Status of the Sardinia Radio Telescope as a receiver of the BIRALET bi-static radar for space debris observations

Space debris are human-made objects, of variable sizes and shapes, that orbit the Earth or reenter the atmosphere. They represent a serious problem for every active spacecraft and satellite, due to the high risk of collision and consequently the generation of new debris. One of the main segments of the Space Situational Awareness program regards space surveillance and tracking activities, with procedures for tracking resident space objects, using a sensor network composed by radars, telescopes and lasers. In this way, it is possible to collect data in order to catalogue and perform orbit predictions of objects orbiting the Earth, with the aim of avoiding collisions between them. One of the Italian radars for space and surveillance tracking functions is represented by the BIRALET system, an acronym which stands for Bistatic Radar for LEO Tracking. This radar operates in P-band at 410-415 MHz, is a bi-static configuration composed of a transmitting 7-meter antenna and the SRT (Sardinia Radio Telescope) as receiver, with a baseline of about 20 km. The Sardinia Radio Telescope is a 64-meter fully steerable wheel-and-track antenna, located near San Basilio (Cagliari, Sardinia, Italy). It represents a flexible instrument used for radio astronomy and space science studies, developed to work in a wide frequency range between 300 MHz and 110 GHz. In this paper, we present a review of the status of the SRT for space debris observation. In particular, we describe three possible system configurations, in order to perform Doppler shift and range measurements. In particular, we present a simplified solution based on a spectrum analyzer as a back-end that permits only Doppler shift measurements. Another more complex solution for Doppler shift measurements, is based on the electronic Red Pitaya board. For the Red Pitaya we developed also a dedicated signal acquisition chain with a down-conversion circuit, in order to shift the received signal in the frequency range of the board. Finally, a more complex solution that allows range and range rate measurements, based on the National Instrument USRP board as a back-end. For future developments, we present the possibility to improve our system, using a C-band Phased Array Feed as a receiver

HLA Genotyping in Children With Celiac Disease Allows to Establish the Risk of Developing Type 1 Diabetes

Introduction: Celiac disease (CD) and type 1 diabetes (T1D) often co-occur and share genetic components in the human leukocyte antigen (HLA) class II region. We aimed to study the usefulness of HLA genotyping in predicting the risk of developing T1D in patients with CD and the temporal relationship between these diseases. Methods: A cohort of 1,886 Sardinian patients, including 822 with CD, 1,064 with T1D, and 627 controls, underwent HLA class II typing. Seventy-six of 822 patients with CD were also affected by T1D (CD-T1D), and their HLA genotypes were analyzed for specific HLA associations with CD, T1D, and controls. Results: High-risk HLA-DQ genotypes, including HLA-DQ2.5/DQ8, -DQ2.5/DQ2.5, and -DQ2.5/DQ2.3, were strongly associated with CD-T1D with frequencies of 34.5%, 15.9%, and 18.8%, respectively. Conversely, certain HLA genotypes associated with CD seemed to confer protection against T1D development. Therefore, HLA genotyping allows for the identification of those patients with CD who might develop T1D. The frequency of patients with CD preceding T1D is higher in younger children than older ones, with implications for the early childhood approach to diabetes prevention. Discussion: CD is a condition for future T1D development, and specific HLA genotypes can predict this risk. Early screening for celiac autoimmunity and subsequent HLA typing in CD children could help identify those at high risk of T1D, allowing for proactive interventions and immunotherapies to preserve β-cell function. These findings may support the re-evaluation of HLA typing in children with CD

Advantages of using a C-band phased array feed as a receiver in the Sardinia radio telescope for space debris monitoring

The population of space debris is continuously growing and it represents a potential problem for satellites and spacecraft. In fact, new collisions could exponentially rise the number of debris and so the level of threat represented by these objects. To prevent new collisions, the monitoring of space environment is necessary. For this reason, radar measurements are relevant, in particular to observe Space Debris in Low Earth Orbit. In recent years, the Sardinia Radio Telescope, a fully steerable wheel-and-track 64-m antenna, located in Sardinia (Italy), has been used as a receiver in a Pband bi-static radar for space debris monitoring purposes. In this paper the authors investigate the advantages of using a Phased Array Feed in C-band for space debris monitoring (e.g. improved sensitivity and gain, detection of the object trajectory allowed by multiple beams, improvement of the orbit determination of known and unknown debris), as a receiver of the Sardinia Radio Telescope compared to the already used mono-beam P-band receiver

Space Debris Detection in Low Earth Orbit with the Sardina Radio Telescope

Space debris are orbiting objects that represent a major threat for space operations. In this work a bistatic radar configuration named BIstatic RAdar for LEo Tracking (BIRALET) is used to detect a set of space debris. Signalto- Noise Ratios, Doppler shift measures as well as the frequency specters for each debris are presented

Upgrading the Sardinia Radio Telescope to a bistatic tracking radar for space debris

In order to prevent the harmful impacts for spacecrafts deriving from the presence of space debris, many surveillance and monitoring programs of the space environment have been started in recent years. The Sardinia Radio Telescope is a new comer in such a scenario, but it has already showed its potential. However, since the actual receiving chain is not optimized for the reception of the echoes scattered from the debris, some modifications has been planned to upgrade the telescope and made it suitable for these types of observations

Preliminary Characterization of the Digitally Formed Beams of PHAROS2 Phased Array Feed

We describe the beamforming strategy and the preliminary laboratory characterization results of the beam pattern synthesized by the PHAROS2 Phased Array Feed (PAF), a 4-8 GHz PAF with digital beamformer for radio astronomy application. The PAF is based on an array of 10×11 dual-polarization Vivaldi antennas cryogenically cooled at 20 K along with low noise amplification modules (LNAs) cascaded with a multi-channel Warm Section (WS) receiver. We present the beamforming and test procedures used to, respectively digitally synthesize and characterize the PHAROS2 antenna array beam pattern at 6 GHz. The tests of the array were carried out at room temperature by directly connecting 24 antenna elements to the WS and iTPM digital beamformer in a laboratory measurement setup

Upgrading the Italian BIRALES system to a pulse compression radar for space debris range measurements

Space debris represent a major risk for every spacecraft and satellite. In fact, other than cause serious damages to these structures, new collisions could exponentially increase the amount of debris and so the level of threat represented by the objects. To avoid new impacts, the monitoring of the space environment with space-based and ground-based measurement campaigns is necessary. The ground-based measurement can be implemented with optical or radar technologies. In this paper the upgrade of the Italian BIRALES radar system for space debris, that initially performed only Doppler measurements, is described. With its new features the BIRALES will be able to perform even range measurements

Natural killer-cell immunoglobulin-like receptors trigger differences in immune response to SARS-CoV-2 infection

Background: The diversity in the clinical course of COVID-19 has been related to differences in innate and adaptative immune response mechanisms. Natural killer (NK) lymphocytes are critical protagonists of human host defense against viral infections. It would seem that reduced circulating levels of these cells have an impact on COVID-19 progression and severity. Their activity is strongly regulated by killer-cell immuno-globulin-like receptors (KIRs) expressed on the NK cell surface. The present study's focus was to investigate the impact of KIRs and their HLA Class I ligands on SARS-CoV-2 infection. Methods: KIR gene frequencies, KIR haplotypes, KIR ligands and combinations of KIRs and their HLA Class I ligands were investigated in 396 Sardinian patients with SARS-CoV-2 infection. Comparisons were made between 2 groups of patients divided according to disease severity: 240 patients were symptomatic or paucisymptomatic (Group A), 156 hospitalized patients had severe disease (Group S). The immunogenetic characteristics of patients were also compared to a population group of 400 individuals from the same geographical areas. Results: Substantial differences were obtained for KIR genes, KIR haplotypes and KIR-HLA ligand combinations when comparing patients of Group S to those of Group A. Patients in Group S had a statistically significant higher frequency of the KIR A/A haplotype compared to patients in Group A [34.6% vs 23.8%, OR = 1.7 (95% CI 1.1-2.6); P = 0.02, Pc = 0.04]. Moreover, the KIR2DS2/HLA C1 combination was poorly represented in the group of patients with severe symptoms compared to those of the asymptomatic-paucisymptomatic group [33.3% vs 50.0%, OR = 0.5 (95% CI 0.3-0.8), P = 0.001, Pc = 0.002]. Multivariate analysis confirmed that, regardless of the sex and age of the patients, the latter genetic variable correlated with a less severe disease course [ORM = 0.4 (95% CI 0.3-0.7), PM = 0.0005, PMC = 0.005]. Conclusions: The KIR2DS2/HLA C1 functional unit resulted to have a strong protective effect against the adverse outcomes of COVID-19. Combined to other well known factors such as advanced age, male sex and concomitant autoimmune diseases, this marker could prove to be highly informative of the disease course and thus enable the timely intervention needed to reduce the mortality associated with the severe forms of SARS-CoV-2 infection. However, larger studies in other populations as well as experimental functional studies will be needed to confirm our findings and further pursue the effect of KIR receptors on NK cell immune-mediated response to SARS-Cov-2 infection

Exploration of an innovative ranging method for bi-static radar, applied in LEO Space Debris surveying and tracking

Space Situational Awareness (SSA) is referred as one of the capacitive areas of strategic interest to be developed/completed in the future in the short and medium term, for any nation with the target of the access to the space. One of the fundamental components is the Space Surveillance and Tracking (SST) program, considered as the capability to build a spatial mapping of the objects in orbit, their classification and the exact identification of their orbital characteristics. For this reason, radar measurements are relevant, in particular to observe objects in Low Earth Orbit. The Italian National Institute of Astrophysics together with Vitrociset company and Politecnico di Milano, studied and developed a new and innovative method for the range measure applied to bi-static radars to support the European Union Space Surveillance and Tracking (EUSST) program. Several tests have been carried out using the BIRALES and BIRALET sensors for survey and tracking observations respectively. Finally, the results obtained from observations have been compared with the real positions of the targets in order to validate the system. The ranging method relies on the synchronization of the transmitting and receiving antennas and on the correlation of the echo received from the scattering of the orbiting object. To do that, the transmitting antenna emits simultaneously two different signals: a Chirp signal for range measurement and a second “Continuous Wave” (CW) for Doppler shift measurement and object track reconstruction. Overall, we simultaneously obtain time profiles for range, angular position (azimuth and elevation), and Doppler during the passage of the objects inside the sensor Field of View. By virtue of the above plethora of measurements, this method guarantees also the possibility to produce an Initial Orbital Determination (IOD) for unknown objects

Exploitation of bi-static radar architectures for LEO Space Debris surveying and tracking: The BIRALES/BlRALET project

The space debris population is continuously growing and it represents a potential issue for spacecraft. New collisions could exponentially rise the amount of debris and so the level of risk represented by these objects. The monitoring of space environment is necessary to prevent new collisions. For this reason, radar measurements are relevant, in particular to observe objects in Low Earth Orbit. Regarding the Italian contribution, there are two radars based on two different radio telescopes as receivers: the BIRALES and the BIRALET systems. We propose a detailed description of these systems, focusing on hardware and software components that permit to perform range and range rate measurement of resident space objects