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You loved Chavez I you'll love Chavez IIAlongside the RGPP other audits are ongoingIn return the climate equipment has been particularly careful The same said however that the decision is not takenThis model has nevertheless to leap the unions5 million euros often in capital increaseWe are always looking for external expertiseThe elect are organized to be their territoryThe indicator of unemployment rose from 25It also that our work force is adaptable and flexibleAn aerodynamic satellite, it does not run the orbits. With its fins and its contoured looks, Goce will be launched this week, looks more like a ballistic missile at an Orbiter. Thales Alenia Space and EADS engineers have had to venture into this bold configuration to complete the European space agency mission. Goce will fly over the Earth along the atmosphere to measure spatial and temporal gravity variations. We learn in school that g equal 9.81 meters per second square (m/s2), but this is only an approximation. Because the force of gravitation depends on the density of the material, which fluctuates in the world. Therefore, gravity varies on the surface of the globe of 9.78 m/s2 at the equator to 9.83 at the poles. The difference is slight, but it expresses of many physical phenomena in Geoscience.
The measure on the ground or sea of gravity is carried on for decades but only satellites could provide global coverage, says Steven Hosford, responsible of the solid Earth at CNES programs. Provided resolve this paradox: make the lowest possible because the force of gravity varies as the square of the distance. flying outside the atmosphere to avoid turbulence, enemy sensors. Goce designers played the compromise through a flight profile that all satellites are usually fleeing. 250 Kilometers of altitude, there remains enough air for pushing and braking that adventure. However scientists at Goce posed tough requirements on the stability of ultra-sensitive accelerometers provided by Thales and Onera (national Office of studies and aerospace research). It is to measure the value of g to the nearest thousandth and obtain an accuracy of 1 cm on measures of altitude. It was therefore to minimize the aerodynamic drag of the satellite. Its fuselage soared, the apparatus has very reactive ion thrusters that can compensate the blows of the air brake. This innovative propulsion mode however has disadvantage to be powered electrically. It cannot operate when Goce exposes its photovoltaic panels to the Sun. A constraint that will prevent the extent continues over long periods. As the mission will not exceed eighteen months to coincide with a low period of reduced atmospheric drag, solar activity. Finally, the thermal stability of satellite implies a special cooling system that compensates for the difference in temperature between the face lit by the Sun and the dark side.
Hummocky
Goce will measure variations in severity with the statements of its accelerometers. These sensors are another innovation of the mission since they offer for the first time an absolute measure of severity. Schematically, the device includes 6 flyweight spring mounted on spring along the 3 axes (height, width, length). Each of these masses will undergo gravity with very small deviations. For example a mountain Goce is about to fly over. This excess of material first carries a stronger attraction on the rotor mass located at the front of the satellite on the farthest. Once the mountain was passed, it is the opposite. Lowest accelerometer suffer also a movement of attraction towards the Earth more important than the weight of the top.
Goce scientific users will be able to deduct two results. The data will be used to map the geoid with unprecedented accuracy. Because of its rotation, the Earth is not a sphere but a shape elliptical, flattened 21 km at the poles. This form is even more tortuous as the planet's surface is lined with hollow and bumps that produce gaps up to 100 metres. Good surveyors, researchers have therefore designed a virtual reference surface, geoid, which corresponds to a constant gravity: a raised top ball would not. For oceanographers, this also corresponds to the theoretical mean sea level. This concept is valuable because it provides a basis for measuring heights (Geophysics, construction, etc.), changes in the level of the seas, the effect of the wind and surface currents. The geoid was done country by country so far. Goce establish a homogeneous version at the global level.
Solid and liquid
Goce will also map the gravity field because it reflects the mass between the centre of the Earth and the satellite. I.e. the solid Earth, the water in the basement, sea, ice, lakes and clouds. Considering as constant rock volume, oceanographers date back to the movement of water, ocean circulations. A longer scale, geologists can improve their understanding of the formation of sedimentary basins and their oil tanks for example. Basins are the result of temperature anomalies, source of gravity variation. Researchers also hope with Goce understand the origin of the rift zones. These major collapses of the Earth's crust coincide with upwellings of hot material, less dense that the Earth's mantle, disrupts gravity. According to Steven Hosford, dynamic data from the satellite Grace (see opposite) has already proved very interesting for hydrologists, who could calculate the variation of certain reserves of groundwater or the Amazon basin. The disturbing estimation of the melting of the Greenland ice comes for a share of the benefits of the mission.
