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21.10.2013
After nearly tripling its planned lifetime, the Gravity field and steady-state Ocean Circulation Explorer – GOCE – has completed its mission and will soon reenter our atmosphere.
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With a sleek, aerodynamic design responsible for it being dubbed the ‘Ferrari of space’, GOCE has mapped variations in Earth’s gravity with extreme detail. Scientists further exploited these data to create the first global high-resolution map of the boundary between Earth’s crust and mantle – called the Moho – and to detect sound waves from the massive earthquake that hit Japan on 11 March 2011, among other results.
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In mid-October, the mission came to a natural end when it ran out of fuel and the satellite began its descent towards Earth from a height of about 224 km.
All of the latest information on the mission’s scientific results and reentry can be found here:
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21 October 2013
GOCE’s end of mission was declared today when the fuel tank ran out of xenon. Data acquisition and satellite operations will continue for about two more weeks until its systems stop working because of the harsh environmental conditions at such a low altitude. At this point, the satellite will be switched off, marking the end of activities for the GOCE flight control team. The satellite is expected to reenter our atmosphere within the next three weeks.
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N° 33–2013: ESA’S GOCE MISSION COMES TO AN END
21 October 2013
After mapping variations in Earth’s gravity with unprecedented detail for four years, the GOCE satellite has run out of fuel and the end of mission has been declared.
Since March 2009, the Gravity field and steady-state Ocean Circulation Explorer – GOCE – has been orbiting Earth at the lowest altitude of any research satellite.
Its ‘gradiometer’ – the sensitive instrument measuring gravity in 3D – was the first in space and has mapped variations in Earth’s gravity with unrivalled precision. The result is a unique model of the ‘geoid’, which is essentially the shape of an ideal global ocean at rest and therefore critical for accurate measurements of ocean circulation and sea-level change.
GOCE has provided dynamic topography and circulation patterns of the oceans with unprecedented quality and resolution, improving our understanding of the dynamics of world oceans.
Scientists further exploited GOCE’s data to create the first global high-resolution map of the boundary between Earth’s crust and mantle – called the Moho.
The satellite also became the first seismometer in orbit when it detected sound waves from the massive earthquake that hit Japan on 11 March 2011.
Although the planned mission was completed in April 2011, the fuel consumption was much lower than anticipated because of the low solar activity, enabling ESA to extend GOCE’s life.
In August 2012, the control team began to lower the satellite’s orbit – from about 255 km to 224 km. Dubbed ‘GOCE’s second mission’, the lower orbit increased the accuracy and resolution of GOCE’s measurements, improving our view of smaller ocean features such as eddy currents.
“This innovative mission has been a challenge for the entire team involved: from building the first gradiometer for space to maintaining such a low orbit in constant free-fall, to lowering the orbit even further,” said Volker Liebig, ESA’s Director of Earth Observation Programmes.
“The outcome is fantastic. We have obtained the most accurate gravity data ever available to scientists. This alone proves that GOCE was worth the effort – and new scientific results are emerging constantly.”
On 21 October, the mission came to a natural end when it ran out of fuel. The satellite is expected to reenter Earth’s atmosphere in about two weeks.
Data acquisition and satellite operations will continue for about two more weeks until its systems stop working because of the harsh environmental conditions at such a low altitude. At this point, the satellite will be switched off, marking the end of activities for the GOCE flight control team.
While most of the satellite will disintegrate in the atmosphere, Some smaller parts are expected to reach Earth’s surface. When and where these parts might land cannot yet be predicted, but the affected area will be narrowed down closer to the time of reentry.
An international campaign is monitoring the descent, involving the Inter-Agency Space Debris Coordination Committee. The situation is being continuously watched by ESA’s Space Debris Office, which will periodically issue reentry predictions.
ESA will keep its Member States and the relevant authorities permanently updated.
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18 October 2013
The pressure in GOCE’s fuel system has dropped below 2.5 bar, which is the pressure needed to fire the ion engine. It is estimated that there is about 350g of xenon left in the fuel tank. All eyes are now on the performance of the ion engine out of its nominal pressure range. If it functions until the tank is empty, orbital decay would start around 26 October. However, controllers expect the ion engine to terminate well before that.
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14 October 2013
The Spacecraft Operations Manager estimates that GOCE will run out of fuel after the end of this week. The xenon tank pressure is now below 5 bar – ion propulsion is expected to stop after pressure drops below 2.5 bar (foreseen on 19 October).
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7 October 2013
Spacecraft Operations Manager gives overview of what to expect during GOCE’s final weeks.
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After more than four years mapping Earth’s gravity with unrivalled precision, ESA's GOCE mission will soon be over: In mid-October, the mission will come to a natural end when it runs out of fuel and the satellite begins its descent towards Earth from a height of about 224 km.
The satellite's final days will be closely monitored by the mission control team at ESOC, ESA's operations centre, Darmstadt, Germany.
Below, Spacecraft Operations Manager Christoph Steiger has provided an update on estimates of the craft's final fuel run-out date.
GOCE is indeed not far from running out of fuel for its ion propulsion system. We expect to deplete fuel between now and end of October, probably in about two weeks from now.
We don't have a more precise date due to uncertainties in
Estimating the amount of fuel left
The behaviour of the ion propulsion system once the tank starts getting empty
The highly variable level of solar activity (impacting the atmospheric drag and hence the fuel consumption).
Once GOCE has run out of fuel, the orbit will start decaying. It will take about two to three weeks before the spacecraft re-enters the Earth's atmosphere.
We will initially keep operating the spacecraft, switching it off when its subsystems stop working due to the harsh environmental conditions at lower altitudes. This marks the end of activities for the GOCE flight control team.
The descent and the final re-entry will be monitored closely by ESA's Space Debris Office, in the frame of an international campaign of the Inter-Agency Space Debris Coordination Committee (IADC).
We have collected a wealth of science data over the last 4.5 years. GOCE has lasted much longer than the originally planned 20 months thanks to the low solar activity in the last few years. To get even more precise gravity measurements, in its last year of life, the orbit of GOCE was lowered from 255 km down to an extremely low altitude of only 224 km. The results are fantastic – we have obtained the most accurate gravity data ever available to scientists.
Personally, I feel sorry to see GOCE, a project on which I have spent seven intense years, come to end. Then again, it is also a good feeling to know that we have really gotten the most out of this mission before its natural end – much more than what we could have hoped for.
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13 September 2013
ESA’s GOCE mission to end this year and begin its descent towards Earth in the weeks following. While most of GOCE will disintegrate in the atmosphere, several parts might reach Earth’s surface.
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After more than four years mapping Earth’s gravity with unrivalled precision, GOCE’s mission is nearing its end and the satellite will soon reenter our atmosphere.
The Gravity field and steady-state Ocean Circulation Explorer – GOCE – has been orbiting Earth since March 2009 at the lowest altitude of any research satellite.
With a sleek, aerodynamic design responsible for it being dubbed the ‘Ferrari of space’, GOCE has mapped variations in Earth’s gravity with extreme detail.
The result is a unique model of the ‘geoid’, which is essentially a virtual surface where water does not flow from one point to another.
In mid-October, the mission will come to a natural end when it runs out of fuel and the satellite begins its descent towards Earth from a height of about 224 km.
While most of GOCE will disintegrate in the atmosphere, several parts might reach Earth’s surface.
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ESA's GOCE mission has delivered the most accurate model of the 'geoid' ever produced, which will be used to further our understanding of how Earth works.
The colours in the image represent deviations in height (–100 m to +100 m) from an ideal geoid. The blue shades represent low values and the reds/yellows represent high values.
A precise model of Earth's geoid is crucial for deriving accurate measurements of ocean circulation, sea-level change and terrestrial ice dynamics. The geoid is also used as a reference surface from which to map the topographical features on the planet. In addition, a better understanding of variations in the gravity field will lead to a deeper understanding of Earth's interior, such as the physics and dynamics associated with volcanic activity and earthquakes.
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When and where these parts might land cannot yet be predicted, but the affected area will be narrowed down closer to the time of reentry. Reentry is expected to happen about three weeks after the fuel is depleted.
Taking into account that two thirds of Earth are covered by oceans and vast areas are thinly populated, the danger to life or property is very low.
About 40 tonnes of manmade space debris reach the ground per year, but the spread and size mean the risk of an individual being struck is lower than being hit by a meteorite.
An international campaign is monitoring the descent, involving the Inter-Agency Space Debris Coordination Committee. The situation is being continuously watched by ESA’s Space Debris Office, which will issue reentry predictions and risk assessments.
ESA will keep its Member States and the relevant safety authorities permanently updated.
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10 September 2013
Data acquired at GOCE’s super-low orbit sheds new light on Earth’s interior. Geophysicists are using GOCE gravity gradient measurements to gain new insights into the geodynamics associated with the lithosphere.
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With a catalogue of triumphs that range from delivering novel information about winds at the edge of the atmosphere to mapping the structure of Earth’s crust 200 km below our feet, ESA’s GOCE satellite is in the limelight at this week’s Living Planet Symposium.
Carrying the first 3D gravity gradiometer in space and orbiting lower than any other research mission, this state-of-the-art satellite has measured Earth’s gravity with unprecedented accuracy, resulting in a series of four geoid models, each more accurate than the last.
And, a fifth is expected in the middle of next year that will include GOCE’s last measurements.
These final data will be even more accurate because they are being taken from an orbit 31 km lower than the satellite’s original mapping height – at the very limit of its capability but maximising its scientific return.
While the GOCE geoid is being used to understand how oceans transport huge quantities of heat around the planet and used to develop a global height reference system, the mission’s gravity-field measurements are also shedding new light on Earth’s interior.
Geophysicists are using GOCE gravity gradient measurements to gain, for example, new insights into the geodynamics associated with the lithosphere.
Jörg Ebbing from the Geological Survey of Norway said, “To understand the processes and dynamics of tectonic plate movement we need to know how the lithosphere is structured.
“Earth’s crust and the uppermost mantle form the lithospheric plates, which are moved by plate tectonics and mantle convection.”
Dr Ebbing went on to explain that there is a difference between oceanic and continental lithosphere.
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The Moho and lithosphere for the northeast Atlantic. Both crust and lithosphere thicken from the oceanic part beneath the Fennoscandian shield, which is a large area of rock in Scandinavia.
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“The oceanic lithosphere is young in geological terms, less than 200 million years old, and associated with sea-floor spreading and the widening of oceans. Continental lithosphere is older and thicker, and we know from seismology that it can be very heterogeneous in structure.
“However, a better understanding of the thermal structure and composition of the lithosphere is needed to understand, for instance, how mountain belts develop.”
Seismology as well as thermal and electromagnetic studies provide information about the lithosphere, but since variations in gravity reflect the inhomogeneous nature of Earth’s interior, accurate gravity data also prove invaluable.
Using GOCE measurements, the animation above shows gravity gradients from horizontal slices of the lithosphere at different depths under the northeast Atlantic region.
This area covers the warm young oceanic lithosphere under the Atlantic Ocean, the continental lithosphere beneath the Norwegian shelf and Scandinavian mountains, and the old thick lithosphere in the centre of the ‘Fennoscandian shield’.
The main gravity gradients are caused by variations in the thickness of the crust.
In addition, the high sensitivity to the depth of 150 km is shown. This depth, close to the crustal base, is poorly imaged in most seismological models.
“The use of GOCE gravity gradients is enabling us to distinguish whether density is influenced by temperature or by the composition of the upper mantle,” said Dr Ebbing.
“This is giving us unprecedented detail on how the crust and upper mantle are linked.”
These new results complement other research that used GOCE data to produce the first high-resolution map of the depth of the Mohorovičić discontinuity, or Moho – the boundary between the crust and mantle.
The new findings go a step further than the classical Moho mapping by linking static geophysical imaging to dynamic processes inside the Earth.
While of huge scientific importance, results such as these are also of practical use. As the global population continues to grow, as does our need for natural resources stored in Earth’s crust. So better understanding its composition is likely to lead to more efficient exploration.
“Now that we have a procedure to use gravity gradients for geophysics, the community can look forward to the release of global gravity gradient grids in 2014,” commented ESA’s Roger Haagmans.
Although GOCE will soon have completed its mission, new results continue to emerge as scientists find ever-more imaginative ways of using its data to further our knowledge of Earth.
As Prof. Reiner Rummel said, “GOCE offers a fresh look into Earth’s interior, in particular, when using the gravity gradients directly as now shown. The gradients provide, for the first time, a 3D image of Earth from gravity.”
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30 May 2013
GOCE’s orbit lowered even further to about 224 km. A lower orbit means a stronger atmospheric drag pulls the satellite towards Earth. But GOCE was designed to fly low, so the tiny thrust of its ion engine continuously compensate for any drag.
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8 March 2013
Scientists find that GOCE detected sound waves from the massive earthquake that hit Japan on 11 March 2011. When the satellite passed through these waves, its accelerometers sensed the vertical displacements of the surrounding atmosphere.
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Satellites map changes in Earth’s surface caused by earthquakes but never before have sound waves from a quake been sensed directly in space – until now. ESA’s hyper-sensitive GOCE gravity satellite has added yet another first to its list of successes.
Earthquakes not only create seismic waves that travel through Earth’s interior, but large quakes also cause the surface of the planet to vibrate like a drum. This produces sound waves that travel upwards through the atmosphere.
The size of these waves changes from centimetres at the surface to kilometres in the thin atmosphere at altitudes of 200–300 km.
Only low-frequency sound – infrasound – reaches these heights. It causes vertical movements that expand and contract the atmosphere by accelerating air particles.
On Monday, Japan remembers the 20 000 people who died in the earthquake and tsunami that devastated its northeastern coast two years ago. New studies have revealed that this massive quake was also felt in space by ESA’s GOCE satellite.
Since it was launched in 2009, GOCE has been mapping Earth’s gravity with unrivalled precision, orbiting at the lowest altitude of any observation satellite. But at less than 270 km up, it has to cope with air drag as it cuts through the remnants of the atmosphere.
The cleverly designed satellite carries an innovative ion engine that instantly compensates for any drag by generating carefully calculated thrusts. These measurements are provided by very precise accelerometers.
While the measurements ensure that GOCE remains ultra-stable in its low orbit to collect ultra-precise measurements of Earth’s gravity, atmospheric density and vertical winds along its path can be inferred from the thruster and accelerometer data.
Exploiting GOCE data to the maximum, scientists from the Research Institute in Astrophysics and Planetology in France, the French space agency CNES, the Institute of Earth Physics of Paris and Delft University of Technology in the Netherlands, supported by ESA’s Earth Observation Support to Science Element, have been studying past measurements.
They discovered that GOCE detected sound waves from the massive earthquake that hit Japan on 11 March 2011.
When GOCE passed through these waves, its accelerometers sensed the vertical displacements of the surrounding atmosphere in a way similar to seismometers on the surface of Earth. Wave-like variations in air density were also observed.
Raphael Garcia from the Research Institute in Astrophysics and Planetology said, “Seismologists are particularly excited by this discovery because they were virtually the only Earth scientists without a space-based instrument directly comparable to those deployed on the ground.
“With this new tool they can start to look up into space to understand what is going on under their feet.”
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ESA's GOCE satellite detected sound waves from the massive earthquake that hit Japan on 11 March 2011. At GOCE's orbital altitude, the concentration of air molecules is very low so weak sound waves coming up from the ground are strongly amplified. Variations in air density owing to the earthquake were measured by GOCE and combined with a numerical model to show the propagation of low frequency infrasound waves.
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Quelle: ESA
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Update: 3.11.2013
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As of Nov. 1, GOCE's re-entry was predicted to occur between Nov. 5 and Nov. 10, according to Christoph Steiger, the mission's spacecraft operations manager at the European Space Operations Center in Darmstadt, Germany.
Quelle: ESA
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Update: 8.11.2013
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Where and when will it hit?
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ESA scientists are trying to constrain this further, but for now, they've estimated that the satellite will fracture into 25 to 45 pieces that will make impact on Sunday or Monday, Nov. 10-11. A day before entry, they hope to have that pinned down to a 4-5 hour window. They'll have help from the Inter-Agency Space Debris Coordination Committee, the Defense Department's Space Control and Space Surveillance (SCSS), ESA's Space Debris Office, and NASA's Orbital Debris Program Office.
During its mission, GOCE (pronounced go-chay) orbited Earth every 88 minutes. Since running out of fuel on Oct. 21, it has fallen like a hang glider, slowly coasting downward.
Quelle: ESA
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Update: 9.11.2013
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Saturday GOCE status update from ESOC
This sent in just a couple hours ago by ESA's GOCE Operations Manager Christoph Steiger, at ESOC.
This morning GOCE was at an altitude of around 160 km. As expected, the drag levels have increased very much, with the average now around 90 mN (milliNewton).
Despite the extreme environmental conditions, we had a problem-free acquisition of signals from the spacecraft this morning (meaning that the ground station found GOCE pretty much in the orbital position it was predicted to be). The attitude control of the spacecraft is performing very well. Data from the Gradiometer is now only usable for part of the orbit, when drag levels are below 80 mN and the accelerometers are hence not saturated.
Recently we have noticed a significant temperature increase in several areas of the spacecraft, arguably linked to GOCE encountering a more and more dense atmosphere as its orbit keeps dropping.
GOCE is expected to fall by over 13 km today, with the final re-entry into the atmosphere probably less than 2 days away.
Quelle: ESA
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Update: 10.11.2013
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Spacecraft doing great: GOCE at 133 km
Update from GOCE Operations Manager Christoph Steiger at ESOC
Less than 10 hours before re-entry, we have just had another ground contact with GOCE at 15:37 CET using KSAT's Svalbard station.
The spacecraft is now at an altitude of just 133km, with the decay rate around 1.5 km per hour (and increasing quickly). The average drag level is well over 200 mN (milliNewton).
The spacecraft is still doing great, with good attitude control. The Gradiometer has been switched off by us, as the accelerometers were saturated at these high drag levels. The scientific GPS receivers of GOCE keep working very well. Temperatures close to the front of the spacecraft keep increasing steadily: the central computer is now at around 40 degC, an increase by over 25 degC since 1.5 days ago. We have a few more ground contacts left this evening and will try to make the most out of them.
Quelle: ESA
A 2,000-pound European satellite has run out of fuel and is expected to plunge back to Earth sometime between 1:30 PM EST and 7:00 PM, scientists with Europe's Space Debris Office said Sunday.
As of 9:30 A.M. EST it was over Greenland and racing toward Canada; it will pass over the Dakotas, Colorado and New Mexico shortly. Where precisely it will crash remains up in the air.
As the whizzing GOCE -- or Gravity field and steady-state Ocean Circulation Explorer -- descends, scientists are carefully monitoring it to determine the landing site and ensure public safety. With each orbit, it descends from a current altitude of under 84 miles by about 0.6 miles per hour.
"With a very high probability, a re-entry over Europe can be excluded," wrote Heiner Klinkrad, Head of ESA's Space Debris Office, on an ESA website Sunday. Klinkrad, who is closely monitoring the GOCE re-entry, cited radar measurements and satellite-to-satellite tracking.
“The most probable impact ground swath runs over oceans and polar regions, as well as uninhabited areas of Australia,” he said.
Quelle: Fox-News
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Update: 11.11.2013
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The European Space Agency says its 1.2-ton GOCE gravity-mapping satellite plunged through the atmosphere on Sunday and broke up into bits over the South Atlantic Ocean.
In an online update, ESA said that GOCE re-entered Earth's atmosphere around 7:16 p.m. ET Sunday (0016 GMT Monday). The agency said that assessment was made after consultation with the U.S. Strategic Command, which monitors orbital debris.
The satellite hit the atmosphere over a spot due south of the Falkland Islands, around the coordinates of 60 degrees west and 56 degrees south, ESA said. "This would put the main area over which any possible GOCE remnants fell to the southernmost regions of the Atlantic Ocean," ESA's Daniel Scuka said.
About 500 pounds (250 kilograms) worth of debris was expected to have survived the car-sized satellite's re-entry, but no damage or eyewitness sightings of the fiery plunge were immediately reported.
Quelle: ESA
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Update: 12.11.2013
Falkland farewell for 'Space Ferrari'
The fragmenting satellite cut a white trail across the sky above the Falkland Islands
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The final moments of the Goce satellite were caught on camera as it blazed across the sky above the South Atlantic.
Falkland Islander Bill Chater managed to record the scene as he returned from a day's outing to see penguins.
“We saw what we first thought was a shooting star,” Bill told me.
“It soon became obvious it was the satellite we had heard about on BBC Radio News an hour before.
“It left a long trail of smoke which was bright white in the dark sky, presumably lit by the Sun which we could no longer see.”
Goce's fall to Earth on Sunday night made it the first European Space Agency (Esa) mission to make an uncontrolled re-entry into the atmosphere in more than 25 years.
The Italian-built Goce satellite was dubbed the "Ferrari of space"
Esa has looked at the pictures acquired on East Falkland and says they represent - "in all likelihood" - the destructive end of its one-tonne probe.
Dubbed the "Ferrari of space" because of its sleek Italian design, Goce had spent the past four years making precise maps of Earth's gravity.
Its plunge through the atmosphere on Sunday became inevitable once the electric engine it had employed to stay in orbit ran out of fuel.
Tracking systems were deployed to monitor the rapid descent, with a final estimate for the location of the re-entry put close to the tip of South America, just east of Tierra Del Fuego.
American military data timed this event to have occurred at 00:16 GMT, or 21:16 local Falkland time - just as Bill, his wife Vicky, and dad, Tony Chater, were making their way home after spending the day with King Penguins.
“We were returning home from Volunteer Point,” says Bill.
“It was just getting dark following a long, spectacular sunset and as we came over Wall Mountain, heading south, we saw what we first thought was a shooting star.
“It was leaving a thick white trail of smoke and split into a couple of bits, before again breaking up into several smaller parts which all flew over our heads and disappeared northwards over Wall Mountain behind us.”
The description of the event fits, as does the location and timing. The direction of the fireballs – moving south to north – also matches what would have been Goce’s death trajectory.
Bill says he has video of the event but cannot share it because of the islands’ slow internet connection.
Goce started its descent from an operational altitude of 224km, and took a total of three weeks to fall to Earth.
The thermal and mechanical stresses that ultimately tore the satellite apart would have begun to take hold while it was still 80km from the Earth's surface. Experts had suggested some 200-250kg could have survived all the way down. If they did, these twisted and charred materials are now at the bottom of the Atlantic Ocean.
It was a violent end for one of the most delicate and sensitive space instruments ever built.
Goce’s data lives on, however.
Its exquisite maps of the subtle variations in gravity across the surface of the Earth will influence a diverse array of disciplines - from ocean and climate research to geology and civil engineering.
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Esa says the pictures show - "in all likelihood" - the destructive end of its one-tonne probe
Quelle: BBC
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