Medium Earth Orbit dynamical survey and its use in passive debris removal

The Medium Earth Orbit (MEO) region hosts satellites for navigation, communication, and geodetic/space environmental science, among which are the Global Navigation Satellites Systems (GNSS). Safe and efficient removal of debris from MEO is problematic due to the high cost for maneuvers needed to directly reach the Earth (reentry orbits) and the relatively crowded GNSS neighborhood (graveyard orbits). Recent studies have highlighted the complicated secular dynamics in the MEO region, but also the possibility of exploiting these dynamics, for designing removal strategies. In this paper, we present our numerical exploration of the long-term dynamics in MEO, performed with the purpose of unveiling the set of reentry and graveyard solutions that could be reached with maneuvers of reasonable DV cost. We simulated the dynamics over 120-200 years for an extended grid of millions of fictitious MEO satellites that covered all inclinations from 0 to 90deg, using non-averaged equations of motion and a suitable dynamical model that accounted for the principal geopotential terms, 3rd-body perturbations and solar radiation pressure (SRP). We found a sizeable set of usable solutions with reentry times that exceed ~40years, mainly around three specific inclination values: 46deg, 56deg, and 68deg; a result compatible with our understanding of MEO secular dynamics. For DV <= 300 m/s (i.e., achieved if you start from a typical GNSS orbit and target a disposal orbit with e<0.3), reentry times from GNSS altitudes exceed ~70 years, while low-cost (DV ~= 5-35 m/s) graveyard orbits, stable for at lest 200 years, are found for eccentricities up to e~0.018. This investigation was carried out in the framework of the EC-funded "ReDSHIFT" project.Comment: 39 pages, 23 figure

Dynamical cartography of Earth satellite orbits

We have carried out a numerical investigation of the coupled gravitational and non-gravitational perturbations acting on Earth satellite orbits in an extensive grid, covering the whole circumterrestrial space, using an appropriately modified version of the SWIFT symplectic integrator, which is suitable for long-term (similar to 120 years) integrations of the non-averaged equations of motion. Hence, we characterize the long-term dynamics and the phase-space structure of the Earth-orbiter environment, starting from low altitudes (similar to 400 km) and going up to the GEO region and beyond. This investigation was done in the framework of the EC-funded "ReDSHIFT" project, with the purpose of enabling the definition of passive debris removal strategies, based on the use of physical mechanisms inherent in the complex dynamics of the problem (i.e., resonances). Accordingly, the complicated interactions among resonances, generated by different perturbing forces (i.e., lunisolar gravity, solar radiation pressure, tesseral harmonics in the geopotential) are accurately depicted in our results, where we can identify the regions of phase space where the motion is regular and long-term stable and regions for which eccentricity growth and even instability due to chaotic behavior can emerge. The results are presented in an "atlas" of dynamical stability maps for different orbital zones, with a particular focus on the (drag-free) range of semimajor axes, where the perturbing effects of the Earth's oblateness and lunisolar gravity are of comparable order. In some regions, the overlapping of the predominant lunisolar secular and semi-secular resonances furnish a number of interesting disposal hatches at moderate to low eccentricity orbits. All computations were repeated for an increased area-to-mass ratio, simulating the case of a satellite equipped with an on-board, area-augmenting device. We find that this would generally promote the deorbiting process, particularly at the transition region between LEO and MEO. Although direct reentry from very low eccentricities is very unlikely in most cases of interest, we find that a modest "delta-v" (Delta V) budget would be enough for satellites to be steered into a relatively short-lived resonance and achieve reentry into the Earth's atmosphere within reasonable timescales (similar to 50 years). (C) 2018 COSPAR. Published by Elsevier Ltd. All rights reserved.European Commission [687500]; General Secretariat for Research and Technology (GSRT); Hellenic Foundation for Research and Innovation (HFRI)24 month embargo; available online 12 September 2018.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Massive GPU Parallelisation for Cislunar Debris Mitigation Analyses

Nowadays, the issue of space debris is becoming central to any operation in space. Future lunar exploration missions won’t be exempted from this issue, with the aggravating factor of operating in a gravitational multi-body chaotic environment. Debris-related analyses often involve propagating numerous trajectories independent from each other. These allow, for example, estimating probabilities of further interaction of space debris with the Earth and other protected regions of space; additionally, initial uncertainties on the object’s state or the magnitude and direction of manoeuvres can be introduced in the analyses. This can translate into massive grid searches or Monte-Carlo runs, to map the totality of the solution space. Op- erators and mission designers can then use this cartography to support the design of normal mission and disposal phases. A similar approach can also help identify the areas most susceptible to chaotic behaviours, or the risk posed by a spacecraft fragmentation in such locations. All these efforts are often paired with the necessity to propagate for very long times with high precision, which increases the load on the com- putational infrastructure. This paper discusses the application of Graphics Processing Units (GPUs) to implement massive parallelisation of the propagation of motion in the Sun-Earth-Moon gravitational envi- ronment. GPUs, when compared to Central Processing Units (CPUs), are capable of performing simpler independent tasks in parallel in a much faster fashion. CUDAjectory, a CUDA-based software developed by the European Space Operations Centre, has been employed: parallel computations are used to obtain, in reasonable amounts of computational time, dynamical maps starting from hundreds of thousands of starting states. Some example cases are discussed, in an effort to show the type of analyses that can be performed, showing the logic followed in the samples creation, propagation and post-processing. The inner workings of the propagating tools are also introduced, showing how the advantage with respect to CPU parallelisation is achieved. The results of this work are the creation of a set of pictorial maps to visualise cislunar dynamical behaviours and patterns. The paper focuses on some example starting locations, considered as of interest for future exploration, such as Near Rectilinear Halo Orbits, or Distant Retrograde Orbits. These maps can, for example, link initial states and manoeuvres magnitudes to possible future disposal locations, such as lunar impacts or escapes in solar orbit

Chaotic transport of navigation satellites

Navigation satellites are known from numerical studies to reside in a dynamically sensitive environment, which may be of profound importance for their long-term sustainability. We derive the fundamental Hamiltonian of Global Navigation Satellite System dynamics and show analytically that near-circular trajectories lie in the neighborhood of a Normally Hyperbolic Invariant Manifold (NHIM), which is the primary source of hyperbolicity. Quasicircular orbits escape through chaotic transport, regulated by NHIM's stable and unstable manifolds, following a power-law escape time distribution P (t) ∼ t - α, with α ∼ 0.8 - 1.5. Our study is highly relevant for the design of satellite disposal trajectories, using manifold dynamics

Cislunar Debris Mitigation: Development of a Methodology to Assess the Sustainability of Lunar Missions

The Moon appears to be the next, natural step in the exploration of the Solar System. Human lunar activity will soon increase significantly: plans for an orbiting international laboratory in the Moon’s vicinity, the “Gateway”, are now well established together with surface exploration missions, and the coming years will seemingly experience a steadily growing traffic towards the cislunar space. Unsurprisingly, to avoid the unregulated utilisation of space and the accumulation of orbital debris, this growth should be accompanied by a proper framework to manage the end of service and disposal of the spacecraft employed. In this paper, available strategies to mitigate the accumulation of space debris in the cislunar space are characterised with respect to their technical feasibility and compliance to international regulations. Preliminary calculations in the Circular Restricted 3­Body Problem (CR3BP) are used to study the dynamical characteristics of trajectories in the Earth­Moon system. Then, a high fidelity model is employed to simulate the dynamics of spacecraft under the influence of perturbations and other bodies’ gravitational pulls for long propagation times. Parallel computing capabilities are used to propagate a high number of trajectories with varying starting conditions. Final states are then analysed in search for families of disposal trajectories with similar behaviours, producing a dynamical cartography of the cislunar space. Starting from methods applied to Earth­bound orbital debris mitigation, a set of metrics and indices is defined to characterise orbits in the Earth­Moon system, to assess their sustainability with respect to the debris environment. The final scope of this research is to propose a methodology to assess the compliance of lunar missions with the available mitigation actions, depending on their operational orbits and mission constraints, and test this approach with current and planned missions