NASA's Voyager Probes Maintained by 1960s Technology for Almost Half a Century
Powering Deep-Space Missions with Nuclear Batteries:
Navigating the treacherous territory of outer space may seem like an uphill battle, given the intense solar flares, radiation, and frigid temperatures that spacecraft must endure. But fear not, as ingenious solutions have been devised to keep those far-flung missions humming along. One such innovation is the Radioisotope Thermoelectric Generator (RTG), a nuclear-powered battery that can provide power for decades, all while being hundreds of millions of miles from our humble abode, Earth.
These generators have been the driving force behind some of the most remarkable deep-space missions, such as the Mars Curiosity and Perseverance rovers, and the New Horizons spacecraft that paid a visit to Pluto in 2015. They've even propelled the Voyager missions, launched in 1977, on a grand tour of our solar system's outer bounds and beyond.
So, what exactly are RTGs, and how do they work their magic? Let's delve a bit deeper into this fascinating technology.
The Science Behind RTGs
RTGs rely on the radioactive decay of elements to generate heat, because, you know, science is cool like that. While this concept may sound reminiscent of nuclear power plants, RTGs run on a different principle. Most RTGs are built using plutonium-238 (Pu-238) as the energy source of choice.
When an unstable atomic nucleus, like Pu-238, spontaneously and randomly emits particles and energy to reach a more stable configuration, it results in radioactive decay. This process often causes the element to change into another element, since the nucleus can lose protons or neutrons. In the case of Pu-238, it emits alpha particles, which consist of two protons and two neutrons. The release of an alpha particle transforms Pu-238 into uranium-234, shedding two protons in the process.
The heat generated by this radioactive decay allows RTGs to create electricity through the Seebeck effect, a principle discovered by Thomas Seebeck in 1821. This effect describes how two wires of different conducting materials joined in a loop produce a current in that loop when exposed to a temperature difference. The heat from the decaying Pu-238 creates such a temperature difference, allowing the RTG to generate electricity.
Designing an RTG
At the heart of an RTG lies a container filled with Pu-238 and wrapped in a protective layer of foil insulation. Surrounding the container is a large array of thermocouples, attached to the insulation. The thermocouples have been designed to create a substantial temperature difference by exposing one side to the blistering heat generated by the Pu-238 decay and the other side to the icy chill of deep space. Thanks to this temperature gradient, the electricity generated by the thermocouples is sufficient to power spacecraft, from communications systems to science instruments, including the five current NASA missions.
But, before imagination starts running wild aboutDIY RTGs for household use, let's remember that these devices can only generate a few hundred watts of power - appealing, perhaps, for powering a standard laptop, but hardly enough to satisfy your gaming needs with a powerful GPU.
For deep-space explorations, however, those couple hundred watts of power prove more than adequate. One of the major benefits of RTGs is their ability to provide predictable and consistent power, thanks to the constant radioactive decay of Pu-238. About 90 years pass before half the Pu-238 in an RTG has decayed away, ensuring steady energy production. Additionally, RTGs have an exemplary safety record, featuring built-in safeguards to securely contain radioactive material in normal use and during potential accidents.
The Legend of Voyager
Voyager 1 and Voyager 2, launched in 1977, have been the crown jewels of RTGs' success, traveling to the outer reaches of our solar system and venturing beyond. Each craft is equipped with three RTGs, which initially produced 470 watts of power at launch. As we approach 50 years since their launch, both Voyagers are still active science missions, sending back valuable data to Earth about the far reaches of our cosmic backyard. Surprisingly, even at their present extreme distances of nearly 25 billion kilometers and 21 billion kilometers (for Voyager 1 and 2, respectively), those humble RTGs continue to provide power. These spacecraft serve as testaments to the brilliant minds who conceived the RTGs, ushering in a new era of deep-space exploration and enduring our fascination with the mysteries of the cosmos.
Benjamin Roulston, Assistant Professor of Physics, Clarkson University. This article is republished from The Conversation under a Creative Commons license. Read the original article at The Conversation*.
- The future of deep-space missions may emphasize the use of Radioisotope Thermoelectric Generators (RTGs), a technology that harnesses the heat from the radioactive decay of elements such as plutonium-238 to generate power.
- Despite their small output of a few hundred watts, RTGs are crucial for deep-space exploration because they can provide predictable and consistent power for decades, thanks to the constant radioactive decay of plutonium-238.
- Engineering advancements in solar technology and other alternative power sources may one day subsidiary the use of RTGs, but for now, these generators have been designily to work efficiently in the extreme conditions of deep space.
- The use of RTGs has been instrumental in powering some of the most notable deep-space missions, such as the Mars Curiosity and Perseverance rovers, the New Horizons spacecraft, and the Voyager missions, which continue to provide valuable data from their positions far beyond our solar system.
