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

Human space exploration is undertaken to serve a variety of national and international interests.
Indeed, the President, Congress, and the American public play a greater role in shaping the humanexploration
agenda than the scientific community. Human exploration can provide important
opportunities to advance science, but science is not the primary motivation. Measurements using remote
sensing across the electromagnetic spectrum, atmospheric measurements, or determinations of particle
flux density are by far best and most economically conducted using robotic spacecraft. But there is an
important subset of planetary exploration that can benefit from human space flight. These are missions to
the surfaces of solid bodies whose surface conditions are not too hostile for humans. For the foreseeable
future, humans can only realistically explore the surfaces of the Moon, Mars, Phobos and Diemos, and
some asteroids (Figure 2.8). The determination of which asteroids might be realistic human exploration
targets will include considerations of gravity, safety, orbit, and richness of scientific return based on
precursor measurements. It is likely that the subset of asteroids that are true potential targets is much
smaller than the observed inventory of NEOs and should be the subject of a separate study. If the
development of a heavy-lift launch vehicle proceeds as planned, the surface of the Moon or a near-earth
asteroid is potentially accessible by humans sometime after 2022, but Mars remains a more distant goal
for human exploration.
Precursor Robotic Missions
If the Apollo experience is an applicable guide, robotic missions to targets of interest will
undoubtedly precede human landings. Human exploration precursor measurement objectives focus
mainly on issues regarding health and safety and engineering practicalities, rather than science. While
there are a number of examples where the interests intersect, for example finding a resource like water,
the motivation and ultimate data applications of the two goals are typically quite different.
A positive example of synergy is the current Lunar Reconnaissance Orbiter mission (Figures 2.7
and 2.8). This project was conceived as a precursor for the human exploration program, but ultimately
was executed in concert with the planetary science community. With one exception, a science peerreview
process was followed for instrument selection. In fall 2010, after the end of the exploration phase
of LRO’s mission, responsibility for the spacecraft was turned over to PSD. Some 23 participating
scientists were added to ensure that top-quality science is executed. By building on lessons learned from
LRO, an effective approach to exploration-driven robotic precursor missions can be constructed.
Despite the positive recent example of LRO, the committee is concerned that, as demonstrated in
the recent past, human spaceflight programs can cannibalize space science programs. The committee
agrees with the statement by the Human Spaceflight Plans Committee report that “it is essential that
budgetary firewalls be built between these two broad categories of activity. Without such a mechanism,
turmoil is assured and program balance endangered.” 9
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