<p>We discuss a concept of probabilistic orbit. If correctly constructed, an ensemble of equally plausible orbits is a proper representation of the underlying true and unknown probability distribution of orbits. Hence, the probabilistic orbit is determined by the entire sample and its statistical properties rather than any individual ensemble member. We explore the concept by starting from an ensemble of atmospheric state estimates generated at ECMWF (N=51). The ensemble mean closely corresponds to the most likely atmospheric state estimate, and the ensemble spread to its inherent uncertainty. We compute separately a GNSS orbit solution for each unique atmospheric state (N=51). Thus, we essentially sample one uncertain information source the GNSS orbits are known to be sensitive for. Thereby, uncertainty in the atmospheric state estimate is explicitly propagated to the ensemble of orbit solutions. The concept leads to interesting corollaries. Precise point positioning using the probabilistic orbit, for instance, becomes probabilistic, too.</p>

This book stems from the work carried out by students during a single semester of the course Space Resources and Planetary Settlements of the Master degree in Space and Aeronautical Engineering of the Universitat Politècnica de Catalunya. It aims to provide a scientific and engineering view on the Moon as a place where humans can live and work for the benefit of humanity, sustainably. After a review of the Moon’s environmental conditions and natural resources, important issues such as energy, life support systems and the analysis of robotic vs. human activities are discussed in detail. Travel to and from the Moon is also considered, including the lessons learned about transportation strategies on continuous round trips to and from the International Space Station during the early 21st century. Finally, a set of different activities that can be carried out and, in the authors’ opinion, fully justify the return to our natural satellite, are treated in some detail.tail. Travel to and from the Moon is also considered, including the lessons learned about transportation strategies on continuous round trips to and from the International Space Station during the early 21st century. Finally, a set of different activities that can be carried out and, in the authors’ opinion, fully justify the return to our natural satellite, are treated in some detail.

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