GNC of a cargo spacecraft for on-orbit servicing of Herschel at L2

t is anticipated that space exploration will need to rely on In Situ Resource Utilization (ISRU) in order toextend spacecraft lifetime and/or reduce the missions cost and/or the cruise time. For the Moon and, inthe future, Mars colonization, relying on in-situ resources is a necessary step to become independent fromthe Earth. The possibility to produce resources on the Moon is advantageous for those missions that aretoo far from the Earth to be resupplied. At the SnT Research Centre, the Luxembourg Space Agency issupporting a feasibility study to assess the benefit of on-orbit servicing (OOS), exploiting lunar resourcesfor the Herschel Space Observatory. Herschel ended its operations in 2013 as a consequence of the depletionof its coolant and, in turn, of the capability of cooling down its instruments. To extend its operations,a resupply mission has been envisaged relying on an adapted cargo spacecraft employed in lunar gatewayoperations. This paper deals with the trajectory design and optimization of the cargo on its journey from theMoon to rendezvous with Herschel and with orbit and attitude control. Considering Herschel’s orientationon its orbit, with the sunshield in the direction of the Sun and the need to access to Herschel’s rear panelto perform the resupply operation, a final approach along the negative x-axis, where the primaries lie, isconsidered. A multiple shooting technique is used to perform a flanking manoeuvre. Moreover, an attitudecontrol algorithm is adopted to track the attitude trajectory provided by the guidance algorithms which, inturn, ensure minimum thrusting errors of the cargo spacecraft and a continuous visibility of Herschel. Infuture works, different perturbations will be considered and angular rates induced by the movement of therobotic arms will be compensate

Spectrum of bound fermion states on vortices in 3^3He-B

We study subgap spectra of fermions localized within vortex cores in $^3$He-B. We develop an analytical treatment of the low-energy states and consider the characteristic properties of fermion spectra for different types of vortices. Due to the removed spin degeneracy the spectra of all singly quantized vortices consist of two different anomalous branches crossing the Fermi level. For singular $o$ and $u$ vortices the anomalous branches are similar to the standard Caroli-de Gennes -Matricon ones and intersect the Fermi level at zero angular momentum yet with different slopes corresponding to different spin states. On the contrary the spectral branches of nonsingular vortices intersect the Fermi level at finite angular momenta which leads to the appearance of a large number of zero modes, i.e. energy states at the Fermi level. Considering the $v$, $w$ and $uvw$ vortices with superfluid cores we show that the number of zero modes is proportional to the size of the vortex core.Comment: 6 pages, 1 figur

Statistics of Sunyaev-Zel'dovich Cluster Surveys

We describe a detailed analytic model for predicting statistical quantities (such as number counts, redshift distributions and sizes) of clusters detected in blank-field, thermal Sunyaev-Zel'dovich effect experiments. We include in this model the possibility of non-Gaussian density perturbations in the early Universe and also describe a simple model for the effects of preheating on cluster Sunyaev-Zel'dovich effect fluxes. We use this model to explore the current state of the theoretical uncertainties present in this type of analytic modelling, highlighting where further improvement will be necessary to fully exploit forthcoming surveys. We then go on to explore the constraints on cosmological parameters, the presence of any non-Gaussianity and the degree of cluster preheating which may be obtained from both the BOLOCAM and PLANCK experiments. We find that, providing redshifts can be measured for all detected clusters, the BOLOCAM experiment may provide detections of non-Gaussianity or preheating and could give approximate measurements of these effects if prior knowledge of the various cosmological parameters is taken into account. The PLANCK experiment Sunyaev-Zel'dovich effect cluster survey is predicted to provide highly accurate (~5%) measurements of the degree of non-Gaussianity and preheating while also providing measurements of several cosmological parameters to accuracies of a few percent independent from those constraints that will be derived from its detections of primordial cosmic microwave background anisotropies.Comment: 15 pages, 13 figures, submitted to MNRA

Planck pre-launch status : The Planck-LFI programme

Peer reviewe

Planck early results I : The Planck mission

Peer reviewe

Planck pre-launch status : The Planck mission

Peer reviewe

Influence of Binary Polymer Mixtures on the Nonlinear Growth Regimes of Polyelectrolyte Multilayer Films

We report on ellipsometric studies of the nonlinear growth regimes of electrostatically assembled polyelectrolyte multilayer films under <i>in situ</i> conditions. Poly­(styrenesulfonate) (PSS) and poly­(diallyl­methyl­ammonium) (PDADMA) with different molecular weights in 0.1 mol/L NaCl are used. Always, the linear growth is preceded by a parabolic growth regime. For films made from binary PDADMA mixtures, the compositions in the film and the adsorption solution are nearly identical. To explain these findings, a molecular model that describes the parabolic growth quantitatively is introduced. Neutron reflectivity of films prepared from PSS molecular weight above a threshold, >25 kDa, shows that its center of mass is vertically immobile, in both the parabolic and linear growth regimes. Below 25 kDa, the multilayer buildup starts with an exponential growth regime, and pronounced PSS interdiffusion is found with neutron reflectivity. The exponential buildup regime is extended on decrease of PSS molecular weight. For films made from binary PSS mixtures, addition of less than 1 mol % PSS with molecular weight above the threshold, 25 kDa, prevents the formation of an exponential growth regime and addition of 10 mol % suppresses the influence of low molecular weight PSS on film buildup

Branched Poly ethylenimine as Barrier Layer for Polyelectrolyte Diffusion in Multilayer Films

Linearly assembled polyelectrolyte multilayers (PEMs) are prepared by sequential adsorption of polyanions and polycations from 0.1 mol/L NaCl. The internal structure of PEMs is investigated with neutron reflectivity. The films are made from poly­(ethylenimine) (PEI), poly­(diallyl­dimethyl­ammonium) (PDADMA) and poly­(styrene­sulfonate) (PSS or deuterated PSS-d). Each film consists of a protonated and a deuterated block, built from <i>m</i> protonated and <i>n</i> deuterated polycation/polyanion layer pairs, respectively. Annealing in salt solution (1 mol/L NaCl) allows the polyelectrolytes to gain entropy by adopting a more coiled conformation and by intermixing. During annealing the internal interface between the two blocks broadens due to interdiffusion; thus, the PSS diffusion coefficient is measured. Eventually the annealing leads to a uniform distribution of protonated and deuterated PSS throughout the film. Yet, if one polycation layer in the film center is branched PEI, then this PEI layer serves as a diffusion barrier, which is impenetrable for up to 33% of PSS macromolecules. The equilibration time of the remaining mobile PSS fraction increases which is attributed to the low permeation rate through the barrier layer. Possibly, some PSS molecules have a conformation that hinders them to cross the barrier layer, or the barrier layer gets clogged with time

Exploring Prime-Boost Vaccination Regimens with Different H1N1 Swine Influenza A Virus Strains and Vaccine Platforms

In a previous vaccination study in pigs, heterologous prime-boost vaccination with whole-inactivated H1N1 virus vaccines (WIV) induced superior antibody responses and protection compared to homologous prime-boost vaccination. However, no pan-H1 antibody response was induced. Therefore, to stimulate both local and systemic immune responses, we first vaccinated pigs intranasally with a pseudorabies vector vaccine expressing the pH1N1 hemagglutinin (prvCA09) followed by a homologous or heterologous WIV booster vaccine. Homologous and heterologous WIV&ndash;WIV vaccinated groups and mock-vaccinated or prvCA09 single-vaccinated pigs served as control groups. Five weeks after the second vaccination, pigs were challenged with a homologous pH1N1 or one of two heterologous H1N2 swine influenza A virus strains. A single prvCA09 vaccination resulted in complete protection against homologous challenge, and vector&ndash;WIV vaccinated groups were significantly better protected against heterologous challenge compared to the challenge control group or WIV&ndash;WIV vaccinated groups. Furthermore, vector&ndash;WIV vaccination resulted in broader hemagglutination inhibition antibody responses compared to WIV&ndash;WIV vaccination and higher numbers of antibody-secreting cells in peripheral blood, draining lymph nodes and nasal mucosa. However, even though vector&ndash;WIV vaccination induced stronger antibody responses and protection, we still failed to induce a pan-H1 antibody response