1,721,024 research outputs found
European Expert Centre for Space Safety providing services and support for space surveillance and traffic management.
No full textDeveloped within ESA’s SSA and Space Safety Programme (S2P), the Expert Centre for Space Safety provides subject matter expertise and operational services to coordinate SST data acquisition by a multitude of diverse sensors. It supports a variety of applications including tasked tracking, survey, and characterization observations by means of passive optical, satellite laser ranging (SLR), and radar techniques. A core service consists in the validation and qualification of sensors for the mentioned applications. The service includes technical support to sensor operators by experts to achieve compliance with data calibration and quality, as well as data formatting requirements. All formats and interfaces used by the Expert Centre are based on international standards and the data quality requirements are derived by the user community.
Coordinating observation campaigns for customers, in particular ESA, is another important service offered by the Centre. Such campaigns may include very heterogeneous types of sensors operated by commercial companies, academia, government, and inter-governmental institutions. The Expert Centre takes care of the sensor planning, the data quality control, calibration and reformatting of the data if necessary, as well as the monitoring of key performance indices defined in service level agreements.
In terms of object characterization, the Expert Centre focuses in particular on establishing and maintaining a catalogue of attitude information by fusing observations from different techniques, such as light curves, SLR and radar measurements.
The paper will illustrate the different services and operational capabilities with examples of sensor qualifications and extensive survey, tracking and characterization observation campaigns which involved more than a dozen optical, SLR and radar sensors.
The Expert Centre is hosted and operated by the Astronomical Institute of the University of Bern, Switzerland (AIUB) and may serve as a reference for future national expert centres and site-specific deployments within ESA
Multi-sensor space object tracking for tumbling motion characterization.
No full textThe knowledge of the attitude dynamics of passive space objects or decommissioned satellites gains importance in the rapidly growing sector of Close-Proximity Operations (CPO) for In-Orbit Servicing or Active Debris Removal. In particular, knowing the spin axis orientation, the spin period and the rate of change of such parameters in the reference frame of choice is necessary for the optimum decision on the method that will be used to perform the in-orbit operation safely and efficiently.
In this paper we report the efforts and the results obtained in a study supported by ESA which aims at the development of methods for the determination of the spacecraft attitude motion and its evolution. Multiple detection technologies were operated during the project, including Satellite and Space Debris Laser Ranging, CCD and Single Photon Avalanche Diode (SPAD) photon-counter light curves, as well as measurements from tracking and imaging radars. The data from these observation techniques can be exploited in a complementary way through two different approaches for attitude determination known as “amplitude” and “epoch” methods. CCD photometric measurements are more suited to the former method, which is based on the amplitude of the intensity variations in the light curve. On the other hand, laser ranging data and single-photon counter light curves better fulfil the requirements for the temporal analysis in the epoch method, which extracts the tumbling parameters from the embedded temporal signals and benefits from the difference between synodic and sidereal rotation rate of the object. In addition to the combination of these two approaches, radar measurements of selected objects-of-interest (OOI) were performed for validation during a joint tracking campaign.
Models for the attitude evolution were analysed and simulated using the In-Orbit Tumbling Analysis (ιOTA) tool, which was further improved and validated in the current project. The comparison of the propagated attitude with the one determined from measurements serves as validation for the attitude determination methods, the simulator, and the evolution models
Tracking the Dark Side on a shoe-string budget
No full textMeaningful SSA work on earth-orbiting satellites can be done on a shoe-string budget, with modest, off the shelf equipment. This has been shown by an informal group of self-funded Independent Space Observers (“ISO’s”) organized around the Seesat-L mailing list. Literally from their backyards, they track some 200 “classified” objects – objects that are not in the public orbital catalogues – using very simple equipment: from binoculars and stopwatch on the ‘old skool’ end, to DSLR’s or sensitive CCTV or CMOS/CCD cameras with fast photographic lenses and GPS time control on the sophisticated end. In this paper, a brief outline is provided on the techniques and equipment used by Seesat-L members and an example is given on how a new 'classified' launch is located and tracked, often within hours of launch. It is discussed why the whole concept of keeping the orbits of certain space assets “classified” is problematic: not only is it unrealistic, but it also goes against core notions of transparency and accountability regarding activities in space.Astrodynamics & Space Mission
Optimization of Observation Strategy to Improve Re-Entry Prediction of Objects in HEO
No full textDuring the last decade the number of space debris moving on high elliptical orbit (HEO) has grown fast. Many of these resident space objects (RSO) consist of medium and large spent upper stages of launch vehicles, whose atmosphere re-entry might violate on-ground casualty risk constraints. Increasing the accuracy of re-entry predictions for this class of RSO is therefore a key issue to limit the hazards on the Earth assets. Traditional computational methods are mainly based on the exploitation of Two Line Elements (TLEs), provided by the United States Strategic Command (USSTRATCOM) and currently the only public data source available for these kind of analyses. TLE data however, are characterized by low accuracies, and in general come without any uncertainty information, thus limiting the achievable precision of the re-entry estimates. Better results on the other hand, can be obtained through the exploitation of observational data provided by one or more Earth sensors. Despite the benefits, this approach introduces a whole new set of complexities, mainly related with the design of proper observation campaigns. This paper presents a method based on evolutionary algorithms, for the optimization of observation strategies. The effectiveness of the proposed approach is demonstrated through dedicated examples, in which re-entry predictions, attainable with existing and ideal sensor architectures, are compared with corresponding results derived from TLE data
Improving orbit prediction via thermospheric density calibration
No full textThe uncertainty on Thermospheric Mass Density (TMD), as derived from atmospheric models, can reach extremely high values. This effect is noteworthy in Low Earth Orbit (LEO), where atmospheric drag is the main perturbing force, as well as the most uncertain. LEO harbours almost 18,000 space objects at the end of 2021, around 60% of the total space debris population, and the rate of growth is increasing every year. Increasing the accuracy of TMD models, and thus the uncertainty characterisation, is important to ensure space environment sustainability in this congested and contested region. Accurate TMD modelling is a decisive factor in all space applications below the exopause, from LEO mission design to Space Situational Awareness (SSA) service provision: from conjunction assessment to re-entry and fragmentation analysis To enhance empirical TMD models, atmospheric density observations derived from satellite measurements are assimilated.This paper presents a novel approach for assimilating thermospheric density observations into atmospheric models to improve the accuracy of orbit predictions in short- to medium- term propagations. First, Global Navigation Satellite System (GNSS) derived density data from Swarm satellites are ingested from the publicly available Level 2 data products of the European Space Agency (ESA). In a second step, density data is assimilated into the empirical model NRMLSISE-00, using Principal Component Analysis (PCA) to decompose into the main temporal and spatial modes, providing useful physical insight into the main variables driving the model. Thirdly, the model is tested on several cases, whose data was not assimilated, such as LEO satellites that are well-tracked with GNSS-derived positions: Sentinel, and GRACE. The model is also tested with objects with less accurate reference trajectories, such as catalogued space debris in LEO. Finally, the orbits are propagated, using the improved drag model that includes the neutral density from the assimilation of the GNSS-derived observations into NLRMSISE-00. The accuracy of the method is assessed and compared to non-assimilated models. During the discussion of the results, other sources of uncertainty are analysed. To name a few, geomagnetic activity, solar radiation pressure coefficient, attitude knowledge, and spacecraft parameters such as mass, area, drag coefficient, and so on. The improvement on the state accuracy and uncertainty realism after a medium-term propagation is analysed and the application to catalogue maintenance discussed.Astrodynamics & Space Mission
Space Surveillance Network Capabilities Evaluation Mission
No full textThe last years saw the diffusion of nano, pico and femto satellite missions launched by multiple entities thanks to the launch cost reduction and the electronics miniaturization. Such missions usually present limited capabilities in terms of precise orbit determination and extremely small radar and optical cross-sections. Often these missions carry one or more laser retro-reflectors for precise orbit determination but precise orbital measurements cannot be found in the literature. Miniaturized GNSS receivers are also often carried out but due to the experimental nature of such missions, the reliability and time span of such measurements is limited, leaving radar tracking as the only reliable tracking method. Due to the size of such satellites, the signal-to-noise ratio of such radar measurements is typically low and satellite identification (when launched on ride-share launches with a hundred or more other satellites) proves difficult and time-consuming.Being these very small satellites at the edge of the radar detection capabilities and not providing independent orbit determination means, their position uncertainty could be quite significant, leading to an increased orbit collision perceived risk.With this paper, we present a dedicated small satellite formation, made by multiple nano and pico satellites to evaluate the space surveillance network tracking capabilities and limits. The formation is made by a 3U CubeSat to be deployed as part of a rideshare launch. The satellite would be equipped with multiple means to track it, including a GNSS receiver, a set of multiple laser retro-reflectors, and LEDs for optical, laser, and radar tracking, allowing to characterize also different detection means in terms of capabilities. Such a satellite is made of two independent smaller satellites that can be un-docked in orbit upon command, reducing the satellite size and cross-section. This would push the detection limit for the space surveillance networks starting from an already acquired object and with limited clutter around it. Independent laser and GNSS tracking would allow ground measurement validation and validate position estimations. Further pico-satellites would be deployed by each sub-satellite to further push the detection limits and validate up to which size objects are trackable (still optically, radar and GNSS), thanks to miniaturized GNSS receivers already flown by several other missions.Sub-satellite separation is implemented upon command to ensure the process can be followed and executed at lower altitudes to limit the orbital lifetime of eventually hard-to-track small objects that could worsen the space debris problem. Ground characterization (in terms of optical and radar properties) will be performed, also including polarimetric measurements used to identify the separate satellites. All these technologies together would contribute to creating a unique tool to estimate the tracking capabilities of multiple instruments, specifically tailored for very small objects, the hardest to track, as compared to other characterization activities performed on much bigger objects.Space Systems Egineerin
AIUB Space Safety Expert Center multi-sensor data acquisition campaign - overview, results and lessons learned.
No full textAiming to test the available observing infrastructure, the Expert Centre for Space Safety (ExpCen) coordinated the observation campaign to a predefined set of target objects using different measurement techniques. The coordination of the campaign included interfacing with the involved stations, sensor planning and tasking, data exchange, with emphasis on formats and standardized procedures, besides a critical analysis on the performance for both ends: the involved observing stations and the ExpCen. The multi-sensor observing network consists of six passive optical and one radar sensor. The array of passive optical sensors included telescopes with apertures ranging from 0.2 to 1m tasked to do tracking, photometry and survey observations. The radar system consists of a S-band (3GHz) fully-steerable 25m single dish antenna, focused on tracking targets flying in Low Earth Orbit (LEO). In this work, we present the obtained results after the coordination of the campaign. One of the highlights of the campaign was the simultaneous data acquisition between radar and passive optical. We report our findings including challenges and lessons learned applicable to future campaigns
AIUB Space Safety Expert Centre validation and qualification procedure for sensors acquiring light curve observations.
No full textThis contribution presents the Validation and Qualification (V&Q) procedure for Light Curve (LC) observations with passive optical sensors. Our primary goal is to present our current vision of the procedure, solicit input and feedback from the community to improve the V&Q process
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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