The accurate navigation of Mars' orbiters requires the precise modeling the radio tracking measurements. The Martian atmosphere perturbs the optical path of the radio links leading to significant ...Doppler shifts (i.e., up to 5–10 Hz) that affect the spacecraft orbit determination solutions. To process the data occulted by the Martian atmosphere, we present a method that fully calibrates the path delays induced by the neutral atmosphere and ionosphere. Mars’ atmospheric models are used to predict the refractive index of these media, and the estimation of scale factors enables a complete compensation of these perturbative effects. This technique allowed us to reanalyze MRO radio tracking data that were previously discarded to avoid aliasing in the results of our gravity investigation. This precise calibration of the Martian atmosphere will also impact the navigation of future missions during aerobraking phases and science operations at low altitudes.
•Mars atmosphere strongly perturbs spacecraft radio tracking data.•We propose a method to fully calibrate atmospheric effects on Doppler data.•This calibration method is well-suited to recover ~10% of the entire MRO dataset.•Highly accurate navigation in orbit around Mars will require this data calibration.
The Mercury Orbiter Radio Science Experiment (MORE) of the ESA mission BepiColombo will provide an accurate estimation of Mercury’s gravity field and rotational state, improved tests of general ...relativity, and a novel deep space navigation system. The key experimental setup entails a highly stable, multi-frequency radio link in X and Ka band, enabling two-way range rate measurements of 3 micron/s at nearly all solar elongation angles. In addition, a high chip rate, pseudo-noise ranging system has already been tested at 1-2 cm accuracy. The tracking data will be used together with the measurements of the Italian Spring Accelerometer to provide a pseudo drag free environment for the data analysis. We summarize the existing literature published over the past years and report on the overall configuration of the experiment, its operations in cruise and at Mercury, and the expected scientific results.
Understanding the interior structures of icy moons is pivotal for addressing their origins and habitability. We introduce an approach employing the gravity field spectrum as an additional constraint ...for the inversion of differentiated icy bodies' interior structures. After developing the general methodology, we apply it to Europa, utilizing the predicted measurement capability of NASA's Europa Clipper mission, and we prove its effectiveness in resolving key geophysical parameters. Notably, we show that using the gravity field spectrum in combination with the mass and moment of inertia of the body allows us to estimate, depending on the considered end-member interior structure, the hydrosphere thickness with 4–20 km uncertainty and reliably determine the seafloor maximum topographic range and elastic thickness to within 100–600 m and 5–15 km, respectively, together with the power–degree relationship of the seafloor topography. We also show that the proposed method allows us to determine the density of the silicate mantle and the radius of the core to within 0.25 g cc−1 and 50 km, respectively.
Understanding the processes that led Venus to its current state and will drive its future evolution is a major objective of the next generation of orbiters. In this work we analyze the retrieval of ...the spin vector, the tidal response and the moment of inertia of Venus with VERITAS, a NASA Discovery-class mission. By simulating a systematic joint analysis of Doppler tracking data and tie points provided by the onboard synthetic aperture radar we show that VERITAS will provide accuracies (3σ) in the estimates of the tidal Love number k_2 to 4.6×10^(-4), its tidal phase lag to 0.05°, and the moment of inertia factor to 9.8×10^(-4) (0.3% of the expected value). Applying these results to recent models of the Venus interior, we show that VERITAS will provide much improved constraints on the interior structure of the planet.
Deciphering the genesis and evolution of the Martian polar caps can provide crucial understanding of Mars' climate system and will be a big step forward for comparative climatology of the terrestrial ...planets. The growing scientific interest for the exploration of Mars at high latitudes, together with the need of minimizing the resources onboard landers and rovers, motivates the need for an adequate navigation support from orbit. In the context of the ARES4SC study, we propose a novel concept based on a constellation that can support autonomous navigation of different kind of users devoted to scientific investigations of those regions. We study two constellations, that differ mainly for the semi-major axis and the inclination of the orbits, composed of 5 small satellites (based on the SmallSats design being developed in Argotec), offering dedicated coverage of the Mars polar regions. We focus on the architecture of the inter-satellite links (ISL), the key elements providing both ephemerides and time synchronization for the broadcasting of the navigation message. Our concept is based on suitably configured coherent links, able to suppress the adverse effects of on-board clock instabilities and to provide excellent range-rate accuracies between the constellation's nodes. The data quality allows attaining good positioning performance for both constellations with a largely autonomous system. Indeed, we show that ground support can be heavily reduced by employing an ISL communication architecture. Periodic synchronization of the clocks on-board the constellation nodes with terrestrial time (TT) is enabled through the main spacecraft (the mother-craft), the only element of the constellation enabling radio communication with the Earth. We report on the results of numerical simulations in different operational scenarios and show that a very high-quality orbit reconstruction can be obtained for the constellation nodes using a batch-sequential filter or a batch filter with overlapping arcs, that could be implemented on board the mother-craft, thus enabling a high level of navigation autonomy. The assessment of the achievable positioning accuracy with this concept is fundamental to evaluate the feasibility of a future positioning system providing a global coverage of the red planet.
•Polar constellation of small satellites on Mars.•Provide navigation services for Martian landers, rovers, and orbiters.•Quasi-autonomous constellation ephemeris reconstruction.•Novel tracking technique for inter-satellite link.
Abstract
Funding Acknowledgements
Type of funding sources: None.
Background
Visually guided laser balloon ablation (LBA) is a promising method for pulmonary vein (PV) isolation in the treatment of ...atrial fibrillation (AF). To reduce procedural times, the rapid mode feature (RM), which offers an automated continuous 360° lesion for pulmonary vein isolation, was implemented in the latest version of the laser balloon system.
Purpose
We evaluated the learning curve for LBA in the treatment of AF
Method
We enrolled the first 74 patients with paroxysmal or persistent AF treated with LBA in our centre between September 2020 and December 2021. Exclusion criteria were any contraindication for the procedure. 3 different time intervals were considered (time 1 T1, time 2 T2 and time 3 T3), which included the first 25 patients, the next 25 patients and the last 24 patients, respectively. We compared fluoroscopy and procedural time and the number of pulmonary veins isolated by RM >90% (>324°) among the three group were compared.
Results
There was no difference between the three intervals in terms of age (61.2 ±9.00 vs 63.9 ±11.4 vs 58.4 ±12.9; p=n.s.), sex (68% vs 64% vs 81%; p=n.s.) and clinical characteristics. The procedural time (see picture 1) was significantly reduced from T1 to T2 (199 ±51.8 in T1 vs 159 ±38.6 in T2; p< 0.01), while there was no variation between T2 and T3 (159 ±38.6 in T2 vs 153 ±51.9 in T3; p=n.s.). We detected a reduction in fluoroscopy time between T1 and T2 (38.8 ±15.2 in T1 vs 28.8 ±10.5 in T2; p<0.01) but not further reduction was observed between T2 and T3 (28.8 ±10.5 in T2 vs 30.5 ±16.7 in T3; p =n.s.). Considering the use of (RM) feature, there was a progressive increase in the number of PVs isolated by RM >90% over time (1.0 ±0.7 PVs in T1 vs 2.0 ±1.2 PVs in T2 vs 3.3 ±0.9 in T3: p <0.01). Five pinhole balloon ruptures were observed, three in the T1 group, two in the T3 group. Temporary phrenic nerve dysfunction occurred in 1 patient in the T3 interval. No other complications were reported.
Conclusions
PV isolation by visually guided LBA is a safe procedure even during the learning curve. The system is user friendly and procedural time and fluoroscopy time reduced after a limited number of procedures.
This paper deals with the simulation of the backscattered electric field from a random surface being characterized by some statistical parameters.
The approach to this problem has not been undertaken ...from a statistical point of view; on the contrary, an electromagnetic approach has been used in order to evaluate the backscattered field from the surface under examination, being generated as a realization of a random process and hence having a different electromagnetic behavior from another surface belonging to the same random process. Only geometrical contributions have been taken into account—terrain material contributions or other contributions have not been considered.
Lots of analytical models are available, reporting the average backscatter as a function of the statistical parameters of the surface. The backscattered echo simulated using this approach, averaged over many surfaces from the same random process, has been compared with some analytical models and a good agreement has been found.
More realistic behavior than the one predicted by the analytical models at large incidence angles has been found. Comparison has also been made with measured data, after extraction of the terrain material contribution.
Deciphering the genesis and evolution of the Martian polar caps can provide crucial understanding of Mars' climate system. The growing scientific interest for the exploration of Mars at high ...latitudes, and the need of minimizing the resources onboard landers and rovers, motivates the need for adequate navigation support from orbit. We propose a novel concept based on a constellation that can support autonomous navigation of different kind of users devoted to scientific investigations of those regions. We study two constellations, that differ mainly for the semi-major axis, composed of 5 small satellites (based on the SmallSats design being developed in Argotec), offering dedicated coverage of the Mars polar regions. We focus on the architecture of the inter-satellite links (ISL), the key elements providing both ephemerides and time synchronization for the broadcasting of the navigation message. Our concept is based on suitably configured coherent links, able to suppress the adverse effects of on-board clock instabilities and to provide excellent range-rate accuracies between the constellation's nodes. The data quality allows attaining good positioning performance for both constellations with a largely autonomous system. Indeed, we show that ground support can be heavily reduced by employing an ISL communication architecture.
Children with Down Syndrome (DS) suffer from immune deficiency with a severe reduction in switched memory B cells (MBCs) and poor response to vaccination. Chromosome 21 (HSA21) encodes two microRNAs ...(miRs), miR-125b, and miR-155, that regulate B-cell responses. We studied B- and T- cell subpopulations in tonsils of DS and age-matched healthy donors (HD) and found that the germinal center (GC) reaction was impaired in DS. GC size, numbers of GC B cells and Follicular Helper T cells (T
) expressing BCL6 cells were severely reduced. The expression of miR-155 and miR-125b was increased in tonsillar memory B cells and miR-125b was also higher than expected in plasma cells (PCs). Activation-induced cytidine deaminase (AID) protein, a miR-155 target, was significantly reduced in MBCs of DS patients. Increased expression of miR-155 was also observed
. MiR-155 was significantly overexpressed in PBMCs activated with CpG, whereas miR-125b was constitutively higher than normal. The increase of miR-155 and its functional consequences were blocked by antagomiRs
. Our data show that the expression of HSA21-encoded miR-155 and miR-125b is altered in B cells of DS individuals both
and
. Because of HSA21-encoded miRs may play a role also in DS-associated dementia and leukemia, our study suggests that antagomiRs may represent pharmacological tools useful for the treatment of DS.
Memory B cells (MBCs) epitomize the adaptation of the immune system to the environment. We identify two MBC subsets in peripheral blood, CD27(dull) and CD27(bright) MBCs, whose frequency changes with ...age. Heavy chain variable region (VH) usage, somatic mutation frequency replacement-to-silent ratio, and CDR3 property changes, reflecting consecutive selection of highly antigen-specific, low cross-reactive antibody variants, all demonstrate that CD27(du)(ll) and CD27(bright) MBCs represent sequential MBC developmental stages, and stringent antigen-driven pressure selects CD27(du)(ll) into the CD27(bright) MBC pool. Dynamics of human MBCs are exploited in pregnancy, when 50% of maternal MBCs are lost and CD27(du)(ll) MBCs transit to the more differentiated CD27 bright stage. In the postpartum period, the maternal MBC pool is replenished by the expansion of persistent CD27(du)(ll) clones. Thus, the stability and flexibility of human B cell memory is ensured by CD27(du)(ll) MBCs that expand and differentiate in response to change.
PDF
