Effect of engine, tank and propellant specific cost on single stage recoverable booster economics

Reusable first stages using hydrogen-oxygen, hydrogen-fluorine and kerosine-oxygen are compared with non-reusable stages using a solid in addition to the liquid combinations. The criterion used for comparison is the minimum specific cost of the "loaded and ready for launch" stage cost per unit of stage payload mass. A closed form relationship is used in which the empty stage mass without payload is taken to scale in part proportional to propellant mass, and in part to mass flow rate. The stage specific cost is proportional to specific cost of engine (or nozzle) tank and propellant. In the second part the hydrogen-oxygen combination is consiaered,in more detail. The sensitivity of the results to changes in various specific costs including that of refurbishing are described. Throughout, the stage velocity increments are compared in the 3000-6000 metres/second range with losses

The enigmatic archaeal virosphere

International audienceOne of the most prominent features of archaea is the extraordinary diversity of their DNA viruses. Many archaeal viruses differ substantially in morphology from bacterial and eukaryotic viruses and represent unique virus families. The distinct nature of archaeal viruses also extends to the gene composition and architectures of their genomes and the properties of the proteins that they encode. Environmental research has revealed prominent roles of archaeal viruses in influencing microbial communities in ocean ecosystems, and recent metagenomic studies have uncovered new groups of archaeal viruses that infect extremophiles and mesophiles in diverse habitats. In this Review, we summarize recent advances in our understanding of the genomic and morphological diversity of archaeal viruses and the molecular biology of their life cycles and virus-host interactions, including interactions with archaeal CRISPR-Cas systems. We also examine the potential origins and evolution of archaeal viruses and discuss their place in the global virosphere