Guidance, Navigation and Control System Design of Envisat Active Debris Removal

Space debris is becoming one of the major risks to be suffered by operating and future space missions. Recent studies show that the number of potentially hazardous uncontrolled orbital bodies is growing with time, increasing the probability of impact with operational satellites. To counteract this problem, several studies are being suggested to remove these dangerous objects from space. Among these, ESA proposed the e.Deorbit mission, whose objective would be the capture, detumbling and deorbit of the large inoperative satellite Envisat. However, the final deorbit phase encompasses a set of challenges and issues that are still to be tackled. The present thesis provides an approach for the guidance, navigation and control system design that solves those challenges and that can safely and robustly remove the spacecraft from orbit. For this purpose, the latest configuration of a rigid stack composed by Envisat and the chaser spacecraft is considered, in which it is deorbited using a series of perigee lowering maneuvers using a single main engine. The work proposes a guidance algorithm that can autonomously deorbit the stack using a pseudo-mean anomaly as control variable and the Linear Tangent Guidance concept for the final targeting. This algorithm is shown to robustly deorbit the stack regardless of its initial position in its orbit or of the initial mass of the target spacecraft within the specified uncertainty. Secondly, the work proposes a MEKF navigation filter based on the navigation sensors which are proposed for the chaser as of the latest configuration. Finally, a control law utilizing the INDI controller principles is suggested as a robust solution to the uncertainty in the inertia of the target spacecraft. It is shown that this controller behaves robustly against mismatches on the dynamic model. The complete integrated solution is then analyzed, exhibiting a promising behavior towards the correct active debris removal, and future investigation is encouraged. The work presented lays the foundations for the GNC design on a challenging yet necessary line of technological development towards the deorbit of large space debris for a more sustainable space environment.Aerospace Engineerin

Mission Analysis, GNC and ATD for Reusable Launch Vehicles within ASCenSIon: multi-orbit multi-payload injection, re-entry and safe disposal

Reusable Launch Vehicles (RLVs) are not only key for an economically and ecologically sustainable space access but also represent a paramount innovation towards the increasing demand for smaller satellites and mega- constellations. In order to ensure Europe's independent space access capabilities, ASCenSIon (Advancing Space Access Capabilities - Reusability and Multiple Satellite Injection) is born as an innovative training network with fifteen Early Stage Researchers, ten beneficiaries, and fourteen partner organisations across Europe. This paper provides an overview of the mission, ranging from the ascent to the re-entry of the reusable stages and including the multi-orbit injection and the safe disposal. A special focus is put on the activities developed within ASCenSIon regarding Mission Analysis (MA), Guidance Navigation and Control (GNC) and Aerothermodynamics (ATD). The foreseen methods, approaches and goals of the project are presented. These topics require innovation within and a high level of collaboration due to their interconnection. The pre-flight design capability drives the necessity of a MA and GNC missionisation tool coupled with ATD software to test/explore re-entry solutions. Such a reliable and efficient tool will require the development of GNC algorithms for the re-entry of the launcher. Additionally, specific challenges of trajectory optimization for RLVs are addressed, such as integrated multi-disciplinary vehicle design and trajectory analysis, fast and reliable on-board methods. The results of this study are subsequently used to develop the controlled strategy. Moreover, to perform the novel multi-orbit multi-payload injection. This activity is followed by the development of, a GNC architecture capable of optimally steering the vehicle towards a targeted landing site under precision and soft-landing constraints. In addition, ATD affects the mission profile at multiple phases and needs to be considered at each design step. Due to complexity and limited computational resources during the preliminary design phase, surrogate models with low response times are required to predict wall heat fluxes along the considered trajectories based on the pressure topology. The complete profile is wrapped up with the Post Mission Disposal strategies to be used by the launchers in order to ensure the compliance with the space debris mitigation guidelines, as well as preliminary reliability aspects of these strategies. The paper provides a preliminary analysis of the discussed topics and their interconnections within the work-frame of ASCenSIon paving the way towards the development of novel cutting-edge technologies for RLVs

Conceptual study of technologies enabling novel green expendable upper stages with multi-payload/multi-orbit injection capability

The growing demand for cheaper space access calls for a more economically and environmentally sustainable approach for launchers. Concurrently, the shift to smaller satellites and the rise of constellations necessitate launchers capable of precise multi-payload/multi-orbit injection. ASCenSIon (Advancing Space Access Capabilities - Reusability and Multiple Satellite Injection), a Marie Sklodowska-Curie Innovative Training Network funded by Horizon 2020 (H2020), aims to respond to these demands. This paper describes the activities explored within ASCenSIon dedicated to developing novel green upper stages with multi-payload/multi-orbit injection capability. The aspects investigated here include the general system architecture, innovative solutions for the propulsion system (e.g. Hybrid Rocket Engines (HREs). green propellants and electric pump feeding). Guidance Navigation and Control (GNC) solutions for the multi-payload/multi-orbit injection capability, and reliability aspects of upper stages. First, relevant space market considerations are raised. Then, solutions for more environmentally friendly propulsion systems are proposed. Since identifying a good substitute for toxic hydrazine recently became a priority, the use of green propellant technologies will be assessed, tackling specific problems such as benchmarked propulsive performances, storability and material compatibility. Another promising solution for future propulsion systems with lower environmental impact are HREs. They bring benefits in terms of flexibility, safety and cost. However, high residual mass, oxidizer-to-fuel ratio (O/F) shift during operation, low regression rate and combustion inefficiency are some of the challenges that still need to be addressed in their application. In addition, electric pump fed systems, powered by green propellants. may be a game-changer technology for future upper stages. Compared to pressure-fed. it can provide improved performance and lower inert mass. With respect to turbopumps, it may also be advantageous in terms of simplicity and costs. On the other hand, battery mass and thermal control represent some of the drawbacks to overcome. Additionally, the implementation of novel GNC solutions is critical to ensure the multi-payload/multi-orbit injection capability. The challenges brought by the design of such a system are presented, including the correlation with the overall upper stage definition. Finally, the reliability of the launchers is a key aspect to protect both the space environment and the safety of the missions. Novel methods for reliability modelling of launchers are discussed and advantageous system architectures are proposed. These novel technologies being jointly assessed, this paper presents a preliminary analysis of the discussed topics and their interconnections within ASCenSIon, aiming at satisfying new requirements for novel green upper stages.SCOPUS: cp.pinfo:eu-repo/semantics/publishe