This article gives an overview about the activities of the Leipzig Institute of Meteorology (LIM) within the HALO (High Altitude and Long Range Aircraft) Scientific Priority Program (SPP 1294 funded by DFG). HALO offers unique possibilities for atmospheric research and Earth observations. It can carry a scientific payload of up to 3 t, cover a range of 10000 km and reach a ceiling of 15 km. The LIM contributes to the instrumentation of HALO with the Spectral Modular Airborne Radiation measurement sysTem (SMART). SMART was deployed during the first HALO mission TECHNO in 2010. During subsequent five HALO campaigns SMART measurements provided valuable insights regarding cloud properties and the Earth’s radiative budget. Three further missions, which are scheduled for the coming years, will make use of SMART measurements as well. / Dieser Bericht gibt einen Überblick über die Aktivitäten des Leipziger Instituts für Meteorologie (LIM) im HALO Schwerpunktprogramm (SPP 1294 der DFG). HALO bietet einzigartige Möglichkeiten für die Atmosphärenforschung und Erdbeobachtung. Es kann eine wissenschaftliche Nutzlast von 3 t aufnehmen, eine Reichweite von 10000 km zurücklegen und eine maximale Flughöhe von 15 km erreichen. Das LIM trägt zur Instrumentierung von HALO mit dem Spectral Modular Airborne Radiation measurement sysTem (SMART) bei. SMART wurde 2010 bei der ersten HALO Mission TECHNO eingesetzt. In fünf folgenden HALO Kampagnen verschafften SMART Messungen wertvolle Erkenntnisse bezüglich Wolkeneigenschaften und dem Strahlungsbudget der Erde. Drei weitere HALO Missionen, die für die kommenden Jahre geplant sind, werden ebenfalls SMART nutzen.

A newly proposed F-class mission by the European Space Agency (ESA) in 2019,Comet Interceptor, aims to dynamically intercept a New Solar System Objectsuch as a Dynamically New Comet (DNC). The Spacecraft will be placed in aperiodic (Halo) orbit around the Sun-Earth L2 Lagrangian point, waiting for furtherinstructions about the passage of a comet or an asteroid, which could well bereached within the stipulated mission constraints.A major part of the detection of these bodies will be owed to the Large SynopticSurvey Telescope (Currently under construction in Chile), which hopes to vastlyincrease the ability to discover a possible target using the catalogue of LongPeriod Comets and a set of its orbits. It is suggested that, in a mission length of<5 years, discoveries and warnings are possible so that optimization of thetrajectory and characterisation of the object are done within the set windows.This thesis is aimed at facilitating a transfer to a Potentially Hazardous Asteroid(PHA), a subset of the Near-Earth Objects (NEO), as a secondary choice on theoff-chance that the discovered comet could not be reached from the L2 Librationpoint within the mission constraints.The first section of this thesis deals with the selection of a Potentially HazardousAsteroid for our mission from the larger database of the Near-Earth Objects,based on a measure of impact hazard called the Palermo Scale, while the secondsection of the thesis aims to obtain a suitable Halo orbit around L2 through ananalytical construction method. After a desired orbit is found, the invariantmanifolds around the Halo orbit are constructed and analysed in an attempt toreduce the ΔV, where from the spacecraft can intercept the Potentially Hazardous Asteroid through the trajectory demanding the least energy.

The Milky Way's halo is an approximately spherical distribution of stars surrounding the Galaxy that carries the history of the Milky Way. The outer halo is a Galactic region with long dynamical timescales largely built up by accreted material. Probing its stellar constituents has been historically difficult due to the distances of outer halo stars, making them appear faint. To characterise the distant halo and unravel the history of our galaxy, we thus need to use stars that are intrinsically bright, i.e. giant stars. To draw useful conclusions about the distant halo, these target giants should have metallicity and kinematics information. Therefore a catalogue of distant halo giants with Pristine survey metallicities, Gaia mission data and distances has been created in this work. The cuts used to create this catalogue are made to remove as many dwarf stars as possible and have been tested on a training sample containing spectroscopic metallicities and surface gravities as well as Gaia mission data. Defining giants as being all stars with log(g) < 3.5 dex, we can calculate the purity and completeness of the sample after the cuts have been applied to test which cuts optimise the catalogue. The methods used to cut away the dwarfs are to first plot all stars with positive Gaia parallaxes and fractional parallax uncertainties smaller than 50% in a colour-absolute magnitude diagram and remove all stars from the sample that in this plot populate the main sequence. We then colour-code the colour-apparent magnitude diagram by purity and completeness after this parallax cut has been performed, and select a region in this diagram in which both purity and completeness are maximised, with the final region being (GBP,0 - GRP,0) > 0.8 and G0 < 17.6. The distances to the stars in this region are then computed by comparing their apparent magnitudes to the absolute ones of isochrones. These cuts are then applied to a sample of 6,884,547 stars with Pristine survey and Gaia mission data. The final catalogue is kinematically unbiased and contains 345,303 halo giants. It contains 78% giants and only 4% of giants are erroneously deselected.  With the final sample we are able to probe as deep as 103 kpc into the halo and have created preliminary metallicity distribution functions of different regions of the halo. This sample will be used to further investigate the distant halo metallicity structure and its substructure that was created through merger events.

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According to the paradigm of lambda-CDM cosmology, the stellar halo ofour Galaxy has been built-up over time through the accretion of other galaxiesand star clusters. The remnants of some of these are still observable today asstellar streams, but are typically very faint and difficult to resolve amidst the farmore numerous foreground Milky Way stars. The VelHel-4 stream, discoveredby Helmi et al. [2017], consists of seven members selected based on their energiesand angular momenta. Further studies of these stars has shown evidence ofglobular cluster (GC) abundance patterns, suggesting that the stream originatedfrom a GC progenitor, but a larger sample is needed to verify this signature. Theobjective of this thesis is to find new candidate members of the VelHel-4 stellarstream in order to better characterize its properties and to confirm a possibleGC origin.The preliminary selection of stars was done kinematically, by computing theorbital actions and energies using astrometric data and radial velocities for abright subset of the Gaia DR3 database, and then analyzing the clustering ofstream members in different combinations of action space. The selected samplewas then cleaned by analyzing the positions of these stars in a colour-magnitudediagram. In total, 34 stars were included in the final selection. Follow-up high-resolution spectroscopy of these candidates is needed to study their stellar abun-dances and confirm the possible GC origin of this stream.

The lightning is the natural source of electromagnetic radiation. It is an atmospheric electrical discharge.  However, since recent times, it was discovered that there are other types of lightning besides those that are visible to the naked eye. They are called TLEs (Transient Luminous Event) and take place above the clouds during thunderstorms. Distinct classification is applied to the various existing TLEs in compliance with their shapes, size, color, altitude, origin and duration. Thus, all Transient Luminous Events are categorized to the following types: elves, spites, halos, blue jets, blue starters, gigantic jets, trolls, gnomes, pixies and ghosts. TLE investigation missions are important for several scientific purposes. They allow to gain an understanding of the lightning creation processes, contribution on global electric circuits as well as chemical influence on the Earth’s climate.  TLE observations can be performed by lightning detection and location systems which differs according to their location. They can be ground-based, space-based as well as carried on aircraft or balloon. Lightning location systems in space are usually conducted on large-, medium- or micro-sized satellites.  The main scope of this thesis is to explore and describe all possible and known methods and techniques of TLE investigation as well as discussions of gained observation results for better understanding and further analysis of more suitable instruments for TLE detection mission on LEO orbit. Analysis of suitable equipment will be done according to the conclusion made from considered lightning detection systems with similar missions and pursuant to nanosatellite requirements.

<p dir="ltr">The Global Navigation Satellite System (GNSS) is heavily relied on for the navigation of Earth satellites. For satellites in cislunar space and beyond, GNSS is not readily available. As a result, other sources such as NASA's Deep Space Network (DSN) must be relied on for navigation. However, DSN is overburdened and can only support a small number of satellites at a time. Furthermore, communication with external sources can become interrupted or deprived in these environments. Given NASA's current efforts towards cislunar space operations and the expected increase in cislunar satellite traffic, there will be a need for more autonomous navigation options in cislunar space and beyond.</p><p dir="ltr">In this thesis, a navigation system capable of accurate and computationally efficient orbit determination in these communication-deprived environments is proposed and investigated. The emphasis on computational efficiency is in support of cubesats which are constrained in size, cost, and mass; this makes navigation even more challenging when resources such as GNSS signals or ground station tracking become unavailable.</p><p dir="ltr">The proposed navigation system, which is called GRAVNAV in this thesis, involves a two-satellite formation orbiting a planet. The primary satellite hosts an Extended Kalman Filter (EKF) and is capable of measuring the relative position of the secondary satellite; accurate attitude estimates are also available to the primary satellite. The relative position measurements allow the EKF to estimate the absolute position and velocity of both satellites. In this thesis, the proposed navigation system is investigated in the two-body and three-body problems.</p><p dir="ltr">The two-body analysis illuminates the effect of the gravity model error on orbit determination performance. High-fidelity gravity models can be computationally expensive for cubesats; however, celestial bodies such as the Earth and Moon have non-uniform and highly-irregular gravity fields that require complex models to describe the motion of satellites orbiting in their gravity field. Initial results show that when a second-order zonal harmonic gravity model is used, the orbit determination accuracy is poor at low altitudes due to large gravity model errors while high-altitude orbits yield good accuracy due to small gravity model errors. To remedy the poor performance for low-altitude orbits, a Gravity Model Error Compensation (GMEC) technique is proposed and investigated. Along with a special tuning model developed specifically for GRAVNAV, this technique is demonstrated to work well for various geocentric and lunar orbits.</p><p><br></p><p dir="ltr">In addition to the gravity model error, other variables affecting the state estimation accuracy are also explored in the two-body analysis. These variables include the six Keplerian orbital elements, measurement accuracy, intersatellite range, and satellite formation shape. The GRAVNAV analysis shows that a smaller intersatellite range results in increased state estimation error. Despite the intersatellite range bounds, semimajor axis, measurement model, and measurement errors being identical for both orbits, the satellite formation shape also has a strong influence on orbit determination accuracy. Formations that place both satellites in different orbits significantly outperform those that place both satellites in the same orbit.</p><p dir="ltr">The three-body analysis primarily focuses on characterizing the unique behavior of GRAVNAV in Near Rectilinear Halo Orbits (NRHOs). Like the two-body analysis, the effect of the satellite formation shape is also characterized and shown to have a similar impact on the orbit determination performance. Unlike the two-body problem, however, different orbits possess different stability properties which are shown to significantly affect orbit determination performance. The more stable NRHOs yield better GRAVNAV performance and are also less sensitive to factors that negatively impact performance such as measurement error, process noise, and decreased intersatellite range.</p><p dir="ltr">Overall, the analyses in this thesis show that GRAVNAV yields accurate and computationally efficient orbit determination when GMEC is used. This, along with the independence of GRAVNAV from GNSS signals and ground-station tracking, shows that GRAVNAV has good potential for navigation in cislunar space and beyond.</p>

The study was based on cognitive biases with the aim of investigating the extent to which the individual's physical appearance affects the hiring process, and whether individuals who are perceived as more attractive are ascribed more positive characteristics. The study was conducted with a quantitative method, where the data collection was done via an online survey with 62 respondents, the majority of whom had previous experience of decision- making in a recruitment context. The respondents were asked to rate perceived attractiveness, characteristics and employability in four different individuals by looking at different facial images. All questions and rating scales on the questionnaire were based on the validated instruments Competence and warmth scale (CWS) and Job Suitability Scale (JSS). The results showed that more attractive people have a higher mean value than less attractive people in CWS and JSS. It was concluded that the individual's appearance has a significant impact in the hiring process, and that there is a tendency to attribute more positive characteristics to people who are considered more attractive compared to those who are judged to be less attractive. / Studien utgick från kognitiva fördomar med syftet att undersöka i vilken grad individens fysiska utseende påverkar anställningsprocessen, samt om individer som uppfattas som mer attraktiva tillskrivs mer positiva egenskaper. Studien genomfördes med en kvantitativ metod, där datainsamlingen skedde via en online-enkät med 62 respondenter, varav majoriteten hade tidigare erfarenhet av beslutsfattande inom rekryteringssammanhang. Respondenterna fick skatta upplevd attraktivitet, egenskaper och anställningsbarhet hos fyra olika individer genom att titta på olika ansiktsbilder. Samtliga frågor och skattningsskalor på enkäten utgick utifrån de validerade instrumenten Competence and warmth scale (CWS) och Job Suitability Scale (JSS). Resultatet visade att mer attraktiva personer har högre medelvärde än mindre attraktiva personer i CWS och JSS. Sammanfattningsvis drogs slutsatsen att individens utseende har en betydande inverkan i anställningsprocessen, samt att det finns en tendens att attribuera mer positiva egenskaper till personer som anses vara mer attraktiva jämfört med de som bedöms som mindre attraktiva.

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