Evaluating the impact of space activities in low earth orbit

Abstract 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

Evolution of the Debris Cloud Generated by the Fengyun-1C Fragmentation Event

The cloud of cataloged debris produced in low earth orbit by the fragmentation of the Fengyun-1C spacecraft was propagated for 15 years, taking into account all relevant perturbations. Unfortunately, the cloud resulted to be very stable, not suffering substantial debris decay during the time span considered. The only significant short term evolution was the differential spreading of the orbital planes of the fragments, leading to the formation of a debris shell around the earth approximately 7-8 months after the breakup, and the perigee precession of the elliptical orbits. Both effects will render the shell more "isotropic" in the coming years. The immediate consequence of the Chinese anti-satellite test, carried out in an orbital regime populated by many important operational satellites, was to increase significantly the probability of collision with man-made debris. For the two Italian spacecraft launched in the first half of 2007, the collision probability with cataloged objects increased by 12% for AGILE, in equatorial orbit, and by 38% for COSMO-SkyMed 1, in sun-synchronous orbit

Testing gravitation with satellite laser ranging and the LARASE experiment

The International Laser Ranging Service (ILRS) provides range measurements of pas- sive satellites around the Earth through the powerful Satellite Laser Ranging (SLR) technique. These very precise measurements of the distance between an on-ground laser station and a satellite equipped with cube corner retro-reflectors (CCRs) make possible precise tests and measurements in fundamental physics and, in particular, in gravitational physics. The LAGEOS (NASA 1976) and LAGEOS II (NASA/ASI 1992) satellites are outstanding examples of very good test particles because of their very low area-to-mass ratio as well as the high quality of their tracking data and, consequently, of the precise orbit determination (POD) we can obtain after a refined modeling of their orbit. The aim of our research program LARASE (LAser RAnged Satellites Experi- ment) is to go a step further in testing gravitation in the field of Earth by means of the joint analysis of the orbits of the two LAGEOS satellites together with that of the most recently launched LARES (ASI, 2012) satellite. Therefore, our work falls in the so-called weak field and slow motion (WFSM) limit of Einstein’s general relativity (GR) where, in terms of Newtonian physics, relativistic effects appear as two new fields to be added to the classical gravitational field: the gravitoelectric and the gravitomagnetic fields. A fundamental ingredient to reach such a goal is to provide high-quality updated models for the perturbing non-gravitational perturbations (NGP) acting on the surface of these satellites. In fact, regardless of their minimization thanks to a smaller value for the area-to-mass ratio, the subtle and complex to model perturbing effects of the NGP play a crucial role in the POD of the considered satellites, especially in the case of the thermal thrust effects. A large amount of SLR data of LAGEOS and LAGEOS II has been worked out using a set of dedicated models for the satellite dynamics and the related post-fit residuals have been analyzed. A parallel work was performed with LARES, although at a preliminary stage. Our recent work on the orbit modeling and on the data analysis of the orbit of such satellites is presented and discussed

A 1% Measurement of the gravitomagnetic field of the earth with laser-tracked satellites

A new measurement of the gravitomagnetic field of the Earth is presented. The measurement has been obtained through the careful evaluation of the Lense-Thirring (LT) precession on the combined orbits of three passive geodetic satellites, LAGEOS, LAGEOS II, and LARES, tracked by the Satellite Laser Ranging (SLR) technique. This general relativity precession, also known as frame-dragging, is a manifestation of spacetime curvature generated by mass-currents, a peculiarity of Einstein’s theory of gravitation. The measurement stands out, compared to previous measurements in the same context, for its precision (≃7.4×10−3, at a 95% confidence level) and accuracy (≃16×10−3), i.e., for a reliable and robust evaluation of the systematic sources of error due to both gravitational and non-gravitational perturbations. To achieve this measurement, we have largely exploited the results of the GRACE (Gravity Recovery And Climate Experiment) mission in order to significantly improve the description of the Earth’s gravitational field, also modeling its dependence on time. In this way, we strongly reduced the systematic errors due to the uncertainty in the knowledge of the Earth even zonal harmonics and, at the same time, avoided a possible bias of the final result and, consequently, of the precision of the measurement, linked to a non-reliable handling of the unmodeled and mismodeled periodic effects

The LARASE Spin Model of the two LAGEOS and LARES satellites

Satellite Laser Ranging (SLR) represents a very important technique of the observational space geodesy. In fact, Lunar Laser Ranging, Very Long Baseline Interferometry, Global Navigation Satellite Systems, Doppler Orbitography and Radiopositioning Integrated by Satellite, together with SLR constitute the Global Geodetic Observing System (GGOS). In the context of the GGOS activities, improvements in technology and in modeling will produce advances in Geodesy and Geophysics as well as in General Relativity (GR) measurements. Therefore, these important research fields are not independent, but tightly related to each other. The LARASE (LAser RAnged Satellites Experiment) research program has its main objectives in tests and measurements of Einstein's theory of GR via Precise Orbit Determination (POD) of a set of geodetic satellites. In order to reach such goals by means of very precise measurements of a number of relativistic parameters (and, at the same time, to provide a robust and unassailable error budget of the main systematic effects), we are also reviewing previous models and we are developing new models for the main perturbations (both gravitational and non-gravitational) that act on the orbits of the two LAGEOS and on that of LARES satellites. Within this paper we focus on modeling the spin vector of these satellites. The spin knowledge, both in orientation and rate, is of fundamental importance in order to correctly model the thermal effects acting on the surface of these satellites. These are very important non-gravitational perturbations (NGP) that produce long-term effects on the orbit of the cited satellites, especially for the two LAGEOS, and improvements in their modeling will be very useful both in the field of GR measurements and in those of space geodesy and geophysical applications. Indeed, the current RMS value of the range residuals of the LAGEOS satellites, obtained by the Analysis Centers of the International Laser Ranging Service, is at the level of a few cm since 1992, down to a cm or less during the last years. However, because of the incompleteness in current knowledge of dynamical models, empirical accelerations have been heavily employed to obtain such results. In this context, any step forward in the models developed for the NGP will be useful to reduce the use of empirical accelerations; it also represents an essential prerequisite to reach a sub-mm precision in the RMS of the SLR range residuals and the corresponding benefits in Geophysics and Geodesy, regarding e.g. stations coordinates knowledge, Earth's geocenter and reference frame realization. The paper will focus upon the improvements we obtained with respect on previous models of the spin of the two LAGEOS satellites based on averaged equations for the external torques in the rapid-spin approximation, as well as in a new general model that we developed and based on the solution of the full set of Euler equations

Testing General Relativity vs. Alternative Theories of Gravitation with the SaToR-G Experiment

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

Argentine Consensus of congenital toxoplasmosis

La transmisión vertical de la infección por Toxoplasma gondii ocurre cuando la madre se infecta por primera vez en el transcurso del embarazo. El diagnóstico de la infección materna y la del re cién nacido se logra con el conjunto de pruebas serológicas, hallazgos clínicos y ecográficos. El reconocimiento temprano de la infección materna permite un tratamiento que reduce la tasa de transmisión y el riesgo de daño en el producto de la concepción. El objetivo de este consenso de expertos fue revisar la literatura científica para actualizar las recomendaciones de práctica clínica respecto de la prevención, el diagnóstico y el tratamiento de la toxoplasmosis congénita en nuestro país.Mother-to-child transmission in Toxoplasma gondii infection occurs only when the infection is acquired for the first time during pregnancy. Diag nosis of maternal infection and the newborn is achieved by a combination of serological tests, clinical features and ultrasound images. An early diagnosis of maternal infection allows treatment that offers a reduction both in transmission rate and risk of congenital damage. The aim of this expert consensus was to review the scientific literature which would enable an update of the clinical practice guideline of prevention, diagnosis and treatment of congenital toxoplasmosis in our country.Fil: Durlach, Ricardo A.. Asociación Argentina de Zoonosis; ArgentinaFil: Freuler, Cristina. Hospital Aleman; ArgentinaFil: Messina, Matías. Hospital Aleman; Argentina. Asociación Argentina de Zoonosis; ArgentinaFil: Freilij, Hector León. Gobierno de la Ciudad de Buenos Aires. Instituto Multidisciplinario de Investigaciones en Patologías Pediátricas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto Multidisciplinario de Investigaciones en Patologías Pediátricas; ArgentinaFil: Gonzalez Ayala, Silvia Elena. Universidad Nacional de La Plata. Facultad de Ciencias Médicas; ArgentinaFil: Venturini, María Cecilia. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Departamento de Epizootiología y Salud Pública. Laboratorio de Inmunoparasitología; ArgentinaFil: Kaufer, Federico. Hospital Aleman; ArgentinaFil: García, Fabiana. Centro de Estudios Infectológicos Dr. Daniel Stamboulia; ArgentinaFil: Ceriotto, Mariana. Gobierno de la Ciudad de Buenos Aires. Hospital de Infecciosas "Dr. Francisco Javier Muñiz"; ArgentinaFil: Pardini, Lais Luján. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Departamento de Epizootiología y Salud Pública. Laboratorio de Inmunoparasitología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Nadal, Mónica Zaida. Hospital Materno Infantil Ramon Sarda ; Gobierno de la Ciudad Autonoma de Buenos Aires;Fil: Ortiz de Zárate, Marcela. Hospital Materno Infantil Ramon Sarda ; Gobierno de la Ciudad Autonoma de Buenos Aires;Fil: Schneider, Vanessa. Hospital Aleman; ArgentinaFil: Mayer Wolf, Micaela. Hospital Aleman; ArgentinaFil: Jacob, Néstor. Gobierno de la Ciudad Autonoma de Buenos Aires. Hospital General de Agudos Doctor Cosme Argerich.; ArgentinaFil: Abuin, Juan Carlos. Gobierno de la Ciudad de Buenos Aires. Hospital de Infecciosas "Dr. Francisco Javier Muñiz"; ArgentinaFil: Altcheh, Jaime Marcelo. Gobierno de la Ciudad de Buenos Aires. Instituto Multidisciplinario de Investigaciones en Patologías Pediátricas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto Multidisciplinario de Investigaciones en Patologías Pediátricas; ArgentinaFil: Fiameni, Facundo. Hospital Aleman; ArgentinaFil: Salomon, Cristina del Carmen. Universidad del Aconcagua. Facultad de Ciencias Médicas; ArgentinaFil: Ledesma, Bibiana. Dirección Nacional de Instituto de Investigación. Adm.nacional de Laboratorio E Instituto de Salud "dr.c.g.malbran". Instituto Nacional de Enfermedades Infecciosas. Departamento de Parasitología; ArgentinaFil: Guarnera, Eduardo. Asociación Argentina de Zoonosis; Argentin