Multi-Mission Radioisotope Thermoelectric Generator

Multi-Mission Radioisotope Thermoelectric Generator

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Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) are a type of Radioisotope Thermoelectric Generator
Radioisotope thermoelectric generator
A radioisotope thermoelectric generator is an electrical generator that obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples.RTGs can be...

 developed for NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 space missions including manned ones such as the Apollo program as well as unmanned ones ranging from Viking 1
Viking 1
Viking 1 was the first of two spacecraft sent to Mars as part of NASA's Viking program. It was the first spacecraft to successfully land on Mars and perform its mission, and until May 19, 2010 held the record for the second longest Mars surface mission of 6 years and 116 days .- Mission :Following...

 through the Mars Science Laboratory
Mars Science Laboratory
The Mars Science Laboratory is a National Aeronautics and Space Administration mission with the aim to land and operate a rover named Curiosity on the surface of Mars. The MSL was launched November 26, 2011, at 10:02 EST and is scheduled to land on Mars at Gale Crater between August 6 and 20, 2012...

. Units are produced for NASA by Rocketdyne Propulsion and Power, currently under the umbrella of Pratt and Whitney.

Background


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.

History


In June 2003, the Department of Energy
Department of Energy
The term Department of Energy is used by government departments in a number of countries and may refer to:* Secretariat of Energy * Department of Energy * United States Department of Energy...

 (DOE) awarded the MMRTG contract to a team led by the Boeing Company's Rocketdyne
Rocketdyne
Rocketdyne was a Rocket engine design and production company headquartered in Canoga Park, California, United States. The company was related to North American Aviation for most of its history. NAA merged with Rockwell International, which was then bought by Boeing in December, 1996...

 Propulsion and Power Division. Boeing and Teledyne
Teledyne
Teledyne Technologies Incorporated is an industrial conglomerate primarily based in the United States but with global operations. It was founded in 1960, as Teledyne, Inc., by Henry Singleton and George Kozmetsky....

  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
Pioneer 10
Pioneer 10 is a 258-kilogram robotic space probe that completed the first interplanetary mission to Jupiter, and became the first spacecraft to achieve escape velocity from the Solar System. The project was managed by the NASA Ames Research Center and the contract for the construction of the...

 and Pioneer 11
Pioneer 11
Pioneer 11 is a 259-kilogram robotic space probe launched by NASA on April 6, 1973 to study the asteroid belt, the environment around Jupiter and Saturn, solar wind, cosmic rays, and eventually the far reaches of the solar system and heliosphere...

 missions as well as the Viking 1
Viking 1
Viking 1 was the first of two spacecraft sent to Mars as part of NASA's Viking program. It was the first spacecraft to successfully land on Mars and perform its mission, and until May 19, 2010 held the record for the second longest Mars surface mission of 6 years and 116 days .- Mission :Following...

 and Viking 2
Viking 2
The Viking 2 mission was part of the American Viking program to Mars, and consisted of an orbiter and a lander essentially identical to that of the Viking 1 mission. The Viking 2 lander operated on the surface for 1,281 Mars days and was turned off on 11 April 1980 when its batteries failed...

 landers.

Design and specifications


Like the earlier GPHS-RTG
GPHS-RTG
GPHS-RTG or General Purpose Heat Source Radioisotope Thermoelectric Generator. These are a specific American design of Radioisotope Thermoelectric Generator used on space missions GPHS-RTG or General Purpose Heat Source Radioisotope Thermoelectric Generator. These are a specific American design of...

s (made by Teledyne) they are powered by Pu-238
Plutonium-238
-External links:**...

 dioxide GPHS
General Purpose Heat Source
The General Purpose Heat Source is a radioactive heat source designed for Radioisotope Thermoelectric Generators or Stirling radioisotope generators . It is meant for space applications and is packaged as a stackable module.-Characteristics:...

 modules (8 for MMRTG).
Initially an MMRTG will generate about 2 kW thermal power.

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 125W electrical power at the start of mission, falling to about 100W after 14 years. With a mass of 43 kg they provide about 2.8 We/kg (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


Radioiostope 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. Similar RHUs which provide heat to critical electronics have been used on Apollo 11 as well as the first 2 generations of Mars rovers.

The Mars Science Laboratory
Mars Science Laboratory
The Mars Science Laboratory is a National Aeronautics and Space Administration mission with the aim to land and operate a rover named Curiosity on the surface of Mars. The MSL was launched November 26, 2011, at 10:02 EST and is scheduled to land on Mars at Gale Crater between August 6 and 20, 2012...

rover, launched on November 26th, 2011 is using power from an
MMRTG to supply heat and electricity for its components and science instruments. Reliable power
from the MMRTG would allow it to operate for at least one Mars year (687 Earth days) over a wide
range of candidate landing sites.