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Flying a satellite at very low earth orbit is a technological challenge. It presents advantages, such as increase resolution in optical payloads, reduce costs of launch and enhance the use of air breathing propulsion and specular materials. The density of the atmosphere at these altitudes is much higher, behaving as a free molecular flow. This has severe implications in the increase of drag torques and forces that has to be analyzed in depth. We analyze the effects and the perturbations to small satellites, affecting their dynamics, performance and lifetime by implementing and analyzing realistic models of the environment at VLEO.

PURPOSE: To outline the incidence, presenting features, treatment response, and outcome of human immunodeficiency virus (HIV)–associated malignancies in infancy and childhood, together with the estimated risk of HIV-associated cancer in children born to mothers infected with HIV. PATIENTS AND METHODS: The Italian Register for HIV Infection in Children collected data by specific registration and follow-up forms. By March 1999, 5,060 children were recruited, including 4,889 with perinatal exposure to HIV-1. Overall, 1,331 infected children were enrolled onto the Register and classified according to current Centers for Disease Control criteria; of them, 1,163 were vertically infected (24% of those with perinatal exposure). Of these 1,163, 569 (49%) were considered to have been prospectively followed-up since they had been registered at birth or within the first 3 months of age. RESULTS: Of the 1,331 children observed for a median time of 6.5 years, 35 developed 36 malignancies, four of which occurred in patients with blood-borne risk. For the 1,163 vertically infected children, the cumulative number of years of observation was 7,178 child-years and the cumulative incidence of HIV-associated tumors was 4.18 per 1,000 children/yr (95% confidence interval [CI], 2.92 to 5.98). When only the 569 vertically infected children prospectively followed up since birth were considered, the cumulative number of years of observation was 2,803 child-years. In this group, 10 tumors were observed, with a cumulative incidence of HIV-associated tumors of 3.57 per 1,000 children per year (95% CI, 1.92 to 6.63). CONCLUSION: The risk of cancer was significantly higher but not restricted to symptomatic and/or immune-compromised children. Cancer-directed treatment should be given promptly to these patients, who have a fair chance to survive their tumor in view of potential highly aggressive antiretroviral therapy–associated improvement in survival and quality of life.

BACKGROUND: The diagnosis of X-linked agammaglobulinemia (XLA) is not always clearcut. Not all XLA conform to the classic phenotype and less than 50% of affected boys have a family history of immunodeficiency. Mutations in the gene for Bruton's tyrosine kinase (BTK) are responsible for the majority of agammaglobulinemia cases. However, a certain proportion of patients may have mutations involving other genes, although they show with an XLA phenotype. We performed BTK gene mutation analysis in 37 males with presumed XLA and analyzed the pattern of X-chromosome inactivation (XCI) in 31 mothers to evaluate the relevance of these approaches to diagnosis and genetic counseling. MATERIALS AND METHODS: Twenty affected males with a sporadic occurrence and 17 familial cases belonging to nine families were enrolled within the framework of the Italian Multicenter Clinical Study on XLA. We used non-isotopic RNase cleavage assay (NIRCA), followed by cDNA sequence determination to screen for BTK mutations and X-chromosome inactivation analysis for carrier detection. RESULTS: Using the cDNA-based approach, the identification of BTK gene abnormalities confirmed the clinical diagnosis of XLA in 31 of 37 affected infants. Missense was the most frequent mutational event and the kinase domain was mostly involved. In addition, nine novel mutations were identified. In sporadic cases, BTK gene abnormalities were identified in 9 out of 10 patients whose mothers had a nonrandom pattern of XCI and in 5 out of 6 patients whose mother had a random pattern of XCI. With the exception of one family, all patients with a familial occurrence and born to mothers with a nonrandom pattern of XCI had mutations of the BTK gene. CONCLUSIONS: Our findings indicate that in sporadic cases BTK gene sequencing is the only reliable tool for a definitive diagnosis of XLA and support XCI as the first diagnostic tool in the mothers of affected males in multiple generations. Furthermore, our molecular analysis confirms that 10-20% of BTK-unaltered patients have disorders caused by defects in other genes.

To extend missions lifetime at very low altitudes, an efficient propulsion system is required to compensate for aerodynamic drag. One solution is Atmosphere-Breathing Electric Propulsion (ABEP). It collects atmospheric particles to be used as propellant for an electric thruster. The system ideally nullifies the requirement of onboard propellant storage. An ABEP system can be applied to any celestial body with atmosphere (Mars, Venus, Titan, etc.), enabling new mission at low altitude ranges for longer times. Challenging is operation of the thruster on reactive chemical species, such as atomic oxygen (AO), that is highly present in low Earth orbit, as they cause erosion of (not only) propulsion system components, i.e. acceleration grids, electrodes, neutralizers, and discharge channels of conventional EP systems. For this reason, a contactless plasma thruster is developed: the RF helicon-based plasma thruster (IPT). The paper describes the thruster design, implementation, and first ignition tests. The thruster presents a novel antenna called the birdcage antenna that is implemented for decades in magnetic resonance imaging (MRI) machines. The design is supported by the simulation tool XFdtd®. The IPT is aided by an externally applied static magnetic field that provides the boundary condition for the helicon wave formation within the plasma discharge. The antenna working principle allows to minimize losses in the electric circuit and provides, together with the applied magnetic field, acceleration of a quasi-neutral plasma plume.

The DISCOVERER project is developing technologies to enable commercially-viable sustained-operation of satellites in very low Earth orbits for communications and remote sensing applications. Operating closer to the surface of the Earth significantly reduces latency for communications applications and improves link budgets, whilst remote sensing also benefits from improved link budgets, the ability to have higher resolution or smaller instruments, all of which provide cost benefits. In addition, all applications benefit from increased launch mass to lower altitudes, whilst end-of-life removal is ensured due to the increased atmospheric drag. However, this drag must also be minimised and compensated for. DISCOVERER is developing several critical technologies to enable commercially viable operations in at these lower altitudes including aerodynamic materials, aerodynamic attitude and orbit control methods, atmosphere breathing electric propulsion and an in-situ environment monitoring payload. The current status of these developments are summarised, along with the plans for the coming year.

In very low Earth orbits (VLEO), below 450 km altitude, the aerodynamic properties of satellites are primarily determined by the flow regime, free molecular flow, and the interaction of atomic oxygen with the surfaces of the spacecraft. The Rarefied Orbital Aerodynamics Research (ROAR) facility is a novel experimental facility designed to simulate these conditions in a controlled environment to characterise the aerodynamic properties of materials. It is built as part of DISCOVERER, a Horizon 2020 project developing the different technologies required to enable the sustainable operation of satellites in VLEO. Because ROAR isn’t intended to perform erosion studies, it differs quite significantly from other atomic oxygen exposure experiments and its characteristics are discussed in this work. ROAR consists of an ultrahigh vacuum system, responsible for generating the free molecular flow conditions, a source of hyperthermal oxygen atoms at orbital velocities, and mass spectrometers; the latter used to characterise the gas-surface interactions, and therefore the material’s aerodynamic performance. This paper includes a description of ROAR’s main components, together with the experimental methodology for materials testing and early results. Among the main parameters to be considered are atomic oxygen flux, beam shape and energy spread, mass resolution, and signal-tonoise ratio.

Given that the rationale for empirical antifungal therapy in neutropenic children is limited and based on adult patient data, we performed a prospective, randomized, controlled trial that evaluated 110 neutropenic children with persistent fever. Those at high risk for invasive fungal infections (IFI) received caspofungin (Arm C) or liposomal amphotericinB (Arm B); those with a lower risk were randomized to receive Arm B, C, or no antifungal treatment (Arm A). Complete response to empirical antifungal therapy was achieved in 90/104 patients (86·5%): 48/56 at high risk (85·7%) [88·0% in Arm B; 83·9% in Arm C (P = 0·72)], and 42/48 at low risk (87·5%) [87·5% in control Arm A, 80·0% Arm B, 94·1% Arm C; (P = 0·41)]. None of the variables tested by multiple logistic regression analysis showed a significant effect on the probability to achieve complete response. IFI was diagnosed in nine patients (8·2%, 95% confidence interval, 3·8-15·0). This randomized controlled study showed that empirical antifungal therapy was of no advantage in terms of survival without fever and IFI in patients aged

SummaryWe report a case of a combined immunodeficiency (CID) in a child affected by trichothiodystrophy (TTD) characterized by an altered response to ultraviolet (UV) light due to a defect in the XPD gene. The XPD gene encodes a subunit of the transcription factor II H (TFIIH), a complex involved in nucleotide-excision repair (NER) and basal transcription. Our patient showed neurological and immune system abnormalities, including CD4 + lymphopenia never previously reported in TTD patients. In vitro immunological studies revealed a marked reduction in T-cell proliferation in response to mitogens and CD3 cross-linking which was partially recovered by the addition of anti-CD28 antibody or exogenous interleukin-2. The patient's T cells displayed alterations in T-cell receptor (TCR/CD3) proximal signalling characterized by marked reduction in Lck kinase activity coupled with a constitutive hyperactivation of Fyn kinase. Despite these alterations, normal levels of Lck and Fyn proteins were detected. The role of antigen-presenting cells (APCs) in the pathogenesis of the T-cell defect was investigated by analysing dendritic cells (DCs) generated from the patient's blood monocytes. In these cells, flow cytometry revealed significantly reduced expression of the CD86 co-stimulatory molecules and HLA glycoproteins. In addition, the patient's DCs showed a decreased ability to stimulate naive T lymphocytes. Overall, the results of our study suggest that a defective TFIIH complex might result in alterations in T cells and DC functions leading to a severe immunodeficiency.