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| Fig. 1: This is one of the three RTGs of the Cassini-Huygens right before installation. (Courtesy of NASA. Source: Wikimedia Commons) |
October 15, 1997, a space craft known as Cassini- Huygens launched from Cape Canaveral. This space ship was 22 feet by 13.1 feet and weighed 12,593 lbs. [1] NASA constructed and launched this craft with the intentions of researching Saturn and its various moons. In order to enable Cassini to orbit Saturn deep in the solar system, the space craft used nuclear energy to power it electrochemically. This method of using Radioisotope Thermoelectric Generators (RTGs) as its electrical power source enabled Cassini to travel over 2 billion miles to Saturn and orbit the planet while providing powerful new insights about Saturn's rings and moons. [2] The unmanned mission was extended twice and Cassini orbited Saturn and its moons for 13 years after arriving in 2002. Recently, NASA intentionally terminated the prolonged mission by crashing Cassini into Saturn in order to preserve its moons pristinely for future studies. [1]
As aforementioned, deep space travel is made possible by nuclear energy. Following suit from Apollo and Viking Lunar landings, Cassini was also powered by RTGs (see Fig. 1). RTGs are power systems that utilize the energy from the radio nucleotide plutonium. Plutonium is used because its lengthy half-life generates heat to sustain long trips into deep space. The energy generated by the decay of plutonium is converted into electric energy by thermoelectric converters. [2] Cassini- Huygens utilized three RTGs to power the mission to and around Saturn. The space craft had to use 3 RTGs because of RTGs inherent lack of efficiency in that each one can generally only convert 7% of the available energy into electricity. [3] To the right is a picture of one of the three of Cassini's RTGs right before instillation. The enormous amount of energy needed to both power the space craft and allow for communication and images to be sent back to the base at NASA is made possible primarily because of nuclear energy utilized by RTGs like the one shown.
Another energy alternative invented by the European Space Agency is the utilization of solar arrays to power space crafts. [2] Although this alternative fuel source allows for longer travel than a lot of batteries, Cassini would have needed so many solar panels to power its long trip to Saturn and orbit around Saturn that it would have been far too heavy to launch. [4] In addition to making this mission possible, the RTGs proved very reliable in this and other missions that similarly used RTGs.
NASA took into account a number of different factors to ensure the safety of the Cassini- Huygen mission. One such factor is the insurance that the Cassini did not crash nor come close to crashing back into the surface of the earth. RTGs have never caused a malfunction on previous or current missions, though space crafts with RTGs have had safety malfunctions due to other factors. [2] Therefore, NASA went through many testings of Cassini before launch. In fact, 30 years of prior testing revealed that RTGs can withstand extreme conditions. Nonetheless, scientists distributed the fuel in the Cassini-Huygen into 18 separate modules each with a built in heat shield. [2]
Another factor that was of concern before the launch in 1997 was the radiation released if the Cassini did somehow get off track and crash into the earth's surface. Scientists calculated that over 50 years the average person is subjected to 15,000 millirem of background radiation. If in the unlikely event, the Cassini had crashed into the earth, it would have spread very thinly by the time it reached the earth. Most of it would have ended up in the oceans and soils and would have been trapped due to plutoneum's insolubility. Thus, on average, a person near the site of the crash would be expected breath in an excess of less than one millirem of radiation over the next 50 years. [2] This increase in radiation is very small in comparison to the background radiation an average person experiences. Nonetheless, when the Cassini rocket began to run low on fuel in 2017, NASA decided to end its mission by crashing it into Saturn to avoid losing control of the space craft.
Nuclear energy allowed NASA to launch the Cassini-Huygen space exploration for a deep exploration that revealed never before seen footage of Saturn and its moons. The Huygen probe that launched with the intention of studying Saturn's moon, Titan, revealed a possible environment for life. NASA now has thousands of pictures of Saturn and its rings and moon as well as data about Saturn'wis weather patterns and cycles thanks to the use of radioactive isotope thermoelectric generators. With this application of nuclear energy, scientists were able to make groundbreaking discoveries while extending this mission and collecting 13 years worth of data.
© Kaitlyn Merritt. 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] "The Saturn System Through the Eyes of Cassini," U.S. National Aeronautics and Space Administration, July 2017.
[2] "Spacecraft Power for Cassini," U.S. National Aeronautics and Space Administration, July 1999.
[3] S. Copeland "The Role of Nuclear Energy in the Future of Human Spaceflight," Physics 241, Stanford University, Winter 2012.
[4] D. Valiente "Nuclear Energy Preferred in Space Travel," Physics 241, Stanford University, Winter 2015.
