Geology Reference
In-Depth Information
extensions are now evaluated in light of the overall pro-
gram of Solar System exploration.
11.5 Summary
As outlined in Chapter 1 , NASA generally follows the
recommendations of the National Research Council
(NRC, 2011 ) for establishing the priorities in developing
and flying missions. These recommendations place a
high value on the scientist-led missions such as those
proposed through the Discovery and New Frontiers pro-
grams. For example, Discovery missions currently
in ight or soon to be launched include GRAIL to the
Moon, Dawn to the asteroid Vesta, and MAVEN to
Mars. The lower-cost Discovery missions are
own
every 24
36 months and are completely open as to
destination through competition. In contrast, the higher-
cost New Frontiers missions are flown less frequently
and are subject to the priorities identi ed by the NRC.
For the decade 2013 - 2023, priority missions for the New
Frontiers program include sample return from a comet,
sample return from the South Pole
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Figure 11.4. This image of asteroid Vesta was taken by the Dawn
spacecraft in 2011 shortly after orbiting the asteroid. Vesta is about
530 km in diameter and displays a complex geologic history;
differences in albedo among the impact crater ejecta deposits
suggest a heterogeneous composition (NASA PIA14317).
Aiken basin on the
Moon, a Saturn atmospheric probe, a Venus lander, an Io
observer, or a lunar network. However, only one or two
missions are likely to be selected from this set for flight,
by competition among proposals.
The rate and complexity of missions are very much a
function of their costs and the availability of funds.
When the politics of space is also considered, the
result is a great deal of uncertainty regarding which
missions might be sent for future exploration. For exam-
ple, the large-cost, or
-
11.4 Extended missions
When spacecraft projects are approved, they have speci c
scienti c goals and objectives for the primary mission,
which defines the period of operation. Typically, as long
as the spacecraft and all or most of the payload is
functioning, additional funds can be requested for an
extended mission to continue operations. Often, more
than one extension can be obtained, so long as there is
scienticjustication. Part of the rationale is that most of
the costs of space ights are for building the spacecraft
with its payload and for the launch rocket; the cost for
an extended mission is only a small fraction of these
initial expenses. Nonetheless, with numerous missions
in flight, the total cost for extensions can be significant,
with the sum often totaling that for a completely new
mission. Consequently, NASA has established a policy
in which all requests for extended missions are evaluated
together by a panel of senior scientists to determine the
priorities of the requests and to assess the cost
missions of NASA
have Mars sample return to Earth as the highest priority,
followedbyamissiontoexploreJupiter ' s moon Europa.
However, with the poor state of the economy, it is not
clear when these missions might be approved and even-
tually own.
Despite these uncertainties, there is an incredible wealth
of data already returned from missions recently own or
anticipated from spacecraft that are in flight. These data
are waiting to be
“flagship,”
for their scienti c treasures by
current and future planetary scientists, and it is likely that
geosciences will continue to be a hallmark in understand-
ing our Solar System.
mined
bene t
ratios. Thus, what once had been fairly routine
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