A two-impulse method for stabilizing the spacecraft relative motion with respect to a periodic trajectory

International audienceThe article presents an analytical method for computing a two-impulse control law that stabilizes the spacecraft relative motion with respect to an invariant set. The invariant set contains the states belonging to a desired periodic relative trajectory and is described using linear equations. The two impulses are computed analytically based on the prediction of the evolution of the relative trajectory. Closed-loop tests are conducted using the non-linear relative dynamics, for different eccentricities of the reference orbit and for different levels of navigation uncertainty. Encouraging results are obtained using a control strategy that requires very few computational effort

Minimizing the Effects of Navigation Uncertainties on the Spacecraft Rendezvous Precision

International audienceThe ability to robustly and precisely control the spacecraftrelative motion will play an important role in future on-orbitinspection and on-orbit servicing missions. Model predictivecontrol (MPC) is considered to be an effective control strategy forthese types of spacecraft operations, which can easily handle missionspecificconstraintswhileexplicitlyminimizingthefuelconsumption. The maneuvers plan is obtained by solving a finite horizon open-loop optimal control problem starting from the spacecraft relativestate, and the optimal solution consists of a series of control actions out of which only the first one is executed.Some ideas from tube-basedMPCare used in this Note to solve therobust fixed-time spacecraft rendezvous problem for eccentricreference orbits. The purpose is to obtain a sequence of feedbackpolicies that steers the spacecraft from an initial relative state towardan ellipsoidal set centered around a desired final state, in the presenceof navigation uncertainties. This must be done while respecting theactuators saturation constraints and while pursuing a doubleobjective: minimize the fuel cost of the mission and minimize the sizeof the arrival set to guarantee a good rendezvous precision. Thecontrol policies are restricted to affine disturbance feedback policiesto ensure a convex formulation of the control synthesis problem. Theobtained sequence of feedback policies drives the system to theguaranteed arrival set without any need for recurrent optimization

Designing Continuously Constrained Spacecraft Relative Trajectories for Proximity Operations

International audienceThis paper presents a new method for designing an optimal plan of impulsive maneuvers for spacecraft proximity operations. The proposed method accounts for the presence of linear continuous constraints on the spacecraft relative trajectory. Impulsive control and continuous constraints are brought together through the parameterization of the spacecraft relative trajectory between two consecutive maneuvers. This parameterization is used in order to develop a finite convex description of all the admissible trajectories. It enables the transformation of the continuous constraints on the spacecraft relative trajectory into a finite number of polynomial nonnegativity constraints. The resulting optimal control problem can be solved using semidefinite programming

Sécurisation passive du rendez-vous orbital par des polynômes non négatifs

International audienceLe sujet de cet article porte sur l'évitement de col- lision lors de manoeuvres de proximité pour le rendez-vous orbital. Il s'agit d'assurer la sécurité passive de la mission, en imposant au véhicule chasseur, en cas de panne, de res- ter sur une trajectoire périodique comprise dans un cˆone de visibilité de la cible. En s'appuyant sur les expressions ra- tionnelles du mouvement autonome périodique, nous trans- formons les contraintes de visibilité en contraintes de non- négativité de polynômes. Nous formulons ainsi le problème d'évitement de collision comme un problème d'optimisation polynomiale dont la solution garantit une satisfaction des contraintes continue dans le temps. Nous utilisons la pro- grammation semi-définie pour résoudre ce problème poly- nomial

Constrained periodic spacecraft relative motion using non-negative polynomials

International audienceA new method for obtaining constrained periodic relative motion between spacecraft on Keplerian orbits is presented. The periodic relative trajectory is required to evolve autonomously inside a tolerance box centered in a specified position. Unlike the classical time-sampling approaches, our method guarantees continuous satisfaction of the constraints on infinite horizon. This is done by reformulating the tolerance box constraints on the relative trajectory as conditions of non-negativity of some polynomials. The resulting problem is solved using semi-definite programming

Periodic H2 synthesis for spacecraft in elliptical orbits with atmospheric drag and J2 perturbations

International audienceThe problem of the stationkeeping for a small spacecraft is studied and a solution based on periodic feedback control laws is considered. Linearized equations of the relative motion of the satellite near an eccentric reference orbit are derived in the presence of the second zonal gravitational harmonic J2 and atmospheric drag perturbations. The obtained linear continuous-time model of the relative motion is T-periodic where T is the orbital period. After a discretization of the model, a state-feedback control law with performance requirement defined by the generalized H2 operator norm may be computed by a linear matrix inequality-based algorithm. Illustrative non linear simulations show the efficiency of the approach based on the use of linearized spacecraft relative motion dynamics associated to systematic H2 synthesis of stabilizing memoryless N-periodic state-feedback control laws

Deuxième table ronde. Les aspects de droit administratif

— M. Alain Plantey, président : Il s’agit des aspects administratifs du sujet, permettez-moi de vous dire une chose : nous avons des aspects administratifs globaux parce que nous avions un droit administratif nous français. Mais il ne faut pas dire qu’il n’y a pas de droit administratif ailleurs. Le droit administratif existe pratiquement dans tous les pays maintenant, seulement il est fractionné tandis que nous nous avions un droit administratif conçu comme une totalité. — Mm..

Immunoblot analysis of membrane antigens of Schistosoma mansoni, Schistosoma intercalatum, and Schistosoma haematobium against Schistosoma-infected patient sera.

International audienceAntigens present in aqueous n-butanolic extracts (BE) of Schistosoma mansoni (Venezuelan JL strain), Schistosoma intercalatum (Cameroon EDEA strain), and Schistosoma haematobium (Yemen strain) adult worm membranes were compared in immunoblot against sera of patients infected with S. mansoni, S. intercalatum, S. haematobium, Schistosoma japonicum, or Schistosoma mekongi looking for similarities (common antigens) and differences (species-specific antigens). About 17 S. mansoni BE polypeptides (M (r) approximately 8 to >80 kDa) were commonly recognized by S. mansoni-infected patient sera from Venezuela, Senegal, and Ethiopia. S. intercalatum-, S. haematobium-, or S. japonicum-infected sera were almost unreactive with S. mansoni BE. Nonetheless, S. mekongi-infected sera weakly cross-reacted with a approximately 10-15-kDa subset of S. mansoni BE. About 72.7% of S. intercalatum-infected patient sera reacted with a approximately 19-21-kDa complex in S. intercalatum BE and cross-reacted with a similar complex in S. haematobium BE. Conversely, all S. haematobium-infected patient sera reacted with a approximately 19-21-kDa complex in S. haematobium BE and cross-reacted with the approximately 19-21-kDa complex in S. intercalatum BE; S. mansoni- and S. japonicum-infected patient sera did not react with S. intercalatum or S. haematobium BE. Results showed the presence of a common membrane antigen between African schistosome species and species-specific antigens in S. mansoni BE that could be useful to discriminate between species and/or to detect Schistosoma infections

First report of larval stages of Fasciola hepatica in a wild population of Pseudosuccinea columella from Cuba and the Caribbean.

International audienceA wild population of the lymnaeid snail Pseudosuccinea columella infected by larval stages of Fasciola hepatica was discovered in the Pinar del Río Province, Cuba. One of 100 snails was infected in a rice culture field. This is the first time this species has been found acting as intermediate host of F. hepatica under natural conditions, not only for Cuba but also for the Caribbean area

TAROT: a network for space surveillance and tracking operations

International audienceTAROT: a network for space surveillance and tracking operations The TAROT (Télescope à Action Rapide pour les Objets Transitoires – Rapid Action Telescope for Transient Objects) network of telescopes consists of two 25cm aperture telescopes located at the Calern Observatory (TCA, OCA, France), the La Silla Observatory (TCH, ESO, Chile), and a 18cm telescope at Les Makes Observatory, (TRE, France). In addition we use the Zadko 1m telescope at the Gingin Observatory (ZDK, UWA, Australia). A central service in France, called CADOR (Centre d’Analyse des Données des Observatoires Robotiques, Centre for the Data Analysis of Robotic Observatories), acts as an interface for users, runs the scheduling system over the network, archive the data and run the core database. Since 1999 we perform observations of Resident Space Objects (RSO). Over the time we have implemented the observation of RSOs, mostly debris, on the geostationary orbit, and of passing objects in eccentric orbits, such as the GTO, or MEO/HEO. A specific data reduction pipeline with new methods for the image analysis has been developed and implemented by the CNES space debris modelling and risk assessments office to extract, process Space observations and to catalogue RSOs. As an example, in 2015, TCA has performed over 17000 measurements over the GEO monthly (average). TRE has been adapted to the observation of RSOs in November 2016, and it has made for its first 12 nights over 11000 measurements. In 2016, preliminary results show that the availability of the telescopes (TCA and TCH) is on the order of 90%. The TAROT network was recently used to observe the Arianne V233 Galileo launch, allowing observing the separation of the four satellites from the upper stage of the launcher, acquiring rare images of the passivation phase. We are now implementing operational procedures to use the TAROT network for the support of the CAESAR collision assessment system of the CNES. In this paper we present here the TAROT network, the methods and strategies we have developed, as well as statistics of measurements, some specific examples, and the perspective of the network within the context of Space Surveillance and Tracking