Extending Human Presence into the Solar System

An Independent Study for The Planetary Society on Strategy for the Proposed U.S. Policy

July 2004 Study Team

William Claybaugh Owen K. Garriott (co-Team Leader) John Garvey Michael Griffin (co-Team Leader) Thomas D. Jones Charles Kohlhase Bruce McCandless II William O’Neil Paul A. Penzo

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org Table of Contents

Study Team 2 Executive Summary 4 Overview of Exploration Plan 5 Introduction 6 Approach to Human Space Flight Program Design 9 Destinations for the Space Exploration Enterprise 9 International Cooperation 13 1. Roles 13 2. Dependence on International Partners 14 3. Regulatory Concerns 15 Safety and Exploration Beyond LEO 15 The Shuttle and the International Space Station 17 Attributes of the Shuttle 17 ISS Status and Utility 18 Options 18 U.S. Expendable Launch Vehicles 19 Foreign Launch Vehicles 20 Shuttle-Derived Vehicles 21 New Heavy-Lift Launcher 21 Conclusions and Recommendations 22 Steps and Stages 22 Departing Low Orbit 22 Electric Propulsion 24 Nuclear Thermal Propulsion 25 Interplanetary Cruise 27 Human Factors 27 Gravitational Acceleration 27 Radiation 28 Social and Psychological Factors 28 System Design Implications 29 The Cost of Going to Mars 30 Development Costs 30 Production Costs 30 First Mission Cost 31 Subsequent Mission Cost 31 Total 30-Year Cost 31 Sensitivity Analysis 31 Cost Summary 32 Policy Implications and Recommendations for Shuttle Retirement 32 Overview, Significant Issues, and Recommended Studies 33 References 35

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org Executive Summary we recommend phased development of the (modified 08/17/04) new CEV, with the “Block 1” version designed for LEO access and return only, We propose here a staged approach to with a later “Block 2” version suited to the human exploration beyond low Earth orbit requirements of interplanetary missions. The (LEO). We believe such a plan must be CEV would be launched on a new human- adopted if the overall funding profile is to be rated vehicle, possibly based on the existing kept within the bounds that are likely to be Shuttle solid rocket motor (SRM), acceptable to the many future Congresses augmented with a new liquid upper stage. and Administrations that must “sign on” to Such a system could be available before the Exploration Initiative if it is to succeed. 2010. With Orbiter retired after U.S. Core Stage 1 features the development of a complete and with international agreement new crew exploration vehicle (CEV), the to proceed, any remaining assembly tasks completion of the International Space can be completed by the heavy-lift launch Station (ISS), and an early retirement of the vehicle (HLLV) that must be developed to Shuttle Orbiter. Orbiter retirement would be support later stages of the Exploration made as soon as the ISS U.S. Core is Initiative, by use of expendable launch completed (perhaps only 6 or 7 flights) and vehicles (EELVs) as appropriate, or on the smallest number of additional flights suitable international vehicles such as necessary to satisfy our international Ariane or Proton. partners’ ISS requirements. Money saved by Stages 2 and 3 of the proposed early Orbiter retirement would be used to Exploration architecture will require heavy- accelerate the CEV development schedule to lift launch capability well in excess of the minimize or eliminate any hiatus in U.S. 20–25 metric ton capacity of the present capability to reach and return from LEO. evolved EELV fleet. We believe these Stage 2 requires the development of requirements can best be met, at least additional assets, including an uprated CEV initially, by means of designs that utilize capable of extended missions of many existing components (e.g., the months in interplanetary space. Habitation, SRM and External Tank). Some proposed laboratory, consumables, and propulsion Shuttle-derived HLLVs have a payload modules, to enable human flight to the capacity in excess of 100 metric tons and vicinities of the and Mars, the offer a near-term approach to meeting Lagrange points, and certain near-Earth Exploration requirements with a minimum asteroids. Development of human-rated of non-recurring investment. planetary landers is completed in Stage 3, Prompt studies to confirm our allowing human missions to the surface of recommendations are needed in areas of the Moon and Mars beginning around 2020. early CEV design for Block 1 capability to The overall plan is summarized in Table 1. and from LEO, to establish the minimum A key to this vision is the requirement to number of Shuttle flights necessary to meet complete assembly of the ISS and to retire international requirements, to find the best the Shuttle Orbiter, without in the process launch vehicle for the CEV, and to perform incurring another lengthy hiatus in the trade studies for HLLV needs and ability of the United States to conduct configuration. crewed operations. To this end,

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org Overview of Exploration Plan

Stage One, access to LEO, through 2010 • Shuttle-Orbiter return to flight (RTF), complete the ISS through at least “US Core Complete” • Select and demonstrate launch vehicle for CEV • Demonstrate early CEV use for crew transfer at the ISS • Negotiate with international partners to obtain best way to transport remaining heavy modules to the ISS • Retire Orbiter as soon as above steps are completed • Costs distributed across full Exploration window

Stage Two, interplanetary cruise, through 2015 and beyond • Develop interplanetary cruise capability; uprated CEV, and necessary additional modules for the destination selected • Ensure HLLV available, probably a Shuttle-derived HLLV • Enable lunar orbit missions, remote sensing, Rovers with sample return • Enable visits to -Earth-Lagrange #2, , etc. • Enable visit and study of near-earth objects (NEOs) • Enable visits to Mars vicinity, including and . Include remote sensors and Rover with return samples. Begin infrastructure placement. Select sites. • Select destinations as appropriate: science, public, other interests

Stage Three, human surface landings, 2020 and beyond • Prepare infrastructure for moon and/or Mars bases • Build on thorough preparation in preceding stages • Initiate human landings at selected destinations • Plan for future system exploration

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org Introduction The CEV should be designed explicitly to have sufficient on-orbit life that it can be The recent Presidential Directive to focus resident at the ISS for extended periods, thus NASA’s future on exploration via "the Moon and on to Mars" has invigorated the space community and many of the general providing the emergency crew return public. Meeting these goals while remaining capability that, at present, is available only within realistic funding expectations is via the Russian Soyuz spacecraft. The long- foreseen as the major difficulty in meeting duration requirement is an obvious necessity this challenge. The Planetary Society has in an exploration vehicle. In addition, the commissioned this Report to encourage crew-return vehicle (CRV) function requires support for this new venture and to suggest a that it be capable of remaining stable and workable strategy for human exploration of quiescent, with minimal power drain, for the solar system, with the specific goal of long periods. placing humans on the Martian surface at We believe that there are significant the earliest possible moment, while allowing advantages, both for the United States and costs to be managed at reasonable levels. for the ISS partners, associated with It will be suggested below that the developing the new LEO transportation exploration can be conducted in three stages. capability as early as possible. All partners Stage 1 is the early development of a new would benefit from an earlier beginning of Crew Exploration Vehicle (CEV), as the the benefits of having larger multinational President has directed, accompanied by the crews on the ISS. The remaining heavy development of a launch vehicle to transport modules for the ISS might be better the CEV to and from low Earth orbit (LEO). transported to the ISS by means of a Shuttle- Success with the CEV will lead to missions derived HLLV, to be discussed below. It beyond LEO. We are recommending that should again be emphasized that the strong consideration be given to a specific proposed early development of a new LEO design using the Shuttle solid rocket motor transport system is intended to achieve (SRM), together with a new liquid earlier and more frequent access to the ISS propellant upper stage, for this role. We for all partners. The Orbiter would then be believe that this evolutionary development retired promptly to save the high costs of will be the quickest and least expensive path maintaining Orbiter operations, with the cost to realizing a U.S. capability to send humans savings making funds available for Stages 2 to LEO, and beyond, without the use of the and 3. The ISS can be used not only by our Shuttle Orbiter. This capability should be international partners but also by U.S. crews available well before 2010, the date by for tasks associated with solar system which the Orbiter is to be retired. By this exploration, including qualifying personnel time, the International Space Station (ISS) for long-duration missions and for studying should have reached at least the “U.S. Core social-psychological interaction within Complete” stage, and NASA should have larger crews. Remaining cargo can be reached an agreement with our international delivered to the ISS by other vehicles, partners about how best to complete our including non-U.S. launchers. obligations to them. A key Space Shuttle capability that cannot be provided in a CEV designed for

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org voyages beyond LEO, or by the Russian can be decided later, depending on the Soyuz or Progress systems, is the so-called public interest in and scientific importance downcargo capacity of the Shuttle. The of each step. Shuttle’s large cargo bay enables the return Stage 2 requires the development of an from the ISS of rack-sized experiments, interplanetary cruise vehicle configuration samples, and equipment needing to be that must include at least an extended- analyzed, refurbished, or upgraded on the duration CEV or an appropriate derivative ground. (Shuttle downcargo typically also vehicle, in addition to a modest laboratory includes crew laundry, other recyclable for surface robot control, returned sample items, and various waste and trash, but such analysis, and physiological experiments. A use is largely opportunistic rather than habitation module also is required. These reflective of a fundamental need.) However, might be derivatives of the current ISS these items, while valuable, need not be laboratory and habitation module designs. returned in a vehicle designed to meet Such commonality is, however, limited by human-rating safety standards. It should be the fact that considerable differences will possible, indeed relatively easy, to design an exist between the requirements for use on automated semiballistic vehicle, possibly the ISS and those for interplanetary expendable, for the purpose of ferrying missions, including the need for additional standard ISS rack-sized cargo up to the ISS radiation shielding, upgraded avionics, and and returning other items safely to Earth. longer-duration life support. Consumables The basic technology was first proven in the carriers for propellant and other crew Corona program, during which literally expendables also will be required. Human- hundreds of film-carrying capsules were robotic synergism is expected to play an returned to Earth from reconnaissance essential role in the scientific, engineering, satellites. It may be noted further that the and new technology aspects of emerging recently cancelled Alternate Access to Space human exploration of the solar system. As program could also accommodate such, it is expected to become an important substantial downmass capability. component of our Stage 2 program. Finally, Stage 2 initiates human exploration of there will be a clear need for a heavy-lift the solar system, with a variety of vehicle to transport these large items to the destinations including “near Earth objects” selected staging point, whether in LEO (as is (NEOs) such as asteroids; certain unique likely for early missions) or at a Lagrange gravitational locations such as the Sun-Earth point (which may be advantageous in the Lagrange points, which are of special longer term). interest to astronomers; and the vicinities of We believe that the most suitable and the Moon and Mars. The lunar and Mars least expensive heavy-lift option, at least in reconnaissance missions would be the near term, will be an unmanned Shuttle- analogous to the Apollo 8 and 10 missions derived heavy-lift launch vehicle (HLLV). to the Moon more than 30 years ago, but Numerous design configurations for such they would involve extensive robotic and vehicles have been proposed, offering remote sensing activity, controlled either payload capability in the range of many tens from a manned laboratory module or from to more than one hundred metric tons [1]. the Earth, whichever is found to be most Competing options include the use of heavy- appropriate. The eventual sequence of visits lift versions of the Atlas V or Delta IV

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org vehicles, having payload capacity in the 20- Martian resources are used to provide fuel 25 metric ton range, and a variety of new, for the ascent phase. It is likely that a lander “clean sheet of paper” designs. Although we designed for Mars will be an “over-design” have made a specific recommendation, the for use at the Moon. However, the ascent relative merits of the various options should stage of a Mars lander might, by itself, serve be confirmed in trade studies, with due as a single-stage, fully reusable lunar lander. attention to the fact that for some options, It may also be desirable to flight test the mission-enabling hardware of proven Mars vehicle at the Moon. reliability already exists. Depending on the The interplanetary cruise configuration retirement date finally chosen for the Shuttle needed in Stage 3 is largely identical to that Orbiter, the first use of the HLLV could well used in Stage 2, with the addition of the be in connection with completion of the ISS. lander. It is believed that by phasing the new Implementation of Stage 2 should permit designs across three stages of activity, costs visits to any of the destinations above by can be more uniformly distributed across the 2015. Note that human landings on the fifteen-year development period. We believe Moon or Mars are not included in Stage 2, that human landings on the Moon or on although landings on the Martian moons Mars can begin about 2020. (Phobos or Deimos) could be made, as they have negligible gravitational attraction and no atmosphere. This arguably will be both safer and more cost-effective, early on, than going directly to the planetary surfaces, as human landing and ascent vehicles would not be required. In Stage 3, the development of human landers for the Moon and Mars is completed. It is conceptually attractive to using the same basic lander design for both and, indeed, such commonality should be pursued where possible. However, there are several basic differences in the requirements that must be imposed upon the two systems, and for which the final design must account. The lunar lander requires a descent !v of approximately 1.85 km/s from low lunar orbit; in the absence of an atmosphere, the ascent requirement to the same orbit will be similar, for a total !v of approximately 3.7 km/s. A Mars lander must employ an aeroshell for the entry phase, and the descent propulsive !v will be considerably less than for a lunar landing, while the ascent !v alone will be of the order of 4 km/s. Further design differences will arise if in situ

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org Approach to Human Space The United States, however, surely will continue to support a program of manned Flight Program Design spaceflight. To abandon the capability to put humans in space, when other nations can, Destinations for the Space would be to consign America to the second Exploration Enterprise rank of nations, a clearly unacceptable We believe that it is the destiny of position. What is needed today is a steadily humankind to explore deep space progressive, regular, and affordable program personally. It is not a question of “if” but to enable the “where” and “how” to which rather one of “when,” “where,” and “how.” we have referred. Significant new goals and The debate as to whether robotic spacecraft destinations must be reached on a regular alone can adequately and more effectively basis, but the political support necessary to explore space for scientific purposes will sustain a “crash” program like Apollo continue, but it is essentially beside the cannot expected. point. Whether humans should travel and The ultimate “where” for the 21st explore is very much a societal rather than a century is Mars. The human destiny is scientific question and, historically, clearly to explore our most Earth-like whenever the question has been asked, a neighbor , and perhaps one day to significant fraction of humankind has colonize it. But a huge program with Mars answered “yes.” Prior generations have as the immediate and only target is neither thrived by exploring beyond their known technically wise nor politically sustainable boundaries; we are all the descendants of at present. A stepped strategy similar to that successful past explorers. So it will be with developed by the International Academy of the reach of humanity into deep space. Astronautics, “The Next Steps in Exploring “When” is now. We have made Deep Space” [2], provides a very attractive shamefully little progress in exploration foundation for the “how” of initiating a beyond LEO in the decades since Apollo. program of human space exploration today. Thirty-five years ago, men walked on the What is needed to sustain funding and Moon and returned safely to Earth. After a public support for human activities in deep few missions, that marvelous capability was space is an exploration strategy with a series abandoned, and it no longer exists. of intermediate destinations that are publicly Apollo was very much an instrument of exciting and scientifically rewarding, and the Cold War, a peaceful solution to the that incrementally build the capability to problem of how the United States could send humans to Mars. In this report, we compete successfully with the Soviet Union provide one possible approach to the design for influence in the world. Apollo was thus of just such a program. enabled by particular world circumstances Two particular destinations in near-Earth that no longer exist. No other problem of space could serve as useful and interesting similar scope facing America today is first steps toward exploring deep space. The perceived to require a new space enterprise closest is the Moon, which many consider to for its solution, and an Apollo-like effort is be the best first destination for a human therefore deemed irrelevant and space exploration enterprise eventually unaffordable in terms of solving a known leading to Mars. Numerous in situ scientific problem. investigations remain to be performed on the

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org Moon in order to add to our understanding SEL2 is an excellent location for the of the origin and evolution of the Earth, and large space telescopes of the future because many have argued that these investigations it has an unobstructed view of the universe warrant the presence of human intelligence. without interference from planets such as Although the Moon lacks an atmosphere and Earth or the Moon, offers a benign thermal has only half the surface gravitational environment without dust, provides a acceleration of Mars, it may nonetheless weightless environment for large mirrors, offer numerous advantages as a “testing and encompasses a vast expanse for ground” for human missions to Mars, distributed apertures. Travel to SEL2 is lessening the steepness of the learning curve energetically easier than landing on, or even for future Mars expeditions. orbiting, the Moon. Although Scientific interest in returning to the mathematically SEL2 is a “point” in space, Moon remains high, and the Moon has for practical purposes it is a region large potential utility as a stepping-stone for the enough to accommodate countless human . In addition, there will and robotic spacecraft. be great interest in the Moon among Future space telescopes are planned to spacefaring nations that have not yet sent operate at SEL2, including the successor to humans there—both for national prestige the Hubble (HST), the and as a confidence-building step before James Webb Space Telescope. There will be participating in an international Mars a continuing scientific impetus and public expedition. Europe presently has a lunar interest in advanced telescopes that can robotic mission, and Japan, China, and India search for, study, and image Earth-like are all developing their own such missions. planets around nearby stars, as well as The Moon remains a valid destination in its searching for evidence of extraterrestrial own right, and any transportation intelligent life. Any exploration architecture architecture should be designed with this in must recognize the public ownership and mind. support of this objective, because ultimately A second useful destination in near- these telescopes will require servicing just as Earth space is approximately four times as the HST has. far away as the Moon, near the very edge of The tremendously successful, Earth’s gravitational field—the Sun-Earth scientifically productive HST has taught us 2 (SEL2), located 1.5 an early lesson in the importance of human million kilometers from Earth in the anti- servicing of these assets once they are in solar direction. The Lagrange points are five space. Without the human servicing mission locations in space where an object can reside to correct the optics of HST, it would have in equilibrium between the gravitational been a disastrous failure. Without attractions of the Sun and Earth and the subsequent missions to replace ailing centripetal acceleration due to its revolution subsystems and to upgrade its instrument around the Sun. Small, periodic complement, HST would not have been stationkeeping maneuvers (a few meters per remotely as productive as it has been. In the second per year, minuscule by deep space International Academy of Astronautics standards) are required to remain at any of (IAA) architecture, regular servicing of the Lagrange points. SEL2 assets is one element in the logic of placing the interplanetary staging node at

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org SEL2; the appropriate mix of human vs. probable three-year round trip mission to robotic servicing activity is one of many Mars. Once are successfully issues remaining to be addressed. commuting to SEL2 and working there, the As an aside, we note that the tremendous additional capability required to visit an outcry over NASA’s decision to terminate asteroid is essentially the ability to travel in manned Hubble servicing missions space for several months without logistical following the loss of Columbia offers some support from Earth. A larger vehicle with perspective on the value placed by the more onboard life-support resources is public on world-class astronomy. Because needed. However, to “walk” on an asteroid even higher-quality astronomy can be and return samples requires little more than enabled from SEL2, we have some traditional (EVA) confidence in the value, from the public’s equipment for Earth orbit applications, since perspective, of SEL2 as a significant the surface gravity of the asteroid will be destination for the exploration program. negligible. NEOs are of great interest for a SEL2 is also an excellent point from variety of reasons, including the threat they which to stage missions beyond Earth’s present to Earth and their potential as a gravitational field. Such a staging node is of source of raw materials. They are also no value for a single planetary expedition or important scientifically because they are for an architecture built primarily around primordial objects, essentially unchanged expendable mission hardware. Assuming, since the formation of the solar system, and however, that an interplanetary vehicle are thus likely to hold clues to the origins of stationed at SEL2 is reused for many trips to humanity. A near-Earth asteroid mission multiple destinations, the energy savings would have considerable public appeal as an achieved through the use of such a staging exciting and potentially engaging popular node are significant. The vehicle need be adventure, and it is a potentially ideal lifted to this point on the edge of the Earth’s intermediate step to reaching Mars. Such gravity field only once, and fuel and missions can be accomplished with a total supplies can be ferried robotically on slower !v of as little as 4-5 km/s, less even than for but more energy-efficient trajectories, a lunar landing. possibly using electric propulsion (EP) Once humans have visited an asteroid, vehicles. In such an architecture, servicing the next step could be to orbit Mars. To of this vehicle and other SEL2 assets reach Mars orbit and return safely will becomes a routine operation. Astronauts require more support cargo than needed for assembling and servicing these assets at an asteroid mission. Thus, specialized cargo SEL2 will be, at the same time, developing vehicles must be developed and utilized for the capability to live and work in much the this step. Because the cargo can be sent well same environment as for the journey to ahead of the crew, lengthy trip times will not Mars. matter, allowing the use of more efficient Beyond SEL2, the next possible trajectories and low-thrust propulsion destination short of Mars itself would be one systems that would be unsuited to human of the near-Earth asteroids. To rendezvous missions. This capability is not needed early with a near-Earth object (NEO) and return in the human exploration enterprise and would require substantially less than a year, therefore can be developed later and over a a somewhat less ambitious goal than a

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org longer period of time, thus requiring later vehicles and the Mars Ascent Vehicles and more modest year-to-year funding. (MAVs) would be developed in parallel to A Mars orbit mission would provide the the ongoing human Mars orbit or Mars experience of operations in Mars proximity moon missions. These vehicles could be without the challenge of safely descending delivered to Mars’ vicinity robotically, well to the surface and ascending from it to in advance of human missions to the surface. rendezvous with an Earth return vehicle, They would be placed at the staging point exactly the role of the Apollo 8 and 10 lunar for human missions to the surface, either in orbital missions in their time. From Mars orbit about Mars or on a Martian moon. orbit, humans can command robotic vehicles If desired, it would be possible to on the surface in real time, a major step conduct one or more telerobotic test flights toward in situ human intelligence operating of the descent and ascent vehicles before on the surface of Mars, in contrast with the using them to go to the surface and return operational impedance imposed by the 10- safely. Most of the surface excursion to 20-minute round trip speed-of-light delay hardware should be reusable, except for current robotic Mars missions. (possibly) for heat shields and, if used, Investigating Mars from Mars orbit in this parachutes. Thus, the various landing craft manner is functionally much closer to should remain at Mars, as they do not need having human capability on Mars’ surface to be returned to Earth. Refueling would be than it is to the current Earth-based human- accomplished either from propellant operated robotic missions. delivered from Earth as cargo or from in situ To achieve orbit about Mars and to production by pre-emplaced processing depart for Earth from such an orbit is easier plants delivered as cargo. and safer than an excursion to the surface. A It is worth noting that once the landing more ambitious alternative would be to land phase has been initiated at either the Moon and operate on the surface of one of the two or Mars, the use of surface facilities and pre- Martian moons, Deimos or Phobos. Some emplaced assets as an “abort” option minor additional propulsive capability becomes viable. With the inherent would be required, but it is negligible in advantages provided by gravity and material comparison to that needed to land on and for radiation shielding, as well as redundant return from the Martian surface. Also, no sources of and tools, options atmospheric entry systems are required. for surface survival may in some cases be Operating from a Martian moon is indeed better than for an escape to Earth. analogous to Apollo missions operating on We have proposed an exploration our own moon’s surface, but without the architecture that places humans in lunar large propulsive requirement and dangerous and Mars orbit substantially before ascent required to climb out of our moon’s surface landings are contemplated. We potential well. recognize that there will be disagreement Once astronauts have worked over whether to conduct orbital missions successfully in orbit around Mars or on the at the Moon or Mars prior to landing, surface of Deimos or Phobos, they will have and for that matter whether to return to acquired the best possible prerequisites for the Moon prior to initiating an expedition the final step to the Mars surface. The to Mars. In our view, these questions need human entry, descent, and landing (EDL) not be answered at present. When

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org answers are made, they will depend as program and is specifically mandated in the much on the background and perspective National Directive for Moon- of those deciding as upon any specific to-Mars. technical criteria. It is our intent here to point out the destinations that have been 1. Roles “enabled” in each Stage of the proposed European interest in “‘long-term’” robotic architecture, deferring for now any and human exploration of solar system consideration as to which will be pursued, bodies” is evidenced by the initiation in and when. 2001 of the Aurora program, which targets a We have outlined a step-by-step plan for potential human presence on Mars by 2025 progressive human exploration and [3]. Potential roles for Europe as a whole, exploitation of four destinations—the Moon, via the (ESA) and SEL2, near-Earth asteroids, and Mars itself with individual European countries, might each of great scientific importance and each include launch; the development, requiring only one major new advance in construction, and operation of both human capability beyond the prior destination. and robotic spacecraft; the provision of Following this plan, we can make steady instruments for U.S. spacecraft (or vice progress toward placing humans on the versa); and the provision of crew members. surface of Mars, at reasonable costs, while This latter point is, of course, the primary maintaining an exciting human enterprise in incentive for any potential partner to space. The proposed destinations are participate in the overall enterprise. The justified by their public interest, scientific long history of NASA cooperation with ESA merit, and exploration value, and they and European countries suggests that further provide for steady, measurable, and timely such cooperation is potentially available. progress in a logical manner toward the Like Europe, Japan has a long history of ultimate goal of Mars exploration. In this cooperation with the United States, sense, the proposed architecture is analogous beginning before the local development of to the progression from Mercury to Gemini the N-1 launch vehicle based on American to the early Apollo missions in building technology. Japanese interest in lunar toward the final outcome of Moon landing exploration is evidenced by previous and on July 20, 1969. planned probes to the Moon, although the Japanese long-range plan developed several International Cooperation years ago specifies a robotic lunar base as a The authority to conduct international space goal and does not address human activities activities is granted to NASA under Section beyond Earth orbit. The Japanese are 205 of the National Aeronautics and Space potentially capable of providing cooperative Act of 1958. Since its founding, NASA has development of spacecraft and instruments, engaged in thousands of cooperative as well as providing launch capacity and projects with foreign nations ranging from crew members. training and experimentation to the Russia has a long history of interest in construction of the International Space human lunar and Mars exploration, a history Station. Further such cooperation throughout that actually predates the beginning of the the full range of previous activities appears a Space Age. This interest continues to this likely feature of any future Lunar-Mars day with active study of human Mars

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org missions in the context of an international immaturity of their technology, which has so program and development of an unmanned far achieved only one human space flight. Phobos Sample Return project. Russia’s The Chinese have, however, indicated that ability to invest resources in space activities they hope to develop a Mir-like space has, however, been significantly curtailed station by 2010 and plan to launch robotic since the collapse of the Soviet Union. lunar probes in the same time frame; this Nonetheless, as recently as 12 April 2004 latter endeavor is potentially cooperative (Cosmonautics Day), Russian President with U.S. goals. Putin said, “everyone in the leadership of the Leaving aside the issue of potential country understands that space activities fall roles, a central concern with regard to into the category of the most important international cooperation on a program that things” [4]. will last decades is whether potential The Russian role in space exploration partners are even interested. In part, this may be circumscribed by the country’s may hinge on how the ISS partners view the present financial circumstances. eventual outcome of that project. Thus, a Nonetheless, Russian rocket engines are seemingly successful outcome of that effort among the world’s best in terms of price and may affect significantly both the willingness performance, and the use of such engines in and the ability of other nations to join a U.S. the Atlas V vehicle family provides a basis Moon-Mars program. If the continuing cost for suggesting that any “heavy-lift” of the ISS is a significant burden to other capability required in the future could quite countries, that cost alone may mitigate likely benefit from the use of Russian against participation in further human engines or engine technology. Russia has exploration of the solar system. provided consistently reliable human space We emphasize here that, in our view, transportation since the beginning of the successful completion of the ISS to meet Space Age; as this is written, Russian international partner commitments is vehicles offer the only operational means of required. We are proposing—subject to human space transportation to the ISS. Their partner agreement—an alternative means of architectural approaches are very different meeting these commitments, based on early from those of the U.S., featuring long-term CEV development and Shuttle retirement use of working systems and robotic testing and on the use of other launch assets to of human systems. Such approaches may be deliver the international modules to orbit. relevant for international human Moon and We believe such a scheme offers the several Mars mission planning. Russia also has advantages of reducing cost, enhancing crew considerable experience with extended size, and providing earlier partner access to duration human space missions and much the ISS. more recent experience than the United States with nuclear rockets and with the use 2. Dependence on International of nuclear power in space. Partners China is, after the United States and NASA traditionally has organized Russia, the third country to have developed international cooperative programs so as to an indigenous human space flight capability. avoid having any partner on the “critical At present, the Chinese capability is limited path”; that is, the foreign contribution was both by lift capacity and by the relative additive or complementary to the core U.S.

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org effort. Under direction from the NASA home to U.S. firms the absolute necessity of Administrator, this policy changed in the observing these restrictions and, where 1990’s with respect to the International ambiguity exists, adopting conservative Space Station. Russia’s contributions to the interpretations of them. Many aerospace ISS clearly are essential to the effort as a engineers and space scientists can cite “war whole, especially in view of the previously stories” highlighting the difficulty of forging noted U.S. dependence on Russian launch effective international partnerships under capability for both crew rotation and cargo these circumstances. Without significant resupply following the Columbia accident. changes in the existing regulatory Whether this or a similar dependency would framework, it is difficult to imagine a be acceptable in the context of a larger technically rich international partnership in a program of solar system exploration is a new exploration enterprise. matter that can be expected to provoke considerable debate. Some will argue that Safety and Exploration Beyond LEO the United States must be prepared to “go it A total of 21 astronauts and cosmonauts alone” with its own core program in the have been lost in the course of 43 years of event that any given partner elects to end its space flight operations (on space flights or participation in the venture. Others will in ground tests while preparing for space espouse the view that such a situation is not flight), including the Columbia crew a little a true partnership at all, that the partnership more than a year ago. This properly raises is in fact forged by the necessity of mutual concerns about the level of safety that dependence. human explorers can expect when they once again venture out of LEO. How do the risks 3. Regulatory Concerns of leaving Earth orbit compare to those Significant international partnership in the experienced during launch or aboard the Exploration Initiative will be impeded and in International Space Station? What standards some cases prevented if the current U.S. of safety should we set as we explore regulatory environment continues to apply destinations like the Moon, the Lagrange in the future. Export control laws applicable points, the near-Earth asteroids, and Mars? to commercial technology, the Iran Non- Thirty-two years ago, the United States Proliferation Act, and the International completed six history-making expeditions to Traffic in Arms Regulations (ITAR) present the Moon. The was driven an interlocking web of regulation and by the imperatives of the Cold War and procedures designed to prevent technology President Kennedy’s “before the decade is transfer—particularly aerospace out” deadline, but engineers still were able technology—from the United States to other to design a system they thought had a high nations. In many cases, this purpose has probability of returning its crews safely to become moot; numerous international Earth. Apollo’s stated design goals were to competitors have technical capabilities have a 0.999 probability of returning the comparable to, or exceeding, those of U.S. crew safely and a 0.99 probability of firms and are occupying niches formerly mission success [5]. All system components dominated by U.S. companies. were to be designed to meet those overall Nonetheless, several high-profile, high- standards of reliability. The launch escape penalty cases in recent years have driven system, for example, combined with system

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org redundancy gave the crew a variety of abort data on the hazard and to develop effective options. Although scheduling pressures, the countermeasures [6]. breakdown of management controls, and a The Challenger and Columbia accidents flawed safety process led to the tragedy of have underlined the dangers facing space the Apollo 1 fire, a renewed focus on travelers and the consequences of ignoring leadership and safe engineering practices our own human shortcomings in designing produced a redesigned Apollo spacecraft and operating spacecraft. We also have that achieved the lunar landing without the learned how resilient the American public is loss of another crew. All crew members, in facing these risks, as long as human space even those aboard the crippled Apollo 13 flight leaders are seen to be confronting and spacecraft, returned safely to Earth, and six working to reduce them, and as long as the of seven lunar landing attempts were public supports the goals of such flights. The successful. Considering the technology of public recognizes that space flight is risky the day, the safety results were remarkable. but will not tolerate mismanagement or New systems for exploration beyond LEO willful disregard of safety. should aim for even higher levels of Another fatal accident caused by human reliability and safely. negligence or organizational shortcomings Human explorers heading for would likely result in a lengthy American destinations beyond LEO will face more hiatus in human space flight. Although serious space hazards—as well as some new exploration is inherently hazardous, NASA ones—than have astronauts on the Shuttle must execute its reach into the solar system and the ISS. Those risk factors include a with the highest possible attention to safe lengthy mission duration, a high-radiation crew return. environment, microgravity deconditioning, The Columbia and Challenger crews limited communications, numerous were committed to the advancement of our psychological stresses, and, eventually, society’s science and exploration goals; working outside the spacecraft in harsh however, our space program over the past surface conditions. Additional risks arise as two decades has risked human crews for a result of the nature of the very thin many missions that may have been more logistics train that will be available to safely executed by robotic means. Astronaut support the crew. If cargo resupply missions explorers risk their lives whenever they are included as an part of the venture into space. The exploration goals to architecture, reasonable redundancy in their which we commit them should be provisioning must be planned. If it is commensurate in importance with the planned for the crew to be able to operate inherent and significant risks of human for several years without support from space flight. This point was made by the Earth, this too carries certain identifiable Columbia Accident Investigation Board risks. NASA should aggressively pursue (CAIB): the risks undertaken in human parallel efforts to develop technical space flight should be in pursuit of a goal experience and countermeasures in all these worth attaining. The CAIB report makes it areas so that crews face a manageable level quite clear that continuing to fly the Space of mission risk. The radiation hazard in Shuttle to the ISS, with no definite purpose particular is poorly understood today. lying beyond, is not such a goal. Something Concerted efforts must be made to obtain more is required, and we believe that the

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org program of lunar, Lagrange point, NEO, and new exploration vision is to ensure that our Martian exploration discussed here provides destinations and goals are worthy of the precisely the goals needed. risks that await us among the planets. Our experience with failure in human space flight should lead us to adhere, where The Shuttle and the practicable, to the following guidelines in the approach to a new exploration International Space Station architecture: Attributes of the Shuttle • Manned launch systems must provide a The Space Shuttle has performed for more launch escape/abort capability than 20 years as the workhorse of America’s throughout the flight envelope. human space flight effort. It is the world’s first reusable spaceship, and its capabilities • Cargo should be separated from piloted for large payload delivery and return, orbital spacecraft to the extent that it is maneuvering and rendezvous, and robotic possible and reasonable to do so. and EVA operations are still unmatched by Automated systems designed to meet any other system. The Shuttle’s flexibility upcargo requirements should be capable and large cargo capacity have made it the of supporting downcargo requirements linchpin for assembly of the International as well. Space Station. Two fatal accidents and 14 deaths in 113 • Robotic precursor missions should be flights have revealed weaknesses in the employed to understand the Shuttle’s original design and raised environment and validate technologies significant concerns about its ability to and operations prior to initiating human operate safely for another decade or more. In missions. our view, major changes to the Shuttle’s design to improve crew safety dramatically • Intermediate mission milestones and (most significantly, a capable escape destinations should be used to build system) cannot be implemented easily. In confidence and experience before addition, the Shuttle’s high operating costs undertaking deep space voyages. under continued tight NASA budgets consume funds that might be better devoted • Spacecraft should retain an abort to new launch and exploration systems. capability to Earth or to a surface safe Given the unique capabilities of the haven throughout their transit phase. Shuttle (delivery and berthing of large payloads, robotic and EVA capabilities, • Exploration infrastructure should evolve large down-mass capacity), its return to to maximize opportunities for redundant flight is imperative for rapid completion of and emergency operations. the ISS. The tailoring of most completed ISS hardware for Shuttle launch argues for Both the astronauts and the public keeping the Shuttle operational until understand the risks of space flight and delivery of international partner modules. recognize that great discoveries merit the However, most ISS logistical needs might acceptance of danger. Our obligation in any well be met using partner assets like the Russian Progress and the ESA’s Automated

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org Transfer Vehicle (ATV). We see the Shuttle from the date that Shuttle flights resume as essentially important to the ISS only for (now no earlier than March 2005). Some delivery and assembly of major flight lessons from the ISS have already made hardware. Once completed, the ISS should valuable contributions to our future shift to simpler, cheaper, and newer systems exploration planning. In its sixth year of for logistics and crew support. orbital operations, the ISS has demonstrated The Shuttle budget for FY2004 was the technical feasibility of complex orbital nearly $4 billion [7]. If the Shuttle continues assembly. It has begun to generate some of to fly beyond 2010 due to delays in return to the human health and productivity data we flight or in ISS assembly, these funds will will need to plan longer voyages. Its not be available for future exploration technology may in many cases be adapted to efforts. Moreover, as the CAIB report has exploration use (e.g., life support, made clear, if Shuttle flights are extended pressurized volumes, logistics modeling, and beyond 2010, recertification of the fleet will on-orbit maintenance). We suggest a be required, an inevitably expensive and concerted effort by NASA to complete just time-consuming process. For these reasons, such an assessment: What on the ISS is we agree with the directive that once the ISS really applicable to deep-space missions? is complete or, as we have outlined here, Knowing this answer before we proceed to possibly even at the “U.S. Core Complete” Stage 2 will be essential if the most stage, the Space Shuttle should be retired expeditious and economical program plan is [8]. NASA should also focus on options for to be developed. supporting and completing the ISS using Although the ISS does not figure new U.S. cargo and launch systems, or prominently in the Exploration Vision international systems, that may be available beyond about 2016, it will nevertheless be around 2010 and that also have utility for important to the success of that effort. Its beyond-LEO exploration (e.g., the new CEV completion is an important milestone and Shuttle-derived HLLV, Ariane, and capping the success of the ISS partnership; Proton, and heavy-lift versions of the walking away from the program would EELVs). create huge difficulties in garnering international participation in the Exploration ISS Status and Utility Vision. The President has also made the ISS Since Columbia’s loss early in 2003, the ISS the focus for at least a decade of orbital has been in caretaker status, maintained and research aimed at understanding and solving operated by two-man crews launched and the problems posed by long-duration space returned on the Russian Soyuz. Assembly flight: microgravity debilitation, crew has halted, and scientific work is at a low mental health and productivity, limited level due to manpower limitations and a communications, the effects of partial G, limited cargo up- and down-mass capacity. and, to some extent, radiation exposure. One NASA estimates that at least 23 and perhaps important capability the ISS currently lacks closer to 30 Shuttle launches would be is that of housing larger crews of four to required to complete the ISS (through the seven astronauts, necessary for evaluating delivery of international partner crew dynamics and determining the best laboratories). The agency also estimates that crew size and skill mix. Also, the current ISS completion will take at least five years limitation of six-month crew stays should be

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org extended in preparation for human interplanetary transfer vehicles, surface interplanetary flight. habitation modules, landers, and nuclear The ISS orbit offers few, if any, power systems. As discussed below, such advantages for orbital assembly of future launch systems can be derived from present exploration vehicles due to the payload and soon-to-be operational vehicles. This penalty incurred when launching to its high would include Delta IV and Atlas V in the inclination, as well as the penalty exacted by domestic market, with the Proton and Ariane this orbital inclination when departing to V being readily available international other destinations. But the Station’s alternatives. The Long March and H-IIA intelligent use and evolving partnerships upgrades will need extensive political and greatly improve the prospects for the success technical preparation before they can be of the first human expeditions beyond Earth- regarded as viable alternatives for high- Moon space. value cargo. By contrast, bulk cargo such as Launch Vehicle Options propellant, life support system consumables, and radiation shielding should be manifested The Exploration Initiative will create on significantly larger vehicles, the designs extensive, and in many cases unique, of which are intended to reduce costs demands for launch services. Only a subset through economies of scale and of these can be satisfied with the existing commonsense relaxation of reliability global fleet of expendable launch vehicles requirements. For example, the elimination (ELVs), and even then their cost- of crew emergency abort capability will by effectiveness will be a major issue. itself generate numerous cost-saving Although it might be possible to return to opportunities. the Moon using a combination of such assets together with on-orbit assembly, a realistic U.S. Expendable Launch Vehicles Mars exploration scenario will require the The Delta IV and Atlas V families of re-establishment of heavy-lift launch Evolved Expendable Launch Vehicles capability or the development of greatly (EELVs), developed in part under Air Force advanced in-space propulsion technologies sponsorship, are the most obvious U.S. that would reduce the “mass-to-LEO” candidates for supporting the crew and high- delivery requirements. value hardware launch activities. These are Our study findings concur with the modern launch systems with state-of-the art growing consensus that crew missions to launch facilities as well as healthy supplier orbit present more stringent safety and and manufacturing support infrastructures. reliability requirements than bulk cargo Furthermore, the collapse of the commercial shipments, and therefore a mixed-fleet market has resulted approach is the most appropriate path to in surplus capacity for both systems. An pursue. Under this scenario, an initial CEV exploration agenda that exploits this configuration could and should be delivered capacity should attract the backing of EELV to LEO by highly reliable, human-rated stakeholders. The biggest challenge may be launch systems. To the extent possible, these to leverage the EELV capability without same systems should be employed for high- absorbing an excessive share of the massive value or critical hardware elements, such as EELV program overhead. We recommend

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org that NASA pursue multilaunch procurements, the cost-effectiveness of which was first demonstrated by the USAF in its block-buy of Delta II vehicles for launch of the GPS satellite constellation. Technically, evolving the EELV fleet to carry a capsule-like CEV would appear to be a straightforward engineering task, but not so for the earlier winged Orbital Space Plane configuration that would have induced unique torques and lateral loads at the payload interface. A more significant issue could be the launch infrastructure enhancements that will be required to provide crew access and emergency egress from a CEV during the terminal count. As mentioned earlier, we have concluded that in addition to Atlas and Delta, another CEV launch option merits further consideration. This option is based on the development of a new launch system SRB, in-line, medium lift candidate for CEV launch. that combines a cryogenic upper stage with a single Shuttle SRM. This approach has Foreign Launch Vehicles several attractive features. It allows us to Several foreign launch systems can provide take advantage of the existing Shuttle human essentially the same level of medium-lift space flight assets at the Vehicle Assembly capability as Atlas and Delta. Under the Building (VAB) and Launch Complexes current political environment, Ariane V 39A and B that would otherwise become launches from Kourou, Proton operations at idle upon termination of Shuttle operations. Baikonur, and Sea Launch Zenit flights from Furthermore, the SRM has proven to be the the Odyssey platform in the Pacific are the most reliable launch vehicle in the history of most readily available options for CEV-class manned space flight, with no failures in 176 missions. Ariane V offers the fewest flights following the modifications regulatory impediments to U.S. users, and it implemented in the aftermath of the is reasonable to suppose that any French or Challenger accident. Finally, the reusability European participation in the Moon-Mars of the SRM when operated independently of initiative will feature a role for this launch the Space Shuttle could result in significant system. Furthermore, the Ariane Transfer cost savings relative to fully expendable Vehicle (ATV) should be adaptable to other vehicles. A sketch of such a new launch roles besides ISS servicing. Also worth vehicle is provided in Fig. 1, courtesy of noting is the added flexibility and ATK Thiokol. redundancy that could be achieved by launching human missions from Kourou. Such a capability could become available in several years with very little effort, once the

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org planned Kourou-based Soyuz launch Shuttle-Derived Vehicles operations are underway. There are basically three options for Shuttle- Sea Launch presents an unusual situation derived vehicles (SDV). The CEV/SRM due to its multinational makeup. Although it option has been discussed briefly above but is headquartered in and operated from Long has not been studied as a serious launch Beach, , the Sea Launch option. This is likely due in part to the organization must comply with ITAR and relatively recent (i.e., post-Columbia) the other related regulatory requirements emergence of capsule designs as credible and constraints mentioned earlier. In many contenders for the CEV mission. ways this makes Sea Launch a foreign entity In contrast, NASA and its associated as far as domestic users are concerned. contractors spent considerable energy Congressional action will be necessary to assessing alternative heavy-lift Shuttle modify the existing body of regulation to derivatives during earlier Space Station facilitate use of this asset in the Exploration redesign efforts. The most widely known so Initiative. far has been the so-called Shuttle-C Such participation by Sea Launch would configuration, in which the Orbiter would be require several technical changes to present replaced by a functionally equivalent stage operations. First, a CEV delivery to the ISS from which crew systems have been would utilize a two-stage Zenit comparable eliminated. Such a stage might or might not to the original Zenit-2 instead of the Zenit- be recoverable. In the latter case, 3SL that is employed for geosynchronous consideration would need to be given to orbit missions. Furthermore, the potential substituting expendable, lower-cost RS-68 exists for conducting such ISS missions engines for the SSMEs (an option not much closer to the Sea Launch base of available during the earlier trade studies). operations in California. It is also worth The most attractive aspect of this option is noting that the Sea Launch consortium has the relatively small number of modifications been pursuing commercial launch and non-recurring investments required to opportunities at Baikonur for several years. reach operational capability. However, the Should this capability materialize, it will basic Shuttle-C design thus retains many of provide additional flexibility and synergy the unattractive features of the Shuttle as a with ISS servicing missions. payload carrier, including unusual mating If political constraints can be resolved configurations and side-loading. Such favorably, several additional international features might be acceptable if the Shuttle-C launch options would become available for were to be used for completing ISS exploration applications. The Chinese Long assembly, since many of the remaining ISS March (Chang Zheng) family has a proven payloads are already configured and track record that now includes the safe qualified for these environments. launch of a human space mission. Several Perhaps the worst feature of the Shuttle- current and future Long March vehicle C from an exploration perspective is the fact configurations appear to have more than that the sidemount payload carrier adequate performance for CEV-class configuration is exceptionally wasteful of missions, and it is likely that their prices intrinsic lift capacity. The payload carrier is would be competitive with those of Western essentially a Shuttle Orbiter without wings launch providers. or a crew compartment, and it is therefore

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org quite heavy, with a very high recurring cost, in both vehicle and ground infrastructure on the order of $500-600 million per flight. development make this the most expensive The sidemount configuration would not option in terms of non-recurring costs. evolve easily into a more capable design, a Furthermore, as there is no other perceived time-honored practice with most other use for such a vehicle, it would have to be launch vehicles. sponsored and maintained entirely by the In contrast, a more conventional in-line Exploration Initiative. SDV design, in which the payload is Consequently, unless a truly mounted to the top of the External Tank, revolutionary launch vehicle technology can would require more initial effort to be identified, one that leapfrogs current implement but would provide numerous system capabilities, it is difficult to make the operational and performance benefits, the case that an entirely new system is needed. most significant of which is greater payload mass. Again, the SSMEs would be replaced Conclusions and Recommendations by RS-68 engines (or production versions of The nation has three or four technically the SSME) mounted to the base of the viable domestic launch options for External Tank, as with the Energia booster alternative crew access to low Earth orbit in configuration. Although most effective for the near term. The selection of one or more exploration cargo missions, the in-line on approaches ultimately may depend more design would likely require significant on political factors than on cost. For modifications to existing ISS hardware example, will it be acceptable to use a Delta element mounting arrangements, which, as IV or a Sea Launch Zenit-2 to launch noted above, have been designed and astronauts to the ISS if it means closing the qualified for the Shuttle Orbiter payload VAB and Launch Complexes 39A and B? bay. On a global level, there are many reasons to make the CEV compatible with as New Heavy-Lift Launcher many launch systems as possible. An entirely new heavy-lift launch vehicle is Technically, such redundancy will help absolutely necessary only if the most avoid the single-point failure vulnerability efficient mission architecture dictates that of the Shuttle system that is currently payloads on the order of 200 metric tons to paralyzing ISS operations. Second, those LEO are required. At that point, the safety- participants who wish to develop and utilize related issues associated with such a large their own human launch capabilities are vehicle could render it incompatible with more likely to continue to be committed existing U.S. launch ranges. partners during difficult periods. Finally, A new launcher optimized for cargo, selling CEVs to the rest of the world could akin to the old “big dumb booster” concept, become a notable export and could achieve significant operational savings would enable the United States to retain the over an SDV. Comparisons are particularly lead with respect to defining standards and interesting for lox/hydrocarbon vehicles guiding human launch vehicle operations incorporating high-performance engines around the world. The F-35 Joint Strike similar to the RD-170/171 and RD-180 Fighter program may serve as a model in family, or all-solid configurations based on this regard. clusters of SRMs. However, the investment

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org At this point, SDV designs including capability (e.g., six man-days on the lunar both an SRM-based vehicle for CEV surface for the longest missions). In all services and an in-line heavy-lift likelihood, something more will be desired configuration appear to be very attractive for future lunar missions, so it will be options for leveraging the investment in necessary to assemble larger payloads in an infrastructure and people for a quick appropriate location. It is equally clear that a response. The manner in which the Shuttle Mars mission will require at least several phase-out is actually implemented and the hundred metric tons at the assembly node. determination of which infrastructure Construction of the ISS has given us elements will then be available for other considerable experience in the modular applications will be major determining assembly of large vehicles in LEO, and it is factors in whether these vehicles can only natural that a LEO assembly node become viable options for near-term would be considered for deep space applications. missions. Assembly in LEO may well become the method of choice; above all else, Steps and Stages it offers the advantage of a staging area only a few tens of minutes from home. Any LEO Departing Low Earth Orbit assembly node also possesses several The launch vehicle options discussed in the important disadvantages, and some orbits prior section can do no more than deliver are considerably less desirable than others. desired payloads to low Earth orbit. The A given rocket launched from a given desire to go beyond LEO invites site will be able to place a larger payload consideration as to what mission design, or into a lower-inclination (i.e., near- designs, might be most effective, and what equatorial) orbit than into a higher- the criteria for such effectiveness might be. inclination (i.e., near-polar) orbit. Regardless of the chosen mission Neglecting overflight exclusion zones for architectures, any mission to Mars (or even a range safety considerations, a rocket substantive return to the Moon) will require launched from any site can achieve the the use of a “staging area,” or “assembly maximum possible inclination of ±90° (a node,” to marshal the various vehicles and polar orbit), but the lowest achievable systems that are required. Although the inclination from a specified launch site is Apollo landings were executed without such equal to the latitude of the site and is assembly, it is noteworthy that the Saturn 5 achieved by means of a due-east launch launch vehicle developed for the program from the site. (Slightly lower inclinations was capable of placing a payload of about may be attained, with some loss of 140 metric tons in LEO, somewhat larger efficiency, by means of a “dogleg” than can be obtained from any of the maneuver, in which the vehicle first flies approaches discussed in section 4, save toward the equator, then turns east.) Easterly possibly the “clean sheet of paper” design. launch from a low-latitude site is further Even the Saturn 5, using the lunar orbit advantageous in that the rocket can take rendezvous technique, was able to deliver advantage of the Earth’s rotational velocity, only about 35 metric tons to low lunar orbit, which is greater for a lower-latitude site. and 8 metric tons to the lunar surface. This Thus, near-equatorial launch sites such as provided a bare minimum of mission Kourou are favored in two ways: the full

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org range of orbital inclinations (±90°) can be vector be very nearly tangent to Earth’s orbit attained, and more mass can be placed in about the Sun during the launch window, a orbit. Launch sites such as Baikonur, at period of a few weeks duration every 26 approximately 50° North latitude, and months for the most favorable opportunities. Vandenberg, which is at approximately 35° If the plane of the LEO assembly node is not North latitude but has significant overflight so aligned as to contain the departure vector constraints for easterly launches, are greatly as discussed above—and the probability of disadvantaged in this respect. such an alignment is low unless the node is If it is politically necessary that the placed in an orbit selected, well in advance, launch sites of all spacefaring nations be to favor a particular opportunity—then the able to access the chosen LEO assembly mission cannot leave Earth orbit. The rapid node, then the node must be in a high- nodal regression—several degrees per day inclination orbit, and the mass of any for moderate inclination low Earth payload delivered to that orbit will be orbits—may restrict the usable portion of the degraded by 10-20%, depending on the site window even further. latitude and the design of the launch vehicle. For travel to the Moon, or to the Earth- (Use of an equatorial launch site does not Moon Lagrange Points (e.g., EML1), eliminate this penalty when launching to a departure opportunities from a LEO node high-inclination orbit.) This will have a occur roughly every two weeks. For the measurable economic impact on the Sun-Earth Lagrange Points, opportunities Exploration Initiative. During the time frame would occur less often. addressed by this report—the next several Although no LEO node can be optimally decades—the cost of access to Earth orbit located for travel to both the Moon and can hardly be less than several thousand Mars, or even to either destination all the dollars per kilogram, and, as we have time, near-equatorial orbits are heavily discussed, even a Spartan expedition to favored in terms of performance as Mars will require many hundreds of metric compared to higher-inclination orbits tons of material to be delivered to LEO. It is because the required plane changes to reach easily seen that the cost of using a high- the desired destination will be smaller. inclination LEO staging area will be In summary, departing from Earth orbit substantially higher than it would be at can result in plane change penalties, will lower inclinations. Other physical substantially restrict the available departure constraints exist as well. To depart for the times, and will place restrictions on other Moon or Mars from a staging area in LEO conditions. This is not the case when requires, among other things, that the orbital launching from the surface of the Earth, plane of the assembly node contain the where the planetary rotation provides access departure direction during the available to any required launch plane orientation at launch window. If this geometrical least once per day. requirement is not satisfied, an expensive This conclusion provides the rationale and quite possibly prohibitive orbital plane for the use of the Lagrange Points, either change will be required. Earth- or solar-referenced, as staging areas Departure from low Earth orbit to Mars in cislunar space for travel to the Moon or (or another destination beyond the Earth- Mars. Use of these locations also involves Moon system) requires that the departure performance penalties, but they are typically

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org less than those for plane change maneuvers and nuclear-electric propulsion (NEP) is and are consistent over time, freeing the useful irrespective of proximity to the Sun. mission architecture from critical Like all space propulsion schemes, dependence on specific launch window electric propulsion requires the generation constraints. and expulsion of a directed mass flow from In this vein, very high Earth orbits the vehicle, which is then accelerated in the (HEO) may become attractive as staging opposite direction, according to Newton’s area locations. The required plane change to 3rd Law of Motion. However, EP employs a the target inclination can be accomplished different fundamental mechanism for quite cheaply, at the apogee of the LEO- transferring energy to the fluid stream than departure transfer orbit. Nodal regression for do chemical rockets (or even nuclear high, near-equatorial orbits is negligible, so thermal rockets, discussed below). Through the staging area will remain useful the mechanism of the converging-diverging throughout a given launch window and for supersonic nozzle, chemical rockets are multiple opportunities. devices for converting the thermal energy of combustion into a highly directed propellant Electric Propulsion stream. With EP, the electrical energy is If an HEO assembly node, including a node used to strip electrons from the atoms of an at EML1, is selected, it is possible to easily ionized, preferably heavy, element substantially improve the mass delivery (e.g., xenon). The heavy positive ions are efficiency of the architecture. The assembled then accelerated in an electromagnetic field vehicle, or more likely sub-elements of it, and ejected from the back of the “rocket” in can be delivered to the higher orbit perhaps a stream of high speed particles. (The several months before departure for the previously stripped electrons must be Moon, Mars, or an NEO, at a time when the allowed to recombine with the ions as they orbit plane orientation will be correct for the exit to prevent buildup of a net charge on the anticipated departure. spacecraft.) The higher orbit can be reached The major advantage of EP is the fuel efficiently using low-thrust electric efficiency it offers; a specific impulse in the propulsion (EP). This would require several range of thousands of seconds is easily months, but once in high orbit a crew could achieved. However, EP systems offer very rendezvous with the assembled vehicle, low thrust, several orders of magnitude departing either from Earth’s surface or below that of chemical propulsion systems. from LEO. Then, chemical propulsion could Moreover, a large mass of hardware is be used for the remainder of the outbound required to generate this thrust, nullifying to mission at a fraction of the requirement for some extent the efficiency of the basic LEO departure, allowing a shorter trip. For engine; much of the presumed payload departure to Mars, a dual propulsion system advantage of EP systems is used to may be useful, with chemical propulsion accelerate the mass of the powerplant. used for fast departure and arrival, and The feasibility of large-scale nuclear electric propulsion used during the several electric propulsion is likely to be months of interplanetary travel. Solar- demonstrated first during the Jupiter Icy electric propulsion (SEP) has been Moons Orbiter (JIMO) mission, a robotic considered for operations in cislunar space, mission currently planned for launch in 2015

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org [9]. The mission is anticipated to use a or some comparable propellant via electric reactor in the range of several hundred or magnetic fields. kilowatts and to require a mass of some 20 NTP is attractive because of the high metric tons in LEO, of which 10-13 metric thrust level it can provide, similar to that of tons will be xenon fuel, the favored choice conventional chemical rockets and several for such a system. The actual science orders of magnitude greater than NEP. For payload is projected to be in the range of maneuvers within planetary gravity wells, 1,500 kg; much of the remainder of the particularly Earth escape, such high thrust overall mission mass is absorbed by the can reduce transit times from months to hardware (reactor, energy conversion hours. Although NTP is not as fuel-efficient system, radiators, structure, etc.) required in terms of specific impulse as NEP, the for the NEP system. reduced trip time to and from Mars offers Human missions will require megawatt- significant benefits in terms of reducing the class reactors and comparable increases in crew exposure to microgravity and radiation, the mass of fuel required. The availability of while at the same time reducing xenon in such large quantities could be in requirements for consumable supplies. question. Xenon is present in amounts The major advantage of NTP compared in the atmosphere and is extracted in the to chemical propulsion is that the energy course of liquid oxygen and nitrogen contained in the exhausted propellant (a key production. Current world production of factor in determining a rocket engine’s xenon is on the order of 10 million liters per maximum potential performance) is not year (59 metric tons at standard temperature constrained to the energy available from the and pressure), at an average price of about chemical combustion of a fuel and an $10 per liter, or about $1,700 per kilogram oxidizer. The hydrogen exhaust from an [10]. Unless substantial progress is made in NTP engine can be hotter than for chemical this area, use of a less desirable fuel will be propellants, limited only by the thermal necessary. tolerance of the engine materials themselves. Also, the lighter molecular weight of the Nuclear Thermal Propulsion pure hydrogen exhaust greatly improves the Of the technologies so far proposed for overall operating efficiency. These effects radically transforming the architecture of together offer essentially double the 450 Moon and Mars exploration, nuclear thermal seconds of specific impulse typical of a propulsion (NTP) is among the most high-performance lox-hydrogen upper stage credible in terms of both fundamental engine. With such enhanced performance, physics and engineering development the amount of propellant needed for the maturity. NTP is based on the direct transfer mission can be reduced by more than half, of fission-generated heat from a solid with a concomitant reduction in launch nuclear core (we omit here any discussion of costs. gaseous core nuclear reactors) to a working The advantages of NTP are mitigated by fluid (hydrogen) that also serves as the numerous material compatibility issues. The propellant. By contrast, with NEP the heated hydrogen tends to erode the reactor original thermal energy undergoes several fuel core, and as with any conversions, and therefore losses in overall there is a high level of high-energy radiation efficiency, before being imparted to xenon emitted, which severely constrains the

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org design and configuration of the overall tolerant of any nuclear systems. Moreover, vehicle. the government and industrial nuclear Also, although the higher specific infrastructure has atrophied considerably in impulse does offer the capability to carry the last 30 years as a result of the demise of more payload or less fuel, the improvement commercial nuclear power and the end of in overall performance as compared with the Cold War. chemical propellants is not as great as might As discussed in connection with NEP, be suggested from consideration of the NASA is beginning to resurrect nuclear improved specific impulse. Because of the propulsion options in general. The weight of the reactor and associated capabilities now under development through structure, the overall thrust-to-weight ratio in preparation for NEP of an NTP system will be substantially missions such as JIMO can also help lay the poorer than for a chemical system, foundation for a more extensive program nullifying part of the presumed payload that includes NTP. However, unlike NEP, advantage. Even with these reservations, the NTP can be justified only for human potential of NTP as a tool in the exploration missions, where there is major benefit to be of the solar system is enormous, and it has obtained by reducing trip time and been recognized as such for decades. increasing payload. Because of this potential, the U.S. Our team endorses these, and stronger, Atomic Energy Commission (the efforts by NASA, because nuclear power predecessor to ERDA and thence DoE), and and propulsion is ultimately necessary for then NASA, invested significantly in NTP the exploration of the solar system. At the development during the 1950s and 1960s, same time, however, very effective missions with projects known as Rover and NERVA to Mars clearly can be designed using the (Nuclear Energy for Rocket Vehicle combination of chemical propulsion for Applications). These efforts resulted in the departure from Earth and for return from development and testing of multiple reactors Mars, and aeroassist upon arrival at Mars and rocket engines at the Nevada Test Site. and when returning to Earth. The mission These tests validated the general operational architecture can be made substantially more feasibility of NTP by 1973, when the effort efficient by extracting propellant from the was terminated as part of the overall Martian atmosphere, which eliminates a retrenchment from human space exploration substantial part of the logistical burden, after Apollo [11]. although of course a production plant must Arguments concerning performance be pre-emplaced. , aspects of NTP relative to other options are though desirable, is thus not essential for the as valid today as they were in 1972. exploration of Mars. However, the social environment for Nuclear power is a separate and initially conducting technical R&D related to nuclear more critical issue for the exploration of systems has changed dramatically, making both the Moon and Mars. Mars’ distance any such task much more difficult than in from the sun degrades the output of a given earlier decades. International treaty solar array by a factor of approximately 2.2, obligations preclude the open air testing making the generation of useful surface techniques employed for the original NTP a rather cumbersome affair, one testing, while public opinion is far less that is further compromised by the

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org accumulation of dust on the panels. The cosmic rays. Various areas of concern will two-week lunar night poses an even greater be discussed below. design challenge for lunar missions if they are to remain through the night. The Gravitational Acceleration compelling solution to these problems is the Humans have evolved in our present development of space nuclear power gravitational environment of “1-g,” about reactors, a solution we consider to be 9.8 m/s2, for many millennia. At the of essential to implement. manned spaceflight, 45 years ago, there existed real concern as to how the human Interplanetary Cruise body would respond to the near-weightless Many options have been proposed environment of space flight. Experience in concerning classes of trajectories that may both the U.S. and Soviet/Russian space be used for travel between Earth and Mars. programs, for durations of up to almost 15 These include the Aldrin cycler concept, as months, has shown that most physiological well as other types of cyclers, and the use of systems adapt quite well to low gravity flybys. But chemical propulsion is within days or weeks and then return to suitable for six- to eight-month transits from normal upon return to Earth. The principal a high Earth orbit to a high Mars orbit, such exception is in “mineral balance,” especially as EML1 to Phobos or Deimos. This avoids the calcium in human bones, which relates the high !v requirements to achieve a low to their strength and resistance to fracture. circular orbit. If only chemical propulsion is So-called “bone loss” remains a serious used, the transfer vehicle will have to refuel problem, and NASA continues to pursue at Mars. If a combination of chemical and research in this area as a high priority. electric propulsion is used, a round trip may Part of the difficulty in studying this be possible. The same is true if a chemical- problem lies in the low rate of mineral loss, aerobrake mission design is selected. But comparable to that observed in bed-rest certainly cargo vehicles will be needed and, studies on Earth. The issue is further if missions are not time critical, these complicated by the normal decrease in vehicles could be operated with low thrust mineral content of adult bones with aging. alone. Of course, the infrastructure for The ultimate concern for some is the risk of continuous operations, as with the various weight-bearing bone fracture upon return to cycler concepts, would have to be developed Earth after several years in weightlessness. at Earth and placed at both planets. It is reassuring to note that, after all the Human Factors long-duration flights to date in , MIR, or the ISS, there have been no fractures of weight-bearing bones for any astronaut or Many of the human factors important to cosmonaut after returning to Earth. long-duration space flight outside the Still, some argue for more positive protection of the Earth’s can preventive action to eliminate the slow be addressed in long-duration missions on mineral loss that has been observed. Dietary the ISS. The principal exception is in the and pharmacological studies continue to be area of radiation exposure in interplanetary pursued. Exercise protocols that provide space, where Earth’s magnetic field is not compression stress to the leg bones, such as available to deflect most of the energetic solar particles and some of the lower energy an in-flight treadmill with crewmembers

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org anchored by bungee cords, have been obtain accurate data about the radiation flux employed with positive results. The ISS beyond the magnetosphere. At this point, we currently employs the Interim Resistive must assume that some combination of the Exercise Device (IRED) to enable crews to various design approaches will be found to load muscle and bone with vigorous strength reduce the radiation risk to humans to an training exercises. The IRED has shown acceptable level for several years of some initial promise in slowing bone loss. interplanetary travel. Finally, a large rotating structure has been envisaged that can provide variable Social and Psychological Factors acceleration levels by centrifugal force. The social-psychological aspects of crew Whether or not this is required will have to selection, training, and in-flight problem await more studies on the ISS;, if required, resolution have been neglected for many such a structure will be a major design effort years, particularly in the U.S. space for the interplanetary spacecraft. program. In the early days of U.S. space In summary, numerous problems and flight, crews were small (three members or inefficiencies result from the microgravity fewer, until the Space Shuttle arrived), environment. Relative to the overall scope potential selectees were few (usually fewer of an expedition to Mars, however, they are than 50 candidates for a mission were inconveniences rather than show-stoppers. available in the Astronaut office), all had trained and worked together for many years Radiation (allowing them to become aware of the The biological effects of radiation in the strengths and weaknesses of their currently have an crewmates), the selections for flight were estimated uncertainty factor of about four made principally by senior fellow-astronauts [5]. Radiation biology is clearly a very (Chief of Astronaut Office and Director of important factor in the design of Flight Crew Operations, who knew all flight interplanetary spacecraft, but with such large crew candidates well), and mission durations uncertainties in the effects of radiation, we were short (less than two weeks). In these must await further research and the circumstances, it was expected that development of expert understanding before compatible crews with little social- definitive design rules can be developed. psychological friction should be the norm, Lacking such, there is much that can be and (with minor exceptions) this was found done by designing spacecraft to contain to be true. “storm shelters” for protection against However, as crews have become larger energetic solar protons. Hydrogen is one of (six or seven members on a Shuttle flight) the best materials for such shielding; likely and included both genders, as well as those the storm shelter will be a central region of of different nationalities and professional the spacecraft surrounded by water tanks backgrounds, often with restricted time and possibly some degree of magnetic available to train together, some increased shielding from heavier and more energetic psychological stress is to be expected. The galactic cosmic rays. Pharmacological minimal crew interpersonal friction protection is also being considered. NASA encountered so far (at least publicly) is should expedite radiation studies at therefore a remarkable achievement. Credit dedicated accelerator facilities, and it should should perhaps go to the high motivation of

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org all crewmembers (some friction is simply resolution, if and when required, should be overlooked or resolved), good selection of handled on this private loop. Cross-skills crews by senior astronauts and cosmonauts, training is mandatory because the number of and a command structure that makes each crewpersons is expected to be rather small. individual’s responsibilities clear. Cross training ensures both availability of For future missions in interplanetary competent personnel and better space, it is recommended that additional understanding among crewmembers of the time be given to train a number of others work objectives. NASA should candidates together (at least a year), in conduct studies to determine the needed several locations, before the final crew skills for each destination planned. The ISS composition is determined. Possible may provide a good training ground for locations for Mars mission preparation could some of these. include areas in the Arctic or Antarctic, the Food systems should be entirely pre- ISS if adequate transportation is available, packed, as was done in the Skylab program or lunar missions of shorter duration, with more than 30 years ago. Although pleasant technical and scientific work to be done. and enjoyable, fresh-frozen items can be Social interaction with families of other omitted. Worth noting also is that radiation- nationalities should be included. A Russian stabilized foods can provide a very useful proverb, publicly related years ago by alternative to frozen foods for long-term cosmonaut Oleg Atkov, states roughly that storage. Onboard growth of foods is a “individuals should never undertake a research task appropriate to the ISS, rather difficult and risky task until they had than it being a critically needed operational consumed together 20 kg of salt.” The system. Although freshly grown foods seem obvious interpretation is that they should to have a positive psychological effect on share many meals together, becoming well long-duration flights on the ISS, their known to each other. Although difficult for production should not be a mandatory mission planners to achieve, this seems to be requirement for continuing an interplanetary the best way to ensure a smoothly flight. performing, compatible mix of Artificial gravity via rotation of the crewmembers for interplanetary missions. entire space assembly is a major design consideration. If used, some large-radius, System Design Implications relatively slow rotation should be used to For these longer missions, human factors minimize coriolis forces. However, become increasingly important. Exercise weightlessness (free-fall) has proven quite facilities are essential to maintaining the satisfactory on all previous long-duration good health required in flight, as well as at missions, and the ISS will have provided the destination and eventually for return to much more experience before these Earth. Additional training in medical care interplanetary missions are flown. It and procedures is important, especially if an therefore seems best to rely on a “free-fall” MD is not included in the crew. Individual design until it is shown to be unacceptable private video conferencing capability should for reasons presently unknown. It should be available for discussion of medical also be noted that, to the extent that problems and especially for any treatment microgravity exposure is deemed a problem, required. Social-psychological problem faster transit times provide considerable

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org relief. The additional design cost and that about 500 metric tons is required in low complexity attendant to large, rotating Earth orbit for a mission based on chemical spacecraft may well be better invested in propulsion. nuclear propulsion systems, which, as noted above, allow significantly shorter transit Development Costs times. We can estimate the design, development, test, and evaluation costs for a human Mars The Cost of Going to Mars mission by noting that, of the approximately 500 metric tons required in LEO at the Seventy years of aerospace system outset of the expedition, at least 250 metric development data show a strong correlation tons consist of propellant, with the between the weight of aerospace hardware, remainder being the so-called “dry properly segregated according to category, spacecraft,” to which our hardware and the cost of its development. The development cost estimate will apply. NASA/Air Force Cost Model (NAFCOM) Assuming traditional NASA program reveals the median cost for development of management, but including 30 years of 2% human-rated spacecraft to be about $420 K productivity growth, we find that human- per kilogram and the median cost for the rated spacecraft should have a median cost first production unit of such spacecraft to be of about $230 K per kg at the beginning of about $29 K per kilogram. (FY 2004 dollars the 10-year development program in 2014. are used throughout this discussion.) This results in a development cost estimate However, no human-rated spacecraft has of $58 B, or an average of about $5.8 B per been developed in the past 20 years. Further, year over that 10-year period. the President’s Exploration program does not reach the funding levels needed for a Production Costs Mars program until 2014; thus, 30 years of Again assuming 250 metric tons of human- productivity gains will have occurred before rated spacecraft and accounting for 40 years any such program begins. Assuming that it of productivity gains before this spacecraft will require 10 years to develop the enters production, we estimate first unit hardware to launch the first human Mars production cost at about $13 K per kg in expedition, there will be another decade of 2024. This gives a total first unit production productivity improvement before the cost of $3.2 B. spacecraft enters production. The above results must therefore be adjusted for the First Mission Cost productivity improvements that have The direct cost of the first Mars expedition occurred and that will occur before the first will be the cost of the human-rated Mars expedition could leave Earth. Because spacecraft, the (negligible) cost of the future productivity gains are unknowable, propellant, and the cost of launching all the we will assume 2% annually for the entire required mass to LEO. Observing that there period as a conservative estimate; this is has been no significant change in the cost of lower than the level of productivity growth space launch over the past 40 years (we note in the U.S. economy over the past 20 years. that beginning about 1994, some sovereign Finally, we observe that the majority of competitors in the space launch business human Mars expedition studies have found started pricing below cost), we will assume

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org that the present launch costs of $9-11 K per rocket can be expected to save at least 100 kg will continue for the next 40 years. On metric tons of propellant. This represents a this basis, we estimate the cost of placing savings of $0.9-1.1 B in launch costs for 500 metric tons in LEO at about $4.4-5.5 B each mission. Discounting at the U.S. per mission. Summing these results, we Government’s 7% cost of money across the conclude that the first human Mars entire 40 year period (2004-2044) suggests Expedition will have a direct cost of around that investment of up to $1.1 B is $7.6-8.7 B. economically justified today if the development of a for Subsequent Mission Cost a human Mars mission will save 100 metric The production of aerospace hardware tons of LEO mass, given current space characteristically shows a “learning curve” launch prices. of about 85% (i.e., each doubling of the We can similarly determine the production quantity results in a cost economic value of lower space launch costs. reduction to about 85% of the earlier level). Halving the cost of launch to $4-6 K per kg Thus, the second set of Mars expedition would result in a savings of about $2.5 B per hardware can be expected to cost about $2.7 human Mars mission; these savings have a B, the fourth set about $2.3 B, and so forth. present value of $3.1 B if the first Mars Summing this well-established effect expedition starts 20 years from today. Such over 20 years (9 missions to Mars) results in savings on a Mars exploration program a total hardware cost of $20.9 B. Adding to beginning in 20 years would therefore this the $40-50 B for placing nine missions economically justify Government spending worth of mass into LEO yields an average of up to $3.1 B today if that investment mission cost, over 20 years, of $6.8-7.9 B. results in halving the cost of space launch. This result assumes that no new hardware This estimate of the economic value of development is initiated over the two-decade lower cost space launch does not include the period between the first and ninth missions, benefit that such a lowering of cost would which may be unrealistic. have to all other government payloads over the next 40 years, nor does it include any Total 30-Year Cost benefit it might have for the national Summing the 10 years of development costs economy. and mission execution costs for 9 missions We may also note that there is a over 20 years, we estimate a total program significant discrepancy between the cost over the 30-year period 2014-2044 of historical $420 K per kg cost of developing $119-129 B. For comparison, the Apollo human-rated spacecraft and the program cost about $130 B in FY2004 approximately $55 K per kg cost of dollars spent over about a decade. developing commercial aircraft over the same period. Because NASA’s traditional Sensitivity Analysis program management methods are largely a Based on the above analysis, we can function of organizational culture, it may be estimate the present value of using a nuclear instructive to ask what might be the value of thermal rocket instead of chemical rockets reducing the cost of developing human-rated for LEO-Mars-LEO transportation. In spacecraft to two-thirds of previous levels. addition to reducing the travel time, such a In that case, we can estimate the present

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org value of the future savings at about $1.2 B this view; we believe that the Orbiter will be today. Thus, it is economically worthwhile adequately safe to fly more missions into to invest up to $1.2 B in changing the space, although its retirement should be manner in which NASA manages its accomplished as soon as practicable, given programs, if that change will result in that it will have seen 25 years of use. We lowering future development costs to two- believe it is reasonable to fly again to thirds of historical levels. complete construction of the ISS, at least to the “U.S. Core Complete” stage, which Cost Summary should be reached after only six to eight A Mars Exploration Program starting in additional Orbiter missions and about two 2014, launching a first mission in 2024 and years. It appears, however, that to reach a mission every 26 months thereafter “Assembly Complete,” with the through 2044, is estimated to have a total international modules (JEM and Columbus) cost of no more than $129 B over that and perhaps the U.S. Habitation module in period, or about $4.3 B per year. place, will take more than 20 additional Development of a nuclear thermal rocket flights and an additional four or five years. has the potential to save $7.9-10 B if space This appears to be stretching the program launch costs remain at current levels. too far and, perhaps equally important, Lowering space launch costs to 50% of extending funding for the Shuttle Orbiter too current levels would save $20-25 B. far into the next decade, limiting funds Reducing the cost of NASA human-rated available to move into succeeding Stages of spacecraft development to two-thirds of the Exploration Initiative. There seems to be historical levels could save an additional some official ambiguity on this point. $19.3 B. NASA has indicated that the Orbiter will be retired in 2010, though this is likely to be Policy Implications and well before “Assembly Complete” and would once again place the United States Recommendations for Shuttle with no capability to reach LEO or the ISS, Retirement presumably necessitating reliance on the Russian Soyuz once again. We assume that the Shuttle Orbiter will We propose instead that NASA plan to return to flight in 2005, as NASA has use the Orbiter only to “U.S. Core indicated. However, regardless of the safety Complete” and plan to deliver the other measures incorporated, it will remain heavy modules to the ISS with other launch inherently deficient in its capability to vehicles, provided that agreement on this provide the crew with an escape option in point can be reached with the international the event of a catastrophic failure at some partners. Launch options are described in point in the mission. Such a failure is section 4, above. In this way, larger and inevitable if the Shuttle continues to fly international crews can begin to utilize the indefinitely; we therefore agree with the ISS even earlier than in the current planning. Administration’s decision to retire the Also essential to this plan is the early vehicle in the 2010-2011 time frame. development of a simple and robust CEV, Indeed, some have advocated that the designed to transport four to six Shuttle be retired now. We do not advocate crewmembers to and from LEO , and to

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org remain with the crews during their stays at Before the internal steps along the route the ISS. When this is done, which should be through these three Stages can be fully before 2010, then the Orbiter can be retired defined, a number of confirming or defining and human access to space for the United studies must be completed. States will not suffer another painful hiatus. The CEV design for this first stage might be • We have suggested that the earliest identical externally to the more capable version (e.g., “Block 1”) of the CEV be versions adapted for interplanetary travel in a simple design capable of carrying a a later Stage of Exploration. It can be crew of four to six to and from LEO. It simpler, less massive, and cheaper to would not be intended for long periods develop at this early phase because it will of independent free-flight or trips not be required to spend long manned beyond LEO but would provide U.S periods in space, travel to distant access to LEO and the ISS and allow destinations, or survive reentry at hyperbolic the Shuttle Orbiter to be retired. The speeds. CEV Block 1 design would allow the ISS be used by the United States both to Overview, Significant Issues, qualify more and larger crews for later interplanetary travel and to assure and Recommended Studies mission planners that the internal dynamics of crew selection and skill We have described a three-stage plan for provision were appropriate for long Moon/Mars Exploration. Stage 1 firmly duration missions. It would also allow establishes our Earth orbital capabilities our international partners to begin their with a new CEV capable of carrying four to long-delayed research in the U.S. Lab six persons to and from LEO, including the and other existing facilities at the ISS, before 2010. It requires the concurrent earliest possible time. It is expected that qualification of an appropriate launch this Block 1 design could be available vehicle, which we have suggested could be for testing by 2008 and manned by based on a single SRM augmented with a 2010. The question of the proper design new lox-hydrogen upper stage (Fig. 1). With configuration remains, and is important, this system in place, and with the because successive versions will be concurrence of the international partners, the unlikely to (and should not) alter the Shuttle Orbiter can be retired at any stage of vehicle’s basic mould lines. ISS assembly following “U.S. Core Complete.” • The mass of the Block 1 CEV should be In Stage 2 of the Exploration program, in the 13-15 metric ton range, including destinations at the Moon, NEOs, the the abort system. We have suggested Lagrange points, and the vicinity of Mars, that the most suitable launch vehicle for including the Martian moons Deimos and the LEO CEV could consist of a single Phobos, become possible. Each of these SRM, with a new lox-hydrogen upper locations offers the potential of fascinating stage. Candidate upper stage engines scientific return and broad public interest, could include the Apollo-era J-2S or the while remaining within reasonable fiscal SSME (likely modified for cheaper bounds. Finally, in Stage 3, human landings production if it is to be expended upon on the Moon and Mars are achieved.

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org each use). Heavy-lift versions of Delta • NASA must define the fleet of U.S. IV and Atlas V have been mentioned launch vehicles desired to support frequently as candidates for a CEV human exploration beyond LEO. launcher and have ample payload capacity for the task, though • We have assumed that, at least initially, considerable work may be required to the assembly node for the collected human-rate them. Some study should be modules will be in low-inclination devoted to determining which option is LEO, and we have pointed out some of best suited to early use; what choices the penalties associated with the use of would be the most cost-effective, safest, higher-inclination orbits. We have and most reliable; and what additional addressed some of the advantages of infrastructure would be required for high-altitude assembly nodes but have each option. not considered them likely candidates for early use. These issues should be • It would seem sensible to consider addressed in more detail. using various international launch vehicles at sites other than KSC—particularly Kourou, befitting its advantageous location—for launching both the CEV and other exploration hardware. Whether this is politically viable or practically implementable remains to be determined, but it should be studied.

• It will be necessary to upgrade the CEV to a “Block 2” version for missions beyond LEO. The Block 2 version will have requirements yet to be determined, but at a minimum it must be capable of long-duration interplanetary cruise missions to any of the destinations listed for Stage 2 or 3 exploration, presumably in combination with other modules (e.g., Hab, Lab, Consumables, Propulsion), which must be attached to 2the CEV before departure on interplanetary trips. We are confident that a CEV “growth strategy” along these lines will allow an exploration version of the vehicle to be developed at the least possible incremental cost.

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org References 7. President’s FY 2005 NASA Budget 1. Morring, Jr., Frank, “Off the Ground,” Request: Aviation Week and , 28 http://www.nasa.gov/pdf/55385main_01%2 June, 2004, p. 26. 0Front%20page%20Total%20Summary%20 Table.pdf 2. "The Next Steps in Exploring Deep Space," a cosmic study by the International 8. Planetary Society Workshop: Stepping Academy of Astronautics, Review Draft 23 into the Future, a Workshop in Memory of March 2004 the Columbia 7, April 29-30, 2003. http://www.iaanet.org/commissions/ http://planetary.org/workshop/index.html presentation.pdf 9. Morring, Jr., Frank, “Space Nuclear 3. http://www.esa.int/SPECIALS/Aurora/ Power,” Aviation Week & Space ESA9LZPV16D_0.html Technology, Vol. 60, No. 22, May 31, 2004, p. 66. 4. “Putin Acknowledges Budget Problems in Space Exploration,” Moscow, ITAR_TASS 10. http://www.alfanaes.freeserve.co.uk/ in English, 1730 GMT, 12 April 2004. Session981.htm

5. Murray, Charles, and Cox, Catherine Bly, 11. Dewar, James A., To the End of the “Apollo: The Race to the Moon.” (1989), Solar System—The Story of the Nuclear pp. 100-102. Rocket, The University Press of Kentucky, Lexington, KY, 2004. 6. Setlow, R.B., “Mitigating Hazards of Space Travel,” Space News, 15 Mar 04, p. 13.

The Planetary Society**65 N. Catalina Avenue, Pasadena, CA 91106-2301**(626) 793-5100** Fax (626) 793- 5528**E-mail: [email protected]** Web: http://planetary.org