting human life for long-term space missions continues to evolve as researchers investigate potential technologies and configurations. To facilitate the decision process the development of acceptable, flexible, and dynamic mathematical computer modeling tools capable of system level analysis is desirable. Object-oriented techniques have been adopted to develop a dynamic top-level model of an ALS system.This approach has several advantages; among these, object-oriented abstractions of systems are inherently modular in architecture. Thus, models can initially be somewhat simplistic, while allowing for adjustments and improvements. In addition, by coding the model in Java, the model can be implemented via the World Wide Web, greatly encouraging the utilization of the model. Systems analysis is further enabled with the utilization of a readily available backend database containing information supporting the model. The subsystem models of the ALS system model include Crew, Biomass Production, Waste Processing and Resource Recovery, Food Processing and Nutrition, and the Interconnecting Space. Each subsystem model and an overall model have been developed. Presented here is the procedure utilized to develop the modeling tool, the vision of the modeling tool, and the current focus for each of the subsystem models.     

Performance characteristics of lithium ion cells at low temperatures

The low temperature charge and discharge characteristics of experimental MCMB-Li/sub x/Ni/sub y/Co/sub 1-y/O/sub 2/ cells containing different electrolytes were investigated. The use of low ethylene carbonate (EC)-content electrolyte formulations has resulted in good discharge performance to temperatures as low as -40/spl deg/C. The effect of charge voltage and charge current upon the individual electrode potentials at low temperature was investigated using the three electrode cells (containing lithium reference electrodes). In some cases, lithium plating was observed to occur upon low temperature charge, and found to be facilitated by high charge voltages, high charge currents, and poor anode kinetics. Electrochemical characterization of the cells has helped to establish the conditions under which lithium plating can occur by providing information regarding the polarization effects present at each electrode.     

Is the North Atlantic Oscillation modulated by solar and lunar cycles? Some evidences from Hurst autocorrelation analysis

Several studies have suggested that the Sun and Moon cycles affect the Earth climatic dynamics. Nevertheless, there is a long-standing controversy whether solar variability and tides can significantly generate climate change, and how this may occur. Spectral analysis of climatic indices has provided only indirect evidences of the effects of solar–tidal periodicities in the Earth climate. This work addresses the issue by considering the dynamics of the daily North Atlantic Oscillation index over the period from 1950 to 2009. In contrast to previous studies, this work proposes that external cycles can be detected in the autocorrelation dynamics rather than in the raw North Atlantic Oscillation index series. Here, the R/S-scaling analysis is used to quantify, via the so-called Hurst exponent, the presence of autocorrelations along the studied years. Fourier analysis scan of the autocorrelation series thus show two prominent spectral components near (±3%) the lunar tidal 4.425 and the solar 11 years cycles. Intermediate spectral components near 6.4, 7.75 and 8.9 years are proposed to be, at least partially, a result of energy capture from internal mechanisms into cycles resulting from the nonlinear resonance of the fundamental solar–tidal cycles. The dominant effect of the solar variability is clarified by showing that in about 70% of the studied period the sunspot number and the Hurst exponent phases are synchronized, indicating that a higher solar activity enhances the North Atlantic Oscillation index predictability.     

Risk-based technology portfolio optimization for early space mission design

The successful design, development, and operation of space missions requires informed decisions to be made across a vast array of investment, scientific, technological, and operational issues. In the work reported in this paper, we address the problem of determining optimal technology investment portfolios that minimize mission risk and maximize the expected science return of the mission. We model several relationships that explicitly link investment in technologies to mission risk and expected science return. To represent and compute these causal and computational dependencies, we introduce a generalization of influence diagrams that we call inference nets. To illustrate the approach, we present results from its application to a technology portfolio investment trade study done for a specific scenario for the projected 2009 Mars MSL mission. This case study examines the impact of investments in precision landing and long-range roving technologies on the mission capability, and the associated risk, of visiting a set of preselected science sites. We show how an optimal investment strategy can be found that minimizes the mission risk given a fixed total technology investment budget, or alternatively how to determine the minimum budget required to achieve a given acceptable mission risk.     

Understanding Interplanetary Coronal Mass Ejection Signatures

While interplanetary coronal mass ejections (ICMEs) are understood to be the heliospheric counterparts of CMEs, with signatures undeniably linked to the CME process, the variability of these signatures and questions about mapping to observed CME features raise issues that remain on the cutting edge of ICME research. These issues are discussed in the context of traditional understanding, and recent results using innovative analysis techniques are reviewed.     

Modeling solar proton access to geostationary spacecraft with geomagnetic cutoffs

Solar energetic particle (SEP) cutoffs at geosynchronous orbit are sensitive to moderate geomagnetic activity and undergo daily variations due to the day–night asymmetry of the magnetosphere. At geosynchronous orbit, cutoff rigidity also has a large directional dependence, with the highest cutoff rigidity corresponding to ions arriving from magnetic east and lowest cutoff rigidity corresponding to ions incident from the west. Consequently, during geomagnetically quiet periods, the SEP flux observed by an eastward facing particle detector is significantly lower than observed by a westward facing particle detector. During geomagnetically disturbed periods the cutoff is suppressed allowing SEPs access well inside of geosynchronous, so that the east–west SEP flux ratio approaches unity. Variations in the east–west SEP flux ratio observed by GOES Energetic Particle Sensors (EPS) have recently been reported by Rodriguez et al. (2010). In NOAA’s operational processing of EPS count rates into differential fluxes, the differential flux is treated as isotropic and flat over the energy width of the channel. To compare modeled SEP flux with GOES EPS observations, the anisotropy of the flux over the EPS energy range and field of view must be taken into account. A technique for making direct comparisons between GOES EPS observations and SEP flux modeled using numerically computed geomagnetic cutoffs is presented. Initial results from a comparison between modeled and observed flux during the 6–11 December 2006 SEP event are also presented. The modeled cutoffs reproduce the observed flux variations well but are in general too high.     

The Solar Wind Around Pluto (SWAP) Instrument Aboard New Horizons

The Solar Wind Around Pluto (SWAP) instrument on New Horizons will measure the interaction between the solar wind and ions created by atmospheric loss from Pluto. These measurements provide a characterization of the total loss rate and allow us to examine the complex plasma interactions at Pluto for the first time. Constrained to fit within minimal resources, SWAP is optimized to make plasma-ion measurements at all rotation angles as the New Horizons spacecraft scans to image Pluto and Charon during the flyby. To meet these unique requirements, we combined a cylindrically symmetric retarding potential analyzer with small deflectors, a top-hat analyzer, and a redundant/coincidence detection scheme. This configuration allows for highly sensitive measurements and a controllable energy passband at all scan angles of the spacecraft.     

Strategies for detection of putative life on Europa

Planned future exploration missions to the Jovian satellite Europa have a strong astrobiological motivation. Characterization of the potential habitability of the liquid water environments, and searching for life signals are the main astrobiological objectives of these missions. To meet these objectives specific strategies and instrumentation are required. Here we discuss some scenarios for the development of Europa potential biospheres. These scenarios are based on assumptions of the life similarity concept and knowledge about terrestrial life in extreme environments. Since the potential habitable environments on Europa are in the interior of the satellite it is not possibly to directly detect life. However, there are processes that link aqueous sub-surface environments with the near-surface environment, such as tectonism or magmatism. Therefore, by analysing endogenous materials that arise from the interior it is possible to make predictions about what is in the sub-surface. We propose some measurements and instrumentation for future missions to detect biosignatures on the upper layers of Europa, including the simple physico-chemical traces of metabolism to complex biomolecules or biostructures. Raman spectroscopy or biosensor technologies are the future for in situ exploration of the Solar System.     

Experimental and numerical analysis of non-symmetric breakage of liquid columns in an axial gravitational field rotating around an eccentric axis

An experiment in microgravity conditions aboard the TEXUS-23 mission was performed to obtain the deformation up to breakage of a cylindrical liquid column in isorotation around an eccentric axis. In previous work, breakage rotation speed was predicted by a numerical method. This method was validated by comparison with analytical and experimental results. The non-symmetric breakage of the liquid column observed in the experiment, however, was not explained by the combined effect of rotation and eccentricity.