Gravity field and steady-state ocean circulation explorer
The Gravity field and steady-state ocean circulation explorer ( GOCE ) was a geoscientific man-made satellite, which has been developed since about 1995 by the ESA. He was on mission to measure gravity and the steady state of the ocean circulation, one of the Erderkundungsmissionen in the research program of the ESA Living Planet, and to serve the high-precision gradiometry. Astrium is a member of the core team selected by the ESA project partners with the prime contractor Thales Alenia Space and is responsible for the development of the platform. The launch took place on 17 March 2009, at 14:21 UTC. After the end of fuel supplies, the satellite burned up on 11 November 2013, the Earth's atmosphere.
Tasks and technology used
GOCE will measure regional variations in the Earth's gravity field in unprecedented detail. A major goal is to determine a reference surface for the observation of ocean currents, which are crucial for the climate through their large contribution to global heat transport.
The measuring instruments of GOCE gradiometer are not in the proper sense, but measure the gravity gradient indirectly by a differential method ( " gravity gradiometry "). These are high-precision accelerometers ( 3-axis accelerometers Schweregradiometer 6 ), which are mounted on ultra- stable carbon honeycomb structures and booms and in orbit continuously to measure all nine values of the gravity tensor. In addition, highly accurate twelve- channel GPS receiver are on board and the flight path should be checked with the aid of laser distance measurements, for which corresponding reflectors are installed. Thus it is hoped that a determination of the global geoid with centimeter accuracy at least at a spatial resolution of about 100 kilometers.
In combination with other measurements (especially GPS and satellite altimetry ) are important contributions to oceanographic and other earth sciences expected. The ongoing since 2004 GRACE satellite project of NASA and DLR is an ideal complement to GOCE: its two satellites determined by SST- distance measurements, the medium -wave components of the gravity field and its temporal variations.
Overall, the arrowhead similar, long satellite with the basic form of an eight -sided prism has a launch mass of 1100 kg, a length of 5.3 meters and a diameter of about one meter. For orbit correction (Standing drive to hold the orbit against the braking upper atmosphere ) working with xenon ion thrusters from Kaufmann- type with 1.0 to 20 mN thrust it is (one as backup only active one ,) with two small equipped. The Xenon stock is 40 kg. For position control GOCE is equipped with star sensors and Magnettorquer. The power supply serving cells (1300 watt ) are mounted on the surface of the satellites and of the small wings.
The launch in Plesetsk was scheduled first for the 10 September 2008. Due to an error in navigation and guidance system provided for the start Rockot launcher he has been postponed to 16 March 2009. Just before take-off the start but has been aborted because of launch tower not work as intended automatically retired. The launch on March 17, 2009 at 14:21:13 UTC clock was successful and GOCE achieved a 283.5 km high orbit, the first signal was received at 14:51 UTC.
The satellite moving in a circular, sun-synchronous polar orbit ( orbital inclination 96.7 ° ) around the Earth. The amount of the final orbit was only 255 km. Although these low height allowed for a more precise measurement of the geoid, but led to the deceleration of the satellite by the residual atmosphere at this altitude. To compensate for this deceleration, the satellite is driven by one of two low thrust ion propulsion. These are in the thrust range between 1 and 20 mN in real time controllable to the decelerating force optimally adapt and keep the trajectory stable. Unusual for a satellite aerodynamic shape helps in that the air resistance is minimized. Without these measures, the satellite would in a short time so strongly braked, that he would penetrate into denser layers of the atmosphere and eventually burn up.
After starting GOCE fell to its use altitude of 255 km, in which he carried out the primary mission. In August 2012, GOCE has been prepared for a mission extension until the end of 2013. For this, the orbit was lowered until February 2013 to 235 km altitude.
GOCE afforded the hitherto most accurate image of the Earth's gravity field. The resolution of the height profile should be accurate to two centimeters to the evaluation of all data. The triggered by the massive earthquake in March 2011 in Japan infrasonic waves could be recorded and evaluated by GOCE. This was previously managed with anyone yet other satellites. The analysis of all collected with GOCE data will continue for at least until mid 2014.
The development of the satellite cost about 300 million euros. The primary project partner of ESA is in this mission, the Italian- French company Thales Alenia Space. A further 45 European industrial partners were involved in the development and construction of the satellite. Operating costs amount to approximately 8 million Euro annually.
Project center in Germany
The GOCE Project Office is located at the Technical University of Munich in cooperation with the DLR. It gave to the launch of the satellite, the evaluation of the mission before - as well as the use of the GOCE results in various geosciences. The analysis project was named GOCE - GRAND - an abbreviation for Gravitionsfeld analysis Germany. The coordinator of the research project is Reiner Rummel, who has proposed a global system of Earth Observation ( IGGOS ) years ago. The specific aim is the high-resolution gravity field modeling of GPS and gradiometry measurements of GOCE.
End of Mission
On 21 October 2013, the entrained xenon stock was depleted to the extent that the ion engine stopped the drive. As a result, the orbit lowered slowly, the position control function remained; The heating by the air friction allowed studies up to which temperature the satellite remained functional. The final entry into the Earth's atmosphere was instead of the expected two weeks three weeks later: GOCE occurred on November 11, 2013 at 00:16 UTC clock in the atmosphere and burned up during its flight along a path over Siberia, the Indian Ocean, the Pacific Ocean, and Antarctica to the South Atlantic over.
The debris fell near the Falkland Islands in the sea. The re-entry could be observed from the Falkland Islands and photographically documented. It is believed that approximately one- quarter of the total mass of the satellite reaches the earth's surface. Damage caused by not completely burnt up wreckage are not known.