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Introduction

NASA’s Science Mission Directorate (SMD) currently operates over five dozen missions, with approximately two dozen additional missions in development. These missions span the scientific fields associated with SMD’s four divisions—namely, Astrophysics, Earth Science, Heliophysics, and Planetary Science (referred to in this report by the shorthand “space sciences”). Because a single mission can consist of multiple spacecraft, NASA SMD is responsible for nearly 100 operational spacecraft.¹ Of these many dozens of spacecraft, very few receive significant public and political attention. Those that do tend to be NASA’s large strategic missions, often referred to as “flagships.”

Many of NASA’s large strategic space science missions have become household names, such as the Hubble Space Telescope (HST) and the Curiosity rover on Mars. Other large strategic missions are less well known to the public but are famous within their respective scientific communities. These missions have led to many exciting discoveries, reported on in thousands of publications in the past decade. The data from these missions are widely distributed and influential, and are used not only in the United States but also in countries on every continent.

Owing to these achievements, the United States is seen as a leader both in building and in launching innovative, bold space missions and enabling scientific discovery that inspires and engages the public at home and around the world. NASA technical expertise used to develop these spacecraft is sought by other space agencies, leading to joint projects of benefit to all.

In general, in the space sciences, NASA operates “directed” missions that are developed by a NASA center or Jet Propulsion Laboratory (JPL), “competed” missions that are selected as part of a competition and usually include a cost cap, and missions where NASA contributes instruments to spacecraft operated by other agencies of the U.S. government or non-U.S. space agencies. Large strategic missions in astrophysics and Earth sciences have been directed to NASA’s Goddard Space Flight Center, and planetary missions have been directed to Caltech’s JPL, although the Johns Hopkins University Applied Physics Laboratory currently plays a substantial role in the Europa

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¹ In some cases NASA uses the term “mission” to refer to space science instruments hosted on non-NASA spacecraft, or on platforms like the International Space Station. The committee is not using “mission” in that way in this report, and the numbers cited here do not refer to these instruments as missions.

Clipper and is building the Parker Solar Probe.² (The Chandra space telescope was directed to the Marshall Space Flight Center.) Although large strategic missions are usually directed, the instruments on these missions may be competed through the use of Announcements of Opportunity (AOs), and as a result, instruments may be developed by other institutions such as universities, research organizations, and other NASA centers. In addition, these major missions are done largely by NASA “out of house,” involving job-creating competitive contracts with the aerospace contractor community that often bring their technology, as well as facilities and skill, to these missions.

Competed missions are conducted through a process starting with an AO, and they can be led by non-NASA principal investigators (PIs). Large strategic missions are typically more expensive missions based on high-value science targets that have been identified in the decadal surveys conducted by the National Academies of Sciences, Engineering, and Medicine (National Academies). Competed missions are selected based on science value with a fixed cost cap. Although some competed missions can be of strategic importance to accomplishing science goals, they are not the most expensive missions the agency undertakes, and therefore are not often recognized for their strategic role.

The decadal surveys identify the highest priority science missions, which they generally refer to as “flagship” missions. Flagship missions are usually large and expensive—typically the most expensive mission within their science discipline. Starting around 2014, the SMD began using the term “large strategic missions” in place of “flagship” missions. According to former NASA associate administrator for the SMD John Grunsfeld, the agency introduced the term “large strategic missions” because these missions advance many parts of the science agenda. NASA can also implement “directed” missions that may not have been prioritized in a decadal survey but are considered by agency leadership to be important to agency goals.³ NASA has a variety of different acquisition approaches and types of space science missions. Although the committee understands what the agency is referring to with the terminology “large strategic missions,” it notes that “strategic” can also refer to other missions within the agency’s portfolio, and in fact a coordinated campaign consisting of multiple missions—for instance, the multiple NASA Mars spacecraft launched between 1998 and 2011—can serve long-range, overarching strategic goals, such as the search for environments that could support life.

For the SMD, the term “strategic” is defined not necessarily by the size of the missions, but by their relationship to major science goals. Examples of different-size strategic missions can be seen in the James Webb Space Telescope (JWST; over $8 billion), Curiosity (over $2.5 billion), and Spitzer (over $720 million). According to a NASA official, all large missions are by definition strategic, but not all strategic missions are large.

Although the terminology can seem confusing to outsiders, within the science disciplines most members of the community understand what the largest missions are in terms of cost, and understand what constitute large, medium-size, and small missions within their respective divisions, although they may struggle with the definition of “strategic.” Within astrophysics and planetary science, the large strategic missions are usually in excess of $1 billion. Within Earth science and heliophysics, the large strategic missions are usually in excess of $500 million. Within planetary science, “medium-size” missions cost approximately $1 billion, whereas “small” missions cost approximately $500 million. This is in contrast to Earth science and heliophysics, where “small” missions are generally defined as less than $250 million.

According to information presented to the committee by the SMD, over the years missions greater than $1 billion have accounted for approximately 30 percent of SMD’s overall budget. About 46 percent of SMD’s budget is used for the formulation and development of new missions of all sizes, while about 12 percent goes toward operating extended missions that are regularly reviewed to ensure relevant and cost-effective science. The remainder of SMD’s budget covers a variety of subjects, including non-mission-specific research support.

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² The Johns Hopkins University Applied Physics Laboratory (APL) has played a major role in numerous NASA missions, including most recently the Parker Solar Probe, the New Horizons mission, and the Van Allen Probes. APL is not a NASA center, and most of the missions it has performed for NASA have been competed missions.

³ An example of a directed mission that was not prioritized in the decadal survey is the Lunar Reconnaissance Orbiter (LRO), which was funded by the Human Exploration Operations Mission Directorate with participation from the Science Mission Directorate (SMD). A primary objective of the LRO was to map possible landing sites for future human missions to the lunar surface. When this phase of the mission was complete, responsibility for LRO shifted to the Science Mission Directorate. LRO was therefore a directed mission, serving strategic requirements for human spaceflight.

Although space science missions are usually funded by a single division within the SMD, the SMD has an integrated program that enables scientific findings in the fields of astrophysics, Earth science, heliophysics, and planetary science, with scientists working across disciplines. According to current SMD associate administrator Thomas Zurbuchen, the interconnected nature of the SMD programs supports the asking and answering of many questions at the frontiers of the space sciences, and, in addition, the discoveries in one scientific discipline have a direct route/correlation to other areas of study. Indeed, a core aspect of strategic missions in astrophysics, such as Hubble and Spitzer, involves solar system investigations by planetary scientists. Hubble discovered four of the five moons of Pluto, auroras in Jupiter’s atmosphere, and much more. Spitzer discovered the largest ring around Saturn, and both telescopes (including others in astrophysics) have discovered and characterized Kuiper Belt objects (KBOs), dwarf planets, and asteroids; monitored clouds in outer gas giants; monitored the Martian atmosphere; and more. Large strategic missions can also be used to ensure the success of other NASA cross-disciplinary missions. For example, Hubble was key to the success and safety of the New Horizons mission by surveying for possible debris in the vicinity of Pluto that could have impacted the spacecraft. Hubble was also instrumental in finding a KBO target for New Horizons after the Pluto flyby.

There are other missions that also demonstrate this interconnectivity. For example, the Magnetospheric Multiscale (MMS) mission, which is funded within the Heliophysics Science Division, has provided science findings in heliophysics (solar dynamics), but that are also of value to Earth science, planetary science (history of water on Mars), and astrophysics (stellar formation). The Juno spacecraft, currently orbiting Jupiter, was funded within the Planetary Science Division, and is a medium-size mission within the planetary program’s context. Juno is in the early stages of science operations and may provide individual benefits in the fields of heliophysics (strong magnetic fields and auroras), Earth science (cloud circulation formulation and dynamics), planetary science (water in the Jupiter formation region), and astrophysics (exoplanets). Large strategic missions also can contribute to multiple scientific disciplines and have a greater impact on them because of the amount of data they collect and the size of their science teams.

The committee developed a budget “sand chart” based on data provided to the committee by NASA. The chart shows yearly expenditures for development costs for large NASA missions, corrected for inflation. (See Figure 1.1.) Each band shows the cost of the given mission in fiscal year (FY) 2015 dollars, with the total plot running from FY1969 as projected though FY2026.⁴ The chart illustrates that the Viking missions of the mid-1970s (left of chart) represented a substantial expenditure for the agency over a relatively short period of time. The Hubble and JWST missions (at bottom) also represent large budgetary expenditures. According to the committee’s calculations, Hubble has been the most expensive large strategic mission developed by NASA when calculating the initial development costs and the development costs for the multiple servicing missions (while excluding launch and operations costs). Also notable is the emergence of several large Earth science missions, such as Terra in the 1990s.

Each of NASA’s four science divisions is currently operating or developing large strategic missions.

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⁴ Accounting changes have been dealt with in this chart as follows: (1) All figures prior to FY2004 include a rough estimate for Civil Service labor (actuals are not broken out in the records). (2) Launch services were not part of the Science budget before FY2000, but good data are available and are included here for each mission. Shuttle launch costs for Magellan, Galileo, Compton Gamma Ray Observatory, Upper Atmospheric Research Satellite, Hubble (launch and servicing missions), and Chandra were not consistently estimated and are not included as part of the mission costs here. (3) The “transition quarter” between the end of FY1976 and beginning of FY1977 (July 1, 1976, to September 30, 1976) has been absorbed. The large peak in the decade of the 1970s is driven by the design, development, and launch of Voyager 1 and 2 (to the outer solar system—both spacecraft still operating and returning data) and the Viking 1 and 2 orbiters and landers to Mars (the Viking 1 and 2 landers were still operational—the landers continued functioning until the early 1980s, when problems with the batteries on each lander resulted in termination of operations).

The top five missions in FY2015 dollars are (millions): Hubble, $11,288.124; JWST, $8,645.214; Viking, $6,790.746; Chandra, $3,440.968; Cassini, $3,188.699. The next five in order are Galileo, MSL/Curiosity, Wide-Field Infrared Survey Telescope-Astrophysics Focused Telescope Assets, Europa Clipper (estimated, since the spacecraft has not yet been built), and Terra.

ASTROPHYSICS SCIENCE DIVISION

The objective of the study of astrophysics is to further humankind’s scientific endeavor to understand the universe and humanity’s place in it. Astrophysics seeks to answer questions such as: How did our universe begin and evolve? How did galaxies, stars, and planets come to be? Are we alone?⁵

The current astrophysics mission portfolio includes large and medium-size strategic NASA-led missions, and medium-size and small PI-led missions. Astrophysics also is involved in supporting PI-led and strategic non-NASA missions.

The total NASA astrophysics budget for FY2016 was $1.33 billion (including the JWST development), with over half allocated toward mission development and the remaining funds put toward missions in operation, research and technology, and infrastructure and other essentials.

Current astrophysics mission sizes vary greatly depending on the science goals. Small missions within the Astrophysics Science Division are PI-led and are selected through AOs through the Astrophysics Explorers Program (the Explorer program is actually part of the Heliophysics Science Division, and a small number of these missions

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⁵ Presentation by Paul Hertz, Astrophysics Science Division, NASA, to the Committee on NASA Large Strategic Space Science Missions, October 5, 2016.

are devoted to astrophysics); they typically do not exceed $250 million. Large strategic missions are recommended by the decadal survey and cost over $1 billion, the most recent example being the Wide-Field Infrared Survey Telescope (WFIRST) mission.

According to the current director of the Astrophysics Science Division, Paul Hertz, within the division there are many benefits of large strategic missions to astrophysics. They have the ability to accomplish science that smaller missions would be unable to fulfill; they can provide general-purpose observatories for the community; and they can drive development of new capabilities that can be infused later into smaller missions without further technical development.

The committee notes that these attributes also generally apply to large strategic missions in fields other than astrophysics, although in astrophysics the “Great Observatories” aspect of such missions—that is, their ability as an ensemble to cover a broad range of wavelengths and to serve multiple users over a long period of time—may be greater than in some of the other science fields. Hertz stressed that large mission costs need to be carefully managed in order to preserve programmatic balance defined by the decadal survey, which is also true of the other divisions.

According to Hertz, large strategic missions should be managed by experienced management teams. These large missions can also provide development training opportunities for people to become PIs on smaller missions, instruments, and suborbital investigations. Large strategic missions also offer opportunities for international partnerships. Hertz explained that there is a general expectation within the astrophysics community that future large strategic missions will be the result of international collaboration, but there is no similar expectation for small and medium-size missions.

The instruments of large strategic missions are analogous to Explorer-class programs at universities. These are coherent $100+ million projects that combine science, engineering, and technology, largely developed at U.S. universities and other research institutions through PI teams involving faculty, postdoctorate candidates, and students. These instruments are an excellent method for training students.

Currently, the Astrophysics Science Division operates both the Hubble and Chandra missions, the Spitzer Observatory, as well as the airborne Stratospheric Observatory for Infrared Astronomy (SOFIA). It is also developing both the JWST and the WFIRST. Hubble was a decadal survey priority and was launched in 1990 and has become one of the most visible science programs in the world. Its science achievements span most of modern-day astrophysics and include countless discoveries that were not envisioned by its designers. The Hubble program has produced over 14,000 refereed science publications with more than 600,000 citations. Hubble remains one of SMD’s most scientifically productive missions, with 881 papers published in 2016, higher than any other year. There are more than 1,000 research proposals being received each year at an oversubscription rate of 5:1 and an orbit oversubscription rate of 7:1 in 2016. There have been more than 15,000 users of the observatory.⁶

Guided by the science prioritization in the decadal surveys, large strategic missions in astrophysics drive the development of new and ambitious technologies. These are achieved through partnerships between NASA, industry, and academia. For example, for JWST, there were 10 technologies successfully invented to achieve the mission’s design requirement. This includes the first space-based multi-object spectrograph with 250,000 shutters, segmented beryllium mirrors with nanometer precision, tennis-court-size sunshields to achieve hundreds of degrees of passive cooling, ultrasensitive infrared detectors, and more. Many of these technologies also have spinoff applications in aerospace, commercial research, and medical fields (i.e., the treatment of laser eye surgery and diagnosis of ocular diseases has been improved due to the application of JWST wavefront sensing techniques). Similarly, the future large strategic mission WFIRST is creating state-of-the-art light suppression techniques to directly image exoplanets that are one billion times fainter than their host stars. Although the Astrophysics Division has its own technology development program, it can also directly involve NASA’s Space Technology Mission Directorate and often benefits from industrial partnerships where there is heritage of new technologies that have been successfully applied to non-NASA programs. The opportunity to create these technologies and apply them to future science missions (large or small) rests largely with the strategic missions. Smaller astrophysics programs are not expected

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⁶ Space Telescope Science Institute, Summary 2016 Annual Report, p. 2, http://www.stsci.edu/institute/annual-reports/2016-annual-report.pdf.

to develop such new technologies, although they sometimes do so if necessary. The Astrophysics Science Division funds technology development via separate methods, including AOs.

EARTH SCIENCE DIVISION

The Earth Science Division provides critical insight into understanding Earth as an integrated system, and for developing and testing applications to deliver direct societal benefit. There are four major components to the Earth Science Division: measurements, research, societal benefit and capacity building, and technology development.⁷ The measurements component refers to the ability to monitor and observe Earth and its environment from space, which advances science, develops applications for societal benefit, and supports other mission agencies. The research component furthers the understanding of Earth as an integrated system through research that is multidisciplinary and uses all relevant measurements (not limited to satellites). The societal benefit and capacity-building component of the Earth Science Division develops and tests new information products, which are tailored to the needs of end users, and increases users’ capacity to exploit the information. Finally, technology development advances instruments, information systems, and communications technologies that support new missions, research, and applications.

The Earth Science Division received $1.92 billion in FY2016. Currently, the division has several large strategic science missions in operation: the Aura, Aqua, and Terra missions. All three were implemented as part of the Earth Observing System (EOS) in the late 1980s, with launches starting in the late 1990s. A more recent example of a large mission is the Plankton, Aerosol, Cloud, Ocean Ecosystem (PACE) mission, which will use advanced ocean color and polarimetric technologies to understand and quantify global ocean biogeochemical cycling and ecosystem function in response to anthropogenic and natural environmental variability and change. The mission will allocate approximately $705 million to mission/project implementation and $100 million to science.

The Earth Science Division has shifted its focus to development of smaller missions. According to Michael Freilich, the director of NASA’s Earth Science Division, large strategic missions are not essential for the division’s future work. A broad portfolio of smaller missions—launched, flown, and analyzed in coordinated and integrated ways—allows for optimization of resources and flexible provision of capabilities to achieve scientific objectives. For example, Ice, Cloud, and Land Elevation Satellite (ICESat) and Soil Moisture Active Passive (SMAP) are strategic in the sense that they acquire needed information to fulfill important science objectives. In the case of SMAP, it was initially proposed as an Earth System Science Pathfinder (ESSP) mission with a cost cap in the $300 million range but was deemed important enough to warrant more investment.

According to NASA the capabilities provided by multiple smaller missions can be adjusted in an iterative fashion, providing mission implementation flexibility. However, it is not clear if this approach will support the extended investments over time across multiple Earth Science subdisciplines required to meet Earth science objectives related to high-accuracy long-term trending and investigations into coupling and feedback mechanisms across the Earth system. As discussed in Chapter 2, the committee concluded that this is a subject that the current Earth science decadal survey is best equipped to address.

In recent years the Earth Science Division has also begun to explore smaller capabilities to conduct critical measurements. An example of a small satellite Earth Science mission is the Cyclone Global Navigation Satellite System (CYGNSS) (Figure 1.2). This mission comprises an eight-satellite microsatellite constellation that measures air-sea interactions in tropical storms using reflected GPS signals to achieve the horizontal coverage that is required to address scientific questions concerning hurricane formation and intensification. Another example is the Time-Resolved Observations of Precipitation Structure and Storm Intensity with a Constellation of SmallSats (TROPICS), which is a 12-satellite CubeSat constellation and the first science-focused CubeSat constellation, now in development. Both of these missions have been developed under the Earth Venture (EV) program.

The ESSP program provides periodic opportunities to address new and emerging science priorities defined by the decadal surveys. ESSP missions are now part of the EV class of missions defined as being competitively

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⁷ Presentation by Earth Sciences Division Director Michael Freilich to the Committee on Large Strategic NASA Science Missions, October 5, 2016.

selected, relatively low to moderate cost, and small to medium-size. They can be full orbital missions, instruments for orbital missions of opportunity, or suborbital projects. Originally, they were competed missions. ESSP projects are high-return Earth science missions that include advanced remote sensing instrument approaches to achieve science priorities and can include partnerships with other U.S. agencies or international scientific research and space organizations. Examples of such missions include Aquarius, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), CloudSat, and Gravity Recovery and Climate Experiment (GRACE), which are all in extended operations; OCO-2 (Orbiting Carbon Observatory), still in its prime mission; and OCO-3, which is in formulation. Some of these missions such as OCO-2, OCO-3, and GRACE 2 are legacy ESSP projects originally selected under prior AOs. As follow-on missions they do not perfectly align with the Venture-class structure as the the original mission concept was not recompeted. Large strategic missions are not typically used for technology development in the Earth Science Division. Instead, technology development is conducted in the Earth Science Technology Program (ESTP). Smaller missions can also provide opportunities for technology development. Currently, the Earth Science Technology Office (ESTO) has a separate technology development line with a budget of approximately $60 million per year. The development of Earth science technology within the ESTP plays a critical role in enabling Earth science research, applications, and flight missions. ESTO also enables new science investigations, improves existing measurement capabilities, and reduces the cost, risk, and development time of Earth science instruments and information systems. ESTO performs analysis of science requirements for technology needs, selects and funds technologies through competitive solicitations and partnership opportunities, actively

manages funded technology development projects, and facilitates the infusion of mature technologies into science campaigns and missions.

HELIOPHYSICS SCIENCE DIVISION

Heliophysics can be defined as humankind’s scientific endeavor to understand the Sun and its interactions with Earth and the solar system. Questions that may be addressed by heliophysics include: What causes the Sun to vary? How do the geospace and planetary space environments and the heliosphere respond? What are the impacts on humanity? Heliophysics is a complex and sophisticated field that needs to be studied as a coupled system, which involves the different subdisciplines of heliophysics and how they interact and cause feedback with each other. For example, Earth’s ionosphere and magnetosphere are very closely coupled. To understand what is happening with the ionosphere requires studying the Sun to understand the solar wind and how it interacts with the magnetosphere.

NASA’s enacted Heliophysics Science Division budget for 2016 was $649.8 million. Over half of the heliophysics budget (55 percent) is spent on development. Research, operating missions, and suborbital costs are each around 11 to 12 percent of the budget. The remaining 11 percent is spent on missions in the primary science phase, management, and data systems.

The MMS, launched in 2015, uses four identical spacecraft flying in formation to examine Earth’s magnetosphere. It is an example of a currently operating large strategic mission in heliophysics. (See Figure 1.3.) Two large strategic heliophysics missions now in development are the Parker Solar Probe and the European Space Agency (ESA)’s Solar Orbiter, which includes NASA participation. The Parker Solar Probe, which is scheduled for launch

in 2018, will make multiple close flybys of the Sun. It will employ a combination of in situ measurements and imaging to achieve the mission’s primary scientific goal of understanding how the Sun’s corona is heated and how the solar wind is accelerated.

The Solar Orbiter Collaboration project will examine how the heliosphere is created and controlled by the Sun. The spacecraft will gather information about the Sun’s magnetic field, solar energetic particles, the solar wind, the heliospheric magnetic field, and transient interplanetary disturbances. This project is a collaborative effort between NASA and ESA.

Currently, the size of heliophysics missions can vary and depend on a multitude of factors. There are small competitive missions of opportunity, small Explorers (SMEXs), and medium Explorers (MIDEXs). MIDEX cost for last round was $250 million plus launch vehicle. The Solar Dynamics Observatory (SDO), launched in 2010 and costing $810 million, is an example of a large strategic mission, as is the Van Allen Probes mission, launched in 2012. The Heliophysics Division has also made investments in smaller spacecraft, such as MinXSS (Miniature X-Ray Solar Spectrometer) and CuSP (CubeSat to Study Solar Particles), as precursors to future multipoint measurements of the interplanetary space environment and its impact on Earth.

Compared to the other NASA science disciplines, within the heliophysics field much training and education are accomplished with small Explorer-class and even suborbital flights. In addition, the heliophysics discipline includes ground-based solar observatories that can also provide training and education opportunities. Although these are not within NASA’s portfolio, they do affect the overall health of the heliophysics community. Those observatories can in some cases rival the cost of smaller space missions, but are not funded by NASA.

PLANETARY SCIENCE DIVISION

The primary goal of planetary science is to ascertain the content, origin, and evolution of the solar system and the potential for life elsewhere.⁸ NASA currently operates spacecraft in orbit around the Moon, Mars, Jupiter, Saturn, and the minor planet Ceres. The agency also has two rovers operating on Mars, and the New Horizons spacecraft heading toward a rendezvous with a KBO.⁹

Cassini is one of two operating large strategic missions in planetary science. The spacecraft orbited Saturn starting in 2004 and ended its mission in September 2017. There have been over 5,250 publications based on the Cassini mission, including its Huygens Titan probe mission. In addition to Titan, the Cassini mission has also conducted critical studies on Saturn’s moon Enceladus.

The Mars Science Laboratory (MSL)/Curiosity program is a large strategic mission that has made many contributions to the planetary science field, particularly within the global mineralogical and geomorphological context provided by the last 20 years of remote sensing and landed missions at Mars. Curiosity has identified a clearly habitable environment with the necessary ingredients for life, demonstrated the first radiometric age dating of exposure ages of Martian rocks, constrained deuterium/hydrogen ratios of ancient Martian water, and identified unexpected (and unexplained) variability in methane concentrations over time. (See Figure 1.4.)

The Mars 2020 rover currently in development is an international collaborative program that includes instruments from France, Spain, and Norway. The other large strategic mission in development is the Europa Clipper mission scheduled for launch in 2022, which is planned to make multiple flybys of Jupiter’s moon Europa.

The Planetary Science Division also operates the Discovery and New Frontiers program lines. The Discovery program was established in 1992 and had a cost cap of $450 million per mission (excluding the launch vehicle) in FY2015 dollars for the most recent Announcement of Opportunity. Discovery is an open science competition for all solar system objects except Earth and the Sun. The New Frontiers program was established in 2001 and has a cost cap of $850 million per mission (excluding launch vehicle). Both of these programs address high-priority science objectives in solar system exploration. The Planetary Science Division is also investigating the potential

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⁸ Presentation by Planetary Science Division Director Jim Green to the Committee on Large Strategic NASA Science Missions, October 5, 2016.

⁹ Kuiper Belt objects (KBOs) orbit the Sun at the edge of the solar system, from the orbit of Neptune at 30 astronomical units (AU) out to 50 AU.

of small satellite missions to meet some exploration goals. Under the NASA Planetary Science Deep Space SmallSat Studies (PSDS3) program, 10 studies to develop mission concepts using small satellites to investigate Venus, Earth’s moon, asteroids, Mars, and the outer planets were selected. The total value of the awards is $3.6 million, where flight systems are defined as less than 180 kilograms.

The Planetary Science Division’s large strategic missions can support technology development, although the division’s goal is to support technology development via other methods than in the programs. The division uses targeted instrument calls and a mid-technology readiness level call, which are funded by the Research and Analysis program to help both strategic and PI-led missions. PI-led mission proposals requiring new technology development are typically not considered. The Planetary Science Division has a separate technology development program and also seeks to benefit from projects funded by NASA’s Space Technology Mission Directorate. Some newly developed technology has been transferred from separate development programs into operational missions. However, the need to be competitive has also driven PI teams to propose missions containing no new technology. The Planetary Science Division has thus sought opportunities to make new technology attractive to proposal teams.

According to the head of the Planetary Science Division, Jim Green, there have been clear differences in cost overruns between large strategic missions and smaller class missions. In the past large strategic missions were typically considered too scientifically important to cancel, depending on when the cost overrun occurs, and overruns need to be handled through de-scopes and replanning (cost and schedule readjustments). But from the start of the Mars 2020 rover program a cost cap concept was developed and used for strategic missions for the Planetary Science Division. This approach is also being applied to the Europa Clipper mission. The basic concept is to limit a strategic mission’s ability to affect other missions in the division’s portfolio and manage them like a PI-led mission. Smaller, PI-led missions have a cost cap and are usually terminated if there are significant cost overruns before confirmation. Examples of canceled small missions include the Clark Earth science mission, and the GEMS, FAME, and SPIDR Explorer missions. (The issue of cost estimation and overruns is addressed in Chapter 3.)

THE DECADAL SURVEYS AND LARGE STRATEGIC MISSIONS

The National Academies undertakes the decadal surveys in each of the four space science disciplines. NASA uses the decadal surveys to guide its programs, particularly new mission development and new science explorations. All of the decadal surveys have prioritized large strategic science missions and they may be explicitly directed to do so in their statements of task.

In 2015 the National Academies produced a study of its most recent decadal surveys. The report, The Space Science Decadal Surveys: Lessons Learned and Best Practices, outlined the importance of large strategic missions for each of the space science divisions. The report stated that the costs of such missions and facilities have increased, posing a substantial challenge for future decadal surveys.

Among the questions that the study addressed were the following:

• How can robust evaluations of the costs of such missions be made, and cost growth be contained, to protect other missions and activities?
• How can multidecade programs be managed successfully?
• How might we protect important human resources—for example, the education and research support of the next generation of scientists, especially those with skills in technology development?

The report stated the positives related to high-profile, strategic missions. Large strategic missions can have large-scale impacts by addressing critical science goals or questions for the decade. Large strategic missions continue to be critical to their scientific disciplines because certain missions cannot simply be broken down in an efficient or effective manner into smaller components and still accomplish the science goal.

The characteristics of these large-scale missions are unique, and they follow an implementation strategy that is performance driven rather than cost constrained. This is in contrast with PI-led cost-capped missions where de-scopes are required if a performance requirement cannot be met within preestablished cost constraints (in fact, many PI-led missions require a de-scope plan at their initiation, indicating which instruments or functions will be eliminated to keep a mission within the cost cap). Because a large part of science research originates in smaller missions, the decadal surveys attempt to strike a balance between larger, noncompeted, high-profile missions and the competed line of smaller missions. (The issue of balance is discussed in Chapter 2.)

The report concluded that based on the contributions seen from various missions across the disciplines, large strategic missions are important and critical for advancing science. The report also noted that the importance of large strategic science projects is not unique to space science. For example, Fermilab, the Large Hadron Collider, and the Laser Interferometer Gravitational-Wave Observatory (LIGO) have all made significant contributions to fundamental physics, and ITER is a major project in applied physics. Their investigations could not have been accomplished at smaller scales.

While there are many positives that derive from large strategic missions, the report also discussed and summarized the challenges they may face. The main challenges come from difficulties in the organization, management, building, and operation of an unprecedentedly complex machine. Often large strategic missions become what the report referred to as “high-profile missions.” These are missions of significant importance to a program and can have substantial negative impact on program health if not implemented successfully or within fiscal constraints. (See Box 1.1.) Their importance to the community’s science ambitions means that large strategic missions have the potential for a significant negative impact on performance across all activities within a division, and possibly across the SMD.

INTERNATIONAL COOPERATION AND LARGE STRATEGIC MISSIONS

It is common for NASA to engage international partners in the development and operation of its large strategic missions. Both the HST and the JWST have included international partners who have provided support in return for observing time on the telescope. The Cassini-Huygens mission included the ESA Huygens probe that descended to Titan in January 2005. Conversely, the United States will participate in the European Euclid dark

energy mission and will contribute three detector systems for the spacecraft’s near-infrared instrument. These are only a few examples, and international cooperation is common for NASA space science missions of all sizes.¹⁰

NASA currently has international partnerships on smaller missions, including competed missions. Large strategic missions offer greater opportunity for international participation in some instances because the spacecraft carry more instruments, some of which could be contributed by international partners. They also are higher profile and more attractive missions for potential partners. For example, the ability to gain observing time on a world-class space telescope appeals to astrophysics communities around the world.

International participation in a large strategic mission can create complications, but it also has advantages. One obvious advantage is that including international partners in a mission that the United States initiates, develops, and is responsible for demonstrates U.S. leadership in the field. Practically by definition, leading requires partners. But equally important, such partnerships also enable NASA to access scientific capabilities and expertise around the world, potentially including some that the United States may not possess itself.

Because of the intricacies of international affairs, cooperative agreements have usually been negotiated on a “no exchange of funds” basis, with the cooperation taking the form of an exchange of services or equipment. For example, the JWST will be launched on a European-supplied Ariane 5 rocket, and the Huygens probe was supplied by the ESA. In practice, NASA, ESA, and other space agencies have approached international collaboration on large strategic missions such that that one partner is a clear leader and the other partners play a supporting role. This approach allows clean management interfaces and unambiguous decision making and accountability.

At least one manager of a large strategic mission noted that the international partnership made their mission less vulnerable to cancellation. The committee heard no evidence indicating that international partnerships can reduce the cost of a mission, and the transaction costs for partnerships are difficult, perhaps impossible to measure. But as one NASA official noted, there is often an expectation within the scientific community that any large strategic mission will have a substantial international component.

THE VALUE OF LARGE STRATEGIC SCIENCE MISSIONS

Although each of NASA’s four science divisions has different requirements for and experiences with large strategic missions, it is possible to generalize their roles across all four divisions. Large strategic missions and small competed missions have different purposes. Large strategic missions tend to

• Focus on reconnaissance and on conducting a broad suite of objectives;
• Have longer lifetimes and sustained attention to details regarding consistency of operations and calibration;
• Operate with an evolving science program that responds to what has been learned as the mission proceeds, as opposed to a more-fixed science program;
• Travel to hard-to-reach destinations or challenging environments; and
• Carry a large number of and larger and heavier scientific instruments.

In contrast, smaller missions generally

• Focus on a single objective or a small number of tightly related objectives,
• Travel to easier-to-reach destinations or to more benign environments, and
• Carry fewer and smaller instruments.

A strategic mission that can achieve an order of magnitude gain in capability (e.g., sensitivity, resolution, field of view, wavelength coverage, multiplexing) can tackle foundational research questions and open new discovery space. Large strategic missions provide unique opportunities to perform critical scientific observations. Large strategic missions are one approach to achieve such goals, but challenges of complexity, expense, and cadence

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¹⁰ For further information, see National Research Council, Assessment of Impediments to Interagency Collaboration on Space and Earth Science Missions, The National Academies Press, Washington, D.C., 2011.

have drawn interest within the science community to explore emerging alternative small and medium-size mission designs, and in some cases some science questions require small spacecraft. Technology and capability advancements are rapidly changing how unique scientific measurements can be performed, where small and medium-size missions are emerging as competitive ways to contribute to critical scientific measurements. The ability to lead small and medium-size missions is compelling for the recent generation of scientific investigators, and the level of creativity within this community to conceive new, unique, and critical measurements (independent of what a large mission may be capable of performing) is growing rapidly.

The committee heard from congressional staff that an additional difference between large strategic “flagship” missions and medium-to-small-size missions is that the large missions are usually the only ones that members of Congress are familiar with and get engaged with. Smaller-size missions are below a budget and prestige threshold for them.

• Capture science data that cannot be obtained in any other way, owing usually to the physics of the data capture driving the scale and complexity of the mission;
• Answer many of the most compelling scientific questions facing the scientific fields supported by NASA’s Science Mission Directorate, and most importantly develop and deepen humanity’s understanding of Earth, our solar system, and the universe;
• Open new windows of scientific inquiry, expanding the discovery space of humanity’s exploration of our own planet and the universe, and providing new technology and engineering approaches that can benefit future small, medium-size, and large missions;
• Provide high-quality (precise and with stable absolute calibration) observations sustained over an extended period of time;
• Support the workforce, the industrial base, and technology development;
• Maintain U.S. leadership in space;
• Maintain U.S. scientific leadership;
• Produce scientific results and discoveries that capture the public’s imagination and encourage young scientists and engineers to pursue science and technical careers;
• Receive a high degree of external visibility, often symbolically representing NASA’s science program as a whole; and
• Provide greater opportunities for international participation, cooperation, and collaboration as well as opportunities for deeper interdisciplinary investigations across NASA science areas.

Although it is possible for smaller missions to provide some of the benefits in the preceding list, large strategic missions are more likely to provide more of them due to their more challenging goals, their larger size (i.e., supporting more instruments), and larger budgets.

Each division has different mission sizes in terms of cost, and therefore what qualifies as “small” in one division might qualify as a large mission in another. The best evaluation of mission sizes is within the respective division relative to the division’s total budget.

• Higher cadence,
• Greater agility and responsiveness to new scientific discoveries, and
• Different acceptance of risk.¹¹

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¹¹ NASA has different risk acceptance levels for payloads. Class A missions are considered high priority, very low (minimized) risk; Class B missions are considered high priority, low risk; Class C missions are considered medium priority, medium risk; and Class D missions are

The open-competition aspect of smaller missions also encourages ingenuity. There have been dramatic capability improvements in what small and medium-size missions can accomplish, particularly within the last few years. Nevertheless, large strategic missions remain vital to all of NASA’s space science disciplines because these lie at the cutting edge of the possible.

In the past decade there has been dramatic growth in the capabilities of small satellites, often generically referred to as CubeSats, but including both smaller and larger satellites than the formal CubeSat definition. This improvement in capabilities has created the impression among some people that large spacecraft are no longer required for the space sciences. But in many fields of space science large spacecraft represent the only way to answer the most important and challenging questions.

In 2016 the Academies produced the report Achieving Science with CubeSats: Thinking Inside the Box, which noted that many high-priority science investigations of the future will require data from constellations or swarms of 10 to 100 spacecraft. The report noted that in the past, large constellations of satellites were prohibitively expensive, but that this may be changing. In the near future, constellations of many small satellites collectively addressing important strategic science goals will qualify as “large strategic missions.” The committee concluded that this will be particularly true for heliophysics and Earth sciences. These scientific communities are already discussing future mission proposals of this type, and CubeSats can be useful for training future generations of scientists and engineers.

Any focus on missions by their size, complexity, and cost naturally leads to questions about how to accommodate the largest missions without draining all available resources for other smaller-size missions. That requires a discussion of the proper balance between large and small missions and how to achieve such balance, particularly when resources become constrained. That is the topic of the next chapter.

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considered low priority, high risk. Risk level calculations include such factors as redundancy for critical functions such as communications and propulsion. Large strategic missions are always Class A missions. Smaller missions are usually Class B, C, or D.