1,721,021 research outputs found
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
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
Five Years of SMARTnet: Data, Processing, and Improvements.
No full textSMARTnet, operated by the Astronomical Institute of the University of Bern (AIUB) and the German Aerospace Center (DLR), went online and became open to the public in 2017 with two telescope stations located in Zimmerwald, Switzerland, and Sutherland, South Africa. Over its five-year operational timespan, new Partners have joined while one Partner left, leaving telescope stations distributed today over Australia, South Africa, and Europe. All stations combined, 10 passive-optical telescopes are actively providing data to the network.
New contributors are currently in the applicant phase and will, together with further stations planned by DLR, enhance the network’s capabilities. The retrieved data are used for research, collision warnings, catalogue maintenance, or for deriving data products, which can be sold to third parties. For the aforementioned points, the Backbone Catalogue of Relational Debris Information (BACARDI) was developed at DLR. BACARDI processes input data received from SMARTnet to data products such as ephemerides or orbit information for telescope observation planning, and attempts to detect new objects where an association of observations to already known objects is unsuccessful. To better operate the telescope stations, a dedicated software, called SMARTies, is under development as a joint project by AIUB and DLR. With this software, the telescope stations operations can be optimised to increase the daily data acquisition. It is planned to release SMARTies as Open Source software.
To avoid deteriorating accuracy of the orbital information, ephemerides forecasted by BACARDI are combined with the planning tool “Optimal Catalog Maintenance and Survey Tasking” (OMST), which will help to keep all resident space objects in the data base. Furthermore, OMST will allow to search for new objects in the vicinity of the telescopes’ fields of view in so-called “dead-times”
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
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
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
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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