HERMES is a scientific mission composed of 3U nanosatellites dedicated to the detection and localization of high-energy astrophysical transients, with a distributed space architecture to form a constellation in Earth orbits. The space segment hosts novel miniaturized detectors to probe the x-ray temporal emission of bright events, such as gamma-ray bursts, and the electromagnetic counterparts of gravitational wave events, playing a crucial role in future multimessenger astrophysics. During operations, at least three instruments separated by a minimum distance shall observe a common area of the sky to perform a triangulation of the observed event. An effective detection by the nanosatellite payload is achieved by guaranteeing a beneficial orbital and pointing configuration of the constellation. The design has to cope with the limitations imposed by small space systems, such as the lack of on-board propulsion and the reduced systems budgets. We describe the methodologies and the proposed strategies to overcome the mission limitations, while achieving a satisfactory constellation visibility of the sky throughout the mission duration. The mission design makes use of a high-fidelity orbit propagator, combined with an innovative mission analysis tool that estimates the scientific performances of the constellation. The influence of the natural relative motion, which is crucial to achieve an effective constellation configuration without on-board orbit control, is assessed. The presented methodology can be easily extended to any kind of distributed scientific space applications, as well as to constellations dedicated to Earth and planetary observation. In addition, the visibility tool is applicable in the context of the constellation flight dynamics operations, yielding optimized results and pointing plans based on actual satellite orbital positions. © 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)
HERMES (High Energy Rapid Modular Ensemble of Satellites)Technological and Scientific pathfinder is a space borne mission based on a LEO constellation of nano-satellites. The 3U CubeSat buses host new miniaturized detectors to probe the temporal emission of bright high-energy transients such as Gamma-Ray Bursts (GRBs). Fast transient localization, in
Near Rectilinear Halo Orbits (NRHO) have been recently identified as suitable location for a cislunar space station, to orbit in the Earth-Moon vicinity and offer long-term infrastructural services to manned and unmanned missions to the Moon and further. Indeed, to reliably perform rendezvous and docking/undocking phases between space vehicles orbiting on highly non-Keplerian orbits, such as NRHOs, represents a fundamental key technology. Rendezvous is well-known for Earth-centred missions, while no mission ever performed it on non-Keplerian orbits. The paper critically discusses the adopted approach and the obtained results in modelling the non-Keplerian relative dynamics and in synthesizing the guidance, to safely rendezvous and dock on NRHOs. The entire study is strongly driven by engineering constraints and mission requirements which lead the practical implementation. The dynamics intrinsic non-linearity-which makes the trajectories highly sensitive to small deviations-is here exploited to benefit both rendezvous operations and safety. The paper shows the relative trajectories, designed in a way that both NRHO central and unstable manifolds are used: the former to ensure the chaser relative orbit to be periodic with respect to the target, the latter to answer the passive safety philosophy here preferred. In fact, chaser deviation from target is naturally obtained, whenever on an unstable direction. Along the approaching trajectory, two holding points are assumed: on the central manifold the farthest, at about 100 km from the target, to prepare for the final approach; if a no-go is commanded, the spacecraft hovers on the central manifold, waiting for the next approach opportunity. The closest holding point is designed to lay on the unstable manifold direction, to privilege risk mitigation through passive safety, since if no active control occurs, the chaser-now just meters away from the target-naturally drifts away. The relative trajectory and approach strategy design, driven by the guidance and mission operations definition in nominal and non-nominal scenarios, is discussed in the paper: the simulations and the analyses that led to the approach corridor shape, keep-out zones radius and collision avoidance manoeuvres settling are here reported. The practical case of the cislunar space gateway servicing is here exploited to present the proposed rendezvous and approach techniques for non-Keplerian scenarios and to highlight the GRANO software tool-developed by the authors at Politecnico di Milano, ASTRA Team-flexibility for general application in the n-body framework.
A space station in the vicinity of the Moon can be exploited as a gateway for future human and robotic exploration of the Solar System. The natural location for a space system of this kind is about one of the Earth-Moon libration points.The study addresses the dynamics during rendezvous and docking operations with a very large space infrastructure in a EML2 Halo orbit. The model takes into account the coupling e↵ects between the orbital and the attitude motion in a Circular Restricted Three-Body Problem environment. The flexibility of the system is included, and the interaction between the modes of the structure and those related with the orbital motion is investigated. A lumped parameters technique is used to represents the flexible dynamics.The parameters of the space station are maintained as generic as possible, in a way to delineate a global scenario of the mission. However, the developed model can be tuned and updated according to the information that will be available in the future, when the whole system will be defined with a higher level of precision.
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