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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.

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.

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.

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.