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Radar Beam-Park Experiments (BPEs) are regularly conducted in order to get insights into the statistical distribution of the space debris environment, especially at low altitudes. Signal processing techniques are necessary to process the data collected during BPEs. An improvement in these techniques may result in a corresponding improvement in terms of radar detection performance and space object parameter estimation. To this end, a transition from incoherent to coherent pulse integration could be of help, thanks to the resulting improvement in terms of Signal to Noise Ratio (SNR). Before assessing the potential of new signal processing schemes, the expected variations of the radar observables over the acquisition time have to be investigated. Indeed, deriving a priori bounds on the possible values the observables can assume, would allow adapting the BPE settings (e.g., the radar waveform or the boundaries of the matched filter) in order to optimize the processing speed and the overall detection performance. To carry out this investigation, two BPEs were simulated and the resulting beam crossing lists were exploited to understand how the satellite parameter space maps into the radar parameter subspace. This paper presents and discusses the results of the two simulations.

著者人数: 19名, 形態: カラー図版あり, Number of authors: 19, Physical characteristics: Original contains color illustrations, Accepted: 2021-01-14, 資料番号: PA2110015000

In recent years some countries have established national regulation related to space debris mitigation, while many others are currently considering to follow similar steps. In general, this involves the adoption of already existing and widely accepted standards and international guidelines, such as ISO 24113 or the UN Space Debris Mitigation Guidelines. In order to support the verification of the compliance with existing recommendations, guidelines or even national laws, ESA has been developing the Debris Risk Assessment and Mitigation Analysis (DRAMA) software tool suite. Since 2014, when an ESA instruction came into force rendering space debris mitigation requirements applicable for any ESA satellite mission, DRAMA is being an essential part in mission design and subsequent compliance verification by the Agency. Today more than 1000 users world-wide from industry, academia and agencies are working with the software to address issues such as the remaining orbital lifetime of the spacecraft after disposal or the associated on-ground risk for an uncontrolled re-entry. The recent upgrade to DRAMA 3.0 entails the incorporation of the latest Meteoroid And Space debris Terrestrial Environment Reference (MASTER) model, evolving from MASTER-2009 to MASTER-8; an extensive analysis of Conjunction Data Messages(CDM) which serve as the crucial input to estimate annual collision avoidance manoeuvre rates; a dedicated Python framework to run parametric analyses; and a significant extension of SARA, the tool used for the assessment of on-ground risk upon atmospheric re-entry. The latter includes improvements in the materials database, the aerothermodynamics and aerodynamics as well as an update of the world’s population model. In this paper, the improvements in DRAMA 3.0 are introduced with a focus on showing instructive examples of how the new DRAMA software is being used in the context of verifying compliance with space debris mitigation requirements.

Since 2010 the International Organization for Standardization (ISO) has been publishing a comprehensive set of international standards on space debris mitigation based on guidelines and best practices from the IADC and other bodies. This paper describes the structure and content of the ISO debris standards and how they are evolving to address the needs of space environment sustainability within the context of a rapidly changing space industry. Particular emphasis is placed on ISO 24113 (Space systems – Space debris mitigation requirements), which was published as a third edition during July 2019. The new requirements are compared with those in the previous edition and the rationale for the various changes is discussed. Most notably, the requirement for a spacecraft or orbital stage to exceed a specified threshold for its probability of successful disposal has been made more demanding. With the launch of numerous small spacecraft into LEO and the imminent launch of constellation systems comprising thousands of satellites, it is likely that the ISO debris standards will have to implement even stricter requirements in the future. The challenge is to do this in a way that is fair and reasonable for the entire space industry.

In recent years, several metrics have been proposed to quantify the impact of a mission on the space debris environment. In our previous work, we introduced the environmental capacity as the number and typology of missions that are compatible with the stable evolution of the debris environment. This concept enables the evaluation of the effectiveness of mitigation guidelines by looking at the use of environmental capacity due to existing missions. The current work will investigate how the same concept can also be applied as a tool during the design of a mission, facilitating the comparison of different mission architectures depending on their overall contribution to the debris environment. First, the paper will present the latest updates to the debris index used as a metric of the environment capacity, including the inclusion of a penalisation for objects with low trackability and an improved model for the break-up probability. Then, several application cases will be discussed to demonstrate its use as design driver. First, the relevance of adopting operational best practices (i.e. collision avoidance and disposal manoeuvres) will be studied for different spacecraft classes as a way of quantifying better than required behaviour. Then, the environmental impact of a mission will be analysed considering the case when the mission is realised through a single large satellite or through a constellation of smaller satellites. Finally, different end-of-life scenarios will be assessed to demonstrate the use of the method to discriminate between various technologies on a case-by-case basis. The adoption of passive de-orbiting systems will be compared to conventional disposal through de-orbit burns or operations at lower altitudes to gain insight into how two different options, both compliant to existing guidelines, differ in terms of the resulting environmental impact. Finally, a scenario with active-debris-removal will be considered, showing how the quantification of the impact on the debris environment can support the selection of parameters such as the rendez-vous altitude, based on the expected success rate of the capture and final disposal phase.

The current debris mitigation guidelines are formulated by considering single objects, so they cannot dynamically account for variations in the space traffic, or for the actual current level of implementation and success of post-mission disposal manoeuvres. To address this limitation, the concept of space traffic management based on the environment capacity was proposed. Following this approach, a mission (single or multiple satellites and launch vehicles) is evaluated, before its launch, not only with respect to existing mitigation guidelines, but also with respect to what can be accommodated by the environment (e.g. not exceeding a defined risk level), considering objects already in orbits and other planned future missions. In this way, similarly to the approach used for frequency allocation in GEO, each mission can use a share of the environment capacity through a process that may define, for example, a maximum capacity consumption per year. In order to implement such a scheme, a measure of the debris environment criticality is required. Different formulations for such a metric have been proposed and, in the present work, the ECOB index (Environmental Consequences of Orbital Breakups) is applied. This work will give a brief overview of the most recent changes in the formulation of the index and will discuss examples of applications to the current environment. Different Post-Mission Disposal success rates and future launch traffic scenarios will be analysed. In this context, the evaluation provided by the debris index will be compared to other formulations available in literature and to the one from other indicators such as number of objects and catastrophic collisions. A comparison with operational data from ESA's collision avoidance service will be also presented. Finally, it will be analysed how such an index can be connected to the concept of the environment capacity and a concept for its inclusion within a space traffic management process will be formulated.

The European Space Agency (ESA) has been developing the Meteoroid and Space Debris Terrestrial Environment Reference (MASTER) software as the European reference model for space debris for more than 25 years. It is an event-based simulation of all known individual debris-generating events since 1957, including breakups, solid rocket motor firings and nuclear reactor core ejections. In 2014, the upgraded version of the Debris Risk Assessment and Mitigation Analysis (DRAMA) tool suite was released. In the same year an ESA instruction made the standard ISO 24113:2011 on space debris mitigation requirements, adopted via the European Cooperation for Space Standardization (ECSS), applicable to all ESA missions. In order to verify the compliance of a space mission with those requirements, the DRAMA software is used to assess collision avoidance statistics, estimate the remaining orbital lifetime and evaluate the on-ground risk for controlled and uncontrolled re-entries. In this paper, the approach to validate the MASTER and DRAMA tools is outlined. For MASTER, recent observation campaign results shall be discussed. In DRAMA, the assessment of collision avoidance statistics is based on orbit uncertainty information derived from Conjunction Data Messages (CDM) provided by the Joint Space Operations Center (JSpOC). The way this information is going to be used in a future DRAMA version is outlined and the comparison of estimated manoeuvre rates with real manoeuvres from the operations of ESA spacecraft is shown.

As the number of satellites in low Earth orbit grows by leaps and bounds, accurate calculations of the effects of atmospheric drag on their trajectories are becoming critically important.

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

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.

A sensitivity analysis of aerodynamic coefficients has been performed by coupling a Direct Simulation Monte Carlo method and a High Dimensional Model Representation based uncertainty quantification approach. The study has been performed on the Gravity Field and Steady-State Ocean Circulation Explorer satellite. The uncertainty on aerodynamics has been quantified with respect to atmospheric parameters, which have been obtained using the NRLMSISE-00 atmospheric model, within a free molecular flow regime in the Low Earth Atmosphere. The aerodynamic simulations have been performed with the dsmcFoam code, based on the open-source OpenFOAM platform.

This paper presents the work to characterize and propagate the uncertainties on the atmospheric re-entry time of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite done with the framework of an ESA ITT project. Non-intrusive techniques based on Chebyshev polynomial approximation, and the Adaptive High Dimensional Model Representation multi-surrogate adaptive sampling have been used to perform uncertainty propagation and multivariate sensitivity analyses when both 3 and 6 degrees-of-freedom models where considered, considering uncertain-ties on initial conditions, and atmospheric and shape parameters. Two different uncertainty quantification/characterization approaches have been also proposed during the project. The same interpolation techniques used for non-expensive non-intrusive methods for uncertainty propagation, allowed the development of two methods based on direct optimization approaches, the Boundary Set Approach and the Inverse Uncertainty Quantification. Moreover, an innovative approach to treat the empirical accelerations has been proposed, based on polynomial expansions in the state variables. The method has been tested and further developed to consider uncertainties in the initial conditions, leading to a statistical characterization of the coefficients and representation of the possible trajectories. Finally, the investigation on the use of meta-modeling techniques to directly map a range of initial conditions and model uncertainties, as well as characteristics of the considered object, into the parameters of the skew-normal distribution that usually characterizes the re-entry time windows, bringing to a very fast characterization of the output PDF not requiring any further propagation at all, is also briefly described.

In recent years, awareness concerning the on-ground risk posed by un-controlled re-entering space systems has increased. On average over the past decade, an object with mass above 800 kg re-enters every week from which only a few, e.g. ESA’s GOCE in 2013 and NASA’s UARS in 2011, appeared prominent in international media. Space agencies and nations have discussed requirements to limit the on-ground risk for future missions. To meet the requirements, the amount of debris falling back on Earth has to be limited in number, mass and size. Design for demise (D4D) refers to all measures taken in the design of a space object to increase the potential for demise of the object and its components during re-entry. SCARAB (Spacecraft Atmospheric Re-entry and Break-Up) is ESA’s high-fidelity tool which analyses the thermal and structural effects of atmospheric re-entry on spacecraft with a finite-element approach. For this study, a model of a representative satellite is developed in SCARAB to serve as test-bed for D4D analyses on a structural level. The model is used as starting point for different D4D approaches based on increasing the exposure of the satellite components to the aero-thermal environment, as a way to speed up the demise. Statistical bootstrapping is applied to the resulting on-ground fragment lists in order to compare the different re-entry scenarios and to determine the uncertainties of the results. Moreover, the bootstrap results can be used to analyse the casualty risk estimator from a theoretical point of view. The risk reductions for the analysed D4D techniques are presented with respect to the reference scenario for the modelled representative satellite.

On 2015 November 13, the small artificial object designated WT1190F entered the Earth atmosphere above the Indian Ocean offshore Sri Lanka after being discovered as a possible new asteroid only a few weeks earlier. At ESA's SSA-NEO Coordination Centre we took advantage of this opportunity to organize a ground-based observational campaign, using WT1190F as a test case for a possible similar future event involving a natural asteroidal body., Icarus, In Press. 5 pages, 2 figures

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.

In 2015, ESA's “ESA Space Debris Mitigation Compliance Verification Guidelines” handbook was released, dealing with the practical aspects of how missions can demonstrate their compliance to, among others, the applicable maximum on-ground risk figures. Therefore, to provide algorithms and methods allowing spacecraft system designers and operators to prove the compliance of their spacecraft with the applicable regulations, ESA's Space Debris Office decided to carry out the upgrade of the “Debris Risk Assessment and Mitigation Analysis” (DRAMA) software suite implementing up-to-date methods as well as innovative and unique functionalities. The tools provided by DRAMA enable an assessment of mitigation strategies for the operational and disposal phases of a mission, including the risk posed due to mission's space debris and the effectiveness of an end-of-life strategy. Within this framework, DEIMOS Space is responsible for the SESAM (Spacecraft Entry Survival Analysis Module) module of DRAMA, being subcontractor of HTG under an ESA contract.

Two novel methods are developed for detecting space events based on the analysis of their two-line elements history. These methods are tuned for detecting orbital maneuvers of satellites and the characterization thereof. The first method detects nonnatural anomalous events in low Earth orbit based on a consistency check between arbitrary two-line element sets of the same object. The use of background models that enable one to estimate the variable noise in the two-line element consistencies for different orbital regimes is found to further increase the detection rate. The second method uses the time series of an object containing the orbital elements, or a derived quantity thereof, and evaluates it for any type of unexpected changes by methods from robust statistics and harmonic analysis. Both methods can process the entire two-line element catalog with a minimal operator interference while yielding good results in the different orbital regimes. The generated orbital maneuvering data are used to assess th...

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.

Numerical integration of orbit trajectories for a large number of initial conditions and for long time spans is computationally expensive. Semi-analytical methods were developed to reduce the computational burden. An elegant and widely used method of semi-analytically integrating trajectories of objects subject to atmospheric drag was proposed by King-Hele (KH). However, the analytical KH contraction method relies on the assumption that the atmosphere density decays strictly exponentially with altitude. If the actual density profile does not satisfy the assumption of a fixed scale height, as is the case for Earth's atmosphere, the KH method introduces potentially large errors for non-circular orbit configurations. In this work, the KH method is extended to account for such errors by using a newly introduced atmosphere model derivative. By superimposing exponentially decaying partial atmospheres, the superimposed KH method can be applied accurately while considering more complex density profiles. The KH method is further refined by deriving higher order terms during the series expansion. A variable boundary condition to choose the appropriate eccentricity regime, based on the series truncation errors, is introduced. The accuracy of the extended analytical contraction method is shown to be comparable to numerical Gauss-Legendre quadrature. Propagation using the proposed method compares well against non-averaged integration of the dynamics, while the computational load remains very low., Comment: Post-print version of 13 February 2019