Gravity field and steady-state ocean circulation explorer

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GOCE
GOCE
Type: Research satellite
Operator: European space agencyESA ESA
COSPAR-ID : 2009-013A
Mission dates
Dimensions: 1100 kg
Size: 1.0 x 5.3 m
Begin: March 17, 2009, 14:21 UTC
Starting place: Plesetsk 133
Launcher: Rockot KM
Re-entry : 11th. November.2013
Orbit data
Track height: 283.5 km
Orbit inclination : 96.7 °

The Gravity field and steady-state ocean circulation explorer ( GOCE ) was a geoscientific artificial earth satellite that had been developed by ESA since around 1995 . He was part of the mission to measure the gravity and the steady state of the ocean circulation , one of Erderkundungsmissionen in the research program Living Planet ESA, and should the high-precision gradiometry serve.

Astrium was a member of the core team of project partners selected by ESA with the main contractor Thales Alenia Space and was responsible for developing the platform. The launch took place on March 17, 2009 at 14:21 UTC.

After the fuel had been used up, the satellite burned up on November 11, 2013 in the earth's atmosphere.

Tasks and technology used

Earth's gravity field, deviations greatly exaggerated

GOCE measured regional variations in the Earth's gravity field more accurately than ever before. One of the main objectives was to determine a reference area for observing ocean currents , which are crucial for the climate due to their large contribution to global heat transport .

GOCE's measuring instruments were not actually gradiometers, but measured the gradients of gravity indirectly using a differential method (“gravitational gradiometry”). These were high-precision acceleration sensors (3-axis gravity gradiometer with 6 accelerometers) that were mounted on ultra-stable carbon honeycomb structures and arms and were supposed to measure all nine values ​​of the gravity tensor continuously in orbit . In addition, high-precision twelve-channel GPS receivers were on board, and the flight path was to be checked with the help of laser distance measurements, for which appropriate reflectors were installed. It was hoped that this would enable the global geoid to be determined with at least centimeter accuracy with a spatial resolution of around 100 kilometers.

In combination with other measurements (especially GPS and satellite altimetry ) important contributions to oceanography and other geosciences were expected. The satellite project GRACE of NASA and DLR, which has been running since 2004, supplemented GOCE: its two satellites determined the medium-wave components of the gravitational field and its temporal changes using SST distance measurements .

Overall, the long satellite resembling an arrowhead with the basic shape of an eight-sided prism had a launch mass of 1100 kilograms, a length of 5.3 meters and a diameter of about one meter. For orbit correction (constant drive to hold the orbit against the braking high atmosphere ) it was equipped with two small (only one active, one as a reserve), xenon- working ion thrusters of the Kaufmann type with 1.0 to 20 mN thrust. The xenon supply was 40 kg at the start. GOCE was equipped with star sensors and magnetic gateways for position control. The solar cells (1300 watts of power) used for the energy supply were attached to the surface of the satellite and the small wings.

begin

The launch from the Plesetsk Cosmodrome was initially planned for September 10, 2008. Due to an error in the guidance and navigation system of the Rockot launcher, it was postponed to March 16, 2009. Shortly before the planned take-off, however, the take-off was canceled because the launch tower did not automatically retract as intended. A second attempt at launch on March 17, 2009 at 2:21 pm UTC was successful and GOCE reached a 283.5 km high orbit; the first signal was received at 14:51 UTC. On March 30th and March 2nd the two ion thrusters were switched on and they worked without any problems.

Orbit

The satellite moved in a circular, sun-synchronous and polar orbit ( orbit inclination 96.7 °) around the earth. After take-off, it sank to its operational altitude of 255 km, in which it carried out the primary mission. Although this lower altitude allowed the geoid to be measured more precisely, it also caused the satellite to be decelerated by the exosphere at this altitude. To compensate for this deceleration, the satellite was propelled by one of two low- thrust ion thrusters. These could be regulated in real time in the thrust range between 1 and 20 mN in order to optimally adapt to the braking force and to keep the trajectory stable. The aerodynamic shape, which is unusual for a satellite , helped to keep air resistance to a minimum. Without these measures, the satellite would have been decelerated so severely within a short period of time that it would have penetrated into denser layers of the atmosphere and finally burned up.

In August 2012, GOCE was prepared for a mission extension until the end of 2013. For this purpose, the orbit was lowered to 235 km by February 2013.

Mission Results

GOCE provided the most accurate image of the earth's gravity field up to now. The resolution of the height profile should be accurate to two centimeters after all data has been evaluated.

The infrasound waves triggered by the severe earthquake in Japan in March 2011 could also be recorded and evaluated by GOCE. No other satellite had done this before.

Development costs

45 European industrial partners were involved in the development and manufacture of the satellite, with the Italian-French company Thales Alenia Space in charge . The development of the satellite cost approx. 300 million euros, the operating costs amounted to approx. 8 million euros annually.

Project center in Germany

The GOCE project office was located at the Technical University of Munich and cooperated with the DLR . Until the launch of the satellite, it prepared the evaluation of the mission, as well as the use of the GOCE results in various geosciences .

The analysis project was named GOCE-GRAND - an abbreviation for Gr avitionsfeld- An alyse D eutschland.

The coordinator of the research project is or was Reiner Rummel , who had proposed a global system of earth observation ( IGGOS ) years before . The specific goal was the high-resolution gravity field modeling from GPS and gradiometric measurements by GOCE.

Mission end

On October 21, 2013, the xenon supply carried along was used up to such an extent that the ion engine stopped the propulsion.

As a result, the orbit slowly descended, with the attitude control remaining in function; the heating by the air friction allowed studies to be carried out into the temperature up to which the satellite could still function. The final entry into the earth's atmosphere took place three weeks later instead of the expected two weeks: GOCE entered the atmosphere on November 11, 2013 at 12:16 a.m. UTC and burned up during its flight along a path over Siberia , the Indian Ocean , the Pacific Ocean and Antarctica to over the South Atlantic .

The debris fell into the sea near the Falkland Islands . The re-entry could be observed from the Falkland Islands and documented photographically. It is believed that roughly a quarter of the satellite's total mass has reached the surface of the earth. Damage caused by not completely burned-up wreckage is not known.

See also

literature

  • A. Albertella et al. a .: GOCE - The Earth Field by Space Gradiometry . Celestial Mechanics and Dynamical Astronomy 83 (2002): 1-15
  • Mark Drinkwater et al. a .: GOCE: Obtaining a Portrait of Earth's Most Intimate Features. ESA Bulletin 133 (Feb. 2008): 4–13 ( PDF )
  • Michael Fehringer u. a .: A Jewel in ESA's Crown - GOCE and its Gravity Measurement Systems. ESA Bulletin 133 (Feb. 2008): 14–23 ( PDF )
  • Rune Floberghagen u. a .: GOCE's Measurements of the Gravity Field and Beyond. ESA Bulletin 133 (Feb. 2008): 24–31 ( PDF )
  • J. Müller: The satellite gradiometry mission GOCE: theory, technical realization and scientific use. DGK series C, issue 541 (2001)
  • R. Rummel: Satellite Gradiometry . Conference contribution in Hans Sünkel (Ed.): Mathematical and Numerical Techniques in Physical Geodesy. Lecture Notes in Earth Sciences 7 (1986)

Web links

Individual evidence

  1. ↑ a b GOCE completes its mission. ESA, October 23, 2013, accessed on October 23, 2013 .
  2. ↑ a b article: "A new image of the earth: GOCE satellite has burned out" on heise.de; Accessed November 11, 2013
  3. ↑ a b ESA: GOCE's electric ion propulsion engine switched on. April 6, 2009, accessed June 20, 2018 .
  4. ↑ FliegerRevue November 2008, pp. 46–49, Space Ferrari for the Earth - ESA Gravity Mission GOCE
  5. ↑ ESA: GOCE launch delayed until 2009. October 24, 2008, accessed on June 20, 2018 (English).
  6. ^ ESA: Launch of ESA's gravity mapping satellite delayed. March 16, 2009, accessed March 16, 2009 .
  7. ↑ GOCE: Critical operations ongoing. ESA, March 18, 2009, accessed March 20, 2009 .
  8. ↑ ESA satellite GOCE reaches calculated trajectory. In: Sputnik News. RIA novosti, March 17, 2009, accessed March 17, 2009 .
  9. ↑ ESA: ESA starts_with GOCE its first earth research satellite. March 17, 2009. Retrieved June 20, 2018 .
  10. ↑ Stephen Clark: GOCE gravity-mapper drops closer to Earth for science. Spaceflight Now, November 16, 2012, accessed December 14, 2012 .
  11. ↑ ESA: GOCE: The first seismometer in orbit. March 8, 2013, accessed November 11, 2013 .
  12. ↑ ESA: GOCE Earth explorer satellite to look at the Earth's surface and core. August 22, 2008, accessed June 20, 2018 .
  13. ↑ An apple and the weight of the world Article on derstandard.at of August 12, 2008.
  14. ↑ ESA's GOCE mission to end this year. ESA, September 13, 2013, accessed October 15, 2013 .
  15. ↑ Roland Rischer: GOCE - logbook at the end of the mission (updates) , in Raumfahrer.net, date: 11./12. November 2013. Retrieved November 15, 2013
  16. ^ ESA: GOCE Re-entry Region. November 11, 2013, accessed June 20, 2018 .
  17. ↑ ESA: GOCE reenters atmosphere. November 12, 2013, accessed June 20, 2018 (Photo by Bill Chater).
  18. ↑ ESA: GOCE gives in to gravity. November 11, 2013, accessed June 20, 2018 .