Investigations of free space and deep space optical communication scenarios

The link performance of free space optical communications (FSOC) and deep space optical communications (DSOC) are investigated by considering two scenarios in space communications, for example, for the downlink and uplink between the earth ground stations and the near earth geostationary (GEO) satellites, and between the earth and spacecraft with large distance of 1 astronomical unit (AU) to the earth. Generally a distance larger than 0.01 AU or approximately 1,500,000 km from Earth is considered as deep space. In these theoretical investigations, different realistic system parameters for the optical lasers, transmitters, receivers, avalanche photodiodes (APDs), optical telescopes, atmospheric disturbances like scintillation and absorption are considered. The simulation results are compared with existing project data and valuable ESA experimental results to verify and improve the simulation models. The comparison in this paper shows that the simulation models for the link budget and the scintillation estimation are feasible for the investigations of FSOC and DSOC, and can be used to investigate improved design and implementation of DSOC projects for planned long-term and medium-term space missions.

Zooming in on the place of rocky planet formation: infrared interferometric observations of protoplanetary disks

<div>Spatially resolved observations from ALMA or direct imaging instruments revealed an extreme diversity and complexity of structures and substructures in the outer parts of protoplanetary disks.</div> <div>However, these techniques do not resolve the inner regions of protoplanetary disks, typically at less than 5 astronomical units from the star.</div> <div>These inner regions are crucial to understand the formation of telluric planets.</div> <div>They are also the theatre of strong interactions between the star and the disk that can influence planet formation.</div> <div>Thanks to infrared interferometry we can reach an angular resolution of ~1mas reaching sub-astronomical unit physical scales.</div> <div>We can, therefore use infrared interferometry to reveal and study the structure, composition, and dynamics of the inner parts of protoplanetary disks.</div> <div>In the past few years, the advent of infrared interferometers combining four telescopes such as PIONIER, MATISSE or GRAVITY enabled us to study these disks with an unprecedented detail.</div> <div>In this talk, I will review the recent results of near and mid-infrared interferometric observations of protoplanetary disks.</div>

Earth’s carbon deficit caused by early loss through irreversible sublimation

Carbon is an essential element for life, but its behavior during Earth’s accretion is not well understood. Carbonaceous grains in meteoritic and cometary materials suggest that irreversible sublimation, and not condensation, governs carbon acquisition by terrestrial worlds. Through astronomical observations and modeling, we show that the sublimation front of carbon carriers in the solar nebula, or the soot line, moved inward quickly so that carbon-rich ingredients would be available for accretion at 1 astronomical unit after the first million years. On the other hand, geological constraints firmly establish a severe carbon deficit in Earth, requiring the destruction of inherited carbonaceous organics in the majority of its building blocks. The carbon-poor nature of Earth thus implies carbon loss in its precursor material through sublimation within the first million years.

Galactic Cosmic Ray Modulation at Mars and beyond measured with EDACs on Mars Express and Rosetta

<p>Galactic Cosmic Rays (GCRs) are an intrinsic part of the heliospheric radiation environment, and an inevitable challenge to long-term space exploration. Here we show solar cycle induced GCR modulation at Mars in the period 2005-2020, along with GCR radial gradients, by utilising Mars Express and Rosetta engineering parameters compared to sunspot number time series. The engineering parameter used is called EDAC (Error Detection And Correction), a cumulative counter which is triggered by charged energetic particle causing memory errors in on-board computers. EDAC data provides a new way of gaining insight into the field of particle transport in the heliosphere, allowing us to circumvent the need for dedicated instrumentation as EDAC software is present on all spacecraft.</p><p>This data set can be used to capture variations of GCRs in both space and time, yielding the same qualitative information as ground-based neutron monitors. Our analysis of the Mars Express EDAC parameter reveals a strong solar cycle GCR modulation, yielding an anticorrelation coefficient of -0.5 at a time lag of ~5.5 months. By combining Mars Express with Rosetta data, we calculate a 5.3% increase in EDAC count rates per astronomical unit, attributed to a radial gradient in GCR fluxes in accordance with established literature.</p><p>The potential of engineering data for scientific purposes remains mostly unexplored. The results obtained from this work demonstrates, for the first time for heliophysics purposes, the usefulness of the EDAC engineering parameter, data mining and the utility of keeping missions operational for many years, providing complimentary data to nominal science instruments.</p>

Preliminary results of Space Weather conditions encountered by BepiColombo during the first phase of its cruise

<p>Planetary Space Weather is the discipline that studies the state of the Sun and how it interacts with the interplanetary and planetary environments. It is driven by the Sun’s activity, particularly through large eruptions of plasma (known as coronal mass ejections, CMEs), solar wind stream interaction regions (SIR) formed by the interaction of high-speed solar wind streams with the preceding slower solar wind, and bursts of solar energetic particles (SEPs) that form radiation storms. This is an emerging topic, whose real-time forecast is very challenging because among other factors, it needs a continuous coverage of its variability within the whole heliosphere as well as of the Sun’s activity to improve forecasting. <br />The long cruise of BepiColombo constitutes an exceptional opportunity for studying the Space Weather evolution within half-astronomical unit (AU), as well as in certain parts of its journey, can be used as an upstream solar wind monitor for Venus, Mars and even the outer planets. This work will present preliminary results of the Space Weather conditions encountered by BepiColombo since its launch until mid-2020, which includes data from the solar minimum of activity and few slow solar wind structures. Data come from three of its instruments that are operational for most of the cruise phase, i.e., the BepiColombo Radiation Monitor (BERM), the Mercury Planetary Orbiter Magnetometer (MPO-MAG), and the Solar Intensity X-ray and particle Spectrometer (SIXS). Modelling support for the data observations will be also presented with the so-called solar wind ENLIL simulations.</p>

Study of flux-rope characteristics at sub-astronomical-unit distances using the Helios 1 and 2 spacecraft

ABSTRACT Magnetic flux ropes observed as magnetic clouds near 1 au have been extensively studied in the literature and their distinct features are derived using numerous models. These studies summarize the general characteristics of flux ropes at 1 au without providing an understanding of the continuous evolution of the flux ropes from near the Sun to 1 au. In the present study, we investigate 26 flux ropes observed by the Helios 1 and 2 spacecraft (from 0.3 to 1 au) using the velocity-modified Gold–Hoyle model. The correlation and regression analyses suggest that the expansion speed, poloidal speed, total magnetic helicity and twist per au of the flux rope are independent of heliospheric distance. The study implies that the aforementioned features are more strongly influenced by their internal properties compared with external conditions in the ambient medium. Moreover, the poloidal magnetic flux and magnetic energy of the studied flux ropes exhibit power-law dependence on heliospheric distance. A better understanding of the underlying physics and corroboration of these results is expected from the Parker Solar Probe measurements in the near future.

A family portrait of disk inner rims around Herbig Ae/Be stars

Context. The innermost astronomical unit (au) in protoplanetary disks is a key region for stellar and planet formation, as exoplanet searches have shown a large occurrence of close-in planets that are located within the first au around their host star. Aims. We aim to reveal the morphology of the disk inner rim using near-infrared interferometric observations with milli-arcsecond resolution provided by near-infrared multitelescope interferometry. Methods. We provide model-independent reconstructed images of 15 objects selected from the Herbig AeBe survey carried out with PIONIER at the Very Large Telescope Interferometer, using the semi-parametric approach for image reconstruction of chromatic objects. We propose a set of methods to reconstruct and analyze the images in a consistent way. Results. We find that 40% of the systems (6/15) are centrosymmetric at the angular resolution of the observations. For the rest of the objects, we find evidence for asymmetric emission due to moderate-to-strong inclination of a disk-like structure for ~30% of the objects (5/15) and noncentrosymmetric morphology due to a nonaxisymmetric and possibly variable environment (4/15, ~27%). Among the systems with a disk-like structure, 20% (3/15) show a resolved dust-free cavity. Finally, we do not detect extended emission beyond the inner rim. Conclusions. The image reconstruction process is a powerful tool to reveal complex disk inner rim morphologies, which is complementary to the fit of geometrical models. At the angular resolution reached by near-infrared interferometric observations, most of the images are compatible with a centrally peaked emission (no cavity). For the most resolved targets, image reconstruction reveals morphologies that cannot be reproduced by generic parametric models (e.g., perturbed inner rims or complex brightness distributions). Moreover, the nonaxisymmetric disks show that the spatial resolution probed by optical interferometers makes the observations of the near-infrared emission (inside a few au) sensitive to temporal evolution with a time-scale down to a few weeks. The evidence of nonaxisymmetric emission that cannot be explained by simple inclination and radiative transfer effects requires alternative explanations, such as a warping of the inner disks. Interferometric observations can therefore be used to follow the evolution of the asymmetry of those disks at an au or sub-au scale.

Virtual global project management in eighteenth-century astronomy

Purpose This paper aims to demonstrate that virtual project management can be based on a common spirit and mutual trust to achieve project objectives, rather than the use of modern electronic devices to lower communication costs. Design/methodology/approach Evidence from the eighteenth-century files of Academies of Science and from astronomical literature is used to characterize the projects and to show how major elements of project management (such as identification of benefits to stakeholders, management of uncertainties, communication and data aggregation across related projects) were applied. Findings The analysis shows how the initiative to better measure the Astronomical Unit defined a megaproject, and how this was broken down at local Academies of Science into major projects or programs. This, in turn, resulted in individual expeditions. It demonstrates that innovations arose from the projects, and that learning from earlier expeditions resulted in the final success of the megaproject. Research limitations/implications The literature used was not written to demonstrate project management. In this respect, both the original sources and the later reports may lack information with respect to the present topic. Today’s project management might learn from the study that coordination and communication can greatly benefit from a joint vision of the project if based on a common spirit and mutual trust. Practical implications Present day project management might benefit from the finding that common values reduce communication costs in a similar way as recent electronic communication devices. Originality/value The author believes that this is the first paper to analyze the Venus transit projects from the project management perspective. This was a complex and global megaproject. The approaches taken to achieve the objectives relevant to different stakeholders provide lessons for today’s management of megaprojects.

Photolysis of diatomic molecules as a source of atoms in planetary exospheres

We calculated the cross sections of photolysis of OH, LiO, NaO, KO, HCl, LiCl, NaCl, KCl, HF, LiF, NaF, and KF molecules using quantum chemistry methods. The maximal values for photolysis cross sections of alkali metal monoxides are on the order of 10−18 cm2. The lifetimes of photolysis for quiet Sun at 1 astronomical unit are estimated as 2.0 × 105, 28, 5, 14, 2.1 × 105, 225, 42, 52, 2 × 106, 35 400, 486, and 30 400 s for OH, LiO, NaO, KO, HCl, LiCl, NaCl, KCl, HF, LiF, NaF, and KF, respectively. We performed a comparison between values of photolysis lifetimes obtained in this work and in previous studies. Based on such a comparison, our estimations of photolysis lifetimes of OH, HCl, and HF have an accuracy of about a factor of 2. We determined typical kinetic energies of main peaks of photolysis-generated metal atoms. Impact-produced LiO, NaO, KO, NaCl, and KCl molecules are destroyed in the lunar and Hermean exospheres almost completely during the first ballistic flight, while other considered molecules are more stable against destruction by photolysis.