The European Space Agency is one step closer today to restoring data transmission from it’s Earth Observation satellite. First launched on 17 March 2009 (see ‘Gravity Mission to launch’) the Gravity and Ocean Circulation Experiment (GOCE) is renowned for it’s high resolution datasets on earth’s gravity gradients. However on 18 July 2010, 17 months into the mission, the satellite lost the ability to transmit science data. The satellite had previously developed computer glitches in February 2010 and data transmission was finally suspended when the back-up computer system developed communication problems.
Following earlier reports on the satellite’s status (see BBC) the outlook today is looking more positive. “We’re in a better situation and making progress” says Mark Drinkwater, head of the mission science division, European Space Research and Technology Centre (ESTEC) headquarters in Noordwijk, The Netherlands.
“Today is an important milestone in solving the telemetry anomaly because we have applied software patches to the satellite’s computer systems which enable monitoring of the onboard health of the satellite by downloading status information" explains Drinkwater who has been involved with the design and development of the GOCE ‘Earth Explorer’ mission since the end of the 1990’s.
And the science has continued despite telemetry glitches. “There is no reason to believe that the gradiometer, GPS and star trackers are not perfectly nominal and working fine – we just can’t get science data to the ground” Drinkwater explains.
As the lowest orbiting environmental spacecraft, the GOCE satellite circles in the earth’s atmosphere just 250 km above the surface. This allows extremely accurate environmental datasets at an unprecedented spatial resolution with a real societal benefit.
“The GOCE datasets are set to revolutionize scientist’s ability to monitor and predict sea level rise, a growing concern in a changing climate” says Drinkwater.
The instrument in question is the first three-dimensional gradiometer. “Previous gravity data measurements could be regarded as monochrome by comparison to the fantastic new technicolour details captured in GOCE gradiometer gravity gradient data. Meanwhile, its uniform global high resolution products at 100 km grid scale, such as the geoid height – a proxy for sea level – is approaching the unprecedented accuracy of 1-2cm” says Drinkwater.
And this may be just the beginning of a new age in earth observation satellites. As part of ESA’s Living Planet Programme the GOCE satellite was the first of a series of Earth Explorer satellites now in orbit, including the SMOS and CRYOSAT satellites for soil saturation and ice cover respectively. And the GOCE datasets also complement other established missions.
“The GOCE satellite complements a well established satellite mission called GRACE” says Drinkwater. Launched in 2002 as a Joint mission by NASA and the German Space Agency, the Gravity Recovery and Climate Experiment (GRACE) satellite mission was designed for assessing gravity changes over time, whilst the GOCE satellite offers the first high resolution static (average) gravity field data. “The combination of GRACE and GOCE data is a very powerful thing” he continues.
The current testing, says Drinkwater, is an ongoing operation which may take weeks although it is hoped that the full telemetry could be implemented as early as mid September. And the project may have a longer life-span than first thought “Completion of the nominal GOCE mission was originally foreseen in April 2011. But thanks to the low solar activity there remain sufficient on-board fuel resources that would theoretically allow continuation of satellite operations through the end of 2013.” says Drinkwater.
Image: GOCE first global gravity model / ESA – GOCE High Level Processing Facility