|Fig. 1: Sukhoy Nos on Novaya Zemlya, the location of the nuclear test. (Adapted from Wikimedia Commons)|
The Tsar Bomb is the nickname for the AN602 hydrogen bomb, the most powerful nuclear weapon ever detonated. Its October 30, 1961 test remains the most powerful artificial explosion in human history.
On November 4, 1958 the USSR entered into a moratorium on nuclear testing with the United States and Britain. By that time, the USSR was in the military-technical terms behind in nuclear testing.  The United States at that time had fielded 196 nuclear tests and had created a powerful thermonuclear arsenal composed of 7,500 nuclear and thermonuclear charges (17.3 Gt). During the period of the moratorium in 1960, the number of warheads the U.S. nuclear arsenal increased to 18,600 (20.5 Gt). [1,4] United States in the mid-50s conducted a series of heavy-duty (5-15 Mt TE) tests of thermonuclear weapons, some of which were adopted. [1,5] It was a period of unconditional U.S. nuclear superiority, and in U.S. interests to "freeze" the situation. While the Soviet Union had already created "article 49" and several other thermonuclear weapons, necessary replication thermonuclear charges in various dimensions and weight categories had not yet been achieved.
Moreover, USSR lagged significantly behind in the number of vehicles for nuclear weapons and nuclear warheads. The available submarines, heavy bombers and long-range missiles were not efficient for delivering of nuclear weapons from the USSR to the USA.  It was thought that creation of a super-bomb would allow overcoming the above-mentioned problem and help achieve parity in nuclear power between the US and USSR.
Due to deteriorating Soviet-American relations, the September 1, 1961 moratorium on nuclear testing was interrupted, and a period of development of a new generation of thermonuclear weapons was begun in the USSR. During this short period (16 months), 138 nuclear tests were conducted, one of of which was AN602. [1,5]
On July 10, 1961, project AN602 was begun with the following scientists in charge: Y. Khariton, A. Sakharov, V. Adamsky, Y. Babayev, Y. Smirnov and Y. Trutnev.  It grew out of Project-202, a 1956 effort to develop a 38 Mt nuclear bomb. However, Project-202 was never constructed and tested.  So, the AN602 was not created in few months as sometimes claimed, but rather used many ideas developed in previous research.  For example, the original parachute system used for the project RDS-202 was later used for AN602 (and also Gagarin's space trip). [2,4] The hull of AN602 was a slightly modernized version of RDS-202. Even the delivery plane Tu-95V initially was modernized for RDS-202 delivery. 
The Tsar Bomb was a hydrogen bomb with a three-stage Teller-Ulam design.  This design could have yielded 100 Mt, but that would have produced too much radioactive fallout, very likely killing the crew of the delivery plane.  Uranium-238 was replaced by lead tamper in the third stage, which reducee the power to 50 Mt and slightly lightened the overall mass of the bomb. 
|Fig. 2: Comparison of nuclear blast radii. Data taken from Greshilov et al., and Ryabev et al. [1,6]|
The explosion took place at 11:32 on October, 30 1961 in the Sukhoy Nos area (see Fig. 1). [1,5] Two planes were used: one bomber carriage (crew - 9 people) and one laboratory plane (crew - 5 people).  It took 189 seconds for the bomb to land and explode, allowing both planes to be 40 km away from the explosion center. The development of the mushroom cloud lasted 40 minutes. The upper bound of the explosion cloud reached a height of 30 km in 45 sec. 35 minutes after the explosion, the cloud was two-level structure with a diameter of 95 km (outer level) and 70 km (inner level). The mushroom cloud retained its shape for very long time and could be seen at a distance of 800 km. Air waves circled the globe three times. [3,4] According to measurements, contamination from the resulting explosion presented little danger to trial participants, residents of areas adjacent to the landfill, or fishing areas. Testing of such a powerful bomb with a relatively low impact on the environment was a technological breakthrough at the time. 
The main purpose of this test was to demonstrate ownership by the Soviet Union of the unlimited power of weapons of mass destruction. The TNT equivalent of the most powerful thermonuclear bomb of the number tested by the time the United States was almost four times less than the AN602 (see Fig. 2). [1,4] The documentary video of the explosion was used as a convincing diplomacy negotiation tool between the USSR and other small nations.  An extremely important scientific result was the experimental verification of the principles of calculation and multi-stage thermonuclear charge design. One possible way of applying these superpower nuclear warheads proposed by Sakharov was never accepted by Khrushchev: The idea was to surround U.S. maritime borders by several dozen nuclear warheads with duty capacity of 200-500 Mt to prevent an arms race.  While many other powerful and very accurate bombs were developed afterwards, the Tsar Bomb still reminds how powerful and destructive a nuclear weapon ever made.
© Ruslan Iskhakov. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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