Curiosity Rover Power
November 5, 2012
There's more electrical power on Mars than at my own home. This is discouraging, since the available Martian power is just a little more than a hundred watts, and I'm expected to be off the grid for at least another week. My lack of power is because of Hurricane Sandy, which hit my area of New Jersey especially hard.
The electrical power on Mars is concentrated at the Curiosity rover, a robotic science mission that's been on Mars since August 6, 2012. Curiosity has snapped a self-portrait of itself, as shown below. This photograph is actually a composite image created with 55 snaps of a camera, called the Mars Hand Lens Imager, attached to the rover's robotic arm.
The Curiosity is powered by a simple nuclear power source called a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) which was designed to provide power for at least a Martian year (687 Earth days), but potentially up to fourteen Earth years. This radioisotope thermoelectric generator functions by converting the heat of the radioactive decay of the plutonium isotope, plutonium-238, (238Pu) in plutonium dioxide. The initial decay reaction is straightforward, with production of uranium and an alpha particle; viz.,
238Pu -> 234U + 4He
The half-life of plutonium-238 is 87.7 years, so the power source remains fairly active for many years. The energy output of plutonium-238 by radioactive decay is 560 watts/kg. The emitted alpha particles transfer their energy to the mass of the isotope and its surroundings to create heat. The generator in the Curiosity rover contains 4.8 kg (10.6 lb.) of plutonium dioxide, which creates about 2,000 watts of heat. A schematic of the generator is shown below.
Conversion of this heat energy to electrical power is done through use of the Seebeck effect, which relies on the temperature differential between the hot plutonium and the colder Martian environment. As we know from the second law of thermodynamics, we need a temperature differential to do useful work. Junctions of n- and p-doped lead telluride perform this conversion, but the efficiency is low.[3-5] The 2,000 watt thermal power produces just a little more than a hundred watts of electrical power when the plutonium is fresh, and decreasing power thereafter.
Curiosity is not the first time that such a plutonium power source has been used. As I wrote in a previous article (Radioactive Heat, July 26, 2011), the Cassini-Huygens spacecraft to Saturn contained 7.8 kilograms of plutonium-238 as the heat source. Since it's colder at Saturn than on the surface of Mars, this generator produced more electrical power per unit weight of plutonium than the Curiosity generator.
Similar thermoelectric conversion, using heat sources other than radioisotopes, has been proposed for energy-harvesting applications. These include power generation from automotive exhaust systems. You can experiment with this technology, since commercial modules are available.
- High-Resolution Self-Portrait by Curiosity Rover Arm Camera, NASA/JPL, November 1, 2012.
- Curiosity Rover, Mars Science Laboratory Web Site, NASA/JPL.
- Space Radioisotope Power Systems, Multi-Mission Radioisotope Thermoelectric Generator, US Department of Energy.
- Ralph Wyrick and Henry Levinstein, "Thermoelectric Voltage in Lead Telluride," Phys. Rev., vol. 78, no. 3 (May, 1950), pp. 304-305.
- William E. Kortier, John J. Mueller and Philip E. Eggers, "Thermoelectric module," US Patent No. 4,211,889, July 8, 1980.
- Thermoelectric Power Generation Products, Tellurex Corporation.
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Linked Keywords: Electric power; electrical power; Mars; watt; Hurricane Sandy; Morris County; New Jersey; Curiosity Rover; robotic spacecraft; science; self-portrait; photograph; composite image; camera; Mars Hand Lens Imager; robotic arm; Bradbury Landing; Gale Crater; Ray Bradbury; science fiction; The Martian Chronicles; radioisotope thermoelectric generator; NASA; Jet Propulsion Laboratory; JPL; California Institute of Technology; Caltech; Malin Space Science Systems; nuclear fission; Multi-Mission Radioisotope Thermoelectric Generator; Earth day; Earth year; radioisotope thermoelectric generator; heat; radioactive decay; plutonium; isotope; plutonium-238; plutonium dioxide; nuclear reaction; decay reaction; uranium; alpha particle; 238Pu; 234U; alpha particle; 4He; half-life; energy; mass; decay heat; kilogram; kg; pound; lb.; lead telluride; US Department of Energy; Seebeck Effect; second law of thermodynamics; temperature; junction; n-type semiconductor; p-type semiconductor; energy conversion efficiency; Cassini-Huygens spacecraft; Saturn; radionuclide; radioisotope; energy-harvesting; automotive; exhaust system; experiment.
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