Experimental results from the ST7 mission on LISA Pathfinder

The Space Technology 7 Disturbance Reduction System (ST7-DRS) is a NASA technology demonstration payload that operated from January 2016 through July 2017 on the European Space Agency’s (ESA) LISA Pathfinder spacecraft. The joint goal of the NASA and ESA missions was to validate key technologies for a future space-based gravitational wave observatory targeting the source-rich millihertz band. The two primary components of ST7-DRS are a micropropulsion system based on colloidal micro-Newton thrusters (CMNTs) and a control system that simultaneously controls the attitude and position of the spacecraft and the two free-flying test masses (TMs). This paper presents our main experimental results and summarizes the overall performance of the CMNTs and control laws. We find the CMNT performance to be consistent with preflight predictions, with a measured system thrust noise on the order of 100  nN/√Hz in the 1  mHz≤f≤30  mHz band. The control system maintained the TM-spacecraft separation with an RMS error of less than 2 nm and a noise spectral density of less than 3  nm/√Hz in the same band. Thruster calibration measurements yield thrust values consistent with the performance model and ground-based thrust-stand measurements, to within a few percent. We also report a differential acceleration noise between the two test masses with a spectral density of roughly 3  fm/s2/√Hz in the 1  mHz≤f≤30  mHz band, slightly less than twice as large as the best performance reported with the baseline LISA Pathfinder configuration and below the current requirements for the Laser Interferometer Space Antenna mission

Immunogold labelling of beet necrotic yellow vein virus particles inside its fungal vector, Polymyxa betae K

Many aspects of the association of Polymyxa betae with beet necrotic yellow vein virus during transmission have not been elucidated. In order to study the specificity of virus acquisition by the vector and its transmission to the host, thin sections were made through sugar beet roots infected both by the virus and the fungus. Immunogold labelled virus was identified at different stages of the fungus (plasmodia, zoosporangia and mature zoospores). However, specifically labelled clusters of virions have not yet been observed in mature resting spores.Marquage à l'or colloïdal du virus des nervures jaunes et nécrotiques de la betterave dans le champignon vecteur Polymyxa betae K. De nombreuses questions relatives à l'association entre Polymyxa betae et le virus de la rhizomanie qu'il transmet restent sans réponse. Dans le but de mieux appréhender la spécificité de l'acquisition du virus par son vecteur ainsi que sa transmission à la plante hôte, des coupes ultrafines ont été réalisées dans des radicelles de betterave sucrière infectées à la fois par le virus et le champignon, puis soumises au marquage immunocytochimique. Du virus marqué à l'or colloïdal a été détecté dans différents stades du champignon (plasmodes, zoosporanges, zoospores bien différenciées). Cependant, des amas caractéristiques de BNYVV n'ont pu être mis en évidence dans les cystosores et les spores de repos, probablement en raison de la difficulté de pénétration des résines dans de tels tissus