GOCE completes its mission

13 November 2013

Data from GOCE’s final days will be used by the scientific community to learn more about atmospheric density and wind, and improve reentry modelling.

“The fact that GOCE kept functioning so well for nearly the entire de-orbiting phase opens exciting new science opportunities,” said Rune Floberghagen, GOCE Mission Manager.

“ESA will make sure all data relevant to the investigation of this phase are made readily available to the scientific community as soon as possible.”

In close cooperation with NASA, ESA’s Space Debris Office confirms that atmospheric interface occurred at 01:16 CET this morning over the South Atlantic Ocean near the Falkland Islands, at an approximate altitude of 80 km.

Fragments reached Earth’s surface over the southernmost regions of the South Atlantic. More information will be released as it becomes available.

On a short pass over the Troll ground station that ended at 21:18 CET, while GOCE flew at an altitude of only 122 km, the satellite was still showing amazing system performance and delivered 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 reentry time window between 23:50 CET and 01:50 CET. The most probable reentry area lies on a descending orbit pass that mainly runs across the Pacific and the Indian Oceans. 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.

Contact was made nominally at 20:50 CET at Antarctica’s Troll station. The temperature of the central computer and battery is around 54ºC. Next visibility is expected again over Troll at 22:16 CET.

Correction: Estimation for reentry of GOCE predicts a time window between 23:30 to 01:30 CET.

GOCE is now below an altitude of 130 km. The spacecraft was still in good shape when last seen around 18:30 CET at ESA's Kiruna ground station in northern Sweden.

Attitude control is working perfectly. Temperatures of the battery and central computer are now at about 45ºC. Next contact with GOCE is expected at Kiruna for around 20:00 CET.

Less than 10 hours before reentry, another ground contact was made with GOCE at 15:37 CET using KSAT's Svalbard station.

The spacecraft is now at an altitude of just 133 km, with the decay rate around 1.5 km per hour.

The Gradiometer has been switched off. GOCE’s scientific GPS receivers keep working very well. Temperatures close to the front of the spacecraft are increasing steadily: the central computer is now at around 40ºC.

ESA’s Space Debris Office says that reentry is expected to occur between 19:30 today and 01:00 tomorrow (CET). The most probable impact ground swath runs over oceans and polar regions. The probability of reentry over Europe can be excluded.

With measurements from the Tracking and Imaging Radar, GOCE’s satellite-to-satellite tracking and orbit data from the Inter-Agency Space Debris Coordination Committee, the reentry of GOCE could be predicted with an accuracy of about +/-2 orbits.

Less than one day before the predicted reentry into the atmosphere, the spacecraft is still functioning well and standard spacecraft operations activities are proceeding.

The satellite is at an altitude of about 147 km, dropping at a rate of more than 1 km an hour.

Drag levels are now too high to be measured by the accelerometers. Based on the results of the orbit determination, average drag levels are at about 165 mN (milli Newton). Temperatures of units and subsystems close to the front of the spacecraft continue to increase, but have not yet reached levels threatening the correct functioning of GOCE.

The orientation of the spacecraft is as it should be, with the attitude control system continuing to work well. Owing to its aerodynamic shape, it is estimated that the spacecraft is kept in the correct orientation by atmospheric drag forces alone.

Given the fast altitude drop and change of environmental conditions, the end of flight operations is getting close.

This morning, GOCE was at an altitude of about 160 km. As expected, drag levels have increased with a current average of about  90 mN (milli Newton). There are significant temperature increases in several areas of the spacecraft, possibly linked to GOCE encountering increasingly dense atmosphere as its orbit drops.

GOCE is expected to fall by over 13 km today.

Reentry of GOCE  into Earth’s atmosphere is predicted to occur during the night between Sunday and Monday. Break-up of the spacecraft will occur at an altitude of approximately 80 km. At the moment, the exact time and location of where the fragments will land cannot be foreseen.

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

Updated predictions will be communicated on this page and in the related blog.

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