Review of US Concepts for Post-ISS Space Habitation Facilities and

AIAA 2010-8695

AIAA SPACE 2010 Conference & Exposition 30 August - 2 September 2010, Anaheim, California

Review of US Concepts for Post-ISS Space Habitation Facilities and Future Opportunities Harley A. Thronson1 NASA Goddard Space Flight Center, Greenbelt, MD 20771 Daniel Lester2 University of Texas, Austin, TX 78712 Rud V. Moe3 NASA Goddard Space Flight Center, Greenbelt, MD 20771 Greg Sullivan4 The Jefferson Institute, Reno, NV 89502

Over the past decade, a modest number of groups has pursued concepts for future long-duration, highly capable human habitation systems in free space, building upon and following the International Space Station (ISS). In general, the designs have derived from the TransHab technologies and the Decade Planning Team architecture of the late-1990s and early-2000s: expandable habitation at an “operations node” – typically an Earth-Moon libration point or geosynchronous orbit – that enabled a wide range of science and human space flight activities via a single facility. This design work has direct applicability to future NASA plans for human space flight. Advocates for these systems point to (1) the importance of sustaining successful operation in free space if there are to be human missions to Mars; (2) continued development of key technologies beyond that which ISS alone will achieve; and (3) the value of a habitation system at a useful venue in cis-lunar space: e.g., support of lunar surface sorties, service and upgrade complex science facilities, maintenance of on-orbit depot systems. With the identification of Mars as the “ultimate destination” for human space flight, the capability to operate in free space comfortably and successfully for long periods of time remains a major priority. We close by summarizing some possible “next steps” that NASA might take with respect to long-duration human operations in space.

I. Introduction: The ISS as Free-Space Habitation 1.0

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ith NASA’s commitment to the International Space Station (ISS) now all but assured for the coming decade,

serious consideration may be given to long-duration US in-space operations beyond the mid-2020s, when presumably the ISS will be retired. Indeed, both ESA and Roscosmos, in addition to their unambiguous commitment to sustained ISS, have published concepts for extended post-ISS habitation. In the US, engineers and scientists have for a decade been working both within and outside NASA to assess designs for long-term post-ISS habitation and operations, although interrupted by changing priorities for human space flight, Congressional direction, and constrained budgets. The evolving work of these groups is described here, and has special relevance with last year’s

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Associate Director for Advanced Concepts and Planning, Astrophysics Division, Code 660, Science and Exploration Directorate, NASA Goddard Space Flight Center, Greenbelt, MD 20771 2 Research Fellow, Department of Astronomy, University of Texas, Austin, TX 78712 3 Mission Systems Engineer, Systems Engineering Services and Advanced Concepts Branch, Code 592, NASA Goddard Space Flight Center, Greenbelt, MD 20771 4 Principal, The Jefferson Institute, 5190 Neil Road, Suite 430, Reno NV 89502

1 American Institute of Aeronautics and Astronautics This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

major review of the nation’s human space flight program, and an eventual consensus by Congress and the White House on implementation. A. The ISS: Free-Space Habitation 1.0 The ISS is in the process of demonstrating essential capabilities for safe and comfortable long-duration space habitation that would advance prospects for a human mission to Mars. However, this facility’s basic structure and construction materials, interior layout and use of volume, operational modes and application of information technology/robotics, systems and sub-systems for closed-cycle life support, vehicle systems management (e.g., thermal management systems), method of assembly – indeed, the technological solutions to the many challenges of space flight – are extremely unlikely to be those that will be used on a mission to Mars three or four decades from now. That is, the ISS was successfully designed in the 1980s and built over the past two decades to operate in the special environment of LEO with, for example, regular opportunities for resupply. The particular engineering solutions that produced the ISS – and, to some degree, Skylab and Mir before it – may be referred to as Free-Space Habitation 1.0: humanity’s first generation of successful long-duration human occupation of the cosmos. B. Considerations for Free-Space Habitation 2.0 A number of lessons have been learned during the construction and operation of the ISS, which have been presented elsewhere more completely1. Relevant to this paper and the issue of a follow-on habitation facility, key lessons include 1. While maintaining sufficient working volume for astronaut comfort and effectiveness, reduce the number of launches required for assembly; that is, launch facility segments that are as large as feasible. 2. Likewise reduce the number of astronaut EVAs necessary for assembly. 3. Design systems from the start that are assembled, serviceable, and/or upgradeable in orbit, either with astronauts or with robots. 4. A successful space habitation program should be part of a sustained and long-duration architecture that achieves multiple goals and “feeds forward” to further capabilities in human space flight and science. [NB: it is interesting to note that relatively few of the in-depth architectures for human space flight developed and advocated over the past half century incorporated a LEO space station as a critical element of human space exploration. It was not part of the Apollo Program, of course, although Von Braun identified it in the 1950s as a keystone element of humanity moving beyond the Earth. More recently, it seems that only NASA’s Decade Planning Team (See Section IIA) and the Augustine Committee (See Section IIC) placed LEO ISS operations as an essential part of a broad architecture in human space flight. These lessons have been applied in the design work that we discuss here and proposed architectures for human space flight proposed over the past decade as options to follow the ISS and operate beyond LEO. Sufficient experience with ISS has been accumulated to assess in some depth candidates for its successor (and next major “stepping stone” for human missions to Mars), which will almost certainly be very different in almost every way from its predecessor. The International Space Station and its precursors were impressive accomplishments that were intended to operate close to the Earth with replacement systems (and crews) readily available. Onboard experiments and technology development were governed by available budgets and, of course, changing long-range goals in human spaceflight.* Even though the ISS is a highly capable and accessible platform for ambitious experiments, if humans are ever to travel beyond the immediate vicinity of the Earth, further development of on-orbit technologies seems necessary to make such voyages safe, comfortable, sustainable, and effective. Expandable (or inflatable) architectures have been evaluated at least since 2000 as candidate large-volume, multi-purpose, free-space habitats often designed to be launched via a single vehicle. Expandable systems respond to an early lesson learned from the ISS experience: make as much volume available for the astronauts with the fewest number of launches. [Interestingly, the giant “wheel” space station described in the early 1950s by Werner von Braun and colleagues combined inflated nylon and a steel skeleton to save weight and maximize volume.] From the *

During a recent one-year period the formal overarching goal for NASA’s human space flight went from a minicolony at the lunar south pole to a sortie-like or fly-by mission to Mars.

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beginning of this past decade, these expandable concepts were proposed to be simultaneously the next major onorbit facility after the ISS that would be operated as a key human space flight “stepping stone” on the way to Mars, support lunar surface operations, including space depots, while serving as a “work site” for major satellite repair and upgrade.

II. Evolving Concepts for Post-ISS Human Habitation Facilities (2000 – 2010) A. TransHab and the Decade Planning Team The attractive features of expandable space habitation systems appear to be first generally applied in design work in the late 1980s at Lawrence Livermore National Laboratory in collaboration with ILC Dover and presented as an option for the NASA Space Exploration Initiative (SEI) work. Within two years, however, SEI was terminated and design work on expandable systems for in-space habitation virtually ceased. About a decade later, an advanced concepts development team at NASA Johnson Space Center (JSC) resumed studies of an expandable space habitat and shortly thereafter the concept was introduced into a combined science/human space flight architecture by NASA Administrator Daniel Goldin’s Decade Planning Team (DPT)2. The TransHab – a contraction of Transit Habitation – was a concept begun in the late-1990s with the goal of developing for demonstration on ISS a lighter-weight candidate for eventual human missions to Mars. Proposed habitation volumes for such ambitious missions would require, if using the aluminum shell structure of the ISS design, a total mass likely to be prohibitively – and unnecessarily – heavy. The TransHab team, working with ILC Dover, instead applied high-strength fibers, which permitted a structure that could be collapsed around a rigid core for launch, but expand to an impressive usable volume when on orbit. According to histories of the program and later interviews3 TransHab suffered the controversies and increased costs of ISS to the point where the US House of Representatives banned NASA from conducting further development of the concept. In retrospect, perhaps fortunately, the TransHab patents and designs were purchased by Bigelow Aerospace for the purpose of building “hotels” in orbit for a variety of purposes. Almost simultaneously with the Congressionally mandated termination of TransHab design work at JSC, the DPT in 1999 began its assessment of TransHab-based designs to extend human presence beyond LEO using an engineering design team from JSC. The goal of the DPT and its successor, the NASA Exploration Team (NExT) was much more ambitious than that of the TransHab team: an agency-wide future architecture that combined science and human space flight beyond LEO. The expandable design4 was incorporated into a “technology-driven, stepping-stone” human space flight architecture by the DPT and NExT. These teams recommended extensive utilization of ISS, followed as a next step by extending LEO-based capabilities to a facility deeper in space – dubbed the “Gateway” – which was intended to be the first in a series of increasingly ambitious operations sites in preparation for humans leaving the Earth-Moon system. Produced by the NASA JSC Advanced Development Office and funded by DPT/NEXT, this extensive architecture study met a handful of key requirements for its on-orbit habitation facility. Briefly, these were 1.

2. 3. 4. 5. 6.

Simultaneously support human and robotic lunar surface operations, upgrade and construct major in-orbit science facilities, oversee depot systems, and demonstrate key capabilities necessary for long-duration human spaceflight. Have a design lifetime of 15 years. Support a crew of four for mission durations of up to a few weeks. Use existing or near-future launch vehicle infrastructure. After autonomous transfer from LEO, operate at Earth-Moon L1 or L2 (or equivalent venue). Operate without human attendance for up to several weeks at a time.

From the start, it was obvious to the DPT/NEXT/JSC team that the same technological solutions adopted to make ISS successful would not generally work for a candidate follow-on system. In particular, maximizing living volume while minimizing total launch mass (and cost) drove the designers of the Gateway to an expandable solution, just as had been the case earlier with the TransHab, Lawrence Livermore, and ILC Dover teams. Moreover, DPT/NEXT concluded (and advocated) for sustained technology investments that would permit humanity after the ISS to travel to multiple destinations. That is, as an alternative to optimization for a single specific destination, the DPT and NEXT recommended investing in a handful of key technologies identified by the breadth of options made available to human space flight: e.g., libration point operations for support to the lunar surface, large science facility assembly

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and maintenance, logistics support to cis-lunar and Mars-bound operations, and development of long-duration human presence in deep space.

Figure 1. Expandable space operations and habitation facility: the “Gateway.” A 2006 depiction developed from the DPT/NEXT designs in 2001 for a post-ISS human operations facility at an Earth-Moon L1,2 (or equivalent) venue and proposed as an option to the NASA Constellation Program. This facility was derived from experience with the ISS and would simultaneously support lunar surface operations, upgrade or prepare major on-orbit science missions and depots, and develop essential capabilities for future human missions to Mars. [Image courtesy of the Future In-Space Operations (FISO) working group and John Frassanito & Associates.] The resulting DPT/NEXT Gateway (hereafter, Gateway 2001, which refers to the date that the final design report was completed) is shown in Figure 1. It was recommended as “the cornerstone in a series of elements that comprise the Gateway Architecture, as it serves as the primary mission staging platform through which [multiple priority activities] will be performed” (Executive Summary, Gateway Design Report). As with the earlier TransHab team and learning the lessons from the ISS design experience, the DPT/NEXT/JSC team recognized the importance of minimizing the complexity of in-space infrastructure, including numbers of required launches. The final Gateway 2001 design used a single Delta IV EELV vehicle to place the hybrid expandable/rigid shell structure into a lowEarth orbit. The rigid shell portion offered load-bearing support and the inflatable portion offered increased volumeper-mass: in a single launch of a 23 mT payload, a pressurized volume of 275 m3 was available for four astronauts for a few weeks up to a few months at a time. In comparison, the Skylab volume was 361 m3 for three people for about three months, the Bigelow Aerospace BA330 space habitat is proposed to have 330 m3, and upon completion ISS will have somewhat less than 1000 m3 for up to six astronauts for a six-month tour of duty. The original Orion crew exploration vehicle in the recently cancelled Constellation Program was designed to have an interior volume of roughly 15 m3 and, of course, was not intended to be occupied for more than several days at a time. For comparison, recent work based on historical data and in support of NASA’s Constellation Program recommends about 300 m3 as “optimal” for a crew of four for a half-year of occupation5. In other words, the Gateway 2001 design was close to the optimal recommended for a four-person crew.

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Figure 2. The “Earth’s Neighborhood” flexible architecture based on an expandable habitat in cis-lunar space. As they developed an architecture for human exploration beyond LEO, the DPT/NEXT recognized the advantages of operating from a location that provided low-∆v access to multiple locations, as well as being an attractive venue itself (e.g., for telescope assembly and upgrade). [Figure from the Future In-Space Operations (FISO) working group 2006 adaptation of DPT/NEXT studies.] The DPT/NEXT’s challenge was to design a single-launch habitation module that would serve as a “stepping stone” – a key DPT/NEXT concept – for subsequent science and human spaceflight goals in the era following the ISS. With this as a requirement, the Gateway architecture studies advocated the Earth-Moon (E-M) L1 (or, about equivalently, L2) venue as the site in the Earth-Moon system where most major NASA goals could be achieved, while enabling future growth potential for one day sending humans to Mars (Figure 2). However, sending Gateway 2001 beyond LEO required additional outfitting and propulsion systems. In the Gateway 2001 architecture, two additional launches to LEO are required to support operations at E-M L1,2: a space shuttle-based supply and outfitting mission and an EELV launch of a solar electric propulsion (SEP) unit to dock with the outfitted and inflated Gateway in LEO. The combined Gateway-SEP system would then spiral outward over several months to its final location, about 60,000 km from the Moon; the SEP module would then return to LEO for re-use. [Multiple-use or re-use was another priority for DPT/NEXT architectures.] Astronauts would be sent to the Gateway via chemical propulsion using a dedicated, re-usable transfer stage. In the DPT/NEXT/JSC design, Gateway 2001 over its 15-year lifetime could support each year, for example, the combination of two Apollo-like short-stay sortie missions with astronauts to the lunar surface and two upgrade/support missions with major science facilities and/or depots (Figure 3). Operations would be carried out to build upon experience and technologies learned from ISS, guaranteeing that they would not be lost when the ISS program ended. Although the DPT/NEXT estimated that Gateway 2001 could be deployed within about a decade with sustained investment, there was not in 2000 a national goal of human missions beyond LEO.

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Figure 3. A 2006 notional depiction of how the DPT/NEXT Gateway might be used to maintain a complex in-space depot “farm” in support of human operations beyond the immediate vicinity of the Earth. A combined crew module/lunar excursion vehicle is shown approaching the Gateway habitat from the lower right, with a lunar surface supply ship at the extreme left. [Image courtesy of the Future In-Space Operations (FISO) working group and John Frassanito & Associates.] In late 2001, Dan Goldin departed NASA and much of the DPT/NEXT work was taken over by the new Space Architect office at NASA HQ, although Gateway design work was not pursued in greater depth at that time. Moreover, the Space Architect position was terminated by Goldin’s successor, so concepts, options, technology priorities, and combined science/human space flight goals developed by the DPT/NEXT languished. B. Bigelow Aerospace and the Future In-Space Operations Working Group A few years after the DPT, NEXT, and the Space Architect activities were terminated, the Vision for Space Exploration (VSE) was announced in early 2004 by the White House and about a year later, new NASA Administrator Michael Griffin established the Exploration Systems Architecture Study (ESAS) to develop the implementation strategy for the VSE. Options for sustained human libration-point operation of various kinds were considered, but rejected, by the ESAS team, presumably due to the significantly different human space flight requirements and goals from that of DPT/NEXT. Specifically, the ESAS process identified long-stay lunar surface operations at a single location as the overriding human spaceflight goal, rather than multiple destinations (including the lunar surface), as developed and advocated by the DPT/NEXT. Shortly before the ESAS began, the ad hoc Future In-Space Operations (FISO) working group was established specifically to assess how whatever human space flight architecture that emerged from the ESAS could also be adapted to additional purposes. In essence, the FISO working group approximated the Apollo Applications Program of four decades earlier: evaluating how human space flight hardware might be broadly applicable in addition to the Apollo lunar surface sortie missions. In the event, a core element of the Constellation architecture – the Ares V heavy-lift vehicle – was identified by the FISO working group as permitting a major advancement in capabilities for a future post-ISS Gateway facility. Working in 2006 with John Frassanito & Associates (JF&A) and a small engineering team, members of the FISO working group resurrected the TransHab/Gateway 2001 designs and adapted them to take advantage of the capabilities offered by elements of NASA’s new Constellation architecture. At the time, the particular version of heavy-lift design could place about 95 mT into LEO, so from the start this new design (hereafter “Gateway 2006”) was both much larger and used a single launch to put into orbit a combined habitation/propulsion system that did not

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require subsequent outfitting launches. To propel the system to its final operations site at E-M L1,2, the Gateway 2006 design used both chemical and SEP systems. Superficially, Gateway 2006 (Fig. 1) was indistinguishable from Gateway 2001 and the FISO team also further developed the multi-destination architecture of the DPT/NEXT (Fig. 2). However, Gateway 2006 was far more capacious than its predecessor, with an interior volume of about 575 m3. This approaches 60% of the final pressurized volume of ISS, which is made possible by the assumed availability of the heavy-lift vehicle and, of course, the expandable technology. Figure 1 shows the FISO team’s concept for a lunar lander and an Earth-toGateway human transfer stage on the far side of the habitation system, and a servicing site on the near side. Although the flexible Gateway-based architectures explicitly included support for multiple human lunar surface operations, including depoting and re-supply, surface operations via a Gateway did not offer “immediate return to Earth,” an ESAS requirement. As with the earlier Gateway 2001 design, the updated version was sized to support a crew of four for a few weeks up to a few months at a time, two lunar surface sortie missions and two satellite upgrade/construction missions annually (Figure 4), along with extended development and testing of free-space capabilities in support of future human missions to Mars. This updated Gateway architecture and concept for adapting Constellation systems was proposed to the NASA HQ Exploration Systems Mission Directorate (ESMD) in spring 2006. However, ESMD declined to support further design work, concerned that evaluating concepts for free-space human space flight would be excessively distracting from work on NASA’s priority lunar south pole “outpost.” This was the fourth time in about 15 years that advanced designs and architectures based on expandable systems for human operations in space beyond LEO ended.

Figure 4. A future large-aperture telescope (foreground), attended by robotic assistants, stands off from a Gateway habitat/servicing site and depot “farm” in an Earth-Moon L1 “job site” (Ref. 6). This depiction is based on concepts developed by the Future In-Space Operations (FISO) working group and proposed in 2006 as an option for NASA’s human space flight program. [Image courtesy of the FISO working group and John Frassanito & Associates.] Even while NASA-centered teams were advocating within the agency to develop the capabilities for humans to work productively in free space beyond LEO, an independent commercial group was designing and building the first on-orbit facility to achieve similar goals. As already noted, Bigelow Aerospace a decade ago acquired the TransHab

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patents and designs from NASA and set about to offer to multiple customers, including space agencies, an opportunity to operate a “station” in LEO or elsewhere7. Ironically, about the same time that NASA terminated design work on the Gateway 2006 “stepping stone” and the FISO’s architecture for multiple destinations, the first (of two) unoccupied Bigelow Genesis prototypes were successfully launched. According to company plans, the first expandable facility (Sundancer) that can be occupied will be launched in about 2014, which will be followed by the larger and more capable BA 330. C. Resurrected Once Again: The Augustine Committee and “Stepping Stones” Beyond LEO About three years after work on the FISO Gateway ended, in 2009 the concept of a broadly capable, expandable post-ISS long-duration human habitation system beyond LEO was once again resurrected, this time as part of last year’s OSTP-directed Review of Human Space Flight Plans Committee8, chaired by Norman Augustine. One of the scenarios considered in depth by the Augustine Committee was the so-called “Flexible Path,” which proposed a multi-faceted program to develop the capabilities for human space flight to multiple destinations in preparation for missions to Mars, beginning with extensive use of the ISS. After a sustained investment program in key technologies, humans would travel to multiple locations as determined by the availability of the technology, major science goals, and/or priority human space flight goals (e.g., Mars). The similarity has been widely noted of the “Flexible Path” with the architecture advocated a decade earlier within NASA by the DPT/NEXT, which can be found at Reference 2. Within the Flexible Path is an option for, once again, a post-ISS TransHab/Gateway-like system. Or, as Augustine Committee member, Prof. Edward Crawley wryly remarked during a recent colloquium at NASA GSFC, “I guess we can say that our committee re-discovered [this architecture] for the first time.”

III. Proposed Design Work: Building on ISS and Stepping Toward Mars Taking advantage of the report of the Augustine Committee to NASA, an ad hoc team of two dozen scientists, engineers, and senior managers proposed this past spring to NASA once again to assess formally options for longduration in-space habitation and operations during the lengthy period between ISS end-of-life and the first human mission to Mars. This design work is proposed to begin in the near future, so that experience and personnel will not be lost in the “gap” between the end of the ISS program and when key capabilities are needed to support development of travel to Mars. As this article is being written, the proposed work is in abeyance, largely due to the uncertainty as Congress debates NASA’s future for human space flight. Nevertheless, it seems certain that whatever may emerge from the current debate over major goals in human space flight, Mars will in some manner be the “ultimate goal,” although a campaign to reach that planet will take place decades after the ISS is no longer available. As a consequence, a few key requirements of a post-ISS habitation system seem obvious (and are the core of the current assessment proposed to NASA): 1.

2.

3.

Apply both the experience of building the ISS, as well as especially its current capabilities, specifically a. To design a follow-on facility that maximizes the usable volume-to-mass ratio of the final structure b. To design a follow-on facility that minimizes numbers of launches and EVA construction activities for completion c. To design a follow-on facility with systems/sub-systems that are upgradeable, replaceable, and serviceable d. To design a follow-on facility capable of supporting needed developments for safe and productive long-term human operations in the solar system radiation and microgravity environment e. To use ISS to demonstrate “pathfinder” or precursor experiments necessary in advance of assembly and operation of the facility to follow ISS Design and operate the future habitation system as a key component of a broadly applicable architecture for science and human space flight: e.g., support for lunar surface sorties, assembly and upgrade of complex science facilities, maintenance of depot systems. Design and operate future space habitation systems to “feed forward” to subsequent more capable systems as part of a sustained program of human exploration beyond the Earth-Moon system; that is, develop a series of in-space “stepping stone” missions enabling humans to travel to increasingly challenging locations.

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In addition, coordination with likely international partners from the start, although always challenging, will ease all subsequent development activities. In any case, as noted in our opening, both European and Russian groups have for some time been giving thought to what free-space facilities will follow the ISS. Finally, with a set of design studies for a future long-duration free-space habitation system, near-term technology assessments, projections, and investments can be made that will be guided by being required to enable those future habitats. That is, investment priorities will be developed within the context of well-developed goals.

References 1 Scimemi, S., “International Space Station: Assembly Lessons Learned,” First International Workshop on Satellite Servicing, http://servicingstudy.gsfc.nasa.gov/workshop_1_presentations.htm [Cited 8 August 2010] 2 Garber, S., and Asner, G., “NASA's Decadal Planning Team and the Policy Formulation of the Vision for Space Exploration” http://history.nasa.gov/DPT/DPT.htm [Cited 8 August 2010] 3 Kennedy, K., “Lessons from TransHAB: An Architect’s Experience,” AIAA Space 2002, paper 6105 4 Geffre, J. and the NASA Decade Planning Team, ““Lunar L1 Gateway Conceptual Design Report,” JSC EX15-01-001, 2001 [Hereafter, “Gateway Design Report.”] 5 Kennedy, K., Toups, L., and Smitherman, D., “Lunar Habitation Strategies,” AIAA Space 2007, paper 627 6 Lester, D., “First Stop for the Flexible Path?”, The Space Review, #1521, November 30, 2009 7 http://www.bigelowaerospace.com/ [Cited 8 Agust 2010] 8 ”Seeking a Human Spaceflight Program Worthy of a Great Nation,” Review of the U.S. Human Spaceflight Plans Committee (The Augustine Committee), http://www.nasa.gov/offices/hsf/home/index.html [Cited 8 August 2010]

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