Abstract The Collaborative Research Centre (CRC) 1667 “Advancing Technologies of Very Low Altitude Satellites—ATLAS” was established in April 2024 with the scientific goal of addressing the fundamental challenges of making satellite operations in Very Low Earth Orbits (VLEO) sustainable. These orbits are beneficial for satellite services that have become indispensable to our modern society. Moreover, access to VLEO offers the opportunity to operate satellites without exposure or contribution to the increasing contamination of traditional orbits with space debris. Seventeen highly interlinked research projects have been selected to investigate and advance accurate numerical and experimental methods for gas–surface interactions, novel concepts utilising the residual atmosphere and minimising the satellite sizes, and mission-related challenges of a selected scenario. In addition, support projects cover topics related to public outreach and academic exchange and assist in achieving the strategic goal of positioning the University of Stuttgart as a key contributor to this internationally very important research area. In summary, the CRC ATLAS aims to constitute a research-oriented profile-building measure at the University of Stuttgart with a strong international reputation.

Abstract Satellites operating in the Very-Low-Earth-Orbit regime, that is, at altitudes where the residual atmosphere significantly impacts spacecraft dynamics, encounter notable aerodynamic forces, which are traditionally considered disturbances in spacecraft attitude control design. Instead, active control methods seek to harness these forces using the torques generated by adjustable aerodynamic surfaces as an additional means of external actuation. In this work, we examine the nonlinear structure of the control problem for a satellite featuring a reference geometry in a feathered configuration with four rotatable surfaces. We argue that challenges for the control design include uncertainty in aerodynamic and atmospheric models as well as time-varying parameters such as density and thermospheric temperature. Furthermore, our work emphasizes that low lift-to-drag ratios not only reduce control authority around the roll axis but also significantly restrict the region of validity of the linearized system, complicating actuator allocation procedures. To highlight the effects on control performance, we introduce a custom simulation tool designed for testing rotatable panel geometries under VLEO conditions and present a case study that illustrates the limitations of linear control design methods. Finally, we discuss potential nonlinear control strategies and the need for stability guarantees to further advance the field of aerodynamic attitude control in VLEO.

Abstract The use of Very Low Earth Orbit (VLEO) has often been cited as a possible solution to the growing problem of space debris, especially as we enter the era of mega-constellations of thousands of satellites. By definition, interaction with the residual atmosphere in VLEO induces drag which rapidly pulls debris and failed satellites from orbit, minimising any long-term impact on the debris population. As such, it provides a relatively consequence free environment, at least in terms of debris considerations, for rapid and high-risk technological innovation. There are many benefits achieved from operating satellites at lower altitudes, such as improved resolution for Earth observation and reduced latency and power requirements for communications constellations. These benefits, combined with the self-cleaning nature of VLEO and rapidly reducing launch costs, continue to drive growing use and interest in VLEO. However, the sustainable use of space also demands the consideration of other impacts of the use of low Earth orbit generally, including VLEO, on the Earth and orbital environments. These go beyond debris considerations to include light and radio pollution for optical and radio astronomy, and the carbon footprint of the space industry. Meanwhile, the impact on the atmosphere of satellites re-entering the atmosphere at end-of-life is known to have impacts on ozone depletion and the Earth’s radiative balance, the significance of which is still being assessed. One can imagine that in the future, with the drive for a circular space economy, moving end-of-life satellites to a reprocessing facility in-orbit becomes mandated; but this is realistically still a long-term goal. In the near term, what are the opportunities and benefits that VLEO can provide to space sustainability, and how do these need to develop to continue to be part of the solution in the long term? This paper reviews factors driving the growing interest in the use of VLEO, including benefits for sustainability, alongside the longer-term technology challenges that need to be addressed to ensure that VLEO remains a sustainable solution in a future circular economy for space.

Abstract This research deals with an innovative Blowdown-Induction System powered by a Low Velocity Oxygen-Fueled (L-VOF) gun; the system has been designed and built to mimic various flow scenarios related to sustained hypersonic flight. The fundamental concepts behind the facility are thoroughly examined, followed by a detailed discussion of its individual subsystems, their interrelations, and the methods developed to address specific technical challenges inherent to its design. The performances of the system are then assessed through prototype applications; in particular, evidence is provided that, in the cold flow case, the plant can achieve pressures high enough to create supersonic flow by directly drawing air from the surrounding environment. Notably, under heated flow conditions, the same system can consistently generate pressures sufficient for supersonic speeds, yielding Mach numbers close to those observed in the cold flow experiments. The heated tests involve significantly higher energy levels, closely resembling the intense thermal conditions typical of hypersonic flight.