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Operating satellites in Very Low Earth Orbit (VLEO) benefit the already expanding New Space industry in applications including Earth Observation and beyond. However, long-term operations at such low altitudes require propulsion systems to compensate for the large aerodynamic drag forces. When using conventional propulsion systems, the amount of storable propellant limits the maximum mission lifetime. The latter can be avoided by employing Atmosphere-Breathing Electric Propulsion (ABEP) system, which collects the residual atmospheric particles and uses them as propellant for an electric thruster. Thus, the requirement of on-board propellant storage can ideally be nullified. At the Institute of Space Systems (IRS) of the University of Stuttgart, an intake, and a RF Helicon-based Plasma Thruster (IPT) for ABEP system are developed within the Horizons 2020 funded DISCOVERER project. To assess possible future use cases, this paper proposes and analyzes several novel ABEP-based mission scenarios. Beginning with technology demonstration mission in VLEO, more complex mission scenarios are derived and discussed in detail. These include, amongst others, orbit maintenance around Mars as well as refuelling and space tug missions. The results show that the ABEP system is not only able to compensate drag for orbit maintenance but also capable of performing orbital maneuvers and collect propellant for applications such as Space Tug and Refuelling. Thus, showing a multitude of different future mission applications., This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 737183. This reflects only the author’s view, and the European Commission is not responsible for any use that may be made of the information it contains, Peer Reviewed, Postprint (author's final draft)

After decades of traditional space businesses, the space paradigm is changing. New approaches to more efficient missions in terms of costs, design, and manufacturing processes are fostered. For instance, placing big constellations of micro- and nano-satellites in Low Earth Orbit and Very Low Earth Orbit (LEO and VLEO) enables the space community to obtain a huge amount of data in near real-time with an unprecedented temporal resolution. Beyond technology innovations, other drivers promote innovation in the space sector like the increasing demand for Earth Observation (EO) data by the commercial sector. Perez et al. stated that the EO industry is the second market in terms of operative satellites (661 units), micro- and nano-satellites being the higher share of them (61%). Technological and market drivers encourage the emergence of new start-ups in the space environment like Skybox, OneWeb, Telesat, Planet, and OpenCosmos, among others, with novel business models that change the accessibility, affordability, ownership, and commercialization of space products and services. This chapter shows some results of the H2020 DISCOVERER (DISruptive teChnOlogies for VERy low Earth oRbit platforms) Project and focuses on understanding how micro- and nano-satellites have been disrupting the EO market in front of traditional platforms.

For a satellite formation to maintain its intended design despite present perturbations (formation keeping), to change the formation design (reconfiguration) or to perform a rendezvous maneuver, control forces need to be generated. To do so, chemical and/or electric thrusters are currently the methods of choice. However, their utilization has detrimental effects on small satellites’ limited mass, volume and power budgets. Since the mid-80s, the potential of using differential drag as a means of propellant-less source of control for satellite formation flight is actively researched. This method consists of varying the aerodynamic drag experienced by different spacecraft, thus generating differential accelerations between them. Its main disadvantage, that its controllability is mainly limited to the in-plain relative motion, can be overcome using differential lift as a means to control the out-of-plane motion. Due to its promising benefits, a variety of studies from researchers around the world have enhanced the state-of-the-art over the past decades which results in a multitude of available literature. In this paper, an extensive literature review of the efforts which led to the current state-of-the-art of different lift and drag-based satellite formation control is presented. Based on the insights gained during the review process, key knowledge gaps that need to be addressed in the field of differential lift to enhance the current state-of-the-art are revealed and discussed. In closer detail, the interdependence between the feasibility domain/the maneuver time and increased differential lift forces achieved using advanced satellite surface materials promoting quasi-specular or specular reflection, as currently being developed in the course of the DISCOVERER project, is discussed., Peer Reviewed, Postprint (author's final draft)

Using several small, unconnected satellites flying in formation rather than a single monolithic satellite has many advantages. As an example, separate optical systems can be combined to function as a single larger (synthetic) aperture. When the aperture is synthesized, the independent optical systems are phased to form a common image field with its resolution determined by the maximum dimension of the array. Hence, a formation is capable of much finer resolution than it could be accomplished by any single element. In order for the formation to maintain its intended design despite present perturbations (formation keeping), to perform rendezvous maneuvers or to change the formation design (reconfiguration) control forces need to be generated. To this day, using chemical and/or electric thrusters are the methods of choice. However, their utilization has detrimental effects on small satellites’ limited mass, volume and power budgets. In the mid-eighties, Caroline Lee Leonard published her pioneering work [1] proving the potential of using differential drag as a means of propellant-less source of control for satellite formation flight. This method consists of varying the aerodynamic drag experienced by different spacecraft, thus generating differential accelerations between them. Since its control authority is limited to the in-plane motion, Horsley [2] proposed to use differential lift as a means to control the out-of-plane motion. Due to its promising benefits, a variety of studies from researches around the world have enhanced Leonard’s work over past decades which results in a multitude of available literature. Besides giving an introduction into the method the major contributions of this paper is twofold: first, an extensive literature review of the major contributions which led to the current state-of-the-art of different lift and drag based satellite formation control is presented. Second, based on these insights key knowledge gaps that need to be addressed in ord, Peer Reviewed, Postprint (published version)