A simplified approach to analyze the space debris evolution in the low earth orbit

During the past 60 years the number of objects on Earth orbits has increased. So has the risk of collisions, which is likely to be the main driver for space debris generation in the future. This is important, for example, in densely populated regions like the sun-synchronous orbit at around 800 km altitude. In order to predict the future development of the debris environment numerical simulations can be used. These simulations are usually based on initial assumptions like the launch rate, the probability distribution of success of post mission disposal measures and the likelihood for catastrophic collisions. The computationally expensive Monte-Carlo method is employed for the random sampling of the defined events. Additionally, a propagator needs to process the objects to determine potential collision partners, increasing the demand for computing power even further. In this paper an analytical model is presented, which is based on source and sink mechanisms, like launches, collisions and explosions. In this approach different altitude shells and diameter bins, as well as four different object classes for intact objects and fragments, each on circular and eccentric orbits are considered. By using pre-computed tables for orbital lifetimes and decay rates, both the computational effort and complexity of the model are decreased. The model can be adjusted to reflect different forecasts by altering the decay and collision rates. The paper concludes by showing preliminary results and a discussion of the generic approach, which allows the model to be fitted against more computationally expensive Monte-Carlo simulations

Progress in melanoma modeling in vitro

Melanoma is one of the most studied neoplasia, although laboratory techniques used for investigating this tumor are not fully reliable. Animal models may not predict the human response due to differences in skin physiology and immunity. In addition, international guidelines recommend to develop processes that contribute to the reduction, refinement and replacement of animals for experiments (3Rs). Adherent cell culture has been widely used for the study of melanoma to obtain important information regarding melanoma biology. Nonetheless, these cells grow in adhesion on the culture substrate which differs considerably from the situation in vivo. Melanoma grows in a 3D spatial conformation where cells are subjected to a heterogeneous exposure to oxygen and nutrient. In addition, cell-cell and cell-matrix interaction play a crucial role in the pathobiology of the tumor as well as in the response to therapeutic agents. To better study melanoma new techniques, including spherical models, tumorospheres, and melanoma skin equivalents have been developed. These 3D models allow to study tumors in a microenvironment that is more close to the in vivo situation, and are less expensive and time consuming than animal studies. This review will also describe the new technologies applied to skin reconstructs such as organ-on-a-chip that allows skin perfusion through microfluidic platforms. 3D in vitro models, based on the new technologies, are becoming more sophisticated, representing at a great extent the in vivo situation, the "perfect" model that will allow less involvement of animals up to their complete replacement, is still far from being achieved. This article is protected by copyright. All rights reserved

GPS Based Attitude Determination for the Flying Laptop Satellite

This paper introduces the GPS based attitude determination system (GENIUS) onboard the university small satellite Flying Laptop. The attitude determination algorithm which is based on a Kalman Filter and processes single differences of the C/A-code and carrier phase measurements is shortly described. The algorithm uses the LAMBDA-method to resolve the integer ambiguities of the double differences of the carrier phase measurements. These resolved ambiguities are then used to fix the single difference ambiguities in the filter. The results of ground based tests and numerical simulations are introduced and the accuracy of the attitude determination algorithm is assessed

Sensitization of malignant melanoma to TRAIL in an organotypic tumor-testsystem

Das Maligne Melanom, der schwarze Hautkrebs, ist die aggressivste und tödlichste Form von Hautkrebs mit einer weltweit stark steigenden Inzidenz. Insbesondere für Patienten mit metastatischen Stadien bleibt das Maligne Melanom bis heute auf Grund einer hohen Resistenz gegenüber Radio- und Chemotherapien bis auf wenige Ausnahmefälle unheilbar. Die Suche nach neuen, spezifischen Therapien nimmt folglich einen großen Stellenwert in der aktuellen Melanomforschung ein. In diesem Zusammenhang hat der Todesligand TRAIL zunehmend an Interesse und Bedeutung gewonnen, da er selektiv Apoptose in Tumorzellen induzieren kann ohne dabei normale, gesunde Zellen zu schädigen. Trotz der apoptotischen Wirkungsweise von TRAIL sind viele Melanomzelllinien und das primäre Melanom resistent gegenüber diesem Todesliganden. Erstmals konnte im Rahmen dieser Arbeit gezeigt werden, dass sich TRAIL resistente Melanomzellen nicht nur in der 2D-Zellkultur, sondern auch unter in vivo ähnlichen Bedingungen, nämlich in dreidimensionalen Tumorsphäroiden und organotypischen Hautmodellen, tumorselektiv gegenüber TRAIL sensitivieren lassen, indem sie mit TRAIL und UVB oder Cisplatin kostimuliert werden. Die Sensitivierung geht dabei mit der Degradation von IκBα und somit indikativ mit der Aktivierung von NFκB, der Depletion des anti-apoptotischen Proteins XIAP und der Aktivierung von Caspase 3 einher. Die in dieser Arbeit hergestellten Tumorsphäroide und Vollhautmodelle mit integrierten Melanomzellen simulierten in hohem Maße das Milieu und die Histomorphologie eines in vivo Tumors. Daraus resultierend konnte also gezeigt werden, dass die Behandlung des Malignen Melanoms mit TRAlL in Kombination mit UVB oder Cisplatin nicht nur eine in vitro, sondern auch eine in vivo Relevanz besitzt. Weiterhin konnte in dieser Arbeit durch die Integration von Tumorsphäroiden spezifischer Größe in funktionelle Vollhautmodelle ein neuartiges, organotypisches Tumor-Testsystem mit hoher klinischer Relevanz etabliert werden. Dieses simulierte nicht nur die dreidimensionale Struktur und die Zellheterogenität eines soliden, avaskulären kutanen Malignen Melanoms, sondern auch dessen mögliche Mechanismen der Langzeitresistenz. Dieses neu entwickelte humane und in vivo ähnliche Tumor-Testsystem bietet sich also zur präklinischen Evaluierung und Selektion von Substanzen oder Therapien für das Maligne Melanom an.Malignant Melanoma also called „black skin cancer“ is the most aggressive and deadliest form of skin cancer with an increasing incidence worldwide. In particular patients with metastatic melanoma are generally considered incurable since advanced stages of melanoma are highly resistant to radio- and chemotherapy. Therefore, there is the great effort in ongoing melanoma research to find new and specific treatment options for this disease. In this regard the death ligand TRAIL has gained considerable interest and relevance as a potential anticancer agent, given its ability to induce apoptosis in transformed cells without doing harm to normal, healthy cells. However treatment with this tumor-selective death ligand is confined by the fact that many melanoma cell lines and primary melanoma are resistant against TRAIL-induced apoptosis. In the context of this work it could be shown for the first time that TRAIL-resistant melanoma cells could be highly sensitised to TRAIL-induced apoptosis not only in 2D-cell culture but also under in vivo like conditions, namely in tumor spheroids and organotypic skin models by stimulating the melanoma cells with TRAIL in combination with UVB or cisplatin. Sensitization correlates with the degradation of IκBα and thus indicatively with the activation of NFκB, the depletion of the anti-apoptotic protein XIAP and the activation of capase 3. Produced tumor spheroids and full skin models with integrated melanoma cells highly simulated the milieu and the histomorpholgy of a native tumor. Resulting from this it could be demonstrated that treating malignant melanoma with TRAIL in combination with UVB or cisplatin not only has an in vitro but also an in vivo relevance. Furthermore, an innovative organotypic tumor test system of high clinical relevance was developed by integrating tumor spheroids of a specific size in functional full skin models. This test system not only mimicked the three-dimensional structure and the cellular heterogeneity of a solid, avascularized cutaneous malignant melanoma but also its possible mechanisms of long-term resistance. Therefore, this newly developed human and in vivo like tumor test system might serve for the preclinical evaluation and selection of drugs and therapies for malignant melanoma

In Orbit Debris Detection based on Solar Panels

The Solar Genarator based Space Debris Impact-Detector (SOLID) currently under development at DLR, has a large impact area and offers high orbital flexibility. Once placed in orbit, it will collect Space Debris (SD) and Micro-Meteoroids (MM) impact data for software validation (e.g. MASTER or ORDEM). The verification of SOLID itself will be based on High-Velocity-Impact testing (HVI-testing) anticipated at the Fraunhofer EMI (Ernst-Mach-Institute for High-Speed Dynamics in Freiburg, Germany). This paper presents the current state of SOLID development. Furthermore the setup of the engineering model as well as corresponding assumptions made in terms of the manufacturing process are presented

HVI-TEST SETUP OF IN-SITU SPACE DEBRIS DETECTOR

Collisions of spacecraft in orbit with Space Debris (SD) or Micro-Meteoroids (MM) lead to payload degradation, anomalies or failures in spacecraft operation or even to loss of a whole mission. Existing flux models and impact risk assessment tools, like MASTER or ORDEM, PIRAT, ESABASE2 and BUMPER II are used to analyze the mission risk concerning this hazard potential. The validation of the flux models so far is partly based on SD and MM impact data from in-situ impact detectors, e.g. DEBIE, GORID, capture cells and on the analyses of retrieved hardware from space, e.g. LDEF, HST or EURECA. However the knowledge on the small objects populations (millimeter down to micron sized) in space is rather limited and needs to be enhanced for reliable models. As a contribution Deto soft-ware validation in terms of data acquisition, a new type of impact detector is currently under development at DLR. The Solar Generator based Space Debris Impact Detector (SOLID) makes use of spacecraft solar panels and there-fore offers a large sensor area and high flexibility regarding the orbit. This paper presents the impact detector design as well as the Hyper-Velocity-Impact (HVI) test setup, foreseen for corresponding tests at the Fraunhofer Institute for High-Speed-Dynamics, Ernst-Mach-Institut (EMI) in Freiburg, Germany

REFLECTIVITY OF NAK DROPLETS

ABSTRACT An important contribution to the space debris population near 900 km orbital altitude are the NaK droplets. Sixteen nuclear powered satellites of the type RORSAT launched between 1980 and 1988 activated a reactor core ejection system close to this altitude. The core ejection causes an opening of the primary coolant circuit. The liquid coolant has been released into space during these core ejections, forming droplets up to a diameter of about 5.5 cm. These droplets consist of an alloy of two alkali metals, sodium and potassium (NaK). In this paper the monochromatic and the total reflectivity of NaK is calculated using theoretical models. The reflectivity depends on the alloy composition and temperature of a droplet. The alloy composition may change due to evaporation, resulting in an enrichment of sodium especially at the droplet surface. According to the literature, there is only a limited number of available measurement data concerning the optical properties of NaK alloys. Furthermore the published data for pure sodium and potassium are controversial. Thus it is necessary to investigate the optical properties of alkali metals and their alloys. Mainly two types of optical absorption, the intraband and the interband absorption, are considered. The intraband absorption is calculated using the Drudemodel which uses electrical properties to derive the optical constants of pure metals or alloys. Drude assumes that the valence electrons can be treated as free electrons. The electrons behave like an ideal gas of uncharged particles. The theory of free electrons is a very simple model for the description of the valence electrons in metals. This assumption is sufficient for alkali metals, because they show a nearly free electron behavior. For the interband absorption the classical Butcher-model is used. Furthermore an absorption anomaly which has been observed in some alkali metals is discussed. Especially for potassium, some measurements revealed an unexpected absorption in the visible and the near infrared. This absorption can be determined using a model according to Overhauser who assumes charge-density waves (CDW). But the existence of the anomalous absorption is controversial. The influence of the different models on the reflectivity is discussed. The reflectivity is calculated depending on the alloy composition at the surface of a droplet. The results are compared to measurement data from the literature. It is shown that NaK droplets have a very high total reflectivity

Development of in-situ Space Debris Detector

Due to high relative velocities, collisions of spacecraft in orbit with Space Debris (SD) or Micrometeoroids (MM) lead to payload degradation, anomalies or failures in spacecraft operation, or even to loss of a whole mission. Flux models and impact risk assessment tools, such as MASTER or ORDEM, and ESABASE2 or BUMPER II, are used to analyse the mission risk concerning this hazard potential. The validation of the ux models is based on SD and MM impact data from in-situ impact detectors; e.g. DEBIE, GORID and capture cells; and on the analysis of retrieved hardware from space; e.g. LDEF, HST or EURECA. However, the knowledge about the population of small (millimeter down to micron sized) objects in space is limited, and needs to be enhanced for reliable models. This paper provides an overview and assessment of SD and MM impact detectors and proposes an innovative detection concept, which utilises existing spacecraft components for detection purposes. The detector concept would be an active large area sensor and could be own in any orbit

Development of in-situ Space Debris Detector, Advances in Space Research

Due to high relative velocities, collisions of spacecraft in orbit with Space Debris (SD) or Micrometeoroids (MM) can lead to payload degradation, anomalies as well as failures in spacecraft operation, or even loss of mission. Flux models and impact risk assessment tools, such as MASTER (Meteoroid and Space Debris Terrestrial Environment Reference) or ORDEM (Orbital Debris Engineering Model), and ESABASE2 or BUMPER II are used to analyse mission risk associated with these hazards. Validation of flux models is based on measured data. Currently, as most of the SD and MM objects are too small (millimeter down to micron sized) for ground-based observations (e.g. radar, optical), the only available data for model validation is based upon retrieved hardware investigations e.g. Long Duration Exposure Facility (LDEF), Hubble Space Telescope (HST), European Retrievable Carrier (EURECA). Since existing data sets are insufficient, further in-situ experimental investigation of the SD and MM populations are required. This paper provides an overview and assessment of existing and planned SD and MM impact detectors. The detection area of the described detectors is too small to adequately provide the missing data sets. Therefore an innovative detection concept is proposed that utilises existing spacecraft components for detection purposes. In general, solar panels of a spacecraft provide a large area that can be utilised for in-situ impact detection. By using this method on several spacecraft in different orbits the detection area can be increased significantly and allow the detection of SD and MM objects with diameters as low as 100 lm. The design of the detector is based on damage equations from HST and EURECA solar panels. An extensive investigation of those panels was performed by ESA and is summarized within this paper. Furthermore, an estimate of the expected sensitivity of the patented detector concept as well as examples for its implementation into large and small spacecraft are presented