Evolution of the Rocket Engine Testing Process

Since summer 2001 the DLR test facility P5 in Lampoldshausen, Germany looks back on ten years of testing the ARIANE 5 main engine VULCAIN on engine level. A few months prior the identical facility PF50 at SNECMA in Vernon, France already had this anniversary. During this period the test facilities had to fulfil quite various requirements for the engine tests. The principle task of the facilities was always to simulate the conditions on the launcher to the VULCAIN engine. The environment and all interfaces of the rocket motor were achieved to match this target. Small and vast modifications of the test facilities were performed to evaluate the engine behaviour under standard and special conditions, expected and unexpected phenomena were detected and investigated. The schedule of pre-test and post-test operations for a hot run has in principle not changed yet the different steps were optimised due to the increasing number of objectives per test, a high desired cadence of tests, due to adding other flight hardware to the tested specimen and due to the basic request of maintaining a high level of quality and safety. It was mandatory to optimise and to create new procedures for consequent application in order to reach a high level of reliability of the facilities and to guarantee a high level of availability despite all non avoidable anomalies. Both test facilities will also be available for future developments of the VULCAIN engine. In their design concept it is foreseen that the facilities can be modified up to a configuration in which twin engines of 200 kN thrust each can be tested

A refined model of how Yersinia pestis produces a transmissible infection in its flea vector

International audienceIn flea-borne plague, blockage of the flea's foregut by Yersinia pestis hastens transmission to the mammalian host. Based on microscopy observations, we first suggest that flea blockage results from primary infection of the foregut and not from midgut colonization. In this model, flea infection is characterized by the recurrent production of a mass that fills the lumen of the proventriculus and encompasses a large number of Y. pestis. This recurrence phase ends when the proventricular cast is hard enough to block blood ingestion. We further showed that ymt (known to be essential for flea infection) is crucial for cast production, whereas the hmsHFRS operon (known to be essential for the formation of the biofilm that blocks the gut) is needed for cast consolidation. By screening a library of mutants (each lacking a locus previously known to be upregulated in the flea gut) for biofilm formation, we found that rpiA is important for flea blockage but not for colonization of the midgut. This locus may initially be required to resist toxic compounds within the proventricular cast. However, once the bacterium has adapted to the flea, rpiA helps to form the biofilm that consolidates the proventricular cast. Lastly, we used genetic techniques to demonstrate that ribose-5-phosphate isomerase activity (due to the recent gain of a second copy of rpiA (y2892)) accentuated blockage but not midgut colonization. It is noteworthy that rpiA is an ancestral gene, hmsHFRS and rpiA2 were acquired by the recent ancestor of Y. pestis, and ymt was acquired by Y. pestis itself. Our present results (i) highlight the physiopathological and molecular mechanisms leading to flea blockage, (ii) show that the role of a gene like rpiA changes in space and in time during an infection, and (iii) emphasize that evolution is a gradual process punctuated by sudden jumps