Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 257
9
Recommended Flight Investigations: 2013-2022
CRITERIA FOR JUDGING MISSION AND RELATED PRIORITIES
The statement of task for this study (Appendix A) called for creation of a prioritized list of flight investiga-
tions for the decade 2013-2022. This chapter addresses that request. A prioritized list implies that the elements
of the list have been judged and ordered with respect to a set of appropriate criteria. Four criteria were used. The
first and most important was science return per dollar invested. Science return was judged with respect to the key
science questions described in Chapter 3; costs were estimated via a procedure described below. The second was
programmatic balance—striving to achieve an appropriate balance among mission targets across the solar system
and an appropriate mix of small, medium, and large missions. The other two criteria were technological readiness
and availability of trajectory opportunities within the 2013-2022 time period.
The recommendations in this chapter are also informed by the key findings and recommendations included
in Chapters 4 through 8. These are summarized in Table 9.1.
UNDERLYING PROGRAMMATIC REQUIREMENTS
The individual flight projects for the coming decade must be considered within the context of the broader
program of planetary exploration. The goal is to develop a fully integrated strategy of flight projects, technology
development, and supporting research that maximizes the value of scientific knowledge gained over the decade.
All of the recommendations in this chapter are made under the assumption that the following basic programmatic
requirements are fully funded:
• Continue missions currently in flight, subject to approval obtained through the appropriate senior review
process. These missions include the Cassini mission to the Saturn system, several ongoing Mars missions, the New
Horizons mission to Pluto, ongoing Discovery missions, and others. Ensure a level of funding that is adequate for
successful operation, analysis of data, and publication of the results of these missions, and for extended missions
that afford rich new science return.
• Continue missions currently in development. These include the GRAIL Discovery mission, the Juno New
Frontiers mission, and the Mars Science Laboratory (MSL) and MAVEN missions to Mars.
• Increase funding for fundamental research and analysis grant programs, beginning with a 5 percent increase
above the total finally approved fiscal year (FY) 2011 expenditures and then growing at an additional 1.5 percent
257
OCR for page 258
258 VISION AND VOYAGES FOR PLANETARY SCIENCE
TABLE 9.1 Key Findings and Recommendations from Chapters 4 Through 8
Chapter 4
The Primitive Chapter 5 Chapter 6 Chapter 7 Chapter 8
Bodies The Inner Planets Mars The Giant Planets Satellites
Flagship Not proposed; use Top and only Initiate the Mars Top and only priority Continue Cassini
missions limited resources to priority is the Sample Return for a new flagship mission.
initiate technology Venus Climate campaign. mission is the Uranus
program to ensure Mission. Orbiter and Probe. Highest-priority new
that cryogenic First and highest- missions in priority
comet sample priority element is Jupiter Europa Orbiter order:
return can be Mars Astrobiology should: 1. Jupiter Europa
carried out in the Explorer-Cacher. —Maintain Jupiter Orbiter component of
2020s. system science as Europa Jupiter System
high priority Mission (EJSM)
—Designate Jupiter 2. Titan flagship
system science as mission
top-ranked priority 3. Enceladus Orbiter.
during approach and
early tour phases
—Incorporate Jupiter
system science
specific needs into
jovian tour design.
New Raise the cost cap. Regular cadence is Neither Mars Current cost cap is Io Observer is a
Frontiers highly desirable. Geophysical insufficient to permit higher priority than
missions Goals in priority Network nor Mars many of the highest- Ganymede Orbiter.
order: Goals in priority Polar Climate interest missions.
1. Comet Surface order: missions is
Sample Return 1. Venus In Situ recommended at Only possible current
2. Trojan Tour and Explorer this time. mission is Saturn
Rendezvous. 2. South Pole- Probe.
Aitken Basin
Sample Return
3. Lunar
Geophysical
Network.
Discovery Ensure an Ensure a regular Small spacecraft Allow proposals —
missions appropriate cadence cadence of missions can for targeted and
of future Discovery future Discovery make important facility-class orbital
missions. missions. contributions to the space telescopes in
study of Mars. Discovery program.
International — Continue support MSR could proceed — Encourage continued
cooperation via participating as a NASA- collaboration between
scientist programs only program, NASA, ESA, and
and Missions of but international JAXA to enable the
Opportunity. collaboration is implementation of all
needed to make three components of
real progress; Mars EJSM.
Trace Gas Orbiter is
an appropriate start.
OCR for page 259
259
RECOMMENDED FLIGHT INVESTIGATIONS: 2013-2022
per year above inflation for the remainder of the decade (Chapter 10). This increase will make it possible to reap
the full scientific benefits of ongoing and future flight projects.
• Establish and maintain a significant and steady level of funding (6 to 8 percent of the NASA planetary
budget) for development of technologies that will enable future planetary flight projects.
• Continue to support and upgrade the technical expertise and infrastructure in implementing organizations
that support solar system exploration missions.
• Continue to convey the results of planetary exploration to the general public via a robust program of educa-
tion and public outreach.
MISSIONS RECOMMENDED PREVIOUSLY AND COST CONSIDERATIONS
The 2003 planetary science decadal survey recommended a total of nine missions: 1
• The Europa Geophysical Explorer, which was the highest-priority flagship-class mission recommended in
the report;
• Five candidate New Frontiers missions—Kuiper Belt-Pluto Explorer, South Pole-Aitken Basin Sample
Return, Jupiter Polar Orbiter with Probes, Venus In Situ Explorer, and Comet Surface Sample Return; and
• Three Mars missions—Mars Science Laboratory, Mars Upper Atmosphere Orbiter, and Mars Long-Lived
Lander Network.
Mars Sample Return was regarded by the 2003 decadal survey as an important mission for the decade 2013-
2022, and technology development for the mission was recommended for the decade covered by that survey.
A subsequent National Research Council (NRC) report expanded the list of potential New Frontiers missions
to include Network Science, Trojan/Centaur Reconnaissance, Asteroid Rover/Sample Return, Io Observer, and
Ganymede Observer.2
Of the missions recommended in the 2003 decadal survey, Kuiper Belt-Pluto Explorer has been implemented
with the first New Frontiers mission, New Horizons, launched in 2005. The second New Frontiers mission, Juno,
scheduled for launch in 2011, will accomplish most of the goals of the Jupiter Polar Orbiter with Probes mission,
albeit without the probes. The MSL has been built and is scheduled for a 2011 launch; as built it is significantly
more ambitious and costly than the MSL mission described in the 2003 decadal survey report. The MAVEN Mars
Scout mission addresses the objectives of the Mars Upper Atmosphere Orbiter. Missions responsive to the science
goals of the South Pole-Aitken Basin Sample Return, the Venus In Situ Explorer, and the Asteroid Rover/Sample
Return are now in competition for selection as the third New Frontiers mission. 3
For the current decadal survey, only missions that already had a new start (i.e., the president’s budget requested
funding for them, the Congress approved this request, and the president signed the budget bill) were assumed a
priori to be part of NASA’s plan. All other missions were evaluated on an equal basis to one another. In contrast
to the 2003 decadal survey, Mars missions were considered on an equal basis with all other planetary missions.
This decadal survey places considerable emphasis on cost realism. Although NASA has been responsive to
the priorities set out in the 2003 decadal survey, the planetary program has been plagued by overly optimistic
assumptions about mission costs. Planetary science is not unique in this regard; optimism in the face of techni-
cal challenges is common to many costly endeavors.4 Nevertheless, the result has been that far fewer missions
have flown than were recommended. Noteworthy examples include the cost growth of the MSL, the periods of
reduced tempo of Discovery missions, and the fact that neither of the very high priority missions to orbit Europa
and return samples from Mars has yet been initiated. To achieve greater cost realism, this decadal survey has
relied heavily on detailed mission studies and cost estimates derived using a methodology specifically designed
to quantify technical, schedule, and cost risks inherent in assessing concepts with differing degrees of technical
maturity (see Appendix C).
OCR for page 260
260 VISION AND VOYAGES FOR PLANETARY SCIENCE
MISSION STUDY PROCESS AND COST AND TECHNICAL EVALUATION
In the course of this decadal survey, the committee commissioned technical studies of many candidate mis-
sions (Appendix G) selected for study on the basis of white papers submitted by the scientific community and
recommendations made by the survey committee’s five panels. Each study was led by one or more “science
advocates” selected by each panel from among its members on the basis of their expertise to represent the panel’s
science interests. Conducted by the Jet Propulsion Laboratory, the Applied Physics Laboratory, Goddard Space
Flight Center, or Marshall Space Flight Center, the studies were funded by and transmitted to NASA, which then
delivered them to the decadal survey committee. Although NASA was aware of the contents of the studies, it was
not involved in directing the studies themselves or in their prioritization by the decadal survey.
Using the four prioritization criteria listed above, the committee then selected a subset of the mission studies
for further cost and technical evaluation (CATE) analysis by the Aerospace Corporation, a contractor to the NRC.
The CATE analysis was designed to provide an independent assessment of the technical feasibility of the mission
candidates, as well as to produce a rough estimate of their costs. Because it takes into account many factors
when evaluating a mission’s potential costs, including the actual costs of analogous previous missions, the CATE
analysis reflects cost impacts that may be beyond the control of project managers and principal investigators.
It includes a probabilistic model of cost growth tied to technical and schedule risks, and hence projects cost
growth resulting from insufficient technical maturity identified as part of the technical evaluation. Following
NASA policy, costs were estimated at the 70 percent confidence level. Appendix C discusses the CATE analysis
in more detail.
The CATE analysis typically returned cost estimates that were significantly higher than the estimates produced
by the study teams, primarily because CATE estimates are based on the actual costs of analogous past projects
and thus avoid the optimism inherent in other cost estimation processes. Only the independently generated CATE
cost estimates were used by the committee in evaluating the candidate missions and in formulating its final rec-
ommendations. This intentionally cautious approach was designed to help prevent the unrealistic cost estimates
and consequent replanning that have sometimes characterized the planetary program in the past. In the sections
below, the committee presents a recommended plan reflecting these conservative cost estimates and also offers
recommendations for what could be added to the plan if the estimates prove to be too conservative.
The committee emphasizes that the studies carried out were of specific “point designs” for the mission can-
didates identified by the committee’s panels. These point designs are a “proof of concept” that such a mission
may be feasible, and they provide a basis for developing a cost estimate for the purpose of the decadal survey.
The actual missions as flown may differ in their detailed designs and their final costs from what was studied, but
in order to maintain a balanced and orderly program, the missions’ final costs must not be allowed to grow
significantly beyond those estimated here. This fact is one of many reasons that a cautious approach to cost
estimation is appropriate. The sections below also make specific recommendations for steps that should be taken
if the projected costs of certain missions grow beyond expected bounds.
DEFINITION OF MISSION COST CLASSES
The committee’s statement of task divides NASA’s planetary missions into three distinct cost classes: small
missions costing less than $450 million current-year dollars, medium missions costing between $450 million and
$900 million, and large missions costing more than $900 million current-year dollars. The first cost class corre-
sponds to the Discovery and Mars Scout programs, the second to the New Frontiers program, and the third to the
so-called flagship missions. According to the statement of task, it is within the committee’s purview to recommend
changes to the classes, including their cost ranges.
As discussed in some detail below, the Discovery program remains vibrant and highly valuable, allowing the
science community to propose a diverse range of low-cost missions with short development times and focused
science objectives.
The New Frontiers program fills the middle ground between the small and relatively inexpensive Discovery
missions and the much larger and more costly flagship missions. Inspired by the success of the Discovery program,
OCR for page 261
261
RECOMMENDED FLIGHT INVESTIGATIONS: 2013-2022
New Frontiers missions are also selected in a competitive process and led by a principal investigator (PI). In con-
trast to those for the Discovery program, solicitations for New Frontiers are more strategic, restricting proposals
to a small number of specific mission goals. New Frontiers missions address focused science goals that cannot be
implemented within the Discovery cost cap but that do not require the resources of a flagship mission.
More expensive than the New Frontiers cost cap, flagship missions can cost up to several billion dollars.
Strategic in nature and designed to address a wide range of important science objectives at high-priority targets,
flagship missions often involve multi-agency and international cooperation. Because of their scientific breadth
and high cost they are not PI-led, but they typically carry a large and sophisticated payload of instruments headed
in large part by individual PIs. Some also carry so-called facility instruments that typically are provided by the
institution that builds the spacecraft. Despite their high costs, flagship missions consistently deliver high science
return per dollar invested.
BALANCE AMONG MISSION COST CLASSES
The issue of finding the optimum balance among small, medium, and large missions has been addressed in a
recent NRC study.5 The report of a subsequent NRC workshop touched on balance in the context of the decadal
survey process: “[The discussion] reinforced the concept of the decadal survey as a strategic package. That is,
decadal studies need to provide the best balance of scientific priorities and prioritized missions.” 6
The challenge is to assemble a portfolio of missions that achieves a regular tempo of solar system exploration
and a level of investigation appropriate for each target object. For example, a program consisting of only flagship
missions once per decade may result in long stretches of relatively little new data being generated, leading to a
stagnant planetary science community. Conversely, a portfolio of only Discovery-class missions would be incapable
of addressing important scientific challenges such as in-depth exploration of the outer planets.
Mission classes are differentiated not only by their costs but also by the timescale of their execution, span
of technology, and involvement of the scientific community. Flagship missions like Viking, Galileo, and Cassini
ordinarily have a ~10-year development cycle. They require very capable launch vehicles and involve large teams
of investigators and a complex of supporting institutions. Each flagship mission is unique in terms of its science
objectives and frequently also in terms of the spacecraft used, and so each is often a new development with little
use of heritage hardware.
New Frontiers missions, while still complex and challenging, can be executed on timescales of significantly
less than a decade. These missions have less extensive, more focused science objectives than do flagship missions
and typically take advantage of technological developments from recent prior missions. The institutional arrange-
ments are less complex and the launch vehicle requirements less demanding.
Discovery missions can respond rapidly to new discoveries and changes in scientific priorities. Rapid (~3-year)
mission development is feasible, providing opportunities for student participation, rapid infusion and demonstra-
tion of technology, and a rapid cadence of missions pursuing science goals. These missions are executable using
relatively small launch vehicles.
In studying any given object, there is a natural progression of mission types, from flyby to orbital investigation
to in situ exploration to sample return. The missions early in this progression are generally simpler and less costly
than the later ones. Because the long-term goals of planetary science involve thorough study of many objects, a
balanced portfolio may thus contain a variety of mission categories, depending on the level of investigation con-
ducted previously.
The 2006 NRC report mentioned above developed criteria by which a scientific program might be assessed. 7
Although written almost 5 years ago, the criteria, slightly rephrased, are still relevant to the current decadal
survey’s goals:
• Capacity to make steady progress—Does the proposed program make reasonable progress toward the sci-
ence goals set forth in the decadal survey? Are the cadence of missions and the planning process such that new
scientific discoveries can be followed up rapidly with new missions, such as small missions in the Discovery
program? Does the program smoothly match and complement programs initiated by prior decadal surveys?
OCR for page 262
262 VISION AND VOYAGES FOR PLANETARY SCIENCE
• Stability—Can one construct an orderly sequence of missions, meeting overarching science goals, develop-
ing advanced technology, nurturing an appropriately sized research and technical community, and providing for
appropriate interactions with the international community? Is the program stable under the inevitable budgetary
perturbations as well as the occasional mission failures?
• Balance—Is the program structured to contain a mix of small, medium, and large missions that together
make the maximum progress toward the science goals envisioned by this decadal survey? Can some of the science
objectives be reached or approached with missions of opportunity and by means of piggyback or secondary flights
of experiments on other NASA missions?
• Robustness—Is the program robust in that it provides opportunities for the training and development of the
next generation of planetary scientists? Is it robust in that it lays the technological foundation for a period longer
than the present decade?
The four criteria cited above are not orthogonal. “Balance” in various guises permeates the other three criteria.
For example, a balanced portfolio of missions enhances overall program stability; a balanced portfolio of mis-
sions provides better assurance of a continuing stream of visible results. A balanced portfolio also helps prevent
large fluctuations in demands for workforce and in cost, therefore fitting more easily into the relatively smooth
year-to-year NASA budget.
Several factors can upset balance across mission types. Foremost among these are a lack of control and a lack
of predictability of mission costs. A 30 percent overrun in the cost of a mission priced at several billion dollars
can distort the entire program of planetary science recommended in a given decadal survey. 8 Or, as stated in stark
language in the NRC report An Assessment of Balance in NASA’s Science Programs, “The major missions in space
and Earth science are being executed at costs well in excess of the costs estimated at the time when the missions
were recommended in the NRC’s decadal surveys for their disciplines. Consequently, the orderly planning process
that has served the space and Earth science communities well has been disrupted, and the balance among large,
medium, and small missions has been difficult to maintain.”9 That report continues with the recommendation that
NASA should undertake independent, comprehensive and systematic evaluations of the costs to complete each of
its space and Earth science missions for the purpose of determining adequacy of budget and schedule.
NASA’s suite of planetary missions for the decade 2013-2022 should consist of a balanced mix of Dis-
covery, New Frontiers, and flagship missions, enabling both a steady stream of new discoveries and the
capability to address larger challenges such as sample return missions and outer planet exploration. The
program recommended below was designed to achieve an appropriate balance. To prevent the balance among mis-
sion classes from becoming skewed, it is crucial that all missions, particularly the most costly ones, be initiated
with a good understanding of their probable costs. The CATE process used in this decadal survey was designed
specifically to address this issue by taking a realistic approach to cost estimation.
The cost containment record of missions selected through Announcements of Opportunity (AOs) is relatively
commendable, with a few notable exceptions of underestimation of mission complexity or other factors. The com-
mittee endorses a recent NRC report’s recommendations that NASA undertake the following actions: 10
• Ensure that there are adequate levels of project funds for risk reduction and improved cost estimation prior
to final selection; and
• Develop a comprehensive, integrated strategy to control cost and schedule growth and enable more frequent
science opportunities.
SMALL MISSIONS
Within the category of small missions are three elements of particular interest: the Discovery program,
extended missions for ongoing projects, and Missions of Opportunity.
OCR for page 263
263
RECOMMENDED FLIGHT INVESTIGATIONS: 2013-2022
The Discovery Program
The Discovery program was initiated in 1992 as a way to ensure frequent access to space for planetary sci-
ence investigations through competed PI-led missions. The low cost and short development times of Discovery
missions provide flexibility to address new scientific discoveries on a timescale of significantly less than 10 years.
The Discovery program is therefore outside the bounds of a decadal strategic plan, and this decadal survey makes
no recommendations for specific Discovery flight missions. The committee stresses, however, that the Discovery
program has made important and fundamental contributions to planetary exploration and can continue to
do so in the coming decade. The committee gives the Discovery program its strong support.
Chapters 4 through 8 provide examples of the rich array of science that can be addressed with future Discovery
missions. At Mercury, orbital missions complementary to MESSENGER could characterize high-latitude, radar-
reflective deposits of volatiles, map the mineralogy of the surface, characterize the atmosphere and the magneto-
sphere, and precisely determine the long-term rotational state. At Venus, platforms including orbiters, balloons,
and probes could be used to study the chemistry and dynamics of the lower atmosphere; surface geochemistry and
topography; and current and past surface and interior processes. The proximity of the Moon makes it an ideal target
for future Discovery missions using both orbital and landed platforms, building on the rich scientific findings of
recent lunar missions, and the planned GRAIL and Lunar Atmosphere and Dust Environment Explorer missions.
Potential Discovery missions to Mars include a 1-node geophysical pathfinder station, a polar science orbiter,
a dual spacecraft atmosphere-sounding and/or gravity mission, a mission to collect samples of the atmosphere and
return them to Earth, a Phobos/Deimos surface exploration mission, and an in situ aerial mission to explore the
region of the martian atmosphere not easily accessible from orbit or from the surface. The committee notes that
NASA does not intend to continue the Mars Scout program beyond the MAVEN mission, nor does the commit-
tee recommend that NASA do otherwise. Instead, the committee recommends that NASA continue to allow
proposals for Discovery missions to all planetary bodies, including Mars.
Investigations of primitive bodies are ideally suited for Discovery missions. The vast number and diversity of
asteroids and comets provide opportunities to benefit from frequent launches. The proximity of some targets allows
missions that can be implemented within the context of the Discovery program. Near the limit of the Discovery
cost cap, it may be possible to collect and return samples from near-Earth objects (NEOs). The diversity of targets
means that proven technologies may be reflown to new targets, reducing mission risk and cost. And the population
of scientifically compelling targets is not static, but rather is continually increasing as a consequence of discoveries
in the supporting research and analysis programs.
Because there is still so much compelling science that can be addressed by Discovery missions, the committee
recommends continuation of the Discovery program at its current level, adjusted for inflation, with a cost
cap per mission that is also adjusted for inflation from the current value (i.e., to about $500 million FY2015).
The committee does note that NASA has increased the size and number of external project reviews for
Discovery missions to the point that some reviews are counterproductive and disruptive. The committee endorses
the recommendation in a recent NRC report that NASA should reassess its approach to external project reviews
to ensure that:11
• The value added by each review outweighs the cost (in time and resources) that it places on projects;
• The number and the size of reviews are appropriate given the size of the project; and
• Major reviews, such as preliminary design review and critical design review, occur only when specified
success criteria are likely to be met.
Program Tempo
Discovery AOs were released in 1994, 1996, 1998, 2000, 2004, 2006, and 2010. The selected missions are
listed in Table 9.2. Because Discovery missions are so important for planetary exploration, and so that the com-
munity can plan them effectively, the committee recommends a regular, predictable, and preferably rapid
(≤24-month) cadence for Discovery AO releases and mission selections. Because so many important missions
OCR for page 264
264 VISION AND VOYAGES FOR PLANETARY SCIENCE
TABLE 9.2 Discovery Program Mission Selections to Date
Year of AO Mission Selected Launch Date Description
n/a Near-Earth Asteroid February 17, 1996 Asteroid orbiter and rendezvous
Rendezvous/Shoemaker
n/a Mars Pathfinder December 4, 1996 Mars lander and Sojourner rover
1994 Lunar Prospector January 6, 1998 Lunar orbiter
1994 Stardust February 7, 1999 Comet coma sample return
1996 Genesis August 8, 2001 Solar wind sample return
1996 CONTOUR July 3, 2002 Flyby of two comet nuclei (lost contact 6 weeks after launch)
1998 MESSENGER August 3, 2004 Mercury orbiter
1998 Deep Impact January 12, 2005 Comet impactor and flyby
2000 Dawn September 27, 2007 Orbit of two main-belt asteroids, Vesta and Ceres
2000 Kepler March 6, 2009 Telescope for the detection of extrasolar planets via transit technique
2004 No selection
2006 GRAIL Expected 2011 Twin lunar orbiters for gravity mapping
determineda
2010 To be To be determined To be determined
a
On May 5, 2011, following the completion of this report, NASA announced that the candidates for the next Discovery mission are as fol-
lows: the [Mars] Geophysical Monitoring Station, Titan Mare Explorer, and the Comet Hopper. A final selection will be made in 2012. Launch
is expected in 2016.
can be flown within the current Discovery cost cap (adjusted for inflation), the committee views a steady tempo
of Discovery AOs and selections to be more important than increasing the cost cap, as long as launch vehicle costs
continue to be excluded.
The committee notes with some concern the increase in time between AO release and mission launch as
indicated in Table 9.2. Beginning with Lunar Prospector and continuing through Kepler, the interval from selec-
tion to launch for Discovery missions grew steadily from 4 to 9 years. (The expected launch of GRAIL in 2011
would be an exception to this trend.) A hallmark of the Discovery program has been rapid and frequent mission
opportunities. The committee urges NASA to assess schedule risks carefully during mission selection, and to plan
program budgeting so as to maintain the original goals of the Discovery program.
Additional AO Opportunities
New knowledge regarding solar system objects has come increasingly from a combination of ground- and space-
based telescopic platforms. However, there currently is no explicitly defined program in NASA planetary science
that provides for proposals for an orbital mission for observation of solar system objects. Although the Discovery
program AO issued in 2010 allows missions to “target” any body in the solar system, except the Sun and Earth, it is
silent on the meaning of the verb “target.” Based on presentations to the committee’s panels, it appears that a highly
capable planetary space telescope in Earth orbit could be accomplished as a Discovery mission. Such a mission
could be particularly valuable for observations of the giant planets and their satellites. The committee recommends
that future Discovery Announcements of Opportunity allow proposals for space-based telescopes, and that
planetary science from space-based telescopes be listed as one of the goals of the Discovery program.
Extended Missions for Ongoing Projects
Mission extensions can be significant and highly productive, and may also enhance missions that undergo
changes in scope because of unpredictable events or opportunities. The Cassini and Mars Exploration Rover
OCR for page 265
265
RECOMMENDED FLIGHT INVESTIGATIONS: 2013-2022
extensions are examples of the former, and the “re-purposing” of missions such as Stardust (NExT) and Deep
Impact (EPOXI) are examples of the latter. In some cases, particularly the re-purposing of operating spacecraft,
fundamentally new science can be enabled. These mission extensions, which require their own funding arrange-
ments, can be treated as independent, small-class missions. The committee supports NASA’s current senior review
process for deciding the scientific merits of a proposed mission extension. The committee recommends that early
planning be done to provide adequate funding of mission extensions, particularly for flagship missions and
missions with international partners.
Missions of Opportunity
Near the end of the past decade, NASA introduced a new acquisition vehicle called Stand Alone Missions of
Opportunity (SALMON). This umbrella announcement allows for five different types of Missions of Opportunity:
1. Investigations involving participation in non-NASA space missions through provision of a critical compo -
nent of the mission, such as a science instrument, technology demonstrations, hardware components, microgravity
research experiments, or expertise in critical areas of the mission;
2. Missions with a participating U.S. co-investigator (non-hardware) selected for a science or technology
experiment to be built and flown by an agency other than NASA;
3. Investigations that propose a new scientific use of existing NASA spacecraft;
4. Small complete missions that enable realization of science or technology investigations within the specified
cost cap; and
5. Focused investigations that address a specific, NASA-identified flight opportunity, a SALMON type under
which the U.S.-provided instruments for the 2016 Mars Trace Gas Orbiter were recently acquired.
In addition to their science return, Missions of Opportunity provide a chance for new entrants to join the
field, for technologies to be validated, and for future PIs to gain experience. The success of this program will
depend on a process that emphasizes flexibility and agility. The committee welcomes the introduction of the
highly flexible SALMON approach and recommends that it be used wherever possible to facilitate Mission
of Opportunity collaborations.
Mars Trace Gas Orbiter
An important special case of a small mission is the proposed joint European Space Agency (ESA)-NASA
Mars Trace Gas Orbiter. A Mars orbiter to study the concentrations, temporal variations, sources, and sinks of
atmospheric trace gases, particularly methane, is identified in Chapter 6 of this report as having a high scientific
priority. The mission would launch in 2016, with NASA providing the launch vehicle, ESA providing the orbiter,
and both agencies providing a joint science payload that was recently selected. Based on the mission’s high science
value and its relatively low cost to NASA, the committee supports flight of the Mars Trace Gas Orbiter in
2016 as long as the division of responsibilities with ESA outlined above is preserved. Holding to the 2016
launch schedule is important, because failure to do so could significantly affect other missions, particularly
to Mars, that are recommended below. As discussed in greater detail below, the Mars Trace Gas Orbiter is
intended to be part of a long-term NASA-ESA collaboration on the exploration of Mars.
PRIORITIZED MEDIUM- AND LARGE-CLASS FLIGHT MISSIONS: 2013-2022
Optimum Balance Across the Solar System
As described above, NASA’s program of planetary exploration should have an appropriate balance among
small, medium, and large missions. It is also important that there be an appropriate balance among the many poten-
tial targets in the solar system. Achieving this balance was one of the key factors informing the recommendations
OCR for page 266
266 VISION AND VOYAGES FOR PLANETARY SCIENCE
for medium and large missions presented below. The committee notes, however, that there should be no entitlement
in a publicly funded program of scientific exploration. Achieving balance must not be used as an excuse for failing
to make difficult but necessary choices.
The issues of balance across the solar system and balance among mission sizes are related. For example, it is
difficult to investigate targets in the outer solar system with small or even medium missions. Some targets, how-
ever, are ideally suited to small missions. The committee’s recommendations below reflect this fact and implicitly
assume that Discovery missions will address important questions whose exploration does not require the capacity
provided by medium or large missions.
It is not appropriate to achieve balance simply by allocating certain numbers or certain sizes of missions to
certain classes of objects. Instead, a scientifically appropriate balance of solar system exploration activities
must be found by selecting the set of missions that best addresses the highest priorities among the overarch-
ing science questions in Chapter 3. The recommendations below are made in accordance with this principle.
Medium-Class Missions
The current New Frontiers cost cap, inflated to FY2015 dollars, is $1.05 billion, including launch vehicle costs.
The committee recommends changing the New Frontiers cost cap to $1.0 billion FY2015, excluding launch
vehicle costs. This change represents a modest increase in the total cost of a New Frontiers mission provided that
the cost of launch vehicles does not rise precipitously; the increase is fully accounted for in the program recom-
mendations below.12 As shown below, this change will allow a scientifically rich and diverse set of New Frontiers
missions to be carried out. Importantly, it will also help protect the science content of the New Frontiers program
against increases and volatility in launch vehicle costs. Use of technologies like low-thrust propulsion that reduce
requirements for launch vehicle performance (and thereby cost) should be given credit in the proposal evaluation
process.
High-Priority Medium-Class Mission Candidates
The New Frontiers program to date has resulted in the selection of the New Horizons mission to Pluto (now
in flight) and the Juno mission to Jupiter (in development). A competition to select a third New Frontiers mission
is now underway, with selection scheduled for 2011.13 In this report the committee addresses subsequent New
Frontiers missions, beginning with the fourth, to be selected during the decade 2013-2022.
The committee’s statement of task (Appendix A) calls for a list of specific mission objectives for New Frontiers
missions. On the basis of their science value and projected costs, the committee identified seven candidate New
Frontiers missions for the decade 2013-2022. All of these missions address broad and important questions in plan-
etary science and have been judged to have high science merit when considered in light of the community-derived
science priorities described in Chapter 3. All are also judged to be plausibly achievable within the recommended
New Frontiers cost cap (although, for some, not within the previous cap). 14 In alphabetical order, the seven can-
didate New Frontiers missions recommended by the committee are as follows:
• Comet Surface Sample Return—The objective of this mission is to acquire and return to Earth a macro-
scopic sample from the surface of a comet nucleus using a sampling technique that preserves organic material in
the sample. The mission would also use additional instrumentation on the spacecraft to determine the geologic and
geomorphologic context of the sampled region. Because of the increasingly blurred distinction between comets
and the most primitive asteroids, many important objectives of an asteroid sample return mission could also be
accomplished by this mission.
• Io Observer—The focus of this mission is to determine the internal structure of Io and to investigate
the mechanisms that contribute to the satellite’s intense volcanic activity. The spacecraft would go into a highly
elliptical orbit around Jupiter, making multiple flybys of Io. Specific science objectives would include characteriza-
tion of surface geology and heat flow, as well as determination of the composition of erupted materials and study
of their interactions with the jovian magnetosphere.
OCR for page 267
267
RECOMMENDED FLIGHT INVESTIGATIONS: 2013-2022
• Lunar Geophysical Network—This mission consists of several identical landers distributed across the lunar
surface, each carrying instrumentation for geophysical studies. The primary science objectives of this mission
are to characterize the Moon’s internal structure, seismic activity, global heat flow budget, bulk composition, and
magnetic field. The mission’s duration would be several years, allowing detailed study of lunar seismic activity
and internal structure.
• Lunar South Pole-Aitken Basin Sample Return—The primary science objective of this mission is to return
samples from this ancient and deeply excavated impact basin to Earth for characterization and study. In addition
to returning at least 1 kg of samples, this mission would also document the geologic context of the landing site
with high-resolution and multispectral surface imaging.
• Saturn Probe—This mission is intended to determine the structure of Saturn’s atmosphere as well as abun-
dances of noble gases and isotopic ratios of hydrogen, carbon, nitrogen, and oxygen. The flight system consists of
a carrier-relay spacecraft and a probe to be deployed into Saturn’s atmosphere. The probe would make continuous
in situ measurements of Saturn’s atmosphere as it descends ~250 km from its initial entry point and relays mea-
surement data to the carrier spacecraft.
• Trojan Tour and Rendezvous—This mission is designed to examine two or more small bodies sharing the
orbit of Jupiter, including one or more flybys followed by an extended rendezvous with a Trojan object. Primary
science objectives for this mission include characterization of the bulk composition, interior structure, and near-
surface volatiles.
• Venus In Situ Explorer—The primary science objectives of this mission are to examine the physics and
chemistry of Venus’s atmosphere and crust. This mission would attempt to characterize variables that cannot be
measured from orbit, including the detailed composition of the lower atmosphere and the elemental and mineralogic
composition of surface materials. The mission architecture consists of a lander that would acquire atmospheric
measurements during descent and then carry out a brief period of remote sensing and in situ measurements on the
planet’s surface.
The current competition to select the third New Frontiers mission includes the SAGE mission to Venus and
the MoonRise mission to the Moon. These missions are responsive to the science objectives of the Venus In Situ
Explorer and the Lunar South Pole-Aitken Basin Sample Return, respectively. The committee assumes that the
ongoing NASA evaluation of these two missions has validated their ability to be performed at a cost appropriate
for New Frontiers. For the other five listed above, the CATE analyses performed in support of this decadal survey
have shown that it may be possible to execute them within the New Frontiers cost cap (see Appendix C).
The committee’s list of recommended New Frontiers mission candidates differs somewhat from that in the
most recent NRC report on New Frontiers.15 One mission has been added (Saturn Probe), two have been removed
(Asteroid Rover/Sample Return and Ganymede Observer), and one has been narrowed in focus (Network Science).
These changes are a result of the committee’s application of the selection criteria listed at the beginning of this
chapter, and they reflect changes in scientific knowledge and programmatic realities since the time of the 2008
report.
Medium-Class Mission Decision Rules
To achieve an appropriate balance among small, medium, and large missions, NASA should select two
New Frontiers missions in the decade 2013-2022. These are referred to below as New Frontiers Mission 4 and
New Frontiers Mission 5.
Because preparation and evaluation of New Frontiers proposals places a substantial burden on the community
and NASA, it is important to restrict each New Frontiers solicitation to a manageable number of candidate mis-
sions. New Frontiers Mission 4 should be selected from among the following five candidates:
• Comet Surface Sample Return,
• Lunar South Pole-Aitken Basin Sample Return,
• Saturn Probe,
OCR for page 272
272 VISION AND VOYAGES FOR PLANETARY SCIENCE
like those other two missions, the Uranus Orbiter and Probe mission should be subjected to rigorous independent
cost verification throughout its development and should be 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, respec-
tively. To maintain an appropriate balance among small, medium, and large missions, the Enceladus Orbiter and
the Venus Climate Mission 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 emphasized 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 cost containment 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. 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 ques-
tions identified by the planetary science community, and their cost realism is based on CATE analyses 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 and further growth at 1.5 percent per year above inflation, and
$100 million FY2015 annually for technology development.
The recommended program can be conducted assuming a budget increase sufficient to allow a new start for
JEO. The cost-constrained program can be conducted assuming the currently projected NASA planetary budget
(see Appendix E). The recommended program captures the highest priorities of the planetary science community,
but because it does not meet the test of current affordability, the cost-constrained program is also put forward.
Notional funding profiles for the two programs are shown in Figure 9.1. The recommended program shown assumes
TABLE 9.3 Two Alternative Flight Programs for the Decade 2013-2022
Recommended Program Cost-Constrained Program
Discovery program funded at the current level adjusted for Discovery program funded at the current level adjusted for
inflation inflation
Mars Trace Gas Orbiter conducted jointly with ESA Mars Trace Gas Orbiter conducted jointly with ESA
New Frontiers Mission 4 New Frontiers Mission 4
New Frontiers Mission 5 New Frontiers Mission 5
MAX-C at $2.5 billion MAX-C at $2.5 billion
Jupiter Europa Orbiter descoped Uranus Orbiter and Probe
Uranus Orbiter and Probe
NOTE: The recommended program can be conducted assuming an increase in the NASA budget that allows a new start for the Jupiter Europa
Orbiter. The cost-constrained program can be conducted within the currently projected NASA Planetary Science Division budget. The ordering
of items does not imply priority.
OCR for page 273
273
RECOMMENDED FLIGHT INVESTIGATIONS: 2013-2022
FIGURE 9.1 Notional funding profiles for the recommended (top panel) and cost-constrained (bottom panel) programs, in
real-year dollars, for fiscal years 2013-2022. The heavy black line shows the projected available funding for the NASA Plan-
etary Science Division (PSD), accounting for all current commitments (including the Mars Trace Gas Orbiter). The available
funding grows sharply in the first few years of the decade as some current programs come to an end. See Appendix E for details
regarding projected available funding. The cost assumed for the Jupiter Europa Orbiter is $4.7 billion, illustrating clearly why
a reduction in the scope and cost of this mission is necessary. SOURCE: Fiscal year 2011 PSD budget wedge data provided
by NASA Science Mission Directorate.
OCR for page 274
274 VISION AND VOYAGES FOR PLANETARY SCIENCE
the full $4.7 billion projected for JEO, but the committee emphasizes that this cost can and should be reduced
significantly through reductions in mission scope.
Figure 9.1 shows that a scientifically rich program can be carried out for the funds expected to be available in
the decade 2013-2022, and that a scientifically exceptional program can be carried out with a much-needed budget
augmentation. Table 9.4 shows how the recommended program is tied to the three crosscutting themes identified
in Chapter 3. The costs projected in Figure 9.1 (bottom) exceed projected funding in some years and fall below
it in others, and the year-to-year budget tuning necessary to fit a profile precisely is best left to NASA managers.
As noted, the recommended and cost-constrained programs make realistic assumptions about mission costs,
based on the CATE analyses conducted in support of this decadal survey. Plausible circumstances could improve
the picture presented above. For example, if the mission costs presented above are overestimates, the budget
increase required for the recommended program would be correspondingly smaller. Increased funding for planetary
TABLE 9.4 Crosscutting Science Themes, Key Questions, and the Missions in the Recommended Plan That
Address Them
Crosscutting Theme Priority Questions Missions
Building new worlds 1. What were the initial stages, conditions, and processes Comet Surface Sample Return, Trojan Tour
of solar system formation and the nature of the interstellar and Rendezvous, Discovery missions
matter that was incorporated?
2. How did the giant planets and their satellite systems Jupiter Europa Orbiter, Uranus Orbiter and
accrete, and is there evidence that they migrated to new Probe, Trojan Tour and Rendezvous, Io
orbital positions? Observer, Saturn Probe, Enceladus Orbiter
3. What governed the accretion, supply of water, chemistry, Mars Sample Return, Venus In Situ Explorer,
and internal differentiation of the inner planets and Lunar Geophysical Network, Lunar South
the evolution of their atmospheres, and what roles did Pole-Aitken Basin Sample Return, Trojan
bombardment by large projectiles play? Tour and Rendezvous, Comet Surface
Sample Return, Venus Climate Mission,
Discovery missions
Planetary habitats 4. What were the primordial sources of organic matter, and Mars Sample Return, Jupiter Europa Orbiter,
where does organic synthesis continue today? Uranus Orbiter and Probe, Trojan Tour and
Rendezvous, Comet Surface Sample Return,
Enceladus Orbiter, Discovery missions
5. Did Mars or Venus host ancient aqueous environments Mars Sample Return, Venus In Situ Explorer,
conducive to early life, and is there evidence that life Venus Climate Mission, Discovery missions
emerged?
6. Beyond Earth, are there contemporary habitats elsewhere Mars Sample Return, Jupiter Europa Orbiter,
in the solar system with necessary conditions, organic Enceladus Orbiter, Discovery missions
matter, water, energy, and nutrients to sustain life, and do
organisms live there now?
Workings of solar 7. How do the giant planets serve as laboratories to Jupiter Europa Orbiter, Uranus Orbiter and
systems understand Earth, the solar system, and extrasolar planetary Probe, Saturn Probe
systems?
8. What solar system bodies endanger Earth’s biosphere, Comet Surface Sample Return, Discovery
and what mechanisms shield it? missions
9. Can understanding the roles of physics, chemistry, Mars Sample Return, Jupiter Europa Orbiter,
geology, and dynamics in driving planetary atmospheres Uranus Orbiter and Probe, Venus In Situ
and climates lead to a better understanding of climate Explorer, Saturn Probe, Venus Climate
change on Earth? Mission, Discovery missions
10. How have the myriad chemical and physical processes All recommended missions
that shaped the solar system operated, interacted, and
evolved over time?
NOTE: See Table 3.1 in Chapter 3 for comparison.
OCR for page 275
275
RECOMMENDED FLIGHT INVESTIGATIONS: 2013-2022
exploration could make even more missions possible. If funding were increased, the committee’s recommended
additions to the plans presented above would be, in priority order:
1. An increase in funding for the Discovery program,
2. Another New Frontiers mission, and
3. Either the Enceladus Orbiter or the Venus Climate Mission.
Not all of the five candidate flagship missions discussed above can be initiated in the decade 2013-2022. The
most likely outcome is that three can be initiated if NASA’s planetary budget is augmented, and two if it is not. It
is therefore important to look ahead to the following decade and to be fully prepared to consider these missions
for flight then. The committee expects that all of the five candidate flagships that are not initiated in 2013-2022
will remain strong candidates at the time of the next decadal survey. Therefore, candidate flagship missions from
the list above that cannot be initiated in 2013-2022 should receive thorough technical studies and technology
investments, so that they will be ready in time for consideration in the next decade.
It is also possible that the budget picture could turn out to be less favorable than the committee has assumed.
This could happen, for example, if the actual budget for solar system exploration is smaller than the projections
the committee used. If cuts to the program are necessary, the committee recommends that the first approach
should be descoping or delaying flagship missions. Changes to the New Frontiers or Discovery programs
should be considered only if adjustments to flagship missions cannot solve the problem. And high priority
should be placed on preserving funding for research and analysis programs and for technology development.
DEFERRED HIGH-PRIORITY MISSIONS
The committee identified a number of additional large missions that are of high scientific value but are not
recommended for the decade 2013-2022 for a variety of reasons. In alphabetical order, these missions are as follows:
• Ganymede Orbiter—This mission’s primary science objectives are characterization of the satellite’s sub -
surface ocean, geology, magnetic field, and origin. These objectives would be addressed through three mission
phases: a Ganymede flyby phase, a pump-down phase, and an orbital tour phase of 3, 6, or 12 months. Consider-
ation of the Ganymede Orbiter is deferred to the decade following 2013-2022 because of its lower science return
per dollar relative to the JEO mission, and because EJSM as currently envisioned would include an ESA-provided
spacecraft to study Ganymede, making this mission largely redundant.
• Mars Geophysical Network—The primary science objectives of this mission are to characterize the internal
structure, thermal state, and meteorology of Mars. The mission includes two or more identical, independent flight
systems, each consisting of a cruise stage, an entry system, and a lander carrying geophysical instrumentation.
Science data would be relayed from each lander to an existing orbiting asset to be transmitted back to Earth. Con-
sideration of the Mars Geophysical Network is deferred to the decade following 2013-2022 because of its lower
scientific priority relative to the initiation of the Mars Sample Return campaign.
• Mars Sample Return Lander—This, the second component of the Mars Sample Return campaign, consists
of a fetch rover to retrieve cached samples on the martian surface and an ascent vehicle to launch the samples into
Mars orbit. The MAX-C caching rover will have deposited a small cache container of rock cores on the surface for
pickup; the lander would then target a landing ellipse containing the cache and dispatch its fetch rover to retrieve
and return the cache to the ascent vehicle. While the fetch process is underway, regolith samples would be collected
via a scoop on the lander’s arm; these would also be transferred to the ascent vehicle. The ascent vehicle would
then launch the samples into Mars orbit. As noted above, the committee assumes that a significant fraction of the
combined cost of this mission and the Mars Sample Return Orbiter (see below) would be borne by the ESA, as
part of its partnership with NASA to carry out the Mars Sample Return campaign.
• Mars Sample Return Orbiter—This mission is the third component of the Mars Sample Return campaign.
It includes a Mars orbiter, an Earth-entry vehicle, and a terrestrial sample-handling facility. The orbiter is designed
to rendezvous with the sample launched into orbit by the Mars Sample Return Lander’s ascent vehicle, and then
OCR for page 276
276 VISION AND VOYAGES FOR PLANETARY SCIENCE
transfer this sample into the Earth-entry vehicle and return it to Earth. The Mars Sample Return Lander and the
Mars Sample Return Orbiter are deferred to the decade following 2013-2022 because of programmatic balance
and the need to execute MAX-C first. Again, the committee assumes that a significant fraction of the combined
Mars Sample Return Lander and Orbiter costs would be borne by ESA.
• Neptune System Orbiter and Probe—If unforeseen circumstances were to make it impossible to begin the
Uranus Orbiter and Probe mission on the schedule recommended above, Neptune could become an attractive alter-
nate target for most ice-giant system science. The committee’s mission studies indicate, however, that significant
hurdles remain in the area of aerocapture or other mission-enabling technologies for a Neptune System Orbiter
and Probe to be feasible at a reasonable cost.
• Titan Saturn System Mission—This mission addresses key science questions regarding Saturn’s satellite Titan
as well as other bodies in the Saturn system. The baseline mission architecture consists of an orbiter supplied by
NASA and a lander and Montgolfière balloon supplied by ESA. These components would examine Titan, concentrat-
ing on the prebiotic chemical evolution of the satellite. In addition, in transit to Titan the mission would examine the
plumes of Enceladus and take measurements of Saturn’s magnetosphere. As discussed in Chapter 8, consideration
of this mission is deferred to the decade following 2013-2022 primarily because of the greater technical readiness
of JEO. Its high scientific priority, however, is especially noteworthy. Because the Titan Saturn System Mission
is a particularly strong candidate for the future, continued thorough study of it is recommended.
Although consideration of the missions listed above is deferred to the following decade, technology investments
must be made in the decade 2013-2022 to enable them and to reduce their costs and risk. In particular, it is impor-
tant to make significant technology investments in the Mars Sample Return Lander, Mars Sample Return
Orbiter, Titan Saturn System Mission, and Neptune System Orbiter and Probe. The first two are necessary
to complete the return of samples collected by MAX-C. The Titan Saturn System Mission has the highest priority
among the deferred missions to the satellites of the outer planets. Finally, the Neptune System Orbiter and Probe
could be an attractive mission for the next decade if the Uranus Orbiter and Probe cannot be flown in the coming
decade for some reason. All four missions are technically complex, and so early technology investments are important
for reducing cost and risk. The technology needs for these missions are discussed in greater detail in Chapter 11.
LAUNCH VEHICLE COSTS
The costs of launch services pose a challenge to NASA’s program of planetary exploration. Launch costs have
risen in recent years for a variety of reasons, and launch costs today tend to be a larger fraction of total mission
costs than they were in the past.
Superimposed on this trend of increasing launch costs are upcoming changes in the fleet of available launch
vehicles. The primary launch vehicles likely to be available to support the missions described above are the existing
Delta IV and Atlas V families, plus the Taurus II and Falcon 9 vehicles currently under development (Figure 9.2).
Absent from the list of available vehicles is the Delta II rocket that has been so important in launching past
planetary missions. The Delta II, whose production has been terminated, proved to be an exceptionally reliable
and relatively inexpensive launch vehicle. Although a few Delta II vehicles not assigned to missions remain, the
absence of the Delta II will shortly leave a gap in reliable, relatively inexpensive launch capabilities important for
missions to the inner planets and some primitive bodies. New vehicles being developed may help to fill this gap.
Orbital Sciences Corporation is developing the Taurus II and Minotaur V, while Space Exploration Technology
Corporation (SpaceX) is developing the Falcon 9.
As noted, many past missions have relied on the Delta II, and future missions will not have this option. The
concern is that alternative launch vehicles of established reliability, such as the Atlas V and the Delta IV, are sub-
stantially more expensive even in their smallest versions. The situation is complicated further by the volatility of
the costs of these vehicles, and the dependence of costs on future contract negotiations.
Increases in launch costs pose a threat to formulating an effective, balanced planetary exploration program.
There may be some ways of partially reducing this threat, although all of them come with their own complexities
and disadvantages:
OCR for page 277
277
RECOMMENDED FLIGHT INVESTIGATIONS: 2013-2022
FIGURE 9.2 Performance comparison for launch vehicles likely to be available during the time period covered by this decadal
survey, with the soon-to-be discontinued Delta II for comparison. The curves show how each vehicle’s payload mass varies
with the C3 parameter—i.e., the square of the hyperbolic excess velocity.
• Use dual manifesting to reduce individual mission costs. Combining two missions with complementary
science objectives onto one launch vehicle reduces the costs for each mission. Recent examples of this approach
are the Cassini/Huygens mission to Saturn and the Lunar Reconnaissance Orbiter/LCROSS mission to the Moon.
This approach, however, does entail additional technical and managerial complications.
• Use dual manifesting for missions to different destinations. For example, a planetary mission could be
combined with an Earth observation mission. While significant savings may be possible, such a combination of
missions would bring substantial technical and management complications, for example those resulting from the
schedule constraints imposed by planetary launch windows.
• Buy blocks of launch vehicles across all NASA users to reduce unit costs. Block procurement of launch
vehicles reduces unit costs because of increased production efficiencies both at the prime launch vehicle contractor
and at the vendors supplying components and subsystems. According to a 2010 study by the Center for Strategic
and International Studies, inefficiency in the U.S. production of launch vehicles adds 30 to 40 percent to U.S.
launch costs.20 NASA once procured the Delta II in blocks.
• Buy blocks of launch vehicles across organizations to reduce unit costs. At present, NASA and the Depart-
ment of Defense procure launch vehicles separately. Combined procurement across both organizations would result
OCR for page 278
278 VISION AND VOYAGES FOR PLANETARY SCIENCE
in greater production efficiencies and reduced unit costs. Interagency cooperation to bring about such block buys
could be a significant challenge, however.
• Exploit technologies that allow use of smaller, less expensive launch vehicles. For some orbital missions
to planets with atmospheres, use of aerocapture can result in a substantial reduction in spacecraft mass, replacing
propellants with a less massive heat shield. For other missions, low-thrust in-space propulsion may enable trajec-
tories that have less stringent launch performance requirements. In both instances, of course, launch savings are
partially offset by the cost of the necessary technology development.
THE NEED FOR PLUTONIUM-238
Radioisotope power systems (RPSs) are necessary for powering spacecraft at large distances from the Sun; in
the extreme radiation environment of the inner Galilean satellites; in the low light levels of high martian latitudes,
dust storms, and night; for extended operations on the surface of Venus; and during the long lunar night. With
some 50 years of technology development, funded by more than $1 billion, and the use of 46 such systems on
26 previous and currently flying spacecraft, the technology, safe handling, and utility of these units are not in doubt.
Although there are more than 3,000 nuclides, few are acceptable for use as radioisotopes in power sources. For
robotic spacecraft missions, plutonium-238 stands out as the safest and easiest to procure isotope that is compatible
with launch vehicle lift capabilities.
Past NASA use of plutonium-238 in RPSs is well documented. Future requirement planning is subject to
periodic (ideally annual) updates to the Department of Energy. Such plans are complicated by cross-agency bud-
getary expectations, changing NASA plans, and the competitively selected nature of future NASA missions that
may require this isotope.
Unfortunately, production of plutonium-238 in the United States ceased in 1988 with the shutdown of the
Savannah River Site K-reactor, and separation of the isotope from existing inventories stopped in about 1996.
The remaining stock of plutonium-238, largely purchased from Russia, has continued to be drawn down, most
recently for the Multi Mission Radioisotope Thermoelectric Generator (MMRTG) on MSL (~3.5 kg of plutonium).
An additional potential lien against the remaining supply is the use of plutonium-238 in two Advanced Stirling
Radioisotope Generators (ASRGs) on the next Discovery mission (~1.8 kg of plutonium). Although an exact
accounting of plutonium-238 in the United States is not publicly available, previous estimates are consistent with
a current supply of ~16.8 kg, not including the 3.5 kg now on MSL. Recent NASA requirements reported to DOE
are given in Table 9.5.
The projected need decreased from 2008 to 2010 largely due to dropping the lunar rovers associated with the
Constellation program (56 kg of plutonium), but also due to a better understanding of requirements. The current
plan assumes that an additional 10 kg of plutonium-238 will be purchased from Russia, and that an average of
1.5 kg/yr of new domestic production can begin, but no earlier than 2015. Purchase from Russia is subject to ongo-
ing negotiations, and requests for monies for startup of domestic production were rejected in 2010 by the Congress.
Hence, neither of these sources is assured at this time, and without at least 5 kg of new material from Russia as
well as renewed U.S. production, NASA’s current plans for future planetary missions cannot be carried out.
This decadal survey recommends a variety of missions and mission candidates (under the New Frontiers
program) that require RPSs. As such, these recommendations would modify to some degree NASA’s requirements
for plutonium-238. The current supply of plutonium-238 is sufficient to fuel four MMRTGs plus three ASRGs, or
19 ASRGs, or equivalent combinations of the two.
The largest user of plutonium-238 is any mission that has MMRTGs rather than ASRGs as a baseline. Cur-
rently this approach applies only to JEO, for which five MMRTGs are baselined—i.e., one more than can be sup-
ported by the current supply of plutonium-238. The Titan Saturn System Mission is the only other mission that
uses MMRTG as a baseline, and it is deferred until the decade subsequent to this study.
None of the recommended Mars missions use an RPS. Of the potential New Frontiers missions requiring RPSs,
Io Observer requires two ASRGs; LGN, four; Saturn Probe, two; and Trojan Tour and Rendezvous, two. Hence, a
maximum of six ASRGs for two New Frontiers missions brackets potential requirements. The Uranus Orbiter and
Probe and the Enceladus Orbiter each require three ASRGs and cannot be carried out with MMRTGs due to the
OCR for page 279
279
RECOMMENDED FLIGHT INVESTIGATIONS: 2013-2022
TABLE 9.5 Comparison of NASA Requirements for Plutonium-238 as Reported to DOE in 2008 and 2010
NASA Administrator Letter NASA Administrator Letter
of April 29, 2008 of March 25, 2010
Projected Pu-238 Usage Projected Pu-238
Mission Launch Power (We) (kg) Launch Power (We) Usage (kg)
Mars Science Laboratory 2009 100 3.5 2011 100 3.5
—a —a —a
Lunar Precursor 2015 280 1.8
—a —a —a
Mars (radioisotope power 2018 280 1.8
system and heater units)
Outer Planets Flagship 1 2017 700-850 24.6 2020 612 21.3
Discovery 12 2014 250 1.8 2015 280 1.8
Discovery 14 2020 500 3.5 2021 280 1.8
New Frontiers 4 2021 800 5.3 2022 280 1.8
New Frontiers 5 2026 250-800 1.8-5.3 2027 280 1.8
Discovery 16 2026 500 3.5 2027 280 1.8
—b —b —b
Outer Planets Flagship 2 2027 600-1,000 5.3-6.2
—c —c —c
Pressurized Rover #1 2022 2,000 14
—c —c —c
ATHLETE Rover 2024 2,000 14
—c —c —c
Pressurized Rover #2 2026 2,000 14
—c —c —c
Pressurized Rover #3 2028 2,000 14
a Not in plan.
b Deleted from plan.
c Projected Exploration Systems Mission Directorate requirements deleted for human missions.
latter’s prohibitive mass. Discovery 12 is needed to qualify ASRGs, and Discovery 14 and 16 could potentially
use these as well—each is currently baselined with two. Hence, 15 ASRGs and 5 MMRTGs are implied by the
recommended decadal survey plan presented above; the cost-constrained plan would require only 15 ASRGs.
The recommended program cannot be carried out without new plutonium-238 production or completed
deliveries from Russia. The cost-constrained program could be, but only if ASRGs work as currently envisioned
and are certified for flight in a timely fashion. Moreover, unless additional plutonium-238 is acquired, there will
be only three ASRGs available for the subsequent decade, and so there will not be a Europa mission, a Titan
Saturn System Mission, a mission to Neptune, or a long-lived mission to the surface of Venus in future decades.
There are no technical alternatives to plutonium-238, and the longer the restart of production is delayed, the
more it will cost.
As noted above, the largest projected user of plutonium-238 in the recommended program is JEO. Because
the use of MMRTGs on JEO would consume so much of this valuable resource, the committee recommends
that JEO use ASRGs for power production. The duration of JEO is compatible with ASRG use, and this change
would alleviate (though not solve) the immediate plutonium-238 crisis. In addition, because ASRGs are so broadly
important to the future of planetary exploration, the committee recommends that the remaining ASRG develop-
ment and maturation process receive the same priority and attention as a flight project.
All findings in the recent NRC report on RPSs remain valid.21 With the one exception of NASA issuing annual
letters to the DOE defining the future demand for plutonium-238, none of the recommendations of that report
have been adopted. A decision to wait for a “better time” to fund activities required to restart domestic plutonium
production is just a different way of ending the program, eliminating future science missions whose implementa-
tion is dependent on this technology.
OCR for page 280
280 VISION AND VOYAGES FOR PLANETARY SCIENCE
The committee is alarmed at the very limited availability of plutonium-238 for planetary exploration.
Without a restart of domestic production of plutonium-238, it will be impossible for the United States, or
any other country, to conduct certain important types of planetary missions after this decade.
OPPORTUNITIES FOR INTRA-AGENCY, INTERAGENCY,
AND INTERNATIONAL COLLABORATION
There are three main areas in which collaboration with other parts of NASA could benefit the solar system
exploration program. First, as noted above, block buys of launch vehicles across NASA have the potential to lower
launch costs significantly. Second, astronomical telescopes, both ground-based and space-based, can be used to
observe solar system targets. The Hubble Space Telescope has a long history of successful planetary observations,
and this collaboration can be a model for future telescopes such as the James Webb Space Telescope.
A third area of possible intra-agency collaboration is with NASA’s Exploration Systems Mission Directorate
(ESMD). NASA’s plans for future human exploration of the solar system currently include ESMD-funded robotic
precursor missions to the Moon, Mars, and asteroids. Because their focus is preparing for human exploration,
rather than science, these are not substitutes for any of the missions recommended above, nor for Discovery mis-
sions. And, although robotic precursor missions present opportunities for collaboration, NASA’s Planetary Science
Division should be cautious about imposing mission-defining requirements, as the committee noted in Chapter 2.
At the start of mission formulation, ESMD should inform the Science Mission Directorate (SMD) about what
mission resources, if any, it is willing to allocate. Then, given a negotiated agreement between ESMD and SMD,
NASA should offer opportunities for scientists to propose investigations on such missions by issuing AOs in a
manner similar to that for participating on international missions or as was done for Lunar Reconnaissance Orbiter.
Because ESMD robotic precursor missions target planetary bodies, they offer particularly good opportunities
for reducing launch costs via co-manifesting.
The greatest potential for interagency collaboration is also launch vehicle block buys and co-manifesting,
reducing costs for all partner agencies. It will also be important for NASA to form a strong partnership with the
Department of Energy in order to obtain the plutonium-238 needed for upcoming planetary missions.
International collaboration is possible in many forms and offers significant opportunities to strengthen NASA’s
solar system exploration program. Missions of Opportunity allow U.S. investigators to participate in missions
flown by non-U.S. space agencies and should be pursued vigorously. The science of Discovery and New Frontiers
missions can be enhanced at modest instrument accommodation cost to NASA by including instruments and
investigators from other nations. As the capabilities of many potential international partners around the world
grow, these opportunities will multiply.
All three of the flagship missions in the recommended program have the potential for substantial international
collaboration. EJSM would be done collaboratively with ESA, flying both the NASA Jupiter Europa Orbiter and
the ESA Jupiter Ganymede Orbiter. These coordinated missions are a good example of a robust international
partnership. There are no complex hardware interfaces between the two major international components. Each
mission can stand alone on its own scientific merits, but the two conducted jointly can complement and enhance
one another’s science return by making synergistic observations. And each would carry an international payload,
making the most capable scientific instruments available to each, regardless of their nation of origin.
MAX-C is envisioned to be an international mission, with both the NASA sample collection rover and the ESA
ExoMars rover delivered by a NASA-provided derivative of the MSL EDL system. Moreover, it is intended to be
the first element of a three-mission Mars Sample Return campaign, with ESA playing a significant role throughout
the entire campaign. Unlike EJSM, the interfaces between NASA and ESA elements of MAX-C (and, perhaps,
the follow-on elements as well) are complex, and they will have to be managed with great care. As noted above,
a particular concern for MAX-C is that an attempt to accommodate two large and capable rovers as currently
imagined would be likely to force a costly redesign of the MSL EDL system. To keep NASA’s costs for MAX-C
below the recommended $2.5 billion (FY2015), significant reductions in mission scope, including major reductions
in landed mass and volume, are likely to be necessary. So while MAX-C offers an opportunity for international
collaboration, that collaboration must be managed carefully.
OCR for page 281
281
RECOMMENDED FLIGHT INVESTIGATIONS: 2013-2022
The Uranus Orbiter and Probe mission has not yet been discussed as an international collaboration, but it offers
significant potential. As one example, the instrument payload could be selected internationally, strengthening the
science while reducing costs to NASA.
NOTES AND REFERENCES
1 . National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. The National
Academies Press, Washington, D.C.
2 . National Research Council. 2008. Opening New Frontiers in Space: Choices for the Next New Frontiers Announcement
of Opportunity. The National Academies Press, Washington, D.C.
3 . On May 25, 2011, following the completion of this report, NASA selected the OSIRIS-REx asteroid sample-return
spacecraft as the third New Frontiers mission. Launch is scheduled for 2016.
4 . For a well-documented case see, for example, Independent Comprehensive Review Panel, James Webb Space Telescope
(JWST) Independent Comprehensive Review Panel (ICRP): Final Report, NASA, Washington, D.C., October 29, 2010,
available at http://www.nasa.gov/pdf/499224main_JWST-ICRP_Report-FINAL.pdf.
5 . National Research Council. 2006. An Assessment of Balance in NASA’s Science Programs. The National Academies
Press, Washington, D.C.
6 . National Research Council. 2007. Decadal Science Strategy Surveys: Report of a Workshop. The National Academies
Press, Washington, D.C., p. 20.
7 . National Research Council. 2006. An Assessment of Balance in NASA’s Science Programs. The National Academies
Press, Washington, D.C.
8 . For a graphic example of the damage potential of cost growth see, for example, Table 3.1 of National Research Council,
Decadal Science Strategy Surveys: Report of a Workshop, The National Academies Press, Washington, D.C., 2007.
9 . National Research Council. 2006. An Assessment of Balance in NASA’s Science Programs. The National Academies
Press, Washington, D.C., p. 2.
10 . National Research Council. 2010. Controlling Cost Growth of NASA Earth and Space Science Missions. The National
Academies Press, Washington, D.C.
11 . National Research Council. 2010. Controlling Cost Growth of NASA Earth and Space Science Missions. The National
Academies Press, Washington, D.C., p. 38.
12 . The committee excluded launch vehicle costs because the current uncertainty of those costs foiled any attempt to estimate
their likely magnitude over the next decade. See the section “Launch Vehicle Costs” in this chapter.
13 . On May 25, 2011, following the completion of this report, NASA selected the OSIRIS-REx asteroid sample-return
spacecraft as the third New Frontiers mission. Launch is scheduled for 2016.
14 . Note that the CATE costs for these missions presented in Appendix C include launch vehicle costs. While some CATE
estimates (minus launch vehicle costs) exceed the recommended $1.0 billion cost cap, all were judged by the committee
to be close enough to the cap that a PI and team could adjust their scope so that they could fit within the cap.
15 . National Research Council. 2008. Opening New Frontiers in Space: Choices for the Next New Frontiers Announcement
of Opportunity. The National Academies Press, Washington, D.C.
16 . On May 25, 2011, following the completion of this report, NASA selected the OSIRIS-REx asteroid sample-return
spacecraft as the third New Frontiers mission. Launch is scheduled for 2016.
17 . This is the cost of MAX-C only, not the cost of the full Mars Sample Return campaign. Also, the estimate is for the
MAX-C mission as currently conceived; in the text below, the committee recommends reductions in scope to keep the cost
below $2.5 billion FY2015.
18 . This is the version without a solar-electric propulsion stage.
19 . NASA and the European Space Agency. 2009. Jupiter Europa Orbiter Mission Study 2008: Final Report. European Space
Agency, Paris, France, January 30, 2009. Available at http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=48278.
20 . G. Ben Ari, B. Green, J. Hartman, G. Powell, and S. Sanok. 2010. National Security and the Commercial Space Sector:
An Analysis and Evaluation of Options for Improving Commercial Access to Space. Center for Strategic and International
Studies, Washington, D.C. July. Available at http://csis.org/publication/national-security-and-commercial-space-sector.
21 . National Research Council. 2010. Radioisotope Power Systems: An Imperative for Maintaining U.S. Leadership in Space
Exploration. The National Academies Press, Washington, D.C.
OCR for page 282
