WASHINGTON — NASA and the European Space Agency (ESA) are preparing to solicit  proposals for instruments on a proposed flagship-class mission to the Jupiter system in 2020 that would involve both U.S. and European manufacturers, according to NASA officials.

Jim Green, NASA’s planetary science division director, said the Europa Jupiter System Mission calls for sending two probes — one supplied by NASA, the other by ESA — to explore two of Jupiter’s ice-covered moons, Europa and Ganymede.

Although ESA said in February that it would prefer to join NASA on a joint expedition to Jupiter rather than Saturn come 2020, the 18-nation space agency remains several years from deciding whether to undertake the Jupiter trip or instead partner with NASA and the Japan Aerospace Exploration Agency on one of two astrophysics observatories also in the running to be Europe’s next L-class Cosmic Vision mission.

A down select between the Europa Jupiter System Mission, the International X-ray Observatory and the Laser Interferometer Space Antenna is expected to begin in late 2010. However, Green said NASA does not expect ESA to make a final down select until early 2013.

In the meantime, both NASA and ESA will be soliciting instrument ideas for the pair of Jupiter-bound orbiters.

“We’re looking forward in terms of soliciting proposals for instruments. It’s a little early yet, but indeed sometimes you can never start early enough,” Green said in a Sept. 30 interview, adding that NASA and ESA are coordinating announcements for industry solicitations within both agencies. “That takes a little bit of work to do, but we anticipate ESA investigators on the Europa satellite orbiter and NASA investigators on the Ganymede orbiter. The blending of the two teams is really a highlight and an essential part of the joint operation that we’re currently doing.”

Green said the trans-Atlantic partnership has been focused on addressing specific challenges to developing two orbiters with instruments designed to operate in the Jupiter system’s severe radiation environment.

“This July we had a major radiation workshop where we talked about the … instrumentation necessary to build a capability to survive the radiation environment,” Green said, adding that NASA and ESA also initiated a dialogue with industry partners who have worked with radiation hardening capabilities for other agencies, including the Defense Department.

“We want to implement that best knowledge, in terms of radiation protection, for both spacecraft in the Jupiter system.”

Green said a joint workshop is planned for mid-2010 to followup on the results of the first. Although the project has been in the pre-planning stages for some time, he says it has helped sharpen a joint perspective on the work that lies ahead.

“It’s enabled us to uncover, or at least elucidate what technologies we have under our belt before we attempt to pull something off like that is and focus the science in a particular area.”

The Jupiter-bound expedition would send two spacecraft to study Europa and Ganymede in unprecedented detail. NASA would build one orbiter, the Jupiter Europa, while ESA would provide the other, the Jupiter Ganymede, known in 

Europe as Laplace. Each orbiter would be launched in parallel from different spaceports, arriving in tandem by the mid-2020s and spending up to three years studying the planet and its moons in unprecedented detail.

Although the mission is not currently funded, NASA is expected to contribute as much as $3 billion to the effort. In the near term, $10 million has been set aside to continue studying design challenges for the Europa orbiter, though House appropriators included $18 million for concept studies and technology risk reduction for a proposed orbiter and lander mission to Europa by 2020 in the House version of the 2010 Commerce, Justice, Science spending bill that funds NASA.