NASA plans to add a science instrument to a dual-orbiter mission to Mercury called BepiColombo, a joint project of the European and Japanese space agencies.

The U.S. contribution consists of an instrument, called Strofio, which is intended to map the tenuous and ever-changing pocket of gases enveloping the innermost planet of the solar system.

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NASA’s contribution is estimated at $32 million, agency spokesman Michael Braukus wrote in an email to Discovery News.

Overall mission costs are about $1 billion. The European Space Agency is contributing the Mercury Planetary Orbiter, known at MPO. The Japanese Aerospace Exploration Agency, JAXA,  is building  the Mercury Magnetospheric Orbiter (MMO). The satellites are scheduled to fly together on an Ariane 5 rocket in August 2015.

The satellites’ circuitous route to Mercury will take more than six years.

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The mission is named for Guiseppe “Bepi” Colombo, (1920-1984) an Italian scientist and engineer who developed the technique to use the gravity of planets to maneuver satellites.  Quite appropriately, the satellites for his  namesake mission will slingshot around Earth once, Venus twice and Mercury four times before settling into orbit for a one-year mission

The mission follows NASA’s ongoing MESSENGER mission at Mercury.