Communication, Localization and Synchronization of Spacecraft for Swarm Missions

Swarm missions are based on the use of several spacecraft working together to pursue a specific task for a specific mission. To allow these elements to work together, it is necessary for them to be able to communicate with each other and to synchronize themselves within the swarm. Moreover, the mission may likely require knowing the relative or absolute positions of the spacecraft in the swarm. In order to collect simultaneous measurements allowing computing localization and synchronization in the swarm, a full duplex CDMA communication method is studied by CNES. An Inter Satellite Link (ISL) transmitter prototype is currently under development and first performance evaluation is conducted. CNES is also working on measurement signal processing. Based on signal exchange between satellites, one can estimate jointly the distance and clock offset between a pair of satellites. In parallel, CNES is developing a swarm simulator implying both dynamics and functional behavior of each spacecraft in the swarm. First, this simulator will be software only but its architecture will allow integration of hardware equipment in a future version. This simulator will be used for the validation of the services provided by the link at a system level

The Athena X-ray Integral Field Unit (X-IFU)

The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray spectrometer of the ESA Athena X-ray observatory. Over a field of view of 5' equivalent diameter, it will deliver X-ray spectra from 0.2 to 12 keV with a spectral resolution of 2.5 eV up to 7 keV on similar to 5 '' pixels. The X-IFU is based on a large format array of super-conducting molybdenum-gold Transition Edge Sensors cooled at similar to 90 mK, each coupled with an absorber made of gold and bismuth with a pitch of 249 mu m. A cryogenic anti-coincidence detector located underneath the prime TES array enables the non X-ray background to be reduced. A bath temperature of similar to 50 mK is obtained by a series of mechanical coolers combining 15K Pulse Tubes, 4K and 2K Joule-Thomson coolers which pre-cool a sub Kelvin cooler made of a He-3 sorption cooler coupled with an Adiabatic Demagnetization Refrigerator. Frequency domain multiplexing enables to read out 40 pixels in one single channel. A photon interacting with an absorber leads to a current pulse, amplified by the readout electronics and whose shape is reconstructed on board to recover its energy with high accuracy. The defocusing capability offered by the Athena movable mirror assembly enables the X-IFU to observe the brightest X-ray sources of the sky (up to Crab-like intensities) by spreading the telescope point spread function over hundreds of pixels. Thus the X-IFU delivers low pile-up, high throughput (> 50%), and typically 10 eV spectral resolution at 1 Crab intensities, i.e. a factor of 10 or more better than Silicon based X-ray detectors. In this paper, the current X-IFU baseline is presented, together with an assessment of its anticipated performance in terms of spectral resolution, background, and count rate capability. The X-IFU baseline configuration will be subject to a preliminary requirement review that is scheduled at the end of 2018. The X-IFU will be provided by an international consortium led by France, the Netherlands and Italy, with further ESA member state contributions from Belgium, Czech Republic, Finland, Germany, Ireland, Poland, Spain, Switzerland and contributions from Japan and the United States.Peer reviewe

Maires de la Gironde de la Révolution à la Restauration

À l’occasion du bicentenaire de la Révolution française et de la loi municipale de décembre 1789 instituant les communes et les maires, le CESURB-Histoire a lancé une enquête sur “les maires du Sud-Ouest depuis la Révolution". Cet ouvrage présente les résultats d’une première étape de la recherche, consacrée aux chefs-lieux de cantons du département de la Gironde et à la période 1790-1824. L’enquête menée selon la méthode de la prosopographie a poursuivi un triple objectif : dresser le portrait type des hommes qui ont exercé le pouvoir municipal ; mesurer pour les élites locales les continuités et les ruptures au cours d’une époque troublée, entre la Révolution et la Restauration ; tenter d'apprécier l’originalité des maires de Gironde dans l’ensemble national La synthèse montre l'absence de changement brutal magré la diversité des régimes politiques et des modes de recrutement. Les évolutions les plus sensibles sont liées aux renouvellements les plus forts, en 1792 et en 1824. L’originalité des maires girondins se manifeste surtout pour la période révolutionnaire

Simulation and Validation Strategy on Real-Time Autocoded Onboard Software for Formation Flying In-Orbit Ranging Demonstration

International audienceThis article gives an overview of the simulation and validation strategy used for a real- time onboard software (OBSW) module developed on Matlab/Simulink® environment and autocoded into C language using the Real-Time Workshop Embedded Coder® (RTW). This module is the key point of the Formation Flying In-Orbit Ranging Demonstration (FFIORD) on PRISMA satellite mission. To respect requirements on real-time execution conditions and software reliability for space missions, the OBSW module is carefully tested before delivery and integration. Interesting results are obtained based on an inconstancies analysis of the C code produced by RTW, which leads to “good practice” guidelines for Simulink model implementation. Actions realised through this experiment aim at providing a background for the development of adequate Independent Verification and Validation (IV&V) procedures. They give more confidence and experience on the Model-Based Design domain before applying it to large scaled projects

Fair Network Division of Nano-satellite Swarms

International audienceWe address the problem of partitioning a network of nano-satellites to distribute fairly the network load under energy consumption constraints. The study takes place in a context where this swarm of nano-satellites orbits the Moon and works as, but not limited to, a distributed radio-telescope for low-frequency radio interferometry. During an interferometry mission, each nano-satellite collects observation data, then shares them with the other swarm members to compute a global image of space. However, the simultaneous transmission of large volumes of data can cause communication issues by overloading the radio channel, leading to potential packet loss. In this context, we investigate three division algorithms based on graph sampling techniques. We prove that random walk-based algorithms overall perform the best in terms of conservation of graph properties and fairness for group sizes down to 10% of the original graph

On the Network Characterization of Nano-Satellite Swarms

International audienceLow-frequency radio interferometry is crucial to understanding the universe and its very early days. Unfortunately, most of the current instruments are ground-based and thus impacted by the interferences massively produced by the Earth. To alleviate this issue, scientific missions aim at using Moonorbiting nano-satellite swarms as distributed radio-telescopes in outer space, keeping them out of Earth interference range. However, swarms of nano-satellites are systems with complex dynamics and need to be appropriately characterized to achieve their scientific mission. This paper presents a methodology based on graph theory for characterizing the swarm network system by computing graph theory metrics around three properties: the node density, network connectivity and ISL availability. We show that these properties are well-suited for highlighting a possible heterogeneity in a network and adapt a routing strategy accordingly. This work is the first milestone in defining the best-suited routing strategy within the swarm from the derived network properties

Simulation and Validation Strategy on Real-Time Autocoded Onboard Software for Formation Flying In-Orbit Ranging Demonstration

International audienceThis article gives an overview of the simulation and validation strategy used for a real- time onboard software (OBSW) module developed on Matlab/Simulink® environment and autocoded into C language using the Real-Time Workshop Embedded Coder® (RTW). This module is the key point of the Formation Flying In-Orbit Ranging Demonstration (FFIORD) on PRISMA satellite mission. To respect requirements on real-time execution conditions and software reliability for space missions, the OBSW module is carefully tested before delivery and integration. Interesting results are obtained based on an inconstancies analysis of the C code produced by RTW, which leads to “good practice” guidelines for Simulink model implementation. Actions realised through this experiment aim at providing a background for the development of adequate Independent Verification and Validation (IV&V) procedures. They give more confidence and experience on the Model-Based Design domain before applying it to large scaled projects

Development of an enzyme-linked immunosorbent assay for goldfish gonadotropin

An enzyme-linked immwzosorbent assay (ELISA) for goldfish gonadotropin (GTH) was developed with the intent of devising a simple, reliable and non radioisotopic assay for the measurement of GTH in goldfish biological samples. In this assay, soluble GTH of the standards or samples competes with carp GTH (cGTH) immobilized on a solid support (96-well microplate) for the fixation on antibodies to the β-subunit of carp gonadotropin. The immobilized antigen-antibody complexes are then revealed by the peroxidase-antiperoxidase (PAP) technique. After revelation of the peroxidase activity, the absorbance value of each well is measured with a microplate reader. The cGTH concentration used for coating the wells is 2 ng/ml and the final dilution of the specific antibody is 1:80,000. The assay can be performed within 24 h and can be used over a range of 0.125-4 ng/ml. At about 50% binding, the intra- and interassay coefficients of variation are 5% and 9% respectively. The displacement cur.’es generated by goldfish plasma or pituitary perifusion fractions were strictly parallel to the standard cGTH. In addition, the stimulation by salmon gonadotropin releasing hormone of pituitary fractions perjfused in vitro caused an immediate increase in the GTH measured in the collected fractions, strongly reinforcing the assumption that this assay indeed measures GTH

Soil N2O, CH4, and CO2 Fluxes in Forest, Grassland, and Tillage/No-Tillage Croplands in French Guiana (Amazonia)

International audienceThe agricultural landscape of French Guiana (Amazonia) is expected to undergo substantial change as a result of rapid population growth in the region. Such changes in the landscape will lead to the conversion of tropical forests into land destined for agricultural use. Little information is available on the effect of different agricultural systems on greenhouse gas (GHG) emissions in French Guiana. For our experiment, two hectares of forest were cleared, without the use of fire, at the Combi experimental site (sandy-clayey Ferralsol) at the end of 2008. After one year with legume and grass cover, the site was modified to include the following three fertilized agricultural systems: (1) Grassland (Brachiaria ruziziensis, mowed), (2) cropland (maize/soybean rotation) with disc tillage, and (3) cropland (maize/soybean rotation) with no-tillage in direct seeding. Soil N2O, CH4, and CO2 fluxes were measured with dark chambers from May 2011 to November 2014. Our results show that grassland was a significantly lower emitter of N2O but a significantly higher emitter of CH4 compared to the two cropland systems studied. We did not observe significant differences between the two cropland systems for N2O and CH4 fluxes. Measurements of the net ecosystem CO2 exchange would be useful to better compare the role of different agricultural systems as a source of GHGs