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EPJ ST Highlight – Introduction to Celestial Mechanics in the XXIst Century

Space exploration is moving into a new era, the turn of the century has seen past glories fade and the focus of science and research move from one-off achievements and firsts, to the establishment of frameworks that will encourage sustainability. At the same time, the more we learn about space, the more we realise that plans must be put in place to mitigate threats from beyond our own atmosphere. As such, the EPJ Special Topics issue on ‘Celestial Mechanics in the XXIst Century’ reflects this shift in attention by spotlighting research that aims to cement humankind’s place amongst the stars.

Here, we present highlights from this issue where we learn how spacecrafts can get a boost in ‘Aerogravity Assisted’ interactions, how we might reduce the risk of space debris collision, and how a tethered diversion might protect Earth from asteroid impact.

EPJ ST Highlight - Spacecrafts get a boost in ‘Aerogravity Assisted’ interactions

The Voyager 2 probe gained the energy boost to escape the solar system from an AGA (NASA/JPL)

New research examines the effect of rotation and other variables in the applications of ‘aerogravity assisted’ manoeuvres to obtain an energy boost for space craft.

In a recent paper published in EPJ Special Topics, Jhonathan O. Murcia Piñeros, a post-doctoral researcher at Space Electronics Division, Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Brazil, and his co-authors, map the energy variations of the spacecraft orbits during ‘aerogravity assisted’ (AGA) manoeuvres. A technique in which energy gains are granted to a spacecraft by a close encounter with a planet or other celestial body via that body’s atmosphere and gravity.

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EPJ ST Highlight - Reducing the risk of space debris collision

Debris plot by NASA / Public Domain

An increase in space launches requires the development of a method to clear space debris which could collide with valuable equipment. One plausible method of achieving this through the use of a tug vehicle requires a successful connection procedure.

As humanity expands its horizons beyond the Earth and begins to consider space missions with extended duration, sustainability necessitates the launch of more space vehicles, increasing the risk of collision with existing space debris. One method of clearing this debris involves a tug vehicle dragging it to a safe region. In a new paper published in EPJ Special Topics, authors Antônio Delson Conceição de Jesus and Gabriel Luiz F. Santos, both from the State University of Feira de Santana, Bahia, Brazil, model the complex rendezvous manoeuvres a tug vehicle clearing space debris would have to undergo to mitigate the risk of a collision that could cause irreparable damage at the moment of coupling.

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EPJ ST Highlight - Protecting Earth from asteroid impact with a tethered diversion

A depiction of a tether connecting two asteroids

The use of a tether assisted system could prevent an asteroid impacting Earth without the risk of fragmentation.

Our planet exists within the vicinity of thousands of Near-Earth Objects (NEOs), some of which –  Potentially Hazardous Asteroids (PHAs)  –  carry the risk of impacting Earth causing major damage to infrastructure and loss of life. Methods to mitigate such a collision are highly desirable. A new paper published in EPJ Special Topics, authored by Flaviane Venditti, Planetary Radar Department, Arecibo Observatory, University of Central Florida, Arecibo, suggests the use of a tether assisted system to prevent PHA impact.

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EPJ E Highlight - ‘Bottom-heavy squirmers’ adopt characteristic group behaviours

Simulating motions of bottom-heavy squirmers.

Simulated particles which mimic the behaviours of self-propelling microorganisms have distinct collective properties which depend on their velocities and bottom-heaviness.

From starling aberrations to self-turbulent fluids, ‘active systems’ encompass a wide family of phenomena in which individual objects propel themselves forward, allowing them to display intriguing collective behaviours. On microscopic scales, they are found in groups of living organisms which move around by squirming, and are aligned with Earth’s gravitational fields due to their bottom-heavy mass distributions. Through research published in EPJ E, Felix Rühle and Holger Stark at the Technical University of Berlin find that depending on their properties, these objects collectively spend most of their time in one of two states, between which some intriguing behaviours can emerge.

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EPJ A Highlight - Advancing AGATA – Future Science with The Advanced Gamma Tracking Array

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Artist's view of the 4p AGATA spectrometer showing the mechanical holding frame (yellow) and cryostat dewars (blue) of the Ge detectors.

AGATA – the Advanced Gamma Tracking Array is a multi-national European project for the ultimate high-resolution gamma-ray spectrometer for nuclear physics capable of measuring γ rays from a few tens of keV to beyond 10 MeV, with unprecedented efficiency, excellent position resolution for individual γ-ray interactions and correspondingly unparalleled angular resolution, and very high count-rate capability. AGATA will be a flag ship spectrometer and have an enormous impact on nuclear structure studies at the extremes of isospin, mass, angular momentum, excitation energy and temperature. It will enable us to uncover and understand hitherto hidden secrets of the atomic nucleus.

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EPJ D Highlight - Stresses and flows in ultra-cold superfluids

The superfluid flow around obstacles causes exotic forces and stress in quantum liquid. Free-Photos from Pixabay at https://pixabay.com/photos/rocks-stream-water-nature-1246183/

Mathematical modelling of superfluids, which exhibit quantum mechanical properties at a macroscopic scale, shows that they become deformed when flowing around impurities.

Superfluids, which form only at temperatures close to absolute zero, have unique and in some ways bizarre mechanical properties, Yvan Buggy of the Institute of Photonics and Quantum Sciences at Heriot-Watt University in Edinburgh, Scotland, and his co-workers have developed a new quantum mechanical model of some of these properties, which illustrates how these fluids will deform as they flow around impurities. This work is published in the journal EPJ D.

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EPJ D Topical review - Recent total cross section measurements in electron scattering from molecules

Accurate new experimental data on electron interactions with matter are necessary for the understanding of a wide variety of natural and technological processes occurring in complex environments. Knowledge of the efficiency of electron interactions with biomolecules is crucial for the description and modeling of ionizing radiation damage to living cells and biomolecules radiolysis. Accurate experimental data concerning electron interactions are also important for the description of many phenomena occurring in plasma physics and gaseous electronics, including modeling of processes in cometary and planetary atmospheres.

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EPJ Plus Highlight - Mathematical curves predict evolution in Covid-19 spread

Predicting evolution in daily new cases

With the right approach, statistics can be used to reliably track the growth and fall in daily new cases of Covid-19 in China, raising hopes that similar approaches could more accurately predict the spread of the virus in other nations.

Efforts to contain the spread of the Covid-19 pandemic are now the top priority of governments across the globe. As they make these life-saving decisions, it is particularly crucial for policymakers to accurately predict how the spread of the virus will change over time. Through research published in EPJ Plus, Ignazio Ciufolini at the University of Salento, and Antonio Paolozzi at Sapienza University of Rome, identify a clear mathematical trend in the evolution of daily new cases and death numbers in China, and use the same curve to predict how a similar slowdown will unfold in Italy.

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EPJ B Colloquium - Ergodicity and large deviations in physical systems with stochastic dynamics

In ergodic physical systems, time-averaged quantities converge (for large times) to their ensemble-averaged values. Large deviation theory describes rare events where these time averages differ significantly from the corresponding ensemble averages. It allows estimation of the probabilities of these events, and their mechanisms, and has been applied to a wide range of physical systems, including exclusion processes, glassy materials, models of heat transport, proteins, climate models, and non-equilibrium quantum systems.

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