Perseverance on Mars powered by a radioisotope thermoelectric generator (RTG)

Perseverance is powered by a radioisotope thermoelectric generator (RTG) that will last 14 years and will continuously provide energy for the rover and the various sophisticated instrumentation it will use to explore Mars. Perseverance carries a radioisotope power system. This power system produces a dependable flow of electricity using the heat of plutonium's radioactive decay as its "fuel." The power source is called a "Multi-Mission Radioisotope Thermoelectric Generator" or MMRTG for short. The MMRTG converts heat from the natural radioactive decay of plutonium into electricity. This power system charges the rover's two primary batteries. The heat from the MMRTG is also used to keep the rover's tools and systems at their correct operating temperatures.

What is a radioisotope thermoelectric generator (RTG)

A radioisotope thermoelectric generator (RTG, RITEG) is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of suitable radioactive material into electricity by the Seebeck effect. This type of generator has no moving parts.

What is so special about RTG?

RTGs are usually the most desirable power source for unmaintained situations that need a few hundred watts (or less) of power for durations too long for fuel cells, batteries, or generators to provide economically, and in places where solar cells are not practical.

What is radioactive material?

Radioactivity is a process by which certain naturally occurring or artificial nuclides undergo spontaneous decay releasing new energy.

What is radioactive decay?

Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha decay, beta decay, and gamma decay, all of which involve emitting one or more particles or photons.

How and why a substance decay?

Every atom seeks to be as stable as possible. In the case of radioactive decay, instability occurs when there is an imbalance in the number of protons and neutrons in the atomic nucleus. Basically, there is too much energy inside the nucleus to hold all the nucleons together. The status of the electrons of an atom doesn't matter for decay, although they, too, have their own way of finding stability. If the nucleus of an atom is unstable, eventually it will break apart to lose at least some of the particles that make it unstable. Radioactive decay is an exothermic process because the process releases energy.

How the decay is measured?

Radioactive materials decay at known rates measured as a unit called the half-life. The half-life of a radioactive substance is the amount of time it takes for half of the parent atoms to decay. In the image below you can see the number of half-lives of Cobalt-60 isotope. 1 half-life = 5.27 years

Why NASA chose Plutonium as a source of fuel in Perseverance?

What is Plutonium?

Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94.

Why plutonium is radioactive?

Plutonium is the element with the highest atomic number to occur in nature. All 15 plutonium isotopes are radioactive because they are to some degree unstable and therefore decay, emitting particles, and releasing energy. It decays into uranium through alpha decay by releasing neutrons and energy.

Why NASA uses Plutonium 238 space missions?

Plutonium-238 is a special material that emits steady heat due to its natural radioactive decay. Several unique features of plutonium-238 have made it the material of choice to help produce electrical power. Plutonium-238 is the most widely synthesized isotopes with a half-life of 7000 years

What is the Seebeck effect? How it converts thermal radiation from radioactive decay to electricity?

Seebeck effect

 This is known after the name of German physicist Thomas Johann Seebeck. The Seebeck effect is a phenomenon in which a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances. When heat is applied to one of the two conductors or semiconductors, heated electrons flow toward the cooler one. The cause of this movement of electrons lies in the metallic bonding of metals and in particular in the free delocalized electrons. Delocalized electrons are electrons in a molecule, ion, or solid metal that are not associated with a single atom or a covalent bond. Delocalized means that the electrons are free to move throughout the structure, and gives rise to properties such as conductivity. If a metal wire is only heated at one end, the lattice oscillations and the movements of the free electrons increase there. Because of the heavy collisions, they begin to spread and diffuse to the cold end. There, the kinetic energies of the electrons are lower and the electrons are not repelled again by heavy collisions. The hot end of the wire thus has a smaller number of electrons than the cold end. As a result, an electrical voltage is obtained between the two ends, also known as thermoelectric voltage, and the process of conversion of temperature difference into voltage is called the thermoelectric effect.                                                                   

Credit: Google