A radioisotope thermoelectric generator (RTG) is a simple electrical generator which 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 considered as a type of battery and have been used as power sources in satellites, space probes and unmanned remote facilities. RTGs are usually the most desirable power source for unmanned or unmaintained situations needing a few hundred watts or less of power for durations too long for fuel cells, batteries and generators to provide economically, and in places where solar cells are not viable. “Dynamo” redirects here. ... Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another as a result of a difference in temperature. ... Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ... Lightning strikes during a night-time thunderstorm. ... The Peltier-Seebeck effect, or thermoelectric effect, is the direct conversion of heat differentials to electric voltage and vice versa. ... In electronics, thermocouples are a widely used type of temperature sensor and can also be used as a means to convert thermal potential difference into electric potential difference. ... A Pair of AA Energizer Alkaline Cells Symbols representing a single Cell (top) and Battery (bottom), used in circuit diagrams. ... A fuel cell is an electrochemical device similar to a battery, but differing from the latter in that it is designed for continuous replenishment of the reactants consumed; i. ... Four double-A batteries In science and technology, a battery is a device that stores energy and makes it available in an electrical form. ... “Dynamo” redirects here. ... A solar cell, made from a monocrystalline silicon wafer A solar cell or photovoltaic cell is a device that converts light energy into electrical energy. ...

Design

Diagram of an RTG used on the Cassini probe

The design of an RTG is simple by the standards of nuclear technology: the main component is a sturdy container of a radioactive material (the fuel). Thermocouples are placed in the walls of the container, with the outer end of each thermocouple connected to a heat sink. Radioactive decay of the fuel produces heat which flows through the thermocouples to the heat sink, generating electricity in the process. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... This is an artists concept of Cassini during the Saturn Orbit Insertion (SOI) maneuver, just after the main engine has begun firing. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... In electronics, thermocouples are a widely used type of temperature sensor and can also be used as a means to convert thermal potential difference into electric potential difference. ... CPU heat sink with fan attached A heat sink is an environment or object that absorbs and dissipates heat from another object using thermal contact (either direct or radiant). ...

A thermocouple is a thermoelectric device that converts thermal energy directly into electrical energy using the Seebeck effect. It is made of two kinds of metal (or semiconductors) that can both conduct electricity. They are connected to each other in a closed loop. If the two junctions are at different temperatures, an electric current will flow in the loop. Thermoelectricity is the conversion from temperature differentials to electricity or vice versa. ... Lightning strikes during a night-time thunderstorm. ... The Peltier-Seebeck effect, or thermoelectric effect, is the direct conversion of heat differentials to electric voltage and vice versa. ... This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ...

Fuels

Inspection of Cassini spacecraft RTGs before launch

New Horizons in assembly hall

The radioactive material used in RTGs must have several characteristics: Image File history File links Download high-resolution version (2273x1525, 713 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cassini–Huygens Radioisotope thermoelectric generator ... Image File history File links Download high-resolution version (2273x1525, 713 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cassini–Huygens Radioisotope thermoelectric generator ... Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... Image File history File links Download high resolution version (3008x2000, 474 KB) In the clean room at KSC’s Payload Hazardous Servicing Facility, technicians prepare the New Horizons spacecraft for a media event. ... Image File history File links Download high resolution version (3008x2000, 474 KB) In the clean room at KSC’s Payload Hazardous Servicing Facility, technicians prepare the New Horizons spacecraft for a media event. ... New Horizons is a robotic spacecraft mission conducted by NASA. It is expected to be the first spacecraft to fly by and study the dwarf planet Pluto and its moons, Charon, Nix and Hydra. ...

• The half-life must be long enough that it will produce energy at a relatively continuous rate for a reasonable amount of time. However, at the same time, the half life needs to be short enough so that it decays sufficiently quickly to generate a usable amount of heat. Typical half-lives for radioisotopes used in RTGs are therefore several decades, although isotopes with shorter half-lives could be used for specialized applications.
• For spaceflight use, the fuel must produce a large amount of energy per mass and volume (density). Density and weight are not as important for terrestrial use, unless there are size restrictions.
• It should produce high energy radiation that has low penetration, preferrably alpha radiation. Beta radiation can give off considerable amounts of Gamma/X-ray radiation through bremsstrahlung secondary radiation production, thus requiring heavy shielding. Isotopes must not produce significant amounts of gamma, neutron radiation or penetrating radiation in general through other decay modes or decay chain products.

The first two criteria limit the number of possible fuels to fewer than 30 atomic isotopes within the entire isotope table of elements. Plutonium-238, curium-244 and strontium-90 are the most often cited candidate isotopes, but other isotopes such as polonium-210, promethium-147, caesium-137, cerium-144, ruthenium-106, cobalt-60, curium-242 and thulium isotopes have also been studied. Of the above, ²³⁸Pu has the lowest shielding requirements and longest half-life. Only three candidate isotopes meet the last criterion (not all are listed above) and need less than 25 mm of lead shielding to control unwanted radiation. ²³⁸Pu (the best of these three) needs less than 2.5 mm, and in many cases no shielding is needed in a ²³⁸Pu RTG, as the casing itself is adequate. Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... A radionuclide is an atom with an unstable nucleus. ... Isotopes are atoms of a chemical element whose nuclei have the same atomic number, Z, but different atomic weights, A. The word isotope, meaning at the same place, comes from the fact that isotopes are located at the same place on the periodic table. ... This article or section is in need of attention from an expert on the subject. ... The volume of a solid object is the three-dimensional concept of how much space it occupies, often quantified numerically. ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... An alpha particle is deflected by a magnetic field Alpha radiation consists of helium-4 nuclei and is readily stopped by a sheet of paper. ... Alpha radiation consists of helium nuclei and is readily stopped by a sheet of paper. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... (help· info), (from the German bremsen, to brake and Strahlung, radiation, thus, braking radiation), is electromagnetic radiation produced by the acceleration of a charged particle, such as an electron, when deflected by another charged particle, such as an atomic nucleus. ... Neutron radiation consists of free neutrons. ... In physics, the decay mode describes a particular way a particle decays. ... Nearly all the decay products of radioactive decay are themselves radioactive. ... This isotope table shows all of the known isotopes of the chemical elements, arranged with increasing atomic numbers (proton numbers) from left to right and increasing neutron numbers from top to bottom. ... Plutonium 238, is an isotope of plutonium with a half-life of 86. ... General Name, Symbol, Number Strontium, Sr, 38 Series Alkaline earth metal Group, Period, Block 2 (IIA), 5, s Density, Hardness 2630 kg/m3, 1. ... Polonium-210 is the most readily available isotope of Polonium. ... Promethium-147 is an isotope of Promethium with a half-life time of 2. ... Caesium-137 is a radioactive isotope which is formed mainly by nuclear fission. ... Ruthenium-106 has a halflife of 373. ... Cobalt 60 is a Front 242 side project featuring Front 242s Jean-Luc de Meyer and Dominique Lallement. ... General Name, Symbol, Number thulium, Tm, 69 Chemical series lanthanides Group, Period, Block ?, 6, f Appearance silvery gray Atomic mass 168. ... For Pb as an abbreviation, see PB. General Name, Symbol, Number lead, Pb, 82 Chemical series Post-transition metals or poor metals Group, Period, Block 14, 6, p Appearance bluish gray Standard atomic weight 207. ...

²³⁸Pu has become the most widely used fuel for RTGs, in the form of plutonium(IV) oxide (PuO₂). ²³⁸Pu has a half-life of 87.7 years, reasonable energy density and exceptionally low gamma and neutron radiation levels. Some Russian terrestrial RTGs have used ⁹⁰Sr; this isotope has a shorter half-life, much lower energy density and produces gamma radiation, but is cheaper. Some prototype RTGs, first built in 1958 by USA Atomic Energy Commission, have used ²¹⁰Po; this isotope provides phenomenal energy density, but has limited use because of its very short half-life and significant gamma ray production. A kilogram of pure ²¹⁰Po in the form of a cube would be about 48 mm (about 2 inches) on a side and emit about 63.5 kilowatts of heat (about 140 W/g), easily capable of melting then vaporizing itself. ²⁴²Cm and ²⁴⁴Cm have also been studied well, but require heavy shielding from gamma and neutron radiation produced from spontaneous fission. Plutonium(IV) oxide is a high melting point, yellow-brown, crystalline solid at standard temperature and pressure. ... General Name, Symbol, Number Strontium, Sr, 38 Series Alkaline earth metal Group, Period, Block 2 (IIA), 5, s Density, Hardness 2630 kg/m3, 1. ... Polonium-210 is the most readily available isotope of Polonium. ... Neutron radiation consists of free neutrons. ... Spontaneous fission (SF) is a form of radioactive decay characteristic of very heavy isotopes, and is theoretically possible for any atomic nucleus whose mass is greater than or equal to 100 amu (elements near ruthenium). ...

Americium-241 is a potential candidate isotope with a longer half-life than ²³⁸Pu: ²⁴¹Am has a half-life of 432 years and could hypothetically power a device for centuries. However, the energy density of ²⁴¹Am is only 1/4 that of ²³⁸Pu, and ²⁴¹Am produces more penetrating radiation through decay chain products than ²³⁸Pu and needs about 18 mm worth of lead shielding. Even so, its shielding requirements in a RTG are the second lowest of all possible isotopes: only ²³⁸Pu requires less. General Name, Symbol, Number americium, Am, 95 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass (243) g/mol Electron configuration [Rn] 5f7 7s2 Electrons per shell 2, 8, 18, 32, 25, 8, 2 Physical properties Phase solid Density (near r. ...

Use

Soviet RTGs in dilapidated and vandalized condition, powered by ⁹⁰Sr

The first RTG launched in space by the United States was in 1961 aboard the SNAP 3 in the Navy Transit 4A spacecraft. One of the first terrestrial uses of RTGs was in 1966 by the US Navy at the uninhabited Fairway Rock Island in Alaska, where it remained in use until its removal in 1995. Image from Finnmark regional goverment Apparently from bellona. ... Image from Finnmark regional goverment Apparently from bellona. ... Fairway Rock (65° 37. ...

A common application of RTGs is as power sources on spacecraft. Systems Nuclear Auxiliary Power Program (SNAP) units were used especially for probes that travel far enough from the Sun that solar panels are no longer viable. As such they are used with Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Galileo, Ulysses, Cassini and New Horizons. In addition, RTGs were used to power the two Viking landers and for the scientific experiments left on the Moon by the crews of Apollo 12 through 17 (SNAP 27s). RTGs were also used for the Nimbus, Transit and Les satellites. By comparison, only a few space vehicles have been launched using full-fledged nuclear reactors: the Soviet RORSAT series and the American SNAP-10A. The Systems Nuclear Auxiliary Power Program (SNAP) was a program of experimental radioisotope thermoelectric generators (RTGs) and space nuclear reactors flown during the 1960s by NASA. Odd-numbered SNAPs were RTG tests and even-numbered SNAPs were reactor system tests. ... A laundromat in California with flat-plate solar water heating collectors on its roof. ... Pioneer 10 was the first spacecraft to travel through the asteroid belt, and was the first spacecraft to make direct observations of Jupiter. ... Position of Pioneer 10 and 11 Pioneer 11 was the second mission to investigate Jupiter and the outer solar system and the first to explore the planet Saturn and its main rings. ... Trajectory of Voyager 1 using Celestia The Voyager 1 spacecraft is a 733-kilogram robotic space probe of the outer solar system and beyond, launched September 5, 1977, and is currently operational. ... Trajectory Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977. ... Galileo being deployed after being launched by the Space Shuttle Atlantis on the STS-34 mission Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. ... Ulysses spacecraft Ulysses is an unmanned probe designed to study the Sun at all latitudes. ... Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... New Horizons is a robotic spacecraft mission conducted by NASA. It is expected to be the first spacecraft to fly by and study the dwarf planet Pluto and its moons, Charon, Nix and Hydra. ... Viking mission profile. ... For other uses, see Apollo (disambiguation). ... Apollo 12 was the sixth manned mission in the Apollo program and the second to land on the Moon. ... Apollo 17 was the eleventh manned space mission in the NASA Apollo program. ... The Nimbus satellites were second-generation U.S. unmanned spacecraft for meteorological research and development. ... Operational Transit satellite The TRANSIT system, also known as NAVSAT (for Navy Navigation Satellite System), was the first satellite navigation system to be used operationally. ... Core of a small nuclear reactor used for research. ... Radar-equipped Ocean Reconnaissance SATellite or RORSAT is the western name given to the Soviet Upravlenniye Sputnik-Aktivny (US-A) satellites. ... SNAP-10A was the only spacecraft powered by a nuclear reactor ever launched by NASA as part of the SNAP Program. ...

In addition to spacecraft, the Soviet Union constructed many unmanned lighthouses and navigation beacons powered by RTGs (see Bellona's report). Powered by ⁹⁰Sr, they are very reliable and provide a steady source of power. However, critics argue that they could cause environmental and security problems, as leakage or theft of the radioactive material could pass unnoticed for years (or possibly forever: some of these lighthouses cannot be found because of poor record keeping). There has been even an instance where the radioactive compartments were opened by a thief; it was inferred that the resulting radiation poisoning has already killed the thief.^{[citation needed]} There was also the case of two woodcutters in Siberia who came across one of these units and slept close to it as a heat source during a cold night. They both died of radiation poisoning within a few days afterwards. The unit was eventually recovered and isolated. (From a PBS documentary television broadcast - citation needed.) A HDR image of a traditional lighthouse For other uses, see Lighthouse (disambiguation). ... General Name, Symbol, Number Strontium, Sr, 38 Series Alkaline earth metal Group, Period, Block 2 (IIA), 5, s Density, Hardness 2630 kg/m3, 1. ...

There are approximately 1,000 such RTGs in Russia. All of them have long exhausted their 10-year engineered life spans. They are likely no longer functional, and may be in need of dismantling. Some of them have become the prey of metal hunters, who strip the RTGs metal casings, regardless of the risk of radioactive contamination.

RTG's are also utilized by the United States Air Force to power remote sensing stations for Top-ROCK and Save-Igloo radar systems predominantly located in Alaska[2] The United States Air Force (USAF) is the aerial warfare branch of the United States armed forces and one of the seven uniformed services. ... Official language(s) English[1] Spoken language(s) English 85. ...

In the past, small "plutonium cells" (very small ²³⁸Pu-powered RTGs) were used in implanted heart pacemakers to ensure a very long "battery life". As of 2004 about 90 were still in use. They pose a hazard if the wearer is shot in the chest with a gun. If the wearer dies and the generator is not removed before cremation the device will be subject to great heat. It is unlikely however, if the plutonium is in the form of the dioxide, that contamination will occur. Note that plutonium 238 is more able to disperse than plutonium 239, but the dioxide is an air stable solid which is normally sintered in air at a temperature much higher than that used in the cremation of human remains (although they are designed to survive cremation). A pacemaker A pacemaker (or artificial pacemaker, so as not to be confused with the hearts natural pacemaker) is a medical device designed to regulate the beating of the heart. ... This article or section does not cite its references or sources. ...

Although not strictly RTGs, similar units called radioisotope heater units are also used by various spacecraft including the Mars Exploration Rovers, Galileo and Cassini. These devices use small samples of radioactive material to produce heat directly, instead of electricity. Photo of a disassembed RHU Diagram of a radioisotope heater unit Similar to a tiny radioisotope thermoelectric generator, these units normally provide about 1 Watt of heat each, derived from the decay of a few grams of Plutonium 238. ... Artists Concept of Rover on Mars NASAs Mars Exploration Rover (MER) Mission (since 2003) is a unmanned Mars exploration mission that includes sending two Rovers (robots) to explore the Martian surface and geology. ...

Life span

Most RTGs use ²³⁸Pu which decays with a half-life of 87.7 years. RTGs using this material will therefore lose 1 − 0.5^{1 / 87.7} or 0.787% of their capacity per year. 23 years after production, such an RTG would produce at 0.5^{23 / 87.7} or 83.4% of its starting capacity. Thus, with a starting capacity of 470 W, after 23 years it would have a capacity of 0.834 * 470 W = 392 W. However, the bi-metallic thermocouples used to convert thermal energy into electrical energy degrade as well; at the beginning of 2001, the power generated by the Voyager RTGs had dropped to 315 W for Voyager 1 and to 319 W for Voyager 2. Therefore in early 2001, the thermocouples were working at about 80% of their original capacity. In electronics, thermocouples are a widely used type of temperature sensor and can also be used as a means to convert thermal potential difference into electric potential difference. ... 1. ... Electrical energy can refer to several closely related things. ... Year 2001 (MMI) was a common year starting on Monday (link displays the 2001 Gregorian calendar). ...

This life span was of particular importance during the Galileo mission. Originally intended to launch in 1986, it was delayed by the Space Shuttle Challenger accident. Due to this unforseen event the probe had to sit in storage for 4 years before launching in 1989. Subsequently, its RTGs had decayed somewhat, necessitating replanning the power budget for the mission. Galileo is prepared for mating with the IUS booster Galileo being deployed after being launched by the Space Shuttle Atlantis on the STS-34 mission Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. ... Year 1986 (MCMLXXXVI) was a common year starting on Wednesday (link displays 1986 Gregorian calendar). ... Space Shuttle Challenger (NASA Orbiter Vehicle Designation: OV-099) was NASAs second Space Shuttle orbiter to be put into service. ... STS-51-L was the 25th launch of a Space Shuttle and the tenth launch of the Challenger. ... Year 1989 (MCMLXXXIX) was a common year starting on Sunday (link displays 1989 Gregorian calendar). ...

Efficiency

Image of a mostly thermally isolated, Plutonium RTG pellet glowing red hot.

RTGs use thermoelectric couples or "thermocouples", to convert heat from the radioactive material into electricity. Thermocouples, though very reliable and long-lasting, are very inefficient; efficiencies above 10% have never been achieved and most RTGs have efficiencies between 3-7%. However studies have been done on improving efficiency by using other technologies to generate electricity from heat. Achieving higher efficiency would mean less radioactive fuel is needed to produce the same amount of power, and therefore a lighter overall weight for the generator. This is a critically important factor in spaceflight launch cost considerations. Download high resolution version (884x696, 143 KB)This is an image of a glowing red hot pellet of plutonium-238 dioxide to be used in a radioisotope thermoelectric generator for either the Cassini mission to Saturn (planet) or the Galileo mission to Jupiter. ... Download high resolution version (884x696, 143 KB)This is an image of a glowing red hot pellet of plutonium-238 dioxide to be used in a radioisotope thermoelectric generator for either the Cassini mission to Saturn (planet) or the Galileo mission to Jupiter. ... Molten glassy material glows orange with incandescence in a vitrification experiment. ... This article or section should include material from Thermocouples applied In electronics, thermocouples are a widely used kind of temperature sensor. ...

Energy conversion devices which rely on the principle of thermionic emission can achieve efficiencies between 10-20%, but require higher temperatures than those at which standard RTGs run. Some prototype ²¹⁰Po RTG have used thermionics, and potentially other extremely radioactive isotopes could also provide power by this means, but short half-lives make these infeasible. Several space-bound nuclear reactors have used thermionics, but nuclear reactors are usually too heavy to use on most space probes. Thermionic emission is the flow of electrons from a metal or metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface. ...

Thermophotovoltaic cells work by the same principles as a photovoltaic cell, except that they convert infrared light emitted by a hot surface rather than visible light into electricity. Thermophotovoltaic cells have an efficiency slightly higher than thermocouples and can be overlaid on top of thermocouples, potentially doubling efficiency. Systems with radioisotope generators simulated by electric heaters have demonstrated efficiencies of 20%[3], but have not been tested with actual radioisotopes. Some theoretical thermophotovoltaic cell designs have efficiencies up to 30%, but these have yet to be built or confirmed. Thermophotovoltaic cells and silicon thermcouples degrade faster than thermocouples, especially in the presence of ionizing radiation. Further research is needed in this area. Thermophotovoltaic energy conversion is a direct conversion process from heat differentials to electricity via photons. ... A photovoltaic cell is a device that turns light into electric energy. ... Image of two girls in mid-infrared (thermal) light (false-color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ...

Dynamic generators, unlike thermoelectrics, use moving parts to mechanically convert heat into electricity. Unfortunately, those moving parts can wear out and need maintenance, which may not be possible for certain applications like space probes. Dynamic power sources also cause vibration and RF noise. Even so, NASA has worked on developing a next generation RTG called a Stirling Radioisotope Generator (SRG) that uses Free-Piston Stirling engines to produce power. SRG prototypes demonstrated an average efficiency of 23%, and higher efficiency can be achieved with the use of greater temperature differentials between the hot and cold ends of the generator. The use of magnetically non-contacting moving parts, non-degrading flexural bearings, and a lubrication-free and hermetically sealed environment have, in test units, demonstrated no appreciable degradation over years of operation. Experimental results demonstrate that an SRG could continue running for decades without maintenance. Vibration can be reduced through damping and counter-piston movement. The most likely future use for SRGs may be future Mars Rovers where vibration is less of a worry. It has been suggested that this article or section be merged with Radio waves. ... The Stirling Radioisotope Generator (SRG) is based on a Stirling engine powered by a large radioisotope heater unit. ... Cut away diagram of a Rhombic Drive Beta Stirling Engine Design Pink - Hot cylinder wall, Dark grey - Cold cylinder wall (with coolant inlet and outlet pipes in Yellow), Dark Green - Thermal insulation separating the two cylinder ends, Light Green - Displacer piston, Dark Blue - Power piston, Light Blue - Flywheels, Not Shown... A flexure bearing is a bearing which allows motion by bending a load element. ... A Mars Rover is an unmanned land vehicle for exploration of the planet Mars. ...

Safety

Diagram of a stack of general purpose heat source modules as used in RTGs

Image File history File links Size of this preview: 800 × 513 pixelsFull resolution (844 × 541 pixel, file size: 18 KB, MIME type: image/png) Diagram of general purpose heat source module used in RTGs taken from Cassini final environmental impact statement (page 2-16) http://saturn. ... Image File history File links Size of this preview: 800 × 513 pixelsFull resolution (844 × 541 pixel, file size: 18 KB, MIME type: image/png) Diagram of general purpose heat source module used in RTGs taken from Cassini final environmental impact statement (page 2-16) http://saturn. ...

Radioactive contamination

RTGs may pose a minimal risk of radioactive contamination: if the container holding the fuel leaks, the radioactive material may contaminate the environment. The radiation warning symbol (trefoil). ...

For spacecraft, the main concern is that if an accident were to occur during launch or a subsequent passage of a spacecraft close to Earth, harmful material could be released into the atmosphere; and their use in spacecraft and elsewhere has attracted controversy.^[1][2]

However, this event is not considered likely with current RTG cask designs. For instance, the environmental impact study for the Cassini-Huygens probe launched in 1997 estimated the probability of contamination accidents at various stages in the mission. The probability of an accident occurring which caused radioactive release from one or more of its 3 RTGs (or from its 129 RHUs) during the first 3.5 minutes following launch was estimated at 1 in 1,400; the chances of a release later in the ascent into orbit were 1 in 476; after that the likelihood of an accidental release fell off sharply to less than 1 in a million.^[3] If an accident which had the potential to cause contamination occurred during the launch phases (such as the spacecraft failing to reach orbit), the probability of contamination actually being caused by the RTGs was estimated at about 1 in 10.^[4] In the event, the launch was successful and Cassini-Huygens reached Saturn. Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... Year 1997 (MCMXCVII) was a common year starting on Wednesday (link will display full 1997 Gregorian calendar). ... Similar to a tiny radioisotope thermoelectric generator (RTG), these units normally provide about 1 watt of heat each, derived from the decay of a few grams of plutonium 238. ... Adjectives: Saturnian Atmosphere Surface pressure: 140 kPa Composition: >93% hydrogen >5% helium 0. ...

The plutonium 238 used in these RTGs has a half-life of 87.74 years, in contrast to the 24,110 year half-life of plutonium 239 used in nuclear weapons and reactors. A consequence of the shorter half life is that plutonium 238 is about 275 times more radioactive than plutonium 239 (i.e. 17.3 Ci/g compared to 0.063 Ci/g^[5]). For instance, 3.6 kg of plutonium 238 undergoes the same number of radioactive decays per second as 1 tonne of plutonium 239. Since the morbidity of the two isotopes in terms of absorbed radioactivity is almost exactly the same^[6], plutonium 238 is around 275 times more toxic by weight than plutonium 239. Plutonium-238 glowing from its own heat Plutonium 238, is a radioactive isotope of plutonium with a half-life of 86. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... General Name, Symbol, Number plutonium, Pu, 94 Chemical series actinides Group, Period, Block ?, 7, f Appearance silvery white Atomic mass (244) g/mol Electron configuration [Rn] 5f6 7s2 Electrons per shell 2, 8, 18, 32, 24, 8, 2 Physical properties Phase solid Density (near r. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 km (11 mi) above the epicenter. ... Core of a small nuclear reactor used for research. ... The curie (symbol Ci) is a former unit of radioactivity, defined as 3. ... BIC pen cap, about 1 gram. ... The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. It was assigned to the United States in 1889 and is periodically recertified and traceable to the primary international standard, The Kilogram, held at the Bureau International des Poids et...

The alpha radiation both isotopes emit will not penetrate the skin, but can irradiate internal organs if plutonium is inhaled or ingested. Particularly at risk is the skeleton, the surface of which is likely to absorb the isotope, and the liver, where the isotope will collect and become concentrated. This article does not cite any references or sources. ... The liver is an organ present in vertebrates and some other animals. ...

There have been six known accidents involving RTG-powered spacecraft. The first one was a launch failure on 21 April 1964 in which the U.S. Transit-5BN-3 navigation satellite failed to achieve orbit and burnt up on re-entry north of Madagascar. Its 17,000 Ci (630 TBq) plutonium metal fuel was injected into the atmosphere over the Southern Hemisphere where it burnt up, and traces of plutonium 238 were detected in the area a few months later. The second was the Nimbus B-1 weather satellite whose launch vehicle was deliberately destroyed shortly after launch on 21 May 1968 because of erratic trajectory. Launched from the Vandenberg Air Force Base, its SNAP-19 RTG containing relatively inert plutonium dioxide was recovered intact from the seabed in the Santa Barbara Channel five months later and no environmental contamination was detected. ^[7] is the 111th day of the year (112th in leap years) in the Gregorian calendar. ... 1964 (MCMLXIV) was a leap year starting on Wednesday (the link is to a full 1964 calendar). ... Operational Transit satellite The TRANSIT system, also known as NAVSAT (for Navy Navigation Satellite System), was the first satellite navigation system to be used operationally. ... The becquerel (symbol Bq) is the SI derived unit of radioactivity, defined as the activity of a quantity of radioactive material in which one nucleus decays per second. ... The Nimbus satellites were second-generation U.S. unmanned spacecraft for meteorological research and development. ... May 21 is the 141st day of the year (142nd in leap years) in the Gregorian calendar. ... Year 1968 (MCMLXVIII) was a leap year starting on Monday (link will display full calendar) of the 1968 Gregorian calendar. ... Boeing Delta 4 Medium+ (4,2) lifts off from Space Launch Complex Six (SLC-6) at Vandenberg AFB, California (Official photo by Thom Baur for the Boeing Company) Vandenberg Air Force Base (IATA: VBG, ICAO: KVBG) is a United States military installation with a spaceport, in Santa Barbara County, California... Prepared during the reprocessing of nuclear fuel by calcination of plutonium(IV) oxalate, Pu(C2O4)2. ... Looking south-southwest, across the Santa Barbara Channel; the Channel Islands are in the distance. ...

Two more were failures of Soviet Cosmos missions containing RTG-powered lunar rovers in 1969, both of which released radioactivity as they burnt up. There were also five failures involving Soviet or Russian spacecraft which were carrying nuclear reactors rather than RTGs between 1973 and 1993.^[8] Cosmos is name of a series of satellites which were launched by the Soviet Union and are being launched now by Russia. ...

The failure of the Apollo 13 mission in April 1970 meant that the Lunar Module reentered the atmosphere carrying an RTG and burnt up over Fiji. It carried a SNAP-27 RTG containing 44,500 curies (1,650 TBq) of plutonium dioxide which survived reentry into the Earth's atmosphere intact, as it was designed to do, the trajectory being arranged so that it would plunge into 6-9 kilometers of water in the Tonga trench in the Pacific Ocean. The absence of plutonium 238 contamination in atmospheric and seawater sampling confirmed the assumption that the cask is intact on the seabed. The cask is expected to contain the fuel for at least 10 half-lives (i.e. 870 years). Apollo 13 was the third manned lunar-landing mission, part of Project Apollo under NASA in the United States. ... 1970 (MCMLXX) was a common year starting on Thursday. ... Description Role: Lunar landing Crew: 2; CDR, LM pilot Dimensions Height: 20. ... The Tonga Trench is located in the Pacific ocean and is 32,000 ft (9,900 m) deep. ...

The US Department of Energy has conducted seawater tests and determined that the graphite casing, which was designed to withstand reentry, is stable and no release of plutonium should occur. Subsequent investigations have found no increase in the natural background radiation in the area. The Apollo 13 accident represents an extreme scenario due to the high re-entry velocities of the craft returning from cislunar space. This accident has served to validate the design of later-generation RTGs as highly safe.

To minimise the risk of the radioactive material being released, the fuel is stored in individual modular units with their own heat shielding. They are surrounded by a layer of iridium metal and encased in high-strength graphite blocks. These two materials are corrosion and heat-resistant. Surrounding the graphite blocks is an aeroshell, designed to protect the entire assembly against the heat of reentering the earth's atmosphere. The plutonium fuel is also stored in a ceramic form that is heat-resistant, minimising the risk of vaporization and aerosolization. The ceramic is also highly insoluble. This article is about the chemical element. ... Graphite (named by Abraham Gottlob Werner in 1789 from the Greek γραφειν (graphein): to draw/write, for its use in pencils) is one of the allotropes of carbon. ... Solubility refers to the ability for a given substance, the solute, to dissolve in a solvent. ...

The most recent accident involving a spacecraft RTG was the failure of the Russian Mars 96 probe launch on 16 November 1996. The two RTGs onboard carried in total 200 g of plutonium and are assumed to have survived reentry (as they were designed to do). They are thought to now lie somewhere in a northeast-southwest running oval 320 km long by 80 km wide which is centred 32 km east of Iquique, Chile.^[9] To meet Wikipedias quality standards, this article or section may require cleanup. ... November 16 is the 320th day of the year (321st in leap years) in the Gregorian calendar, with 45 days remaining. ... Year 1996 (MCMXCVI) was a leap year starting on Monday (link will display full 1996 Gregorian calendar). ... Walk Baquedano Iquique (IPA /ikike/) is a city in northern Chile, capital of Tarapacá Region, on the Pacific coast, just west of the Atacama Desert. ...

Many Beta-M RTGs produced by the Soviet Union to power lighthouses and beacons have become orphaned sources of radiation. Several of these units have been illegally dismantled for scrap metal resulting in the complete exposure the Sr-90 source, fallen into the ocean, or have defective shielding due to poor design or physical damage. The US Department of Defense cooperative threat reduction program has expressed concern that material from the Beta-M RTGs can be used by terrorists to construct a dirty bomb. [4] Wikipedia does not yet have an article with this exact name. ... A HDR image of a traditional lighthouse For other uses, see Lighthouse (disambiguation). ... This page discusses Beacons, fires designed to attract attention. ... An orphan source is a self-contained radioactive source that is no longer under proper regulatory control. ... Strontium-90 (90Sr) is a radioactive isotope of strontium, with a half life of 28. ... The United States Department of Defense, abbreviated DoD or DOD and sometimes called the Defense Department, is a civilian Cabinet organization of the United States government. ... This article is becoming very long. ... The term dirty bomb is primarily used to refer to a radiological dispersal device (RDD), a radiological weapon which combines radioactive material with conventional explosives. ...

Nuclear fission

RTGs use a different process of heat generation from that used by nuclear power stations. Nuclear power stations generate power by a chain reaction in which the nuclear fission of an atom releases neutrons which cause other atoms to undergo fission. This allows the rapid reaction of large numbers of atoms, thereby producing large amounts of heat for electricity generation. However, if the reaction is not carefully controlled the number of atoms undergoing fission (and the heat production) can grow exponentially, very rapidly becoming hot enough to destroy the reactor. A nuclear power station. ... A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions. ... For the generation of electrical power by fission, see Nuclear power plant An induced nuclear fission event. ... This article or section does not adequately cite its references or sources. ... In mathematics, exponential growth (or geometric growth) occurs when the growth rate of a function is always proportional to the functions current size. ...

Chain reactions do not occur inside RTGs, so such a nuclear meltdown is not possible. In fact, some RTGs are designed so that fission does not occur at all; rather, forms of radioactive decay which cannot trigger other radioactive decays are used instead. As a result, the fuel in an RTG is consumed much more slowly and much less power is produced. Three Mile Island Nuclear Generating Station consisted of two pressurized water reactors manufactured by Babcock & Wilcox each inside its own containment building and connected cooling towers. ... Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. ...

There are no nuclear proliferation risks associated with plutonium-238 because it is unsuitable for making nuclear weapons. The major reason for this is that plutonium-238 undergoes spontaneous fission at a high rate and thus emits neutrons randomly, causing the chain reaction to start too early in the triggering process. This would cause a plutonium-238 bomb to "fizzle", greatly reducing its reliability and power. Moreover due to the speed of decay, plutonium-238 generates copious amounts of heat and thus would complicate the manufacturing process. World map with nuclear weapons development status represented by color. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 km (11 mi) above the epicenter. ... Spontaneous fission (SF) is a form of radioactive decay characteristic of very heavy isotopes, and is theoretically possible for any atomic nucleus whose mass is greater than or equal to 100 amu (elements near ruthenium). ... A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions. ...

RTG models

"*":The SRG is in fact not an RTG; it is a stirling power device. The Systems Nuclear Auxiliary Power Program (SNAP) was a program of experimental radioisotope thermoelectric generators (RTGs) and space nuclear reactors flown during the 1960s by NASA. Odd-numbered SNAPs were RTG tests and even-numbered SNAPs were reactor system tests. ... Project Apollo was a series of human spaceflight missions undertaken by the United States of America (NASA) using the Apollo spacecraft and Saturn launch vehicle, conducted during the years 1961 – 1975. ... The Apollo Lunar Surface Experiment Package, or ALSEP, was a set of connected scientific instruments left on the Moon when the Apollo program ended. ... Wikipedia does not yet have an article with this exact name. ... Cut away diagram of a Rhombic Drive Beta Stirling Engine Design Pink - Hot cylinder wall, Dark grey - Cold cylinder wall (with coolant inlet and outlet pipes in Yellow), Dark Green - Thermal insulation separating the two cylinder ends, Light Green - Displacer piston, Dark Blue - Power piston, Light Blue - Flywheels, Not Shown...

See also

Wikimedia Commons has media related to:

Radioisotope thermoelectric generator

• Nuclear reactor
• Radioactive isotope
• Cassini-Huygens
• Atomic battery
• Betavoltaics
• Optoelectric nuclear battery
• Radioisotope heater units
• Alkali-metal thermal to electric converter
• Beta-M

Image File history File links Commons-logo. ... The Wikimedia Commons (also called Wikicommons) is a repository of free content images, sound and other multimedia files. ... Core of a small nuclear reactor used for research. ... A radionuclide is an atom with an unstable nucleus. ... Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... The terms atomic battery, nuclear battery and radioisotope battery are used to describe a device which uses the charged particle emissions from a radioactive isotope to directly generate electricity. ... Betavoltaics are generators of electrical current, in effect a form of battery, which use energy from a radioactive source emitting beta particles (electrons). ... An optolectric nuclear battery has been developed by researchers of the Kurchatov Institute in Moscow. ... Photo of a disassembed RHU Diagram of a radioisotope heater unit Similar to a tiny radioisotope thermoelectric generator, these units normally provide about 1 Watt of heat each, derived from the decay of a few grams of Plutonium 238. ... The Alkali Metal Thermoelectric Converter (AMTEC) is a thermally regenerative electrochemical device for the direct conversion of heat to electrical energy. ... Wikipedia does not yet have an article with this exact name. ...

References

• Safety discussion of the RTGs used on the Cassini-Huygens mission.
• Bellona's report on RTG lighthouses.
• Nuclear Power in Space (PDF)
• Detailed report on Cassini RTG (PDF)
• Detailed lecture on RTG fuels (PDF)
• Detailed chart of all radioisotopes
• Stirling Thermoelectic Generator
• Toxicity profile for plutonium,Agency for Toxic substances and Disease Registry, U.S. Public Health Service, December 1990
• Environmental Impact of Cassini-Huygens Mission.
• Expanding Frontiers with Radioisotope Power Systems (PDF)

1. ^ Nuclear-powered NASA craft to zoom by Earth on Tuesday, CNN news report, 16 August 1999
2. ^ Valley says pee-eww to plutonium plan, Idaho Mountain Express and Guide, 22 July 2005
3. ^ Cassini Final Supplemental Environmental Impact Statement, Chapter 4, NASA, September 1997 (Links to other chapters and associated documents can be found at [1])
4. ^ Cassini Final Supplemental Environmental Impact Statement, Appendix D, Summary of tables of safety analysis results, Table D-1 on page D-4, see conditional probability column for GPHS-RTG
5. ^ Physical, Nuclear, and Chemical, Properties of Plutonium, IEER Factsheet
6. ^ Mortality and Morbidity Risk Coefficients for Selected Radionuclides, Argonne National Laboratory
7. ^ A. Angelo Jr. and D. Buden (1985). Space Nuclear Power. Krieger Publishing Company. 
8. ^ IASS Strategic Plan 2005-2009, page 39
9. ^ Mars 96 timeline, NASA

External links

• NASA JPL briefing, Expanding Frontiers with Radioisotope Power Systems - gives RTG information and a link to a longer presentation
• SpaceViews: The Cassini RTG Debate
• Stirling Radioisotope Generator