News Releases

February 2006

First steps of Girafon scheduled in spring, Palaiseau

Various adjustements were made to Girafon after it "tasted" its first rubidium atoms last autumn. According to Alexandre Bresson, engineer in the research unit DOP (Optical Diagnosis and Plasmas), the first experiments of this Experimental Interferometric Gravimeter using Cold Atoms should take place next spring. Precursor of a more ambitious instrument intended for spaceborn applications - Girafe, this prototype of Girafon appears as a ultra-high vacuum chamber inside which rubidium atoms will be be trapped and cooled using lasers' conveyed by optical fibres. "Once the atoms will be in the desired quantum state and at the good temperature, we will have to make them fall into a tube and carry out the measurement of gravity through matter-wave interference, then we will measure the result in asmall cube located at the bottom of the instrument", explains Alexandre Bresson.

Girafon, an experimental platform intended to prepare the design of a new-generation spaceborn apparatus to measure gravimetry

Inertia represents a very good candidate in terms of applications of the cold atoms. In the long term, the prototype Girafe could carry out an gravimetry campaign on board a submarine for the Arms Procurement Agency (DGA). Another project: ICE (Interferometer with coherent sources for space). Carried supported by CNES and carried out in collaboration with the researchers of the Institut of Theoretical and Applied Optics (IOTA) and those of BNM-Syrte of the Observatory of Paris, ICE aims to embark a prototype derived from Girafe on board Airbus Zero G, in order to make measurements for an experiment of fundamental physics. "From a technical point of view, we are ready to start to carry out experiments in airborne environments".

Example of a nice Franco-American co-operation

Last December, at the Kirtland U.S Air Force base, located in Albuquerque, New Mexico, researchers from ONERA and from the Air Force Research Laboratory (AFRL) carried out a five day experiment. Objective: to carry out preliminary comparisons of the two closely-related techniques of infra-red thermography developed in the two laboratories. The result of about fifteen years of studies and research within ONERA's Solid Mechanics and Damage Mechanisms Department (DMSE), the EMIR (Electromagnetic Infra-red) method makes it possible to visualize in 2D the amplitude of an electric field in a broad frequency band (from 500 MHz to more than 20GHz). The sensor used in the technique is made of an extremely thin film (25 microns), which surface is covered with a slightly absorbent deposited layer, and the receiver, made of an infra-red camera. When an electromagnetic wave illuminates the film, the film absorbs a small quantity of the electric power, causing the heating of the material which is detected by the infra-red camera.

Field measurementside at the aperture level of a horn antenna
On the left, with ONERA's film ; on the right, with AFRL's film

"The American method relies on a thermal model of the heating of the film, which is correlated with the power absorbed by this film. A kind of inversion procedure is then made in order to assess the amount of electromagnetic energy collected by the film. All the thermal phenomena like convection and conduction come into play in these models. Nevertheless, in EMIR, they are completely processed as noise because they are put aside by the modulation-demodulation technique", specifies Jean-Philippe Parmantier, researcher in charge of the "EM Compatibility and Detection" research group within the Electromagnetism and radar Department (DEMR). This explains the idea to carry out this first campaign, in order to compare the two types of approaches, but also to use the American films designed by Dupont de Nemours, whose technology is different from the French one.

 

Mesure EMIR de l'échauffement avec le film américain

"These tests confirmed that EMIR is an operational method to characterize the antennas or diffractions of objects. For its part, the American method seems more favourable to a temporal analysis, owing to the fact that one observes the evolution of the film heating in the course of the time", explains the DEMR researcher who insists on the complementarity of the two methods. "If one applies a method with the same camera and a film which could be the result of an optimization between French and American films, it would be possible, using the same device, to characterize at the same time the antenna and the pulse". A second campaign of the same type is considered for 2006 in France with ONERA. "The ideal thing would be to carry out a more important campaign on a applicatif topic in 2007 ", concludes Jean-Philippe Parmantier who is pleased with this nice Franco-American co-operation.

Success of ONERA's thin layer gauges

Within the framework of the Research Program "High Temperature Thin Film Strain Gauges", launched in 2002 and financed by SPAé (DGA), the three partners, SNECMA, TURBOMECA and ONERA carried out last November ultimate validation tests. In this program, the Thin Film Laboratory, directed by Patrick Kayser within the Physics, Instrumentation and Sensing Department (DMPH), had to optimize the procedures of making the thin film gauges and to deposit them on turbine blades with the technological assistance of the two partners. "We had to provide six blades instrumented with gauges during the last year, in order to validate them in realistic conditions", summarizes Patrick Kayser.

A high temperature thin film strain gauge
developed by ONERA

These validation tests occurred last November, during three days, at TURBOMECA, near Pau, on the Arriel 2 engine turbine. For the first time, these gauges endured a temperature of 940°C. Exploitable measurement signals could be recovered at these temperatures, "the signals were at least as good -if not better- as the signals obtained with traditional gauges", specifies the person in charge of the Laboratory. New information should be collected at the blade level, regarding vibrations or stresses. The tests also made it possible to validate the mechanical resistance of the thin film measurement systems compared to the traditional systems. "At the end of the tests, the traditional sensors (thermocouples and gauges) were entirely destroyed by the centrifugal force, the temperature and the accelerations, whereas some of the thin film gauges preserved their integrity and their functionality".

Official startup of the Graves system

The result of a thirteen year work, the Graves system (Radar System Adapted to the Space) was officially commissioned by DGA/SPAé on last 15 December, at the end of a successful two month demonstration. During this period, Graves worked 24 H out of 24 and showed its capacity to create and maintain a data base of orbital elements of low altitude satellites. The reliability and performance of this system correspond exactly with the requirements of the end-user. So the Staff of the Air Force (EMAA) pronounced on last 22 December the startup for the operational exploitation of the radar.

The Graves radar emission site

Graves is located in Metropolitan France, with an emission site in the East, and a reception site in the South-East, 400 km away from each other. This radar is made of two autonomous subsystems: a radar that produces measurements and a computer that transforms the measurements into a catalogue of orbital elements. With a single sensor, the French system is able to observe one quarter of all the objects indexed in the American catalogue, which system is much richer in terms of sensors. " Our processing is probably more coherent ", estimates Jacques Bouchard, the researcher who conceived and developed the orbit computation software of Graves.

Last Update: 17 March 2006- © ONERA 2009 - Terms of use