The X/X/KA-band deep space transponder for the BepiColombo mission to mercury

This paper reports the main characteristics of the deep space transponder (DST) equipment that has been designed, developed and tested by Thales Alenia Space—Italy (TAS-I) for the European Space Agency (ESA) BepiColombo mission to Mercury.     

Lunar lander's three-dimensional translation and yaw rotation motion estimation during a descent phase using optical navigation

Optical navigation for a lunar lander consists of estimating a lander's 3-dimensional (3-D) relative dynamic motion with respect to a preselected landing site using a passive 2-dimensional (2-D) video image sequence. Lunar landing missions require a lander to perform an autonomous accurate landing with simple mechanical structure, easy operation and low cost. These requirements have motivated the need to develop an advanced navigation system. Existing navigation systems trade-off simplicity, accuracy and cost. High accuracy navigation systems typically imply complexity and high cost. In this paper, we consider a scenario where the descending phase starts from an initial altitude of 10 km with a time-of-descent of 100 s. The navigation camera is an off-the-shelf optical instrument used to take the video image sequence of the landing site during the landing phase. It is fed into the motion estimation algorithm to be processed. The continuous wavelet transform (CWT) is used to analyse each image frame of the input digital video image sequence. The output is a 2-D video image motion trajectory map, which represents the projection motion of the landing site. The 2-D video image motion is projected back to the 3-D lander's relative motion based on a geometric analysis. The outputs of this estimation algorithm are the 3-D attitude motion parameters of the lander at a time corresponding to an image being taken. The attitude determination and control system (ADCS) of the lander uses these data to perform the lander's attitude control task. In this article, we provide the motion modelling for a lunar lander during the descending phase. The projection of a 3-D planar to 2-D image plane is analysed which build the correspondence between the 3-D lander's motion and the 2-D image motion. This link provides the evidence for the geometry analysis. CWT is reviewed and CWT for video image sequence analysis is also introduced. Numerical simulation of the estimated 2-D video image sequence under the lander performing a 3-D translation and yaw rotation during the terminal descent are shown to verify the proposed concepts. The analysis of the results show that the proposed method achieves highly accurate 2-D video image motion estimation of less then 1% error with significant savings of cost, mass and volume. It leads to the accurate estimation of the lander's 3-D relative motion with respect to the landing site.     

Preservation of martian organic and environmental records: final report of the Mars biosignature working group

The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars. Orbital images confirm that layered rocks achieved kilometer-scale thicknesses in some regions of ancient Mars. Clearly, interplays of sedimentation and erosional processes govern present-day exposures, and our understanding of these processes is incomplete. MSL can document and evaluate patterns of stratigraphic development as well as the sources of layered materials and their subsequent diagenesis. It can also document other potential biosignature repositories such as hydrothermal environments. These capabilities offer an unprecedented opportunity to decipher key aspects of the environmental evolution of Mars' early surface and aspects of the diagenetic processes that have operated since that time. Considering the MSL instrument payload package, we identified the following classes of biosignatures as within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. Of these, biogenic organic molecules and biogenic atmospheric gases are considered the most definitive and most readily detectable by MSL.     

Deducing Electron Properties from Hard X-ray Observations

X-radiation from energetic electrons is the prime diagnostic of flare-accelerated electrons. The observed X-ray flux (and polarization state) is fundamentally a convolution of the cross-section for the hard X-ray emission process(es) in question with the electron distribution function, which is in turn a function of energy, direction, spatial location and time. To address the problems of particle propagation and acceleration one needs to infer as much information as possible on this electron distribution function, through a deconvolution of this fundamental relationship. This review presents recent progress toward this goal using spectroscopic, imaging and polarization measurements, primarily from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Previous conclusions regarding the energy, angular (pitch angle) and spatial distributions of energetic electrons in solar flares are critically reviewed. We discuss the role and the observational evidence of several radiation processes: free-free electron-ion, free-free electron-electron, free-bound electron-ion, photoelectric absorption and Compton backscatter (albedo), using both spectroscopic and imaging techniques. This unprecedented quality of data allows for the first time inference of the angular distributions of the X-ray-emitting electrons and improved model-independent inference of electron energy spectra and emission measures of thermal plasma. Moreover, imaging spectroscopy has revealed hitherto unknown details of solar flare morphology and detailed spectroscopy of coronal, footpoint and extended sources in flaring regions. Additional attempts to measure hard X-ray polarization were not sufficient to put constraints on the degree of anisotropy of electrons, but point to the importance of obtaining good quality polarization data in the future.     

Optical,ultraviolet, and infrared observations of isolated neutron stars

Forty years passed since the optical identification of the first isolated neutron star (INS), the Crab pulsar. 25 INSs have been now identified in the optical (O), near-ultraviolet (nUV), or near-infrared (nIR), hereafter UVOIR, including rotation-powered pulsars (RPPs), magnetars, and X-ray-dim INSs (XDINSs), while deep investigations have been carried out for compact central objects (CCOs), Rotating RAdio transients (RRATs), and high-magnetic field radio pulsars (HBRPs). In this review I describe the status of UVOIR observations of INSs, their emission properties, and I present the results from recent observations.     

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.     

Characteristics of field line resonance type geomagnetic pulsations and variations of plasmaspheric plasma density distribution

The period of field line resonance (FLR) type geomagnetic pulsations depends on the length of the field line and on the plasma density in the inner magnetosphere (plasmasphere), where field lines are closed. Here as FLR period, the period belonging to the maximum occurrence frequency of the occurrence frequency spectrum (equivalent resonance curve) of pulsations has been considered. The resonance system may be replaced by an equivalent resonant circuit. The plasma density would correspond to the ohmic load. The plasma in the plasmasphere originates from the ionosphere, thus FLR period, occurrence frequency are also affected by the maximum electron density in the ionosphere. The FLR period has shown an enhancement with increasing F region electron density, while the occurrence frequency indicated diminishing trend (possible damping effect). Thus, the increased plasma density may be the cause of the decreased occurrence of FLR type pulsations in the winter months of solar activity maximum years (winter anomaly).     

On the effect of considering more realistic particle shape and mass parameters in MMOD risk assessments

One of the primary mission risks tracked in the development of all spacecraft is that due to micro-meteoroids and orbital debris (MMOD). Both types of particles, especially those larger than 0.1 mm in diameter, contain sufficient kinetic energy due to their combined mass and velocities to cause serious damage to crew members and spacecraft. The process used to assess MMOD risk consists of three elements: environment, damage prediction, and damage tolerance. Orbital debris risk assessments for the Orion vehicle, as well as the Shuttle, Space Station and other satellites use ballistic limit equations (BLEs) that have been developed using high speed impact test data and results from numerical simulations that have used spherical projectiles. However, spheres are not expected to be a common shape for orbital debris; rather, orbital debris fragments might be better represented by other regular or irregular solids. In this paper we examine the general construction of NASA’s current orbital debris (OD) model, explore the potential variations in orbital debris mass and shape that are possible when using particle characteristic length to define particle size (instead of assuming spherical particles), and, considering specifically the Orion vehicle, perform an orbital debris risk sensitivity study taking into account variations in particle mass and shape as noted above. While the results of the work performed for this study are preliminary, they do show that continuing to use aluminum spheres in spacecraft risk assessments could result in an over-design of its MMOD protection systems. In such a case, the spacecraft could be heavier than needed, could cost more than needed, and could cost more to put into orbit than needed. The results obtained in this study also show the need to incorporate effects of mass and shape in mission risk assessment prior to first flight of any spacecraft as well as the need to continue to develop/refine BLEs so that they more accurately reflect the shape and material density variations inherent to the actual debris environment.     

Normalized ionization yield function for various nuclei obtained with full Monte Carlo simulations

Several recent results important for production of ion pairs in the Earth atmosphere by various primary cosmic ray nuclei are presented. The direct ionization by various primary cosmic ray nuclei is explicitly obtained. The longitudinal profile of atmospheric cascades is sensitive to the energy and mass (charge) of the primary particle. In this study different cosmic ray nuclei are considered as primaries, namely Helium, Oxygen and Iron nuclei. The cosmic ray induced ionization is obtained on the basis of CORSIKA 6.52 code simulations using FLUKA 2006 and QGSJET II hadronic interaction models. The energy of the primary particles is normalized to GeV per nucleon. In addition, the ionization yield function Y is normalized as ion pair production per nucleon. The obtained ionization yield functions Y for various primaries are compared. The presented results and their application are discussed.     

Ionization effect of solar protons in the Earth atmosphere – Case study of the 20 January 2005 SEP event

The cosmic ray ground level enhancement on January 20, 2005 is among the largest recorded events in the history of cosmic ray measurements. The solar protons of MeV energies cause an excess of ionization in the atmosphere, specifically over polar caps following major solar disturbances. The ionization effect in the Earth atmosphere is obtained for various latitudes on the basis of solar proton energy spectra, reconstructed from GOES 11 measurements and subsequent full Monte Carlo simulation of cosmic ray induced atmospheric cascade. The estimation of ionization rates is based on a numerical model for cosmic ray induced ionization. The evolution of atmospheric cascade is performed with the CORSIKA 6.52 code using FLUKA 2006b and QGSJET II hadron interaction models. The atmospheric ion rate ionization is explicitly obtained for 40°N, 60°N and 80°N latitudes. The time evolution of obtained ion rates is presented. It is demonstrated that ionization effect is negative for 40°N and small for 60°N, because of accompanying Forbush decrease. The ionization effect is significant only in sub-polar and polar atmosphere during the major ground level enhancement of 20 January 2005.