Multi-Mission Radioisotope Thermoelectric Generator
The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) is a type of Radioisotope Thermoelectric Generator developed for NASA space missions such as the Mars Science Laboratory. The United States Department of Energy's, Office of Space and Defense Power Systems within the Office of Nuclear Energy, and NASA Units are produced for NASA by Rocketdyne Propulsion and Power, currently under the umbrella of Pratt and Whitney.
On November 20, 2013, NASA reported suspending operations on the Mars Curiosity rover in order to diagnose an electrical problem first observed on November 17. Apparently, an internal short in the rover's power source, the MMRTG, caused an unusual and intermittent decrease in a voltage indicator on the rover. On November 23, 2013, Curiosity resumed full science operations, with no apparent loss of capability.
Space exploration missions require safe, reliable, long-lived power systems to provide electricity and heat to spacecraft and their science instruments. A uniquely capable source of power is the radioisotope thermoelectric generator (RTG) – essentially a nuclear battery that reliably converts heat into electricity.
In June 2003, the Department of Energy (DOE) awarded the MMRTG contract to a team led by the Boeing Company's Rocketdyne Propulsion and Power Division. Boeing and Teledyne Energy Systems collaborated on an MMRTG design concept based on a previous thermoelectric converter design, SNAP-19, utilized by Teledyne for previous space exploration missions. SNAP-19s powered Pioneer 10 and Pioneer 11 missions as well as the Viking 1 and Viking 2 landers.
Design and specifications
The GPHS-RTG used SiGe thermoelectric elements but these are no longer in production and the MMRTG will use PbTe/TAGS thermocouples (from Teledyne Energy Systems). The MMRTG is designed to produce 125 W electrical power at the start of mission, falling to about 100 W after 14 years. With a mass of 45 kg they provide about 2.8 W/kg of electrical power at beginning of life (just over half of the earlier GPHS-RTG units).
The design goals for the MMRTG include ensuring a high degree of safety, optimizing power levels over a minimum lifetime of 14 years, and minimizing weight.
Usage in space missions
Radioisotope power has been used on 8 Earth orbiting missions, 8 missions travelling to each of the outer planets as well as each of Apollo missions following 11 to Earth's moon. Some of the outer Solar System missions are the Pioneer, Voyager, Ulyssess, Galileo, Cassini and Pluto New Horizons missions. The RTGs on Voyager 1 and 2 have been operating since 1977. Similar RHUs which provide heat to critical electronics have been used on Apollo 11 as well as the first 2 generations of Mars rovers. In total, over the last four decades, 26 missions and 45 RTGs have been launched in the United States.
Curiosity, a Mars rover that was successfully landed in Gale Crater on August 6, 2012, is using power from an MMRTG to supply heat and electricity for its components and science instruments. Reliable power from the MMRTG will allow it to operate for at least one Mars year (687 Earth days) over a wide range of candidate landing sites.
- Webster, Guy (November 20, 2013). "Rover Team Working to Diagnose Electrical Issue". NASA. Retrieved November 21, 2013.
- Staff (November 25, 2013). "Curiosity Resumes Science After Analysis of Voltage Issue". NASA. Retrieved November 25, 2013.
- This article incorporates public domain material from the United States Department of Energy document "Space Radioisotope Power Systems Multi-Mission Radioisotope Thermoelectric Generator".[dead link]
- SNAP-19: Pioneer F & G, Final Report, Teledyne Isotopes, 1973
- Expanding Frontiers with Radioisotope Power Systems (excerpt from JPL report) (NASA)
- Bechtel, Ryan. "Radioisotope Missions". US Department of Energy.
|Wikimedia Commons has media related to Radioisotope thermoelectric generators.|
- NASA Radioisotope Power Systems website – RTG page
- Idaho National Laboratory MMRTG page with photo-based "virtual tour"