Russian Rocket Lofts ESA Gravity Mapping Satellite

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FRASCATI, Italy — Europe’s gravity-field-measuring satellite, GOCE, was successfully placed into low Earth orbit March 17 by a Russian Rockot vehicle operated from the Plesetsk Cosmodrome in northern Russia.

The satellite sent its first signals to Europe’s Kiruna, Sweden, ground station after separation from the Rockot vehicle, according to European Space Agency (ESA) managers.

GOCE is expected to operate for about 24 months in a near-polar orbit at just 263 kilometers in altitude, compared to 600-900 kilometers for most Earth observation satellites. Mission managers say that, to their knowledge, no nonmilitary satellite has ever operated in this orbit, where residual atmosphere is thick enough to slow the spacecraft and force a premature end to the mission.

To counteract this, the 1,052-kilogram GOCE features a unique design that resembles an arrowhead to provide better aerodynamics and a xenon-ion propulsion engine that will provide gentle thrust to counteract the effects of atmospheric drag. Without the work of the engine, fed by 40 kilograms of xenon gas, GOCE would fall out of orbit in a period of weeks, or at a maximum of three months, depending on solar activity at the time, said Rune Floberghagen, GOCE mission manager at the 18-nation ESA.

GOCE’s main payload is the gradiometer, composed of three pairs of accelerometers that will produce a global map of gravity’s differing pull in different regions of Earth. Its sensitivity to gravity’s effects has been described by Mark Drinkwater, GOCE mission scientist, as the equivalent of being capable of measuring the impact of a snowflake landing on an oil tanker. The accelerometers were built by France’s Onera aerospace-research institute.

Like the xenon-ion propulsion system, built by Qinetiq of Britain, GOCE’s accelerometers have never flown before in space, making GOCE a technology demonstration satellite that has been given an Earth science mission.

GOCE, or the Gravity field and Ocean Circulation Explorer, is the first of a planned seven ESA Earth Explorer satellites. Because of difficulties in building the gradiometer, and later because of a series of delays related to the Rockot launcher, GOCE will begin operations two years later than planned.

But as luck would have it, the current solar cycle has been particularly calm, meaning GOCE will not have to fly in a higher orbit than planned in order to escape additional atmospheric drag caused by increased levels of solar radiation.

GOCE’s budget is 350 million euros ($453 million), including the satellite’s construction and launch, and two years of operation. The satellite was built by Thales Alenia Space of France and Italy. The Rockot launch services were provided by Eurockot Launch Services GmbH of Bremen, Germany, a joint venture between Khrunichev of Russia and EADS of Europe.