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| Fig. 1: Image of the SNAP-27 RTG. It provides space nuclear power using radioisotope decay. [2] (Courtesy of the DOE, Source: Wikimedia Commons |
In space exploration, the quest for sustainable energy sources has been paramount. With origins tracing back to mid-20th-century initiatives led by organizations like NASA and the Atomic Energy Commission (AEC), nuclear power has emerged as a critical solution to the energy demands of space missions. [1]
Early challenges with conventional power sources, particularly in environments with limited sunlight, prompted the AEC to initiate the SNAP (Systems for Nuclear Auxiliary Power) program, aimed at developing radioisotope thermo-electric generators (RTGs) tailored for space applications. [1] (See Fig. 1.) These generators use the radioisotope Pu-238 to provide a continuous and independent power source, facilitating extended missions and supporting scientific experiments. [1]
One early application of the SNAP-27 RTG was its deployment on the Nimbus-3 Meteorological Satellite. Launched on April 14, 1969, from Vandenberg Air Force Base (VAFB), the Nimbus-3 mission marked a milestone as the first U.S. weather satellite to conduct day and night global measurements of atmospheric temperatures from space. [2] The SNAP-27 RTGs were instrumental in powering critical atmospheric-sounder experiments, ensuring continuous operation throughout the mission duration. [2]
Versatility of SNAP-27 RTGs was also demonstrated in missions such as the Lincoln Experimental Satellites 8 and 9 (LES-8/9), where they powered advanced communication technologies. The SNAP-27 RTGs exceeded expectations, showing exceptional reliability and longevity. [2]
The SNAP-27 RTG also found essential utility in NASA's Apollo Lunar Surface Experiments Packages (ALSEPs), deployed on the Moon to facilitate scientific investigations. These RTGs again provided consistent power, even during the lunar night, enabling long-term data collection on lunar composition and atmospheric characteristics. [2]
Nuclear power is a cornerstone technology in the ambitious endeavor of human exploration of Mars. As humanity embarks on sending crewed missions to Mars, nuclear power emerges as a critical enabler, offering unparalleled energy density and endurance to sustain missions in the harsh Martian environment. Furthermore, the independence of nuclear power from solar energy ensures operational flexibility, mitigating risks associated with solar panel degradation and variability in sunlight intensity during the lengthy voyage to Mars. [1]
The power requirements and capabilities of nuclear power sources crucial for space missions, particularly those directed towards Mars exploration, are described by Bennett. [2] For instance, the modified SNAP-19 RTGs employed to energize the Viking Landers 1 and 2 boasted an average Beginning of Mission (BOM) power output of approximately 42.7 We per RTG, while being tasked with meeting a minimum requirement of 35 We per RTG during the 90-day primary mission. Furthermore, the Multi-Hundred Watt Radioisotope Thermoelectric Generators (MHW-RTGs) utilized by the Voyager 1 and Voyager 2 spacecraft exhibited an average BOM power output of about 158 We per RTG.
Other nuclear power sources, such as the General-Purpose Heat Source Radioisotope Thermoelectric Generators (GPHS-RTGs) utilized in missions like Galileo and Ulysses, provide insights into the potential for higher specific power nuclear sources to meet the demanding power needs of extended-duration space missions, including those to Mars.
Nuclear power also stands as central to maintaining space station functionalities, thanks to its steady dependability and autonomy from external factors such as sunlight. [3] The IAEA even posits that nuclear power's remarkable energy density could pave the way for the construction of larger and more advanced space stations, accommodating prolonged missions and enabling cutting-edge scientific investigations. [3]
In summary, nuclear energy is presently playing a central in humanity's endeavors to explore beyond Earth's atmosphere. It seems destined to continue doing so.
© Beck Jurasius. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Nuclear Power on the Moon," IAEA Bull. 12, No. 1, 9 (1970).
[2] G. L. Bennett, "Space Nuclear Power: Opening the Final Frontier," American Institute of Aeronautics and Astronautics, AIAA 2006-4191, June 2006.
[3] D. Valiente, "Nuclear Energy Preferred in Space Travel," Physics 241, Stanford University, Winter 2015.
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