Vision and Voyages for Planetary Science in the - Solar System ...

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 Advance Stirling Radioisotope Generators
(ASRGs) for power production, rather than Multi-Mission Radioisotope Thermoelectric
Generators (MMRTGs), reducing 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
sized. 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. While 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 like those other two missions, the Uranus
Orbiter and Probe should be subjected to rigorous independent cost verification throughout its
development, and descoped or canceled if costs grow significantly above the projected $2.7 billion
FY2015.
The fourth and fifth highest priority Flagship missions are, in alphabetical order, the
Enceladus Orbiter and the Venus Climate Mission. The scientific cases for these missions are
presented in Chapters 8 and 5, respectively. In order to maintain an appropriate balance among small,
medium, and large missions, these missions should be considered for the decade 2013-2022 only if
higher-priority Flagship missions cannot be flown for unanticipated reasons, or if additional
funding makes them possible, as noted below. No relative priority is assigned to these two missions;
rather, any choice between them should be made on the basis of programmatic balance. In particular,
because of the broad similarity of its science goals to those of JEO, NASA should consider flying the
Enceladus Orbiter in the decade 2013-2022 only if JEO is not carried out in that decade.
As stressed several times, the costs of the recommended Flagship missions must not be allowed to
grow above the values quoted in this report. Central to accomplishing this is avoiding “requirements
creep”—i.e., the increase in the scope of a mission that sometimes occurs early in its development. The
CATE process that was used to estimate mission costs accounts for unanticipated technical problems, but
it does not account for a lack of discipline that allows a mission to become too ambitious. In order to
preserve programmatic balance, then, the scope of each of the recommended Flagship missions cannot
be permitted to increase significantly beyond what was assumed during the committee’s cost
estimation process.
Example Flight Programs For the Decade 2013-2022
Following the priorities and decision rules outlined above, two example programs of solar system
exploration can be described for the decade 2013-2022 (Table 9.3). These example programs address the
highest priority questions identified by the planetary science community, and their cost realism is based
on Cost and Technical Evaluations conducted in support of the decadal survey. Both assume continued
support of all ongoing flight projects, a Research and Analysis grant program with a 5 percent increase
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