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.     

Determination of <Emphasis Type="Italic">Foton M-2</Emphasis> satellite attitude motion by the data of microacceleration measurements

The results of reconstruction of uncontrolled attitude motion of the Foton M-2 satellite using measurements with the accelerometer TAS-3 are presented. The attitude motion of this satellite has been previously determined by the measurement data of the Earth’s magnetic field and the angular velocity. The TAS-3 data for this purpose are used for the first time. These data contain a well-pronounced additional component which made impossible their direct employment for the reconstruction of the attitude motion and whose origin was unknown several years ago. Later it has become known that the additional component is caused by the influence of the Earth’s magnetic field. The disclosure of this fact allowed us to take into account a necessary correction in processing of TAS-3 data and to use them for the reconstruction of the attitude motion of Foton M-2. Here, a modified method of processing TAS-3 data is described, as well as results of its testing and employing. The testing consisted in the direct comparison of the motion reconstructed by the new method with the motion constructed by the magnetic measurements. The new method allowed us to find the actual motion of Foton M-2 in the period June 9, 2005–June 14, 2005, when no magnetic measurements were carried out.     

Autonomous navigation of formation flying spacecrafts in deep space exploration and communication by hybrid navigation utilizing neural network filter

Autonomous navigation of spacecrafts is a difficult task, however, which is a must in future deep space exploration. With multiple spacecrafts flying in space, this aim can be achieved by formation flying spacecraft (FFS) utilizing inverse time difference of arrival (ITDOA) and inverse difference Doppler (IDD) methods, which can locate the position of earth-station from one-way uplink signals in the FFS coordinate, and by way of conversion of coordinates, the position of FFS is achieved in earth-centered earth-fixed (ECEF) coordinate. The ability of neural network (NN) filter in navigation to extract position of spacecrafts from random measuring noise of signal arrival time and Doppler shift is studied with different radius of FFS and surveying parameters. The NN filter used by spacecraft group is new way of unidirectional autonomous navigation and is of high precision of hybrid navigation.     

Doppler observations of infrasonic waves of meteorological origin at ionospheric heights

Ionospheric effects of meteorological origin observed by the continuous HF Doppler sounder over the Czech Republic are reported in this paper. We focused on detection of waves of periods 1–10 min. We discuss the influence of dynamics and intensity of active weather systems on the occurrence of short period waves and dependence of the observed ionospheric effects on the height of reflection of the sounding radio wave. We observed 3–5 min waves during a severe weather event in summer and 2.5–4 min waves during a severe weather event in winter. We excluded possible geomagnetic origin of these oscillations by the analysis of fluctuations of the local geomagnetic field. In eight cases of 10, wave activity in the analysed period range was not significantly increased comparing to quiet days. The intensity of weather systems as well as the location of potential sources of waves towards the points of HF Doppler shift observation influence significantly the occurrence of infrasonic waves in the ionosphere. The results in Central Europe differ considerably from those previously obtained in North America. As a possible reason, we discuss different intensity and dynamics of weather systems in both regions.     

Identification of sources of Pc1 geomagnetic pulsations on the basis of proton aurora observations

The relationship between proton aurora and geomagnetic pulsations Pc1, which are an indicator of development of ion-cyclotron instability in the equatorial magnetosphere, are studied on the basis of the observations of proton aurora from the IMAGE satellite, observations of particle fluxes onboard the low-orbiting NOAA satellites, and geomagnetic pulsation observations at the Lovozero observatory. A conclusion is drawn that the subauroral spots in the proton emission projected into the magnetosphere near the plasmapause are two-dimensional images at the ionospheric “screen” of the region of intense scattering of energetic protons into the loss cone at the development of an ion-cyclotron instability.     

Alfven modes of solar coronal magnetic arches: Excitation of ballooning instability and modulation of flare emission

The effect of Alfven-type oscillations in a coronal magnetic arch on modulation of the gyrosynchrotron radiation and development of the ballooning instability in the arch is considered. On the basis of the energy method and the method of normal modes, the expressions are obtained for increments of ballooning instability at its swinging by natural oscillations of the arch. The conclusion is drawn that bending oscillations, which do not actually compress the plasma and, therefore, represent the Alfven-type modes, unlike the radial oscillations, are capable, under solar corona conditions, to effectively swing ballooning instability and, as a consequence, play a part of a trigger for solar flares. The ballooning instability of coronal arches is shown to be capable of causing formation of helmet-shaped structures in the lower solar corona. On the basis of calculations of the intensity modulation depth and the degree of circular polarization of non-thermal gyrosynchrotron radiation, under the assumption of excited Alfven oscillations of a coronal arch, the conclusion is drawn, that microwave observations at a frequency of > 10 GHz can be used for studying the conditions of excitation and propagation of Alfven modes in flare loops. The consequences of obtained results are discussed using the flare on April 15, 2002 as an example.     

An analysis of low-frequency component in microacceleration measurements made onboard the <Emphasis Type="Italic">Foton M-2</Emphasis> satellite

The low-frequency component is investigated in the data of measurements performed onboard the Foton M-2 satellite with the three-component accelerometer TAS-3. Investigations consisted in comparison of this component with its calculated analog found from a reconstruction of the satellite’s attitude motion. The influence of the Earth’s magnetic field on the accelerometer readings is discovered by way of spectral analysis of the functions representing the results of determining the low-frequency microacceleration by two methods. After making correction for this influence, the results obtained by these two methods coincided within a root-mean-square error of less than 10^?6 m/s².     

HIRDES – The High-Resolution Double-Echelle Spectrograph for the World Space Observatory Ultraviolet (WSO/UV)

The World Space Observatory Ultraviolet (WSO/UV) is a multi-national project grown out of the needs of the astronomical community to have future access to the UV range. WSO/UV consists of a single UV telescope with a primary mirror of 1.7 m diameter feeding the UV spectrometer and UV imagers. The spectrometer comprises three different spectrographs, two high-resolution echelle spectrographs (the High-Resolution Double-Echelle Spectrograph, HIRDES) and a low-dispersion long-slit instrument. Within HIRDES the 102–310 nm spectral band is split to feed two echelle spectrographs covering the UV range 174–310 nm and the vacuum-UV range 102–176 nm with high spectral resolution (R > 50,000). The technical concept is based on the heritage of two previous ORFEUS SPAS missions. The phase-B1 development activities are described in this paper considering performance aspects, design drivers, related trade-offs (mechanical concepts, material selection etc.) and a critical functional and environmental test verification approach. The current state of other WSO/UV scientific instruments (imagers) is also described.     

Electric currents from thunderstorms to the ionosphere during a solar cycle: Quasi-static modeling of the coupling mechanism

Conduction and displacement currents, and their sum the Maxwell current, generated over a thunderstorm (TS) with recurrent lightning discharges are investigated theoretically. The aim is to study better the influence of different factors on these currents, which form the link between thunderstorms and the ionosphere in the global atmospheric electrical circuit. The factors studied concern the thunderstorm characteristics (the charge separation current, and the lightning discharge parameters), as well as the atmospheric and cloud conductivity. Some of these factors may show long-term changes with the 11-year solar cycle, possibly realized through an inverse dependence of the cosmic ray flux on solar activity. Earlier investigations have suggested that the lightning-related charge redistribution and subsequent relaxation, rather than the high intensity current, is mainly the source of the energy coupled to the ionosphere. With respect to this, a quasi-electrostatic analytical model is proposed, based on Maxwell’s equations. The currents are generated by a TS modeled as a positive vertical dipole with charges which are first accumulated and then destroyed by lightning. Our computations show that the mean and peak values of the conduction and total Maxwell currents to the ionosphere depend significantly on the charge moment change. The mean currents are also sensitive to the reduction of the conductivity in thunderclouds. Small variations of the stratospheric conductivity (20% at geomagnetic latitude 40° and 40–50% at 55°) with the solar activity do not influence the currents to the ionosphere very much.     

Host–parasite interactions in closed and open microbial cultivation system

The study addresses interaction of bacteria and phages in the host–parasite system in batch and continuous cultures. The study system consists of the auxotrophic strain of Brevibacterium – Brevibacterium sp. 22L – and the bacteriophage of Brevibacterium sp., isolated from the soil by the enrichment method.

1.

Closed system. In the investigation of the relationship between the time of bacterial lysis and multiplicity of phage infection it has been found that at a lower phage amount per cell it takes a longer time for the lysis of the culture to become discernible. Another important factor determining cytolysis in liquid medium is the physiological state of bacterial population. Specific growth rate of bacteria at the moment of phage infection has been chosen as an indicator of the physiological state of bacteria. It has been shown that the shortest latent period and the largest output of the phage are observed during the logarithmic growth phase of bacteria grown under favorable nutrient conditions. In the stationary phase, bacterial cells become “a bad host” for the phage, whose reproduction rate decreases, and the lysis either slows down significantly or does not occur at all.