Venus Express—Science observations experience at Venus

The Venus Express mission is the European Space Agency's (ESA) first spacecraft at Venus. It was launched in November 2005 by a Soyuz–Fregat launcher and arrived at Venus in April 2006. The mission covers a broad range of scientific goals including physics, chemistry, dynamics and structure of the atmosphere as well as atmospheric interaction with the surface and several aspects of the surface itself. Furthermore, it investigates the plasma environment and interaction of the solar wind with the atmosphere and escape processes.One month after the arrival at Venus the Venus Express spacecraft started routine science operations. Since then Venus Express has been observing Venus every day for more than one year continuously making new discoveries.In order to ensure that all the science objectives are fulfilled the Venus Express Science Operations Centre (VSOC) has the task of coordinating and implementing the science operations for the mission. During the first year of Venus observations the VSOC and the experiment teams gained a lot of experience in how to make best use of the observation conditions and payload capabilities. While operating the spacecraft in orbit we also acquired more knowledge on the technical constraints and more insight in the science observations and their results.As the nominal mission is coming to an end, the extended mission will start from October 2007. The Extended Science Mission Plan was developed taking into account the lessons learned. At the same time new observations were added along with specific fine-tuned observations in order to complete the science objectives of the mission.This paper will describe how the previous observations influence the current requirements for the observations around Venus today and how they influence the observations in the mission extension. Also it will give an overview of the Extended Science Mission Plan and its challenges for the future observations.     

The microbial habitability of weathered volcanic glass inferred from continuous sensing techniques

Basaltic glasses (hyaloclastite) are a widespread habitat for life in volcanic environments, yet their interior physical conditions are poorly characterized. We investigated the characteristics of exposed weathered basaltic glass from a surface outcrop in Iceland, using microprobes capable of continuous sensing, to determine whether the physical conditions in the rock interior are hospitable to microbial life. The material provided thermal protection from freeze-thaw and rapid temperature fluctuations, similar to data reported for other rock types. Water activity experiments showed that at moisture contents less than 13% wet weight, the glass and its weathering product, palagonite, had a water activity below levels suitable for bacterial growth. In pore spaces, however, these higher moisture conditions might be maintained for many days after a precipitation event. Gas exchange between the rock interior and exterior was rapid (< 10 min) when the rocks were dry, but when saturated with water, equilibration took many hours. During this period, we demonstrated the potential for low oxygen conditions within the rock caused by respiratory stimulation of the heterotrophic community within. These conditions might exist within subglacial environments during the formation of the rocks or in micro-environments in the interior of exposed rocks. The experiments showed that microbial communities at the site studied here could potentially be active for 39% of the year, if the depth of the community within the outcrop maintains a balance between access to liquid water and adequate protection from freezing. In the absence of precipitation, the interior of weathered basaltic glass is an extreme and life-limiting environment for microorganisms on Earth and other planets.     

Sunspot dynamics are reflected in human physiology and pathophysiology

Periodic episodes of increased sunspot activity (solar electromagnetic storms) occur with 10-11 and 5-6 year periodicities and may be associated with measurable biological events. We investigated whether this sunspot periodicity characterized the incidence of Pap smear-determined cervical epithelial histopathologies and human physiologic functions. From January 1983 through December 2003, monthly averages were obtained for solar flux and sunspot numbers; six infectious, premalignant and malignant changes in the cervical epithelium from 1,182,421 consecutive, serially independent, screening Pap smears (59°9″N, 4°29″E); and six human physiologic functions of a healthy man (oral temperature, pulse, systolic and diastolic blood pressure, respiration, and peak expiratory flow), which were measured ～5 times daily during ～34,500 self-measurement sessions (44°56″N, 93°8″W). After determining that sunspot numbers and solar flux, which were not annually rhythmic, occurred with a prominent 10-year and a less-prominent 5.75-year periodicity during this 21-year study span, each biological data set was analyzed with the same curve-fitting procedures. All six annually rhythmic Pap smear-detected infectious, premalignant and malignant cervical epithelial pathologies showed strong 10-year and weaker 5.75-year cycles, as did all six self-measured, annually rhythmic, physiologic functions. The phases (maxima) for the six histopathologic findings and five of six physiologic measurements were very near, or within, the first two quarters following the 10-year solar maxima. These findings add to the growing evidence that solar magnetic storm periodicities are mirrored by cyclic phase-locked rhythms of similar period length or lengths in human physiology and pathophysiology.     

Summary of quantitative interpretation of IMAGE far ultraviolet auroral data

Direct imaging of the magnetosphere by instruments on the IMAGE spacecraft is supplemented by simultaneous observations of the global aurora in three far ultraviolet (FUV) wavelength bands. The purpose of the multi-wavelength imaging is to study the global auroral particle and energy input from the magnetosphere into the atmosphere. This paper describes the method for quantitative interpretation of FUV measurements. The Wide-Band Imaging Camera (WIC) provides broad band ultraviolet images of the aurora with maximum spatial resolution by imaging the nitrogen lines and bands between 140 and 180 nm wavelength. The Spectrographic Imager (SI), a dual wavelength monochromatic instrument, images both Doppler-shifted Lyman-α emissions produced by precipitating protons, in the SI-12 channel and OI 135.6 nm emissions in the SI-13 channel. From the SI-12 Doppler shifted Lyman-α images it is possible to obtain the precipitating proton flux provided assumptions are made regarding the mean energy of the protons. Knowledge of the proton (flux and energy) component allows the calculation of the contribution produced by protons in the WIC and SI-13 instruments. Comparison of the corrected WIC and SI-13 signals provides a measure of the electron mean energy, which can then be used to determine the electron energy flux. To accomplish this, reliable emission modeling and instrument calibrations are required. In-flight calibration using early-type stars was used to validate the pre-flight laboratory calibrations and determine long-term trends in sensitivity. In general, very reasonable agreement is found between in-situ measurements and remote quantitative determinations.     

A wavelet multiresolution analysis for spatio-temporal signals

The wavelet filters of the conventional 3D multiresolution analysis possess homogeneous spatial and temporal frequency characteristics which limits one's ability to match filter frequency characteristics to signal frequency behavior. Also, the conventional 3D multiresolution analysis employs an oct-tree decomposition structure which restricts the analysis of signal details to identical resolutions in space and time. This paper presents a 3D wavelet multiresolution analysis constructed from nonhomogeneous spatial and temporal filters, and an orthogonal sub-band coding scheme that decouples the spatial and temporal decomposition processes     

Charge measurement circuit for electric vehicle batteries

Calculating the state of charge (SOC) of an electric vehicle (EV) battery is an inherently error prone process that depends on several variables. However, the accuracy of the required charge flow measurements can be greatly improved by using a voltage to frequency (V/F) converter in conjunction with a digital counter to integrate the measured battery current.     

The Genesis Solar-Wind Collector Materials

Genesis (NASA Discovery Mission #5) is a sample return mission. Collectors comprised of ultra-high purity materials will be exposed to the solar wind and then returned to Earth for laboratory analysis. There is a suite of fifteen types of ultra-pure materials distributed among several locations. Most of the materials are mounted on deployable panels (‘collector arrays’), with some as targets in the focal spot of an electrostatic mirror (the ‘concentrator’). Other materials are strategically placed on the spacecraft as additional targets of opportunity to maximize the area for solar-wind collection. Most of the collection area consists of hexagonal collectors in the arrays; approximately half are silicon, the rest are for solar-wind components not retained and/or not easily measured in silicon. There are a variety of materials both in collector arrays and elsewhere targeted for the analyses of specific solar-wind components. Engineering and science factors drove the selection process. Engineering required testing of physical properties such as the ability to withstand shaking on launch and thermal cycling during deployment. Science constraints included bulk purity, surface and interface cleanliness, retentiveness with respect to individual solar-wind components, and availability. A detailed report of material parameters planned as a resource for choosing materials for study will be published on a Genesis website, and will be updated as additional information is obtained. Some material is already linked to the Genesis plasma data website (genesis.lanl.gov). Genesis should provide a reservoir of materials for allocation to the scientific community throughout the 21st Century. This revised version was published online in August 2006 with corrections to the Cover Date.     

Element Abundances and Isotope Ratios in the Giant Planets and Titan

This paper reviews our present knowledge about elemental and isotopic ratios in the Giant Planets and Titan. These parameters can provide key information about the formation and evolution of these objects. Element abundances, especially after the results of the Galileo Probe Mass Spectrometer in Jupiter, strongly support the formation model invoking an initial core formation (Mizuno, 1980; Pollack et al., 1996). They also suggest that solar composition icy planetesimals (SCIPs) brought the heavy elements to Jupiter. The Jupiter value of D/H appears to be representative of the protosolar value, while the D/H enrichment observed on Uranus and Neptune is consistent with the formation scenario of these planets. The ¹⁵N/¹⁴N measurement in Jupiter seems to be representative of its protosolar value. Future measurements are expected to come from the Cassini and Herschel space mission, as well as the ALMA submillimeter observatory. This revised version was published online in August 2006 with corrections to the Cover Date.     

Induction machine based flywheel energy storage system

This study introduces a field oriented controlled (FOC) induction machine based flywheel energy storage (FES) system fed from a 20 kHz high frequency (HF) ac link and pulse density modulated (PDM) Converter. The feasibility of FES system is investigated both in software and hardware and is demonstrated successfully in both cases. The investigated system offers a good potential as a temporary energy storage system for various applications from automobile industry to aerospace applications.     

Venus lightning

Although it is not unanimously accepted, many independent observations lead to the conclusion that lightning is prevalent on Venus. The electromagnetic signals detected by all 4 Venera landers are most readily explained as generation by lightning. The Venera 9 spectrometer appears to have observed a lightning storm on one occasion. The Pioneer Venus plasma wave instrument detects waves both below the electron gyrofrequency that may be due to lightning and signals above the electron gyrofrequency but at very low altitudes that may be due to the near field of the lightning. The VLF observations suggest that Venus lightning must be an intra-cloud phenomenon which is most frequent in the afternoon and evening sector. The occurrence rate is likely to be greater than on Earth.