Return to Europa: Overview of the Jupiter Europa orbiter mission

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.     

Compact frequency standard using atoms trapped on a chip

We present a compact atomic frequency standard based on the interrogation of magnetically trapped ⁸⁷Rb atoms. Two photons, in the microwave and radiofrequency domain excite the atomic transition. At a magnetic field of 3.23 G this transition from ∣F = 1, m_F = −1〉 to ∣F = 2, m_F = 1〉 is 1st order insensitive to magnetic field variations. Long Ramsey interrogation times can thus be achieved, leading to a projected stability in the low 10⁻¹³ at 1 s. This makes this device a viable alternative to LITE and HORACE as a good candidate for replacing or complementing the rubidium frequency standards and passive hydrogen masers already on board of the GPS, GLONASS, and GALILEO satellites. Here we present preliminary results. We use an atom chip to cool and trap the atoms. A coplanar waveguide is integrated to the chip to carry the Ramsey interrogation signal, making the physics package potentially as small as (5 cm)³. We describe the experimental apparatus and show preliminary Ramsey fringes of 1.25 Hz linewidth. We also show a preliminary frequency stability σ_y = 1.5 × 10⁻¹²τ^−1/2 for 10 < τ < 10³ s. This represents one order of magnitude improvement with respect to previous experiments.     

Does the endolymph pass through the base of the cupula?

Whether the endolymph of the semicircular canal passes the cupular partition or not was examined using the lateral semicircular canal system of adult pigeons (Columba livia). By applying various pressures by means of injection of a dye solution through the membranous canal, it was found that the dye solution, was seen to pass the cupula even under very low pressures when the pressure was increased gradually. When pulled by a magnet, the ultrafine particles of the dextran magnetite contained in the injected fluid were found to pass through the subcupular space without evident increase of the ampullary pressure.     

Strategies for telecommunications and navigation in support of Mars exploration

The planned exploration of Mars will pose new and unique telecommunications and navigation challenges. The full range of orbital, atmospheric, and surface exploration will drive requirements on data return, energy-efficient communications, connectivity, and positioning. In this paper we will summarize the needs of the currently planned Mars exploration mission set, outline design trades and options for meeting these needs, and quantify the specific telecommunications and navigation capabilities of an evolving infrastructure.     

On ULF Signatures of Lightning Discharges

Recent works on magnetic signatures due to distant lightning discharges are reviewed. Emphasis is laid on magnetic signatures in the ULF range (in the old definition from less than 1 mHz up to 1 Hz), that is in the frequency range below the Schumann resonance. These signatures are known to be of importance for the excitation of the ionospheric Alfvén resonator (IAR) which works only at night time conditions. This emphasizes the difference between night and day time ULF signatures of lightning. The IAR forms a link between the atmosphere and magnetosphere. Similarities and differences of this link in the VLF (Trimpi effect) and ULF range are worked out. A search for a unique signature of sprite-associated positive cloud-to-ground (⁺CG) lightning discharges ended with a negative result. In this context, however, a new model of lightning-associated induced mesospheric currents was built. Depending on mesospheric condition it can produce magnetic signatures in the entire frequency range from VLF, ELF to ULF. In the latter case it can explain signatures known as the Ultra Slow Tail of ⁺CG lightning discharges. A current problem on the magnetic background noise intensity has been solved by taking more seriously the contribution of ⁺CG lightning discharges to the overall background noise. Their low occurrence rate is more than compensated by their large and long lasting continuing currents. By superposed epoch analysis it could be shown that the ULF response to ^?CG is one to two orders smaller that in case of ⁺CG with similar peak current values of the return stroke.     

Mercury Ion Analyzer (MIA) onboard Mercury Magnetospheric Orbiter: MMO

The Mercury Magnetopsheric Orbiter (MMO) is one of the spacecraft of the BepiColombo mission; the mission is scheduled for launch in 2014 and plans to revisit Mercury with modern instrumentation. MMO is to elucidate the detailed plasma structure and dynamics around Mercury, one of the least-explored planets in our solar system. The Mercury Plasma Particle Experiment (MPPE) on board MMO is a comprehensive instrument package for plasma, high-energy particle, and energetic neutral particle atom measurements. The Mercury Ion Analyzer (MIA) is one of the plasma instruments of MPPE, and measures the three dimensional velocity distribution of low-energy ions (from 5 eV to 30 keV) by using a top-hat electrostatic analyzer for half a spin period (2 s). By combining both the mechanical and electrical sensitivity controls, MIA has a wide dynamic range of count rates for the proton flux expected around Mercury, which ranges from 10⁶ to 10¹² cm⁻² s⁻¹ str⁻¹ keV⁻¹, in the solar wind between 0.3 and 0.47 AU from the sun, and in both the hot and cold plasma sheet of Mercury’s magnetosphere. The geometrical factor of MIA is variable, ranging from 1.0 × 10⁻⁷ cm² str keV/keV for large fluxes of solar wind ions to 4.7 × 10⁻⁴ cm² str keV/keV for small fluxes of magnetospheric ions. The entrance grid used for the mechanical sensitivity control of incident ions also work to significantly reduce the contamination of solar UV radiation, whose intensity is about 10 times larger than that around Earth’s orbit.     

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.