Future improvements in conjunction assessment and collision avoidance using a combined laser tracking/nudging network

The expected significant increase of space launch activities in the next years, both from spacefaring nations and in the private sector, yields an enhanced risk of space debris generation. In this regard, space situational awareness (SSA) is mandatory not only for the protection of active space missions, but as a prerequisite to prevent aggravation of the space debris environment by cascading effects of secondary debris generation due to in-space collisions. High accuracy in laser ranging to space objects (within a meter or better) has already been demonstrated, e.g., by the International Laser Ranging Service (ILRS) network. Thus, laser ranging can be considered as a highly promising sensor technology for space surveillance in the Low Earth Orbit (LEO) which has the potential to complement existing radar facilities in terms of achievable state vector accuracy. Furthermore several laser-based concepts on orbit modification have been proposed in the recent years. In particular, momentum transfer to space debris via photon pressure appears to become feasible, due to advancements in adaptive optics and the commercial availability of high power lasers with an average power output beyond the 10 kW level. This allows for the setup of a network of comparably cost-efficient laser stations for momentum transfer in the near future paving the way for the capability to remotely operate space debris in particular in terms of debris vs. debris collision avoidance maneuvers. In the scope of the conceptual study LARAMOTIONS (SSA P3-SST-XV) funded by the European Space Agency (ESA) simulations of a ground-based laser tracking and momentum transfer network have been carried out in order to estimate the subsequent improvements in conjunction assessment and collision avoidance for operational satellites as well as for debris vs. debris encounters. Therefore, the software generates reference trajectories from a Two-Line-Element (TLE) catalogue for any number of target objects in LEO. From these trajectories station passes as well as random measurement samples are computed and the orbit determination process is simulated yielding the collision rate and false alert rate of the given network. Special emphasis is taken on considering station downtimes due to weather conditions by introducing a station-specific duty cycle based on the analysis of historical weather data. Afterwards a momentum transfer network can be simulated. In order to achieve this, forces induced by photon pressure are computed from tabulated data of target-specific Laser-Matter-Interaction simulations and are applied to the object’s trajectories. A second laser tracking simulation based on the modified orbits eventually shows the advantages of the given system in terms of conjunction analysis and avoidance, in particular considering debris vs. debris collisions for which at present collision avoidance maneuvers are not yet available. The paper will outline the software architecture as well as the results for different network geometries considering the number of stations, their geographical distribution and different duty cycle values. Among the results, the effects of the network geometry and station distribution on the achievable orbit accuracy will be presented. Two operational scenarios will be compared: On-demand tracking in response to conjunction alerts and a laser catalog scenario yielding the maximum number of objects, which can continuously be tracked by a given network independently from radar-based SSA data. Finally, an outlook will be given regarding future simulations and possible enhancements of the simulation environment

Potential of using ground-based high-power Lasers to decelerate the evolution of Space Debris in LEO

High-power lasers offer a unique potential for debris collision avoidance and orbit lowering for removal purposes within the debris mitigation scenario. Photon pressure and surface ablation are explored as suitable mechanisms to remotely apply the required velocity increment to debris targets. The appropriate regime of laser intensity and fluence, respectively, is discussed in terms of technical maturity and laser safety. Laser power beaming from ground to space is analysed considering atmospheric constraints like aerosol attenuation, cloud cover and turbulence including possibilities and limitations of technical counter-measures. Operational risks comprise uncertainties in momentum transfer as well as thermo-mechanical side effects highlighting the necessity of target reconnaissance. Moreover, making space debris touchable from ground might raise concerns of third parties regarding their own space assets not to be tackled by high-power lasers. Hence, the need for global governance of this approach for space debris mitigation is reflected

Conceptual Study on Laser Networks for Near‐Term Collision Avoidance for Space Debris in the Low Earth Orbit

Due to the increasing amount of space debris, several laser‐based concepts for orbit modification have been proposed in the recent years. Since the sparse availability of pulsed lasers with high energy (> 10 kJ) seems to render laser‐ablative debris nudging for collision avoidance into a solution only for the long run, alternative options which can be realized earlier are mandatory to counter the rapidly increasing number of space debris in low Earth orbit. In this regard, high‐power CW lasers (> 10 kW) have been proposed in the past for debris nudging by photon pressure. With momentum coupling being 3 – 4 orders of magnitude lower than in the case of laser ablation, this might appear as a poor alternative at first glance, but the opposite is the case when a greater number of laser stations are combined forming an international network for laser tracking and momentum transfer (LTMT). From this viewpoint, we report on our findings on photon momentum transfer to space debris from our work performed under the conceptual study LARAMOTIONS (SSA P3‐SST‐XV) funded by the European Space Agency (ESA) in the framework of ESA’s Space Situational Awareness Program. Commercial availability of high power CW lasers allows for the setup of a network of relatively cost‐efficient laser stations in the next decade. Such an LTMT network would serve for both momentum transfer to space debris as well as for high precision laser tracking as a prerequisite for conjunction alert assessment and high‐power laser beam pointing. Depending on the network size, geographical distribution of stations, orbit parameters and remaining time to conjunction, multi‐pass irradiation enhances the efficiency of photon momentum coupling by 1 – 2 orders of magnitude and has the potential to eventually yield a promisingly significant reduction of the collision rate in low Earth orbit

The RESET project: constructing a European tephra lattice for refined synchronisation of environmental and archaeological events during the last c. 100 ka

This paper introduces the aims and scope of the RESET project (. RESponse of humans to abrupt Environmental Transitions), a programme of research funded by the Natural Environment Research Council (UK) between 2008 and 2013; it also provides the context and rationale for papers included in a special volume of Quaternary Science Reviews that report some of the project's findings. RESET examined the chronological and correlation methods employed to establish causal links between the timing of abrupt environmental transitions (AETs) on the one hand, and of human dispersal and development on the other, with a focus on the Middle and Upper Palaeolithic periods. The period of interest is the Last Glacial cycle and the early Holocene (c. 100-8 ka), during which time a number of pronounced AETs occurred. A long-running topic of debate is the degree to which human history in Europe and the Mediterranean region during the Palaeolithic was shaped by these AETs, but this has proved difficult to assess because of poor dating control. In an attempt to move the science forward, RESET examined the potential that tephra isochrons, and in particular non-visible ash layers (cryptotephras), might offer for synchronising palaeo-records with a greater degree of finesse. New tephrostratigraphical data generated by the project augment previously-established tephra frameworks for the region, and underpin a more evolved tephra 'lattice' that links palaeo-records between Greenland, the European mainland, sub-marine sequences in the Mediterranean and North Africa. The paper also outlines the significance of other contributions to this special volume: collectively, these illustrate how the lattice was constructed, how it links with cognate tephra research in Europe and elsewhere, and how the evidence of tephra isochrons is beginning to challenge long-held views about the impacts of environmental change on humans during the Palaeolithic. © 2015 Elsevier Ltd.RESET was funded through Consortium Grants awarded by the Natural Environment Research Council, UK, to a collaborating team drawn from four institutions: Royal Holloway University of London (grant reference NE/E015905/1), the Natural History Museum, London (NE/E015913/1), Oxford University (NE/E015670/1) and the University of Southampton, including the National Oceanography Centre (NE/01531X/1). The authors also wish to record their deep gratitude to four members of the scientific community who formed a consultative advisory panel during the lifetime of the RESET project: Professor Barbara Wohlfarth (Stockholm University), Professor Jørgen Peder Steffensen (Niels Bohr Institute, Copenhagen), Dr. Martin Street (Romisch-Germanisches Zentralmuseum, Neuwied) and Professor Clive Oppenheimer (Cambridge University). They provided excellent advice at key stages of the work, which we greatly valued. We also thank Jenny Kynaston (Geography Department, Royal Holloway) for construction of several of the figures in this paper, and Debbie Barrett (Elsevier) and Colin Murray Wallace (Editor-in-Chief, QSR) for their considerable assistance in the production of this special volume.Peer Reviewe

Der interne Wandel d. Beschaeftigungssystems d. Bundesrepublik Deutschland, 1961 bis 1982

Summary in EnglishAvailable from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel C 154191 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Two-dimensional ultrafast transient absorption spectrograph covering deep-ultraviolet to visible spectral region optimized for biomolecules

We report on the implementation of a multi-kHz single-shot referenced non-coherent two-dimensional UV spectrograph based on conventional pump-probe geometry. It has the capability to cover a broad spectral region in excitation from 270-to-380 nm and in the detection from 270-to-390 nm and 320-to-720 nm. Other setups features are: an unprecedented time resolution of 33 fs (standard deviation); signals are photometrically corrected; a single shot noise of <1 mOD. It has the capability to operate with sample volumes as small as few μl which is an accomplishment in studying biological or biomimetic systems. To show its performances and potentials, we report two preliminary studies on the photophysics of phenanthrenes hosted in a multichromophoric antenna system and of aromatic amino acids in a blue-copper azurin

Development cycle 2 of the Modular Earth Submodel System (MESSy2)

The Modular Earth Submodel System (MESSy) is an open, multi-institutional project providing a strategy for developing comprehensive Earth System Models (ESMs) with highly flexible complexity. The first version of the MESSy infrastructure and process submodels, mainly focusing on atmospheric chemistry, has been successfully coupled to an atmospheric General Circulation Model (GCM) expanding it into an Atmospheric Chemistry GCM (AC-GCM) for nudged simulations and into a Chemistry Climate Model (CCM) for climate simulations. Here, we present the second development cycle of MESSy, which comprises (1) an improved and extended infrastructure for the basemodel independent coupling of process-submodels, (2) new, highly valuable diagnostic capabilities for the evaluation with observational data and (3) an improved atmospheric chemistry setup. With the infrastructural changes, we place the headstone for further model extensions from a CCM towards a comprehensive ESM. The new diagnostic submodels will be used for regular re-evaluations of the continuously further developing model system. The updates of the chemistry setup are briefly evaluated

3x30coaching - Grundverständnis und Umsetzung eines innovativen Beratungssettings

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