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The Constellation System and Opportunities for Science

NASA asked the National Research Council (NRC), through the Space Studies Board and the Aeronautics and Space Engineering Board, to establish an ad hoc committee to assess potential space and Earth science research concepts that could take advantage of the capabilities of the Constellation System of launch vehicles and spacecraft and could launch in the period between 2020 and 2035. The Constellation System is being developed by NASA to implement the initial phases of the Vision for Space Exploration. The system consists of the Orion spacecraft, the Altair lunar lander, and the Ares I and Ares V launch vehicles (for an overview of the system, see Chapter 5).

In response to NASA’s request, the NRC established the Committee on Science Opportunities Enabled by NASA’s Constellation System. The committee conducted its assessment in two phases: (1) an interim report was released in May 2008,1 (2) followed by the completion of this final report.

This report is not intended as a review or endorsement of the Constellation System as a whole or of any of its elements, nor is the report intended to make any suggestions regarding potential changes to the Constellation System. Rather, this report accepts the Constellation System as it was defined for the committee, and seeks to assess a set of proposed science missions and to identify those that could benefit from Constellation’s capabilities and would potentially fly sometime after the next decade.2 In addition, this report does not prioritize science goals for NASA, a responsibility that lies with the NRC’s decadal survey process.3

This report consists of five chapters. Chapter 1 provides introductory and background information and a discussion of potential costs and benefits of Constellation science missions. Chapter 2 consists of summaries and evaluations of 12 different science mission concepts reviewed by the committee. It should be noted that this report treats these concepts as examples of potential missions, rather than as specific mission proposals. They are as follows:

  • Advanced Technology Large-Aperture Space Telescope (ATLAST),

  • Dark Ages Lunar Interferometer (DALI),

1

National Research Council, Science Opportunities Enabled by NASA’s Constellation System: Interim Report, The National Academies Press, Washington, D.C., 2008.

2

Marc Timm, NASA, “Constellation Overview,” presentation to the Committee on Science Opportunities Enabled by NASA’s Constellation System, February 2008.

3

The decadal survey process is the method by which the National Research Council, through its study committees, advises NASA, the National Science Foundation, and other government agencies on science priorities in particular disciplines at roughly one-decade intervals, looking out through the next decade. The astronomy and astrophysics decadal survey has been conducted since the 1960s. The first decadal surveys in solar system exploration, heliophysics, and Earth science were commissioned within the past decade.



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1 The Constellation System and Opportunities for Science NASA asked the National Research Council (NRC), through the Space Studies Board and the Aeronautics and Space Engineering Board, to establish an ad hoc committee to assess potential space and Earth science research concepts that could take advantage of the capabilities of the Constellation System of launch vehicles and spacecraft and could launch in the period between 2020 and 2035. The Constellation System is being developed by NASA to implement the initial phases of the Vision for Space Exploration. The system consists of the Orion spacecraft, the Altair lunar lander, and the Ares I and Ares V launch vehicles (for an overview of the system, see Chapter 5). In response to NASA’s request, the NRC established the Committee on Science Opportunities Enabled by NASA’s Constellation System. The committee conducted its assessment in two phases: (1) an interim report was released in May 2008,1 (2) followed by the completion of this final report. This report is not intended as a review or endorsement of the Constellation System as a whole or of any of its elements, nor is the report intended to make any suggestions regarding potential changes to the Constellation System. Rather, this report accepts the Constellation System as it was defined for the committee, and seeks to assess a set of proposed science missions and to identify those that could benefit from Constellation’s capabilities and would potentially fly sometime after the next decade.2 In addition, this report does not prioritize science goals for NASA, a responsibility that lies with the NRC’s decadal survey process. 3 This report consists of five chapters. Chapter 1 provides introductory and background information and a discussion of potential costs and benefits of Constellation science missions. Chapter 2 consists of summaries and evaluations of 12 different science mission concepts reviewed by the committee. It should be noted that this report treats these concepts as examples of potential missions, rather than as specific mission proposals. They are as follows: • Advanced Technology Large-Aperture Space Telescope (ATLAST), • Dark Ages Lunar Interferometer (DALI), 1 National Research Council, Science Opportunities Enabled by NASA’s Constellation System: Interim Report, The National Academies Press, Washington, D.C., 2008. 2 Marc Timm, NASA, “Constellation Overview,” presentation to the Committee on Science Opportunities Enabled by NASA’s Constellation System, February 2008. 3The decadal survey process is the method by which the National Research Council, through its study committees, advises NASA, the National Science Foundation, and other government agencies on science priorities in particular disciplines at roughly one-decade intervals, looking out through the next decade. The astronomy and astrophysics decadal survey has been conducted since the 1960s. The first decadal surveys in solar system exploration, heliophysics, and Earth science were commissioned within the past decade. 

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0 LAUNCHING SCIENCE • 8-Meter Monolithic Space Telescope, • Exploration of Near Earth Objects via the Crew Exploration Vehicle, • Generation-X (Gen-X), • Interstellar Probe, • Modern Universe Space Telescope (MUST), • Neptune Orbiter with Probes (2 studies), • Solar Polar Imager, • Solar Probe 2, • Stellar Imager, and • Titan Explorer. Chapter 3 provides a discussion of technology that may be required by many of these missions and an over- view of NASA technology development efforts relevant to the mission concepts that were evaluated. Chapter 4 addresses the potential of human and robotic servicing of space missions, discussing relatively new capabilities that Constellation and other projects will provide. Finally, Chapter 5 provides an overview of the Orion spacecraft, the Constellation launch vehicles, and alternative launch vehicles available to space science missions. The committee chose the 12 concepts listed above to evaluate as types of missions that could be conducted using Constellation (see Chapter 2). The committee determined that the 5 mission concepts listed below would not be enabled by Constellation (these 5 concepts are summarized in Appendix B): • Advanced Compton Telescope (ACT), • Kilometer-Baseline Far-Infrared/Submillimeter Interferometer, • Single Aperture Far Infrared (SAFIR) Telescope, • Solar System Exploration/Astrobiology Vision Mission (Palmer Quest), and • Super-EUSO (Extreme Universe Space Observatory). THE RELATIONSHIP BETWEEN LAUNCH VEHICLE SIZE AND MISSION COST The kinds of proposed science missions presented to the committee for evaluation for this report are relatively large and ambitious. They all fall into a category that is generally referred to as flagship-class missions. The committee grouped the missions into three “cost bins” for the purpose of this study: those with preliminary cost estimates of less than $1 billion, of $1 billion to $5 billion, and of more than $5 billion. Of the mission concepts evaluated, only one was considered to be marginally in the “less-than-$1 billion” category, and seven were con- sidered to be in the “more-than-$5 billion” category, which would make them larger than any other space science mission developed by NASA to date. Finding: The scientific missions reviewed by the committee as appropriate for launch on an Ares V vehicle fall, with few exceptions, into the “flagship” class of missions. The preliminary cost estimates, based on mis- sion concepts that at this time are not very detailed, indicate that the costs of many of the missions analyzed will be above $5 billion (in current dollars). The Ares V costs are not included in these estimates. The committee notes that expensive space science programs will place a great strain on the space science budget, which has been essentially flat for several years and is already under strain from an ambitious slate of  flight missions.4 To estimate the costs of potential, large space science missions, the committee used NASA’s Advanced Mis- sions Cost Model and estimated the costs of three new-design planetary science missions representing the three 4 NASA’s science program as of Spring 2008 consisted of 94 flight missions—53 in operation plus 41 in development (Alan Stern, NASA Science Mission Directorate, presentation to the Space Studies Board, March 10, 2008).

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 THE CONSTELLATION SYSTEM AND OPPORTUNITIES FOR SCIENCE FIGURE 1.1 Estimated spacecraft costs as a function of payload dry mass for three classes of difficulty for solar system ex- ploration missions, using NASA’s Advanced Missions Cost Model. NOTE: For comparison, the Cassini-Huygens mission’s Figure 1.1.eps dry mass was approximately 2.5 metric tons (the cost of the Cassini-Huygens mission was approximately $2 billion in 1997 dollars, and may not reflect the total cost of the mission owing to European Space Agency involvement). Note that the Ares V Bitmap image - Low resolution capabilities would actually span a number of payload masses in this figure. For example, Ares V could launch 10 metric tons to Uranus or Neptune and significantly more to Jupiter and Mars. levels of technological difficulty used in NASA’s model.5 Illustrated in Figure 1.1, the results indicate the correla- tion between rising payload mass and higher cost. The committee was not provided cost estimates of either the Ares I or the Ares V launch vehicle, but Ares V can be expected to be more expensive than even the largest Evolved Expendable Launch Vehicle (EELV) currently in the U.S. inventory—the Delta IV Heavy, with a launch cost of about $250 million. 6 The committee notes that the combined effect of expensive payloads and expensive launchers would distort the balance of the space science program. The advent of the Ares V boosters promises to enable very large, very heavy science payloads to be delivered to orbits of interest. The Ares V lift capability is expected to be about five times larger than that of the current largest U.S. booster—the Delta IV Heavy. Similarly, the very large payload shroud of the Ares V will be capable of housing payload volumes some three times larger than are currently feasible with a Delta IV. Detailed com- parisons between the capabilities expected of the boosters in the Constellation System and those possible with the current family of boosters are provided in Chapter 5. 5The Advanced Missions Cost Model is available at http://cost.jsc.nasa.gov/AMCM.html. 6The committee bases the conclusion that the Ares V will be significantly more expensive than the Delta IV Heavy on several factors, but one of the most straightforward is counting the number of engines: the Delta IV Heavy has three RS-68 main engines, whereas the Ares V is expected to have six RS-68s, plus two 5.5-segment solid rocket boosters.

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 LAUNCHING SCIENCE The various mission proposals discussed in this report have identified multiple ways to take advantage of the increased lift capability and payload volume afforded by the Ares V. Those benefits can be loosely grouped in three areas: simplification of spacecraft or mission design; elimination of the reliance on advanced, immature technologies; and increased scientific capabilities. The Large Ultraviolet/Optical Modern Universe Space Telescope (LUVO-MUST)7 and the 8-Meter Monolithic Space Telescope are examples of reduced complexity of spacecraft design, where the increased payload volume of the Ares V would obviate the need for complex packaging and on- orbit system deployment. For Generation-X, the Ares V would eliminate the need for multiple launches, complex packaging, and on-orbit assembly. The reliance on technologies such as aerocapture, nuclear electric propulsion, solar electric propulsion, or solar sails can potentially be eliminated from missions such as the Solar Polar Imager, Interstellar Probe, Titan Explorer, and Neptune Orbiter with Probes. The 16-meter telescope identified in the ATLAST proposal would take advantage of the added capabilities of the Ares V to increase the scientific capabil- ity of the mission, whereas the DALI mission and Exploration of Near Earth Objects via the Crew Exploration Vehicle could only be accomplished with the Ares V system. The variety of ways in which the scientific teams that developed the mission concepts took advantage of the Ares V calls into question the long-held belief that increased payload capability leads to larger payloads resulting in higher mission costs. Long experience has demonstrated that there is a relationship between the mass of a pay- load and its cost—bigger payloads inevitably cost more than smaller payloads do. In addition, payload mass often expands to fill the available launch vehicle capability. However, it is likewise clear that complexity of spacecraft design is also a critical cost driver. These relationships are captured in NASA’s Advanced Missions Cost Model. 8 The question is then whether programs can be carefully managed within cost budgets, or whether the appetite for increased scientific knowledge will drive system growth to the physical limits of the launch system. If the former is true, the curves depicted in Figure 1.1 would no longer apply. An increased weight allowance, for example, could be used to reduce complexity, thus changing the slope of the cost-versus-weight curve drastically, and pos- sibly resulting in a negative slope. The three ultraviolet (UV)/optical telescope options presented to the committee are clear examples of the cost-versus-capability tug-of-war. The baseline concept for MUST, a 10-meter-diameter telescope to be flown on a Delta IV Heavy, required complex packaging with on-orbit, robotic assembly. The 8-Meter Monolithic Space Telescope built on this concept, optimizing the design to take full advantage of the payload volume and lift capa- bility of the Ares V to minimize the design complexity and reduce reliance on advanced technologies in order to minimize total development costs. On the opposite end of the cost-versus-capability spectrum is ATLAST. Recognizing the significant increase in scientific value afforded with larger space telescopes, the ATLAST team developed a concept for a 16-meter segmented mirror design that takes full advantage of both the lift capability and payload volume of the Ares V (see Figure 1.2). The added design complexity associated with packaging and deployment, as well as the lightweight mirrors, would significantly increase the cost of the mission. According to the Advanced Missions Cost Model, a very-low-complexity design that fully utilizes the lift capability of the Ares V (such as the 8-Meter Monolithic Space Telescope) would cost on the order of $3 billion, whereas a highly complex design (such as ATLAST) could easily cost in excess of $10 billion. Virtually all of the mission concepts evaluated by the committee are large, complex, and costly. The capabili- ties of the Ares V will enable even larger, more complex, and more capable systems than these—systems that can dramatically increase scientific return. With the advent of the Ares V, the challenge for program managers will be to temper the appetites of scientists who will clearly recognize the dramatic scientific benefits enabled by the launch system. There will need to be an enforced paradigm shift where cost, rather than launch system capability, is the design limiter. The committee was unable to locate any systematic engineering analysis that tested the proposition that relaxation of weight and volume constraints will lead to relatively cheaper payloads. Prior spaceflight experience demonstrates that payloads fill all available weight and volume budgets (and power and telemetry budgets as well) 7 LUVO is considered to be a class of telescopes, and MUST is a specific mission-concept proposal within that class. 8 See http://cost.jsc.nasa.gov/AMCM.html.

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 THE CONSTELLATION SYSTEM AND OPPORTUNITIES FOR SCIENCE FIGURE 1.2 An example of the growth in space telescope apertures. The Hubble Space Telescope (HST) has been in orbit since 1990. The James Webb Space Telescope (JWST) has substantially increased area. Two proposals, the 8-Meter Monolithic Space Telescope and the Advanced Technology Large-Aperture Space Telescope (ATLAST) 16-meter telescope, demonstrate Figure 1.2.eps the significant growth in aperture made possible by the Ares V launch vehicle. SOURCE: Courtesy of NASA. Bitmap image - Low resolution and that heroic measures are frequently undertaken to reduce weights sufficiently to fit within the launch vehicle’s capabilities. However, the differences between the capabilities of a Delta IV Heavy, for example, and those of an Ares V are so large that, indeed, a new regime of payload construction might be possible. The testing of this proposition by means of a comprehensive, systems-engineering-based analysis merits NASA’s attention. Recommendation: NASA should conduct a comprehensive systems-engineering-based analysis to assess the possibility that the relaxation of weight and volume constraints enabled by Ares V for some space science missions might make feasible a significantly different approach to science mission design, development, assembly, integration, and testing, resulting in a relative decrease in the cost of space science missions. OPPORTUNITIES FOR SCIENCE Exciting new science may be enabled by the increased capability of Ares V. The larger launch mass, large volume, and increased C3 capability are only now being recognized by the science community. (C3 is km 2/s2 the square of the hyperbolic excess velocity, in other words, the amount of velocity that the vehicle can provide to the spacecraft beyond that needed to escape Earth’s gravitational field.) During the course of this study, NASA sponsored several workshops on the potential of Ares V for future science missions.9 The first workshop, Ares V Astronomy Workshop, sponsored by the NASA Ames Research Center and held April 26-27, 2008, focused on the Ares V and possible astronomy missions, the majority of which are also evaluated in this study. The second workshop, Ares V Solar System Science Workshop, also sponsored by Ames and held August 16-17, 2008, focused on the Ares V and potential solar system exploration. 9 See http://event.arc.nasa.gov/aresv/ and http://event.arc.nasa.gov/aresv-sss/index.php?fuseaction=home.home. The Astronomy Workshop is summarized in S. Langhoff, D. Lester, H. Thronson, and R. Correll, eds., Workshop Report on Astronomy Enabled by Ares V, NASA/CP-2008- 214588, August 2008, available at http://event.arc.nasa.gov/main/home/reports/CP-2008-214588-AresV.pdf. The Solar System Workshop is summarized in S. Langhoff, T. Spilker, G. Martin, and G. Sullivan, eds., Workshop Report on Ares V Solar System Science, NASA/CP-2008- 214592, August 2008, available at http://event.arc.nasa.gov/main/home/reports/CP-2008-214592-AresV-SSS_Print.pdf.

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 LAUNCHING SCIENCE The mission concepts that the committee evaluated, along with the criteria used to rank them, are described in Chapter 2. In general, the mission concepts fall into two broad groups—those involving the universe and those involving our solar system. The universe group includes large-aperture telescopes or arrays of telescopes leading to the “Greater Observatories”—that is, the astronomical instruments that will succeed the Hubble Space Telescope, the Chandra X-ray Observatory, the Spitzer Space Telescope, and the Compton Gamma-Ray Observatory. The primary factors for most of the missions in the universe group are the volume and mass availability of the Ares V. For the solar system group of missions, the primary driver is the C3 capability. The astronomy and astrophysics community has long desired increasingly larger apertures for its observatories and naturally had several concepts for large-aperture space telescopes that could take advantage of the capabilities of a large launch vehicle like the Ares V (for instance, see Figure 1.2). However, other space science communities have been more constrained by the capabilities of the existing family of launch vehicles and have only recently begun to consider the potential of the Ares V. Because NASA is only beginning to study the potential of this new launch vehicle for science missions, other mission concepts may emerge that are as exciting as the ones identified in this report. The committee notes that it received three separate proposals for large UV/optical telescopes to be flown at the Earth-Sun Lagrangian point L2, essentially an eventual successor to the highly successful Hubble Space Telescope. Two of these proposals, ATLAST and MUST, presented a science case that listed several general astrophysics themes as their goals. (For example: How are galaxies formed and how do they evolve?) However, the mission concepts did not provide detailed answers to show how the specific observations would be made and the scientific results that their respective missions would uniquely provide to answer these questions. The committee observes that in the past, merely stating general science goals for a larger telescope, suggest- ing that the well-known “discovery space” results will be enough to justify the mission cost and launch, has been insufficient to elevate UV/optical telescopes to high-priority science missions. A more effective approach requires specifying high-priority science questions to be answered and directly identifying how a proposed mission and instruments will answer the questions. As indicated in its evaluations in Chapter 2, the committee ranked the 8- Meter Monolithic Space Telescope higher than ATLAST and MUST because it provides the best possibility of extrasolar planet imaging and spectroscopy, a high-interest topic with paradigm-changing possibilities. This mis- sion has the additional benefit that many new “discovery space” science results will also occur. If the scientific community seeks to develop a new large UV/optical space telescope to follow Hubble, it must clearly identify significant scientific questions that the telescope will answer and a path for answering them, and not rely on the vague assertion, however accurate, that a larger aperture will automatically result in further discoveries. OTHER POSSIBLE MISSIONS As mentioned above, after this study had started, NASA undertook several workshops that paralleled the work of the committee.10 The Ares V Astronomy Workshop focused on the Ares V and possible astronomy missions, most of which this study also evaluates. The Ares V Solar System Science Workshop focused on the Ares V and potential solar system exploration. With the exception of the mission concept for sending an Orion spacecraft to a near-Earth object (evaluated in this study), there were few well-defined mission concepts discussed by the participants. This highlights the fact that the planetary science community has had less incentive or opportunity to consider the capabilities presented by a significantly larger launch vehicle than has the astronomy and astrophysics community. There are several reasons for this, but one primary explanation is that astronomers are always interested in larger-aperture telescopes and therefore ready for larger launch vehicles, whereas planetary science missions are more tightly constrained not only by payload shrouds but also by the energy required to reach distant targets. The planetary scientists at NASA’s Ares V Solar System Science Workshop discussed ideas that generally split into two different themes: (1) maximizing the science capabilities of a mission (i.e., filling the available volume and mass of the Ares V) and (2) finding methods of adding relatively inexpensive capabilities to missions in the current cost categories. One of the latter ideas was the concept of “cheap, dumb mass” that could be added 10 See http://event.arc.nasa.gov/aresv/ and http://event.arc.nasa.gov/aresv-sss/index.php?fuseaction=home.home.

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 THE CONSTELLATION SYSTEM AND OPPORTUNITIES FOR SCIENCE to a spacecraft, such as additional fuel, radiation shielding, or an impactor such as that used for the Deep Impact and the Lunar Crater Observation and Sensing Satellite (LCROSS) missions. Other participants proposed adding moderate additional capabilities to missions, such as increasing the aperture size of an imager or adding a relatively inexpensive icy moons gravity-measuring spacecraft to a Europa or Jupiter system mission. Many of the comments suggested that although the additional C3 capability of an Ares V would be beneficial in a number of cases, some of this capability could be traded for incremental improvements in instrumentation as well. Ares V’s mass capabilities also offer potential for sample-return missions. Mars seems to be the most likely beneficiary, although only one Mars sample-return concept was discussed at the workshop. The Ares V Solar System Science Workshop participants were particularly intrigued by the possibility that Ares V could enable sample-return missions to the outer solar system. Although the participants discussed Europa and Titan missions, several participants noted that one possibility was a mission to Enceladus. 11 In 2007, NASA sponsored a study of a potential Enceladus flagship-class mission that included a possible sample-return option. But the incredibly long duration of this mission (18 to 20 years), plus the high velocity at which a collection spacecraft would fly through the vapor plumes at Enceladus (probably destroying the samples), made this concept unlikely. Ares V offers the possibility of flying a fast trajectory to Enceladus, slowing down to collect the samples, and then accelerating back to Earth. What both the Ares V Astronomy Workshop and Ares V Solar System Science Workshop also highlighted was the requirement for incorporating certain features into the Ares V that would enable science missions. The astronomy community stressed the need for a clean launch shroud environment (so as not to contaminate optics, either on the ground, during launch, or at fairing separation) and noise and vibration levels equivalent to or better than those on the space shuttle. The planetary science community emphasized requirements for removing the heat produced by radioisotope thermoelectric generators (RTGs) inside the shroud, as well as on-pad access (i.e., shortly before launch) to the spacecraft inside the shroud. Because virtually all planetary missions require some sort of upper stage, and because NASA recently increased the overall length of Ares V, the Ares V Solar System Science Workshop participants were particularly concerned about the amount of usable volume inside the shroud. According to one rough estimate, adding a Centaur upper stage to Ares V would leave only 4 meters from the top of the Centaur to the top of the shroud—significantly less than the length of a flagship-class spacecraft such as Cassini. (The Ares V height cannot be significantly increased because of size limitations in the Vehicle Assembly Building.) THE CONSTELLATION SYSTEM AND EARTH SCIENCE The mission concepts evaluated in this report represent only a subset of the potential missions that could benefit from the Constellation System. During the course of this study, no Earth science mission concepts were proposed to the committee. A proposed NASA workshop on the Constellation System and Earth science was canceled due to lack of interest, and only the most basic ideas about using Constellation for Earth science were discussed at the Ares V Solar System Science Workshop. The majority of the mission concepts evaluated in this study are the result of NASA’s Vision Mission effort, which did not include Earth science because at that time Earth science was separated organizationally within NASA from space science. Had NASA included Earth sciences in the Vision Mission studies it might have generated advanced concepts that could also benefit from the Constellation System. However, the committee lacked data for determining why it did not receive any Earth science responses to its request for information. The committee suspects that although there may be potential Earth science uses for the Constellation System, no such uses are currently apparent. The explanation may simply be that there were no concepts sufficiently mature for presenta- tion to the committee. Finding: The committee did not receive any Earth science proposals and found it impossible to assess the potential of the Constellation System to meet the future needs of Earth-oriented missions. 11 See http://www.lpi.usra.edu/opag/Enceladus_Public_Report.pdf.

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 LAUNCHING SCIENCE INTERNATIONAL COOPERATION The original NASA solicitation for the Vision Missions—mission concepts for future space science missions studied at the initiation of NASA between 2004 and 2006—did not require that respondents address opportunities for international cooperation. In reviewing many of the individual Vision Missions, however, the committee noted parallel or complementary activities on the part of potential international partners. For example, the Advanced Compton Telescope (see Appendix B), which does not require an Ares V-class launch vehicle, does require a low- inclination orbit such as could be provided by the European Space Agency’s (ESA’s) Ariane V launch vehicle. Similarly, both the Interstellar Probe and the Solar Polar Imager correspond to missions that are under study by the ESA. It is beyond the scope of this report to make recommendations regarding international cooperation, but the committee nevertheless considers it important to point out that due to cost, many of these extremely large missions would probably require some degree of international cooperation or collaboration in order to be feasible. The cost, schedule, and performance implications of such international cooperation are not considered in this report. BOX 1.1 Cautionary Tale 1: The Voyager-Mars Mission In 1960, NASA began establishing long-term plans for lunar and planetary missions. The Voyager-Mars program arose from these early concepts, prompted by a desire to explore the solar system and reach Mars before the same goal was achieved by the then-USSR. The Voyager-Mars mission was a Jet Propulsion Labo- ratory (JPL)-led program (not to be confused with the Voyager outer planets program of the 1970s).1 NASA selected Avco and General Electric to propose ambitious robotic Mars exploration spacecraft. While their proposals differed, both companies proposed spacecraft equipped with biological equipment for life detection, geophysical-geological tools to explore seismic activity and planetary composition, and atmospheric devices. General Electric proposed two landers and one orbiter, whereas Avco suggested one lander and one orbiter. In 1964, NASA managers decided to set a launch date for Voyager. A test flight would take place in 1969, followed by two launches in 1971 and four in 1973. The total projected cost of the mission was $1.25 billion, making it the most expensive robotic spacecraft program proposed by NASA at the time. Mariner 4 conducted a Mars flyby in 1964. Contrary to NASA’s expectations about the red planet, Mariner 4 gave scientists a bleak prognosis with respect to the chances that there had been life on Mars. In addition, atmospheric occultation data indicated a surface pressure of 5 to 7 millibars, whereas Voyager had been designed for a surface pressure of 10 or 11 millibars. The thinner atmosphere necessitated reworking the lander’s atmospheric entry method. From the beginning there was friction between NASA Headquarters and JPL over the design of the mission. NASA Headquarters ordered that the Saturn IB-Centaur rocket that was part of the original design proposal be changed to a Saturn V. However, the Saturn V possessed substantially more payload capability than that required for the Voyager spacecraft. The cost of the Saturn V rocket was also projected to be the same as that for constructing two Saturn IB-Centaur rockets. To take advantage of this additional capability, spacecraft designers decided to launch two independent Voyager craft on the same Saturn V launch vehicle. (See Figures 1.1.1 and 1.1.2.) NASA’s decision made program costs soar, and NASA representatives developed a new estimate for program costs—$2.2 billion through fiscal year 1977, in addition to about $95 million in associated costs. Al- though it is difficult to calculate these projected costs in current-year dollars, it is clear that the Voyager-Mars mission would have cost over $10 billion in today’s dollars. With most of NASA’s funding dedicated to the Apollo program, Congress was skeptical about the rising costs of a Voyager mission. In the latter half of the 1960s, NASA canceled the 1969 test flight and the 1971 flight owing to lack of funds. These setbacks spelled the end for Voyager. The Vietnam War’s demands on the U.S. budget, the growing cost of the Apollo program, and widespread civil unrest made Congress reprioritize how the government should spend its money. In 1967, the Voyager-Mars mission was slashed entirely as the

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 THE CONSTELLATION SYSTEM AND OPPORTUNITIES FOR SCIENCE Finding: International cooperation could provide access to international scientific expertise and technology useful for large, complex, and costly mission concepts and could reduce costs through provision of instru- ments and infrastructure by international partners. CAUTIONARY TALES: THE VOYAGER-MARS MISSION AND PROJECT PROMETHEUS Of all the components of the Constellation System, the Ares V rocket offers the greatest potential benefit to science. However, there is anecdotal evidence from NASA’s own past about the pitfalls of designing large science missions to fit on large launch vehicles. See Boxes 1.1 and 1.2. FIGURE 1.1.2 NASA’s Saturn V launch vehicle— the largest launch vehicle ever built—inside the Vehicle Assembly Building in the late 1960s. In FIGURE 1.1.1 Test of the aeroshell for the Voy- addition to launching the Apollo missions to the ager-Mars lander in the mid-1960s. Voyager was Moon, NASA planned on using a Saturn V to to be a large spacecraft launched atop a Saturn V launch the Voyager spacecraft to Mars. SOURCE: rocket. SOURCE: Courtesy of NASA. Courtesy of NASA. Senate Appropriations Committee made its final allocations. The cancellation set back NASA’s Mars explora- tion by several years. Eventually NASA launched two Viking missions to Mars in the mid-1970s to accomplish many of the goals of Voyager. Although significantly less expensive than the Voyager-Mars mission, the Viking missions remain NASA’s most expensive planetary spacecraft. 1E.C. Ezell and L. Neuman Ezell, On Mars: Exploration of the Red Planet 1958-1978, NASA, Washington, D.C., 1984, pp. 85-86.

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 LAUNCHING SCIENCE BOX 1.2 Cautionary Tale 2: Project Prometheus Project Prometheus was a program to develop a nuclear fission reactor and high-power electric pro- pulsion systems for a range of outer-planet applications. The plan first circulated as early as 2001, but the program was not formally started until March 2003. Initially it was a science program, but it was subsequently transferred to the NASA Exploration Systems Mission Directorate when that directorate was established in February 2004. Although the overall project was named Prometheus, the initial emphasis of the program was to develop a spacecraft known as the Jupiter Icy Moons Orbiter (JIMO). (See Figure 1.2.1.) JIMO’s mission was to search for evidence of global subsurface oceans on Jupiter’s three icy moons: Europa, Ganymede, and Callisto. JIMO was intended to launch in 2011, with an approximate 12-year lifespan (the proposed launch date was later slipped to 2015). It would reach Jupiter 8 years after launch and have an operational mission time frame of 40 months. JIMO would have more than 10,000 watts of available power, compared with 885 watts for the radioiso- tope-powered Cassini mission (633 watts at the end of the mission). The available power, higher in comparison with that of radioisotope thermoelectric generators, would have allowed JIMO to carry a more extensive suite of instruments and also to transmit significantly more data back to Earth—some 500 gigabits of science data vol- ume returned to Earth, over five times more data than received from Cassini, Voyager, and Galileo combined. To develop the technologies required for Prometheus, other agencies partnered with NASA, including the Department of Energy, the U.S. Navy’s Naval Reactors Division, and the Department of Defense’s Office of the Director of Defense Research and Engineering. As Prometheus progressed, mission designers realized that prior to launching the JIMO mission, they would first have to launch a demonstration mission to prove that the reactor design would operate success- fully for the many years required for outer-planetary missions. This demonstration mission became known as Prometheus-1. In the summer of 2005, NASA canceled the Prometheus program after the expenditure of nearly $464 million (this did not include the costs to the contractors that prepared expensive bids to win the Prometheus contract—costs that were in the tens of millions of dollars each). The project was officially discontinued effective October 2, 2005. Of the $100 million allocated in fiscal year 2006, $90 million was spent to pay closeout costs on canceled contracts. The final report on Project Prometheus, released on October 1, 2005, provided a detailed cost analysis of a Jupiter Icy Moons Orbiter, which would have cost $16 billion through Phase E (i.e., science data collection), not counting the additional estimated $5 billion for the launch system.1 This $21 billion for a single solar system exploration mission presumably did not include the development costs for the nuclear reactor and associated systems, which would have been developed to support the Prometheus-1 demonstration mission. Prometheus serves as an example of the risks associated with pursuing ambitious, expensive space science missions. Despite the expenditure of hundreds of millions of dollars over a relatively short period of time, no spacecraft was ever developed. 1Jet Propulsion Laboratory, Prometheus Project Final Report, 982-R120461, October 1, 2005, p. 178.

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 THE CONSTELLATION SYSTEM AND OPPORTUNITIES FOR SCIENCE FIGURE 1.2.1 Artist’s conception of the Jupiter Icy Moons Orbiter spacecraft. SOURCE: Courtesy of NASA.