A final point regarding MAX-C is that its success depends in part on the success of the MSL EDL system. If that system functions properly in 2012, then a $2.5 billion MAX-C mission should go forward for launch in 2018. If it fails, however, then NASA will have to reconsider the priority and schedule for MAX-C. If the cause of failure can be determined and appropriate and affordable changes can be made in time to preserve a 2018 launch, then MAX-C can continue on schedule. But if uncertainties remain or if the necessary changes cannot be made by 2018, then MAX-C should slip in priority and schedule relative to other large-class missions.

The second-highest-priority flagship mission for the decade 2013-2022 is Jupiter Europa Orbiter. However, as it is currently designed, JEO has a cost that is so high that both a decrease in mission scope and an increase in NASA’s planetary budget are necessary to make it affordable.

The Europa Geophysical Explorer, from which the JEO concept is derived, was the one flagship mission recommended in the 2003 planetary science decadal survey. The scientific case for this mission was compelling then, and it remains compelling now. There is strong evidence that Europa has an ocean of liquid water beneath its icy crust. Because of this ocean’s potential suitability for life, Europa is one of the most important targets in all of planetary science. As its name implies, JEO will also accomplish other important science in the Jupiter system, including studies of other moons and of the planet itself. Like MAX-C, JEO directly addresses all three of the crosscutting themes of Chapter 3 and is, in particular, central to the theme of planetary habitats. Substantial technology work has been done on JEO over the past decade, with the result that NASA is much more capable of accomplishing this mission than was the case 10 years ago.

The difficulty in achieving JEO is its cost. The projected cost of the mission as currently designed is $4.7 billion FY2015. If JEO were to be funded at this level within the currently projected NASA planetary budget, it would lead to an unacceptable programmatic imbalance, eliminating too many other important missions. Therefore, while the committee recommends JEO as the second-highest-priority flagship mission, close behind MAX-C, JEO should fly in the decade 2013-2022 only if changes to both the mission and the NASA planetary budget make it affordable without eliminating any other recommended missions. These changes are likely to involve both a reduction in mission scope and a formal budgetary new start for JEO that is accompanied by an increase in the NASA planetary budget.

It is clearly crucial to keep as small as possible the budget increase required to enable JEO. Because of the maturity of the current JEO mission concept, the committee did not attempt to redesign the mission for lower cost. However, such a redesign is essential for this important mission to be viable. Possible pathways to lower cost include use of a larger launch vehicle that would reduce cost risk by shortening and simplifying the mission design, and a significant reduction in the science payload. Other possible descopes were listed in section 4.1.5 of the 2008 JEO mission study final report.19NASA should immediately undertake an effort to find major cost reductions for JEO, with the goal of minimizing the size of the budget increase necessary to enable the mission. As noted below, the committee also recommends that JEO switch to Advanced Stirling Radioisotope Generators for power production, rather than using Multi-Mission Radioisotope Thermoelectric Generators, to reduce the amount of plutonium-238 necessary to carry out the mission.

The third-highest-priority flagship mission is the Uranus Orbiter and Probe mission. Galileo, Cassini, and Juno have performed or will perform spectacular in-depth investigations of Jupiter and Saturn. The Kepler mission and microlensing surveys have shown that many exoplanets are ice-giant size. Exploration of the ice giants Uranus and Neptune is therefore the obvious and important next step in the exploration of the giant planets. A mission to one of these planets addresses all three of the crosscutting themes in Chapter 3. These planets are fundamentally different from Jupiter and Saturn, and a comprehensive mission to study one of them offers enormous potential for new discoveries.

The committee carefully investigated missions to both Uranus and Neptune. Although both missions have high scientific merit, the conclusion was that a Uranus mission is favored for the decade 2013-2022 for practical reasons. These reasons include the lack of optimal trajectories to Neptune in that time period, long flight times incompatible with the use of Advanced Stirling Radioisotope Generators for spacecraft power, the risks associated with aerocapture at Neptune, and the high cost of delivery to Neptune. Because of its outstanding scientific potential and a projected cost that is well matched to its anticipated science return, the Uranus Orbiter and Probe mission should be initiated in the decade 2013-2022 even if both MAX-C and JEO take place. But

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