Oct 23, 2013

As GOCE Mission Ends, The Work Has Only Just Begun

Estimated Article Reading Time: 2 min.

The European Space Agency’s (ESA) GOCE mission ended earlier this week, but the mission’s discoveries have only just begun. The ESA said that although the GOCE gravity satellite is entering its final weeks in orbit, the most exciting scientific analysis of the mission’s data is just beginning.

GOCE has the first three-dimensional gravity gradiometer in space and it orbits lower than any other research satellite. The satellite has spent more than four years measuring variations in Earth’s gravity, creating the most accurate model of the geoid every produced.

The satellite was designed to fly at just 150 miles above the Earth, which is about 300 miles lower than most Earth observation satellites. GOCE features a unique electric ion engine that compensates for drag experienced at flying at low altitude. This engine generates carefully calculated thrust, enabling GOCE to remain stable throughout its life in orbit.

Scientists have used the thruster and accelerometer measurements taken by the satellite to create a new dataset of upper atmosphere densities and wind speeds. This new dataset has recently been made available to the science community.

“The accurate accelerometers that are part of GOCE’s gravity gradiometer instrument, in combination with information from its drag-free control system, can be used to detect the aerodynamic force on the satellite,” said Eelco Doornbos from Delft University of Technology in the Netherlands.

“This force is caused by molecules and atoms in the upper layer of the atmosphere bouncing off the satellite’s outer surfaces. Through careful processing, we have been able to gain four years’ worth of data on upper-atmospheric density and winds from these accelerations.”

Doornbos said this dataset is helping to shed new light on the impact that solar activity has on the upper atmosphere. Usually, variations in the density of the upper atmosphere are dominated by solar activity. The solar activity has gradually increased since launching GOCE in 2009 from a minimum to a maximum.

“This means that the mission has offered us an excellent opportunity to study the relationship between solar activity and density and wind,” Doornbos said.

During the first year of GOCE’s observations, the Sun was calm and solar activity was almost absent. Observations of density and wind during this period were ideally suited to study how waves originating in the lower layers of the atmosphere influence the upper atmosphere.

“My interest lies in understanding coupling processes between the lower layers of the atmosphere and the upper atmosphere,” said Professor Jeffrey Forbes from the University of Colorado. “This new dataset from GOCE helps to fill this gap. It allows us to investigate how the wave spectrum in the upper atmosphere evolves with height.”

Rune Floberghagen, ESA’s GOCE mission manager, said although the mission is coming to an end, they are seeing work that goes beyond the original objectives of the mission.

“The type of science addressed here not only looks at the bulk density and winds in the upper atmosphere, but also at the interactions between the various layers of our precious atmosphere,” Floberghagen said. “It is almost as if we can see weather patterns in the GOCE data.”