Radioisotope power systems were first flown on U.S. space vehicles more than 40 years ago. They offer the key advantage of operating continuously, independent of sunlight, for a long time. They have little or no sensitivity to cold, radiation or other effects of the space environment. More than two dozen NASA spacecraft have conducted their missions using such systems for electrical power and/or heating. For example, the Viking landers, each with a radioisotope thermoelectric generator, landed on Mars in 1976 and operated on Mars for four and six years respectively. The solar-powered 1997 Mars Pathfinder mission's Sojourner rover used radioisotope heaters to keep its electronics box warm. The solar-powered Mars Exploration Rovers Spirit and Opportunity also use radioisotope heaters.

New Capabilities

The need for reliable, long-lived power systems is important for future, increasingly sophisticated Mars missions. NASA and the Department of Energy are developing a new generation of these long-lived, reliable nuclear power systems to enable a broader range of important science missions. They are ideally suited for missions involving autonomous operations in the extreme environments of space and on planetary surfaces.

One of these next-generation space power systems was chosen as the electrical power system for the Mars Science Laboratory -- the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG).

The use of this power source will enable:

Access to More of Mars

This type of power supply will give the mission an operating lifespan on Mars' surface of a full Martian year (687 Earth days, a little less than two Earth years) over a wide latitude range. That means it opens up more regions of Mars to exploration, giving mission planners more choices in selecting landing sites that have characteristics related to Mars' potential as a habitat for life. With more of Mars accessible, Mars Science Laboratory can better meet its science goal of understanding the planet's potential as a past or present habitat for life.

Greater Mobility, More Operational Flexibility, and More Science

Compared to the solar power alternative studied, the MMRTG-powered rover provides significantly greater mobility and operations flexibility and more science payload capability.

Thermal Stability for the Rover

The MMRTG is also crucial for the rover's thermal stability. Waste heat from the unit is circulated throughout the rover system to keep instruments, computers, mechanical devices and communications systems within their operating temperature ranges. This system-wide thermal control does not draw on the rover's electrical power, and precludes the need for radioisotope heater units for spot heating.

Optimized Power and a Long Lifetime

The MMRTG optimizes power levels over a minimum lifetime of 14 years.

Smaller Size and Minimized Weight

With its smaller size, the MMRTG adds more flexibility to spacecraft and mission designs. Compared to the solar power alternative studied, the MMRTG minimizes weight.

Safety

The design requirements of the MMRTG include ensuring a high degree of safety. The design of the generator's General Purpose Heat Source (GPHS) module, which contains the radioisotope heat source, is enhanced and provides added factors of safety in the event of impact or inadvertent reentry.