Spacecraft Skims Venus Atmosphere for Science

A European-built spacecraft has used its solar wings as sails to skim through the sweltering atmosphere of Venus at the planet's outermost border with space.

The European Space Agency's (ESA) Venus Express spacecraft conducted five "aerodrag" maneuvers last week, which used the orbiter as a sensor capable of very accurately measuring the atmospheric density just 111 miles (180 km) above the cloud-enshrouded planet.

To do these aerodrag measurements, the solar panels of Venus Express were rotated through five sets of orientations, which changed daily, to exposed the wings to the vanishingly faint wisps of Venus' atmosphere at its boundary with space.

The solar wing configuration generated a tiny but measurable amount of aerodynamic torque, or rotation, on the probe. This torque can be measured very accurately based on the amount of correction that must be applied by reaction wheels, which counter-rotate inside the spacecraft to maintain its orientation in space.

That correction data, in turn, tells scientists just how thick or thin the atmosphere of Venus is at the point the spacecraft was during the maneuver.

On the last day of the aerodrag campaign, which ended on April 16, the solar arrays were rotated at plus and minus 45 degrees to the atmospheric flow, mimicking the vanes of a windmill. They maneuver allowed Venus Express to gather more information on the behavior of the molecules of Venus' atmosphere as they bounced off the probe's solar wings.

"The aerodrag campaign went without problem, and conclusively demonstrated that Venus Express can be securely and accurately used to sense the density of the planet's atmosphere," said Octavio Camino, the probe's spacecraft operations manager. "Venus Express has shown once again that it is a very capable satellite."

Camino said that the mission operations team will study last week's results to develop an optimised configuration for aerodrag campaigns in October and in 2011. Aerodrag testing was also conducted in 2008, 2009 and February 2010.

Continued positive results may enable Venus Express to conduct more sophisticated investigations deeper in the atmosphere, which would be of immense interest to planetary scientists.

The spacecraft launched toward the cloud-covered second planet of the solar system in 2005 and arrived at Venus a year later. The mission was extended for four months in May 2009, and then received another reprieve in September 2009 ? this time, extending the mission to 2010.

Aerobraking demonstrations are expected to follow through at least 2011 or 2012, ESA officials have said.

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