USE OF EISCAT 3D FOR OBSERVATIONS OF SPACE DEBRIS

Conference paper from 7th European Conference on Space Debris ESA/ESOC, Darmstadt/Germany 18 - 21 April 2017We investigate the capabilities of the next generation ionospheric research radar EISCAT 3D (E3D) for observations of space objects. The radar is multi-static, and is therefore capable of observing instantaneous threedimensional vector velocity and position by observing round-trip delay and Doppler shift between the transmitter and three receiver sites. The radar is to be located in Northern Scandinavia, which provides a high revisitrate for high inclination objects. To model the performance of E3D for space object observations, we have included radar equation based analysis of object detectability as a function of range and size. To study the performance of the radar for orbital elements determination, we have used a linearized error covariance analysis for idealized Keplerian elements. The analysis includes range and range-rate errors due to signal-to-noise and ionospheric radio propagation. To estimate the fraction of total debris that can be observed with E3D, we have used the MASTER model [FGW+09]. E3D uses a relatively low VHF frequency (233 MHz), which experiences more radio wave propagation effects than more conventional higher frequency space surveillance radars. Our modeling shows that ionospheric ray-bending and group delay are severe enough that these effects need to be modeled in order to determine accurate orbital elements. As EISCAT 3D is an ionospheric research radar, there will be high quality ionospheric electron density measurements that can be utilized for radio propagation modeling. Our simulations indicate that the radar can be used for observations of orbital elements of objects down to 5 cm in diameter. It is therefore feasible that the radar could provide to be a useful source of accurate information of orbital elements of space debris

Поликультурное образование как направление деятельности открытого университета

Авторы дают определение понятий "поликультурное образование" и "открытый университет"; обращаются к правовым актам и учебным программам, целью которых является поликультурное просвещение, и приходят к выводу о значимости этого направления в деятельности открытого образования в условиях многокультурного информационного общества

2018 Beam-park observations of space debris with the EISCAT radars

Source at https://conference.sdo.esoc.esa.int/proceedings/neosst1/paper/480.Monitoring the evolution of the space debris environment requires regular radar observations of the space debris population. This study presents the results from 24 hours of beam-park observations of space objects conducted simultaneously with the EISCAT Svalbard and Tromsø radars on and between January 4th and 5th, 2018. The measurements are processed with a new matched filter bank analysis program, which doubles the coherent integration time, and hence sensitivity, compared with the previous program. We observe 2077 objects with the Tromsø radar and 2400 objects with the Svalbard radar. The detections are correlated with the NORAD catalog. We find that 68% of the Tromsø and 85% of the Svalbard radar detections are from objects in the NORAD catalog, with most of the catalog object detections being in the side lobes of the radar antenna. The beam-park data are compared with a simulated beam-park experiment for catalog objects. The simulation uses a radar detection model that includes the effects of coherent integration and an antenna beam shape with side lobes. We find that the simulation agrees well with the measurements, indicating that the radar sensor response is accurately modeled. Our results highlight the importance of modeling antenna side lobes when analyzing beam-park measurements. Not taking taking into account side lobe detections can lead to an underestimation of radar cross-sections and an overestimation of population density

Simulation of the space debris environment in LEO using an analytical approach

Several numerical approaches exist to simulate the evolution of the space debris environment. These simulations usually rely on the propagation of a complete population of objects in order to determine the collision probability for each object. Using a Monte Carlo (MC) approach the chances for events, such as explosions and collisions, are triggered based on an assumed probability distribution. So in many different scenarios different objects are fragmented and contribute to a different version of the space debris environment. Finally, the results of the different scenarios are averaged to get a statistically significant estimation. This method is computationaly very expensive due to the propagation of the objects and the application of the MC method. At the Institute of Aerospace Systems (ILR) an analytical model capable of describing the evolution of the space debris environment has been developed and implemented. The model is based on source and sink mechanisms, where yearly launches as well as collisions and explosions are considered as sources. The natural decay and post mission disposal measures are the only sink mechanisms. This method reduces the computational costs tremendously. In order to achieve this benefit a few simplifications have been applied. The approach of the model partitions the LEO into altitude shells. Only two kinds of objects are considered, intact bodies and fragments, which are also divided into diameter bins. As an extension to the previously presented model the eccentricity has additionally been taken into account with 67 eccentricity bins. While a set of differential equations has been implemented in a generic manner, the Euler method has been chosen to integrate the equations for a given time span. For this paper parameters have been chosen so that the model is able to reflect the results of the numerical MC-based simulation LUCA, which is also being developed at the ILR. The evolution of the population in LEO for a 200 years time span is shown and compared for both approaches using step sizes of 1 year. For selected objects in LEO the flux and environmental criticality values are shown. In conclusion the field of application for such a fast analytical model is shown

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

Obeticholic acid for the treatment of non-alcoholic steatohepatitis: interim analysis from a multicentre, randomised, placebo-controlled phase 3 trial

Background Non-alcoholic steatohepatitis (NASH) is a common type of chronic liver disease that can lead to cirrhosis. Obeticholic acid, a farnesoid X receptor agonist, has been shown to improve the histological features of NASH. Here we report results from a planned interim analysis of an ongoing, phase 3 study of obeticholic acid for NASH. Methods In this multicentre, randomised, double-blind, placebo-controlled study, adult patients with definite NASH,non-alcoholic fatty liver disease (NAFLD) activity score of at least 4, and fibrosis stages F2–F3, or F1 with at least oneaccompanying comorbidity, were randomly assigned using an interactive web response system in a 1:1:1 ratio to receive oral placebo, obeticholic acid 10 mg, or obeticholic acid 25 mg daily. Patients were excluded if cirrhosis, other chronic liver disease, elevated alcohol consumption, or confounding conditions were present. The primary endpointsfor the month-18 interim analysis were fibrosis improvement (≥1 stage) with no worsening of NASH, or NASH resolution with no worsening of fibrosis, with the study considered successful if either primary endpoint was met. Primary analyses were done by intention to treat, in patients with fibrosis stage F2–F3 who received at least one dose of treatment and reached, or would have reached, the month 18 visit by the prespecified interim analysis cutoff date. The study also evaluated other histological and biochemical markers of NASH and fibrosis, and safety. This study is ongoing, and registered with ClinicalTrials.gov, NCT02548351, and EudraCT, 20150-025601-6. Findings Between Dec 9, 2015, and Oct 26, 2018, 1968 patients with stage F1–F3 fibrosis were enrolled and received at least one dose of study treatment; 931 patients with stage F2–F3 fibrosis were included in the primary analysis (311 in the placebo group, 312 in the obeticholic acid 10 mg group, and 308 in the obeticholic acid 25 mg group). The fibrosis improvement endpoint was achieved by 37 (12%) patients in the placebo group, 55 (18%) in the obeticholic acid 10 mg group (p=0·045), and 71 (23%) in the obeticholic acid 25 mg group (p=0·0002). The NASH resolution endpoint was not met (25 [8%] patients in the placebo group, 35 [11%] in the obeticholic acid 10 mg group [p=0·18], and 36 [12%] in the obeticholic acid 25 mg group [p=0·13]). In the safety population (1968 patients with fibrosis stages F1–F3), the most common adverse event was pruritus (123 [19%] in the placebo group, 183 [28%] in the obeticholic acid 10 mg group, and 336 [51%] in the obeticholic acid 25 mg group); incidence was generally mild to moderate in severity. The overall safety profile was similar to that in previous studies, and incidence of serious adverse events was similar across treatment groups (75 [11%] patients in the placebo group, 72 [11%] in the obeticholic acid 10 mg group, and 93 [14%] in the obeticholic acid 25 mg group). Interpretation Obeticholic acid 25 mg significantly improved fibrosis and key components of NASH disease activity among patients with NASH. The results from this planned interim analysis show clinically significant histological improvement that is reasonably likely to predict clinical benefit. This study is ongoing to assess clinical outcomes

Deriving a priority list based on the environmental criticality

The collision of Iridium 33 and Cosmos 2251 as well as the fragmentation of Fengyun 1C showed the consequences such events can have for the space debris environment. In order to avoid future fragmentations disused satellites and rocket bodies should be removed from orbit to reduce the buildup of new space debris, as suggested by the Space Debris Mitigation Guidelines. For objects that are posing great risk of being fragmented and thus generating new fragments, but are unable to maneuver, active debris removal missions can be considered. Such elaborate and costly missions have to be planned carefully so they unfold the required effect on the space debris environment. For the selection of target objects priority lists can be compiled, ranking the objects by urgency of removal. The ranking of the objects depends on the criteria that are chosen to be applied. For example it is common to estimate the flux an object is exposed to, or based on its mass the impact it has on the environment when fragmented, or even a combination of both. In this paper a criteria called environmental criticality (EC) is used to generate a new priority list based on the current catalogue of on orbit objects. The EC is defined as a product of the risk of fragmentation and the impact the fragmentation has on the space debris environment. Because the impact on the overall population for the given time span of 300 years is evaluated an analysis of the fragmentation in every year is necessary. This approach puts great computational constraints on the traditional Monte-Carlo based simulations of the future space debris environment. For this reason a new simulation tool based on an analytical model, which has been developed at the Institute of Aerospace Systems, is used to estimate the impact of a given fragmentation on the future space debris environment. A metric for the interpretation of the results of the criticality is proposed. The ranking objects is compared to lists, which have been derived based on different criteria

Extending the ECOB space debris index with fragmentation risk estimation

In recent years several formulations of debris indices have been proposed to provide a fast assessment of the criticality of a space object in terms of its impact on the debris environment. In a previous work, we proposed a formulation (ECOB, Environmental Consequences of Orbital Breakups) based on the evaluation of the consequences of the fragmentation of the studied object in terms of the increase in the collision probability for operational satellites. This work discusses the extensionof that approach by considering not only the effect of the fragmentation but also its likelihood. In addition, a method to take into account different End-of-Life scenarios and the application to constellations are discussed