...gravity map of Earth, but its orbit is now being lowered in order to obtain even better results.
The Gravity field and steady-state Ocean Circulation Explorer (GOCE) has been orbiting Earth since March 2009, reaching its ambitious objective to map our planet’s gravity with unrivalled precision. Although the planned mission has been completed, the fuel consumption was much lower than anticipated because of the low solar activity over the last two years. This has enabled ESA to extend GOCE’s life, improving the quality of the gravity model.
To be able to measure the strength of Earth’s gravity, the satellite was flying in an extraordinarily low orbit about 255km high—about500 km lower than most Earth observation satellites. Based on a clear preference from the GOCE user community, ESA’s Earth Scientific Advisory Committee recommended lowering the orbit to 235 km starting in August.
Lowering the orbit increases the accuracy and resolution of GOCE’s measurements, improving the view of smaller ocean dynamics such as eddy currents. The control team began the manoevers in August, lowering GOCE by about 300m per day. After coming down by 8.6km, the satellite’s performance and new environment were assessed. Now, GOCE is again being lowered while continuing its gravity mapping. Finally, it is expected to reach 235km in February.
As the orbit drops, atmospheric drag increasingly pulls the satellite towards Earth. But GOCE was designed to fly low, the tiny thrust of its ion engine continuously compensating for any drag. The expected increase in data quality is so high that scientists are calling it GOCE’s ‘second mission.’
The first ‘geoid’ based on GOCE’s gravity measurements was unveiled in June 2010. It is the surface of an ideal global ocean in the absence of tides and currents, shaped only by gravity. A geoid is a crucial reference for conducting precise measurements of ocean circulation, sea-level change and ice dynamics. The mission has also been providing new insight into air density and wind in space, and its information was recently used to produce the first global high-resolution map of the boundary between Earth’s crust and mantle.