Voyager 1, shown in this illustration, has worked for decades thanks to a radioisotopian power system. Credit: NASA via ap
The feeding of space vehicles with sun energy may not seem like a challenge, given how intense the light of the sun can feel on earth. Space vehicles near the earth use large solar panels to exploit the sun for the electricity necessary to manage their communication systems and scientific tools.
However, further in the space you go, weaker than the sunlight becomes and the less useful for power supply systems with solar panels. Also in the internal sun system, space vehicles such as Lunar or Mars Rovers need alternative power sources.
As astrophysicist and physics professor, I teach a senior -level aerospace engineering course on the space environment. One of the key lessons that I emphasize my students is what space can be ruthless. In this extreme environment in which space vehicles must resist intense solar rockets, puzzle and changes in temperature from hundreds of degrees below zero to hundreds of degrees above zero, the engineers have developed innovative solutions to feed some of the most remote and isolated spatial missions.
So, how do engineers feed the missions in the external rays of our Solar System and beyond? The solution is the technology developed in the 1960s on the basis of scientific principles discovered two centuries ago: radio -resistant thermoelectric generators or RTG.
RTG are essentially nuclear propulsion batteries. But unlike AAA batteries in the TV remote control, RTGS can provide energy for decades while hundreds of millions to billion miles from the earth.
Nuclear energy
Radioisotopo thermoelectric generators are not based on chemical reactions such as batteries in the phone. Instead, they are based on the radioactive decay of the elements to produce heat and finally electricity. While this concept seems similar to that of a nuclear power plant, RTGS works on a different principle.
Most RTGs are built using the Plutonium-238 as a source of energy, which cannot be used for nuclear power plants since it does not support fission reactions. Instead, Plutonio-238 is an unstable element that will undergo a radioactive decay.
Radioactive decay, or nuclear decay, occurs when an unstable atomic nucleus spontaneously and accidentally emits particles and energy to achieve a more stable configuration. This process often causes the element to change in another element, since the nucleus can lose protons.
When the plutonium-238 decade, it emits alpha particles, which consist of two protons and two neutrons. When the plutonium-238, which begins with 94 protons, releases an alpha particle, loses two protons and turns into Uranium-234, which has 92 protons.
These Alfa particles interact and transfer the energy to the material surrounding the plutonium, which warms that material. The radioactive decay of the Plutonium-238 releases enough energy that can be shone red from your heat, and it is this powerful heat that is the source of energy to feed an RTG.
Heat
Radioisotopo thermoelectric generators can transform heat into electricity using a principle called Seeback Effect, discovered by the German scientist Thomas Seeback in 1821. As a further advantage, the heat of some types of RTG can help maintain electronics and the other components of a deep mission with warm and functioning space.
In its basic form, the Seebeck effect describes how two threads of different guidance materials have joined a cycle produce a current in that cycle when exposed to a temperature difference.
The devices that use this principle are called thermoelectric or thermocopy couples. These thermochurpies allow RTG to produce electricity from the difference in temperature created by the heat of the decay of the plutonium-238 and the cold cold of the space.
Design of the thermoelectric generator Radioisotopo
In a basic radioisotop thermoelectric generator, you have a plutonium-238 container, stored in the form of plutonium dioxide, often in a solid ceramic state that provides further safety in the event of an accident. The plutonium material is surrounded by a protective layer of lamina insulation to which a large anchor of thermocopy is attacked. The entire assembly is inside a protective aluminum envelope.
The interior of the Art and one side of the thermocopy are kept hot – close to 1,000 degrees Fahrenheit (538 degrees Celsius) – while the outside of the Art and the other side of the thermocopy are exposed to space. This external layer aimed at space can be cold like a few hundred fahrenheit degrees below zero.
This strong temperature difference allows an RTG to transform heat from radioactive decay into electricity. That electricity feeds all types of space vehicles, from communication systems to scientific tools to rover on Mars, including five current NASA missions.
But don’t be too enthusiastic about buying an RTG for your home. With the current technology, they can produce only a few hundred watts of power. It may be enough to power a standard laptop, but not enough to play video games with a powerful GPU.
For deep missions, however, those two hundred watts are more than enough.
RTG’s real advantage is their ability to provide predictable and coherent power. The radioactive decay of the plutonium is constant – every second of each day for decades. Over the course of about 90 years, only half of the plutonium in a RTG will have lapsed. An RTG does not require moving parts to generate electricity, which makes them much less likely to break or stop working.
In addition, they have an excellent security record and are designed to survive their normal use and be safe in the event of an accident.
RTGS in action
The RTGs were fundamental for the success of many of the solar systems of NASA and the missions of deep space. The curiosity of Mars and the Perseverance Rover and the New Horizons space vehicle that visited Pluto in 2015 used all the RTGs. New Horizons is traveling from the Solar System, where its RTGs will provide energy in which solar panels could not.
However, no mission captures RTG’s power like Voyager missions. NASA launched the Voyager 1 and Voyager 2 twin spatial vehicle in 1977 to take a tour of the external solar system and then travel further.
Each profession was equipped with three RTGs, providing a total of 470 watts of power at launch. Almost 50 years have passed since the launch of the Voyager probes and both are still active scientific missions, collected and sending data to Earth.
Voyager 1 and Voyager 2 are about 15.5 billion miles and 13 billion miles (almost 25 billion kilometers and 21 billion kilometers) from the earth, making them respectively the most distant objects ever. Also to these extreme distances, their RTGs are still providing them with coherent power.
These spatial vehicles are a testimony of the ingenuity of the engineers who designed RTG for the first time in the early 60s.
Benjamin Roulston is assistant professor of physics at Clarkson University. They do not work, consult, have shares or receive funding from any company or organization that would benefit from this article and have not disclosed relevant affiliations beyond their academic appointment.
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