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Pluto & the Kuiper Belt

Astronomy is a scientific field in a constant state of change as we learn more about the universe around us. New discoveries frequently challenge old beliefs and force us to revise theories about space and our local solar system. One of the ideas that has recently become a subject of intense debate is the status of Pluto. Pluto was first discovered by an American astronomer named Clyde Tombaugh in 1930. The search for this world had begun at least two decades earlier when several astronomers speculated that discrepancies in the orbits of the large planets Uranus and Neptune must be caused by an additional large planet in the outer solar system.

The greatest advocate of the existence of this ninth planet was American astronomer Percival Lowell who searched for the so-called "Planet X" until his death in 1916. Lowell as well as the astronomers William Pickering and Venkatesh Ketakar had each made calculations predicting where this undiscovered planet might be. Although Clyde Tombaugh discovered Pluto very close to the location the earlier astronomers had predicted, the new object was far too small to account for any of the presumed anomalies in the orbits of Uranus and Neptune. In fact, these discrepancies turned out to be non-existent and were only the result of errors made in estimating the mass of each of these large worlds. It was pure coincidence that the predictions of Lowell and his colleagues happened to come close to where tiny Pluto was ultimately found.

View of Pluto taken by NASA

Since Tombaugh and other astronomers were actively searching for a new planet at the time Pluto was discovered, they naturally assumed the new object was indeed a planet and never questioned whether it might be otherwise. As more was learned about this distant planet, however, it became clear the world was an anomaly. The four inner planets of the solar system are all relatively small with a similar rocky composition while the next four planets are massive gas giants. Pluto, by comparison, is a tiny world smaller than any other planet and consists largely of ice.

Pluto also follows a very unusual orbit compared to the other planets of the solar system. All planets orbit the Sun in an elliptical path that is slightly elongated from a true circle. This elongation from a perfect circle is referred to as eccentricity. The more elliptical an orbit is, the greater its eccentricity. The eccentricity of the orbits of most of the planets is generally quite small. Pluto's orbit is so eccentric that it actually crosses that of Neptune, making Neptune the furthest planet from the Sun for about 20 Earth years. The orbits of most of the planets also lie within the same ecliptic plane. Pluto, on the other hand, is inclined over 17° away from this plane.

Comparison between the orbits of Pluto and Neptune

Despite these unusual characteristics, Pluto appeared to be a unique object and astronomers accepted it as a planet for decades. That assumption remained unchallenged until 1992 when astronomers began discovering additional large objects beyond the orbit of Neptune. Now called Trans-Neptunian Objects (TNO), astronomers have discovered hundreds of bodies in this region of the solar system. Many of these objects are icy bodies comparable in size and orbital characteristics to Pluto. Some are even called "Plutinos" because they are so similar to the planet. The discovery of so many of these objects caused the astronomy community to begin questioning whether Pluto still deserves to be considered a planet and also raised the larger question of how a planet should be defined in the first place.

The question of Pluto's status is not the first time this type of debate has erupted in the scientific world. Perhaps the most famous example began in the 1500s when Nicolaus Copernicus challenged the belief that Earth was at the center of the universe and proposed Earth was instead a planet orbiting the Sun. That battle caused a reevaluation of the very foundations of what we now call astronomy. The science of astronomy dates back to the earliest civilizations on Earth. Many of the ideas about our solar system that dominated early astronomy came from the ancient Greeks. Indeed, the English word planet is derived from the Greek word planetes that means "wanderer." This term originated because the points of light created by the planets appear to move, or wander, across the night sky when viewed from Earth. These wandering lights were clearly different from the fixed points of light we now know to be distant stars. The objects that were considered to be planets included not only the five planets known at the time--Mercury, Venus, Mars, Jupiter and Saturn--but also the Sun and the Moon. It was the existence of these seven heavenly bodies that had a profound influence on the religious beliefs and customs of the earliest human civilizations.

As we learned more about the structure of the solar system, these ideas gradually changed. A major revision came with the acceptance that the Sun was at the center of the solar system rather than the Earth. This belief resulted in a reclassification of objects in the solar system once it was realized that the Sun is a star and the Earth a planet orbiting around it. Further clarification came in the 1600s with the discovery of moons around Jupiter and Saturn. While these bodies were originally considered planets, just as our own Moon still was, it was eventually accepted that these worlds should be reclassified as moons in orbit around their parent planets and that only bodies in orbit around the Sun should be called planets.

Main asteroid belt between Mars and Jupiter

Still more evolution in our understanding of the heavens came with the discovery of the asteroid belt between Mars and Jupiter. The first of these objects to be discovered was Ceres found in 1801. Like the moons of Jupiter and Saturn, Ceres was also hailed as a new planet upon its discovery. Still more of these objects in nearly the same orbit were to be found over the following decades. By the mid-1800s, four of these bodies were counted as planets while the discovery of a dozen more had prompted debate over the status of such objects. The famous British astronomer William Herschel first suggested these objects be renamed as asteroids, meaning "starlike," during the 1810s, but it was not until the 1860s that astronomers finally demoted the asteroids Ceres, Pallas, Juno, and Vesta from the ranks of planets. Today, objects like asteroids are often referred to as minor planets to distinguish them from the major planets like Jupiter and Earth. While minor planets orbit the Sun, they are too small to meet the modern definition of a true planet.

The same debate that once centered on whether asteroids should be considered as planets is now focused on Pluto and the Trans-Neptunian Objects. To confuse matters even further, TNOs consist of three different types of objects differentiated by their distance from the Sun. Closest to the Sun are objects in the Kuiper Belt. This region extends from the orbit of Neptune at 30 astronomical units (AU) to 50 AU, slightly beyond the furthest point in Pluto's orbit. The Kuiper Belt is home to many small icy objects including short-period comets like Halley's Comet.

Hypothetical structure of Trans-Neptunian space

Further out from the Sun is a region recently dubbed the Scattered Disk. While containing objects similar to those in the Kuiper Belt, the Scattered Disk extends outward much further and the bodies within it are in far more erratic orbits. Kuiper Belt objects tend to orbit in more circular paths relatively close to the ecliptic plane while those in the Scattered Disk are often far more eccentric and inclined from the ecliptic. Astronomers speculate objects in the Scattered Disk formed within the Kuiper Belt but were thrown outward into their unusual orbits by interactions with the gas giants. Beyond the Scattered Disk at the edge of the Trans-Neptunian region, astronomers speculate that an enormous spherical cloud of icy comets may exist between 50,000 and 100,000 AU from the Sun. Known as the Oort Cloud, this region of space may contain millions or billions of icy objects. Collisions between them or external disturbances occasionally cause some of these objects to fall inward toward the Sun to create comets.

It is this new understanding of the outer regions of the solar system that has forced astronomers to once again reconsider the definition of a planet. Pluto falls within the Kuiper Belt, and the discovery of several similar objects within the same region of space raises the question of whether they should be considered as major or minor planets. Among these new objects are Quaoar that is about one-third the size of Pluto, Orcus with an orbit very similar to Pluto's but at a different inclination, and Sedna that may be two-thirds the size of Pluto but has an extremely eccentric orbit. The debate was most recently brought to a head in 2005 when astronomers announced the discovery of a Trans-Neptunian Object even larger than Pluto. Originally called 2003 UB₃₁₃ but later renamed Eris, this object lies in a very eccentric and highly inclined orbit that extends from inside the orbit of Neptune out into the Scattered Disk. Given its size and that it has at least one moon in orbit, the discoverers of this object have claimed it should be considered the tenth planet of the solar system.

Size comparison of Earth, Pluto, and several Trans-Neptunian Objects

Other astronomers disagree since the orbit of Eris is far too unusual compared to the traditional planets. The International Astronomical Union (IAU) has instead classified Trans-Neptunian Objects as minor planets since they do orbit the Sun but are too small, often unusually shaped, and follow orbital paths too erratic to be considered major planets. That decision brings into question whether Pluto should still be considered a major planet or be demoted to a minor planet as several asteroids like Ceres had been before. Several observatories have taken matters upon themselves and decided to demote Pluto from the ranks of planets.

The IAU has so far voted to retain Pluto as a planet, doing so most recently in 1999. The same does not hold for Eris since the international organization has classified this world as a minor planet. The reason Pluto still holds its status as a planet while other Trans-Neptunian Objects have not been so honored is primarily one of tradition. Pluto has been accepted as a planet for over 70 years and the general public has been reluctant to accept its demotion. Opponents instead argue that Pluto no longer meets our modern standards of a planet just like Ceres and other asteroids ceased to be classified as planets after the 1860s. Further bolstering their position is the fact that if Pluto were to be discovered today, it would just be considered another Kuiper Belt Object and not a planet.

Comparison of orbital distance and inclination of several objects in the outer solar system

To help avoid future confusion over this issue and settle the question once and for all, the IAU is currently attempting to decide upon an official definition of a planet. If successful, it is hoped that this definition can be used to classify future discoveries within our own solar system as well as those around distant stars far from Earth. The topic is due to be voted upon at the IAU General Assembly meeting in Prague during August 2006.

More information on this exciting area of solar system research can be found in the books Beyond Pluto by John Davies and The New Solar System.
- answer by Justine Whitman, 16 April 2006

What are the colors of the planets?

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Names of the Planets

What were the ancient Greek names for the original nine planets?
- question from RoyLee Hall

As we previously described in an article about the days of the week, the names of the planets that we still use today are derived from the names given to these celestial bodies by ancient civilizations. However, I should point out that the ancients were only aware of the Sun, Moon, and the five planets closest to Earth. The outer planets were not discovered until relatively recently after the invention of the telescope, and these were named by the astronomers who discovered them.

NASA photos of the planets and the Moon

Uranus was discovered by the British astronomer William Herschel in 1781. Herschel originally planned to name the new planet Georgium Sidus, Latin for "George's Star" in honor of King George III. Luckily, fellow astronomer Johann Bode convinced Herschel to follow the tradition of naming planets in honor of mythological gods. The name Herschel chose was Uranus, the Roman god of the heavens who was the father of Saturn and the grandfather of Jupiter. The equivalent of Uranus in Greek mythology is Ouranos.

The next planetary discovery was perhaps one of the greatest accomplishments in the history of astronomy. After studying the orbit of Uranus during the late 1700s and early 1800s, discrepancies were noted between the location of the planet predicted by Kepler's laws of orbital motion and the actual position of the planet. Several astronomers concluded that there must be another large planet whose gravitational attraction was perturbing Uranus from its proper orbit. Englishman John Adams and Urbain Leverrier of France were both mathematicians who independently solved for the location of this hypothetical planet in 1845 and 1846. Shortly thereafter, German astronomer Johann Galle observed a new planet located almost exactly where it was predicted to be. The planet was given the name Neptune after the Roman god of the sea. Neptune's counterpart in Greek mythology is Poseidon.

Astronomers of the late 1800s also believed that yet another planet must exist beyond Neptune to account for additional discrepancies in the orbit of Uranus. One of the greatest advocates of this belief was American astronomer Percival Lowell. Lowell carefully calculated a position for this planet and searched for it until his death in 1916. Unfortunately, Lowell's position placed the body in the same region of the sky as the Milky Way. This region is densely packed with stars making it difficult to detect the motion of a distant object against the brightly-lit background. It wasn't until 1930 that American astronomer Clyde Tombaugh finally confirmed Lowell's calculations when he discovered an object very close to the predicted position. Ironically, the presumed perturbations in the orbit of Uranus that led to its discovery later proved to be non-existent, but the discovery of this tiny world was still a remarkable achievement. Though it is no longer considered a true planet, the object was named Pluto for the Roman god of the underworld. The Greek god of the underworld had been called Hades.

That brings us back to the inner planets, the motions of which had been observed by ancient peoples since long before the dawn of recorded history. The names of the planets Mercury, Venus, Mars, Jupiter, and Saturn as well as the Sun and the Moon (which the ancients believed were planets as well) are derived from Latin names given to these bodies by the Romans. These names were simply substitutions of Roman gods in place of names given by the earlier Greeks. It is believed that the names given by the Greeks were also inspired by even earlier civilizations going back to the ancient Sumerians. The Sumerians were the earliest civilization in recorded history, dating back to about 3500 BC. Much of the knowledge and many of the practices of the Sumerians were passed down through the Babylonians, the Assyrians, the Hittites, the Phoenicians, the Greeks, and the Romans to modern Western civilization. The naming of the planets after mythological gods is only one of the many Sumerian traditions that we still use today.

While the exact names of some of the early gods for which the planets were named have become a bit sketchy with time, the following table compares how those names are believed to have evolved over the course of history.

Names of the Planets
Mythological Origin	Sumerian	Babylonian	Phoenician	Greek	Latin	English
goddess of the earth	Ki or Ninhursag	Aruru	Athirat	Gaea	Terra	Earth
god or goddess of the moon	Nanna	Sin	Yarikh	Selenê	Luna	Moon
god of knowledge or communication	Enki	Ea or Nabû	Taaut	Hermes	Mercurius	Mercury
goddess of love	Inanna	Ishtar	Astarte	Aphroditê	Venus	Venus
god of the sun	Utu	Shamash	Shamash	Helios	Sôl	Sun
god of death or war	Gugalanna	Nergal	Resheph	Ares	Mars	Mars
supreme god, god of the sky and storms	Enlil	Marduk	Hadad or Ba'al	Zeus	Iuppiter	Jupiter
god of harvests or agriculture	Ninurta	Ninurta	El	Kronos	Saturnus	Saturn

When compared in this form, the progression from ancient beliefs to the modern day becomes quite clear. Indeed, it is extraordinary to realize that the names of the planets we still use in our modern age can be directly traced back to the religious practices of the earliest civilizations over 5,000 years ago. Furthermore, there is evidence that the design of the Jewish religious symbol called the menorah, with its seven branches, was inspired by these seven celestial objects.
- answer by Molly Swanson, 11 April 2004

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Broken Arrow Nuclear Weapon

Accidents

Has the United States or any other country ever had a plane carrying a nuclear bomb crash? Has a nuclear weapon ever been lost?
- question from Sandy Joulkowski

Accidents involving nuclear weapons have occurred almost since such devices were first developed, and these events were a common occurrence during the Cold War. However, the US and other countries possessing nuclear arms developed various safety systems to prevent accidental thermonuclear reactions within these weapons even under the most extreme circumstances in order to avoid potential catastrophes. Even so, non-thermonuclear detonations of the conventional high explosives carried within nuclear weapons still pose a serious threat since they can spread dangerous radioactive contamination much like a so-called "dirty bomb." This scenario has occurred several times during aircraft accidents when high speed impacts or burning fuel caused the high explosive charges on nuclear weapons to ignite.

At least three dozen serious accidents and incidents involving atomic or nuclear weapons have occurred since 1950. Many of these cases cost the lives of military personnel, led to the release of radioactive material, or resulted in the loss of the weapon itself. Most of these weapons fell into the ocean where the nuclear material could not be recovered given the limits of current technology. It is estimated that over 50 nuclear warheads have been lost in the world's oceans following aircraft or naval accidents. Another 26 nuclear reactors from ships and submarines have also been lost or deliberately dumped at sea.

Bow section of the sunken USS Scorpion containing two nuclear torpedoes on the sea floor

Before explaining these accidents in greater detail, it is helpful to explain how a nuclear accident or incident is defined. The US Department of Defense has adopted the following definitions.

Nuclear Weapon Accident: An unexpected event involving nuclear weapons or nuclear weapons components that results in any of the following.

Accidental or unauthorized launching, firing, or use, by US or allied forces, of a nuclear-capable weapon system that could create the risk of an outbreak of war

Nuclear detonation, non-nuclear detonation or burning of a nuclear weapon or radioactive weapon component, including a fully assembled nuclear weapon, an unassembled nuclear weapon, or radioactive nuclear weapon components

Radioactive contamination

Seizure, theft, or loss of a nuclear weapon component, including jettisoning

Public hazard whether it be actual or implied

Nuclear Weapon Incident: An unexpected event involving a nuclear weapon, facility, or component, resulting in any of the following, but not constituting a nuclear weapon accident.

An increase in possibility of explosion or radioactive contamination

Errors committed in the assembly, testing, loading or transportation of equipment, and or the malfunctioning of equipment and material that could lead to an unintentional operation of all or part of the weapon arming and/or firing sequence, or that could lead to a substantial change in yield, or increased dud probability

Any act of God, unfavorable environment, or conditions resulting in damage to the weapon, facility or component

In addition to these DOD definitions, the US Navy also devised further definitions for types of nuclear weapon accidents and incidents. These subdivisions help to clarify the severity of the event.

Nucflash: Any accidental or unauthorized incident involving a possible detonation of a nuclear weapon by US forces that could create the risk of nuclear war.

Broken Arrow: The accidental or unauthorized detonation, or possible detonation of a nuclear weapon (other than war risk) including the non-nuclear detonation or burning of a nuclear weapon; radioactive contamination; or seizure, theft, or loss of a nuclear weapon or component (including jettisoning).

Bent Spear: Any nuclear weapon significant incidents other than accidents or war risk detonations.

Dull Sword: Any nuclear weapon incident other than significant incidents.

Faded Giant: Any nuclear reactor or radiological accidents involving equipment used in connection with naval nuclear reactors or other naval nuclear energy devices while such equipment is under the custody of the Navy.

Thankfully, no Nucflash accident has ever occurred due to the safeguards designed into American nuclear weapons. Several Broken Arrow cases have occurred, however, during which nuclear weapons have been lost. These events are described in greater detail below. Note that this list includes mostly American accidents since Russia has always been more secretive about its failures and only acknowledges those that can no longer be kept from the public. Other countries that maintain stockpiles of nuclear arms include the United Kingdom, France, China, Israel, India, Pakistan, and North Korea. None of these nations have ever released details of any accidents involving nuclear weapons.

Mk 4 atomic bomb like that lost in 1950

13 February 1950: While flying a simulated combat mission from Eielson Air Force Base in Alaska to Carswell AFB in Texas, a B-36 Peacemaker bomber experienced engine problems. The aircraft was carrying a single Mk 4 atomic bomb containing depleted uranium but the plutonium core required for a fission reaction had been removed. Ice buildup on the carburetors forced the pilot to shut down three engines and reduced the power output of the remaining three. As weather conditions continued to worsen, the crew decided to abandon the aircraft. The unarmed bomb was jettisoned over the Pacific Ocean and its conventional explosives either detonated in mid-air or upon impact with the water. The plane then turned over a nearby island where the crew bailed out. Twelve were rescued from the frigid conditions but five were never found. The B-36 apparently continued on autopilot for a considerable distance before crashing in northern British Columbia. The wreck was later located and studied to confirm that no nuclear material remained aboard.

11 April 1950: All thirteen crewmembers aboard an American B-29 Superfortress were killed when their plane crashed near Kirtland AFB in New Mexico shortly after takeoff. The bomber had been carrying an atomic bomb with its nuclear core stored separately and four spare detonators. The impact of the crash and a massive fire destroyed the outer casing of the bomb, and its high explosives detonated when exposed to burning fuel. Since the weapon was partially disassembled for safety, there was no chance of an atomic explosion. All nuclear components were recovered from the accident scene intact and no radiation leak was detected.

13 July 1950: A B-50 Superfortress from Biggs AFB in Texas was on a training flight when the bomber pitched nose down and crashed near Lebanon, Ohio. All sixteen crew were killed. The conventional high explosives of an onboard atomic weapon detonated on impact, but the plane carried no nuclear capsule.

5 August 1950: A US Air Force B-29 carrying an unarmed atomic bomb with no fissile core was taking off from Fairfield-Suisun AFB in California when the bomber experienced several malfunctions. While attempting an emergency landing, the plane crashed and burst into flames. The fire set off the bomb's high explosives killing 19 crewmembers and rescue personnel. Among the fatalities was Brigadier General Robert Travis, and the base was later renamed in his honor.

10 November 1950: A B-50 Superfortress was ferrying a Mk 4 atomic weapon from Canada to a base in the United States when it suffered engine trouble. Fearing they could not make an emergency landing while carrying the heavy weapon, the crew jettisoned the bomb over the St. Lawrence River off the shore of Quebec. The weapon was set to self-destruct and detonated in mid-air. A plutonium core was not installed but the explosion scattered some 100 lb (45 kg) of depleted uranium across the river below.

10 March 1956: A B-47 Stratojet of the US Air Force disappeared while carrying the cores of two nuclear weapons in special transport cases. The aircraft was on a non-stop flight eastward from MacDill Air Force Base in Florida to an overseas base. Two in-flight refuelings were scheduled along the way. While the first was completed successfully, the B-47 never reached the second tanker over the Mediterranean Sea. The plane presumably went down somewhere over the Mediterranean but no trace of the plane, its crew, or its nuclear payload was ever found despite an extensive search.

B-47 Stratojet strategic bomber

27 June 1956: An accident occurred at the NATO air base at Lakenheath, England, when an American B-47 bomber skidded off the runway and crashed into a storage igloo. The facility contained three Mk 6 atomic bombs but no nuclear cores. The weapons were quickly engulfed in flames by burning jet fuel from the exploding B-47, but firefighters were able to extinguish the conflagration quickly. A bomb disposal expert on the scene concluded it was, "...a miracle that one Mark six with exposed detonators sheared didn't go."

27 May 1957: An Air Force B-36 bomber was ferrying a weapon from Texas to New Mexico when the bomb broke loose and tore the bomb bay doors off the plane as it fell. Although a retarding parachute deployed, it had little effect because of the plane's low altitude at the time of the release. The bomb's conventional explosives detonated as it impacted on the grounds of Kirtland Air Force Base. The blast completely destroyed the bomb leaving a large crater and scattering debris over a wide area. The weapon's nuclear capsule was aboard the plane but was carried separately eliminating the possibility of a nuclear detonation. Low levels of radioactivity were detected but were contained completely within the impact crater.

28 July 1957: A C-124 Globemaster II cargo plane of the US Air Force left Dover AFB in Delaware transporting three nuclear weapons and one fissile core stored separately. Shortly into the flight, the plane lost power to two engines. The crew determined the plane could not maintain flight with the weight of the cargo and decided to jettison two of the weapons overboard. The weapons sank off the coast of New Jersey and were never located. The C-124 was able to make an emergency landing near Atlantic City with the remaining weapon and nuclear capsule.

11 October 1957: A B-47 had just taken off from Homestead AFB in Florida when one of its outrigger tires exploded. The plane crashed and fire engulfed an atomic weapon and its nuclear core stored in a separate case. The fire smoldered for about four hours during which two low order detonations of the conventional explosives were observed. Much of the weapon had been destroyed but the nuclear capsule was recovered intact with no radiation released.

31 January 1958: The first accident involving a fully operational armed nuclear weapon occurred at a base in Morocco. A B-47 was conducting a simulated takeoff when one of its landing gear wheels failed and the plane's tail struck the ground. The impact ruptured one of the bomber's fuel tanks causing a fire. The onboard bomb was damaged but did not detonate after lying in a smoldering fire for seven hours. Some radioactive contamination was detected in the immediate vicinity but was cleaned.

5 February 1958: An Air Force B-47 Stratojet from Homestead AFB was on a simulated combat mission when the plane collided with an F-86 Sabre near Savannah, Georgia. The B-47 was carrying one Mk 15 hydrogen bomb without its core at the time of the accident. The plane made three unsuccessful landing attempts at Hunter Air Force Base before the weapon was jettisoned over the Atlantic Ocean to avoid the risk of a high explosive detonation at the base. The bomb was dropped several miles from the mouth of the Savannah River in Wassaw Sound off Tybee Island. Though an intensive nine-week search was launched using divers and sonar equipment, the weapon was never found. Another unsuccessful search was mounted in 2001, and reports of radiation detected less than a mile from shore led to speculation of the bomb's discovery in 2004. Further investigation concluded the radioactivity was naturally occurring and the weapon remains missing.

Mk 15 hydrogen bomb

11 March 1958: A B-47E carrying an unarmed atomic weapon without a fissile core departed Savannah, Georgia, on a routine training flight. While flying over Florence, South Carolina, the bomb lock failed and the warhead fell onto a house in the suburban neighborhood below. The impact set off the conventional explosives causing several injuries on the ground.

4 November 1958: While taking off from Dyess AFB in Texas, a B-47 bomber of the US Air Force caught fire. The three crew ejected, although one was killed, and the plane crashed while carrying one atomic weapon. The conventional explosives were set off by the crash creating a large crater, but all nuclear components were recovered.

26 November 1958: A B-47 Stratojet caught fire while on the ground at Chennault AFB in Louisiana. The conflagration destroyed an onboard weapon releasing some radioactive contamination in the immediate vicinity of the wreckage.

18 January 1959: An American F-100 Super Sabre was on the ground conducting a practice alert at an unidentified base in the Pacific. The aircraft was carrying three external fuel tanks and a nuclear weapon without a nuclear capsule. As the starter button was depressed, the external fuel tanks were accidentally jettisoned causing an explosion. The fire was put out quickly and no contamination was detected.

6 July 1959: While taking off from Barksdale AFB in Louisiana, a C-124 transport carrying one nuclear weapon crashed. The resulting fire destroyed the weapon but safety devices prevented any nuclear or conventional explosions. A small amount of radioactive contamination was found directly beneath the weapon.

25 September 1959: A P-5M Marlin patrol aircraft of the US Navy was conducting a mission off Whidbey Island, Washington, while carrying one unarmed nuclear depth charge without its fissile core. The aircraft crashed into Puget Sound and the weapon was never recovered.

12 October 1959: An American B-52 Stratofortress had rendezvoused with a KC-135 Stratotanker near Hardinsberg, Kentucky. As the B-52 was being refueled, the two planes collided. Five of the bomber's nine crew and all four aboard the tanker were killed. The B-52 also carried two unarmed nuclear weapons that were recovered intact with little or no damage.

B-52 Stratofortress strategic bomber

7 June 1960: A BOMARC air defense missile in storage at McGuire Air Force Base in New Jersey was destroyed after a high-pressure helium tank burst. The blast ruptured the missile's fuel tanks and ignited a large fire. Although the warhead was also destroyed, its high explosives did not detonate and contamination was limited to a small area.

24 January 1961: An Air Force B-52 was carrying two 20-megaton Mk 39 hydrogen bombs while on airborne alert over North Carolina. While flying at an altitude of 10,000 ft (3,050 m), leaking fuel in the right wing caused a mid-air explosion and a major structural failure. The wreckage fell to Earth near Goldsboro killing three of eight crew, and the two weapons came free of the plane as it broke apart. One of the bombs deployed its parachute and landed with minimal damage. The second, however, struck the ground and broke apart spreading its components over a wide area. Reports suggest the weapon nearly detonated since five of its six safety devices failed and only a single switch prevented a catastrophe. The Air Force launched a massive search of the area and recovered the bomb's plutonium, but most of the thermonuclear stage including highly enriched uranium was never found. To prevent its accidental discovery at a later date, the service purchased and fenced off the property and monitors it regularly for radiation. The accident prompted the US to develop improved safeguards to prevent accidental nuclear detonations, and the Soviet Union was encouraged to do likewise.

14 March 1961: A failure of the pressurization system aboard a B-52 and lack of fuel forced the crew to abandon the bomber near Yuba City, California. Two nuclear weapons aboard the plane were torn loose when it struck the ground, but safeguards worked properly and prevented any detonation. No radioactive contamination was released.

4 June 1962: The United States attempted its first high-altitude atmospheric nuclear test by placing a nuclear device atop a Thor rocket. The rocket was launched from Johnston Atoll in the Pacific Ocean but the tracking system failed during flight and the rocket had to be destroyed. The rocket's nuclear payload is believed to have vaporized before reaching the ocean.

20 June 1962: A second attempt to detonate a nuclear weapon at high altitudes also failed when the Thor booster rocket shut down prematurely a minute after launch. The vehicle had to be destroyed at an altitude of about 35,000 ft (10,670 m) above Johnston Atoll. The nuclear device being tested also fell into the Pacific Ocean and was not recovered, but pieces of debris contaminated by plutonium were found around the island. Neither this nor the previous incident has been acknowledged by the US government.

Launch of a Thor booster rocket

10 April 1963: The USS Thresher (SSN-593) was an American nuclear-powered attack submarine. While on a test to its maximum diving depth, an accident occurred that caused the vessel to sink in the Atlantic Ocean about 220 miles (355 km) east of Cape Cod, Massachusetts. It is believed a pipe in the engine room ruptured under the great pressure at its depth causing the nuclear reactor to shut down. Without power, the Thresher had no ability to surface and continued diving until the increasing water pressure crushed the hull. It is not believed the submarine was carrying any nuclear weapons at the time of its sinking but the Thresher did take its reactor and 129 men to the ocean floor 8,400 ft (2,560 m) deep. Later investigation of the wreckage indicated the Thresher had been violently torn apart as it sank but the reactor compartment remained intact. The accident led to a major program to improve the quality of welding in submarine hulls that has been successful to this day.

13 November 1963: The US Atomic Energy Commission operated a facility in Medina, Texas, where obsolete nuclear weapons were disassembled. An explosion in a storage igloo at the site involved 123,000 lb (55,800 kg) of high explosive components causing minor injuries to three employees. Low levels of radioactive contamination from nuclear components stored in another part of the structure was detected.

13 January 1964: A B-52D bomber enroute from Massachusetts to Georgia crashed near Cumberland, Maryland, due to strong turbulence and structural failure. Only two of the five crewmembers survived. The plane was carrying two nuclear weapons in a ferry configuration, and these were recovered with minor damage.

21 April 1964: The United States had launched a Transit-5BN-3 nuclear-powered navigational satellite that failed to reach orbit and burned up over the Indian Ocean. The satellite's nuclear reactor partially burned during re-entry releasing small amounts of plutonium into the stratosphere. The remainder of the reactor fell into the ocean.

Maintaining a Minuteman missile in its silo

5 December 1964: During maintenance operations at a Minuteman I nuclear missile silo in South Dakota, a retrorocket below the Re-entry Vehicle (RV) fired and caused the RV to fall about 75 ft (20 m) to the silo floor. The RV's arming and fusing system was torn loose removing power, and safety devices prevented any possibility of detonation. Although the RV was damaged considerably by the fall, no radioactive contamination escaped.

8 December 1964: A B-58 Hustler bomber was taxiing into position for takeoff at what became Grissom AFB in Indiana when it slid off the runway and caught fire. The three crew ejected but one perished due to a hard impact of his escape capsule. Five nuclear weapons were aboard the plane and several were damaged in the fire. Contamination was released but confined to the immediate vicinity of the wreckage.

11 October 1965: Minor contamination occurred when a C-124 transport caught fire as it was being fueled at Wright-Patterson AFB in Ohio. The plane was carrying nuclear weapon components but no complete weapons. The contamination was removed by normal cleaning.

5 December 1965: The US Navy aircraft carrier USS Ticonderoga was returning from a Vietnam deployment to the naval base at Yokusuka, Japan. While cruising about 70 miles (110 km) from the Ryukyu Islands, an A-4E Skyhawk attack plane rolled over the side of the ship with its pilot aboard. The plane was carrying one B-43 thermonuclear bomb at the time. The plane, its pilot, and the bomb sank in water 16,000 ft (4,875 m) deep and could not be recovered. Because of the great pressure at that depth, some have expressed concern that the weapon might have imploded spreading radioactive material, but there is no evidence this occurred.

B-43 nuclear bomb

17 January 1966: One of the most embarrassing accidents in the history of nuclear weapons occurred when a B-52 Stratofortress carrying four B-28 thermonuclear bombs suffered a mid-air collision with a KC-135 tanker. The B-52 was on airborne alert and conducting a routine air refueling operation while returning to Seymour Johnson AFB in North Carolina. The bomber was attempting its third refueling over the village of Palomares, Spain, when the nozzle of the tanker's boom struck the plane. The boom ripped open the B-52 causing it to break into pieces while the KC-135's payload of jet fuel exploded, destroying the aircraft and killing its crew of seven. The debris of the two planes scattered over 100 square miles (260 sq km). One of the bomber's four weapons came down on land with minor damage while a second was lost in the ocean. This Broken Arrow was later recovered intact after one of the largest search and recovery operations ever mounted. The three month search required 33 ships and over 3,000 Navy personnel before the weapon was recovered. While these two weapons suffered little damage, the high explosive casing of the other two bombs detonated upon impacting land spreading low levels of radioactive contamination over Palomares and the surrounding countryside. Under pressure from the local inhabitants, the US spent enormous sums to transport 1,400 tons of contaminated soil and vegetation from Spain to the United States for storage.

Late 1966 or Early 1967: Although the exact date and details remain a mystery, the Soviet icebreaker Lenin suffered a nuclear reactor accident that killed several crew. The vessel had to be abandoned for over a year until radiation levels dropped low enough for repairs to be made. The ship's three reactors were removed and dumped into the Kara Sea. Two new reactors were installed and the ship again entered service in 1970.

21 January 1968: An American B-52 from Plattsburgh AFB in New York was on airborne alert in the Arctic Circle when a fire broke out in the navigator's compartment. As the plane approached Thule AFB in Greenland to attempt an emergency landing, it crashed about 7 miles (11 km) southwest of the runway while carrying four nuclear bombs. The B-52 burst into flames as it impacted causing the high explosive casing on at least one of the weapons to detonate. The blast spread radioactive plutonium from the bomb's inner core about 1,000 ft (305 m) to either side of the wreck. Due to the intensity of the fire, two of the four bombs fell through the melting ice and sank to the ocean floor. One of these Broken Arrows was not recovered until 1979, and the second weapon remains lost on the floor of Baffin Bay.

11 April 1968: The Soviet Golf II class diesel-powered ballistic missile submarine K-129 sank in over 16,000 ft (4,875 m) of water in the Pacific Ocean several hundred miles northwest of Hawaii. The entire crew of 98 was lost and the vessel sank with three ballistic nuclear missiles plus two nuclear torpedoes. The reason for the sinking is unknown but evidence suggests an explosion in the battery compartment or a missile tube. In one of the most amazing tales of the Cold War, America's Central Intelligence Agency launched "Project Jennifer" to recover the vessel and its nuclear weapons from the deep seabed. The CIA secretly funded the construction of a massive ship called the Glomar Explorer that was ostensibly built for undersea mining. In reality, the vessel carried an enormous crane designed to grapple the Soviet submarine and lift it to the surface for study. It is unknown how successful the effort was, but the US has admitted to recovering at least a portion of K-129.

Glomar Explorer while in service with the CIA

18 May 1968: An American attempt to launch the spacecraft Nimbus B-1 failed when the booster rocket had to be destroyed at an altitude of 18.5 miles (30 km). The satellite carried two radioisotope generators that fell into off the coast of California. The nuclear material was recovered intact from a depth of 330 ft (100 m) with no release of radioactivity.

21 May 1968: The attack submarine USS Scorpion (SSN-589) was returning to the United States following a three month deployment when the vessel sank in the Atlantic Ocean about 500 miles (805 km) southwest of the Azores. While details of the sinking remain a mystery, it is believed a battery within one of the submarine's torpedoes overheated and ignited. The subsequent fire caused one or more torpedo warheads to detonate and blasted open the torpedo loading hatch at the top of the forward compartment. A flood of water through this hatch sent the Scorpion over 10,000 ft (3,050 m) deep to the ocean floor. The vessel broke into two major sections as it sank with the forward hull containing the torpedo room and control spaces located some distance from the aft hull containing the reactor. The Scorpion was lost with its entire crew of 99, one nuclear reactor, and two nuclear-tipped torpedoes. The US Navy continues to monitor the wreck for signs of disturbance and environmental impact but no release of radioactive material has been detected to date.

24 May 1968: Soviet submarine K-27 was conducting sea trials when the reactor overheated and began spreading radiation through the vessel. The entire submarine was scuttled in the Kara Sea in 1981 with its reactor still aboard.

12 April 1970: The Soviet November class nuclear-powered attack submarine K-8 sank in the Bay of Biscay about 300 miles (480 km) northwest of Spain. The vessel suffered a fire that broke out in two aft compartments. The captain's order to abandon ship was countermanded and the submarine sank in heavy seas, taking the lives of 52 members of its crew. K-8 was powered by two nuclear reactors and possibly carried multiple nuclear torpedoes. Rumors suggest that shortly before the sinking, K-8 had lain tactical atomic torpedoes in the Bay of Naples for use as mines against the US fleet in case of war. The vessel was carrying 24 of these torpedoes and only four were found inside the sunken wreck. It is unknown whether the remainder still lie on the ocean floor near Italy or if the Soviets recovered them at a later date. Nevertheless, this tale is based largely on information from an Italian investigator named Mario Scaramella whose credibility has since become suspect. K-8 had also suffered an earlier reactor accident in 1960 that contaminated the vessel and injured several crewmen.

17 April 1970: As Apollo XIII returned to Earth following its aborted mission to the Moon, the crew jettisoned a radioisotope thermoelectric generator (RTG) that would have been left on the lunar surface had the landing been successful. The RTG, containing plutonium, survived re-entry and came to rest in the Tonga Trench at the bottom of the Pacific Ocean where it still remains.

8 September 1977: The Soviet submarine K-171, a Delta I class ballistic missile boat, accidentally jettisoned one of its missiles overboard into the Pacific Ocean near Kamchatka. Pressure had been building up in the missile launch tube causing the missile and its nuclear warhead to be ejected. Though initially classified as a Broken Arrow, the warhead was later located and recovered following an intense search.

1978: A Soviet barge named Nikel was transporting low and medium level radioactive waste products when it sank during a storm sometime in 1978. The vessel was lost approximately 20 miles northwest of Kolguyev Island in the Barents Sea and no recovery attempts were made.

24 January 1978: The Soviet ocean reconnaissance satellite Kosmos 954 fell into the atmosphere and burned up over Canada. The satellite was powered by a nuclear reactor, but the majority was apparently destroyed in re-entry. Only small radioactive pieces were recovered.

Titan II missile silo

19 September 1980: While conducting routine maintenance on a Titan II ballistic missile at a silo in Arkansas, a repairman dropped a heavy wrench that punctured a pressurized fuel tank. The fuel vapor later ignited killing one and injuring 21 more US Air Force personnel. The blast also threw the missile's re-entry vehicle out of the silo, but it was recovered intact with no leak of radiation.

7 February 1983: A Soviet nuclear-powered reconnaissance satellite called Kosmos 1402 re-entered the atmosphere and burned up over the southern Atlantic Ocean. It is unknown whether the reactor survived intact, but the remains fell into the ocean about 1,000 miles (1,600 km) east of Brazil.

24 June 1983: The Soviet submarine K-429, a Charlie-class nuclear-powered cruise missile submarine, sank in Savannaya Bay in the Bering Sea killing at least 16 of its 120 crew. The vessel has been ordered to conduct a submerged torpedo launch even though still undergoing maintenance. In the haste to put to sea, ventilation systems had not been properly sealed and ballast tank valves were left misaligned. As the submarine submerged in shallow waters for a test dive, the open ventilation system led to massive flooding in forward compartments. The captain attempted to resurface the vessel but was foiled by the faults in the ballast tank system. K-429 settled to the shallow seabed about 130 ft (40 m) down. Luckily, most of the crew was still alive and the vessel was equipped with escape capsules to reach the surface. Two crewmen volunteered to ascend into the frigid Arctic waters and swim ashore to summon help. Despite being arrested upon reaching the coast, the men were able to bring word of the sinking to naval commanders so a rescue attempt could be launched. With ships waiting above, the remainder of the crew used the escape capsules to ascend to the surface. The vessel was salvaged the following August recovering its single reactor and any nuclear weapons aboard. Though later returned to service, the vessel sank again at its moorings in September 1985 killing additional crewmen. K-429 was raised once more and finally removed from service.

6 October 1986: The Soviet Yankee I class nuclear-powered ballistic missile submarine K-219 was on patrol off the Atlantic coast of the US when a missile tube began leaking. The incoming water mixed with liquid rocket propellants that had dripped from the missile to create toxic gases. The buildup of gases resulted in an explosion. Four crewmen perished while fighting the fires and the rest were forced to evacuate because of the toxic fumes. As the submarine was being towed back to port, it sank 680 miles (1,095 km) north of Bermuda taking two nuclear reactors and 16 nuclear missiles to the bottom. Each missile carried two warheads each and it is believed the submarine also held two nuclear torpedoes for a total of 34 nuclear warheads.

K-219 on the surface missing a missile hatch cover following the explosion

20 August 1987: The Soviet Union lost a radioisotope thermoelectric generator into the Sea of Okhotsk following an "emergency disposal." The RTG was never located.

7 April 1989: K-278 Komsomolets was a Soviet Mike class nuclear-powered attack submarine. K-278 was submerged and returning to base when a fire broke out in the aft compartment. The fire spread forward along wires causing electrical short circuits that shut down the reactor. As the vessel began to lose buoyancy, the order was given to surface and abandon ship. Unfortunately, the ship sank off the northern coast of Norway killing 42 of the 69 crewmembers. The submarine carried one nuclear reactor and two torpedoes with nuclear warheads. Later exploration of the wreck revealed large cracks running the length of the hull, major blowout damage to the forward torpedo compartment, and possible damage to the reactor. As radiation levels in the area began to rise and fearing further contamination in these rich fishing waters, Russia made several attempts to hermetically seal K-278 in a jelly-like material. The effort was declared successful in 1996, and monitoring of the wreck since has measured no significant radiation leaks. Nevertheless, the seal is expected to degrade by 2025.

16 November 1996: Mars 96 was a Russian probe launched to study the planet Mars. Following an unsuccessful burn of a booster rocket stage, the spacecraft fell back into Earth's atmosphere over the Pacific Ocean. The remains of the vehicle, containing 18 radioisotope thermoelectric generators, landed off the coast of Chile.

8 August 1997: While flying over the Sea of Okhotsk off the coast of Sakhalin Island, a Russian helicopter was forced to jettison a radioisotope thermoelectric generator it had been transporting. The RTG was not located despite a search.

12 August 2000: The Russian submarine K-141 Kursk, a nuclear-powered cruise missile submarine of the Oscar II class, was participating in military exercises in the Barents Sea north of Russia when a massive explosion rocked the vessel. The blast ruptured the hull sending the Kursk into a terminal dive towards the sea floor 350 ft (105 m) down. Though 23 of the 118 crewmembers survived the initial sinking, attempts to rescue them failed. The men had perished from lack of oxygen and the vessel had completely flooded by the time divers were able to enter the wreck. Subsequent investigations concluded the sinking was caused by a fire in the torpedo room similar to the one that had sunk the USS Scorpion in 1968. A torpedo's propellants ignited creating a large fire that soon caused the warheads of other torpedoes to detonate. The massive explosion ripped the forward part of the submarine open and quickly flooded the forward compartments. Russia indicated that no nuclear weapons were aboard, and the nuclear reactors were recovered in 2001 when the wreck was raised.

30 August 2003: K-159 was an aging Russian November class submarine retired in 1989. The vessel had already suffered a radiation accident in 1965 that was never adequately repaired, and the submarine remained laid up with virtually no maintenance for fourteen years. The hull was in such poor condition that pontoons were welded on to keep K-159 afloat, but these too were in a poor state and had been made in the 1940s. During the 1990s, foreign nations joined together and donated funds to have 16 abandoned Russian submarines towed to a shipyard for disposal. As K-159 was being moved, the submarine encountered a storm that tore off some of the pontoons. The boat eventually sank in 780 ft (240 m) of water with the loss of nine crew. The sunken vessel still carries two nuclear reactors and 1,800 lb (800 kg) of spent fuel. No radiation leakage has been detected so far but plans exist to raise the wreck.

Wreckage of the Kursk after the submarine was raised

While the accidents described above are among the most serious ever experienced, many others not included here have also resulted in reactor accidents, loss of life, or the spread of radioactive materials. One such incident occurred aboard the Soviet submarine K-19 in 1961 and was later dramatized in the film K-19: The Widowmaker. If you'd like to learn more about the Glomar Explorer and the effort to recover the Soviet submarine K-129, check out the book Blind Man's Bluff by Sherry Sontag and Christopher Drew. A final recommendation about the Scorpion sinking is Stephen Johnson's Silent Steel: The Mysterious Death of the Nuclear Attack Sub USS Scorpion.
- answer by Jeff Scott, 2 April 2006

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F-35 JSF Weapon Carriage Capacity

Does the Joint Strike Fighter have an internal gun? What are the weapon loads? It does not seem to have as much internal space as the F-22.
- question from Nicholas

The primary purpose of the F-35 Joint Strike Fighter (JSF) is to fulfill the ground attack duties now performed by aircraft like the F-16 Fighting Falcon, F-18 Hornet, and AV-8B Harrier. In other words, the JSF is often referred to as a "bomb truck" that will attack ground targets once the skies have been cleared of any enemy fighter threat by dedicated air superiority fighters like the F-22 Raptor and F-15 Eagle.

The biggest driver behind the overall design of the JSF is affordability. The military needs to purchase a large quantity of this class of aircraft to complement larger and more capable planes like the F-22 and F-18E/F Super Hornet that are too expensive to buy in large quantities.

It is these two factors--its mission as a ground attack platform and the need for low cost--that largely dictate the size, layout, and weapons carriage capabilities of the F-35.

X-35 research plane and prototype for the F-35 JSF

Since the F-35 is primarily intended to be a replacement for the F-16, it is not surprising that the JSF is of roughly the same overall dimensions as the older craft. The F-22, by comparison, is much larger and comparable in size to the F-15 that it was designed to replace. The overall sizes of the F-16, F-22, and the conventional takeoff and landing (CTOL) version of the F-35 that will be purchased by the US Air Force are compared below.

Comparison of the F-16, F-35, and F-22

It is also not surprising that the weapons to be carried by both the F-35 and F-22 are comparable to those carried by the F-16 and F-15, respectively. Both the F-15 and F-22 were designed primarily for air-to-air combat and feature a corresponding weapons load of air-to-air missiles. As discussed in a previous question about the F-22 weapons carriage capacity, the aircraft is equipped with four internal bays. Two small side bays are designed for the short-range AIM-9M Sidewinder air-to-air missile while the two center bays were each sized around three medium-range AIM-120C AMRAAM missiles. The F-35, being a much smaller aircraft, has only two center bays. The location and size of these two bays, as well as six external wing pylons, can be seen in the following image. The diagram compares the weapons stations on the CTOL and largely identical short takeoff and landing (STOVL) variants of the JSF versus the carrier-based (CV) model that has a larger wing. Note that the bays of the F-35B STOVL variant were redesigned in late 2004 and are now 14 inches shorter, and perhaps reduced in width, compared to the F-35A CTOL model. This decision was made to reduce the weight of the F-35B in order to meet more important performance goals. Otherwise, the following diagram remains accurate.

General layout of weapons bays and external hardpoints on the JSF variants

Compared to the JSF, the F-22 Raptor is indeed larger in size and internal volume. Nevertheless, the F-22 suffers from one key limitation. Its center bays were designed around the AIM-120 AMRAAM that is only about 12 ft (3.65 m) in length and has a maximum fin span of about 1.5 ft (0.45 m). These dimensions are quite sufficient for the aircraft's primary role as an air superiority fighter. However, the end of the Cold War forced the Air Force to change priorities and give the F-22 a stronger ground attack capability. Unfortunately, most air-to-ground weapons are significantly longer, wider, taller, and heavier than the AIM-120, making it difficult to integrate such weapons into the F-22 bays. The only weapon that has been integrated so far is the GBU-32 JDAM, a GPS-guided bomb that is about 10 ft (3.05 m) in length and is based on the 1,000 lb (455 kg) Mk-83 general purpose bomb.

Most air-to-surface weapons are in the 2,000-lb (910 kg) class, however, but these weapons are usually around 12.5 to 14 ft (3.80 to 4.25 m) long and too large to fit within the F-22. Bearing these limitations in mind, JSF designers purposefully sized the two internal bays around these larger 2,000-lb class weapons. The two weapons that have predominantly dictated the overall length and depth of the bays are the AGM-154 JSOW and the GBU-31 2,000 lb (910 kg) version of JDAM.

F-35 weapons bay

Each bay contains two weapons stations, as shown above. Air-to-ground stores like JSOW and JDAM are carried on the outboard station. Air-to-air weapons can also be carried in this position but are carried primarily on the inboard station that is specifically dedicated to that purpose. One of the unique features of the design is that the air-to-air station swings out on a hinged rail as the inboard bay door opens.

The list of weapons that the JSF will carry when it enters service has not yet been finalized. However, it has been decided that all variants will be cleared to carry the same selection of weapons regardless of whether or not each user actually intends to arm its planes with that weapon. For example, the Navy CV variant will be cleared to carry the Wind Corrected Munitions Dispenser (WCMD) even though only the Air Force has that weapon in its inventory. Similarly, all US aircraft will be compatible with the ASRAAM air-to-air missile that only the United Kingdom plans to carry on its planes. The decision to clear all variants with the same weapon loads was made in order to simplify integration requirements, maintain commonality, and lower overall development costs. Note that the above statements are no longer entirely true since the bays of the F-35B STOVL version have been reduced in size as mentioned earlier. As a result, the F-35B is no longer compatible with JSOW and 2,000 lb JDAM weapons. The largest weapon this F-35 variant can carry internally is the GBU-32 1,000 lb version of JDAM. A list of the weapons that are currently planned for internal carriage on the F-35 is shown below.

F-35 internal weapons

Not included in this diagram are weapons in source selection as of this writing that are to be added to the internal carriage list. These weapons include the American GBU-39 Small Diameter Bomb, of which four can be carried on the air-to-ground station in each bay, and a new 500 lb laser guided bomb for the British (ultimately won by the Paveway IV). Another possible addition is a new variant of JDAM being considered by the US that will add a digital scene matching capability for improved accuracy.

The F-35 also has six external pylons, three under each wing. The inboard station is designed for up to 5,000 lb (2,265 kg) loads and will most likely be used to carry external fuel tanks. The pylon can carry 2000-lb class air-to-ground weapons as well. The midboard pylon is also primarily intended for air-to-ground weapons and can carry up to 2,500 lb (1,135 kg). The surface attack weapons compatible with these two pylons include many of the same ones carried internally as well as additional stores that are too large to fit in the bays. The outboard station on each wing, however, is a dedicated air-to-air station carrying up to 300 lb (135 kg) and designed specifically for short-range infrared guided missiles like AIM-9X Sidewinder. A list of weapons currently planned for external carriage is illustrated below. Note that training bombs have not been included in this list.

F-35 external weapons

You also ask about whether the aircraft has a gun, and the answer depends on what variant you ask about. The Air Force's CTOL model is the only version carrying an internal gun. The GAU-12 25-mm cannon is mounted above the engine inlet on the left side of the plane, as shown in the diagram below.

Internal gun carried by the F-35 CTOL variant

The Navy and Marines, meanwhile, have both opted for a specialized external gun pod on their CV and STOVL variants. The same GAU-12 cannon is carried, but in a special tear-drop pod that can be mounted on a dedicated centerline pylon between the aft portion of the weapons bays. The pod is unique in that it employs stealth characteristics and should allow the aircraft to maintain low observability. Other advantages of the gun pod include room for a larger ammunition supply and the ability to remove the pod on missions where a gun is not necessary.

Optional external gun pod that can be carried by the F-35 CV and STOVL variants

A number of sources indicate that the Mauser BK27 27-mm cannon will be carried on the F-35 instead of the GAU-12, but this information is inaccurate. The BK27 is commonly used on European fighters and was the leading candidate to be integrated aboard the JSF. Rights to manufacture the BK27 in the US had been sold to the Ordnance Division of Boeing, a division that is now part of Alliant Techsystems (ATK). The subcontract to develop a cannon for the F-35 became a competition between the BK27 offered by ATK and the GAU-12 manufactured by General Dynamics Armament and Technical Products (GDATP). The GAU-12 was eventually named the winner of the contract, but the decision is not without controversy as most observers feel the BK27 is the superior choice.

The information we gave gathered here is the latest available, but bear in mind that the Joint Strike Fighter design has not yet been finalized. The wish list of weapons that the various services originally asked to be put on the aircraft was enormous and would require tremendous time and cost to fulfill. As a result, the requirements are still under review, and the list has already been pared down significantly to focus on the most critically needed weapons.

Already eliminated from the list of internally carried stores are older unguided weapons like the Mk 82/83/84 general purpose bombs since it is very unlikely that the services would need to send the plane on a stealthy mission while carrying such archaic weapons. External stores that have been eliminated, or at least postponed, include the AGM-84 Harpoon and SLAM-ER, UK laser guided bombs, rocket pods, mines, and various data link, ECM and reconnaissance pods. Maverick and HARM may also be dropped because they do not currently comply with standard 1760 interface requirements.

Also note that production plans for the Joint Common Missile were cancelled in late 2004, and this weapon will no longer be carried by the F-35. Furthermore, the Navy has decided not to purchase JASSM, and it seems likely the Navy would want to integrate SLAM-ER onto the F-35 in its place.
- answer by Jeff Scott, 16 February 2004

Most people seem to be infatuated with the biggest or the fastest. I have the opposite question. What is the smallest plane in the world?

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Largest Plane in the World

I'm confused by the way the record for largest plane is determined. I read that the largest airliner in the world is the 747-400, and then I read it is the An-225. Similarly, I read that the plane with the largest wingspan is the Spruce Goose, and then I read about an airliner called the Bristol Brabazon with a wingspan larger than the 747! Could you please define the records, if any, that these aircraft hold with EXACT wording to the particular record?
- question from Jack

Aircraft records can indeed be confusing. If you need any reminder of that observation, try looking through the records on the FAI website. FAI, short for Fédération Aéronautique Internationale, is the international body that officially recognizes aviation and space records. However, most of the information on that site concerns aircraft performance, such as speed and altitude, rather than size.

Your question really comes down to how you decide to compare one plane to another. One of the measurements you mention is wingspan. While this dimension is often used to compare overall size, it is generally not the most accepted measure. Aircraft are usually ranked by weight, the maximum takeoff weight in particular. By this measure, the world's largest plane is the Antonov An-225 built in Ukraine when it was part of the Soviet Union.

An-225, largest plane in the world

The An-225 is quoted as having a maximum takeoff weight of over 1.3 million pounds (600,000 kg). The FAI gives credit for a slightly lower weight of 1.12 million pounds (508,200 kg), the record set by an An-225 in 1989 for the largest mass ever lifted by an airplane to an altitude of 6,500 ft (2,000 m). The An-225 was originally built to ferry the Soviet Buran space shuttle but it is now used to transport various outsize cargos. Only one example was ever completed, and it is currently available for charter flights through the British company Air Foyle. The An-225 is a cargo transport only and has never been used as an airliner.

If we continue to measure by maximum takeoff weight, the next largest plane in the world would be either the related An-124 transport or the Boeing 747 airliner. Both aircraft are quoted with a maximum weight around 900,000 lb (405,000 kg). The An-124 was also built by the Soviet Union as a large cargo plane for both military and civil use. The basic design was later enlarged and adapted to produce the An-225.

An-124

Over 50 examples of the An-124 were ultimately built, and many are now operated on charter flights through Air Foyle or other commercial firms. The American EP-3 reconnaissance plane that was forced to land after colliding with a Chinese fighter was actually transported back to the US aboard an An-124 chartered by the American government.

Boeing 747

The Boeing 747, meanwhile, is currently the world's largest commercial airliner and typically carries about 400 passengers on intercontinental flights. The 747 will not retain its title for long, however, since the new Airbus A380 will carry over550 passengers and have a takeoff weight over 1.23 million pounds (560,000 kg).

Airbus A380

Once it enters service, the A380 will become the world's largest airliner and at least the second largest plane. Additional stretched models are also planned, and one of these will almost surely supersede the An-225 to take the official title as world's largest plane.

Your question also mentions two other classic aircraft that were certainly enormous by any measure. Unfortunately, both proved to be disastrous follies that were great embarrassments to their proponents. The Spruce Goose, officially known as the Hughes H-4 Hercules, was the brainchild of flamboyant billionaire Howard Hughes. The aircraft had originally been ordered by the US government during World War II as a giant cargo plane ferrying up to 750 armed troops or two 30-ton tanks. As the war concluded, Hughes believed he could adapt the massive plane to revolutionize long-distance transportation in the fledgling airline and air cargo industires. His creation was the world's largest plane at the time and is still the largest flying boat ever built with a maximum takeoff weight of 400,000 lb (180,000 kg). The enormous craft also holds records for the largest wingspan at 319 ft 11 in (97.5 m), tallest airplane at 79 ft 3 3/8 in (24.2 m), and the largest aircraft ever made from wood.

Spruce Goose during its only flight

After pouring $7 million of his own money and another $18 million of government funds into the behemoth, Hughes only succeeded in making a single mile-long flight in 1947. The record-setting plane never flew again and is today a tourist attraction at the Evergreen Aviation Museum in Oregon.

Like the Spruce Goose, the Bristol Brabazon was another a government-sponsored effort intended to advance the state of the art in long-distance travel. The Brabazon was funded by the UK during the 1940s to develop a large airliner capable of non-stop flights between London and New York. Though smaller than the Spruce Goose, the Brabazon would have easily been the largest airliner of the day with a takeoff weight of 250,000 lb (115,000 kg) and a wingspan of 230 ft (70 m).

Bristol Brabazon compared to other planes of the day

If successful, the Brabazon offered the opportunity to challenge American manufacturers for dominance in the commercial aviation market. Unfortunately, the ambitious design failed to receive government certification following the discovery of fatigue cracks in the propeller mountings. While the problem was certainly correctable, the UK decided to cancel further funding in the early 1950s even though £3 million had already been invested. Only one prototype had been built, and it was broken up for scrap in late 1953 after flying only 400 hours. An improved prototype with structural enhancements and turboprop engines was also under construction, but it too was scrapped after the project was cancelled.

Relative size comparison of the Spruce Goose, An-225, A380, and 747

In summary, aircraft sizes are typically compared by weight rather than length or wingspan. The largest plane in the world at the current time is therefore the An-225, though the A380 will likely overtake it in the near future. The largest wingspan, however, still belongs to the Spruce Goose at nearly 320 feet. By this measure, the An-225 would be a distant second place at 290 ft, and the A380 falls short at 262 ft.
- answer by Molly Swanson, 8 August 2004

Additional Rankings:

Since this article was posted, we have received several messages from readers who believe the C-5 Galaxy transport operated by the US Air Force ranks second or third place and should be included. The C-5 was the world's largest plane when it was introduced in the late 1960s, but it has since been overtaken by the jet-powered aircraft discussed above.

C-5 Galaxy

The C-5 remained the world's largest plane until the introduction of the An-124, and the C-5 has since been surpassed by the An-225, enlarged models of the 747, and the new A380 as well. The current ranking of the world's largest aircraft by maximum takeoff weight (MTOW) is shown in the following table.

Rank	Aircraft	MTOW [lb]	Notes
1.	An-225 Mriya	1,300,000	-
2.	Airbus A380	1,230,000	-
3.	Boeing 747-400ER	910,000	the 747-8 under development will reach 960,000 lb
4.	An-124 Ruslan	892,870	-
5.	C-5 Galaxy	840,000	wartime only, peacetime TOW is limited to 769,000 lb
6.	Airbus A340-600 HGW	837,755	high-gross weight variant
7.	Boeing 777-300ER	775,000	highest available weight, loading restrictions apply

With a wingspan of 223 ft, the C-5 currently ranks sixth after the Spruce Goose (320 ft), An-225 (290 ft), A380 (262 ft), An-124 (240 ft), and a tie between the Brabazon and B-36 (230 ft). The C-5 has a larger span than the 747-400 (211 ft) but will soon be narrowly beaten by the new 747-8 variant with a wingspan of nearly 225 ft.
- answer by Greg Alexander, 11 November 2005