Observatories of the Solar Corona and Active Regions (OSCAR)

Coronal Mass Ejections (CMEs) and Corotating Interaction Regions (CIRs) are major sources of magnetic storms on Earth and are therefore considered to be the most dangerous space weather events. The Observatories of Solar Corona and Active Regions (OSCAR) mission is designed to identify the 3D structure of coronal loops and to study the trigger mechanisms of CMEs in solar Active Regions (ARs) as well as their evolution and propagation processes in the inner heliosphere. It also aims to provide monitoring and forecasting of geo- effective CMEs and CIRs. OSCAR would contribute to significant advancements in the field of solar physics, improvements of the current CME prediction models, and provide data for reliable space weather forecasting. These objectives are achieved by utilising two spacecraft with identical instrumentation, located at a heliocentric orbital distance of 1 AU from the Sun. The spacecraft will be separated by an angle of 68° to provide optimum stereoscopic view of the solar corona. We study the feasibility of such a mission and propose a preliminary design for OSCAR

Target acquisition for space applications

Genaue Information über die aktuelle Ausrichtung eines Teleskops ist seit jeher die Vor- aussetzung für hochpräzise astronomische Beobachtungen. Während dies schon für erd- gebundene Teleskope schwierig sein kann, ist es bei weltraumbasierten Teleskopen, auf- grund ihrer ständigen Orbitalbewegung, eine besondere Herausforderung. Die Anforde- rungen an die Genauigkeit sind dabei von Mission zu Mission unterschiedlich und werden in der Regel mit spezieller Hardware für die Lagebestimmung erfüllt. Dabei können dedi- zierte Instrumente wie Stern- oder Sonnensensoren, oder aber auch die wissenschaftliche Instrumentierung direkt zum Einsatz kommen. Im letzteren Fall wird nach der anfängli- chen Ausrichtung die erzielte Lage mit dem Teleskop erneut vermessen und bestätigt bzw. gegebenenfalls korrigiert. Der Characterising ExOPlanet Satellite, oder auch CHEOPS ge- nannt, ist ein Fall, wo diese Technik zum Einsatz kommt. CHEOPS ist für ultrahochprä- zise Photometrie von Sternen mit bekannten Exoplaneten konzipiert und wird die Erde in einem 3-Achsen stabilisierten sonnensynchronen Orbit umkreisen. Dieser Orbit wur- de zwar für ungestörte Beobachtungen bei minimalem Streulicht optimiert, ist bei Pe- rigäumsdurchgängen allerdings thermischen Schwankungen ausgesetzt. Daraus entsteht eine periodische thermoelastische Deformation zwischen der Teleskopstruktur und dem Service-Modul, welche die präzise Ausrichtung zwischen den Sternsensoren und dem Te- leskop beeinflusst und in weiterer Folge eine genaue Platzierung des beobachteten Sterns am CCD verhindert. Da der beobachtete Stern damit nicht auf der geplanten CCD Position abgebildet wird, ist es für die wissenschaftlichen Beobachtungen notwendig diesen über ein dediziertes Sternerkennungssystem zu finden und die Ausrichtung dementsprechend zu korrigieren. Dieses System wurde softwareseitig implementiert und besteht aus Soft- warekomponenten zur Sterndetektierung und zwei unterschiedlichen Algorithmen, um die Sterne am Nachthimmel mittels geometrischen und photometrischen Eigenschaften eindeutig zu identifizieren. Der vermutlich hauptsächlich benutzte geometrische Identi- fikationsalgorithmus wurde ursprünglich für den Einsatz ohne jegliche Information zur momentanen Ausrichtung in Sternsensoren konzipiert. Da diese für CHEOPS bis auf einen bekannten maximalen Ausrichtungsfehler vorhanden ist, wurde er entsprechend adaptiert und optimiert. In dieser Masterarbeit wird das Design, die Implementierung und Konfigu- ration dieses maßgeschneiderten Sternerkennungssystems präsentiert. Zusätzlich wurden Leistungstests unter verschiedensten Beobachtungsbedingungen durchgeführt, um den reibungsfreien Einsatz zu garantieren.The prerequisite for any astronomical high precision observation is accurate knowledge of the telescope pointing. While this can be a difficult task to achieve for ground based observatories, it is especially challenging for the case of space telescopes due to their non stationary nature. The requirements for pointing accuracy are mission and observation de- pendent and are usually achieved with specialised attitude determination hardware such as star trackers or sun sensors. In some cases, it can also be necessary to further improve the pointing by the utilisation of the science instrument. Thus, observations with the final pointing are used to verify or improve the achieved accuracy. The CHaracterising ExO- Planet Satellite (CHEOPS) is such a case. It will perform ultra high precision photometry of stars that are confirmed hosts of exoplanets on a 3-axis stabilised sun-synchronous or- bit. While this orbit is optimised for uninterrupted observations at minimum stray light conditions, it will periodically introduce thermal variations during close approaches for perigee passes. As a result, thermo-elastic deformations between the spacecraft bus and the optical telescope assembly will affect the alignment between the star trackers and the payload instrument. This introduces a periodic high pointing uncertainty, which will not only interfere with the reliable placement of the target star on its intended location, but also its respective identification. Therefore, an additional acquisition system for a distinct target identification became crucial for the nominal mission operation. In its current im- plementation it consists of software to locate star positions on observed full frame images and two independent star identification algorithms, which are designed to identify the target star by its photometric or the geometric properties of the surrounding field of view (FOV). The main acquisition algorithm was built upon an algorithm that was originally developed for the use in star trackers that operate in lost in space scenarios, where no initial attitude information is available. It was adapted and optimised for the special case of CHEOPS, where an initial attitude up to a maximum pointing error is available for each observation. The design, implementation and configuration of said acquisition system is subject of this thesis, which is meant to be a compendium for the CHEOPS science operations staff. In addition, it features a detailed description of the various test campaigns that verified the optimal performance under all anticipated conditions

Disambiguation of Vector Magnetograms by Stereoscopic Observations from the Solar Orbiter (SO)/Polarimetric and Helioseismic Imager (PHI) and the Solar Dynamic Observatory (SDO)/Helioseismic and Magnetic Imager (HMI)

International audienceSpectropolarimetric reconstructions of the photospheric vector magnetic field are intrinsically limited by the $180^{\circ}$ 180 ∘ ambiguity in the orientation of the transverse component. The successful launch and operation of Solar Orbiter have made the removal of the 180 ∘ ambiguity possible using solely observations obtained from two different vantage points. While the exploitation of such a possibility is straightforward in principle, it is less so in practice, and it is therefore important to assess the accuracy and limitations as a function of both the spacecrafts’ orbits and measurement principles. In this work, we present a stereoscopic disambiguation method (SDM) and discuss thorough testing of its accuracy in applications to modeled active regions and quiet-Sun observations. In the first series of tests, we employ magnetograms extracted from three different numerical simulations as test fields and model observations of the magnetograms from different angles and distances. In these more idealized tests, SDM is proven to reach a 100% disambiguation accuracy when applied to moderately-to-well resolved fields. In such favorable conditions, the accuracy is almost independent of the relative position of the spacecraft with the obvious exceptions of configurations where the spacecraft are within a few degrees of co-alignment or quadrature. Even in the case of disambiguation of quiet-Sun magnetograms with significant under-resolved spatial scales, SDM provides an accuracy between 82% and 98%, depending on the field strength. The accuracy of SDM is found to be mostly sensitive to the variable spatial resolution of Solar Orbiter in its highly elliptic orbit, as well as to the intrinsic spatial scale of the observed field. Additionally, we provide an example of the expected accuracy as a function of time that can be used to optimally place remote-sensing observing windows during Solar Orbiter observation planning. Finally, as a more realistic test, we consider magnetograms that are obtained using a radiative-transfer inversion code and the SO/PHI Software siMulator (SOPHISM) applied to a 3D-simulation of a pore, and we present a preliminary discussion of the effect of the viewing angle on the observed field. In this more realistic test of the application of SDM, the method is able to successfully remove the ambiguity in strong-field areas

A space weather mission concept: observatories of the solar corona and active regions (oscar) – Erratum

In this erratum we acknowledge EASCO as one of the inspirational mission concepts that helped the development of our original mission concept OSCAR

A space weather mission concept: observatories of the solar corona and active regions (OSCAR)

International audienceCoronal Mass Ejections (CMEs) and Corotating Interaction Regions (CIRs) are major sources of magnetic storms on Earth and are therefore considered to be the most dangerous space weather events. The Observatories of Solar Corona and Active Regions (OSCAR) mission is designed to identify the 3D structure of coronal loops and to study the trigger mechanisms of CMEs in solar Active Regions (ARs) as well as their evolution and propagation processes in the inner heliosphere. It also aims to provide monitoring and forecasting of geo-effective CMEs and CIRs. OSCAR would contribute to significant advancements in the field of solar physics, improvements of the current CME prediction models, and provide data for reliable space weather forecasting. These objectives are achieved by utilising two spacecraft with identical instrumentation, located at a heliocentric orbital distance of 1 AU from the Sun. The spacecraft will be separated by an angle of 68° to provide optimum stereoscopic view of the solar corona. We study the feasibility of such a mission and propose a preliminary design for OSCAR.This article has an erratum (https://doi.org/10.1051/swsc/2016040) : In this erratum we acknowledge EASCO as one of the inspirational mission concepts that helped the development of our original mission concept OSCAR

A Space Weather mission concept: Observatories of the Solar Corona and Active Regions (OSCAR)

Coronal Mass Ejections (CMEs) and Corotating Interaction Regions (CIRs) are major sources of magnetic storms on Earth and are therefore considered to be the most dangerous space weather events. The Observatories of Solar Corona and Active Regions (OSCAR) mission is designed to identify the 3D structure of coronal loops and to study the trigger mechanisms of CMEs in solar Active Regions (ARs) as well as their evolution and propagation processes in the inner heliosphere. It also aims to provide monitoring and forecasting of geo-effective CMEs and CIRs. OSCAR would contribute to significant advancements in the field of solar physics, improvements of the current CME prediction models, and provide data for reliable space weather forecasting. These objectives are achieved by utilising two spacecraft with identical instrumentation, located at a heliocentric orbital distance of 1 AU from the Sun. The spacecraft will be separated by an angle of 68° to provide optimum stereoscopic view of the solar corona. We study the feasibility of such a mission and propose a preliminary design for OSCAR