Let’s examine what power the rover requires to move, use its science instruments, and communicate with Earth.

The Mars Science Laboratory rover carries a radioisotope power system that generates electricity from the heat of plutonium's radioactive decay. This power source gives the mission an operating lifespan on Mars' surface of at least a full Martian year (687 Earth days) or more while also providing significantly greater mobility and operational flexibility, enhanced science payload capability, and exploration of a much larger range of latitudes and altitudes than was possible on previous missions to Mars.

A radioisotope thermoelectric generator (RTG) is a nuclear battery which basically converts heat into energy.

The particular one used in the Rover is a special case of RTG developed by NASA and the DOE and is called a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG). This generator is capable of operating on planets such as Mars which has an atmosphere, but can also operate in the vacuum of space.

It is a modular design which generates electrical power in small increments, just above 100 watts. The MMRTG is designed for a high degree of safety and a minimum of weight.

NASA programs are no strangers to RTG’s. The Apollo missions to the moon, Viking to Mars, and the Pioneer, Voyager, Ulysses, Galileo, Cassini and Pluto New Horizons (to the outer solar system!) all used RTGs.

The RTGs on Pioneer 10 operated for three decades until the spacecraft signal was too weak to detect in 2003. The Voyager 1 and 2 missions were launched in 1977 and are now on the verge of interstellar space and still operating.

Let’s look at how RTG’s work. (Courtesy of DOE)

Essentially, RTGs convert heat into energy and here is how they do it. There are two major elements: a heat source containing plutonium-238 dioxide and a set of solid-state thermocouples that convert the plutonium’s heat into electricity—the Seebeck effect. An electric voltage is produced when two dissimilar, electrically conductive materials are joined in a closed circuit and the two junctions are kept at different temperatures. These pairs of junctions are known as thermoelectric couples or thermocouples.

The power is a function of the temperature of each junction and the properties of the thermoelectric materials. The heat from the natural radioactive decay of plutonium-238 is applied to the “hot” thermocouple junction and the other “cold” junction uses the cold of outer space.

The MMRTG uses a heat source composed of eight General Purpose Heat Source (GPHS) modules. The MMRTG contains 4.8 kg (10.6 lb.) of plutonium dioxide that initially provides approximately 2 kW of thermal power and 120 watts of electrical power.

GPHS module

Reliable power from the MMRTG will allow it to operate for at least one Mars year ( or 687 Earth days)