Tsar Bomba ( Russian: Царь-бомба ; " Tsar -bomb") was a hydrogen bomb. It is the most powerful nuclear weapon ever detonated. Its test on October 30, 1961, remains the most powerful man-made explosion in human history. It was also referred to as Kuz'kina Mat' ( Russian: Кузькина мать , Kuzma's mother), referring to Nikita Khrushchev's promise to show the United States a "Kuz'kina Mat'" at the 1960 United Nations General Assembly. Developed by the Soviet Union, the bomb had a yield of 50 megaton TNT (210 PJ). In theory, the bomb had a maximum yield of 100 megatons, but because only one bomb was built, this theory was never demonstrated. The single bomb was detonated in the Novaya Zemlya archipelago at Sukhoy Nos.  
The remaining bomb casings are located at the Russian Atomic Weapon Museum, Sarov (Arzamas-16), and the Museum of Nuclear Weapons, All-Russian Research Institute of Technical Physics, Snezhinsk (Chelyabinsk-70). Neither of these casings has the same antenna configuration as the device that was tested.
Many names are attributed to the Tsar Bomba in the literature: Project 7000; product code 202 (Izdeliye 202); article designations RDS-220 (РДС-220), RDS-202 (РДС-202), RN202 (PH202), AN602 (AH602); codename Vanya ; nicknames Big Ivan , Kuz'kina Mat . The term Tsar Bomba was coined in an analogy with other massive Russian objects: the Tsar Kolokol (Tsar Bell), Tsar Tank and the Tsar Pushka (Tsar Cannon). The CIA designated the test as "JOE 111". 
The Tsar Bomba was a three-stage bomb with Trutnev-Babaev  second and third stage design,  with a yield of 50 megatons. This is equivalent to about 1,570 times the combined energy of the bombs that destroyed Hiroshima and Nagasaki, 10 times the combined energy of all the conventional explosives used in World War II, one quarter of the estimated yield of the 1883 eruption of Krakatoa, and 10% of the combined yield of all nuclear tests to date. A three-stage H-bomb uses a fission bomb primary to compress a thermonuclear secondary, as in most H-bombs, and then uses energy from the resulting explosion to compress a much larger additional thermonuclear stage. There is evidence that the Tsar Bomba had several third stages rather than a single very large one.
The initial three-stage design was capable of yielding approximately 100 Mt, but it would have caused too much nuclear fallout and the plane delivering the bomb would not have enough time to escape the explosion. To limit fallout, the third stage and possibly the second stage had a lead tamper instead of a uranium-238 fusion tamper (which greatly amplifies the reaction by fissioning uranium atoms with fast neutrons from the fusion reaction). This eliminated fast fission by the fusion-stage neutrons, so that approximately 97% of the total energy resulted from fusion alone (as such, it was one of the "cleanest" nuclear bombs ever created, generating a very low amount of fallout relative to its yield). There was a strong incentive for this modification since most of the fallout from a test of the bomb would have ended up on populated Soviet territory. 
The components were designed by a team of physicists headed by Academician Yulii Borisovich Khariton and including Andrei Sakharov, Victor Adamsky, Yuri Babayev, Yuri Smirnov, and Yuri Trutnev. Shortly after the Tsar Bomba was detonated, Sakharov began speaking out against nuclear weapons, which culminated in him becoming a dissident. 
The Tsar Bomba was flown to its test site by a specially modified Tu-95V release plane, flown by Major Andrei Durnovtsev. Taking off from an airfield in the Kola Peninsula, the release plane was accompanied by a Tu-16 observer plane that took air samples and filmed the test. Both aircraft were painted with a special reflective white paint to limit heat damage. Despite this effort, Durnovtsev and his crew were assigned only a 50% chance of surviving the test. 
The bomb, weighing 27 metric tons, was so large (8 metres (26 ft) long by 2 metres (6.6 ft) in diameter) that the Tu-95V had to have its bomb bay doors and fuselage fuel tanks removed. The bomb was attached to an 800 kilogram parachute, which gave the release and observer planes time to fly about 45 kilometres (28 mi) away from ground zero. When detonation occurred, the Tu-95V dropped one kilometer in the air because of the shock wave, but was able to land safely. 
The Tsar Bomba detonated at 11:32 (Moscow time) on October 30, 1961, over the Mityushikha Bay nuclear testing range (Sukhoy Nos Zone C), north of the Arctic Circle over the Novaya Zemlya archipelago in the Arctic Ocean. The bomb was dropped from an altitude of 10.5 kilometres (34,000 ft); it was designed to detonate at a height of 4 kilometres (13,000 ft) over the land surface (4.2 kilometres (14,000 ft) over sea level) by barometric sensors. 
The original, November 1961 AEC estimate of the yield was 55–60 Mt, but since 1992 all Russian sources have stated its yield as 50 Mt. Khrushchev warned in a filmed speech to the Supreme Soviet of the existence of a 100 Mt bomb. (Technically the design was capable of this yield.) Although simplistic fireball calculations predicted the fireball would hit the ground, the bomb's own shock wave reflected back and prevented this. The fireball reached nearly as high as the altitude of the release plane and was visible at almost 1,000 kilometres (620 mi) away from where it ascended. The mushroom cloud was about 64 kilometres (40 mi) high (over seven times the height of Mount Everest), which meant that the cloud was above the stratosphere and well inside the mesosphere when it peaked. The cap of the mushroom cloud had a peak width of 95 kilometres (59 mi) and its base was 40 kilometres (25 mi) wide.
All buildings in the village of Severny (both wooden and brick), located 55 kilometres (34 mi) from ground zero within the Sukhoy Nos test range, were destroyed. In districts hundreds of kilometers from ground zero wooden houses were destroyed, stone ones lost their roofs, windows and doors; and radio communications were interrupted for almost one hour. One participant in the test saw a bright flash through dark goggles and felt the effects of a thermal pulse even at a distance of 270 kilometres (170 mi). The heat from the explosion could have caused third-degree burns 100 km (62 mi) away from ground zero. A shock wave was observed in the air at Dikson settlement 700 kilometres (430 mi) away; windowpanes were partially broken to distances of 900 kilometres (560 mi).  Atmospheric focusing caused blast damage at even greater distances, breaking windows in Norway and Finland. The seismic shock created by the detonation was measurable even on its third passage around the Earth.  Its seismic body wave magnitude was about 5 to 5.25.
The Tsar Bomba is the single most physically powerful device ever used by mankind.  For comparison, the largest weapon ever produced by the United States, the now-decommissioned B41, had a predicted maximum yield of 25 megatonnes of TNT (100 PJ). The largest nuclear device ever tested by the United States ( Castle Bravo) yielded 15 megatonnes of TNT (63 PJ) because of an unexpectedly high involvement of lithium-7 in the fusion reaction; the preliminary prediction for the yield was from 4 to 6 megatonnes of TNT (17 to 25 PJ). The largest weapons deployed by the Soviet Union were also around 25 megatonnes of TNT (100 PJ), as in the SS-18 Mod. 3 ICBM warheads.
The weight and size of the Tsar Bomba limited the range and speed of the specially modified bomber carrying it and ruled out its delivery by an ICBM. Much of its high-yield destructiveness was inefficiently radiated upwards into space. It has been estimated that detonating the original 100 Mt design would have released fallout amounting to about 25 percent of all fallout emitted since the invention of nuclear weapons.  It was decided that a full 100 Mt detonation would create too great a risk of nuclear fallout, as well as a near certainty that the release plane (and crew) would be destroyed before it could escape the blast radius. 
- Footage from a Soviet documentary about the bomb is featured in Trinity and Beyond: The Atomic Bomb Movie (Visual Concept Entertainment, 1995), where it is referred to as the Russian monster bomb .  The video states that the Tsar Bomba project broke the voluntary moratorium on nuclear tests. In fact Soviets restarted their tests and broke the unilateral voluntary moratorium two months before Tsar Bomba , and since the moratorium was unilateral there was no multilateral legal obstacle. (Earlier, the U.S. had also declared a one-year unilateral moratorium on nuclear tests, and as that year had expired, the US had already announced that it considered itself free to resume testing without further notice; however, it had not yet resumed testing at the time of the Tsar Bomba test.) 
- A one-hour episode of the PBS documentary series Secrets of the Dead – "World's Biggest Bomb" (2011; Blink Films & WNET) – chronicles the events leading to the detonations of Castle Bravo and the Tsar Bomba .