PARIS — European scientists are proposing that their next large space science mission be a satellite to Jupiter and its moons in 2022 or 2023, a decision that was not unexpected given NASA’s withdrawal, due to budget constraints, of support for the two other competitors.

Europe’s space science decision-making body, the Science Program Committee (SPC), is expected to ratify the choice of the Jupiter Icy Moons Explorer, or Juice mission, when it meets on May 2.

In a decision endorsed April 17 by the science directorate of the 19-nation European Space Agency (ESA), the Space Science Advisory Committee concluded that the Juice mission is the least risky and least costly of the three proposals that were being considered.

A 25-page document detailing the science directorate’s decision was published April 18 by the website ESA’s SPC almost always endorses the advisory committee’s recommendations. Assuming it does in this case, Juice could be decided in time to select industrial contractors by late 2015, with a launch in mid-2022 or mid-2023 aboard a European Ariane 5 rocket.

After a 7.5-year cruise phase, it would arrive in Jupiter orbit in early 2030 and begin a mission of at least three years studying the Ganymede, Europa and Callisto moons.

NASA has indicated it may be interested in contributing to the Juice payload suite. But following the experience of early 2011, ESA science managers this time around are not permitting any agency outside Europe to be able to decide the mission’s fate.

ESA in 2007 selected three so-called L-class, or Large, science missions to compete for the 2022 launch slot. Two of them featured indispensable NASA participation.

The third, which ended as Juice, originally included a NASA-built satellite to Jupiter’s Europa moon that would give the two agencies a more-thorough survey of the Jupiter region.

In March 2011, NASA informed ESA that the U.S. space agency’s budget prospects did not permit it to participate in any substantial way in the L-class missions.

For Juice, that meant adding a visit to Europa to make up for the loss of the NASA mission.

For the two other candidates, the absence of NASA required a stem-to-stern mission reassessment.

The result, which was presented to the science advisory committee April 3-4, was two redrawn missions — one to study gravity waves, the other a large X-ray observatory — that presented cost and schedule risks.

ESA set a budget of 870 million euros ($1.15 billion) for its share of whatever mission was selected. To this would be added contributions from individual ESA member governments and, if available, contributions from NASA or another space agency.

To prevent a repeat of the 2011 experience, the agency had capped at 20 percent the contribution of any agency outside ESA, and had said the mission’s financial and technical feasibility had to stand on its own even if the partner agency eventually bowed out.

The agency also insisted that most, if not all, the key technologies in the proposed missions had to be sufficiently well known to reach Technology Risk Level 5 on a commonly used one-to-10 scale measuring how close a technology is to being proven.

Juice was the only one of the three that met the technological, financial and schedule criteria.

As proposed, Juice is now anticipated to cost ESA 830 million euros. Individual ESA member governments are expected to contribute payload elements valued at 241 million euros.

A NASA contribution of 68 million euros is viewed as possible, but not indispensable, according to the advisory committee assessment.

The two other missions both were more expensive and fraught with technological unknowns.

The Athena — short for Advanced Telescope for High-Energy Astrophysics — mission included technology risks related to development of its mirror modules. NASA and the Japanese space agency, JAXA, were considered possible partners, but even with these two agencies involved the mission would cost ESA 907 million euros and 970 million euros if ESA were to go it alone. Athena would not be ready for launch until 2023.

The NGO — New Gravity-Wave Observatory — mission features a mother and two daughter spacecraft to study gravity waves. The laser links among the three satellites were viewed as a risk, and other elements were viewed as being unproven until the launch of the Lisa Pathfinder, a mission whose technology challenges have already delayed its launch to 2014.

NGO was estimated to cost ESA 1.06 billion euros, with a launch possible no earlier than 2024.

Juice is not without technology risks of its own. The science advisory panel pointed to the high radiation levels it will encounter as one concern, but said radiation-shielding techniques should render this “manageable.”

Another Juice issue concerns its launch weight. The satellite’s current estimated mass is 20 percent below what the Ariane 5 rocket can carry into the required orbit. The advisory panel judged that this was sufficient to conclude that it would remain within the limit even if, as is often the case with science satellites as they move from PowerPoint to the hardware development stage, Juice gains weight.



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Peter B. de Selding was the Paris bureau chief for SpaceNews.