posted 11-01-2013 12:43 AM               

GOCE completes its mission

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.

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.

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.
  
• Spaceflight 101: GOCE - Re-Entry Updates

posted 11-08-2013 05:54 AM               

GOCE status update from ESOC

This update was provided this morning (Nov. 8) by GOCE Spacecraft Operations Manager Christoph Steiger at ESOC.

This morning (Nov. 8), GOCE is at an altitude of roughly 170 km, with atmospheric drag levels at an average of over 50 mN (milli Newton). The geomagnetic field was unsettled yesterday, leading to peaks in drag above 100 mN.

The spacecraft keeps performing excellently at these extreme conditions, exceeding our expectations. We are still getting good acceleration data from the Gradiometer, which may be of much value for atmospheric density studies. We will however be seeing more and more saturation on the accelerometers as drag levels go up. The two scientific GPS receivers – the so-called Satellite-to-Satellite Tracking Instruments (SSTI) – are also still fully operational.

Apart from collecting scientific data, conducting operations at these extremely low altitudes allows us to assess the performance of the spacecraft and the ground segment (i.e. the ground stations) in conditions far outside the original design specifications.

GOCE will drop by more than 8 km today, with the drag now going up rapidly and the final re-entry into the atmosphere drawing closer and closer. As planned, we will keep operating the spacecraft as long as possible.

posted 11-09-2013 04:40 PM               

GOCE flight expected to end shortly

Re-entry of GOCE into the Earth's atmosphere is predicted to occur during the night between Sunday and Monday, Nov. 10-11. Break-up of the spacecraft will occur at an altitude of approximately 80 km.

The estimate is based on the results of detailed analysis, taking in to account a number of changeable factors including the spacecraft's orientation, the functioning of the attitude control system, as well as solar and geomagnetic activity.

As of this morning (Nov. 9), GOCE was at an altitude of roughly 170 km and was expected to sink by more than 8 km within the day.

The Rocket Science blog spoke earlier with Prof Heiner Klinkrad, Head of ESA's Space Debris Office at ESOC, Darmstadt, Germany.

Q: What do we expect to happen GOCE's orbit steadily decays?

HK: When the spacecraft reaches altitudes below 100 km, then atmospheric density will drastically increase. Starting with a velocity of about 25 000 km/hour, air drag with the concomitant aerodynamic pressure and heating will cause a break-up of the spacecraft at approximately 80km altitude, causing a large number of fragments.

Q: Do we expect any of these to reach the surface?

HK: Most of these fragments will completely burn up. A small fraction of the initial spacecraft mass – about 20% or 200kg – is expected to reach ground, distributed across dozens of fragments, spread over a sizable re-entry ground swath.

Q: Is there any risk to anyone on ground?

HK: The risk to the population on ground will be minute. Statistically speaking, it is 250,000 times more probable to win the jackpot in the German Lotto than to get hit by a GOCE fragment. In 56 years of space flight, no man-made space objects that have re-entered into Earth's atmosphere have ever caused injury to humans.

posted 11-09-2013 06:30 PM               

In 56 years of space flight, no man-made space objects that have re-entered into Earth's atmosphere have ever caused injury to humans.

posted 11-10-2013 07:36 AM               

GOCE re-entry forecast from ESA's Space Debris Office

Update from Heiner Klinkrad, Head of ESA's Space Debris Office at ESOC, which is closely monitoring the GOCE re-entry.

With recent orbit data from this morning, based on TIRA radar measurements and GOCE satellite-to-satellite tracking, augmented with orbit data from international partners of the Inter-Agency Space Debris Coordination Committee (IADC), the re-entry of the satellite can be predicted with an accuracy of about plus or minus 2 orbits.

The re-entry is expected to occur between 18:30 UTC - 24:00 UTC, Sunday, 10 November (19:30 CET - 01:00 CET, Sunday to Monday, 10/11 November); the most probable impact ground swath largely runs over ocean and polar regions.

With a very high probability, a re-entry over Europe can be excluded.

posted 11-10-2013 04:27 PM               

Update from ESA Space Debris Office

This latest (and possibly final) forecast was just received from Prof Heiner Klinkrad, Head of the ESA Space Debris Office at ESOC.

On a short pass over the Troll ground station that ended at 21:18 CET (20:18 UTC), while GOCE flew at an altitude of only 122 km, the satellite was still showing an amazing system performance, and dumped highly valuable data to the ground station.

Using these data, that included very accurate navigation fixes along its trajectory, an orbit could be fitted that was used to forecast the re-entry of the spacecraft.

Current estimates lead to a re-entry time window between 22:50 UTC on 10 November and 00:50 UTC on 11 November (23:50-01:50 CET, 5:50 to 7:50 p.m. EST).

The most probable re-entry area lies on a descending orbit pass that mainly runs across the Pacific and the Indian Ocean. ESA will make another attempt to contact GOCE during a Troll station pass, to acquire more science and spacecraft data from an extremely low orbit altitude, and to further reduce the uncertainty in the re-entry forecast.

posted 11-11-2013 04:59 AM               

GOCE gives in to gravity

Close to 01:00 CET on Monday 11 November, ESA's GOCE satellite reentered Earth's atmosphere on a descending orbit pass that extended across Siberia, the western Pacific Ocean, the eastern Indian Ocean and Antarctica. As expected, the satellite disintegrated in the high atmosphere and no damage to property has been reported.

Launched in March 2009, the Gravity field and steady-state Ocean Circulation Explorer – GOCE – has mapped variations in Earth's gravity with unrivalled precision. The result is the most accurate shape of the 'geoid' – a hypothetical global ocean at rest – ever produced, which is being used to understand ocean circulation, sea level, ice dynamics and Earth's interior.

GOCE's innovative ion engine, responsible for keeping the satellite at an incredibly low orbit of under 260 km, together with its accelerometer measurements have also provided new insight into air density and wind speeds in the upper atmosphere.

On 21 October, the mission came to a natural end when it ran out of fuel. Over the past three weeks the satellite gradually descended.

While most of the 1100 kg satellite disintegrated in the atmosphere, an estimated 25% reached Earth's surface.

An international campaign involving the Inter-Agency Space Debris Coordination Committee and ESA's Space Debris Office monitored the reentry.

"The one-tonne GOCE satellite is only a small fraction of the 100–150 tonnes of man-made space objects that reenter Earth's atmosphere annually," said Heiner Klinkrad, Head of ESA's Space Debris Office.

"In the 56 years of spaceflight, some 15 000 tonnes of man-made space objects have reentered the atmosphere without causing a single human injury to date."

For an overview of the satellite's final days and recent scientific discoveries, visit the dedicated webpage.

posted 11-11-2013 05:08 AM               

GOCE re-entry region

In close cooperation with USSTRATCOM, ESA's Space Debris Office gives the following estimated results for GOCE re-entry:

• The atmospheric interface at ~80 km altitude occurred, following a USSTRATCOM confirmation, at the latest, at 01:16 CET (00:16 UTC) 11 November 2013
  
• This would correspond to a geographical location of approx. 60 degree West and 56 degree South, near the Falkland Islands.

This would put the main area over which any possible GOCE remnants fell to the southernmost regions of the Atlantic Ocean.

posted 11-15-2013 08:28 AM               

We saw it burn up from the Falklands at about 9.20pm last night [Nov. 11]. Came from the South breaking up into bits.