Evaluation of time difference of arrival (Tdoa) networks performance for launcher vehicles and spacecraft tracking

Time Difference of Arrival (TDOA) networks could support spacecraft orbit determination or near-space (launcher and suborbital) vehicle tracking for an increased number of satellite launches and space missions in the near future. The evaluation of the geometry of TDOA networks could involve the dilution of precision (DOP), but this parameter is related to a single position of the target, while the positioning accuracy of the network with targets in the whole celestial vault should be evaluated. The paper presents the derivation of the MDOP (minimum dilution of precision), a parameter that can be used for evaluating the performance of TDOA networks for spacecraft tracking and orbit determination. The MDOP trend with respect to distance, number of stations and target altitude is reported in the paper, as well as examples of applications for network performance evaluation or time precision requirement definitions. The results show how an increase in the baseline enables the inclusion of more impactive improvements on the MDOP and the mean error than an increase in the number of stations. The target altitude is demonstrated as noninfluential for the MDOP trend, making the networks uniformly applicable to lower altitude (launchers and suborbital vehicles) and higher altitude (Low and Medium Earth Orbits satellites) spacecraft

Advanced radar absorbing ceramic-based materials for multifunctional applications in space environment

In this review, some results of the experimental activity carried out by the authors on advanced composite materials for space applications are reported. Composites are widely employed in the aerospace industry thanks to their lightweight and advanced thermo-mechanical and electrical properties. A critical issue to tackle using engineered materials for space activities is providing two or more specific functionalities by means of single items/components. In this scenario, carbon-based composites are believed to be ideal candidates for the forthcoming development of aerospace research and space missions, since a widespread variety of multi-functional structures are allowed by employing these materials. The research results described here suggest that hybrid ceramic/polymeric structures could be employed as spacecraft-specific subsystems in order to ensure extreme temperature withstanding and electromagnetic shielding behavior simultaneously. The morphological and thermo-mechanical analysis of carbon/carbon (C/C) three-dimensional (3D) shell prototypes is reported; then, the microwave characterization of multilayered carbon-filled micro-/nano-composite panels is described. Finally, the possibility of combining the C/C bulk with a carbon-reinforced skin in a synergic arrangement is discussed, with the aid of numerical and experimental analyses

Study of the Fabrication Process for a Dual Mass Tuning Fork Gyro

AbstractThe fabrication process of a dual mass tuning for gyroscope presents many different challenges: the aspect ratio of the sidewalls, the Aspect Ratio Dependent Etch (ARDE) which causes different gaps to be etched in different etching time [1], the stiction during the release of the free structures, the notching effect that occurs with a dielectric etch stop layer [2], the thermal contact during the etch process. In this paper are presented different processes and studies of the etching characteristics in order to avoid or minimize these problems

Dependence of Magnetic Field Quality on Collar Supplier and Dimensions in the Main LHC Dipole

C. Santoni, coll. Atlas, to be published in the proceeding of the conferenceIn order to keep the electro-magnetic forces and to minimize conductor movements, the superconducting coils of the main Large Hadron Collider dipoles are held in place by means of austenitic steel collars. Two suppliers provide the collars necessary for the whole LHC production, which has now reached more than 800 collared coils. In this paper we first assess if the different collar suppliers origin a noticeable difference in the magnetic field quality measured at room temperature. We then analyze the measurements of the collar dimensions carried out at the manufacturers, comparing them to the geometrical tolerances. Finally we use a magneto-static model to evaluate the expected spread in the field components induced by the actual collar dimensions. These spreads are compared to the magnetic measurements at room temperature over the magnet production in order to identify if the collars, rather than other components or assembly process, can account for the measured magnetic field effects. It has been found that in one over the three Cold Mass Assemblers the driving mechanism of the magnetic field harmonics b2 and a3 is the collar shape

Effects of atomic oxygen and UV rays ageing on the reflection coefficient of carbon/carbon plates in the 12-18 GHz frequency range

Advanced carbon-based ceramic materials, such as Carbon/Carbon (C/C) are commonly employed in aerospace industry to face the thermo-mechanical stress suffered by the spacecraft external structures during re-entry in earth atmosphere. Thanks to very low thermal expansion and outstanding chemical stability at extreme temperatures, in fact, such materials represent the ideal candidates for re-usable space integrated systems, such as TPS, nozzles and ablation thermal-proof structures. In long-time missions, on the other hand, issues related to continuous and extended exposure of the spacecraft surfaces to the detrimental space environment must be carefully considered. In this frame, also the tracking of satellites by mean of radar systems is a vital aspect for a safe stay in space. In LEO working conditions, the combined effects induced by severe thermal cycles, ultra-high vacuum and UV/Atomic Oxygen(AO) irradiation can be of impediment for the use of C/C as re-entry protection material, since a significant surface oxidation leads to so high TPS damaging as to compromise its main functionality. This surface oxidation can also affect the radar visibility of satellites. Aim of this paper is to evaluate the effects of the AO/UV ageing on C/C plates reflection coefficient, in order to avoid misfunctioning in the radar visibility

Cancer Immunotherapy: Harnessing the Immune System to Fight Cancer

Not availabl

Lymphectomy in the treatment of thyroid cancer in adults and children.

Thyroid carcinoma is thè most frequent endocrine malignancy in Italy and differs in naturai history according to histological type and age of patients. Lymph node metastases are more frequently seen in young patients with papillary carcinoma. However, many clinical series suggested that although thè incidence of lymph node invasion in high-risk patients (over-50s) is slightiy lower than in low-risk patients, thè locai recurrence rate is higher than in thè former. From thè results of our experience, confirmed by other authors, we retain total thyroidectomy with lymphectomy of thè centrai compartment as thè procedure of choice in thè treatment of well-differentiated thyroid carcinoma in thè under-50s. In thè over-50s, functional bilateral lymphectomy improves survival and should be considered mandatory, just as for medullary carcinoma. On thè contrary, thè prognosis of anaplastic carcinoma is not improved by lymphectomy

Cancer immunotherapy: Current and future perspectives on a therapeutic revolution

N/

Cu-catalyzed Si-NWS grown on “carbon paper” as anodes for Li-ion cells

The very high theoretical capacity of the silicon (4200mAh/g more than 10 times larger than graphite), environmental-friendly, abundant and low-cost, makes it a potential candidate to replace graphite in high energy density Li-ion batteries. As a drawback, silicon suffers from huge volume changes (300%) on alloying and dealloying with Li, leading a structural deformation that induces disruption. The use of nanostructured silicon materials has been shown to be an effective way to avoid this mechanical degradation of the active material. In this paper the synthesis of silicon nanowires, grown on a highly porous 3D-like carbon paper substrate by CVD using Cu as the catalyst, is presented. The use of carbon paper allows to achieve remarkable loadings of active material (2-5 mg/cm2) and, consequently, high capacity densities. The silicon electrode was investigated both morphologically and electrochemically. To improve the electrochemical performance various strategies have been carried out. It was observed that a very slow first cycle (C/40), which helps the formation of a stable solid electrolyte interphase on the silicon surface, improves the performance of the cells; nevertheless, their cycle life has been found not fully satisfactory. Morphological analysis of the Si-NWs electrodes before and after cycling showed the presence of a dense silicon layer below the nanowires which could reduce the electrical contact between the active material and the substrate