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Summary In 2004 NASA began implementation of the first phases of a new space exploration policy.1 This imple- mentation effort included the development of a new human-carrying spacecraft, known as Orion; the Altair lunar lander; and two new launch vehicles, the Ares I and Ares V rockets—collectively called the Constellation System (described in Chapter 5 of this report). The Altair lunar lander, which is in the very preliminary concept stage, is not discussed in detail in this report. In 2007 NASA asked the National Research Council (NRC) to evaluate the science opportunities enabled by the Constellation System. To do so, the NRC established the Committee on Sci- ence Opportunities Enabled by NASA’s Constellation System. In general, the committee interpreted “Constellation- enabled” broadly, to include not only mission concepts that required Constellation, but also those that could be significantly enhanced by Constellation. The committee intends this report to be a general overview of the topic of science missions that might be enabled by Constellation, a sort of textbook introduction to the subject. The mission concepts that are reviewed in this report should serve as general examples of kinds of missions, and the committee’s evaluation should not be construed as an endorsement of the specific teams that developed the mission concepts or of their proposals. Additionally, NASA has a well-developed process for establishing scientific priorities by asking the NRC to con- duct a “decadal survey” for a particular discipline. Any scientific mission that eventually uses the Constellation System will have to be properly evaluated by means of this decadal survey process. The committee was impressed with the scientific potential of many of the proposals that it evaluated. However, the committee notes that the Constellation System has been justified by NASA and selected in order to enable human exploration beyond low Earth orbit—not to enable science missions. Virtually all of the science mission concepts that could take advantage of Constellation’s unique capabilities are likely to be prohibitively expensive. Several times in the past NASA has begun ambitious space science missions that ultimately proved too expensive for the agency to pursue. Examples include the Voyager-Mars mission and the Prometheus program and its Jupiter Icy Moons Orbiter spacecraft (both examples are discussed in Chapter 1). 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. 1 See http://www.whitehouse.gov/space/renewed_spirit.html. 

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 LAUNCHING SCIENCE All of the costs discussed in this report are presented in current-year (2008) dollars, not accounting for poten- tial inflation that could occur between now and the decade in which these missions might be pursued. In general, preliminary cost estimates for proposed missions are, for many reasons, significantly lower than the final costs. Given the large cost estimates for many of the missions assessed in this report, the potentially large impacts on NASA’s budget by many of these missions are readily apparent. SCIENCE MISSIONS THAT ARE ENABLED OR ENHANCED BY THE CONSTELLATION SYSTEM The committee evaluated a total of 17 mission concepts for future space science missions (11 were “Vision Missions” studied at the initiation of NASA between 2004 and 2006; the remaining 6 were submitted to the committee in response to its request for information).2 The committee based its initial evaluation of each mis- sion concept on two criteria: (1) whether the concept offered the potential for a significant scientific advance and (2) whether or not the concept would benefit from the Constellation System. The committee determined that all of the concepts offered the possibility of a significant scientific advance, but it cautions that such an evaluation ultimately must be made by the NRC’s decadal survey process referred to above. This report’s evaluations should not be considered to be an endorsement of the scientific merit of these proposals, which must of course be evalu- ated relative to other proposals. The committee determined that 12 of the 17 mission concepts would benefit from the Constellation System, whereas 5 would not. See Table S.1 for a summary of the mission concepts, including their cost estimates, techni- cal maturity, and reasons why they might benefit from the Constellation System. The five mission concepts that the committee deemed not worthy of further study as Constellation missions according to its evaluation criteria simply do not require, or do not appear to benefit highly from, use of the Con- stellation System (see Table S.1). In several cases they should easily fit within existing launch vehicles. In one case, that of Super-EUSO (Extreme Universe Space Observatory), the committee questions the cost-effectiveness of a flagship-class space mission as compared with the expansion of existing ground-based facilities. Notably, the committee did not receive any proposals in the Earth sciences. The committee lacked sufficient data to determine why it did not receive any such proposals, although it notes that the Vision Mission effort that sponsored many of the mission concepts evaluated in this study did not include Earth science, which at the time was separated organizationally within NASA from space science. It is possible that, if invited to consider the matter, the Earth science community may find uses for Constellation that are not readily apparent. 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. The mission concepts reviewed during this study lacked the level of detail necessary for a full evaluation. In particular, the cost estimates were extremely rough. The lack of Earth science concepts also concerned the com- mittee. NASA is still in the early stages of identifying the potential benefits of the Constellation System to the space science program and has not made a dedicated effort to evaluate the potential of the Constellation System for space and Earth science missions. As a result, the committee determined that the agency needs to continue efforts to attract and advance ideas for space and Earth science missions in general, and should develop a method for soliciting potential mission concepts. Recommendation: NASA should solicit further mission concepts that are most likely to benefit from the capabilities of the Constellation System in each of the space and Earth science disciplines: astronomy and astrophysics, Earth science, heliophysics, and planetary science. The agency should seek mission concepts that are studied in a uniform manner with regard to design, system engineering, and costing. 2 In its interim report, the committee selected 7 of the 11 Vision Mission concepts as “worthy of further study as a Constellation mission.” See National Research Council, Science Opportunities Enabled by NASA’s Constellation System: Interim Report, The National Academies Press, Washington, D.C., 2008.

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 SUMMARY The committee focused on the 12 mission concepts that, as shown in Table S.1, it determined are worthy of further study as Constellation missions. Because the committee was charged with determining which studies are “most deserving” of further study, it divided the list of 12 mission concepts into “more deserving” and “deserv- ing” categories. All 12 of these concepts show great promise, but the committee determined that, as indicated in the recommendations below, several in particular serve as examples of what Constellation could provide to space science. The committee’s criteria for determining if a mission concept is more deserving or simply deserving of further study are as follows: • Criterion : Mission Impact on Science in the Field of Study—The mission concept must present well- articulated science goals that the committee finds compelling and worthy of the investment needed to develop the technology. • Criterion : Technical Maturity—The mission concept must be sufficiently mature in its overall concep- tion and technology. If the technology for accomplishing the mission does not currently exist at a high technology readiness level, the mission must provide a clear path indicating how it will be developed. If a mission concept satisfied both criteria to a moderate or high degree, it was designated more deserving of further study. (These criteria are fully explained in Chapter 2.) As a result of these evaluations, the committee identified five missions that it determined are more deserving of further study. Recommendation: NASA should conduct further study of the following mission concepts, which have the most potential to demonstrate the scientific opportunities provided by the Constellation System: 8-Meter Monolithic Space Telescope, Interstellar Probe, Neptune Orbiter with Probes, Solar Polar Imager, and Solar Probe 2. Several of the missions named above, particularly the heliophysics missions, are well defined scientifically and do not require significant study of instruments or related issues. Further study should focus primarily on the relationship between the Ares V capabilities and the missions’ propulsion requirements. Because these are narrow requirements, NASA may have the ability to give further study to other possible Ares V science missions that the committee placed in the “deserving” category. The seven missions in the “deserving” category are also promising and offer great potential science return, but greater amounts of effort will be required to bring them to a similar level of maturity. Recommendation: NASA should consider further study of the following mission concepts: Advanced Technology Large-Aperture Space Telescope, Dark Ages Lunar Interferometer, Exploration of Near Earth Objects via the Crew Exploration Vehicle, Generation-X, Modern Universe Space Telescope, Stellar Imager, and Titan Explorer. Two missions that were placed in the category of “deserving” to be considered for further study did not receive the higher rating (i.e., they were not placed in the “more deserving” category) for reasons largely beyond the control of the proposing teams. Exploration of Near Earth Objects using astronauts is an intriguing and exciting potential future use of the Constellation System. This mission also has significant exploration benefits. Because exploration benefits were not part of the evaluation criteria, the committee could not place this mission in the “more deserving” category despite its strengths. Similarly, the Titan Explorer mission concept evaluated for this report was developed before Cassini reached Saturn, so it reflects an older series of science assumptions and questions; Ares V has great potential for Titan missions. MISSION COSTS The committee accepted the cost estimates provided in the proposals themselves or by the study representa- tives who presented the proposals to the committee, but with some modifications based on the expertise of the

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 LAUNCHING SCIENCE TABLE S.1 Summary of Mission Concepts Evaluated by the Committee Cost Worthy Estimatea of Further (billions of Study as a current-year Constellation Technical Maturityb Mission [2008] $) Mission? Notes ∼1 Advanced Medium No This mission does not benefit from the Constellation Compton System. It can fit in an existing Evolved Expendable Telescope (ACT)c Launch Vehicle (EELV). >5 Advanced Low for mirror Yes The 16-meter folded telescope design can only fit in an Technology technology Ares V payload fairing. Large-Aperture (including mass) Space Telescope Medium for detectors (ATLAST)d and thermal control >5 Dark Ages Lunar Medium for rovers and Yes The large antennas must be landed on the lunar farside. Interferometer interferometrics This requires both the Ares V launch vehicle and the (DALI)d Low for reducing mass Altair lunar lander. and for deploying and operating in a remote location 8-Meter 1-5 High for mirror and Yes The 8-meter-diameter telescope can only fit inside an Monolithic Space structure Ares V payload fairing. Telescoped Low for coronagraphic observation >5 Exploration High for instruments Yes The Orion vehicle is the only U.S. spacecraft envisioned of Near Earth Low for human factors that will be capable of operating beyond low Earth Objects via the such as radiation orbit. The mission also will require substantial payload Crew Exploration capability. This mission fits better within the purview of Vehicled the Exploration Systems Mission Directorate than as a mission of the Science Mission Directorate. >5 Generation-X Low for mirror Yes One Ares V launch of one 16-meter telescope (Gen-X)c development and is significantly simpler than the early proposed operations configurations. The cost estimates are weak. The additional mass capability could significantly reduce mirror development costs. Interstellar Probec 1-5 High for science, Yes Further study is needed of the benefits of Ares V—in instruments, and particular, of alternative propulsion options. mission concept >5 Kilometer-Baseline Low No This mission should be able to fit on an existing Far-Infrared/ EELV; therefore the need for Constellation is Submillimeter questionable, except for human servicing. Interferometerc >5 Modern Universe High for instruments Yes A large, one-piece central mirror rather than a Space Telescope Low for coronagraph robotically assembled mirror is possible with Ares V. (MUST)c and mirror assembly >5 Neptune Orbiter High for mission Yes Ares V could possibly obviate the need for aerocapture with Probesc concept and and/or nuclear-electric propulsion. instruments Low for propulsion and possibly lander >5 Palmer Questc Low No This mission does not benefit from Constellation. It can fit in an existing EELV.

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 SUMMARY TABLE S.1 Summary of Mission Concepts Evaluated by the Committee Cost Worthy Estimatea of Further (billions of Study as a current-year Constellation Technical Maturityb Mission [2008] $) Mission? Notes >5 Single Aperture Medium for mission No This mission does not benefit from Constellation. It Far Infrared concept can fit in an existing EELV. However, it could benefit (SAFIR) Low for cooling and from human servicing. Telescopec detectors ∼1 Solar Polar High for instruments Yes Propulsion options enabled by Ares V should be Imagerc Propulsion not studied considered. in sufficient detail Solar Probe 2d 1-5 High for science, Yes Ares I and Ares V launch vehicles could enable instruments, and spacecraft to be placed in an orbit that could bring it mission concept close to the Sun, accomplishing the major science goals. >5 Stellar Imagerc Low for formation Yes Larger mirrors (2 meters versus 1 meter) and a second flying hub could be launched on a single Ares V launch. Super-EUSO 1-5 Low for mirror No This mission does not benefit from Constellation. (Extreme Significant advances in this science can be made using Universe Space ground-based and alternative approaches. Observatory)d >5 Titan Explorerc High for instruments Yes Launch on Ares V may enable propulsive capture Medium for blimp rather than aerocapture and may shorten transit time. NOTE: The mission concepts are listed in alphabetical order. All of the missions listed are robotic missions, with the exception of the proposal for Exploration of Near Earth Objects via the Crew Exploration Vehicle. aCost estimates are based on data estimates provided to the committee, with modifications based on expertise within the committee. bTechnical maturity is based on data provided to the committee. cThis is 1 of 11 Vision Mission studies initiated by NASA between 2004 and 2006. dThis study proposal was submitted in response to the committee’s request for information. committee. Nevertheless, the committee concluded that these cost estimates are preliminary and are likely to be significantly lower than the actual cost of the missions. The committee is concerned that even according to the preliminary estimates, the costs of these missions will be as high as those of flagship-class missions (i.e., several billion dollars each), if not substantially higher than previous flagship-class missions. The committee was asked to consider missions that could be flown during the period 2020 to 2035; very few such large missions could pos- sibly be funded during that period. However, the committee also heard arguments that the larger payload capability of the Ares V could also possibly balance increased costs by simplifying mission design. Many of the mission concepts evaluated in this study do not require the full mass capabilities of the Ares V, and it is therefore possible that mission concepts could make use of these capabilities to reduce mission cost. This subject remains conjectural and therefore requires further study. 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.

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 LAUNCHING SCIENCE INTERNATIONAL COOPERATION Virtually all of the mission concepts evaluated by the committee are large, complex, and costly. Several are similar to studies currently being undertaken by traditional international partners of the U.S. space program in space science and exploration. As a result, there are opportunities for NASA to undertake joint missions in some of these areas. 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. TECHNOLOGY ISSUES The committee was charged with identifying the benefits of using the Constellation System’s unique capa- bilities relative to alternative implementation approaches. Such approaches include technologies that may allow a mission to be accomplished without the Constellation System, such as the Atlas and Delta launch vehicles that were used as the baseline for many of the Vision Mission studies that the committee evaluated. Such approaches also include technologies like in-space propulsion that might not be necessary if a launch vehicle such as the Ares V is available. The committee notes that the majority of mission concepts evaluated in this study (the NASA-funded Vision Missions) were originally designed to use launch vehicles—the Atlas and Delta—often in combination with technology options (such as ion propulsion) that were necessary because of the lack of mass or change in velocity provided by those launch vehicles. The Constellation System may offer an alternative to those launch vehicles and technologies. During this study, the committee concluded that even the Constellation System alone might be insufficient for some of the missions that it evaluated, and that additional technological developments would be required. NASA currently lacks a technology development strategy for science missions, a gap previously identified by the NRC as a shortcoming,3 and the committee concluded that some of the missions would be enhanced with the availability of additional technology developments. Finding: Advanced in-space propulsion technology may be required for some science missions considered for using the Constellation System. Virtually all of the missions evaluated in this report would introduce substantial new demands on the Deep Space Network (DSN). The committee was briefed on the current demands and plans for the DSN and became concerned about the future of the DSN, but determined that this subject was beyond the committee’s base of expertise or purview. Nevertheless, future Constellation science missions will have a major impact on the DSN. (Technology issues are further discussed in Chapter 3.) Finding: Science missions enabled by the Constellation System will increase the strain on the capabilities of the Deep Space Network. HUMAN AND ROBOTIC SERVICING Various proposers of observatory mission concepts suggested to the committee that large, expensive obser- vatories might benefit from servicing, which would allow them to operate for decades and to be upgraded with the latest instruments. The Orion spacecraft, unlike the space shuttle, offers the possibility of human servicing of spacecraft beyond low Earth orbit, although it lacks the mass and volume required to conduct such missions alone. However, recent developments in robotic servicing also demonstrate that this technology is now reaching a 3 National Research Council, Grading NASA’s Solar System Exploration Program: A Midterm Review, The National Academies Press, Washington, D.C., 2008, pp. 11 and 59-61.

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 SUMMARY mature stage and could provide an alternative method of servicing future spacecraft. (Human and robotic servicing issues are discussed in Chapter 4.) Finding: The Constellation System and advanced robotic servicing technology make possible the servicing and in-space assembly of large spacecraft. Finding: Designing spacecraft components for accessibility is essential for in-space servicing and is also advantageous for preflight integration and testing. The committee was informed that one of the lessons that NASA has learned from decades of spacecraft servic- ing is that it is far easier to service spacecraft specifically designed for access and easy replacement of equipment. This approach has other benefits as well, such as prelaunch servicing and maintenance that may be required during integration and testing. However, because NASA largely abandoned the concept of the human servicing of space- craft and because robotic servicing was not a developed technology, for many years the agency did not consider designing new spacecraft that could benefit from servicing. The new capabilities provided by the Constellation System and robotic servicing technologies highlight the importance of devoting new attention to this subject. Recommendation: NASA should study the benefits of designing spacecraft intended to operate around Earth or the Moon, or at the libration points for human and robotic servicing. SPACECRAFT AND LAUNCH VEHICLES The alternative implementation approaches that the committee was charged with evaluating include technolo- gies that allow the use of launch vehicles smaller than Ares V. Although the Ares V offers significant capabilities not available from other vehicles, the Ares I launch vehicle does not offer capabilities significantly different from those currently available with the Evolved Expendable Launch Vehicle (EELV) family of launch vehicles for science missions. (Launch vehicles are discussed in Chapter 5.) The Ares I is required for launching the Orion spacecraft, and so any science missions that require astronauts will use the Ares I. Finding: The Ares I will not provide capabilities significantly different from those provided by existing launch vehicles. Although the Orion spacecraft is being designed primarily for transporting astronauts to and from the Interna- tional Space Station and to and from the Moon, it will possess additional capabilities, such as the ability to carry secondary payloads, including deployable satellites. During the Apollo program, the Apollo service module was equipped with a bay for carrying science instruments for use while the spacecraft was in orbit around the Moon. NASA is currently seeking to incorporate a similar capability in the Orion spacecraft and has provided for mass and volume reserves in its current design. Although the Ares V offers the greatest potential value to science, the launch vehicle must be made capable of accommodating science payloads. Science missions are more likely to take advantage of the Ares V if these capabilities are designed into the vehicle rather than their needing to be added later. A potentially serious issue for using Ares V for planetary missions concerns the need for a dedicated upper stage to provide high excess escape velocities for spacecraft (velocity squared per second squared, known as C3). 4 Neither the current most likely upper stage, the Atlas V Centaur III Dual Engine Configuration, nor the previous Titan IV Centaur would make efficient use of the Ares V payload shroud volume and may present other design problems such as load (weight)-bearing capability (see Figure S.1). Planetary missions could better use an upper stage that is shorter and takes advantage of the full width of the Ares V; however, the development of such a stage 4 C3 is km2/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.

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 LAUNCHING SCIENCE 4.44 m [ 14.6 7.50 m [ 24.6 12.4 m [ 40.8 ft] 9.70 m [ 31.8 8.80 m 8.80 m [ 28.9 [ 28.9 ft] Baseline Extended Shroud Shroud FIGURE S.1 Two possible configurations of the Ares V shroud—the current baseline shroud and a proposed extended shroud. Shown inside the shrouds are two possible Centaur upper-stage configurations: the Titan IV Centaur (left) and the Atlas V Centaur III Dual Engine Configuration (right). Any spacecraft carried atop an upper stage would have severely restricted volume constraints. Neither shroud option takes advantage of the width of the Ares V shroud. SOURCE: Adapted courtesy of NASA. could be expensive. In order for Ares V to be attractive for future science missions, vehicle designers will have to consider the requirements of potential science missions. Recommendation: If NASA wishes to use the Constellation System for science missions, it should preserve the capability for Orion to carry small scientific payloads and should ensure that the Ares V development team considers the needs of scientific payloads in system design. The Constellation System offers great potential for space science missions, but the costs of the types of mis- sions evaluated in this report may be unaffordable. Many of these missions have such large costs that they might require that funds be taken from numerous other, smaller science missions, which could create imbalances in the science programs in the individual disciplines. These missions will have to be evaluated carefully within the NRC’s decadal survey process. NASA will have to proceed with caution as it develops these new capabilities.