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Summary In 2004 NASA initiated studies of advanced science mission concepts known as the Vision Missions and inspired by a series of NASA roadmap activities conducted in 2003. Also in 2004 NASA began implementation of the first phases of a new space exploration policy, the Vision for Space Exploration. This implementation effort included development of a new human-carrying spacecraft, known as Orion, and two new launch vehicles, the Ares I and Ares V rockets⎯collectively called the Constellation System. NASA asked the National Research Council (NRC) to evaluate the science opportunities enabled by the Constellation System (see Preface) and to produce an interim report on a short time schedule and a final report by November 2008. The committee notes, however, that the Constellation System and its Orion and Ares vehicles have been justified by NASA and selected in order to enable human exploration beyond low Earth orbit, and not to enable science missions. This interim report of the Committee on Science Opportunities Enabled by NASA’s Constellation System evaluates the 11 Vision Mission studies presented to it and groups them into two categories: those more deserving of future study, and those less deserving of future study. Although its statement of task also refers to Earth science missions, the committee points out that the Vision Missions effort was focused on future astronomy, heliophysics, and planetary exploration and did not include any Earth science studies because, at the time, the NRC was conducting the first Earth science decadal survey, and funding Earth science studies as part of the Vision Missions effort would have interfered with that process. Consequently, no Earth science missions are evaluated in this interim report. However, the committee will evaluate any Earth science mission proposal submitted in response to its request for information issued in March 2008 (see Appendix A). The committee based its evaluation of the preexisting Vision Missions studies on two criteria: whether the concepts offered the potential for a significant scientific advance, and whether or not the concepts 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 decadal survey process, and it emphasizes that this interim report’s evaluation should not be considered to be an endorsement of the scientific merit of these proposals, which must of course be evaluated relative to other proposals. The committee determined that seven of these concepts would benefit from the Constellation System, whereas four would not, but it stresses that this conclusion does not reflect an evaluation of the scientific merit of the projects, but rather an assessment of whether or not new capabilities provided by the Constellation System could significantly affect them. Some of the mission concepts, such as the Advanced Compton Telescope, already offer a significant scientific advance and fit easily within the mass and volume constraints of existing launch vehicles. Other mission concepts, such as the Palmer Quest proposal to drill through the Mars polar cap, are not constrained by the launch vehicle, but rather by other technology limitations. The committee evaluated the mission concepts as presented to it, aware nevertheless that proposing a far larger and more ambitious mission with the same science goals might be possible given the capabilities of the Ares V launch vehicle. (Such proposals can be submitted in response to the committee’s request for information to be evaluated in its final report.) See Table S.1 for a summary of the Vision Missions, including their cost estimates, technical maturity, and reasons that they might benefit from the Constellation System. The committee developed several findings and recommendations. 1

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TABLE S.1 Summary of Vision Missions (in Alphabetical Order) Evaluated by the Committee Worthy of Further Cost Study as a Estimatea Constellation Vision Mission (billions) Technical Maturityb Mission? Notes Advanced $1 Medium No This mission does not benefit from Compton Constellation. Telescope (ACT) Generation-X >$5 Low Yes One Ares V launch of one 16-meter (Gen-X) telescope is significantly simpler than the early proposed configurations. Cost estimates are weak. The additional mass capability could significantly reduce mirror development costs. Interstellar Probe $1-$5 High⎯concept, Yes Further study is needed of the instruments benefits of additional launch mass Low⎯propulsion enabled by Ares V, in particular alternative propulsion options. Kilometer-Baseline >$5 Low No The need for Constellation is Far-Infrared/ questionable, except for human Submillimeter servicing. Interferometer Modern Universe >$5 High⎯mission concept, Yes Large one-piece, central mirror is Space Telescope instruments possible with Ares V rather than a (MUST) Low⎯assembly robotically assembled mirror. Neptune Orbiter >$5 High⎯mission concept, Yes Ares V could possibly obviate the with Probes instruments need for aerocapture and/or nuclear- Low⎯propulsion and electric propulsion. possibly lander Palmer Quest >$5 Low No This mission does not benefit from Constellation. Single Aperture Far >$5 Medium⎯mission No This mission does not benefit from Infrared Mission concept Constellation. (SAFIR) Low⎯cooling, detectors Solar Polar Imager $1-$5 High⎯mission concept, Yes Consider propulsion options enabled instruments by Ares V. Low⎯propulsion Stellar Imager $5 Low Yes Could launch larger mirrors (2 meters vs. 1 meter) and a second hub on a single Ares V launch. Titan Explorer >$5 Low⎯requires Yes Launch on Ares V may enable aerocapture propulsive capture rather than aerocapture and shorten transit time. a Cost estimates based on data provided to the committee. b Technical maturity based on data provided to the committee. 2

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Finding 1. The greatly increased payload capability promised by Ares V could lead to much more costly science payloads. Finding 2. The committee determined that the Ares I capabilities are not sufficiently distinct from those of Atlas V and Delta IV to enable different types or a higher quality of space science missions. Finding 3. The following Vision Mission studies might benefit from the opportunities enabled by the Constellation System and are therefore considered more deserving of future study: Generation- X, Modern Universe Space Telescope, Stellar Imager, Interstellar Probe, Solar Polar Imager, Neptune Orbiter with Probes, and Titan Explorer. The committee did not assess the relative scientific priority of the missions within this group. In the final report, these mission concepts will be compared to additional mission concepts (collected in response to the committee’s request for information) that the committee determines to be more deserving of future study, and the committee will produce a consolidated list. According to the committee’s evaluation criteria, the four mission concepts that it deemed less deserving of future study simply do not appear to benefit highly from use of the Constellation System. The committee concluded that the seven more-deserving mission concepts require greater study of their scientific benefits and the technical benefits enabled by the Constellation System. Recommendation 1. NASA should conduct further studies of the scientific benefits as well as the technical benefits to mission execution, such as reduction of mission complexity and risk, enabled by the Constellation System for the following missions: Generation-X, Modern Universe Space Telescope, Stellar Imager, Interstellar Probe, Solar Polar Imager, Neptune Orbiter with Probes, and Titan Explorer. The committee accepted the cost estimates provided by the Vision Mission studies themselves or by the study representatives who presented them to the committee. Nevertheless, the committee concluded that these cost estimates are preliminary. The committee is concerned that the costs of these missions will be high, at least for the flagship-class missions, if not substantially higher. Given the fact that NASA has insufficient funding to support more than one flagship-class mission per decade in two science areas (essentially one for astronomy and astrophysics and one for solar system exploration, with the situation for Earth science and heliophysics being slightly more complicated), each of these missions would place substantial strain on the science budget, and the committee therefore emphasizes that close attention to cost issues is required. Since the committee was asked to consider missions that could be flown during the period 2020-2035, very few such large missions could possibly be funded during that period. Finding 4. There are uncertainties in the cost estimates associated with the Vision Missions listed above when flown on the Ares V vehicle. Although NASA has not yet produced cost estimates for many of the elements of the Constellation System, such as the Ares V launch vehicle, the committee recognized that utilization of the Constellation System, particularly the Ares V, could have a potentially dramatic effect on the costs of these missions. Incorporating the use of an expensive launch vehicle could increase costs. But it could also possibly balance increased costs by simplifying mission design (for instance, by eliminating the requirement for on-orbit assembly or complex deployment mechanisms). 3

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Recommendation 2. NASA should perform cost analysis for the missions that the committee determined could benefit from the Ares V capability (Generation-X, Modern Universe Space Telescope, Stellar Imager, Interstellar Probe, Solar Polar Imager, Neptune Orbiter with Probes, and Titan Explorer). This analysis should use the Ares V technical capabilities together with appropriate upper stages as a baseline. 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 in space exploration. Finding 5. International cooperation could provide access to international scientific expertise and technology useful for these missions, and could reduce costs through provision of foreign instruments and infrastructure. The committee was charged with identifying the “benefits of using the Constellation System’s unique capabilities relative to alternative implementation approaches.” Alternative implementation approaches include technologies that allow the use of smaller launch vehicles (such as in the Evolved Expendable Launch Vehicle class that served as the baseline for the Vision Mission studies). The committee notes that several technology issues are shared by two or more missions. There are benefits to having multiple technology solutions available to achieve objectives, and the committee is concerned that it is risky to rely on only one solution that may never emerge. NASA currently lacks a technology development strategy, a gap identified by the NRC as a shortcoming.1 The impact of technology on these missions and how it may require, or alleviate the need for, the use of the Constellation System requires further study and will be evaluated by the committee in its final report. Finding 6. The committee identified the following technology issues as meriting further attention. Some of these technologies are of a basic, mission-enabling nature; others provide options that can be traded for alternative mission architectures. • Basic enabling technologies ⎯Free-flying constellations ⎯Tethered flight ⎯Next-generation Deep Space Network ⎯Space nuclear reactors • Technologies enabling alternatives to Ares V ⎯Aerocapture ⎯Solar sails ⎯Solar-electric propulsion ⎯Nuclear-electric propulsion ⎯Robotic assembly and servicing • Technologies enhancing Constellation capabilities ⎯Human assembly and servicing 1 See, for example, 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. 4