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

• Uranus Orbiter and Probe—This mission consists of a spacecraft that deploys a small
atmospheric probe to make in situ measurements of noble gas abundances and isotopic ratios for an ice
giant atmosphere. The spacecraft then enters into orbit, with the primary science objectives of making
remote sensing measurements of the atmosphere, interior, magnetic field, and rings, as well as multiple
flybys of the larger uranian satellites during the multi-year tour. As described in more detail below,
Uranus was chosen over Neptune because of issues involving technology readiness and the availability of
appropriate spacecraft trajectories.
• Venus Climate Mission—This mission is designed to address science objectives concerning
the Venus atmosphere, including carbon dioxide greenhouse effects, dynamics and variability,
surface/atmosphere exchange, and origin. The mission architecture includes a carrier spacecraft, a
gondola/balloon system, a mini-probe, and two drop sondes. The mini-probe and drop sondes each have
45-minute science missions as they descend to the surface, and the gondola/balloon system carries out a
21-day science campaign as it travels at a ~55 km float altitude.
The Cost and Technical Evaluations performed for these five candidate Flagship missions have
yielded estimates for the full life-cycle cost of each mission as defined above, including the cost of the
launch vehicle, in fiscal year 2015 dollars. For missions with international components (EJSM and
MAX-C) only the NASA costs are included. The cost estimates are as follows:
• Enceladus Orbiter, $1.9 billion
• Jupiter Europa Orbiter, $4.7 billion
• Mars Astrobiology Explorer-Cacher, $3.5 billion 12
• Uranus Orbiter and Probe, $2.7 billion 13
• Venus Climate Mission, $2.4 billion
These costs are substantial, but based on a long history of cost growth for complex planetary
missions, the committee believes them to be realistic. Because of the high costs of Flagship missions and
the associated impact on the rest of the planetary program, the decision rules and cost caps discussed
below are particularly important.
Large-Class Mission Decision Rules
The committee devoted considerable attention to the relative priorities of the various large-class
mission candidates. In particular, both JEO and the Mars Sample-Return campaign (beginning with
MAX-C) were found to have exceptional science merit when considered in light of the communityderived
science goals described in Chapter 3. Because it was difficult to discriminate between Mars
Sample Return and JEO on the basis of their anticipated science return per dollar alone, other factors
came into play. Foremost among these was the need to maintain programmatic balance by assuring that
no one mission takes up too large a fraction of the planetary budget at any given time.
Notably, Mars Sample Return is broken into three separate missions that can be spaced out over
two or even three decades, reducing the per-year costs, and thus making it easier for programmatic
balance to be maintained. In contrast, the inherent costs of getting any payload to 5 AU are substantial,
and examination of JEO showed that breaking it into several smaller missions would not result in
significant costs savings. The costs of JEO therefore must be incurred over a much shorter period of time.
So Mars Sample Return was prioritized above JEO not primarily because of its science merit, but for
pragmatic reasons associated with the required spending profiles.
The highest priority Flagship mission for the decade 2013-2022 is MAX-C, which will begin
the NASA-ESA Mars Sample Return campaign. However, the cost of MAX-C must be constrained
in order to maintain programmatic balance.
PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION
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