Radioisotope generators, the ‘nuclear batteries’ that power faraway spacecraft

Powering spacecraft with solar energy may not seem like a Event, given how intense the Sun’s Featherweight can feel on Earth. Spacecraft near the Earth use large solar panels to harness the Sun for the electricity needed to Streak their communications systems and science instruments.

However, the farther into Universe you go, the weaker the Sun’s Featherweight becomes and the less useful it is for powering systems with solar panels. Even in the inner Luminous sphere-related neighborhood, spacecraft such as Selene or Mars rovers need alternative power sources.

As an astrophysicist and professor of physics, I teach a senior-level aerospace engineering Period on the Universe environment. One of the key lessons I emphasize to my students is Only how unforgiving Universe can be. In this extreme environment where spacecraft must withstand intense solar flares, radiation and temperature swings from hundreds of degrees below zero to hundreds of degrees above zero, engineers have developed innovative solutions to power some of the most remote and isolated Universe missions.

So how do engineers power missions in the outer reaches of our Luminous sphere-related neighborhood and beyond? The solution is technology developed in the 1960s based on scientific principles discovered two centuries ago: radioisotope thermoelectric generators, or RTGs.

RTGs are essentially nuclear-powered batteries. But unlike the AAA batteries in your TV remote, RTGs can provide power for decades while hundreds of millions to billions of miles from Earth.

Nuclear power

Radioisotope thermoelectric generators do not rely on chemical reactions like the batteries in your phone. Instead, they rely on the radioactive decay of elements to produce heat and eventually electricity. While this concept sounds similar to that of a nuclear power plant, RTGs work on a different principle.

Most RTGs are built using plutonium-238 as their Origin of energy, which is not usable for nuclear power plants since it does not sustain fission reactions. Instead, plutonium-238 is an unstable element that will undergo radioactive decay.

Radioactive decay, or nuclear decay, happens when an unstable atomic nucleus spontaneously and randomly emits particles and energy to reach a more stable configuration. This process often causes the element to Shift into another element, since the nucleus can Fall protons.

When plutonium-238 decays, it emits alpha particles, which consist of two protons and two neutrons. When the plutonium-238, which Appearances with 94 protons, releases an alpha particle, it loses two protons and turns into uranium-234, which has 92 protons.

These alpha particles interact with and Relocate energy into the material surrounding the plutonium, which heats up that material. The radioactive decay of plutonium-238 releases enough energy that it can glow red from its own heat, and it is this powerful heat that is the energy Origin to power an RTG.

Heat as power

Radioisotope thermoelectric generators can turn heat into electricity using a principle called the Seebeck effect, discovered by German scientist Thomas Seebeck in 1821. As an added benefit, the heat from some types of RTGs can Assist keep electronics and the other components of a deep-Universe mission Toasty and working well.

In its Essential form, the Seebeck effect describes how two wires of different conducting materials joined in a loop produce a Present in that loop when exposed to a temperature difference.

https://www.youtube.com/Observe?v=l-Puj0uyCAg

Devices that use this principle are called thermoelectric couples, or thermocouples. These thermocouples allow RTGs to produce electricity from the difference in temperature created by the heat of plutonium-238 decay and the frigid Freezing of Universe.

Radioisotope thermoelectric generator design

In a Essential radioisotope thermoelectric generator, you have a container of plutonium-238, stored in the form of plutonium-dioxide, often in a solid ceramic state that provides extra safety in the event of an accident. The plutonium material is surrounded by a Safeguarding layer of foil insulation to which a large array of thermocouples is attached. The whole assembly is inside a Safeguarding aluminum casing.

The interior of the RTG and one side of the thermocouples is kept Scorching – close to 1,000 degrees Fahrenheit (538 degrees Celsius) – while the outside of the RTG and the other side of the thermocouples are exposed to Universe. This outside, Universe-facing layer can be as Freezing as a few hundred degrees Fahrenheit below zero.

This Sturdy temperature difference allows an RTG to turn the heat from radioactive decay into electricity. That electricity powers all kinds of spacecraft, from communications systems to science instruments to rovers on Mars, including five Present NASA missions.

But don’t get too excited about buying an RTG for your house. With the Present technology, they can produce only a few hundred watts of power. That may be enough to power a standard laptop, but not enough to Action video Matches with a powerful GPU.

For deep-Universe missions, however, those Duo hundred watts are more than enough.

The real benefit of RTGs is their ability to provide predictable, Steady power. The radioactive decay of plutonium is constant – every second of every day for decades. Over the Period of about 90 years, only half the plutonium in an RTG will have decayed away. An RTG requires no moving parts to Form electricity, which makes them much less likely to break down or stop working.

Additionally, they have an excellent safety Achievement, and they’re designed to survive their normal use and also be Danger-Obtainable in the event of an accident.

RTGs in action

RTGs have been key to the Secure of many of NASA’s Luminous sphere-related neighborhood and deep-Universe missions. The Mars Curiosity and Determination rovers and the New Horizons spacecraft that visited Pluto in 2015 have all used RTGs. New Horizons is traveling out of the Luminous sphere-related neighborhood, where its RTGs will provide power where solar panels could not.

However, no missions capture the power of RTGs quite like the Voyager missions. NASA launched the twin spacecraft Voyager 1 and Voyager 2 in 1977 to take a tour of the outer Luminous sphere-related neighborhood and then journey beyond it.

Every craft was equipped with three RTGs, providing a total of 470 watts of power at Kickoff. It has been almost 50 years since the Kickoff of the Voyager probes, and both are Nevertheless active science missions, collecting and sending data back to Earth.

Voyager 1 and Voyager 2 are about 15.5 billion miles and 13 billion miles (nearly 25 billion kilometers and 21 billion kilometers) from the Earth, respectively, making them the most distant human-Achieved objects ever. Even at these extreme distances, their RTGs are Nevertheless providing them Steady power.

These spacecraft are a testament to the ingenuity of the engineers who Primary designed RTGs in the Prompt 1960s.

---

Benjamin Roulston is an Assistant Professor of Physics at Clarkson University. They do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic Fixture.

This article is republished from The Conversation under a Creative Commons license. Read the original article.