Luciano Anselmo

A previous study (Pardini C., Anselmo L, Moe K., Moe M.M., Drag and energy accommodation coefficients during sunspot maximum, Adv. Space Res., 2009, doi:10.1016/j.asr.2009.08.034), including ten satellites with altitudes between 200 and 630 km, has yielded values for the energy accommodation coefficient as well as for the physical drag coefficient as a function of height during solar maximum conditions. The

A space mission is described which consists of a rigid spin-axis-stabilised spacecraft with two small, high-density masses free-falling inside. The gravitational attraction of the masses dominates all perturbations, providing a miniature "planet-satellite" system that can only be realised in space. Unlike any celestial two-body system, the masses can be weighed on Earth before launch. Thus, monitoring their motion by means

Passive laser-ranged satellites, launched for geodynamics and geophysics purposes, not only have contributed to significant measurements in space geodesy that enabled, among several aspects, a deeper knowledge of the Earth's geopotential (both in its static and dynamic behavior), as well as of the geocenter motion and GM value up to the definition of the terrestrial reference frame, but they also provided an outstanding test bench to fundamental physics, as in the case of the first measurement of the Lense-Thirring precession on the combined nodes of the two LAGEOS satellites, or in the case of the total relativistic precession of the argument of pericenter of LAGEOS II. Indeed, the physical characteristics of such satellites -- such as their low area-to-mass ratio -- as well as those of their orbits, and the availability of high-quality tracking data provided by the International Laser Ranging Service (ILRS), allow for precise tests of gravitational theories. The aim of LARASE (LAser RAnged Satellites Experiment) is to go a step further in the tests of the gravitational interaction in the field of Earth, i.e. in the weak-field and-slow motion limit of general relativity, by the joint analysis of the orbits of the two LAGEOS satellites and that of the most recent LARES satellite. One of the key ingredients to reach such a goal is to provide high-quality updated models for the perturbing non-gravitational forces acting on the surface of such satellites. A large amount of Satellite Laser Ranging (SLR) data of LAGEOS and LAGEOS II has been analyzed using a set of dedicated models for satellite dynamics, and the related post-fit residuals have been analyzed. A parallel work is on-going in the case of LARES that, due to its much lower altitude, is subject to larger gravitational and non-gravitational effects; the latter are mitigated in part by its much lower area-to-mass ratio. Recent work on the data analysis of the orbit of such satellites will be presented together with the development of some new refined models to account for the impact of the subtle and complex non-gravitational perturbations. The general relativistic effects leave peculiar imprint on the satellite orbit, namely in the secular behavior of its three Euler angles. Recent results will be provided together with updated constraints on non-Newtonian gravitational dynamics. The measurement error budget will be discussed, emphasizing the role of the modeling of gravitational and, especially, non-gravitational forces on the overall precise orbit determination quality, as well as on future new measurements and constraints of the gravitational interaction. <P /

Abstract A new ranking index was developed and applied to a wide set of rocket body families, characterized by stage dry masses greater than 500 kg and by the presence of at least 5 stages abandoned in LEO. The upper stages selected accounted for more than 80% of the unclassified rocket bodies in LEO and nearly 95% of the associated dry mass. The detailed results obtained for 657 objects clearly identified the most critical altitude-inclination bands and stage models, to be targeted first if and when a debris remediation strategy including the active removal of intact abandoned objects were deemed necessary. Apart from the evaluation of the criticality regarding the long-term evolution of the debris environment, resulting in a priority listing for optimal active removal, the application of the new ranking index is not limited to debris remediation. In fact, if applied before launch to spacecraft and rocket bodies to be disposed in orbit, at the end of mission, it would provide an additional debris mitigation analysis tool for evaluating competing disposal options. Concerning the rocket bodies abandoned in LEO, 274 resulted to have a criticality equal or larger than the average intact object abandoned in an 800 km sun-synchronous orbit. Among them, 243 belonged to the Russian Federation and Ukraine, 25 to China, 5 to Europe and 1 to Japan. In addition to being concentrated in relatively few and narrow altitude-inclinations bands, the most numerous rocket body families often present a quite uniform distribution in right ascension of the ascending node, which is especially convenient for multiple target removal missions.

The analysis of different disposal strategies for the spacecraft belonging to the Global Navigation Satellite Systems (GNSS), with particular emphasis on the European Galileo system is the aim of this study. The results of numerical simulations of the long term evolution scenarios, implementing different disposal strategies, are shown and discussed. A detailed analysis of the collision risk and manoeuvres need, related to the different scenarios, was performed. In terms of the long term evolution, the scenarios where the orbital instabilities are exploited to remove the objects from the operational regions seems favourite. That is, if the focus is on the long term sustainability of the space environment, the possibility to dilute the collision risk and to aim at the re-entry in the atmosphere of a subset of the disposed GNSS spacecraft is the most attractive. The most "problematic" constellations are Glonass and Beidou. This conclusion is driven by the future launch traffi...

Laser ranging to passive (cannonball) satellites like the two LAGEOS still represents a way to extract relevant information on Earth’s internal structure, its surface and the way it interacts with the surrounding medium, the atmosphere. The related precise orbit determination (POD) represents the first issue to be fulfilled, to be followed by a solve for the unknown global parameters. The POD requires two main features: i) high-quality observations and ii) high-quality dynamical models. The first item, i.e., the availability of high-quality tracking data, is provided by the International Laser Ranging Service (ILRS) by means of the very precise Satellite Laser Ranging (SLR) technique. With regard to the second point, a big effort has been done to develop models for the non-gravitational forces (i.e., non-conservative forces) on passive satellites, especially for the two LAGEOS, since early ’80s, with significant results in the literature. However, some of the models built were valid only under particular approximations or simplifications, as for the spin model and the thermal thrust forces, and have not been generalized or tested under different conditions. Other aspects, such as the asymmetric reflectivity of the two LAGEOS satellites, are not fully understood. For instance, one of the main parameters that enters in these models is the spin rate of the satellite and its slowing down due to the coupling of the induced magnetic moment produced by eddy currents with the external geomagnetic field. Once the value of the spin period is close to other characteristics time scales, as the thermal inertia of the cube corner retroreflectors or the orbital period of the satellite, resonances are present and more complicated (non-averaged) equations have to be considered for a reliable model of the spin evolution. In order to account for such effects and also to extend/apply (correctly) the models to the new LARES satellite, new efforts are needed in the field of the non-gravitational forces modelling. This is also particularly important for the role played by these satellites in general relativity theory tests in the field of the Earth, wherever the tiny predictions of Einstein’s geometrodynamics need a quite reliable and robust POD. The aim of LARASE (LAser RAnged Satellites Experiment) is to go a step further in the tests of the gravitational interaction in the field of the Earth and, as highlighted above, a key role to reach such a goal is played by high-quality updated models for the perturbing non-gravitational forces acting on the surface of the satellites. Therefore, in the context of the LARASE collaboration, we started an activity dedicated to revisit, extend and improve current models for the non-gravitational perturbations in the case of LAGEOS-type satellites. We discuss the spin modelling problem and its intimate relationship with the thermal thrust forces; also the atmospheric drag impact on the orbit will be discussed, especially in the case of LARES due to its much lower altitude with respect to that of the two LAGEOS. Finally, we present our recent results on the data analysis of the orbit of the two LAGEOS satellites and on that of LARES. <P /

In recent years, the development of active removal missions, to face the growing risk of catastrophic collisions and new debris generation due to the high density of orbital debris in LEO, is widely discussed in the international space community. Besides legal and political issues, active removal solutions are strongly hampered by the high costs involved. Chemical propulsion might represent the preferred way to carry out the controlled reentry of large abandoned objects, and, in the perspective of cost reduction, hybrid rocket technology is considered a valuable option, due to the potential lower fabrication and operational costs, if compared with bipropellant liquid systems. The possibility to use nontoxic propellants, besides their lower prices, reduces the complexity of handling, storability, and loading operations, decreasing the connected costs and avoiding the need of a special staff. Solid rocket technology allows for very small and compact motor units, although without throttleability and reignition capability and characterized by lower safety level than liquid and hybrid systems. This study deals with the preliminary design and mass budget of solid, liquid, and hybrid propulsion modules, as well as their comparison, to be used for active removal of large abandoned rockets in LEO.

In terms of cataloged debris produced, the anti-satellite test carried out by Russia, in November 2021, at an altitude of about 480 km, leading to the destruction of the old satellite Cosmos 1408, was the second worst to date and represented the third worst fragmentation in orbit. It generated more than 1/4 of the cataloged debris produced over 55 years by all such tests and almost twice as many as were produced by all previous Soviet tests. After placing this event in its historical context, this paper analyzes in detail how the evolution of the Cosmos 1408 debris cloud affected the environment below 600 km in the first seven months, focusing on the two operational space stations and the Starlink large constellation of satellites. During the first six months following the test, the Cosmos 1408 cloud of fragments nearly doubled the average flux of cataloged objects on the International Space Station and increased by about 3/4 that on China's Tiangong. In the same period, the Starlink large constellation saw an average increase in the flux of cataloged objects of about 20%. Some orbital planes, the “counter-rotating” ones with respect to the Cosmos 1408 debris cloud, were more affected than others, and the affected planes gradually changed over time, due to the differential precession of cloud and constellation nodes. However, being the Starlink constellation 70 km higher up, the flux of Cosmos 1408 cataloged debris steadily decreased over the period analyzed, due to the cloud orbital decay, reducing to just over a quarter of its extrapolated initial value after seven months.

The dynamical evolution of objects released in geostationary orbit with area-to-mass ratios (A/M) between 1 and 50 m2/kg was analyzed, both short (a few months) and long-term (54 years), taking into account geopotential harmonics (8 u 8), luni-solar perturbations, direct solar radiation pressure with eclipses and, when applicable, air drag. The results obtained confirm that such objects may be good candidates to explain the recently discovered debris population with mean motions of about one revolution per day and orbital eccentricities as high as 0.55. More specifically, for A/M> 40 m2/kg, orbital decay is attained in less than 40 months due to the eccentricity rise, while, for lower values of the area-to-mass ratio, a lifetime of at least two decades was found. Increasing A/M from 1 to 15 m2/kg, the amplitude of the short-term eccentricity oscillation grows from about 0.03 to 0.3, while the long-term variation increases from approximately 0.02 to 0.5. Above 15 m2/kg, the patter...

The LARASE research program is funded by the Italian National Institute for Nuclear Physics and it is a collaboration between different institutions. LARASE aims to provide very precise and accurate measurements of the General Relativity effects that perturb, from the Newtonian point of view, the trajectory of a satellite orbiting the Earth. The improvements obtained by the LARASE collaboration with respect to the previous year are presented in terms of orbit modelling, precise orbit determination and a preliminary measurement of the Lense-Thirring precession. A preliminary and partial estimate of the corresponding error budget is given and it is discussed with the main difficulties present, and to overcome in order to provide a definitive, robust and reliable estimate of the main systematic sources of error.

In this paper we introduce a new index for evaluating the likelihood of accidental collisions leading to the complete destruction of intact objects in a volume of space in low Earth orbit (LEO). The proposed index is therefore not intended to assess the criticality of individual objects or missions, but rather to estimate the global impact of space activities on a given region of space. Moreover, the new index has been designed to be objective, as simple as possible, built from easily accessible data, as well as smoothly reproducible by third parties. Named “volumetric collision rate index”, it has been developed starting from analytical equations expressing the collision rate as a function of the fluxes of intact objects and cataloged debris pieces. The application of reasonable simplifying assumptions and approximations has finally made it possible to define a dimensionless index that explicitly depends only on the spatial densities of intact objects and cataloged debris pieces. It has therefore been applied to the LEO environment, analyzing its evolution from mid-2008 to mid-2020, a crucial period characterized by an impressive change of space activity patterns, with the launch of lots of small satellites and mega-constellations. We also discuss how the index can be further improved, taking into account the maneuverable satellites, which do not contribute to the collision rate, and the increasing number of cubesats, which in many respects are more similar to debris, finally presenting a preliminary analysis in this direction.

Abstract 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.

In this paper we introduce a new index for evaluating the likelihood of accidental collisions leading to the
complete destruction of intact objects in a volume of space in low Earth orbit (LEO). The proposed index is
therefore not intended to assess the criticality of individual objects or missions, but rather to estimate the global
impact of space activities on a given region of space. Moreover, the new index has been designed to be objective,
as simple as possible, built from easily accessible data, as well as smoothly reproducible by third parties. Named
“volumetric collision rate index”, it has been developed starting from analytical equations expressing the
collision rate as a function of the fluxes of intact objects and cataloged debris pieces. The application of
reasonable simplifying assumptions and approximations has finally made it possible to define a dimensionless
index that explicitly depends only on the spatial densities of intact objects and cataloged debris pieces. It has
therefore been applied to the LEO environment, analyzing its evolution from mid-2008 to mid-2020, a crucial
period characterized by an impressive change of space activity patterns, with the launch of lots of small satellites
and mega-constellations. We also discuss how the index can be further improved, taking into account the
maneuverable satellites, which do not contribute to the collision rate, and the increasing number of cubesats,
which in many respects are more similar to debris, finally presenting a preliminary analysis in this direction.

Over the last 11 years (2010–2020), more than 600 intact objects larger than 1 m2 have re-entered without control into the Earth's atmosphere. The total returned mass was approximately 1100 t, roughly corresponding to the re-entry of nearly 100 t per year, mostly concentrated (79%) in rocket bodies. Objects with a mass greater than 500 kg re-entered every about 8 days, those exceeding 2000 kg every about 2 weeks and those heavier than 5000 kg one or twice per year. The total casualty expectancy associated with uncontrolled re-entries over the past 11 years was of the order of 1.4 × 10−1, that in 2020 was almost 1.7 × 10−2, corresponding to a probability of having had at least one victim of approximately 13% and 2%, respectively. Unlike the alert threshold of 10−4, linked to single re-entry events, no cumulative risk limit exists for satellite re-entries over one year or more. However, the casualty probability, although still relatively small, cannot be considered negligible, even in view of the launches of mega-constellations planned in the coming years. For instance, if no design for demise was implemented, the addition of 4000 spacecraft re-entering annually would increase the probability of having at least one victim to nearly 30% per year, while 20,000 more satellites would boost it to almost 80%.

The substantial space traffic changes occurred since the 2010s are having measurable repercussions even at the altitudes used for human spaceflight. These changes were mainly driven by the deployment of thousands of small satellites and cubesats below 600 km. After having evaluated how the situation evolved, from 2008 to 2021, at the altitudes of the International and Chinese space stations, and discussed the main aspects of the problem that may have an operational impact, the attention was focused on what might be expected in the 2020s, whether the current deployment plans for mega-constellations will be realized in whole or in part. Finally, the rationale for the introduction of a “human spaceflight protected region”, with the associated space traffic management recommendations, is presented and discussed.

Looking at the situation in low Earth orbit (LEO), i.e. below 2000 km, on September 9, 2017, there were 21 Italian satellites, one spent upper stage, crossing most of the region, and one debris related to the OptSat 3000 classified mission, probably a mission related object (MRO). They represented just 0.18% of the objects cataloged in LEO by the US Space Surveillance Network (SSN). Moreover, since the release, in 2002, of the first version of the Mitigation Guidelines compiled by the Inter-Agency Space Debris Coordination Committee (IADC), there had been a significant improvement in the level of compliance with debris mitigation requirements for the Italian satellites, included the so called “25-year” rule, i.e. the limitation of the post-mission disposal lifetime to less than 25 years. Several objects had been, however, launched before the introduction of the IADC Mitigation Guidelines, and also before the more than doubling of the debris population below 1000 km caused, in 2007, by the Fengyun 1C anti-satellite test and, in 2009, by the accidental collision between Iridium 33 and Cosmos 2251.
In this paper, the environmental criticality of the Italian satellites in LEO, from the orbital debris point of view, was evaluated addressing the following issues:
• Their residual lifetime;
• The probability of impact with other objects;
• The probability of catastrophic fragmentation;
• The number of expected fragments in case of catastrophic collisional breakups;
• The possible interference with the orbit of the International Space Station;
• An overall ranking, using a criticality index developed by the authors.
The results obtained not only represented an updated assessment for the Italian objects launched until the summer of 2017, but also a guide for planning and conducting future missions in LEO in a way as safe and sensible as possible.

An extensive calibration of semi-empirical atmospheric density models (JR-71, MSIS-86, MSISE-90, TD-88) was carried out, by analyzing the orbital decay of nine spherical satellites in the 200-1500 km altitude range. The orbital decay data used spanned a full solar activity cycle (1987-1999). The drag coefficients obtained by fitting the observed semimaior axis evolution with a high accuracy orbit propagator were compared with those estimated by theoretical analysis. MSIS-86 and MSISE-90, practically identical above 200 km, resulted to be the best models to compute air density below 400 km, in low solar activity conditions. However, JR-71 seemed more precise at greater altitudes and/or solar activity. TD-88 gave quite mixed results, but generally closer to JR-71. The intrinsic accuracy of JR-71, MSIS-86 and MSISE-90 was generally better than 20%, often better than 15% and, sometimes, close to 10%. But at altitudes greater than 400 km this picture resulted progressively degraded. A better drag coefficient theory and dedicated laboratory measurements will be needed to investigate in detail the deficiencies of the current models and improve the knowledge of the earth atmosphere with satellite drag analysis.

The survivability analysis carried out to support the design of a new tether system, being studied in Italy for spacecraft and upper stages end-of-life de-orbiting, is presented. In particular, the problem represented by meteoroids and orbital debris impacts able to cut the tether was addressed, by considering several system configurations in order to find a solution able to meet the baseline mission requirements. In addition, the not negligible collision risk with large intact space objects, and between the tethers themselves, was analysed as well in its implications.

The paper presents a review of the management of the Mir deorbiting in Italy, with special emphasis on the role played by CNUCE, active in the field of reentry predictions for civil protection purposes since 1979.
After a short historical introduction, the criteria used for the definition of potentially risky space objects are presented and discussed, together with the lessons learned during previous reentry campaigns. The activity carried out for Mir is then described in detail, highlighting the end products needed for the civil protection emergency planning.
Mir was never declared a risk space object in Italy and only a limited alert status was activated, ready to switch to full emergency if needed. However, the event represented a useful training opportunity and a good example of international cooperation, paving the way for the future end-of-life disposal of large low earth spacecraft.

Tethers have been proposed for several space applications, like satellite de-orbiting or re-boost, electric energy generation, scientific research and so on. However, they may be vulnerable to orbital debris and meteoroid impacts.
The problem was assessed, to assist tether systems design, by detailed numerical computations of the average impact rate of artificial debris, taking into account the specific geometric properties of tethers as debris targets, when compared to typical satellites.
The results obtained confirm that, for single-strand tethers in low earth orbit, the probability to be severed by orbital debris and meteoroid impacts is quite significant, making necessary the adoption of innovative designs for long duration missions.

Following the catastrophic collisional breakups of three intact spacecraft (Fengyun 1C, Cosmos 2251 and Iridium 33) occurred in low Earth orbit, a detailed analysis was carried out, with a dedicated software tool (SDIRAT), in order to evaluate the additional impact flux of cataloged objects on the satellites of two operational constellations in high inclination orbits, Iridium and COSMO-SkyMed. As of 1 May 2011, the flux increase with respect to the debris background was 160%, on average, for the Iridium satellites, distributed on six equally spaced orbit planes at 781 km, and 47% at the altitude of the COSMO-SkyMed constellation, using a single orbit plane at 623 km.

In order to estimate the intrinsic accuracy of satellite reentry predictions, the residual lifetimes of 11 spacecraft and five rocket bodies, covering a broad range of inclinations and decaying from orbit in a period of high solar activity, were determined using three different atmospheric density models: JR-71, TD-88, and MSIS-86. For each object, the ballistic coefficient applicable to a specific phase of the flight was obtained by fitting an appropriate set of two-line orbital elements, while the reentry predictions were computed approximately one month, one week and one day before the final orbital decay. No clear correlation between the residual lifetime errors and satellite inclination or type (spacecraft or rocket body) emerged. JR-71 and MSIS-86 resulted in good agreement, with comparable reentry prediction errors (∼10%), semimajor axis residuals, and ballistic coefficient estimations. TD-88 exhibited a behaviour consistent with the other two models, but was typically characterised by larger reentry prediction errors (∼15–25%) and semimajor axis residuals. At low altitudes (<250 km), TD-88 systematically overestimated the average atmosphere density (by ∼25%) with respect to the other two models.

A review of the problem of the long-term uncontrolled growth of man-made objects in earth orbit is presented. After a discussion of the main underlying concepts, the relative effectiveness of the adoption of some mitigation measures over 100 – 200 years is analysed, including the minimisation of mission related objects release, the on-orbit explosion avoidance and the de-orbiting of spacecraft and upper stages in low earth orbit. It is shown that only the implementation of the full set of mitigation measures discussed would be able to guarantee the long-term approximate stabilisation of the population of large objects, maintaining at acceptable levels the growth of millimetre and centimetre sized debris.

Following the admission of the Italian Space Agency (ASI) in the Inter-Agency Space Debris Coordination Committee (IADC), the CNUCE Institute was involved, as the National Technical Contact Point, in the three test re-entry campaigns carried out between 1998 and 2000. The purpose of these campaigns was to test the timely distribution of data and information during high-risk re-entries by means of the IADC international communication network. During the second campaign, a further analysis was also performed at CNUCE to assess the confidence level of our computed re-entry predictions. Different semi-empirical atmospheric density models were used at the same time to predict the satellite's orbital decay as a function of solar activity conditions and altitude. In particular, the performances of two widely used thermospheric models were investigated and the resulting re-entry forecasts compared. The aim of this paper is to present the results obtained and the lessons learned during these international exercises.

EDOARD (Electrodynamic De-Orbiting And Re-entry Device) exploits the basic concepts of electrodynamic drag on conductive tethers to de-boost LEO spacecraft efficiently and reliably. The system is jointly developed by Alenia Spazio and by University " La Sapienza " in view of potential commercial exploitation. An innovative engineering approach has tackled four critical issues: 1) the deployment mechanism, which ensures a purely passive extension of the tether under extremely small gravity gradients; 2) the tether structure and configuration, which guarantees a very high survivability to impacts from artificial and natural debris; 3) the inflatable passive electron collector, which increases the efficiency of the system while reducing the tether length to 4-5 km and 4) the electrodynamic control of the tether librations, which limits the effects of inherent dynamical system instability, while preserving high de-orbiting efficiencies. The configuration ensures de-orbiting times per unit mass of about 0.09 day/kg from a circular, 1500 km altitude, 55 degree inclination.

The uncommon nature of the GOCE reentry campaign, sharing an uncontrolled orbital decay with a finely controlled attitude along the atmospheric drag direction, made the reentry predictions for this satellite an interesting case study, especially because nobody was able to say a priori if and when the attitude control would have failed, leading to an unrestrained tumbling and a sudden variation of the orbital decay rate. As in previous cases, ISTI/CNR was in charge of reentry predictions for the Italian civil protection authorities, monitoring also the satellite decay in the frame of an international reentry campaign promoted by the Inter-Agency Space Debris Coordination Committee (IADC). Due to the peculiar nature of the GOCE reentry, the definition of reliable uncertainty windows was not easy, especially considering the critical use of this information for civil protection evaluations. However, after an initial period of test and analysis, reasonable and conservative criteria were elaborated and applied, with good and consistent results through the end of the reentry campaign. In the last three days of flight, reentries were simulated over Italy to obtain quite accurate ground tracks, debris swaths and air space crossing time windows associated with the critical passes over the national territory still included in the global uncertainty windows.