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Acta Astronautica 53 (2003) 387-397 www.elsevier.com/locate/actaastro

INNOVATIONS KN MISSION ARCHITECTURES FOR EXPLORATION BEYOND LOW EARTH ORBIT

Cooke, D. R. (I), Joosten, B. K. (I), Lo, M. W. (2), Ford, K. M. O);Hansen, R. J. (3) (l)NASA, Johnson Space Cebter, (2) NASA, Jet Propulsion Lab (3) Institute for Human and Machine

Cognition, University of West Florida ,

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Through the application of advanced technologies and mission concepts, architectures for missions beyond Earth orbit have been dramatically simplified. These concepts enable a stepping stone approach to science driven; technology enabled human and robotic exploration. Ntibers and massa of vehicles required are greatly reduced, yet the pursuit of a broader range af science objtitives is enabled. The scope of human missions considered iange Tom the assembly and-maintenance of large aperture telescopes for emplacement at the Sun- Earth libration point I+, to human missions to asteroids, the moon and Mars. The vehicle designs are developed for proof of concept, to validate mission approaches and understand the value of new technologies. The stepping stone approach employs an incremental buildup of capabiliiies, which allows for future decision points on exploration objectives. It enables testing of technologies to achieve greater reliability and understanding of costs for the next steps in exploration. Q 2003 American Institute of Aeronautics and As@~flt~tics. Published by Elsevicr Science Ltd. All rights reserved.

Introduction

Throughout the history of civilization, people have been intrigued with the stars and planets. The heavens have been a source of dreams, mystery, myth, and misconceptions. Through technology the desire for knowledge led to scientific observation and measurement, sometimes leading to further misconceptions and fancifijl accounts in science fiction. In the last century remote observations with evolving optical technology gave way to spacecraft and astronaut explorers traveling to destinations in space. They made higher resolution observations and more accurate measurements. With every step in the development of new capabilities, the

rate of return for scientific knowledge increased dramatically. Incredible discoveries have been made, leading scientists to ask more informed and profound questions. Technologies are within reach for the next great strides in exploration and discovery. Simplified mission architectures are being developed that can reduce the infrastructure and costs while providing for a range of mission destinations.

Steupinp Stone Strategy

Through the work of the National Aeronautics and Space Administration (NASA) Exploration Team (NEXT) a science driven, technology enabled strategy has been formulated. Science objectives are focused on understanding and searching for life in our solar system and the universe beyond. Mission strategies are developed to enable the search for this knowledge. A “Stepping Stone” approach is employed in laying out possible mission architectures. It begins with preparing for the next steps by learning from ongoing research within existing programs. Examples are the International Space Station, the Space Shuttle, Hubble Space Telescope, Mars missions and others. In developing the next steps, technologies are identified for three classes of exploration. Technologies and capabilities are identified that can extend remote sensing of the planets and stars well beyond the capabilities of the Hubble Space Telescope. A goal is to provide the resolution necessary to characterize planets around other stars, search for biomarkers and address other important objectives. Next, technologies and capabilities are identified to expand the knowledge return from robotic spacecraft as they venture beyond where people can currently travel. Robotic spacecraft gather more in depth knowledge in situ than is possible through remote sensing. Third, technologies are identified that enable exploration by humans beyond low earth orbit, providing for their safety, amplifying their unique capabilities and flexibility to explore. The objective is to increase

0094-5765/03/$ - see front matter 0 2003 American Institute of Aeronautics and Astronautics. Published by Elsevicr Science Ltd. AIJ rights reserved. doi: lO.l016/SOO94-5765(03)00156-5

388 D.R. Cooke et al. /Acta Ast.wnautica jJ,@OQ3$-.387-397

the rate a cun rently and robol 9 erienc

lfknl POS!

tic m :e of

sible ~u~r~~otepbs.e~a?ion rissions.and to provide first hand ‘discovery. See figure 1.

impliqa@rS,of~ technologies, he de&u ~~n~$jjs~e used existence proofs and arepOt pV~uJ?$ to b designs. Missiou concepts are su#d,with

sion Architecture StratePies view towards minimizing the infkas~cture support the range of potential dest.matrons.

as efin Ia

lie

Id

The primary objective in developing mission architectures is to define economical approaches to exploration. The science objectives define the potential destinations for human exploration. Mission analyses and development of design

science driven objectives include exploration of the moon, Mars, and asteroids, Objectives also include the construction and maintenance of advanced interferometers to be deployed at the Sun-Earth libration point L2 (figure 2). Common

Libration Points- Figure 2

389

vehicle elements, habitats and other infrastructure are defined over the range of potential destinations to develop an efficient approach. By calculating the benefits of technologies employed through iterative mission analyses, technologies are identified which make considerable improvements in vehicle masses. Even provocative technologies are studied with the purpose of discovering what could be breakthroughs in designs or mission concepts. The primary objective for this process is to identify needed investments in enabling technologies. See figure 3.

Technoloev Imnacts

Approximately 40 Kilograms of mass are required in low Earth orbit to send a kilogram of mass to the Mars surface and bring it Zack to Earth. These masses are made up of supporting systems, propellant, and tanks.

The impact of ap&+fng critical technologies is illustrated in figure ;4. If technologies flown currently on human space flight missions were employed in send:mg a si&le crew to Mars, the mass required iu low Earth orbit to support this mission could be normalized to 100%. If aerocapture is used at Mars to slow the spacecraft into Mars orbit rather than slowing propulsively, mass in low Earth orbit could be

reduced by approximately 50%. This mass could be reduced another 46% by using advanced in- space propulsion, such as solar electric, nuclear electric, or nuclear thermal propulsion. These technologies are much more efficient than the most efficient chemical engines. Through recycling of air and water in closed loop life support systems, consumable masses are reduced. Other technologies shown reduce masses by lower percentages, but the masses are still large. After application of all the technologies shown, the mass in low Earth orbit to send a single crew to Mars is still approximately equivalent to the mass of the International Space Station at assembly complete. This serves to demonstrate the need to search for mass reductions far beyond what has been achieved to date in human space flight.

Earth’s Neighborhood

The first step with humans beyond low Earth orbit is to explore what is termed “EAu&‘s

Neighborhood.” Libration points will play an important role. The ISEE spacecraft was the first to use a libration point at Earth’s Ll to make observations of the Sun. (see Farquhar [ 1] for historical review and references). The Earth- moon libration point Ll has features that make it an attractive staging point for the various destinations of scientific interest. This location

390 D.R. Cooke et al. /Acta Astronautica 53 (2003) 387-397

Mass Reduction Through Technology Mars Mission Example- Figure 4

3 All Propulsive, Chemical

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can be used as a staging pomt for lunar exploration, construction and maintenance of telescopes that would be deployed at the Sun- Earth L2 lrbration point, and possibly as a staging poirnfor buman trips to Mars. See Farqubar [2] for early concepts using libration points for lunar and interplanetary travel. See figure 5.

Lunar Exnloration

Staging at tbe Earth-moon Ll provides approximately equivalent performance and any time access to all lunar locations as opposed to the equatorial orbit rendezvous.approach used during Apollo. The Lunar prospector and Clementine missions discovered potential sources of water ice in the permanently dark

Earth’s Neighborhood Exploration Architecture- Figure 5

Crew Tr8MIIr Vehicle

L, “Gateway” Facility

Lunar Lander -. L.

Lunar Habitat *’

D.R. Cooke et al. /Acta Astronautica 53 (2003) 387-397 391

craters of the polar regions of the moon. The poles could therefore be locations with abundant resources. There are locations near these permanently dark regions, where sunlight is available most of the time, providing a source of nearly continuous power. There are additional science interests in the southern polar Aitken basin region. It is the largest known crater in the solar system, and possibly contains exposed hmar mantle.

,’ Soace Science Telescooe Construction and Maintenance 1’

The Sun-Earth L2 libration point is a potential location for arrays of large aperture telescopes and interferometers. The Earth-moon Ll “Gateway” facility could provide the capability to construct these large-scale telescopes before deployment at the Sun-Earth L2. The “Gateway” is much closer in distance and travel time to the Earth than the Sun-Earth L2. Failed telescopes can be returned. to the “Gateway” facility for repair by.the onboard crew.

Mission Aooroacb for Telcscone Transfers Between Libration Points

There are low-energy pathways that exist between the Earth- moon Ll and Sun-Earth L2. The ISAS HITEN mission used these dynamics to effect a low-energy lunar capture (see Uesugi [3], and Belbruno and &filler [4]). The invariant manifolds of unstable orbits, such as halo orbits, produce these pathways. Telescopes can travel between halo orbits at the two libn@ion points with very little energy by traversing these conduits (see Lo and Ros@]).This has enabled the approach where large aperture telescopes are constructed and maintained at the “Gateway” facility. They are then deployed to L2 along these pathways. The alternative was to send astronauts to the Sun-Earth L2 and have them work there. This required a large spacecraft and one-way travel time of at least twenty-two days. The use of invariant manifolds for vehicle transfersresults in longer trip times. This is acceptable for transferring large masses, which do not include crews. The approach that uses tbe “Gateway” architecture to serve lunar missions, telescope construction, and maintenance missions is especially valuable in reducing vehicle infrastructure.

Earth’s Neiahborhood IntYastructure

Vehicle concepts are developed to support the functions within the Earth’s Neighborhood. These concepts are designed down to the system component level. Teclmalogies are applied in designs to understand how to reduce mass and maximize mission performance. Designs are considered to be existence proofs, and not final designs. They serve to identity the technologies that should be pursued.

The “Gateway” facility employs inflatable module technology, so that tbe large volume needed can be packaged in the Space Shuttle cargo bay or expendable launch vehicle payload shrouds. Its function.5 are as a staging point for crews going to the moon or for construction and maintenance of large space telescopes. It could also be a staging point for crews traveling to

Mars, or a location for repair of outbound planetary missions. Crews would be residing at tbe “Gateway” facility only for the length of time necessary for the mission, due to the unfavorable radiation environment. Tbe “Gateway” facility would be transported to Ll using solar electric propulsion. This highly efftcient form of low thrust propulsion would be used for transport of the large mass vehicle elements over months of

time. It would be used for the “Gateway” facility, lunar lander, and lunar habitat. It would not be used to transport the crew, where it is more critical to have short mission lengths.

The crew would be transported from low Earth orbit in a transfer vehicle with conventional chemical propulsion at higher tbrust levels than is possrble with electric propulsion. Trip times

are therefore kept to a minimum. The crew transfers to the lander at the “Gateway” facility and then goes to the selected site on the moon. If the surface stay is lengthy, a lunar habitat would be used.

In all cases, technologies are investigated for their value in reducing mass of these vehicles. In particular, advanced electric propulsion, aerobraking for Earth return, wireless microelectronics, light weight materials, and closed loop life support are critical for reducing mass. It is also important that these technologies be tested and proven for reliability before Mars missions are undertaken.

D.R. Cooke et al. /Acta Astronautica S3 (2003) 387-397

Mars M issions The possibility of having the spacecraft travel between the Earth-moon Lland the Sun-Mars Ll is being investigated as a first step in human travel to the vicinity of Mars. An attractive feature in traveling between these locations is’ that the nucieardevice co&d,be kept away from low Ear& orbit. The crew could teieoperate multiple robotic devices on the Mats s&ace. At Ll the one-way communicat!bn time to Mars is reduced from as much as twenty minutes, as it is Tom Earth, to approximately 3.6 seconds (figure 7). This would.enable more interactive control and information retrieval at a faster r%tetban is possible from Earth. A tremendous amount of surfaoe information conld bere&evtd, interpretedby the onboard Ll: ,rrew, and shared with scientific tertm~on .&rth. Larg”&%ams on Earth could then advl.se.the~LIer&on fittther investigationsto be made. Asigni%ant amount of Mars surface knowliid~t w6i1ldW availzible before the challenge ofsending orew to the surface is undertaken. A reconitaissanoe capability could ‘be of great value before committing to the challenges of a Mars landing and surface stay.

“‘Earth’s Neighborhood” steps in the overall strategy are preparatory for eventual human missions to Mars. Work is underway to understand the use of the “E&th’s Neighborhood” infrastructure for Mars missions. Once again, development of vehicle concepts in these scenarios serves to help in tmderstattding the required technologies.

Artificial Gravitv Concent

Artificial Gravity Concept- Figure 6

A new design concept is being developed that provides artificial gravity for crews traveling to Mars. l’he rotating spacecraft employs nuclear electric propulsion. The inflatable habitat is mounted at one end of the spacecraft, while the reactor is at the other end away from the crew. Crews traveling on the long Mars missions will remain in better health and physical condition if they live at the designed l-g level. See figure 6.

392

Ultimately crews would be sent to the surface for on site investigations. Using the Mars transit vehicle as a base of operations at LI orin Mars orbit, concepts for smaller landers travel@ to the surface of Mars could carry small crew contingents to various interesting h3cations. With onsite manufacture of fbd develop&Irom the Carbon Dioxide atmosphere or surface sources of water, landers co&lbe refueled on the surface from pre-deployed chemical plants. Multiple trips to various surface locations would be possible. If the Sun-Mars Ll is selected as a

Communication Time- Figure 7

D.R. Cooke et al. /Acta Astronautica 53 (2003) 387-397 393

staging point, access to any location on the Martian surface is possrble at any time with nearly equivalent energy. Crews onboard the transit vehicle would continue to relay information to teams on Earth Tom both robotic devices andMars surface crews. The transit vehicle crew would essentially be the local mission control for crews on the surface.

The landers for transferring the fir11 crew of six to the surface have consistently been the largest mass driver for Mars missions. If smaller crews are sent for shorter durati@s to more locations, landers could be made smaller. A large surface habitat would be unnecessary for the short stays. Eventually, a permanent Mars base is likely, and the large surface habit&could be~built. With the scenario just described, the development of the Mars infrastructure could be’undertaken more gradually. It could begin with the transit habitat at Ll and extensive teleoperation of surface assets. The next step would inchtde small landers, with crews investigating interesting sites over short periods of time. At some point, surface habitats would house crews for long stays. More in depth investigations would be made of the most interesting known site and the surrounding area.

The option still remains for a more aggressive approach in which crews would travel to the surface, beginning with the fast mission to Mars. Decisions between these approaches would be made based on cost benefit analysis, risk, and available budget.

Launch Vehicles

Launch vehicles for human explaration missions must be sized for both the mass and volume requirements of the vehicle element&hat are to be flown. For the architectures described, m- space functionality is divided&et-v&en vebi~les to reduce launched masses to,& bnialleit common denominator.

In the case of the %arth’s Neighborhood,” the minimum Iit% capaI@ty needed is on the order of 40 metric ions, which could be attained with substantial enhancements of Evolved Expendable Launch Vehicles (E&LVs). The Space Shuttle can assist ittthis architecture. Although the vehicle elements can be accommodated with this lift capability, there are a significant number of flights for a single lunar mission.

For Mars the minimum lift capability is on the order of 100 metric tons. This is in the same launch class as the Space Shuttle without carrying the Orbiter into orbit. If this lift capability were available for the Earth’s Neighborhood, the number of launches and operational scenario would be greatly simplified. In this case payload diameters can be increased by approximately a factor of two, providing for more flexibility in volumetric efficiency. It is imperative to keep the number of launches to a minimum for these missions to maximize the overall probability of mission success.

Excitinp New Tecbnoloeies and Recluired Research

There are technologies and capabilities required for future exploration that address basic mission needs and those that improve efficiency and performance of these missions. Ultimately these critical capabiiities and technologies are essential to reduce the cost of these missions. Planners for future missions must be aware of technology development outside the agency and adapt those that are critical to these missions. NASA must then invest in the technologies that are unique to its mission needs.

Humans and Robotics

The scenario just described shows the possibility of extensive teleoperation of robotic resources on the surface. Further integration of human and machine capabilities are being investigated to develop the &II potential of these missions. In understanding the human as a system of sensors, effecters, and computational and reasoning capability, extremely efficient interfaces can be established with machines that enable effective augmentation of human capabilities. This can range from the human interface with onboard systems to augmentation of their capabilities in space suits on the planetary surfaces. Automation of machine capabilities should be pursued to the maximum extent in robots and onboard systems to free the crew from unnecessary tasks. For tasks where the crew participation is important, machines must be adapted to make the combined capability as efficient as possible.

One can envision capabilities in space suits that could extend far beyond current technology. Advances in space suits today are aimed at making them less debilitating to the crew.

394 D.R. Cooke et al. /Acta Astronautica 53 (2003) 387-397

Advances have been made in mobility, materials, gloves, safety and the life support system. Advances could be made in information and computathal capability to provide maximurn resource3 to the astronaut out on the planetary surface through well&signed visor displays and voice reoognition. Retinal sensors couldrelay back, to e&h the actual three-dimensional images seen first-hand by the astronauts, so that people-on Earth could witness the discoveries through the astronauts own eyes. Weight of the suit will be an issue on planetary surfaces due primarily to the weight of the life support system. Strength augmentation, lightweight mater+ and’exoskeletons could he employed to alleviate this problem. Advanced .concepts in actuators could be employed to augment hand strength in working against the pressure in the glove. ~xtqnf$ sensors on the suit, could provide sensory information beyond eyesight. Additional lightweight’s&ors could be integrated to provide scientific information of the surroundings. Eye&&t could be augmented to see inf$yd anUfd other wavelengths. Irnprovetpents of this nature could be employed to make’significant increases in the effectiveness and productivity of astronauts in their mission.

Performance Enhancing Technologies

First, mission elements must be delivered to Earth orbit. Investments must be made to reduce the cost of mass to orbit. Low cost engines are needed. Advanced lightweight materials and systems are also required. Investments are also needed to address ground and flight operations.

While it is important to address the cost of launching mass to orbit, it is just as important to reduce the mass that must be launched, As missions venture farther into spa&s and provisions are made to, return samples and humans, the mssses multiply to a point that dictates the need for technologies that will drive them down significantly. The techno!ogies that have the largest effect in reducing masses are advanced in-space propulsion, aerocap@re, closed loop life support, advanced l@weight materials, in situ resource u&ation, and advanced rnicro/nano wireless electronics.

The most effective technologies for in-space propulsion are solar or nuclear electric and plasma propulsion. These technologies improve efficiency five to six times over current all chemical rocket engines. For human missions to

Mars, mission masses can be reduced by approximately 50% over masses associated with chemical engines.

Aerocapture is the technology of using a plaqtt’s atmosphere to slow a spacecraft into orbit. Using this approach, fuel can be eliminated for performing this function, thus reducing mission mass. This technology can reduce Mars human mission masses by almost 50% as well.

The development of new technologies for the design and opt$n$#ion of nonlirreartmjectories and the automation of these tools should accompany advances for. in-space propulsion. Traditiona] .comc:bas.ed pajectocy design methodologies are uokutger.adequ?e by themselves. Forthe complex “Earth’s Neighborhoodr’ architecture dem+mdsi efficient and effective mission design tools are critical.

Closed Loop life support technologies are very important for long,humap missions. Closing air, water, and eventually fbod loops can considerably reduce consumables required for long human missions.

Lightweight materials are obviously important for reducing masses. Lightweight materials must be developed not only for primary structures, but also for every component of every system In considering the mass 9f every component, the maximum value for apphcation of lightweight materials can be achieved. Inflatable technology has been investrgated for primary structures (figure 8). It combines lightweight characteristics

Inflatribh Habitat- Figure 8

D.R. Cooke et al. /Acra Astronautica 53 (2003) 387-397 395

with relative ease of manufacture and efficient packaging for constrained launch volumes. It is employed in a number of the concepts for vehicle elements in the exploration architecture.

Lightweight equipment for medical diagnosis and care will be essential for long missions. Currently, if there are medical emergencies, crews can be readily returned from the Space Shuttle and International Space Station. For long missions medical capabilities beyond what is currently provided will be necessary. Equipment for these missions will bave to be miniaturixed just as in other systems! Motivation for development of these capabilities may come from outside NASA and can be adapted for space use. NASA may contribute capabilities in this field due to its unique needs.

In situ resource utilization is the technology of using materials located at the destination to augment mission requirements. The most effective use tit in situ resodces is in producing fuels. This reduces the amount of fuel that must be launched from Earth. If water-ice exists in the permanently dark regions of the lunar poles, as is indicated by data from the Lunar Prospector and Clementine missions, it can be broken down into Hydrogen and Oxygen for fuel. Oxygen can also be used for cabin air. At Mars, methane can be produced from the Carbon Dioxide atmosphere. A primary science objective at Mars is to drill for water in search of life forms. If water is found, it can be broken down into Hydrogen and Oxygen as in the lunar case.

Advancements in electronics can be very important for mass reductions. Human spacecraft employ many computers, controllers, instruments and sensors. Employing micro and eventually nano electronics can reduce the considerable masses of these systems. Current flight computers weigh on the order of 40 pounds. This mass could be reduced to ounces. Current electronics and computer designs use significant amounts of power. When power is used, much of it is converted to heat. This heat must be rejected though cold plates and cabin air heat exchangers. If the electronics are miniaturized, significant reductions can also be achieved in power and thermal systems. Wireless sensor and systems designs can eliminate miles of wiring in human spacecrat?. By employing all of these technologies, the mass of spares for systems electronics components can also be drastically reduced.

Some technologies are required just to address basic mission needs. Solar and nuclear power technologies are essential to address basic mission needs for both robotic and human missions. These technologies are important for power on planetary bodies and for providing power to propulsion systems. Advanced solar power is essential for operations and exploration for the inner solar system. As missions are sent outside Earth’s qrbit, where the solar flux rapidly diminishes, nuclear power becomes much more effective. Advancements in autonomy of systems, such as self-diagnosis and self- rectification, are important to enable crewmembers to spend their t ime productively.

Advancements in robotics technology can help to get the most out of machines as they augment human capabilities. Multipurpose rovers and airplanes can augment exploration on planetary surfaces providing reconnaissance and sharing work with the astronauts.

Reauired Research

Possibly the most important need in research for future human missions beyond low Earth orbit is in understanding the physiological effects of the space environment. Galactic cosmic radiation effects on human health and safety must be understood. Technologies must be developed that will address protection of future explorers from this environment. Likewise, further research in the effects of weightlessness and countermeasures is important. Technologies associated with artificial gravity must be addressed as an alternative. The timeliness of obtaining zero gravity research on the International Space Station is important.

For the best possible productivity from these missions, research is needed in understanding how to manage, interpret, disseminate, and react to discoveries and large amounts of scientific data. Management of science and mission operations will be distributed between the astronauts and robots on planetary surfaces, astronauts in nearby orbiting spacecraft, and larger teams on Earth. It will be important to develop sophisticated interpretive capabilities, tools and operations techniques that make the best use of these capabilities.

396 D.R. Cooke et al. /Acta Astronautica 53 (2003) 387-397

Advanced Desian Environments

~rovernents in technology begin with the way vehicle de& OCCURS. Collaborative co~cit-ion zind computational environments are b&g implemented that Wow designers from muRiple erigineering disciplines, operations er$ert&, &id s&fety, reliability and quality assum& experts to work together to efficiently develop’designs. Integrated toolb:devCloped for thii tbkdnkit potentially evolve into tools used &I training and flight control, and to on orbit tools for use during tniisiorts.

Addressing Cost

It is essentjal to a,quratejy predict ,complexity and cost of burnan spacecraft-and operations by filly uqde@ar@g tbe te&nical challenges. Costs, can be reduced tbrougb careful application of new technologies and innovative mission approaches.

Tbe implementation of a stepping stone approach to the exploration architecture can provide the capability to incrementally develop tbe infras@u@re. The stepping stone approach also allows testing of new capabibties at each step tbat are then applied with confidence to tbe next step.

Low cost Earth analogues should he employed to test technologies and capabilities off-&e, where testing failures.bave lessened consequences. The Space Station also provides opportu&ies for engineering research and testing for hardware processes tbat are zero gravity sensitive. An example is two-phased flow, which has differing characteristics in a zero gravity from a gravity environment Physiological testing on the Intema&al~ Space. Station is essential for understanding tbe zero gravity effects on tbe human body.

Leveraging other programs can also provide opportunities. for testing te&ologias and measuring environments. h@rs missions can be leveraged to test lifting,aerosheRs in the, exact atmospheric environment that we will one day send human crews into. Precjsion land&g and hazard avoidance can be proven on robotic missions. This will provide tbe confidence for human missions, while enabling the robotic missions to land safely at increasingly interesting locations. Measurements of Mars soil, dust and

radiation levels will provide an understanding of the environment for reducing uncertainties in designs and for assuring proper protection of crews.

Establishing best practices in management of’ programs will be a key factor in maintaining budget control. Carefully managing in tbe political and international environments will also be incre&nglyimportant.

Slimmiry

New strides have beep taken in understanding bow to take the next steps in exploration, New mission ~appr$aches $nd a “stepping stone” strategy enable a gr$dtilb~.dupfn inhsbuoture witii&re&d filxiiility for changing priorities in exploratjon, scientific d&very,, and for potential ‘comt&ial interests. This strategy provides r&e options than past approach+& *jch tended to * al!’ or nothing moon’ L$ ~,&,~@&$i~. The niission sce$iiiq+. iyj infk@tiiiure concepts are important for.pl&ntriirg investments in critical technologies unique to these missions. A key to suc~sstilspace e.xphuittion willbe to envision new mission concepts and technical solutions tbat are more tban extrapolations of previous concepts.

There are certainly profound discoveries waiting for us in our own solar system and tbe universe beyond. There are beneficial tecbtiologjes I@I unimagined applications that can be developed. Through the scenarios described, these benefits are witbin reach.

AcknowledRetnenQ

Many e@erts, a~ossall of NASA and outside NASA baye ~cqn@&tc<l to these results over a number. of,vearr~ b4& oftbe revt work bas bqzti doxti ~t.Jq&$y NASA Exploration Team (NEXT), whi&.i&i across tbe agency’s centers and enterprises.

References

[ 1] Farq*!, R., “Tbe Flight of ISEEJKE: Ori@,,Mh~~og k&tcii, and a Legacy”, ~AA$AstmdynamicS Specialist Conference, Boston, Massachusetts, August 10-12, l&l.

.a.

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[2] Farquhar, R., “The Utilization of Halo Orbits in Advanced Lunar Operations”, NASA Technical Note D-6365, July 1971.

to-Moon Transfers with Ballistic Capture”, Joumal of Guidance, Control and Dynamics 16,770-775

[3] Uesugi, K., et al., “Japanese First Double Lunar Swingby Mission %ITEN”, Acta Aeronautica, 25, No. 7,347-355, 1991.

[5] M. La, S. Ross, “The Lunar Ll Gateway: Portal to the Stars and Beyond”, AIAA Space 2001 Conference, Albuquerque, New Mexico, August 2&X-30,2001.

[43 Belbruno E., J. Miller, “Sun-Perturbed Earth-