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2021 Report Restricted

Sviluppo di SW a supporto dei servizi SST per lo studio di detriti spaziali
Di Lizia P., Colombo C., Massari M., Purpura G., De Vittori A., Romano M., Trisolini M., Pardini C., Anselmo L., Cicalò S., Guerra F., Bertolucci A.
Questo documento ha lo scopo di descrivere le attività svolte nell'ambito del progetto "Sviluppo di SW a supporto dei servizi SST per lo studio di detriti spaziali" relativamente ai quattro pacchi di lavoro in cui l'attività è stata suddivisa. Nello specifico, il presente documento illustra nel dettaglio: o l'architettura e i risultati della validazione dei software sviluppati nell'ambito dei pacchetti di lavoro WP2000 e WP3000, inerenti all'analisi di frammentazioni e alla simulazione di reti di sensori; o l'analisi e la validazione delle procedure di rientro eseguita nell'ambito del pacchetto di lavoro WP4000. Dopo una descrizione degli obiettivi del lavoro e della Work Breakdown Structure riportati nella Sezione 2, la Sezione 3 e la Sezione 4 dettagliano l'architettura e la validazione dei software. La Sezione 5 è invece dedicata all'analisi e alla validazione delle procedure di rientro. Infine, la Sezione 6 fornisce la lista dei deliverables del progetto.Source: Rapporto Finale - 26 Gennaio 2021, pp.1–50, 2021

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2021 Journal article Embargo

Identifying the 50 statistically-most-concerning derelict objects in LEO
Mcknight D. Witner R., Letizia F., Lemmens S., Anselmo L., Pardini C., Rossi A., Kunstadter C., Kawamoto S., Aslanov V., Dolado Perez J. -c., Ruch V., Lewis H., Nicolls M., Jing L., Dan S., Dongfang W., Baranov A., Grishko D.
This paper describes a process for identifying the intact objects in orbit that (a) pose the greatest debrisgenerating potential risk to operational satellites or (b) would reduce the risk the most if they were removed or prevented from colliding with each other (i.e., remediated). To accomplish this, a number of diverse, international space organizations were solicited to contribute their lists of the 50 statistically-most-concerning objects. The results of the multiple algorithms are compared, a composite ranked list is provided, and the significance of the consolidated list is presented including critical assumptions and key factors in determining this "hit list." It is found that the four primary factors used in these processes are mass, encounter rates, orbital lifetime, and proximity to operational satellites. This cooperative international assessment provides a useful ranking of the most hazardous massive derelicts in low Earth orbit as a prioritized list for remediation to (1) enhance space safety and (2) assure long-term space sustainability. This will hopefully catalyze international action in debris remediation.Source: Acta astronautica 181 (2021): 282–291. doi:10.1016/j.actaastro.2021.01.021
DOI: 10.1016/j.actaastro.2021.01.021

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2021 Contribution to conference Restricted

Thermospheric behavior at low altitude during the deep minimum of solar cycle 24: some operational experiences
Pardini C., Anselmo L.
At the beginning of 2018 (Tiangong-1) and 2019 (Electron Second Stage 2018-010D) we had the occasion of participating to a couple of international reentry prediction test campaigns, carried out during a low minimum of solar activity, characterized by a nearly stable solar flux at 10.7 cm of about 70 standard flux units. With these environmental conditions, the accuracy of the reentry predictions was significantly affected by the more or less predictable occurrence of minor - G1 class - geomagnetic storms, and the operational impact of these uncertainties, in particular for events with civil protection implications, as that involving the Chinese space station, will be presented. In the case of Tiangong-1, due to the relevance of the object, we started systematic reentry predictions at the beginning of 2017, i.e. at an altitude (> 350 km) much higher than the initial one generally found in typical reentry prediction campaigns. This offered the occasion to "probe" the behavior of some atmospheric density models - in particular between 350 km and 250 km, where Tiangong-1 spent more than 1 year - in conditions of quite low solar activity and cold thermosphere. Estimates of the residual lifetime during 2017 and until February 2018 were performed using the NRLMSISE-00 model. Since 1 February 2018, also the GOST2004 model was employed for comparison reasons and for checking the mutual consistency of the forecasts. Concerning the predictions carried out with NRLMSISE-00 during the year 2017 and until the beginning of February 2018, they systematically obtained a nominal re-entry epoch earlier than the actual one. Therefore, a post-reentry analysis was performed to investigate whether the cause of the systematic earlier predicted reentry times was due to a bias in the density model used, or to errors in the forecasts of solar and geomagnetic activity. The second possibility was first verified by replacing the predicted values of the solar and geomagnetic indices with the observed ones, and hence by re-propagating the trajectory under true environmental conditions. In this case, still using NRLMSISE-00, the re-computed nominal reentry times were indeed delayed with respect to the original predictions. Therefore, a "true" representation of the environment would have led to an improvement of the forecasts, by obtaining nominal reentry times closer to the actual one. However, all the revised predictions adopting the real space weather conditions were still systematically anticipated with respect to the actual reentry epoch. The other test consisted in changing the density model used for the thermosphere. For such a posteriori analysis, also JB2008 and GOST2004 were considered, in addition to NRLMSISE-00, to re-calculate the nominal reentry times. Nevertheless, the three density models behaved in a similar way, with a maximum discrepancy, in terms of residual lifetime, of about 9%. In other words, all three found a residual lifetime systematically shorter than the actual one. A possible explanation might be that, under the environmental conditions encountered by Tiangong-1 during its uncontrolled decay (i.e. a deep minimum of the solar activity cycle), each atmospheric model analyzed was probably affected by an intrinsic density bias, with a negative derivative with respect to the geodetic altitude, at least down to 270 km. This lead to a percentage increase in the estimation of the atmospheric density as the spacecraft height decreased, neutralizing the absorption of the bias at higher altitudes through the previous ballistic parameter calibrations and causing the systematic underestimation of the residual lifetime recorded up to the beginning of February 2018.Source: 43rd COSPAR Scientific Assembly 2021 (Hybrid), Sydney, Australia, 28/01/2021 - 04/02/2021

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2021 Contribution to conference Restricted

Atmospheric drag measurements around 1500 km during solar cycle 24
Pardini C., Anselmo L., Lucchesi D. M., Peron R., Bassan M., Lucente M., Magnafico C., Pucacco G., Visco M.
The semi-empirical atmospheric density models widely used by the space community were mainly developed taking into account satellite drag measurements and other observations, either in situ and ground based, acquired at relatively low altitudes, mostly below 500-600 km, and in general below 1000 km. The launch of the Italian geodetic satellite LARES, in 2012, at the altitude of about 1450 km and with an inclination of 70 degrees, offered however the rare possibility of probing the atmosphere at such height. This spherical satellite, fully covered with corner-cube laser retro-reflectors, has the highest area-to-mass ratio of any artificial object launched so far, being therefore not well suited for detecting small non-gravitational forces, like atmospheric drag. However, the very high accuracy of its orbit determinations, made possible by the laser tracking technique, more than compensated its unfavorable area-to-mass ratio, and the signature of atmospheric drag was extremely evident in the measured semi-major axis decay. Such decay, observed since 2012, was therefore used to infer the neutral atmosphere drag at the height of LARES during a 7-year span of solar cycle 24, covering the solar maximum, the declining phase and the beginning of the minimum. These measurements were compared with the predictions of six semi-empirical density models (JR-71, MSIS-86, MSISE-90, NRLMSISE-00, GOST-2004, and JB2008), employed well outside of their typical application ranges. In general, their predictions resulted quite satisfactory, with uncertainties not so far from those already known at lower altitudes. This study was also supplemented by the simultaneous analysis of another spherical geodetic satellite, the Japanese Ajisai, just 50 km higher, but with an area-to-mass ratio nearly 20 times greater than that of LARES and a smaller inclination of 50 degrees. An attempt was also made to estimate the physical drag coefficients of both satellites, in order to derive the mean density biases of the models. None of them could be considered unconditionally the best, the specific outcome depending on solar activity and on the regions of the atmosphere crossed by the satellites. Moreover, during solar maximum conditions, an additional density bias, probably linked to the different high latitudes overflown by the satellites, was detected.Source: 43rd COSPAR Scientific Assembly 2021 (Hybrid), Sydney, Australia, 28/01/2021 - 04/02/2021

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2021 Contribution to conference Restricted

Consequences of mega-constellations for the low LEO region
Pardini C., Anselmo L.
Since the definition of a Low Earth Orbit (LEO) protected region, at the beginning of the 2000s, most of the attention of the space debris mitigation community was focused on heights greater than 600 km. In such orbital regimes, in fact, the average residual lifetimes of inert satellites and rocket bodies become typically higher than 20 years and the highest concentrations of functional satellites and space debris were found. The low LEO region, below 600 km, is however extremely important for space applications. In fact, since the last Apollo mission to the Moon, all human spaceflight was carried out there and also extremely important scientific missions, like the Hubble Space Telescope (HST), are orbiting in this volume of space. In recent years there was a dramatic increase in the launch rate of small satellites and cubesats in low LEO, boosting the number of potentially risky objects to be tracked and monitored. But the most dramatic development currently going on is the deployment of mega-constellations of satellites, with almost 10,000 spacecraft planned only in low LEO in the coming years. Even though any failed satellite of the planned systems will decay from orbit in much less than 25 years, therefore formally complying with current international space debris mitigation guidelines, it is realistic to expect a relatively high number of failures, considering the experimental nature of spacecraft tested in space, and in great numbers, for the first time. The short- and medium-term consequences for the satellite operations in low LEO might therefore be far from negligible, not to mention the negative effects on astronomy and the observation of the night sky. In the coming decade, a significant increase of close approaches and collision avoidance maneuvers in low LEO should be expected mainly due to: 1) The great number of non-maneuverable nanosats launched below 650 km; 2) The failed satellites of the mega-constellations launched there; 3) The disposed satellites of the mega-constellations launched in high LEO, either failed or with reduced maneuverability and/or operability; 4) A greater number of disposed satellites not belonging to mega-constellations, in order to comply with space debris mitigation guidelines or standard. The aim of this presentation is mainly to review the new challenges to be faced by spacecraft and space operations in low LEO due to these quite recent developments and to the current launch forecasts.Source: 43rd COSPAR Scientific Assembly 2021 (Hybrid), Sydney, Australia, 28/01/2021 - 04/02/2021

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2021 Contribution to conference Restricted

SaToR-G: a new experiment for fundamental physics measurements with laser-ranged satellites
Lucchesi D. M., Anselmo L., Bassan M., Lucente M., Magnafico C., Pardini C., Peron R., Pucacco G., Visco M.
We present a new experiment called SaToR-G (Satellites Tests of Relativistic Gravity) which mainly concerns on verifying the gravitational interaction beyond the predictions of General Relativity, looking for possible effects connected with new physics, and foreseen by different alternative theories of gravitation. SaToR-G exploits the improvement of the dynamical model of the two LAGEOS and of LARES satellites performed within the previous research program called LAser RAnged Satellites Experiment (LARASE: 2013-2019) and funded by the Italian INFN (Istituto Nazionale di Fisica Nucleare). Within LARASE we achieved a new measurement of the Lense-Thirring precession with an accuracy better than 2%. To reach the objectives foreseen by SaToR-G, we need to provide a precise orbit determination of a set of laser-ranged satellites, such as the two LAGEOS, LARES, and the forthcoming LARES-2, whose launch is expected before the end of this year. The state-of-the-art regarding the modelling improvements currently reached with LARASE will be presented together with the main objectives of SaToR-G in the fields of relativistic measurements and space geodesy.Source: 43rd COSPAR Scientific Assembly 2021 (Hybrid), Sydney, Australia, 28/01/2021 - 04/02/2021

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2021 Contribution to conference Restricted

A new model for thermal thrust accelerations on LAGEOS satellites
Lucchesi D. M., Anselmo L., Bassan M., Lucente M., Magnafico C., Pardini C., Peron R., Pucacco G., Visco M.
Thermal thrust forces act on the surface of a satellite as a result of a non-uniform distribution of temperature across its surface. A new thermal model for the two LAGEOS satellites will be described with the goal of providing the thermal thrust accelerations acting on their surfaces. The thermal inertia of the satellite components together with the eclipses participate in the production of these perturbations. The main effects are due to the thermal inertia of the Corner Cube Retroreflectors (CCRs) of the satellite, being the direct solar visible radiation modulated by the eclipses and the Earth's infrared radiation the main sources. In addition to these sources, the solar radiation reflected by the complex Earth-atmosphere system, i.e. the Earth's albedo, is also responsible for a non-uniform heating of the surface of the satellite. Contrary to the models previously developed in the literature for the LAGEOS satellites, our new model, that we called LATOS (LArase Thermal mOdel Solutions), is not based on averaged equations. The attitude of the satellite plays an important role in this kind of analysis; we modelled it by means of the LASSOS (LArase Satellites Spin mOdel Solutions) model. This model for the spin was developed within the LARASE (LAser RAnged Satellites Experiment) research program. In our analysis, the CERES (Clouds and the Earth's Radiant Energy System) data have been used to account for the effects of the terrestrial albedo. The results for the thermal thrust accelerations acting on the two LAGEOS satellites will be presented together with their effects on their orbital elements. These effects will be then compared with the orbital residuals of the satellites in the same elements obtained by an independent Precise Orbit Determination (POD). The consequent improvements in the POD through the inclusion of the thermal thrust accelerations in the dynamic model, in such a way to replace the empirical accelerations, will be of fundamental importance for the geophysical products that are determined by analysing the orbits of the two LAGEOS satellites. At the same time, the fundamental physics measurements that are obtained with these satellites can benefit from a more precise determination of their orbit.Source: 43rd COSPAR Scientific Assembly 2021 (Hybrid), Sydney, Australia, 28/01/2021 - 04/02/2021

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2021 Conference article Open Access OPEN

Testing General Relativity vs. Alternative Theories of Gravitation with the SaToR-G Experiment
Lucchesi D. M., Anselmo L., Bassan M., Lucente M., Magnafico C., Pardini C., Peron R., Pucacco G., Visco M.
A new experiment in the field of gravitation, SaToR-G, is presented. The experiment aims to compare the predictions of different theories of gravitation in the limit of weak-field and slow-motion. The ultimate goal of the experiment is to look for possible "new physics" beyond the current standard model of gravitation based on the predictions of General Relativity. A key role in the above perspective is the theoretical and experimental framework within which to confine our work. To this end, we will try to exploit as much as possible the framework suggested by Dicke over fifty years ago.Source: 1st Electronic Conference on Universe (ECU 2021), On-line Virtual Event, 22-28/02/2021
DOI: 10.3390/ecu2021-09274

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2021 Contribution to book Embargo

The use of space and satellites: problems and challenges
Anselmo L.
Since the first artificial satellite was launched in 1957, the outer space around the earth has become a precious environment hosting a growing number of very important civilian, military, scientific and commercial applications. After more than three decades dominated by the competition between the superpowers of the Cold War, the situation rapidly evolved, not only because most of the countries of the world currently own satellites and all depends on their services, but also because near earth space is becoming crowded, China is beginning to challenge the supremacy of the United States and Russia, and many ambitious new private commercial players are entering the field, promising a technological revolution. After an overview of the current utilization of space, the main threats to its peaceful exploitation, that is militarization and warfare, orbital debris and solar storms, are examined in order to identify the problems pending and the challenges ahead.Source: Technology and International Relations: The New Frontier in Global Power, edited by Giacomello G., Moro F.N., Valigi M. (eds.), pp. 109–131, 2021
DOI: 10.4337/9781788976077.00014

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2021 Journal article Open Access OPEN

Evaluating the impact of space activities in low earth orbit
Pardini C., Anselmo L.
The evolution of cataloged orbital debris in low Earth orbit (LEO) over the last quarter of century was analyzed in detail, to gather insights on the development of space activities, on the effectiveness of the debris mitigation measures recommended in the meantime, and on the environmental impact of fragmentations, in particular collisions, both intentional and accidental. The main conclusion was that the observed evolution matched on the whole the predictions of the unmitigated business-as-usual scenarios simulated twenty years ago, and that the benefits caused by the progressive worldwide adoption of mitigation measures were unfortunately offset by a couple of catastrophic collisions and prolonged weak solar activity. Concerning the recorded growth of cataloged fragmentation debris, nowhere have the signs of an exponential increase been revealed so far. Nevertheless, the overall picture has worsened during the last quarter of a century and extreme care is required in planning and conducting new space activities from now on, especially in a phase of increased and ever more rapid exploitation. In order to assess the sustainability of space activities, especially over the next 10-30 years, several environmental criticality indexes have been introduced and discussed, estimating their current values in LEO, as well as their magnitudes associated with specific scenarios of debris growth. They could provide simple tools for evaluating the relative and absolute impact on the debris environment, either in LEO as a whole or in specific altitude shells, of new spacecraft deployments and operations, as in the case of mega-constellations of satellites. The main result of this preliminary analysis was that all indexes were consistent in indicating that from one third to one half of the LEO capacity to sustain long-term space activities - as they are currently conceived - has already been saturated. The 2020s, with their many planned launches, will therefore be crucial years for enforcing more effective debris mitigation and remediation measures.Source: Acta astronautica 184 (2021): 11–22. doi:10.1016/j.actaastro.2021.03.030
DOI: 10.1016/j.actaastro.2021.03.030

See at: ISTI Repository Open Access | CNR ExploRA Open Access | www.sciencedirect.com Open Access | Acta Astronautica Restricted | Acta Astronautica Restricted


2021 Journal article Open Access OPEN

Sounding the atmospheric density at the altitude of LARES and AJISAI during solar cycle 24
Pardini C., Anselmo L., Lucchesi D., Peron R., Bassan M., Magnafico C., Pucacco G., Visco M.
During Solar Cycle 24, the passive spherical satellites LARES and Ajisai, placed in nearly circular orbits with mean geodetic altitudes between 1450 and 1500 km, were used as powerful tools to probe the neutral atmosphere density and the performances of six thermospheric models in orbital regimes for which the role of dominant atomic species is contended by hydrogen and helium, and accurate satellite measurements are scarce. The starting point of the analysis was the accurate determination of the secular semi-major axis decay rate and the corresponding neutral drag acceleration in a satellite centered orbital system. Then, for each satellite, thermospheric model and solar activity level, the drag coefficients capable of reproducing the orbital decay observed were found. These coefficients were finally compared with the physical drag coefficients computed for both satellites in order to assess the biases affecting the thermospheric density models. None of them could be considered unconditionally the best; the specific outcome depending on solar activity and the regions of the atmosphere crossed by the satellites. During solar maximum conditions, an additional density bias linked to the satellite orbit inclination was detected.Source: Transactions of the Japan Society for Aeronautical and Space Sciences 64 (2021): 125–135. doi:10.2322/tjsass.64.125
DOI: 10.2322/tjsass.64.125

See at: ISTI Repository Open Access | CNR ExploRA Open Access | www.jstage.jst.go.jp Open Access | TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES Restricted


2021 Conference article Open Access OPEN

End-of-life disposal in inclined geosynchronous orbits
Anselmo L., Pardini C.
Significantly Inclined Geosynchronous Orbits (IGO) are currently considered for various applications, like satellite navigation systems, intelligence and telecommunications. In the light of these developments, the aim of this report is to review the current definition of the Geosynchronous Protected Region, assessing if it would need an extension. Special attention is paid to the end-of-life disposal, in order to check the potential weaknesses of the current IADC formula and re-orbiting recommendations, focusing on the consequences of having operational orbits characterized by medium or high inclinations.Source: International Scientific Conference "Fundamental and Applied Problems of Mechanics" (FAPM-2020), pp. 225–228, Moscow, Russia, 2-4/12/2020
DOI: 10.18698/2308-6033-2021-3-2067

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2021 Contribution to conference Open Access OPEN

Search of Most-Concerning Space Debris Objects in Low Earth Orbit
Mcknight D., Witner R., Letizia F., Lemmens S., Anselmo L., Pardini C., Rossi A., Kunstadter C., Kawamoto S., Aslanov V., Dolado Perez J. -c., Ruch V., Lewis H., Nicolls M., Jing L., Dan S., Dongfang W., Baranov A., Grishko D.
This report integrates a variety of methods to find internationally agreed list of the most dangerous space debris objects in low Earth orbits. These methods each generate different results based on diverse hypotheses and approaches. A state-of-the-art model consolidation approach was applied for the integration of these reputable models. The significance of the results of this effort is noteworthy -- 19 experts from 13 countries/organizations had their 11 individual assessments aggregated into a list of the 50 statistically-most-concerning (SMC) objects for debris generation. Upon examination of the original 11 lists, it is noted that all of them had between ~40 to 60% objects in common between some other top-list. In addition, it is also important that, even though only two of the 11 approaches specifically disregarded payloads, 39 of the top 50 SMC are derelict rocket bodies; only 11 are non-operational payloads.Source: International Scientific Conference "Fundamental and Applied Problems of Mechanics" (FAPM-2020), pp. 7–8, Moscow, Russia, 2-4/12/2020
DOI: 10.18698/2308-6033-2021-3-2067

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2021 Contribution to conference Restricted

Introduction to the draft report of AI 36.3 "Disposal of high inclination geosynchronous spacecraft and orbital stages"
Anselmo L.
Introduction to the draft report of AI 36.3 "Disposal of high inclination geosynchronous spacecraft and orbital stages"Source: 39th Inter-Agency Space Debris Coordination Committee (IADC) Plenary Meeting, Virtual Event, 26-29/04/2021

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2021 Contribution to conference Restricted

Italian Space Agency space debris mitigation activities - delegation report
Vellutini E., Anselmo L.
ASI delegation report on space debris mitigation activities (from 1 April 2019 to 31 March 2021).Source: 39th Inter-Agency Space Debris Coordination Committee (IADC) Plenary Meeting, Virtual Event, 26-29/04/2021

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2021 Report Restricted

Accordo di collaborazione ASI-INAF N. 2020-6-HH.0, Deliverable TR1_2019-2021: Detriti spaziali - supporto alle attività IADC e SST 2019-2021
Bianchi G., Teofilatto P., Piergentili F., Valentini G., Buzzoni A., Di Lizia P., Colombo C., Rossi A., Pardini C., Francesconi A., Anselmo L.
Questo documento è il terzo deliverable dell'accordo di collaborazione tra ASI e INAF in ambito "Detriti Spaziali- Supporto alle attività IADC e SST 2019-2021".Source: Project report, Accordo di collaborazione ASI-INAF, TR1_2019-2021, 2021

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2021 Journal article Open Access OPEN

Testing gravitational theories in the field of the earth with the SaToR-G experiment
Lucchesi D., Anselmo L., Bassan M., Lucente M., Magnafico C., Pardini C., Peron R., Pucacco G., Visco M.
A new satellite-based experiment in the field of gravitation, SaToR-G, is presented. It aims to compare the predictions of different theories of gravitation in the limit of weak-field and slow-motion. The ultimate goal of SaToR-G is searching for possible "new physics" beyond General Relativity, which represent the state-of-the-art of our current knowledge of gravitational physics. A key role in the above perspective is the theoretical and experimental framework that confines our work. To this end, we will exploit as much as possible the classical framework suggested by R.H. Dicke over fifty years ago.Source: Universe (Basel) 7 (2021). doi:10.3390/universe7060192
DOI: 10.3390/universe7060192

See at: ISTI Repository Open Access | CNR ExploRA Open Access | www.mdpi.com Open Access


2020 Conference article Restricted

Identifying the 50 Statistically-Most-Concerning Derelict Objects in LEO
Mcknight D., Witner R., Letizia F., Lemmens S., Anselmo L., Pardini C., Rossi A., Kunstadter C., Kawamoto S., Aslanov V., Dolado Perez J. C., Ruch V, Lewis H., Nicolls M., Jing L., Dan S., Dongfang W., Baranov A., Grishko D.
This paper describes a process for identifying the intact objects in orbit that (a) pose the greatest debris-generating potential risk to operational satellites or (b) would reduce the risk the most if they were removed or prevented from colliding with each other (i.e., remediated). To accomplish this, a number of diverse, international space organizations were solicited to contribute their lists of the 50 statistically-most-concerning objects. The results of the multiple algorithms are compared, a composite ranked list is provided, and the significance of the consolidated list is presented including critical assumptions and key factors in determining this "hit list." It is found that the four primary factors used in these processes are mass, encounter rates, orbital lifetime, and proximity to operational satellites. This cooperative international assessment provides a useful ranking of the most hazardous massive derelicts in low Earth orbit as a prioritized list for remediation to (1) enhance space safety and (2) assure long-term space sustainability. This will hopefully catalyze international action in debris remediation.Source: 71st International Astronautical Congress (IAC) - The CyberSpace Edition, On-line Virtual Meeting, 12-14/10/2020

See at: CNR ExploRA Restricted | www.iafastro.org Restricted


2020 Journal article Open Access OPEN

Environmental sustainability of large satellite constellations in low earth orbit
Pardini C., Anselmo L.
A specific criticality index, the collision rate percentage increase, was introduced in 2017 to assess the environmental impact of large satellite constellations in low Earth orbit (LEO). That index was estimated in this paper for various constellation arrangements, ranging in altitude from 800 km to 1400 km. The results obtained clearly show that in the regions of space where the current density of cataloged debris is already significant, such as around 800 km, just one hundred more abandoned satellites would increase the current collision rate by ~10%. In less congested LEO regions, as near 1110 km and 1325 km, a comparable increase in the collision rate could be achieved by a number of abandoned satellites between 200 and 500. Taking into account the new planned constellations from 800 km to 1400 km (consisting of approximately 6000 satellites), an increase by nearly 20-30% of the total collision rate among cataloged objects in LEO might be expected, assuming an immediate spacecraft de-orbiting at the end-of-life, with a success probability of 90%. Of course, a greater number of satellites, as well as a reduced probability of successful disposal, would affect the environment even more negatively. Moreover, if the many disposed satellites were not de-orbited immediately, or in a relatively short time, the collision rate in LEO would further increase, at least in the medium term, unless the satellites do not continue to be controlled and maneuverable until they reenter the atmosphere. As an example, if a thousand satellites were disposed on elliptical orbits between 300 km and 1000 km, the collision rate among cataloged objects in LEO might grow by an additional 30% during the few years needed to decay. That said, even assuming a willingness to endure a maximum 50% increase in the collision rate in LEO among objects greater than 10 cm, in the next 25 years, it is clear that an extended and expanded use of large constellations would be consistent with the environment sustainability only if it were possible to increase the post-mission disposal success probability to at least 95%, and hopefully to 99%. At the same time, the de-orbiting phase should be either quite short or fully controlled, in order to avoid the prolonged presence of several hundred or thousands of abandoned satellites in disposal orbits, further increasing the collision rate in low LEO.Source: Acta astronautica 170 (2020): 27–36. doi:10.1016/j.actaastro.2020.01.016
DOI: 10.1016/j.actaastro.2020.01.016

See at: ISTI Repository Open Access | Acta Astronautica Restricted | Acta Astronautica Restricted | Acta Astronautica Restricted | CNR ExploRA Restricted | Acta Astronautica Restricted | www.sciencedirect.com Restricted | Acta Astronautica Restricted


2020 Journal article Open Access OPEN

Monitoring the final orbital decay and the re-entry of Tiangong-1 with the Italian SST ground sensor network
Vellutini E., Bianchi G., Pardini C., Anselmo L., Pisanu T., Di Lizia P., Piergentili F., Monaci F., Reali M., Villadei W., Buzzoni A., D'Amore G., Perozzi E.
The uncontrolled re-entry of spacecraft and upper stages is quite common, occurring nearly every week. Among them, intact objects having a mass greater than five metric tons re-enter, on average, 1-2 times per year. Therefore, the re-entry of the first Chinese Space Station, Tiangong-1, was far from unusual, but attracted anyway a great worldwide attention and some concerns. For these reasons, the Italian component of the European SST (Space Surveillance and Tracking) consortium took this opportunity for carrying out a national exercise. According to Chinese official sources, the ground control of Tiangong-1 was lost in March 2016, precluding the planned de-orbiting in the South Pacific Ocean Unpopulated Area (SPOUA). Tiangong-1 consisted of a cylindrical section, 10:5 m in length and 3:4 m in (maximum) diameter, with two rectangular solar panels of 3 m × 7 m. The mass was estimated to be around 7500 kg. The Italian network of sensors activated for the campaign included mono-static and bi-static radars, optical telescopes, a laser ranging station and a network of all-sky cameras, originally deployed for the observation of fireballs and bolides. In addition to providing complementary information, concerning the orbit, the attitude and the photometry of Tiangong-1, this quite heterogeneous collection of national assets provided also the occasion for testing, in an operational environment, the Italian sensor tasking preparedness and the data acquisition, exchange and processing capabilities within the European SST consortium. In this respect, it is important to remember that in 2014 the European Commission, well aware of the topic criticality, took the commitment to implement a European network of sensors for surveillance and tracking of objects in Earth's orbit by starting a dedicated SST support framework program. Italy, France, Germany, Spain and UK joined it and constituted, together with SatCent, the front desk for SST services, the EUSST Consortium. In this paper, a description of the Tiangong-1 monitoring activities and of the main observations results obtained by the Italian sensor network are reported. Attention is also devoted to the coordination aspects of several Italian entities (military, civil and research organizations) that worked together. Finally, a description of the re-entry prediction and alert procedure for the national civil protection authorities is presented.Source: Journal of Space Safety Engineering (2020). doi:10.1016/j.jsse.2020.05.004
DOI: 10.1016/j.jsse.2020.05.004

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