ESA GOCE: Gravity mapper surfs Earth's upper atmosphere

Europe's ultra-low-flying gravity-mapping satellite, Goce, is being manoeuvred even closer to the planet.

The arrow-shaped spacecraft has spent most of its mission at an altitude of 255km - that's about 500km below most other Earth-observing missions.

Engineers are now bringing it down by 20km to improve its data resolution.

But it will be a tricky operation. Goce will have to fight atmospheric drag to stay aloft and maintain the stability needed to measure Earth's gravity.

"The science benefit that you get from decreasing the altitude and thereby increasing the spatial resolution of the data, and also the precision of what you can measure, is quite spectacular," explained mission manager Dr Rune Floberghagen. (Interviewed here)

"We will get about a 35% increase in the quality of the data," he reported.

GOCE: The Gravity Field and Steady-State Ocean Circulation Explorer was launched in 2009.

It is part of a series of innovative research satellites developed by the European Space Agency (Esa).

It carries super-sensitive instrumentation to detect the tiny variations in the pull of gravity across the surface of the planet.

The maps it produces can have very broad applications. The data is a key reference in civil engineering for relating heights measured at widely separated locations, and for the computer models that need to understand how the oceans move to forecast future changes in climate.

Recent successes include producing the first global high-resolution map of the boundary between the rocks of the Earth's crust and its mantle - the famous Mohorovicic (or "Moho") discontinuity, which lies tens of kilometres below the planet's surface.