European satellite launch delayed on mission to reveal oceanic secrets

Countdown in Russia suspended for the European Space Agency's 'Ferrari' of satellites that will measure gravity around the Earth and help scientists understand how oceans are changing as the planet heats up

Robin McKie
guardian.co.uk, Monday 16 March 2009 13.53 GMT

The launch of Europe's gravity mapping satellite, Gravity and Ocean Circulation Explorer, has been delayed. Controllers at the Plesetsk cosmodrome in Arkangel in north-west Russia suspended its countdown only seven seconds away from blast off on a SS-19 ex-Soviet missile at 1421 GMT today.
The European Space Agency said launch controllers had suspended the countdown when the tower protecting its SS-19 launcher failed to move clear to allow blast-off. Russian space engineers are now studying the problem and if they can correct it easily, a launch may be attempted tomorrow. A press conference will be held later today when further details will be announced.
The satellite is scheduled to map tiny variations in Earth's gravity and reveal new data about the circulation of heat in the oceans. It is not known yet why the delay was ordered - or how long the launch will remain postponed.
It has been described as one of the most stylish, and important, satellites ever built by European scientists. The 16ft torpedo-shaped probe – the Gravity and Ocean Circulation Explorer, or Goce – will be blasted into space on a Russian SS-19 missile from the Plesetsk cosmodrome near Arkangel.
Once in orbit the £200m satellite – constructed by the European Space Agency, Esa - will swoop over the atmosphere to measure Earth's gravity with unprecedented accuracy. The data it returns will be vital to scientists trying to understand the impact of climate change on Earth, and in particular for climate researchers who are seeking to understand how oceans transport heat around the planet.
"Gravity varies depending where you are on the planet," says Professor Marek Ziebert, of University College, London. "And those variations have an effect on how the oceans circulate. Goce will provide crucial information that will allow us to gain a new understanding of how the oceans behave."
But Goce is also distinctive because of its elegant design and its covering of silver-blue solar cells. It has been labelled the Ferrari of space probes by its manufacturers, Thales Alenia Space Italia while Volker Liebig, Director of Earth Observation Programmes at Esa described the craft as "a jewel of innovations".
Liebig added that Goce has been designed to fly at an extremely low orbit, just 250km (155 miles) above Earth, where it will encounter friction from the thin atmosphere: "For this reason it has an eye-catching aerodynamic shape and will actively compensate for the air drag by using the finely controlled thrust of its ion engine."
The probe's T5 ion rocket was built by QinetiQ in the UK and will be fired constantly throughout its 20-month mission in order to keep Goce in its correct orbit. At the same time, computers will send 10 messages a second to its engines to ensure the probe orbits at the right height. Goce will also use GPS devices to plot its exact position and a gradiometer, a machine that can detect fluctuations of a million millionth in Earth's gravity.
This data will then be transmitted daily and used to build a model of Earth's shape, one that is accurate to within a centimetre, as well as putting together a highly accurate gravity map of the planet. "Gravity is the force that drives the circulation of the oceans," added Dr Mark Drinkwater, Goce's project scientist. "Until we understand its exact role we cannot predict how the seas — and planet — will behave as the climate gets warmer. That is why Goce is being launched."
Ocean currents take a third of all the heat that falls on equatorial regions and carry it to higher latitudes. One of the most important currents is the Gulf Stream, which scientists fear could be destroyed or diverted by melting Arctic ice. But they need to know all the gravitational effects that influence the stream's course across the Atlantic before they can make accurate predictions.
The problem is that Earth's gravity is not constant. The planet is flattened at the poles, for example, so gravity is stronger there, and weaker at the equator. Gas fields, mineral deposits, groundwater reservoirs and rock strata also produce variations in gravity.
"There are all sorts of wiggles and bumps in Earth's gravity field," said Dr Chris Hughes, of the Proudman Oceanographic Laboratory in Liverpool. "Each will influence ocean currents, which have a crucial role in moving heat around the world. If we are to understand how climate change is going to affect the planet, we have to have a precise picture of its gravity field.
Once we combine the data we will get from Goce with observations of sea height and ocean current flow — information that is provided by other satellites — we will get a clear idea of what our oceans are doing. Then we will get a better picture of how the seas are changing as the world heats up."