TY - BOOK AU - National Academies of Sciences, Engineering, and Medicine TI - A Midterm Assessment of Implementation of the Decadal Survey on Life and Physical Sciences Research at NASA SN - DO - 10.17226/24966 PY - 2018 UR - https://nap.nationalacademies.org/catalog/24966/a-midterm-assessment-of-implementation-of-the-decadal-survey-on-life-and-physical-sciences-research-at-nasa PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - The 2011 National Research Council decadal survey on biological and physical sciences in space, Recapturing a Future for Space Exploration: Life and Physical Sciences Research for a New Era, was written during a critical period in the evolution of science in support of space exploration. The research agenda in space life and physical sciences had been significantly descoped during the programmatic adjustments of the Vision for Space Exploration in 2005, and this occurred in the same era as the International Space Station (ISS) assembly was nearing completion in 2011. Out of that period of change, Recapturing a Future for Space Exploration presented a cogent argument for the critical need for space life and physical sciences, both for enabling and expanding the exploration capabilities of NASA as well as for contributing unique science in many fields that can be enabled by access to the spaceflight environment. Since the 2011 publication of the decadal survey, NASA has seen tremendous change, including the retirement of the Space Shuttle Program and the maturation of the ISS. NASA formation of the Division of Space Life and Physical Sciences Research and Applications provided renewed focus on the research of the decadal survey. NASA has modestly regrown some of the budget of space life and physical sciences within the agency and engaged the U.S. science community outside NASA to join in this research. In addition, NASA has collaborated with the international space science community. This midterm assessment reviews NASA's progress since the 2011 decadal survey in order to evaluate the high-priority research identified in the decadal survey in light of future human Mars exploration. It makes recommendations on science priorities, specifically those priorities that best enable deep space exploration. ER - TY - BOOK A2 - Mark Wolverton TI - The Depths of Space: The Story of the Pioneer Planetary Probes DO - 10.17226/10739 PY - 2004 UR - https://nap.nationalacademies.org/catalog/10739/the-depths-of-space-the-story-of-the-pioneer-planetary PB - The National Academies Press CY - Washington, DC LA - English KW - Explore Science KW - Space and Aeronautics AB - The first spacecraft to explore the secrets of the Sun, Jupiter, Saturn, and the void beyond Pluto, the Pioneer space probes have been the trailblazers of the space age, truly going where no man has gone before. Emblazoned with the nude figures of a man and a woman, etched representations of our human form, the Pioneer generation of probes were aptly named. Launched into the inky depths of space, they were more than mere machines, they were humanity's first emissaries into deep space. And the pictorial inscriptions that adorned the crafts embodied the hopes and dreams of everyone involved in the Pioneer program. They were our humble attempt to communicate with the extraterrestrial intelligent life we imagined the probes might encounter -- they were our message in a bottle. Perhaps the most efficient, reliable, and cost effective program to come out of NASA, the Pioneer missions are a shining example of how a small and talented group of people can, against all odds, pull something off that has never been done before. Indeed, more than thirty years after its launch in 1972, Pioneer 10 is still cruising into interstellar space, sending back data as it courses through the galaxy while Pioneer 6, in solar orbit, is more than 35 years old and humankind's oldest functioning spacecraft. But despite their enduring contributions, the Pioneer project remains a footnote in space history, little more than a humble prologue to its inheritors. The Depths of Space recounts the long overdue history of Pioneer both as a scientific and technological achievement and as the story of the exceptional people who made the program possible. This tight narrative captures the black-coffee buzz of full-throttle, deadline-driven production, the sharp, intense thrill of discovery, the pang of anxiety that accompanies looming danger and ultimate loss, and the satisfaction and pride of creating an enduring legacy. ER - TY - BOOK AU - Institute of Medicine A2 - John R. Ball A2 - Charles H. Evans, Jr. TI - Safe Passage: Astronaut Care for Exploration Missions SN - DO - 10.17226/10218 PY - 2001 UR - https://nap.nationalacademies.org/catalog/10218/safe-passage-astronaut-care-for-exploration-missions PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - Safe Passage: Astronaut Care for Exploration Missions sets forth a vision for space medicine as it applies to deep space voyage. As space missions increase in duration from months to years and extend well beyond Earth's orbit, so will the attendant risks of working in these extreme and isolated environmental conditions. Hazards to astronaut health range from greater radiation exposure and loss of bone and muscle density to intensified psychological stress from living with others in a confined space. Going beyond the body of biomedical research, the report examines existing space medicine clinical and behavioral research and health care data and the policies attendant to them. It describes why not enough is known today about the dangers of prolonged travel to enable humans to venture into deep space in a safe and sane manner. The report makes a number of recommendations concerning NASA's structure for clinical and behavioral research, on the need for a comprehensive astronaut health care system and on an approach to communicating health and safety risks to astronauts, their families, and the public. ER - TY - BOOK TI - On Continued Operation of the BEVALAC Facility: Letter Report DO - 10.17226/12315 PY - 1992 UR - https://nap.nationalacademies.org/catalog/12315/on-continued-operation-of-the-bevalac-facility-letter-report PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics ER - TY - BOOK AU - National Research Council TI - Lessons Learned from the Clementine Mission DO - 10.17226/5815 PY - 1997 UR - https://nap.nationalacademies.org/catalog/5815/lessons-learned-from-the-clementine-mission PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics ER - TY - BOOK AU - National Research Council TI - Grading NASA's Solar System Exploration Program: A Midterm Report SN - DO - 10.17226/12070 PY - 2008 UR - https://nap.nationalacademies.org/catalog/12070/grading-nasas-solar-system-exploration-program-a-midterm-report PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - The NASA Authorization Act of 2005 directed the agency to ask the NRC to assess the performance of each division in the NASA Science directorate at five-year intervals. In this connection, NASA requested the NRC to review the progress the Planetary Exploration Division has made in implementing recommendations from previous, relevant NRC studies. This book provides an assessment of NASA's progress in fulfilling those recommendations including an evaluation how well it is doing and of current trends. The book covers key science questions, flight missions, Mars exploration, research and analysis, and enabling technologies. Recommendations are provided for those areas in particular need of improvement. ER - TY - BOOK AU - National Research Council TI - Exploration of Near Earth Objects SN - DO - 10.17226/6106 PY - 1998 UR - https://nap.nationalacademies.org/catalog/6106/exploration-of-near-earth-objects PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - Comets and asteroids are in some sense the fossils of the solar system. They have avoided most of the drastic physical processing that shaped the planets and thus represent more closely the properties of the primordial solar nebula. What processing has taken place is itself of interest in decoding the history of our solar neighborhood. Near-Earth objects are also of interest because one or more large ones have been blamed for the rare but devastating events that caused mass extinctions of species on our planet, as attested by recent excitement over the impending passage of asteroid 1997 XF11.The comets and asteroids whose orbits bring them close to Earth are clearly the most accessible to detailed investigation, both from the ground and from spacecraft. When nature kindly delivers the occasional asteroid to the surface of Earth as a meteorite, we can scrutinize it closely in the laboratory; a great deal of information about primordial chemical composition and primitive processes has been gleaned from such objects.This report reviews the current state of research on near-Earth objects and considers future directions. Attention is paid to the important interplay between ground-based investigations and spaceborne observation or sample collection and return. This is particularly timely since one U.S. spacecraft is already on its way to rendezvous with a near-Earth object, and two others plus a Japanese mission are being readied for launch. In addition to scientific issues, the report considers technologies that would enable further advances in capability and points out the possibilities for including near-Earth objects in any future expansion of human exploration beyond low Earth orbit. ER - TY - BOOK AU - National Academies of Sciences, Engineering, and Medicine TI - Space Studies Board Annual Report 2017 DO - 10.17226/25146 PY - 2018 UR - https://nap.nationalacademies.org/catalog/25146/space-studies-board-annual-report-2017 PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - The original charter of the Space Science Board was established in June 1958, three months before the National Aeronautics and Space Administration (NASA) opened its doors. The Space Science Board and its successor, the Space Studies Board (SSB), have provided expert external and independent scientific and programmatic advice to NASA on a continuous basis from NASA's inception until the present. The SSB has also provided such advice to other executive branch agencies, including the National Oceanic and Atmospheric Administration (NOAA), the National Science Foundation (NSF), the U.S. Geological Survey (USGS), the Department of Defense, as well as to Congress. Space Studies Board Annual Report 2017 covers a message from the chair of the SSB, David N. Spergel. This report also explains the origins of the Space Science Board, how the Space Studies Board functions today, the SSB's collaboration with other National Academies of Sciences, Engineering, and Medicine units, assures the quality of the SSB reports, acknowledges the audience and sponsors, and expresses the necessity to enhance the outreach and improve dissemination of SSB reports. This report will be relevant to a full range of government audiences in civilian space research - including NASA, NSF, NOAA, USGS, and the Department of Energy, as well members of the SSB, policy makers, and researchers. ER - TY - BOOK AU - National Academies of Sciences, Engineering, and Medicine TI - Achieving Science with CubeSats: Thinking Inside the Box SN - DO - 10.17226/23503 PY - 2016 UR - https://nap.nationalacademies.org/catalog/23503/achieving-science-with-cubesats-thinking-inside-the-box PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - Space-based observations have transformed our understanding of Earth, its environment, the solar system and the universe at large. During past decades, driven by increasingly advanced science questions, space observatories have become more sophisticated and more complex, with costs often growing to billions of dollars. Although these kinds of ever-more-sophisticated missions will continue into the future, small satellites, ranging in mass between 500 kg to 0.1 kg, are gaining momentum as an additional means to address targeted science questions in a rapid, and possibly more affordable, manner. Within the category of small satellites, CubeSats have emerged as a space-platform defined in terms of (10 cm x 10 cm x 10 cm)- sized cubic units of approximately 1.3 kg each called "U's." Historically, CubeSats were developed as training projects to expose students to the challenges of real-world engineering practices and system design. Yet, their use has rapidly spread within academia, industry, and government agencies both nationally and internationally. In particular, CubeSats have caught the attention of parts of the U.S. space science community, which sees this platform, despite its inherent constraints, as a way to affordably access space and perform unique measurements of scientific value. The first science results from such CubeSats have only recently become available; however, questions remain regarding the scientific potential and technological promise of CubeSats in the future. Achieving Science with CubeSats reviews the current state of the scientific potential and technological promise of CubeSats. This report focuses on the platform's promise to obtain high- priority science data, as defined in recent decadal surveys in astronomy and astrophysics, Earth science and applications from space, planetary science, and solar and space physics (heliophysics); the science priorities identified in the 2014 NASA Science Plan; and the potential for CubeSats to advance biology and microgravity research. It provides a list of sample science goals for CubeSats, many of which address targeted science, often in coordination with other spacecraft, or use "sacrificial," or high-risk, orbits that lead to the demise of the satellite after critical data have been collected. Other goals relate to the use of CubeSats as constellations or swarms deploying tens to hundreds of CubeSats that function as one distributed array of measurements. ER - TY - BOOK AU - National Research Council TI - Radiation Hazards to Crews of Interplanetary Missions: Biological Issues and Research Strategies SN - DO - 10.17226/5540 PY - 1996 UR - https://nap.nationalacademies.org/catalog/5540/radiation-hazards-to-crews-of-interplanetary-missions-biological-issues-and PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics KW - Environment and Environmental Studies AB - NASA's long-range plans include possible human exploratory missions to the moon and Mars within the next quarter century. Such missions beyond low Earth orbit will expose crews to transient radiation from solar particle events as well as continuous high-energy galactic cosmic rays ranging from energetic protons with low mean linear energy transfer (LET) to nuclei with high atomic numbers, high energies, and high LET. Because the radiation levels in space are high and the missions long, adequate shielding is needed to minimize the deleterious health effects of exposure to radiation. The knowledge base needed to design shielding involves two sets of factors, each with quantitative uncertainty—the radiation spectra and doses present behind different types of shielding, and the effects of the doses on relevant biological systems. It is only prudent to design shielding that will protect the crew of spacecraft exposed to predicted high, but uncertain, levels of radiation and biological effects. Because of the uncertainties regarding the degree and type of radiation protection needed, a requirement for shielding to protect against large deleterious, but uncertain, biological effects may be imposed, which in turn could result in an unacceptable cost to a mission. It therefore is of interest to reduce these uncertainties in biological effects and shielding requirements for reasons of mission feasibility, safety, and cost. ER - TY - BOOK AU - National Research Council TI - Review of the Space Communications Program of NASA's Space Operations Mission Directorate SN - DO - 10.17226/11718 PY - 2007 UR - https://nap.nationalacademies.org/catalog/11718/review-of-the-space-communications-program-of-nasas-space-operations-mission-directorate PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - The Space Communications Office (SCO) at NASA has two primary roles. The first is to manage two of the communications networks that enable spaceflight operations and research, and the second is to integrate agency-wide telecommunications issues. In 2005, NASA asked the NRC to review the effectiveness of the SCO in carrying out its responsibilities by assessing the overall quality of the space communications program. This report presents a review of each of the program elements within the SCO—the space network, NASA’s integrated space network (NISN), spectrum management, standards management, search and rescue, communications and navigation architecture, technology, and operations integration. The review focuses on formulation of plans for each element, plan development methodology, connections with the broader community, and overall capabilities. Recommendations for improving SCO operations and organization are provided. ER - TY - BOOK AU - National Research Council TI - Launching Science: Science Opportunities Provided by NASA's Constellation System SN - DO - 10.17226/12554 PY - 2009 UR - https://nap.nationalacademies.org/catalog/12554/launching-science-science-opportunities-provided-by-nasas-constellation-system PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - In January 2004 NASA was given a new policy direction known as the Vision for Space Exploration. That plan, now renamed the United States Space Exploration Policy, called for sending human and robotic missions to the Moon, Mars, and beyond. In 2005 NASA outlined how to conduct the first steps in implementing this policy and began the development of a new human-carrying spacecraft known as Orion, the lunar lander known as Altair, and the launch vehicles Ares I and Ares V. Collectively, these are called the Constellation System. In November 2007 NASA asked the National Research Council (NRC) to evaluate the potential for new science opportunities enabled by the Constellation System of rockets and spacecraft. The NRC committee evaluated a total of 17 mission concepts for future space science missions. Of those, the committee determined that 12 would benefit from the Constellation System and five would not. This book presents the committee's findings and recommendations, including cost estimates, a review of the technical feasibility of each mission, and identification of the missions most deserving of future study. ER - TY - BOOK AU - National Academies of Sciences, Engineering, and Medicine A2 - Robert Pool TI - Report Series: Committee on Biological and Physical Sciences in Space: Using Commercial Lunar Payload Services (CLPS) to Achieve Lunar Biological and Physical Science Objectives: Proceedings of a Workshop SN - DO - 10.17226/26378 PY - 2021 UR - https://nap.nationalacademies.org/catalog/26378/report-series-committee-on-biological-and-physical-sciences-in-space-using-commercial-lunar-payload-services-clps-to-achieve-lunar-biological-and-physical-science-objectives PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - After several decades since the last human visit, NASA is planning to return to the Moon, this time not only to visit but also to carry out extensive scientific experiments, establish a habitat occupied by astronauts, and learn lessons that will help in preparations for the eventual establishment of a human presence on Mars. The Commercial Lunar Payload Services (CLPS) program, overseen by NASA, will provide transport to the Moon for scientists who want to carry out research on the lunar surface or in orbit around the Moon. Recognizing the need to introduce and explain the CLPS program to researchers, the Committee on Biological and Physical Sciences in Space of the National Academies of Sciences, Engineering, and Medicine held a workshop on March 24-25, 2021 entitled "Using Commercial Lunar Payload Services (CLPS) to Achieve Lunar Biological and Physical Science Objectives". The organization of the workshop was guided by the following question: Looking at the period of time prior to the release of the next decadal survey, how can this community support and utilize CLPS to address areas of research? This workshop proceedings summarizes the presentations and discussions from the workshop sessions. ER - TY - BOOK AU - National Research Council TI - Science Opportunities Enabled by NASA's Constellation System: Interim Report SN - DO - 10.17226/12201 PY - 2008 UR - https://nap.nationalacademies.org/catalog/12201/science-opportunities-enabled-by-nasas-constellation-system-interim-report PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - To begin implementation of the Vision for Space Exploration (recently renamed "United States Space Exploration Policy"), NASA has begun development of new launch vehicles and a human-carrying spacecraft that are collectively called the Constellation System. In November 2007, NASA asked the NRC to evaluate the potential for the Constellation System to enable new space science opportunities. For this interim report, 11 existing "Vision Mission" studies of advanced space science mission concepts inspired by earlier NASA forward-looking studies were evaluated. The focus was to assess the concepts and group them into two categories: more-deserving or less deserving of future study. This report presents a description of the Constellation System and its opportunities for enabling new space science opportunities, and a systematic analysis of the 11 Vision Mission studies. For the final report, the NRC issued a request for information to the relevant communities to obtain ideas for other mission concepts that will be assessed by the study committee, and several issues addressed only briefly in the interim report will be explored more fully. ER - TY - BOOK AU - National Academies of Sciences, Engineering, and Medicine TI - Thriving in Space: Ensuring the Future of Biological and Physical Sciences Research: A Decadal Survey for 2023-2032 SN - DO - 10.17226/26750 PY - 2023 UR - https://nap.nationalacademies.org/catalog/26750/thriving-in-space-ensuring-the-future-of-biological-and-physical PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - Research in biological and physical sciences in space provides the critical scientific and technological foundations that make space exploration possible. As humanity looks towards the Moon and Mars for future missions, this work is needed to help astronauts adapt and live in the harsh environments of space. Thriving in Space provides a roadmap for increasing national investment in biological and physical science research, from experiments to infrastructure to education. This report identifies key scientific questions, priorities, and ambitious research campaigns that will enable human space exploration and transform our understanding of how the universe works. Thriving in Space reviews the state of knowledge in the current and emerging areas of space-related biological and physical sciences research and generates recommendations for a comprehensive vision and strategy for a decade of transformative science at the frontiers of biological and physical sciences research in space. This report will help NASA define and align biological and physical sciences research to uniquely advance scientific knowledge, meet human and robotic exploration mission needs, and provide terrestrial benefits. ER - TY - BOOK AU - National Research Council TI - Pathways to Exploration: Rationales and Approaches for a U.S. Program of Human Space Exploration SN - DO - 10.17226/18801 PY - 2014 UR - https://nap.nationalacademies.org/catalog/18801/pathways-to-exploration-rationales-and-approaches-for-a-us-program PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - The United States has publicly funded its human spaceflight program on a continuous basis for more than a half-century, through three wars and a half-dozen recessions, from the early Mercury and Gemini suborbital and Earth orbital missions, to the lunar landings, and thence to the first reusable winged crewed spaceplane that the United States operated for three decades. Today the United States is the major partner in a massive orbital facility - the International Space Station - that is becoming the focal point for the first tentative steps in commercial cargo and crewed orbital space flights. And yet, the long-term future of human spaceflight beyond this project is unclear. Pronouncements by multiple presidents of bold new ventures by Americans to the Moon, to Mars, and to an asteroid in its native orbit, have not been matched by the same commitment that accompanied President Kennedy's now fabled 1961 speech-namely, the substantial increase in NASA funding needed to make it happen. Are we still committed to advancing human spaceflight? What should a long-term goal be, and what does the United States need to do to achieve it? Pathways to Exploration explores the case for advancing this endeavor, drawing on the history of rationales for human spaceflight, examining the attitudes of stakeholders and the public, and carefully assessing the technical and fiscal realities. This report recommends maintaining the long-term focus on Mars as the horizon goal for human space exploration. With this goal in mind, the report considers funding levels necessary to maintain a robust tempo of execution, current research and exploration projects and the time/resources needed to continue them, and international cooperation that could contribute to the achievement of spaceflight to Mars. According to Pathways to Exploration, a successful U.S. program would require sustained national commitment and a budget that increases by more than the rate of inflation. In reviving a U.S. human exploration program capable of answering the enduring questions about humanity's destiny beyond our tiny blue planet, the nation will need to grapple with the attitudinal and fiscal realities of the nation today while staying true to a small but crucial set of fundamental principles for the conduct of exploration of the endless frontier. The recommendations of Pathways to Exploration provide a clear map toward a human spaceflight program that inspires students and citizens by furthering human exploration and discovery, while taking into account the long-term commitment necessary to achieve this goal. ER - TY - BOOK AU - National Research Council TI - Radioisotope Power Systems: An Imperative for Maintaining U.S. Leadership in Space Exploration SN - DO - 10.17226/12653 PY - 2009 UR - https://nap.nationalacademies.org/catalog/12653/radioisotope-power-systems-an-imperative-for-maintaining-us-leadership-in PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - Spacecraft require electrical energy. This energy must be available in the outer reaches of the solar system where sunlight is very faint. It must be available through lunar nights that last for 14 days, through long periods of dark and cold at the higher latitudes on Mars, and in high-radiation fields such as those around Jupiter. Radioisotope power systems (RPSs) are the only available power source that can operate unconstrained in these environments for the long periods of time needed to accomplish many missions, and plutonium-238 (238Pu) is the only practical isotope for fueling them. Plutonium-238 does not occur in nature. The committee does not believe that there is any additional 238Pu (or any operational 238Pu production facilities) available anywhere in the world.The total amount of 238Pu available for NASA is fixed, and essentially all of it is already dedicated to support several pending missions--the Mars Science Laboratory, Discovery 12, the Outer Planets Flagship 1 (OPF 1), and (perhaps) a small number of additional missions with a very small demand for 238Pu. If the status quo persists, the United States will not be able to provide RPSs for any subsequent missions. ER - TY - BOOK TI - The Role of Small Missions in Planetary and Lunar Exploration DO - 10.17226/12285 PY - 1995 UR - https://nap.nationalacademies.org/catalog/12285/the-role-of-small-missions-in-planetary-and-lunar-exploration PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics ER - TY - BOOK AU - National Academies of Sciences, Engineering, and Medicine TI - America's Future in Civil Space: Proceedings of a Workshop–in Brief DO - 10.17226/24921 PY - 2017 UR - https://nap.nationalacademies.org/catalog/24921/americas-future-in-civil-space-proceedings-of-a-workshop-in PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - Since the National Research Council released the report America’s Future in Space: Aligning the Civil Space Program with National Needs in 2009, numerous changes have occurred in the civil space arena. In May 2017, the National Academies of Sciences, Engineering, and Medicine convened a workshop on America’s Future in Civil Space with several objectives, including reviewing the history of U.S. space policy and how it might form a broad policy basis for twenty-first century leadership in space, examining the balance and interfaces between fundamental scientific research in space, human space exploration, robotic exploration, earth observations, and applications of space technology and civil space systems for societal benefits, and discussing the value, purpose, and goals of international cooperation in space. The workshop participants sought to capture what has changed, determine how to harness new opportunities, and decisively inform and encourage bold and timely implementation. This publication briefly summarizes the presentations and discussions from the workshop. ER - TY - BOOK AU - National Research Council TI - Thermionics Quo Vadis?: An Assessment of the DTRA's Advanced Thermionics Research and Development Program SN - DO - 10.17226/10254 PY - 2001 UR - https://nap.nationalacademies.org/catalog/10254/thermionics-quo-vadis-an-assessment-of-the-dtras-advanced-thermionics PB - The National Academies Press CY - Washington, DC LA - English KW - Space and Aeronautics AB - This report evaluates the Defense Threat Reduction Agency prior and present sponsored efforts; assess the present state of the art in thermionic energy conversion systems; assess the technical challenges to the development of viable thermionic energy conversion systems for both space and terrestrial applications; and recommend a prioritized set of objectives for a future research and development program for advanced thermionic systems for space and terrestrial applications. ER -