the South Pacific Ocean, in the vicinity of the Tonga Trench. The Curiosity and Perseverance Mars rover designs selected RTGs to allow greater flexibility A radioisotope thermoelectric generator (RTG, RITEG), or radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioactive material into electricity by the Seebeck effect. This type of generator has no moving parts and is ideal for deployment in remote and harsh environments for extended periods wit The RTG… The RTG was invented in 1954 by Mound Laboratories scientists Kenneth (Ken) C. Jordan (1921–2008) and John Birden (1918–2011). They were inducted into the National Inventors Hall of Fame in 2013. Jordan and Birden worked on an Army Signal Corps contract (R-65-8- 998 11-SC-03-91) beginning on 1 January 1957, to conduct research on radioactive materials and thermocouples suitable for the direct conversion of heat to electrical energy using polonium-210 as the heat source. RTGs were developed in the US during the late 1950s by Mound Laboratories in Miamisburg, Ohio, under contract with the United States Atomic Energy Commission. The project was led by Dr. Bertram C. Blanke. The first RTG launched into space by the United States was SNAP 3B in 1961 powered by 96 grams of plutonium-238 metal, aboard the Navy Transit 4A spacecraft. One of the first terrestrial uses of RTGs was in 1966 by the US Navy at uninhabited Fairway Rock in Alaska. RTGs were used at that site until 1995. A common RTG application is spacecraft power supply. Several generations of RTG design have been used for probes that traveled far from the Sun, rendering solar panels impractical. As such, they have been used for Pioneer 10 and 11; Voyager 1 and 2; Galileo; Ulysses; Cassini; New Horizons; and are planned for the Dragonfly mission to Titan. RTGs were also used instead of solar panels 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). Because the Apollo 13 Moon landing was aborted, its RTG rests in the South Pacific Ocean, in the vicinity of the Tonga Trench. The Curiosity and Perseverance Mars rover designs selected RTGs to allow greater flexibility in landing sites and longer lifespan than the solar-powered option, as used in prior generations of rovers. 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. In addition to spacecraft, the Soviet Union built 1,007 RTGs to power uncrewed lighthouses and navigation beacons on the Soviet Arctic coast by the late 1980s. Many different types of RTGs (including Beta-M type) were built in the Soviet Union for a wide variety of purposes. The lighthouses were not maintained for many years after the dissolution of the Soviet Union in 1991. Some of the RTG units disappeared during this time—either by looting or by the natural forces of ice/storm/sea. In 1996, a project was begun by Russian and international supporters to decommission the RTGs in the lighthouses, and by 2021, all RTGs had been removed. As of 1992, the United States Air Force also used RTGs to power remotely-located Arctic equipment, and the US government has used hundreds of such units to power remote stations globally. Sensing stations for Top-ROCC and SEEK IGLOO radar systems, predominantly located in Alaska, use RTGs. The units use strontium-90, and a larger number of such units have been deployed both on the ground and on the ocean floor than have been used on spacecraft, with public regulatory documents suggesting that the US had deployed at least 100–150 during the 1970s and 1980s. 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 ninety were still in use. By the end of 2007, the number was reported to be down to just nine. The Mound Laboratory Cardiac Pacemaker program began on 1 June 1966, in conjunction with NUMEC. The program was cancelled in 1972, when it was recognized that the heat source would not remain intact during cremation and there was no way to completely ensure that the units would not be cremated with their users' bodies. A launch failure on 21 April 1964 in which the U.S. Transit-5BN-3 navigation satellite failed to achieve orbit and burned up on re-entry north of Madagascar. The 17,000 Ci (630 TBq) plutonium metal fuel in its SNAP-9a RTG was ejected into the atmosphere over the Southern Hemisphere where it burned up, and traces of plutonium-238 were detected in the area a few months later. This incident resulted in the NASA Safety Committee requiring intact reentry in future RTG launches, which in turn impacted the design of RTGs in the pipeline. 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. In 1969 the launch of the first Lunokhod lunar rover mission failed, spreading polonium-210 over a large area of Russia. The failure of the Apollo 13 mission in April 1970 meant that the Lunar Module reentered the atmosphere carrying an RTG and burned up over Fiji. It carried a SNAP-27 RTG containing 44,500 Ci (1,650 TBq) of plutonium dioxide in a graphite cask on the lander leg 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

Perseverance is a NASA rover that has been exploring Mars since February 18, 2021, as part of the Mars 2020 mission. Built and managed by the Jet Propulsion Laboratory, the car-sized rover was launched on July 30, 2020, from Cape Canaveral aboard an Atlas V rocket and landed in Jezero Crater, a site chosen for its ancient river delta that may preserve evidence of past microbial life. The rover's m Perseverance is a NASA rover that has been exploring Mars since February 18, 2021, as part of the Mars 2020 mission. Built and managed by the Jet Propulsion Laboratory, the car-sized rover was launched on July 30, 2020, from Cape Canaveral aboard an Atlas V rocket and landed in Jezero Crater, a site chosen for its ancient river delta that may preserve evidence of past microbial life. The rover's main goals are to search for signs of ancient life, study the planet's geology and climate, and collect rock and regolith samples for possible return to Earth by a future mission. Perseverance also tests technologies intended to support later human exploration, including an experiment that successfully produced oxygen from the thin carbon-dioxide atmosphere. Perseverance carries seven primary scientific instruments, 19 cameras, and two microphones. It also deployed the experimental helicopter Ingenuity, which in April 2021 performed the first powered and controlled flight on another planet. Originally intended for up to five flights, Ingenuity completed dozens of sorties before being retired in 2024. Powered by a radioisotope thermoelectric generator, Perseverance has an expected mission duration of over a decade. It has provided high-resolution panoramas, drilled and cached samples for later retrieval, and identified rocks which may have been habitable for ancient microbial life in Jezero Crater. In July 2024, it discovered the Cheyava Falls rock containing "possible biosignature." As of 8 August 2026, Perseverance has been active on Mars for 1944 sols (1997 total days; 5 years, Perseverance is a NASA rover that has been exploring Mars since February 18, 2021, as part of the Mars 2020 mission. Built and managed by the Jet Propulsion Laboratory, the car-sized rover was launched on July 30, 2020, from Cape Canaveral aboard an Atlas V rocket and landed in Jezero Crater, a site chosen for its ancient river delta that may preserve evidence of past microbial life. The rover's main goals are to search for signs of ancient life, study the planet's geology and climate, and collect rock and regolith samples for possible return to Earth by a future mission. Perseverance also tests technologies intended to support later human exploration, including an experiment that successfully produced oxygen from the thin carbon-dioxide atmosphere. Perseverance carries seven primary scientific instruments, 19 cameras, and two microphones. It also deployed the experimental helicopter Ingenuity, which in April 2021 performed the first powered and controlled flight on another planet. Originally intended for up to five flights, Ingenuity completed dozens of sorties before being retired in 2024. Powered by a radioisotope thermoelectric generator, Perseverance has an expected mission duration of over a decade. It has provided high-resolution panoramas, drilled and cached samples for later retrieval, and identified rocks which may have been habitable for ancient microbial life in Jezero Crater. In July 2024, it discovered the Cheyava Falls rock containing "possible biosignature." As of 8 August 2026, Perseverance has been active on Mars for 1944 sols (1997 total days; 5 years, 171 days) since its landing. JPL built a copy of the Perseverance; a twin rover used for testing and problem solving, OPTIMISM (Operational Perseverance Twin for Integration of Mechanisms and Instruments Sent to Mars), a vehicle system test bed (VSTB). It is housed at the JPL Mars Yard and is used to test operational procedures and to aid in problem solving should any issues arise with Perseverance. In June 2026, it was reported that NASA is considering launching the spare rover to the Moon. The mission is called Polar Rover for Observation, Mapping and In-Situ Exploration, or PROMISE. The successful landing of Perseverance in Jezero Crater was announced at 20:55 UTC on February 18, 2021, the signal from Mars taking 11 minutes to arrive at Earth. The rover touched down at 18.4446°N 77.4509°E / 18.4446; 77.4509, roughly 1 km (0.62 mi) southeast of the center of its 7.7 km × 6.6 km (4.8 mi × 4.1 mi) wide landing ellipse. It came down pointed almost directly to the southeast, with the RTG on the back of the vehicle pointing northwest. The descent stage ("sky crane"), parachute and heat shield all came to rest within 1.5 km of the rover (see satellite image). Having come within five meters (16 ft) of its target, the landing was more accurate than any previous Mars landing; a feat enabled by the experience gained from Curiosity's landing and the use of new steering technology. One such new technology is Terrain Relative Navigation (TRN), a technique in which the rover compares images of the surface taken during its descent with reference maps, allowing it to make last minute adjustments to its course. The rover also uses the images to select a safe landing site at the last minute, allowing it to land in relatively unhazardous terrain. This enables it to land much closer to its science objectives than previous missions, which all had to use a landing ellipse devoid of hazards. The landing occurred in the late afternoon, with the first images taken at 15:53:58 on the mission clock (local mean solar time). The landing took place shortly after Mars passed through its northern vernal equinox (Ls = 5.2°), at the start of the astronomical spring, the equivalent of the end of March on Earth. The parachute descent of the Perseverance rover was photographed by the HiRISE high-resolution camera on the Mars Reconnaissance Orbiter (MRO). Jezero Crater is a paleolake basin.