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Untracked space debris is the principal threat to operational satellites’ functioning whose services have become a fundamental part of our daily life. Though some specialised sensors can detect objects down to sub-cm sizes in geostationary Earth orbit, only objects larger than 30 cm are currently being catalogued. Thus, small debris are only seldom observed, typically for a short amount of time when surveying the sky. Having to deal with short arcs, the data association’s problem becomes relevant: one must find more observations of the same resident space object to precisely determine its orbit. This paper develops a new method enabled by differential algebra for track initialisation and catalogue build-up, within the framework of multi-target tracking. This is compared to literature methods that build on the concept of the admissible region and attributable to solve the problem of correlating sparse observations. The comparison is carried out on synthetic measurements and real optical observations obtained by the ZimSMART telescope on consecutive nights. Furthermore, simulated observations are used to assess whether raw data in the tracklets can be exploited to reduce the admissible region’s size. Though the gain in computational efficiency is only limited, this paper effectively shows an alternative method to the Mahalanobis distance, where the success of correlation is less affected by the time separation of two observations.

Since realising the idea that a man-made object can be intentionally placed into the Earth’s orbit, almost 10,000 satellites have been launched for multiple scientific, commercial and military purposes. These activities produce a huge amount of junk comprised not only of defunct artificial objects that no longer serve a useful purpose, but various collisions, explosions and leaks have produced millions of pieces of objects of size varying from micrometers to meters. Space debris pose a threat to sustainable space and to the near-earth environment at large. As a result, there is a need for the removal of such objects in a controlled and well-planned manner, or at least safeguarding the most precious satellites from collisions. Among the proposed techniques to avoid collisions, the orbital laser momentum transfer method has good potential for altering the orbits of high area-to-mass-ratio objects ( A / m ≳ 1 m 2 / kg , typically a few cm in size), that are too numerous for capturing techniques. The method is based on the idea of illuminating the target with a laser that induces radiation force. Here we show that the control of the debris can be further improved by using the polarisation of the laser beam. Certain amount of debris objects, maybe around 10–20%, pose asymmetric against the beam, and reflect light asymmetrically and significantly polarisation-dependent. This provides an opportunity for the closed-ended problem by introducing an additional degree of freedom for the direction of induced momentum. We present the theory for polarised light dynamics, and develop a new scattering model for reflective space debris. The model is supplemented with laboratory measurements. We show that asymmetry of the targeted object in itself may turn the momentum 1–30° for typical debris objects, and polarisation of the incident beam is capable of further affecting this direction by several degrees.

Satellite laser ranging allows to measure distances to satellites equipped with retroreflectors in orbits up to 36000 km. Utilizing a higher powered laser, space debris laser ranging detects diffuse reflections from defunct satellites or rocket bodies up to a distance of 3000 km. So far space debris laser ranging was only possible within a few hours around twilight while it is dark at the satellite laser ranging station and space debris is illuminated by the sun. Here we present space debris laser ranging results during daylight. Space debris objects are visualized against the blue sky background and biases corrected in real-time. The results are a starting point for all space debris laser ranging stations to drastically increase their output in the near future. A network of a few stations worldwide will be able to improve orbital predictions significantly as necessary for removal missions, conjunction warnings, avoidance maneuvers or attitude determination., Space debris laser ranging is a technique to measure distances to defunct satellites or rocket bodies in orbits around Earth which was only possible within a few hours around twilight. Here, the authors show the first space debris laser ranging results during daylight while correcting inaccurate predictions using a real-time target detection software.

A conceptual study has been carried out on laser station networks to enhance Space Situational Awareness and contribute to collision avoidance in the low Earth orbit by high-precision laser tracking of debris objects and momentum transfer via photon pressure from ground-based high-power lasers. Depending on the network size, geographical distribution of stations, orbit parameters, and remaining time to conjunction, multipass 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.

A major challenge when maintaining a space object catalog is the proper association of new measurements to already cataloged objects. Optical observations are typically associated by comparing the modeled observation to the measured one. The modeled observation is generated from cataloged object states by propagating them to the epoch of observation and transforming them from state space, e.g. orbital elements, to the observation space, e.g. right ascension and declination angles. In addition to propagating the states, their propagated uncertainty distribution is transformed to observation space as well. Statistical distance metrics, such as the Mahalanobis distance, are then evaluated to test whether the observation originated from the cataloged object or not. These distance measures often assume that the uncertainty can be represented with a normal distribution. Assuming that the catalog state uncertainty is properly represented by a normal distribution, it can still loose this property during the propagation in time and the transformation to observation space. The uncertainty of the catalog state is typically much larger than the one from new measurements (only a few arc seconds for optical telescopes) and is therefore more affected by transformation distortions. It is therefore beneficial to perform the comparison in a space advantageous for the state representation. This study will present a projection-based transformation of tracklet information into a favorable frame around the cataloged object state. The effect of the comparison-space selection on cataloguing performance is assessed, i.e. it is systematically tested if it is beneficial to directly compare angles and angular rates, or to compare in the newly proposed projected frame.

This paper describes selected current and planned optical (both passive and laser ranging) and radar observations data acquisition campaigns conducted by ESA's SSA Programme. One of these initiatives comprises the qualification of optical sensors. First qualification results from several telescopes are presented. The concept of an Expert Centre interfacing the SSA Space Surveillance and Tracking (SST) data centre and external sensors (optical passive telescopes and laser ranging sensors) is described that is found relevant for the community of optical observers in SST. Results from the validation and qualification campaigns performed to Borowiec laser station and ESA's Test-bed telescope in Cebreros are reported. ESA's two half-metre class telescopes on robotic mounts have been integrated in the frame of a technology development programme. Following an in-factory qualification programme, under human supervision and involving commercial, off-the-shelf processing software, for full-end autonomy and robustness testing, the deployment to final sites, covering both hemispheres, is expected to finalise in 2018. Main figure of merits of these robotic telescopes are described. ESA's test-bed radars also participated in several coordinated campaigns. We present first results of the quality assessment in this paper.

The solar radio flux at F10.7 cm and F30 cm is required by most models characterizing the state of the Earth's upper atmosphere, such as the thermosphere and ionosphere to specify satellite orbits, re-entry services, collision avoidance maneuvers and modeling of space debris evolution. We develop a method called RESONANCE ("Radio Emissions from the Sun: ONline ANalytical Computer-aided Estimator") for the prediction of the 13-month smoothed monthly mean F10.7 and F30 indices 1-24 months ahead. The prediction algorithm includes three steps. First, we apply a 13-month optimized running mean technique to effectively reduce the noise in the radio flux data. Second, we provide initial predictions of the F10.7 and F30 indices using the McNish-Lincoln method. Finally, we improve these initial predictions by developing an adaptive Kalman filter with the error statistics identification. The root-mean-square-error of predictions with lead times from 1 to 24 months is 5-27 sfu for the F10.7 and 3-16 sfu for F30 index, which statistically outperforms current algorithms in use. The proposed approach based on Kalman filter is universal and can be applied to improve the initial predictions of a process under study provided by any other forecasting method. Furthermore, we present a systematic evaluation of re-entry forecast as an application to test the performance of F10.7 predictions on past ESA re-entry campaigns for payloads, rocket bodies, and space debris that re-entered from June 2006 to June 2019. The test results demonstrate that the predictions obtained by RESONANCE in general also lead to improvements in the forecasts of re-entry epochs., Comment: 28 pages, 15 figures, accepted for publication in the Astrophysical Journal Supplement Series

Space surveillance by radar is especially used for the low Earth orbit to maintain a database, also called catalogue, of objects on orbit. Among others, surveillance radars which are constantly scanning a region of interest in the sky are used for this purpose. The detections from such a radar which cannot be assigned to an already known catalogue object might not contain enough information to obtain a reliable initial orbit for a new catalogue entry from a single measured pass, also called tracklet. Instead, two tracklets can be combined to improve the quality of the initial orbit which leads to the correlation problem. This means that it has to be tested whether two tracklets belong to the same object and an initial orbit has to be derived by combining the tracklets. A common approach to condense the information in the tracklet is fitting them with so-called attributables. Because radar observations include different types of observables, the fitting of these attributables has to be considered as an important part of the entire correlation process. This paper analyses the effect of the attributable fitting considering the achieved accuracy and influence on the tracklet correlation. A new singularity-free coordinate system is introduced, which improves the results of the fitting and correlation. Finally, a test on a simulated survey scenario introduces two additional filters to remove false positive correlations. It is shown that the attributable-based approach can be applied successfully to tracklets of up to three minutes length with different detection frequencies., 36 pages, 33 figures

The Faculty of Mathematics, Physics and Informatics of Comenius University in Bratislava, Slovakia (FMPI) operates its own 0.7-m Newtonian telescope (AGO70) dedicated to the space surveillance tracking and research, with an emphasis on space debris. The observation planning focuses on objects on geosynchronous (GEO), eccentric (GTO and Molniya) and global navigation satellite system (GNSS) orbits. To verify the system’s capabilities, we conducted an observation campaign in 2017, 2018 and 2019 focused on astrometric and photometric measurements. In last two years we have built up a light curve catalogue of space debris which is now freely available for the scientific community. We report periodic signals extracted from more than 285 light curves of 226 individual objects. We constructed phase diagrams for 153 light curves for which we obtained apparent amplitudes.

Optical surveys for space debris in high-altitude orbits have been conducted since more than ten years. Originally these efforts concentrated mainly on the geostationary region (GEO). Corresponding observation strategies, processing techniques and cataloguing approaches have been developed and successfully applied. The ESA GEO surveys, e.g., resulted in the detection of a significant population of small-size debris and later in the discovery of high area-to-mass ratio objects in GEO-like orbits. Comparably less experience (both, in terms of practical observation and strategy definition) is available for eccentric orbits that (at least partly) are in the MEO region, in particular for the Molniya-type orbits. Different survey and follow-up strategies for searching space debris objects in highly-eccentric MEO orbits, and to acquire orbits which are sufficiently accurate to catalog such objects and to maintain their orbits over longer time spans were developed. Simulations were performed to compare the performance of different survey and cataloguing strategies. Eventually, optical observations were conducted in the framework of an ESA study using ESA’s Space Debris Telescope (ESASDT) the 1-m Zeiss telescope located at the Optical Ground Station (OGS) at the Teide Observatory at Tenerife, Spain. Thirteen nights of surveys of Molniya-type orbits were performed between January and August 2013. Eventually 255 surveys were performed during these thirteen nights corresponding to about 47 h of observations. In total 30 uncorrelated faint objects were discovered. On average one uncorrelated object was found every 100 min of observations. Some of these objects show a considerable brightness variation and have a high area-to-mass ratio as determined in the orbit estimation process.

The European Space Agency’s (ESA) Space Debris Office provides a service to support operational collision avoidance activities. This support currently covers ESA’s missions Cryosat-2, Sentinel-1A and -2A, the constellation of Swarm-A/B/C in low-Earth orbit (LEO), as well as missions of third-party customers. In this work, we describe the current collision avoidance process for ESA and third-party missions in LEO. We give an overview on the upgrades developed and implemented since the advent of conjunction summary messages (CSM)/conjunction data messages (CDM), addressing conjunction event detection, collision risk assessment, orbit determination, orbit and covariance propagation, process control, and data handling. We pay special attention to the effect of warning thresholds on the risk reduction and manoeuvre rates, as they are established through risk mitigation and analysis tools, such as ESA’s Debris Risk Assessment and Mitigation Analysis (DRAMA) software suite. To handle the large number of CDMs and the associated risk analyses, a database-centric approach has been developed. All CDMs and risk analysis results are stored in a database. In this way, a temporary local “mini-catalogue” of objects close to our target spacecraft is obtained, which can be used, e.g., for manoeuvre screening and to update the risk analysis whenever a new ephemeris becomes available from the flight dynamics team. The database is also used as the backbone for a Web-based tool, which consists of the visualization component and a collaboration tool that facilitates the status monitoring and task allocation within the support team as well as communication with the control team. The visualization component further supports the information sharing by displaying target and chaser motion over time along with the involved uncertainties. The Web-based solution optimally meets the needs for a concise and easy-to-use way to obtain a situation picture in a very short time, and the support for third-party missions not operated from the European Space Operations Centre (ESOC). Finally, we provide statistics on the identified conjunction events, taking into account the known significant changes in the LEO orbital environment and share ESA’s experience along with recent examples.

We describe a novel data-processing and analysis pipeline for optical observations of moving objects, either of natural (asteroids, meteors) or artificial origin (satellites, space debris). The monitoring of the space object populations requires reliable acquisition of observational data, to support the development and validation of population models and to build and maintain catalogues of orbital elements. The orbital catalogues are, in turn, needed for the assessment of close approaches (for asteroids, with the Earth; for satellites, with each other) and for the support of contingency situations or launches. For both types of populations, there is also increasing interest to detect fainter objects corresponding to the small end of the size distribution. The ESA-funded StreakDet (streak detection and astrometric reduction) activity has aimed at formulating and discussing suitable approaches for the detection and astrometric reduction of object trails, or streaks, in optical observations. Our two main focuses are objects in lower altitudes and space-based observations (i.e., high angular velocities), resulting in long (potentially curved) and faint streaks in the optical images. In particular, we concentrate on single-image (as compared to consecutive frames of the same field) and low-SNR detection of objects. Particular attention has been paid to the process of extraction of all necessary information from one image (segmentation), and subsequently, to efficient reduction of the extracted data (classification). We have developed an automated streak detection and processing pipeline and demonstrated its performance with an extensive database of semisynthetic images simulating streak observations both from ground-based and space-based observing platforms. The average processing time per image is about 13 s for a typical 2k-by-2k image. For long streaks (length >100 pixels), primary targets of the pipeline, the detection sensitivity (true positives) is about 90% for both scenarios for the bright streaks ( SNR > 1 ), while in the low-SNR regime, the sensitivity is still 50% at SNR = 0.5 .

Collision avoidance manoeuvres are considered for mission design and fuel budget allocation, and may have a relevant impact in particular orbital regimes. Current operations for collision avoidance are based on Two-Line Elements (TLE) orbital data or the Conjunction Summary Message (CSM) data. This paper presents the most suitable approach for collision avoidance for several mission types when operations are based on TLE or CSM data, with a detailed analysis of the impact of the orbital accuracy of catalogue data and warning time-to-event on mission design in terms of fuel budget for collision avoidance activities and operational constraints imposed by the avoidance manoeuvres.

The Inter-Agency Space Debris Coordination Committee (IADC) Space Debris Mitigation Guidelines, issued in 2002 and revised in 2007, address the post mission disposal of objects in orbit. After their mission, objects crossing the Low Earth Orbit (LEO) should have a remaining lifetime in orbit not exceeding 25 years. Objects near the Geostationary Orbit (GEO) region should be placed in an orbit that remains outside of the GEO protected region. In this paper, the impact of satellites and rocket bodies performing End-of-Life (EOL) orbital manoeuvres on the collision risk in the LEO and GEO protected regions is investigated. The cases of full or partial compliance with the IADC post mission disposal guideline are studied. ESA's Meteoroid and Space Debris Terrestrial Environment Reference (MASTER) model is used to compare the space debris flux rate of the object during the remaining lifetime estimated for the pre-EOL-manoeuvre and for the post-EOL-manoeuvre orbit. The study shows that, on average, the probability of collision can be significantly decreased by performing an EOL-manoeuver.

Under ESA contract an industrial consortium including Aboa Space Research Oy (ASRO), the Astronomical Institute of the University of Bern (AIUB), and the Dutch National Aerospace Laboratory (NLR), proposed the observation concept, developed a suitable sensor architecture, and assessed the performance of a space-based optical (SBO) telescope in 2005. The goal of the SBO study was to analyse how the existing knowledge gap in the space debris population in the millimetre and centimetre regime may be closed by means of a passive optical instrument. The SBO instrument was requested to provide statistical information on the space debris population in terms of number of objects and size distribution. The SBO instrument was considered to be a cost-efficient with 20 cm aperture and 6° field-of-view and having flexible integration requirements. It should be possible to integrate the SBO instrument easily as a secondary payload on satellites launched into low-Earth orbits (LEO), or into geostationary orbit (GEO). Thus the selected mission concept only allowed for fix-mounted telescopes, and the pointing direction could be requested freely. Since 2007 ESA focuses space surveillance and tracking activities in the Space Situational Awareness (SSA) preparatory program. Ground-based radars and optical telescopes are studied for the build-up and maintenance of a catalogue of objects. In this paper we analyse how the proposed SBO architecture could contribute to the space surveillance tasks survey and tracking. We assume that the SBO instrumentation is placed into a circular sun-synchronous orbit at 800 km altitude. We discuss the observation conditions of objects at higher altitude, and select an orbit close to the terminator plane. A pointing of the sensor orthogonal to the orbital plane with optimal elevation slightly in positive direction (0° and +5°) is found optimal for accessing the entire GEO regime within one day, implying a very good coverage of controlled objects in GEO, too. Simulations using ESA’s Program for Radar and Optical Observation Forecasting (PROOF) in the version 2005 and a GEO reference population extracted from DISCOS revealed that the proposed pointing scenario provides low phase angles together with low angular velocities of the objects crossing the field-of-view. Radiometric simulations show that the optimal exposure time is 1–2 s, and that spherical objects in GEO with a diameter of below 1 m can be detected. The GEO population can be covered under proper illumination nearly completely, but seasonal drops of the coverage are possible. Subsequent observations of objects are on average at least every 1.5 days, not exceeding 3 days at maximum. A single observation arc spans 3° to 5° on average. Using a simulation environment that connects PROOF to AIUB’s program system CelMech we verify the consistency of the initial orbit determination for five selected test objects on subsequent days as a function of realistic astrometric noise levels. The initial orbit determination is possible. We define requirements for a correlator process essential for catalogue build-up and maintenance. Each single observation should provide an astrometric accuracy of at least 1”–1.5” so that the initially determined orbits are consistent within a few hundred kilometres for the semi-major axis, 0.01 for the eccentricity, and 0.1° for the inclination.

ESA’s Space Debris Office provides an operational service for the assessment of collision risks of ESA satellites. Currently, the ENVISAT and ERS-2 missions in low Earth orbits are covered by this service. If an upcoming high-risk conjunction event is predicted based on analysis of Two-Line Element (TLE) data from the US Space Surveillance Network, then independent tracking data of the potential high-risk conjunction object are acquired to improve the knowledge of its orbit. This improved knowledge and the associated small error covariances derived from the orbit determination process scale down the position error ellipsoid at the conjunction epoch. Hence, for the same miss-distance, in most cases an avoidance manoeuvre can be suppressed with an acceptable residual risk. During the past years sophisticated stand-alone tools have been developed and maintained at ESA’s Space Debris Office. The central tools for analysing conjunction events are the collision risk assessment software CRASS and the orbit determination software ODIN. ODIN is used to process tracking data and to determine orbits by least-squares fits of tracking data, or of pseudo-data in terms of osculating orbit states, which can for instance be derived from TLEs. On this basis, estimates of TLE error covariances also can be established as input for initial collision risk assessments. For ESA’s automated routine conjunction event assessments which are embedded in a daily process with 7-day predictions, the handling of high-risk events is work-intensive. This shortcoming has been addressed by the implementation of a job scheduler, and automated procedures to facilitate the processing of tracking data, the update of ephemerides and covariances, and the update of conjunction geometries and collision risk estimates. The application of the upgraded software environment is illustrated through two exemplary, recent conjunction events of ENVISAT (02009A) with Russian Cosmos satellites: the conjunction event on 2008-Jan-09 19:00 (UTC) with the chaser object COSMOS-1624 (85006A), and the conjunction event on 2007-Nov-14 13:49 (UTC) with the chaser object COSMOS-1486 (83079A).

In the framework of ESA's space debris research program optical measurements to search for space debris in high-altitude orbits are performed with the ESA 1-m telescope on Tenerife. Observations have been acquired during more than 500 nights during the past 6 years. Most of the data are ‘statistical’ in the sense that no catalogue of orbital data for individual objects is produced but only a list of ‘detections’ including rough orbital information and a visual magnitude for each of these detections. Moreover due to the narrow field of view of the telescope the optical surveys provide only snapshot-like samples of the space debris environment. There is no simple relation between the observed detection rates and the number of objects. In this paper we compare the ESA optical survey data from the year 2006 with simulated observations for different model populations, including the MASTER-2005 population. The simulations are performed with a software suite that links the ESA PROOF tool to our tools and takes into account the detailed observation scenarios and the details of the telescope and the camera system. A simulation using a geostationary (GEO) population with homogeneously distributed orbital elements is performed to analyze potential selection biases in the orbital element space of the observation scenarios. Of particular interest is the question if the observation scenarios may result in ‘artificial clusters’ in the observed distribution of the orbital planes. The simulation results for a GEO catalogue population are directly comparable with correlated detections and objects from the 2006 survey. The main results in this case are the percentage of detected objects with respect to the used catalogue and the coverage in the orbital element space. Finally the comparison of the observations with the results from simulations using the MASTER population represents an independent validation of the MASTER-2005 model. Using the results from the three mentioned simulations, we derive an estimate for the number of debris objects seen by the ESA 2006 surveys.

In the framework of its space debris research activities ESA established an optical survey program to study the space debris environment at high altitudes, in particular in the geostationary ring and in the geostationary transfer orbit region. The Astronomical Institute of the University of Bern (AIUB) performs these surveys on behalf of ESA using ESA’s 1-m telescope in Tenerife. Regular observations were started in 1999 and are continued during about 120–140 nights per year. Results from these surveys revealed a substantial amount of space debris at high altitudes in the size range from 0.1 to 1 m. Several space debris populations with different dynamical properties were identified in the geostationary ring. During the searches for debris in the geostationary transfer orbit region a new population of objects in unexpected orbits, where no potential progenitors exist, was found. The orbital periods of these objects are clustered around one revolution per day; the eccentricities, however, are scattered between 0 and 0.6. By following-up some of these objects using the ESA telescope and AIUB’s 1-m telescope in Zimmerwald, Switzerland, it was possible to study the properties of this new population. One spectacular finding from monitoring the orbits over time spans of days to months is the fact that these objects must have extreme area-to-mass ratios, which are by several orders of magnitudes higher than for ‘normal-type’ debris. This in turn supports the hypothesis that the new population actually is debris generated in or near the geostationary ring and which is in orbits with periodically varying eccentricity and inclination due to perturbations by solar radiation pressure. In order to further study the nature of these debris, multi-color and temporal photometry (light curves) were acquired with the Zimmerwald telescope. The light curves show strong variations over short time intervals, including signals typical for specular reflections. Some objects exhibit distinct periodic variations with periods ranging from 10 to several 100 s. All this is indicative for objects with complicated shapes and some highly reflective surfaces.

A new population of uncatalogued objects in geosynchronous Earth orbits (GEO), with a mean motion of about 1 rev/day and eccentricities up to 0.6, has been identified recently. The first observations of this new type of objects were acquired in the framework of the European Space Agency’s (ESA) search for space debris in GEO and the geostationary transfer orbit (GTO) using the ESA 1-m telescope on Tenerife. Earlier studies have postulated that the perturbations due to the solar radiation pressure can lead to such large eccentricities for GEO objects with a high area-to-mass ratio ( A / M ). The simulations showed that the eccentricities of GEO objects with large A / M exhibit periodic variations with periods of about one year and amplitudes depending on the value of A / M . The findings of these studies could be confirmed by observations from the ESA 1-m telescope on Tenerife. As opposed to GEO objects, only one GTO object with high A / M has been identified so far. Nevertheless, more such objects probably exist. Simulations were performed in order to study the orbital evolution of GTO objects with high A / M . The objective was on the one hand to find a possible explanation why only one GTO object with a high A / M has been observed so far, and on the other hand to propose suitable search patterns. The A / M values were assumed to vary from 1 to 20 m 2 /kg in our simulations. The semi-major axis a and the eccentricity e of GTO objects have a correlated decrease (in the sense that a (1 − e ) ≈ const.) with time caused by the air drag, leading to a characteristic line in the ( a , e )-diagram. Thus, the initial values of the semi-major axis and the eccentricity were randomly selected along this line. In addition to the evolution of the orbital elements, the dependency of the lifetime on the A / M value was also studied.

Two ESA-funded feasibility studies that aimed to develop observation strategies, to propose suitable sensor architectures, and to assess the expected performance of an independent European Space Surveillance System were carried out during the last years. The French company ONERA led two study teams comprising a number of European companies. The proposed space surveillance system consists of two subsystems, a phased-array radar system that shall be located in the South of Spain, and a network of ground-based electro-optical telescopes at four low latitude sites. This system allows to build-up and to maintain a catalogue of orbital elements of objects in space. It provides means to perform additional space surveillance tasks such as independent detection of fragmentation events, launches or manoeuvres, and allows to acquire the necessary measurements to assess the collision risk between catalogued objects. As a member of both study teams, the Astronomical Institute of the University of Bern (AIUB), Switzerland, contributed to the observation strategy definition, the system design, and the performance estimation of the optical observation part of the space surveillance system. This part of the system is intended to cover the Geostationary Orbit (GEO) and the Medium Earth Orbit (MEO) regions. This paper focuses on the development and evaluation of observation strategies for GEO and MEO within a space surveillance network. Observation requirements, possible strategies fulfilling the requirements, and the expected performance of selected strategies in terms of the coverage of a reference population are addressed. We conclude that GEO and MEO shall be covered by “stripe-scanning” approaches carried out by a network of telescopes. The simulations of the approaches using a reference population reveal that for both regions a nearly complete coverage can be guaranteed within a short time.

This paper presents the capabilities of a Space-Based Space Surveillance (SBSS) demonstration mission for Space Surveillance and Tracking (SST) based on a micro-satellite platform. The results have been produced in the frame of ESA’s "Assessment Study for Space Based Space Surveillance Demonstration Mission" performed by the Airbus Defence and Space consortium.

For space surveillance Europe is currently strongly depending on external sources. Although some European radar and optical facilities for space object tracking exist, there is no operational European space surveillance system. An ESA-funded feasibility study for a future independent European space surveillance capability was performed recently. Some of the main conclusions are presented here. We discuss the surveillance of the geostationary ring (GEO) by evaluating existing and newly designed optical ground-based sensors in terms of their performance. The main performance-related issues – the coverage of the GEO ring and the minimum detectable objects size – are discussed. In order to perform detailed simulations, an observation strategy was defined and algorithms for the correlation of objects with a catalogue and for the maintenance of that catalogue were developed. We used the ESA PROOF software to estimate the sensor performance and AIUB tools to simulate the catalogue correlation. The performance was validated using data from campaigns performed with the ESA Space Debris Telescope at Tenerife, Spain.

Guidelines for space debris mitigation have been formulated by the IADC (Inter Agency Debris Coordination Committee) in 2002. The principal mitigation actions are the passivation of space systems after the end of operations, the limitation of the remaining post-mission dwell time in the LEO and GEO protected region and the limitation of the release of debris. In the past ten years, these recommendations and associated threshold values have been included in several national and international standards and should now be applicable to numerous new missions. Verification of the implementation of mitigation measures in the design of a mission is the responsibility of each nations’ or agencies’ project control during design reviews. The proper implementation of the measures will be followed up by the review of procedures, mission logs and reports.

In 2002, the European Space Agency developed the first generation of conjunction warning tools in order to provide alerts and warnings for operational ESA satellites. Through numerous developments since the initial delivery, this tool became a fundamental part of the operational process for all ESA spacecraft. With the advent of the European Space Surveillance precursor programme, it was seen that the original software would have to be reengineered in order to improve dynamic services to customers outside of ESA. As a result, the first phase of the space surveillance and tracking segment to provide pre-operational services adapted the original software by providing a modern web-based front-end to the core software, hence retaining the original core algorithms but improving the interaction with the end user. This process also identified various requirements to modify the core software in order to comply with the SSA mission requirements. This was performed in phase two of the pre-operational services by dramatically improving the scope and capabilities of the core software as well as providing the ability to form part of a service oriented architecture. This paper will describe and investigate the steps taken in this development journey and the lessons learnt on the way.