Genetic algorithm for space debris and space objects attitude motion reconstruction through optical measurements

Space debris has recently become a major problem in the planning and execution of space missions. Due to the recent widespread placement of satellite mega- constellations in Low Earth Orbits (LEO), where most of the catalogued debris is located, the need to monitor such uncontrolled objects and maintain an up-to-date catalogue has increased. Moreover, estimating the attitude motion of a space object is fundamental to improving methods for orbit determination and supporting eventual Active Debris Removal (ADR) missions. The Sapienza Space System and Space Surveillance Laboratory (S5Lab), whose researchers have years of experience in space debris detection, operates an extensive observation network that can exploit different observation strategies. This paper illustrates the reconstruction of an object’s attitude motion from its light curve, which can be extracted using scientific Complementary Metal-Oxide Semiconductor (sCMOS) sensors installed on high-slew rate telescopes. The method is based on a comparison between the object's actual light curve and a synthetic curve created by changing the initial conditions for the attitude motion, considering the observer's motion, the Sun’s position, the object’s position and its 3D model. A genetic algorithm is used to create multiple synthetic light curves by varying the initial conditions for the attitude motion until one of them matches the observed one. In addition to extracting the light curves and reconstructing the attitude, observational strategies for acquiring light curves are discussed. Finally, the results of the investigation of potentially hazardous debris are presented

From BEXUS to HEMERA: The application of lessons learned on the development and manufacturing of stratospheric payloads at S5Lab

In the last years the S5Lab (Sapienza Space Systems and Space Surveillance Laboratory) from Sapienza University of Rome has given to the students the opportunity to gather knowledge on stratospheric payloads by supporting the design and development of two experiments selected for the participation in the REXUS/BEXUS educational Programme, managed by three european space institutions. The insights and lessons learned gathered during the participations in the REXUS/BEXUS educational programme gave the possibility to the student to take part in the development of a third experiment in the frame of the professional research programme HEMERA and complete it successfully. STRATONAV (STRATOspheric NAVigation experiment) was a stratospheric experiment based on Software Defined Radios (SDRs) technology whose aim was the testing of the VOR (VHF Omnidirectional Range) navigation system, evaluating its performance above the standard service volume, which was launched on BEXUS 22 in October 2016. TARDIS (Tracking and Attitude Radio-based Determination In Stratosphere) was developed as a follow up of STRATONAV between 2018 and 2019. Similarly to its predecessor TARDIS was a stratospheric experiment aimed at exploiting the VOR signal, with the aid of SDRs, to perform in-flight attitude and position determination, and was launched on BEXUS 28 in October 2019. After the launch of TARDIS, a team composed both by former STRATONAV and TARDIS students was formed for the development of a third stratospheric experiment going by the name of STRAINS (Stratospheric Tracking Innovative Systems), conceived by Sapienza University of Rome and ALTEC and supported by ASI. STRAINS main objective was the proof of concept of the possibility of achieving the Time Difference of Arrival (TDOA) and the Frequency Difference of Arrival (FDOA) for navigation purposes with the aid of SDRs. The experiment was developed between 2020 and 2021 exploiting the lessons learned from the former team members of the two BEXUS campaigns and was launched on board of the Hemera H2020 stratospheric balloon in September 2021 from Esrange Space Center, Kiruna, Sweden. After a brief description of the stratospheric payloads design and manufacturing, the paper will present the major lessons learned from the previous stratospheric experiments, STRATONAV and TARDIS, and their application to the development and manufacturing of the latest launched stratospheric experiment STRAINS, as well as their educational return to the students involved in the projects

The role of clinical and neuroimaging features in the diagnosis of CADASIL.

BACKGROUND: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common familial cerebral small vessel disease, caused by NOTCH3 gene mutations. The aim of our study was to identify clinical and neuroradiological features which would be useful in identifying which patients presenting with lacunar stroke and TIA are likely to have CADASIL. METHODS: Patients with lacunar stroke or TIA were included in the present study. For each patient, demographic and clinical data were collected. MRI images were centrally analysed for the presence of lacunar infarcts, microbleeds, temporal lobe involvement, global atrophy and white matter hyperintensities. RESULTS: 128 patients (mean age 56.3 ± 12.4 years) were included. A NOTCH3 mutation was found in 12.5% of them. A family history of stroke, the presence of dementia and external capsule lesions on MRI were the only features significantly associated with the diagnosis of CADASIL. Although thalamic, temporal pole gliosis and severe white matter hyperintensities were less specific for CADASIL diagnosis, the combination of a number of these factors together with familial history for stroke result in a higher positive predictive value and specificity. CONCLUSIONS: A careful familial history collection and neuroradiological assessment can identify patients in whom NOTCH3 genetic testing has a higher yield.The Lombardia GENS project has received funding from the Regione Lombardia Government as a Research Independent Project (DGR n°VIII/006128-12/12/2007). Lombardia GENS is an investigator-driven, academic, non-profit consortium and is publicly funded. Hugh Markus is supported by an NIHR Senior Investigator award and his work is supported by the Cambridge University Hospitals NIHR Biomedical Research Centr

Third harmonic generation in the skin layer of a hot dense plasma

The third harmonic generation of a pump wave, resulting from the electron-ion collision frequency dependence on the electric field in the skin-layer of a hot dense plasma is investigated. The relation of the current third harmonic with the high-frequency field in the skin-layer is established for arbitrary ratios of the electron-ion collision frequency to the field frequency. For arbitrary ratios of these two frequencies the field structure inside the skin-layer is determined, and the field of the wave irradiated by the plasma at tripled frequency too is calculated. It has permitted to find the explicit dependencies of the third harmonic generation efficiency on the plasma and pump fiel

LEO Object’s Light-Curve Acquisition System and Their Inversion for Attitude Reconstruction

In recent years, the increase in space activities has brought the space debris issue to the top of the list of all space agencies. The fact of there being uncontrolled objects is a problem both for the operational satellites in orbit (avoiding collisions) and for the safety of people on the ground (re-entry objects). Optical systems provide valuable assistance in identifying and monitoring such objects. The Sapienza Space System and Space Surveillance (S5Lab) has been working in this field for years, being able to take advantage of a network of telescopes spread over different continents. This article is focused on the re-entry phase of the object; indeed, the knowledge of the state of the object, in terms of position, velocity, and attitude during the descent, is crucial in order to predict as accurately as possible the impact point on the ground. A procedure to retrieve the light curves of orbiting objects by means of optical data will be shown and a method to obtain the attitude determination from their inversion based on a stochastic optimization (genetic algorithm) will be proposed

Improving accuracy of LEO objects Two-Line Elements through optical measurements

Two-Line Elements (TLEs) of LEO objects, consisting in the object orbital parameters released by the North American Aerospace Defense Command (NORAD), are often characterized by low accuracy and short-term reliability. This is mostly due to sparse tracking data and relevant contribution of either unmodeled or poorly modelled perturbations of the orbital dynamics. Frequent updates of the dynamic state estimate are necessary for Space Situational Awareness (SSA) analyses and reliable orbit propagation. The optical Orbit Determination procedure represents a possible approach in order to increase TLE accuracy by processing ground-based optical measurements. In case of one-site observations, fast passes, together with possible bad weather conditions, can lead to a set of largely sparse measures, consequently leading to the impossibility of calculating consistent orbit determination solutions. The Sapienza Space Systems and Space Surveillance Laboratory (S5Lab) research team has developed an orbit determination algorithm aimed to improve TLEs accuracy by exploiting multiple-sites optical observations. The developed algorithm receives as input the astrometric solutions of different sites images, in order to integrate them to produce an improved orbit determination solution in TLE format. The considered observatories, which belong to the Sapienza Scientific Observatory Network (SSON) and to the International Scientific Optical Network (ISON), are MITO (Rome, Italy), RESDOS (Avezzano, Italy) and EQUO OG (Malindi, Kenya) with regards to Sapienza University of Rome, and MMT-9 (Nizhny Arkhyz, Russia) and PH-2A (Nauchny, Crimea) with regards to the ISON network. These telescopes locations allow to acquire less sparse data and increase the time spans, eventually allowing to track multiple arcs of the same orbit. Moreover, the observatories configuration provides redundancy to the data acquisition devices and it increases the optical data availability, even when coping with the different meteorological conditions of the observatories regions. Therefore, a higher accuracy in determining the target orbit is achievable. The developed software validation has been performed by analyzing pre-fit and post-fit residuals with respect to reference measures taken during Tiangong 1 re-entry monitoring campaign performed between February and March 2018. The analysis has demonstrated that the algorithm improves the state estimate accuracy on multiple test cases that will be described in detail. This paper will describe the developed algorithm for optical data integration and TLE improvement. In addition to the integration theoretical model, the validation campaigns and the used observatories features will be exposed

Bi static optical measurements for reentering objects attitude and obit determination

The constant increase of the amount of space debris is becoming a threat for both ground and space infrastructures. The non-negligible risks of collisions in orbit, involving possible damages for active space systems, and concerns over re-entry of large objects are leading to an increasing international interest in Space Surveillance and Tracking. Through a network of observatories, simultaneous optical measurements from different observers allows the 3D reconstruction of the objects’ positions and so the direct estimation of their altitudes. Altitude is directly linked to atmospheric drag, which in turn affects the change in attitude during re-entry. Reconstruction of attitude through photometric analysis is possible thanks to optimization algorithms using data provided by the observation network. The Sapienza Space Systems and Space Surveillance Laboratory (S5Lab) of Sapienza University of Rome, together with the Institute for Complex Systems (ISC) of the Italian Nation Research Council (CNR), have developed a network of observatories capable of simultaneously tracking a space object. The optical system consists of a telescope connected to a scientific Complementary Metal-Oxide Semiconductor (sCMOS) camera, which allows high frame rates, thus increasing the number of obtainable data, improving the accuracy of space debris’ trajectories. The crucial point of this experimental set-up is the integration of two simultaneous bidimensional data, which requires the cameras’ precise synchronization. In this paper, the synchronization tests of the cameras will be described