Multiple Sun–Earth Saddle Point flybys for LISA Pathfinder

LISA Pathfinder is an ESA mission due to be launched in the next two years. The gravity gradiometer onboard has the sensitivity required to test predictions by gravitational theories proposed as alternatives to Dark Matter such as TeVeS. Within the Solar System measurable effects are predicted only in the vicinity of gravitational saddle points (SP). For this reason it has been proposed to fly LPF by the Earth–Sun SP, at some 259,000 km from Earth. This could be done in an extension to the nominal mission which uses a Lissajous orbit about the Earth–Sun L1 point. The responsibility for LPF mission design lies with ESA/ESOC, who have designed the transfer trajectories, orbits about L1, and station keeping strategies. This article describes an analysis performed by Astrium to support a suggestion for a possible mission extension to a saddle point crossing. With only very limited fuel availability, reaching the saddle point is a significant challenge. In this article, we present recent advances in the work on trajectory design. It is demonstrated that reaching the SP is feasible once the LPF mission is completed. Furthermore, in a significant enhancement, it is demonstrated that trajectories including more than one SP flyby are possible, thus improving the science return for this proposed mission extension.     

Saturn kilometric radiation as a monitor for the solar wind?

Since the Voyager mission it is known that Saturn Kilometric Radiation (SKR) is strongly influenced by external forces, i.e., the solar wind and in particular the solar wind ram pressure. Recent studies using Cassini data essentially confirmed these findings for particular periods during the first Cassini orbit of Saturn. The data coverage of SKR by the Cassini/RPWS experiment for the period of six months prior to Saturn Orbit Insertion (July 1, 2004) is rather continuous, whereas there are gaps in the solar wind plasma data. The strong correlation of SKR with the solar wind may provide an indication on the variations of the solar wind plasma, specifically during the gap periods. These periods lacking solar wind data are substituted by Ulysses solar wind data which have been propagated over ∼4 AU, applying magnetohydrodynamic propagation models. Cross correlation studies showed that Ulysses solar wind data can be taken as a substitute for missing Cassini data. The use of SKR as monitor for solar wind variations is discussed. With the present set of observations the SKR proxy lacks significant reliability.     

A search for optical flashes from the “Perseus Flasher”

We report the results of an extended search for short-timescale optical flashes from a four square-degree area centered on the coordinates of the Perseus Flasher, a phenomenon photographed by Katz, et al. /1/. The photographed optical flash was of brightness m_B = −1.7 and had a duration of roughly 0.5 s. In 70 hours of observation with the Explosive Transient Camera /2,3,4/ no celestial optical flashes were detected in the region of the Perseus Flasher to a limiting magnitude of 7.1 for a one-second flash. On 5 February 1986, simultaneous observations with the ETC and the EXOSAT satellite /16/ were carried out. Neither X-ray nor optical flashes were seen. A survey of archived photographic images of the Perseus Flasher revealed no optical transients in over 700 hours of total exposure time to a limiting magnitude of m_B ≅ 4–5 for a one-second flash /15/. Based on the ETC data base, we discuss possible terrestrial sources of optical flashes which might account for the phenomenon reported by Katz et al.     

Image Quality assessment for Chang＇E-1 IIM 2C Data

嫦娥一号干涉成像光谱仪（IIM）获取的多波段图像数据对于月表矿物成分反演具有重要意义.从目视质量、客观参数、几何配准精度、图像质量随时间的变化情况等方面对IIM 2C级的多波段图像数据质量进行了评价.结果显示,其两端波段范围的图像质量较差,不能有效识别月表单元,中间波段图像质量较好;自然色图像显示IIM数据存在明显的横向色调不均一性.利用图像的客观评价指标（辐射精度、清晰度、信息量）将干涉成像光谱仪图像数据与美国Clementine UV-VIS多光谱图像数据进行对比分析,结果表明,IIM数据清晰度好于ClementineUV-VIS,而在方差和信息量上弱于Clementine UV-VIS.将IIM图像数据与Clementine多光谱数据统一到相同的空间分辨率,进行配准精度评价,其最大控制点配准误差为0.63 pixel.此外,还对时间跨度两个月覆盖月表同一区域的IIM图像数据从辐射精度、信息量和清晰度方面进行了评价.     

Is there spectropolarimetric evidence for accretion disks in Active Galactic Nuclei?

A fundamental component of the Active Galactic Nuclei (AGN) paradigm is an accretion disk. However, the nature of this accretion disk is not well understood. In this paper I present the spectropolarimetric observations of active galactic nuclei (AGN) in the Lyman limit (912Å) region and discuss their implications in the context of accretion disks in AGN.     

Input Parameters for Models of Energetic Electrons Fluxes at the Geostationary Orbit

The results of cross-correlation analysis between electrons fluxes (with energies of > 0.6MeV, > 2.0 MeV and > 4.0MeV), geomagnetic indices and solar wind parameters are shown in the paper. It is determined that the electron fluxes are controlled not only by the geomagnetic indices, but also by the solar wind parameters, and the solar wind velocity demonstrates the best relation with the electron fluxes. Numerical value of the relation efficiency of external parameters with the highly energetic electrons fluxes shows a periodicity. It is presented here the preliminary results of daily averaged electrons fluxes forecast for a day ahead on the basis of the model of neuron networks.     

What is the threshold amount of starch necessary for full gravitropic sensitivity?

In preparation for microgravity experiments, we studied the kinetics of gravitropism in seedlings of wild-type (WT) Arabidopsis and three starch-deficient mutants. One of these mutants is starchless (ACG 21) while the other two are intermediate starch mutants (ACG 20 and ACG 27). In root cap cells, ACG 20 and 27 have 51% and 60% of the WT amount of starch, respectively. However, in endodermal cells of the hypocotyl, ACG 20 has a greater amount of starch than ACG 27. WT roots and hypocotyls were much more responsive to gravity than were the respective organs of the starchless mutant, and the intermediate starch mutants exhibited reduced gravitropism but had responses that were close to that of the WT. In roots, ACG 27 (more starch) was more responsive than ACG 20 (less starch), while in hypocotyls, ACG 20 (more starch) had a greater response than ACG 27 (less starch). Taken together, our data are consistent with the starch-statolith hypothesis for gravity perception in that the degree of graviresponsiveness is proportional to the total mass of plastids per cell. These results also suggest that (in roots) 51-60% starch is close to the threshold amount of starch needed for full gravitropism and that the gravity sensing system is "overbuilt."     

Meteoroid and Space Debris Risk Assessment for Satellites Orbiting the Earth/Moon

Interplanetary meteoroids and space debris can impact satellites orbiting the Earth or spacecraft traveling to the Moon. Targeting China Space Station(CSS), 7 satellites selected from the constellation of Beidou Navigation Satellite System Phase Ⅲ(BDS-3), and 3 spacecraft orbiting the Moon, we have adopted in the paper the Meteoroid Engineering Model 3, Divine-Staubach meteoroid environment model, and Jenniskens-Mc Bride meteoroid steam model to analyze the meteoroid environment with the mass ra...     

Wireless Sensor Networks – A potential tool to probe for water on Moon

A Wireless Sensor Network for in situ probing of lunar water/ice is proposed. The mission scenario in single and multi-tier architectures for probing water in a permanently shadowed region of the Moon and different scenarios of exploration are discussed. The ideas presented in the paper are a positive assertion of feasibility for the sensor node hardware, given current levels of technological advancements.     

Which solar EUV indices are best for reconstructing the solar EUV irradiance?

The solar EUV irradiance is of key importance for space weather. Most of the time, however, surrogate quantities such as EUV indices have to be used by lack of continuous and spectrally resolved measurements of the irradiance. The ability of such proxies to reproduce the irradiance from different solar atmospheric layers is usually investigated by comparing patterns of temporal correlations. We consider instead a statistical approach. The TIMED/SEE experiment, which has been continuously operating since February 2002, allows for the first time to compare in a statistical manner the EUV spectral irradiance to five EUV proxies: the sunspot number, the f10.7, Ca K, and Mg II indices, and the He I equivalent width.     

Formation control using μ-synthesis for Inner-Formation Gravity Measurement Satellite System

Inner-Formation Gravity Measurement Satellite System (IFGMSS) is used to map the gravity field of Earth. The IFGMSS consists of two satellites in which one is called “inner satellite” and the other one is named as “outer satellite”. To measure the pure Earth gravity, the inner satellite is located in the cavity of the outer satellite. Because of the shield effect of the cavity, the inner satellite is affected only by the gravitational force, so it can sense Earth gravity precisely. To avoid the collision between the inner satellite and the outer satellite, it is best to perform a real-time control on the outer satellite. In orbit, the mass of the outer satellite decreases with the consumption of its propellant. The orbit angular rate of the inner satellite varies with time due to various disturbing forces. These two parameters’ uncertainties make the C–W function be not so accurate to describe the formation behavior of these two satellites. Furthermore, the thrusters also have some uncertainties due to the unmodelled dynamics. To cancel the effects caused by the above uncertainties, we have studied the robust control method based on the μ-synthesis. This μ-synthesis eliminates the conservativeness and improves the control efficiency comparing with the H_∞ method. Finally, to test the control method, we simulate an IFGMSS mission in which the satellite runs in a sun synchronous circular orbit with an altitude of 300 km. The simulation results show the effectiveness of the robust control method. The performances of the closed-loop system with the μ-controller are tested by the μ-analysis. It has found that the nominal performance, the robust stability and the robust performance are all achieved. The transient simulation results further prove the control response is fast and the accuracy of the relative position meets the demand of the gravity measurement.     

Is the heliospheric interface submagnetosonic? Consequences for the LISM presence in the heliosphere

Based on our best knowledge of the physical parameters of the LISM, one comes to the conclusion that for the solar system a submagnetosonic configuration of the plasma interface between the LISM and the expanding solar wind plasma is established extending to some 1000 AU distance upwind from the sun. In this region with perturbed interstellar plasma conditions the LISM neutral flow directed towards the inner part of the heliosphere is substantially modulated due to charge exchange interaction processes with the ionized LISM component. Flow velocities, temperatures and densities showing up at the border of the inner solar system can thus not be taken as parameters characterizing the LISM conditions. This interface effect is highly variable for different LISM plasma conditions. The range of the most probable LISM parameters to be expected within this physical scenario is discussed.     

A 3—Axis stabilised balloon platform for use during day- and night-time flights

The Balloon Platform developed at the Rutherford Appleton Laboratory (R.A.L.) is being adapted to carry the ZEBRA telescope which requires an arc-minute day- and night- pointing capability. The basic features of the platform and the modifications necessary for the ZEBRA application are briefly described. The new inertial stabilisation system uses 3-axis rate integrating gyros. Problems relating to gyro drifts and the methods of drift compensation to achieve the required pointing accuracy are discussed. The paper concludes by outlining the proposed strategy for setting up the control system in flight.     

Soybean cultivar selection for Bioregenerative Life Support Systems (BLSSs) – Hydroponic cultivation

Four soybean cultivars (‘Atlantic’, ‘Cresir’, ‘Pr91m10’ and ‘Regir’), selected through a theoretical procedure as suitable for cultivation in BLSS, were evaluated in terms of growth and production. Germination percentage and Mean Germination Time (MGT) were measured. Plants were cultivated in a growth chamber equipped with a recirculating hydroponic system (Nutrient Film Technique). Cultivation was performed under controlled environmental conditions (12 h photoperiod, light intensity 350 μmol m⁻² s⁻¹, temperature regime 26/20 °C light/dark, relative humidity 65–75%). Fertigation was performed with a standard Hoagland solution, modified for soybean specific requirements, and EC and pH were kept at 2.0 dS m⁻¹ and 5.5 respectively.     

Passepartout Sherpa – A low-cost,reusable transportation system into the stratosphere for small experiments

The Passepartout sounding balloon transportation system for low-mass (<$<$1200 g) experiments or hardware for validation to an altitude of 35 km is described. We present the general flight configuration, set-up of the flight control system, environmental and position sensors, power system, buoyancy considerations as well as the ground control infrastructure including recovery operations. In the telemetry and command module the integrated airborne computer is able to control the experiment, transmit telemetry and environmental data and allows for a duplex communication to a control centre for tele-commanding. The experiment module is mounted below the telemetry and command module and can either work as a standalone system or be controlled by the airborne computer. This spacing between experiment- and control unit allows for a high flexibility in the experiment design. After a parachute landing, the on-board satellite based recovery subsystems allow for a rapid tracking and recovery of the telemetry and command module and the experiment. We discuss flight data and lessons learned from two representative flights with research payloads.     

Evidence for e−/e+ annihilation mechanism as an initial radiation process in gamma-ray bursts

An unusual spectrum has been obtained over 126 ms at the onset of the intense 1978 November 19 gamma-ray burst recorded by the Franco-Soviet Signe experiments. Evidence is presented for two distinct components above and below 200 keV : a soft emission with a possible low-energy cutoff and a peak around 400 keV with an accompanying high-energy tail. As this peak contains > 95 percent of the total fluence at this time, we suggest the role of the e⁻/e⁺ annihilation as an initial radiation process in gamma-ray bursts and we propose a possible interpretation of the high-energy tail.     

An Improved HVQ Algorithm for Compression and Rendering of Space Environment Volume Data with Multi-correlated Variables

Volume visualization can not only illustrate overall distribution but also inner structure and it is an important approach for space environment research. Space environment simulation can produce several correlated variables at the same time. However, existing compressed volume rendering methods only consider reducing the redundant information in a single volume of a specific variable, not dealing with the redundant information among these variables. For space environment volume data with multi-...     

Are Boltzmann plots of hydrogen Balmer lines a tool for identifying a subclass of S1 AGN?

It is becoming clear that we can define two different types of nearby AGN belonging to the Seyfert 1 class (S1), on the basis of the match of the intensities of their Broad Balmer Lines (BBL) with the Boltzmann Plots (BP). These two types of S1 galaxies, that we call BP-S1 and NoBP-S1, are characterized, in first approximation, by Broad Line Regions (BLR) with different structural and physical properties. In this communication, we show that these features can be well pointed out by a multi-wavelength analysis of the continuum and of the broad recombination Hydrogen lines, that we carry out on a sample of objects detected at optical and X-ray frequencies. The investigation is addressed to verify whether BP-S1 are the ideal candidates for the study of the kinematical and structural properties of the BLR, in order to derive reliable estimates of the mass of their central engine and to constrain the properties of their nuclear continuum spectrum.