Stéphanie Lizy-Destrez

Computing an optimized trajectory between Earth and an EML2 halo orbit

According to the Global Exploration Roadmap, which reflects the international effort to define feasible and sustainable exploration pathways to the Moon, near-Earth asteroids and Mars, the next step for manned space exploration is the Moon as second home in the Solar System. In that perspective, the Earth-Moon Libration points (EML points) have been a topic of great interest in recent years since EML1 and EML2 were suggested as advantageous locations of space hubs in the Moon neighborhood. To materialize this vision, detailed studies are needed to investigate transfers between Earth and the vicinity of EML2 and the strategies to reduce associated maneuver costs. This work is framed within the perspective of a future deep space habitat in halo orbit around EML2, and this paper intends to provide quantitative results so as to select the best deployment scenario of the station. The main purpose is to determine the best transfer trajectory between a low-Earth orbit and a halo orbit around EML2 in terms of cost and duration. Two different kinds of attractive transfer strategies have been identied. Station deployment and cargo missions would use Weak Stability Boundary (WSB) trajectories whereas manned flights would exploit a fly-by strategy as it shows an advantageous compromise between short trip duration and efficiency.

Preliminary Design of a New Hybrid and Technology Innovative Suborbital Vehicle for Space Tourism

The general enthusiasm aroused by space tourism combined with the great technological achievement of Scaled Composites with the SpaceShipOne in 2004 initiated a new era: suborbital space tourism. As of today, most of the vehicles have been designed for performance, combining the most advanced technologies from both aeronautics and astronautics. Nevertheless, in order to become viable, vehicles must be safe enough to carry paying passengers and they must match the increasing demand. Thus, the implementation of a new design process based on adapted requirements led to a new vehicle. The latter is mainly powered by newly designed hybrid rocket engines but it also makes use of turbofans for the first segment of the climb and a safe powered landing. It takes-off and lands horizontally and is able to carry up to eight passengers and two pilots to an altitude of 109 km. The micro-gravity experienced by the passengers lasts approximately 4 minutes while the maximum load factor is reduced to 3.3 g in order to improve the passenger experience.

Analysis of the resilience of the ATV operations

The resilience of a system consists in its capability to maintain a safe and satisfactory mission, in its operational environment, while adapting to changing conditions (foreseen or unforeseen events, losses, failures,...) and mitigating the risk of contingencies. To guarantee the success of the ATV future missions (from ATV2, Johannes Kepler), the operational teams at ATV-CC(ATV Control Center), with the help of the vehicle designers, have built dedicated processes, developed particular tools and set specific advanced training right from the earliest preparation phase. In order to be compliant with strong safety requirements (due to the proximity of and interfaces with the ISS), operational teams have to prepare strategies balancing total automation versus human reaction, or training (at least, one procedure for each foreseen case) versus adaptation. Combining system engineering principles and lesson learnt from ATV Jules Verne mission, the Vehicle Team (VET) at ATV-CC challenges the improvement of the global system resilience through several means (ground and on-board alarms, specialized procedures, specific displays,...) depending on contingencies level, for next missions. The paper describes the strategies (in term of processes and tools) set up by the Vehicle Engineers Team, in accordance to safety requirements, interfaces with the international partners and ATV-CC rules to ensure the ATV operations.

Operational scenarios optimization for resupply of crew and cargo of an International gateway Station located near the Earth-Moon-Lagrangian point-2

In the context of future human space exploration missions in the solar system (with an horizon of 2025) and according to the roadmap proposed by ISECG (International Space Exploration Coordination Group) [1], a new step could be to maintain as an outpost, at one of the libration points of the Earth-Moon system, a space station. This would ease access to far destinations as Moon, Mars and asteroids and would allow testing some innovative technologies, before employing them for far distant human missions. One of the main challenges will be to maintain permanently, and ensure on board crew health thanks to an autonomous space medical center docked to the proposed space station, as a Space haven. Then the main problem to solve is to manage the station servitude, during deployment (modules integration) and operational phase. Challenges lie, on a global point of view, in the design of the operational scenarios and, on a local point of view, in trajectories selection, so as to minimize velocity increments (energy consumption) and transportation duration (crew safety). Which recommendations could be found out as far as trajectories optimization is concerned, that would fulfill energy consumption, transportation duration and safety criterion? What would technological hurdles be to rise for the building of such Space haven? What would be performances to aim at for critical sub-systems? Expected results of this study could point out research and development perspectives for human spaceflight missions and above all, in transportation field for long lasting missions. Thus, the thesis project, presented here, aims starting from global system life-cycle decomposition, to identify by phase operational scenario and optimize resupply vehicle mission. The main steps of this project consist of: - Bibliographical survey, that covers all involved disciplines like mission analysis (Astrodynamics, Orbital mechanics, Orbitography, N-Body Problem, Rendezvous…), Applied Mathematics, Optimization, Systems Engineering…. - Entire system life-cycle analysis, so as to establish the entire set of scenarios for deployment and operations (nominal cases, degraded cases, contingencies…) and for all trajectories legs (Low Earth Orbit, Transfer, Rendezvous, re-entry…) - Trade-off analysis for Space Station architecture - Modeling of the mission legs trajectories - Trajectories optimization Three main scenarios have been selected from the results of the preliminary design of the Space Station, named THOR: the Space Station deployment, the resupply cargo missions and the crew transportation. The deep analysis of those three main steps pointed out the criticality of the rendezvous strategies in the vicinity of Lagrangian points. A special effort has been set on those approach maneuvers. The optimization of those rendezvous trajectories led to consolidate performances (in term of energy and duration) of the global transfer from the Earth to the Lagrangian point neighborhood and return. Finally, recommendations have been deduced that support the Lagrangian points importance for next steps of Human Spaceflight exploration of the Solar system.

CubeSat Attitude Estimation via AUKF Using Magnetometer Measurements and MRPs

In this article the Attitude and Control system of a CubeSat is presented. The attitude estimation design approach used is based on Adaptative Unscented Kalman Filter (AUKF) using three-axismagnetometermeasurements.A set of modified Rodrigues Parameters (MRPs) is used to evaluate the attitude. Finally in order to have an complete ADCS system two control laws are introduced (Bdot and Sliding Mode) to best simulate a real CubeSat mission. The first one allows the spacecraft the control during the detumbling phase (phase at high angular rates) and in case of reaction wheels saturation and the second one is used for the nominal control (phase at low angular rates).

System engineering approach applied to Galileo system

Developing a localization system, with more precise performances than GPS that guarantees Europe autonomy is a complex challenge that ESA and a large number of European economical actors of space industry were decided to meet.