title: Qin (state)

text: During the reign of King Huiwen of Qin, the Chu state to the southeast became a target for Qin's aggression. Although Chu had the largest operation-ready army of all the Seven Warring States at over a million troops, its administrative and military strength was plagued by corruption and divided among the nobles. Zhang Yi, a Qin strategist, suggested to King Huiwen to exercise Qin's interest at the expense of Chu. Over the following years, Zhang engineered and executed a number of diplomatic plots against Chu, supported by the constant military raids on Chu's northwestern border. Chu suffered many defeats in battles against Qin and was forced to cede territories to Qin. King Huai I of Chu was furious and ordered a military campaign against Qin, but he was tricked by Zhang Yi into breaking diplomatic ties with his allies, and his angered allies joined Qin in inflicting a crushing defeat on Chu. In 299 BC, King Huai I was tricked into attending a diplomatic conference in Qin, where he was captured and held hostage until his death. In the meantime, Qin launched several attacks on Chu and eventually sacked the Chu capital city of Chen (陳; present-day Jiangling County, Hubei province). The crown prince of Chu fled east and was crowned King Qingxiang of Chu in the new capital city of Shouchun (壽春; present-day Shou County, Anhui province).


title: Qin (state)

text: In the next five decades after King Huiwen's death, King Zhaoxiang of Qin shifted his attention to the Central Plains after the victories in the south against Chu. In the early years of King Zhaoxiang's reign, the Marquis of Rang (穰侯) served as Qin's chancellor and actively pushed for military campaigns against the Qi state in the far eastern part of China. However, the marquis had personal motives, intending to use Qin's powerful military to gain his own fief in Qi territories, since the lands were not directly linked to Qin and would not be under the Qin government's direct administration.


title: Qin (state)

text: King Zhaoxiang's foreign advisor Fan Sui advised the king to abandon those fruitless campaigns against distant states. King Zhaoxiang heeded this advice and changed Qin's foreign policy to adopting good diplomatic relations with distant states (Yan and Qi), while concentrating on attacking nearby states (Zhao, Han and Wei). As a consequence, Qin began to launch constant attacks on Han and Wei over the next decades, conquering several territories in its campaigns. By then, Qin's territories had expanded to beyond the eastern shore of the Yellow River and Han and Wei were reduced to the status of "buffers" from Qin for the other states in the east.


title: Qin (state)

text: Starting from 265 BC, Qin launched a massive invasion on Han and forced Han to cede its territory of Shangdang (上黨; in present-day Shanxi province). However, Han offered Shangdang to Zhao instead, which led to a conflict between Qin and Zhao for control of Shangdang. Qin and Zhao engaged in the three-year-long Battle of Changping, followed by another three-year siege by Qin on Zhao's capital city of Handan. The conflict at Changping was deemed as a power struggle, as both sides pitted their forces against each other not only on the battlefield, but also in the domestic context. Although Qin had an abundance of resources and vast manpower, it had to enlist every man above the age of 15 for war-related duties, ranging from front-line service to logistics and agriculture. King Zhaoxiang even personally directed his army's supply lines. The extent of mobilization and the exhaustion in the aftermath was not seen in world history for another 2,000 years, until this concept of total war re-entered the stage during World War I. Qin's eventual victory in 260 BC was attributed to its use of schemes to stir up internal conflict in Zhao, which led to the replacement of Zhao's military leaders.


title: Qin (state)

text: Following the Qin victory at the Battle of Changping, the Qin commander Bai Qi ordered the 400,000 prisoners-of-war from Zhao to be executed by burying them alive. Subsequently, the Qin forces marched on the Zhao capital city of Handan in an attempt to conquer Zhao completely. However, the Qin troops were unable to capture Handan as they were already exhausted and also because the Zhao forces put up fierce resistance. King Xiaocheng of Zhao offered six cities to Qin as a peace offer and King Zhaoxiang of Qin accepted the offer after being persuaded by Fan Sui. Within Zhao, many officials strongly opposed King Xiaocheng's decision to give up the cities and subsequent delays caused the siege on Handan to be prolonged until 258 BC. Meanwhile, Bai Qi was consecutively replaced by Wang Xi, Wang Ling and Zheng Anping as the Qin commander at the siege.


title: Qin (state)

text: In 257 BC, Qin was still unable to penetrate Handan after besieging it for three years, and Zhao requested aid from the neighbouring states of Wei and Chu. Wei was hesitant to help Zhao initially, but launched an attack on Qin after seeing that Qin was already exhausted after years of war. The Qin forces crumbled and retreated and Zheng Anping surrendered. The combined forces of Wei and Chu continued to pursue the retreating Qin army and Wei managed to retake part of its original lands that were lost to Qin earlier.


title: Qin (state)

text: In the middle of the third century BC, Zheng Guo, a hydraulic engineer from the Han state, was sent to Qin to advise King Zhaoxiang of Qin on constructing irrigation canals. Qin had a penchant for building large-scale canals, as evident from its Min River irrigation system. King Zhaoxiang approved Zheng Guo's idea on constructing an even bigger canal. The project was completed in 264 BC and the canal was named after Zheng. Qin benefitted from the project as it became one of the most fertile states in China due to the good irrigation system, and also because it could now raise more troops as a consequence of increased agricultural yield.


title: Qin (state)

text: In 247 BC, the 13-year-old Ying Zheng became king of Qin after the sudden death of King Zhuangxiang. However, Ying Zheng did not wield state power fully in his hands until 238 BC, after eliminating his political rivals Lü Buwei and Lao Ai. Ying formulated a plan for conquering the other six states and unifying China with help from Li Si and Wei Liao.


title: Qin (state)

text: In 230 BC, Qin attacked Han, the weakest of the Seven Warring States, and succeeded in conquering Han within a year. Since 236 BC, Qin had been launching several assaults on Zhao, which had been devastated by its calamitous defeat at the Battle of Changping three decades ago. Although Qin faced strong resistance from the Zhao forces, led by general Li Mu, it still managed to defeat the Zhao army by using a ploy to sow discord between King Qian of Zhao and Li Mu, causing King Qian to order Li Mu's execution and replace Li with the less competent Zhao Cong. Zhao eventually fell to Qin in 228 BC after the capital city of Handan was taken. However, a Zhao noble managed to escape with remnant forces and proclaim himself king in Dai. Dai fell to Qin six years later.


title: Qin (state)

text: After the fall of Zhao, Qin turned its attention towards Yan. Crown Prince Dan of Yan sent Jing Ke to assassinate Ying Zheng but the assassination attempt failed and Qin used that as an excuse to attack Yan. Yan lost to Qin at a battle on the eastern bank of the Yi River in 226 BC and King Xi of Yan fled with remnant forces to Liaodong. Qin attacked Yan again in 222 BC and annexed Yan completely. In 225 BC, the Qin army led by Wang Ben invaded Wei and besieged Wei's capital city of Daliang for three months. Wang directed the waters from the Yellow River and the Hong Canal to flood Daliang; King Jia of Wei surrendered and Wei was conquered.


title: Qin (state)

text: In 224 BC, Qin prepared for an attack on Chu, its most powerful rival among the six states. During a discussion between Ying Zheng and his subjects, the veteran general Wang Jian claimed that the invasion force needed to be at least 600,000 strong, but the younger general Li Xin thought that 200,000 men would be sufficient. Ying Zheng put Li Xin in command of the Qin army to attack Chu. The Chu defenders, led by Xiang Yan, took Li Xin's army by surprise and defeated the Qin invaders. The defeat was deemed as the greatest setback for Qin in its wars to unify China. Ying Zheng put Wang Jian in command of the 600,000 strong army as he had requested and ordered Wang to lead another attack on Chu. Wang scored a major victory against the Chu forces in 224 BC and Xiang Yan was killed in action. The following year, Qin pushed on and captured Chu's capital city of Shouchun, bringing an end to Chu's existence. In 222 BC, the Qin army advanced southward and annexed the Wuyue region (covering present-day Zhejiang and Jiangsu provinces).


title: Qin (state)

text: By 221 BC, Qi was the only rival state left. Qin advanced into the heartland of Qi via a southern detour, avoiding direct confrontation with the Qi forces on Qi's western border and arrived at Qi's capital city of Linzi swiftly. The Qi forces were taken by surprise and surrendered without putting up resistance. Following the fall of Qi in 221 BC, China was unified under the rule of Qin. Ying Zheng declared himself "Qin Shi Huang" (meaning "First Emperor of Qin"), founded the Qin Dynasty, and became the first sovereign ruler of a united China.


title: Qin (state)

text: Before Qin unified China, each state had its own customs and culture. According to the "Yu Gong" or "Tribute of Yu", composed in the fourth or fifth century BC and included in the "Book of Documents", there were nine distinct cultural regions of China, which are described in detail in this book. The work focuses on the travels of the titular sage, Yu the Great, throughout each of the regions. Other texts, predominantly military, also discussed these cultural variations.


title: Qin (state)

text: One of these texts was "The Book of Master Wu", written in response to a query by Marquis Wu of Wei on how to cope with the military threat posed by competing states. Wu Qi, the author of the work, declared that the government and nature of the people were reflective of the terrain they live in. Of Qin, he said:


title: Qin (state)

text: According to Wu, the nature of the people is a result of the government, which is in turn a result of the roughness of the terrain. Each of the states is expounded upon by Wu in this manner.


title: Qin (state)

text: Following a visit to Qin in 264 BC, the Confucian philosopher Xun Kuang noted that Qin society was "simple and unsophisticated" and their people stood in awe of their officials, but was completely devoid of Confucian literati. Though disliked by many Confucians of its time for "dangerously lacking in Confucian scholars," Confucian Xun Kuang wrote of the later Qin that "its topographical features are inherently advantageous," and that its "manifold natural resources gave it remarkable inherent strength. Its people were unspoiled and exceedingly deferential; its officers unfailingly respectful, earnest, reverential, loyal, and trustworthy; and its high officials public-spirited, intelligent, and assiduous in the execution of the duties of their position. Its courts and bureaus functioned without delays and with such smoothness that it was as if there were no government at all."


title: Qin (state)

text: In his "Petition against driving away foreigners" (諫逐客書), Li Si mentioned that guzheng and percussion instruments made of pottery and tiles were characteristic of Qin music.


title: Qin (state)

text: List of Qin rulers based on the "Records of the Grand Historian" by Sima Qian, with corrections by Han Zhaoqi:


title: Qin (state)

text: The events during the reigns of Duke Xiao, King Huiwen, King Wu and King Zhaoxiang are romanticised in a series of historical novels by Sun Haohui. The novels are adapted into the television series "The Qin Empire" (2009), "" (2012) and "The Qin Empire III" (2017).


title: Qin (state)

text: The Japanese manga "Kingdom," by Hara Yasuhisa, tells a fictionalised story of the life of Qin Shi Huang and the unification of China with some references to the era of Duke Mu.


title: Qin (state)

text: "A Step into the Past" tells about a 21st-century Hong Kong VIPPU officer who travels back in time to the Warring States period of ancient China. He is involved in a number of important historical events that leads to the first unification of China under the Qin dynasty. The series' first original broadcast ran from 15 October to 7 December 2001 on the TVB Jade network in Hong Kong.


title: Qin (state)

text: Qin is represented by two stars, Theta Capricorni () and 30 Capricorni (), in "Twelve States" asterism. Qin is also represented by the star Delta Serpentis in asterism "Right Wall", Heavenly Market enclosure (see Chinese constellation).


title: One red paperclip

text: One red paperclip is a website created by Canadian blogger Kyle MacDonald, who traded his way from a single red paperclip to a house in a series of fourteen online trades over the course of a year. MacDonald was inspired by the childhood game "Bigger, Better". His site received a considerable amount of notice for tracking the transactions. "A lot of people have been asking how I've stirred up so much publicity around the project, and my simple answer is: 'I have no idea, he told the BBC. The story has inspired countless copycats, who have attempted to trade their way up from a paperclip (or other small item) to something expensive, with varying degrees of success.


title: One red paperclip

text: MacDonald made his first trade, a red paper clip for a fish-shaped pen, on July 14, 2005. He reached his goal of trading up to a house with the fourteenth transaction, trading a movie role for a house. This is the list of all transactions MacDonald made:


title: Atmospheric entry

text: Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: "uncontrolled entry", such as the entry of astronomical objects, space debris, or bolides; and "controlled entry" (or "reentry") of a spacecraft capable of being navigated or following a predetermined course. Technologies and procedures allowing the controlled atmospheric "entry, descent, and landing" of spacecraft are collectively termed as "EDL".


title: Atmospheric entry

text: Objects entering an atmosphere experience atmospheric drag, which puts mechanical stress on the object, and aerodynamic heating—caused mostly by compression of the air in front of the object, but also by drag. These forces can cause loss of mass (ablation) or even complete disintegration of smaller objects, and objects with lower compressive strength can explode.


title: Atmospheric entry

text: Crewed space vehicles must be slowed to subsonic speeds before parachutes or air brakes may be deployed. Such vehicles have kinetic energies typically between 50 and 1,800 megajoules per kilogram, and atmospheric dissipation is the only way of expending the kinetic energy. The amount of rocket fuel required to slow the vehicle would be nearly equal to the amount used to accelerate it initially, and it is thus highly impractical to use retro rockets for the entire Earth reentry procedure. While the high temperature generated at the surface of the heat shield is due to adiabatic compression, the vehicle's kinetic energy is ultimately lost to gas friction (viscosity) after the vehicle has passed by. Other smaller energy losses include black-body radiation directly from the hot gases and chemical reactions between ionized gases.


title: Atmospheric entry

text: Ballistic warheads and expendable vehicles do not require slowing at reentry, and in fact, are made streamlined so as to maintain their speed. Furthermore, slow-speed returns to Earth from near-space such as parachute jumps from balloons do not require heat shielding because the gravitational acceleration of an object starting at relative rest from within the atmosphere itself (or not far above it) cannot create enough velocity to cause significant atmospheric heating.


title: Atmospheric entry

text: For Earth, atmospheric entry occurs by convention at the Kármán line at an altitude of above the surface, while at Venus atmospheric entry occurs at and at Mars atmospheric entry at about . Uncontrolled objects reach high velocities while accelerating through space toward the Earth under the influence of Earth's gravity, and are slowed by friction upon encountering Earth's atmosphere. Meteors are also often travelling quite fast relative to the Earth simply because their own orbital path is different from that of the Earth before they encounter Earth's gravity well. Most objects enter at hypersonic speeds due to their sub-orbital (e.g., intercontinental ballistic missile reentry vehicles), orbital (e.g., the Soyuz), or unbounded (e.g., meteors) trajectories. Various advanced technologies have been developed to enable atmospheric reentry and flight at extreme velocities. An alternative method of controlled atmospheric entry is buoyancy which is suitable for planetary entry where thick atmospheres, strong gravity, or both factors complicate high-velocity hyperbolic entry, such as the atmospheres of Venus, Titan and the gas giants.


title: Atmospheric entry

text: The concept of the ablative heat shield was described as early as 1920 by Robert Goddard: "In the case of meteors, which enter the atmosphere with speeds as high as per second, the interior of the meteors remains cold, and the erosion is due, to a large extent, to chipping or cracking of the suddenly heated surface. For this reason, if the outer surface of the apparatus were to consist of layers of a very infusible hard substance with layers of a poor heat conductor between, the surface would not be eroded to any considerable extent, especially as the velocity of the apparatus would not be nearly so great as that of the average meteor."


title: Atmospheric entry

text: Practical development of reentry systems began as the range, and reentry velocity of ballistic missiles increased. For early short-range missiles, like the V-2, stabilization and aerodynamic stress were important issues (many V-2s broke apart during reentry), but heating was not a serious problem. Medium-range missiles like the Soviet R-5, with a range, required ceramic composite heat shielding on separable reentry vehicles (it was no longer possible for the entire rocket structure to survive reentry). The first ICBMs, with ranges of , were only possible with the development of modern ablative heat shields and blunt-shaped vehicles.


title: Atmospheric entry

text: In the United States, this technology was pioneered by H. Julian Allen and A. J. Eggers Jr. of the National Advisory Committee for Aeronautics (NACA) at Ames Research Center. In 1951, they made the counterintuitive discovery that a blunt shape (high drag) made the most effective heat shield. From simple engineering principles, Allen and Eggers showed that the heat load experienced by an entry vehicle was inversely proportional to the drag coefficient; i.e., the greater the drag, the less the heat load. If the reentry vehicle is made blunt, air cannot "get out of the way" quickly enough, and acts as an air cushion to push the shock wave and heated shock layer forward (away from the vehicle). Since most of the hot gases are no longer in direct contact with the vehicle, the heat energy would stay in the shocked gas and simply move around the vehicle to later dissipate into the atmosphere.


title: Atmospheric entry

text: The Allen and Eggers discovery, though initially treated as a military secret, was eventually published in 1958.


title: Atmospheric entry

text: When atmospheric entry is part of a spacecraft landing or recovery, particularly on a planetary body other than Earth, entry is part of a phase referred to as "entry, descent, and landing", or EDL. When the atmospheric entry returns to the same body that the vehicle had launched from, the event is referred to as reentry (almost always referring to Earth entry).


title: Atmospheric entry

text: The fundamental design objective in atmospheric entry of a spacecraft is to dissipate the energy of a spacecraft that is traveling at hypersonic speed as it enters an atmosphere such that equipment, cargo, and any passengers are slowed and land near a specific destination on the surface at zero velocity while keeping stresses on the spacecraft and any passengers within acceptable limits. This may be accomplished by propulsive or aerodynamic (vehicle characteristics or parachute) means, or by some combination.


title: Atmospheric entry

text: The simplest axisymmetric shape is the sphere or spherical section. This can either be a complete sphere or a spherical section forebody with a converging conical afterbody. The aerodynamics of a sphere or spherical section are easy to model analytically using Newtonian impact theory. Likewise, the spherical section's heat flux can be accurately modeled with the Fay–Riddell equation. The static stability of a spherical section is assured if the vehicle's center of mass is upstream from the center of curvature (dynamic stability is more problematic). Pure spheres have no lift. However, by flying at an angle of attack, a spherical section has modest aerodynamic lift thus providing some cross-range capability and widening its entry corridor. In the late 1950s and early 1960s, high-speed computers were not yet available and computational fluid dynamics was still embryonic. Because the spherical section was amenable to closed-form analysis, that geometry became the default for conservative design. Consequently, crewed capsules of that era were based upon the spherical section.


title: Atmospheric entry

text: Pure spherical entry vehicles were used in the early Soviet Vostok and Voskhod capsules and in Soviet Mars and Venera descent vehicles. The Apollo command module used a spherical section forebody heat shield with a converging conical afterbody. It flew a lifting entry with a hypersonic trim angle of attack of −27° (0° is blunt-end first) to yield an average L/D (lift-to-drag ratio) of 0.368. The resultant lift achieved a measure of cross-range control by offsetting the vehicle's center of mass from its axis of symmetry, allowing the lift force to be directed left or right by rolling the capsule on its longitudinal axis. Other examples of the spherical section geometry in crewed capsules are Soyuz/Zond, Gemini, and Mercury. Even these small amounts of lift allow trajectories that have very significant effects on peak g-force, reducing it from 8–9 g for a purely ballistic (slowed only by drag) trajectory to 4–5 g, as well as greatly reducing the peak reentry heat.


title: Atmospheric entry

text: The sphere-cone is a spherical section with a frustum or blunted cone attached. The sphere-cone's dynamic stability is typically better than that of a spherical section. The vehicle enters sphere-first. With a sufficiently small half-angle and properly placed center of mass, a sphere-cone can provide aerodynamic stability from Keplerian entry to surface impact. (The "half-angle" is the angle between the cone's axis of rotational symmetry and its outer surface, and thus half the angle made by the cone's surface edges.)


title: Atmospheric entry

text: The original American sphere-cone aeroshell was the Mk-2 RV (reentry vehicle), which was developed in 1955 by the General Electric Corp. The Mk-2's design was derived from blunt-body theory and used a radiatively cooled thermal protection system (TPS) based upon a metallic heat shield (the different TPS types are later described in this article). The Mk-2 had significant defects as a weapon delivery system, i.e., it loitered too long in the upper atmosphere due to its lower ballistic coefficient and also trailed a stream of vaporized metal making it very visible to radar. These defects made the Mk-2 overly susceptible to anti-ballistic missile (ABM) systems. Consequently, an alternative sphere-cone RV to the Mk-2 was developed by General Electric.


title: Atmospheric entry

text: This new RV was the Mk-6 which used a non-metallic ablative TPS, a nylon phenolic. This new TPS was so effective as a reentry heat shield that significantly reduced bluntness was possible. However, the Mk-6 was a huge RV with an entry mass of 3,360 kg, a length of 3.1 m and a half-angle of 12.5°. Subsequent advances in nuclear weapon and ablative TPS design allowed RVs to become significantly smaller with a further reduced bluntness ratio compared to the Mk-6. Since the 1960s, the sphere-cone has become the preferred geometry for modern ICBM RVs with typical half-angles being between 10° to 11°.


title: Atmospheric entry

text: Reconnaissance satellite RVs (recovery vehicles) also used a sphere-cone shape and were the first American example of a non-munition entry vehicle (Discoverer-I, launched on 28 February 1959). The sphere-cone was later used for space exploration missions to other celestial bodies or for return from open space; e.g., "Stardust" probe. Unlike with military RVs, the advantage of the blunt body's lower TPS mass remained with space exploration entry vehicles like the Galileo Probe with a half-angle of 45° or the Viking aeroshell with a half-angle of 70°. Space exploration sphere-cone entry vehicles have landed on the surface or entered the atmospheres of Mars, Venus, Jupiter, and Titan.


title: Atmospheric entry

text: The biconic is a sphere-cone with an additional frustum attached. The biconic offers a significantly improved L/D ratio. A biconic designed for Mars aerocapture typically has an L/D of approximately 1.0 compared to an L/D of 0.368 for the Apollo-CM. The higher L/D makes a biconic shape better suited for transporting people to Mars due to the lower peak deceleration. Arguably, the most significant biconic ever flown was the "Advanced Maneuverable Reentry Vehicle" (AMaRV). Four AMaRVs were made by the McDonnell Douglas Corp. and represented a significant leap in RV sophistication. Three AMaRVs were launched by Minuteman-1 ICBMs on 20 December 1979, 8 October 1980 and 4 October 1981. AMaRV had an entry mass of approximately 470 kg, a nose radius of 2.34 cm, a forward-frustum half-angle of 10.4°, an inter-frustum radius of 14.6 cm, aft-frustum half-angle of 6°, and an axial length of 2.079 meters. No accurate diagram or picture of AMaRV has ever appeared in the open literature. However, a schematic sketch of an AMaRV-like vehicle along with trajectory plots showing hairpin turns has been published.


title: Atmospheric entry

text: AMaRV's attitude was controlled through a split body flap (also called a "split-windward flap") along with two yaw flaps mounted on the vehicle's sides. Hydraulic actuation was used for controlling the flaps. AMaRV was guided by a fully autonomous navigation system designed for evading anti-ballistic missile (ABM) interception. The McDonnell Douglas DC-X (also a biconic) was essentially a scaled-up version of AMaRV. AMaRV and the DC-X also served as the basis for an unsuccessful proposal for what eventually became the Lockheed Martin X-33.


title: Atmospheric entry

text: Non-axisymmetric shapes have been used for crewed entry vehicles. One example is the winged orbit vehicle that uses a delta wing for maneuvering during descent much like a conventional glider. This approach has been used by the American Space Shuttle and the Soviet Buran. The lifting body is another entry vehicle geometry and was used with the X-23 PRIME (Precision Recovery Including Maneuvering Entry) vehicle.


title: Atmospheric entry

text: Objects entering an atmosphere from space at high velocities relative to the atmosphere will cause very high levels of heating. Atmospheric entry heating comes principally from two sources:


title: Atmospheric entry

text: As velocity increases, both convective and radiative heating increase, but at different rates. At very high speeds, radiative heating will dominate the convective heat fluxes, as radiative heating is proportional to the eighth power of velocity, while convective heating is proportional to the third power of velocity. Radiative heating thus predominates early in atmospheric entry, while convection predominates in the later phases.


title: Atmospheric entry

text: While Earth entry interface is considered to take place at the Kármán line , the main heating during controlled entry takes place at altitudes of , peaking at .


title: Atmospheric entry

text: At typical reentry temperatures, the air in the shock layer is both ionized and dissociated. This chemical dissociation necessitates various physical models to describe the shock layer's thermal and chemical properties. There are four basic physical models of a gas that are important to aeronautical engineers who design heat shields:


title: Atmospheric entry

text: Almost all aeronautical engineers are taught the perfect (ideal) gas model during their undergraduate education. Most of the important perfect gas equations along with their corresponding tables and graphs are shown in NACA Report 1135. Excerpts from NACA Report 1135 often appear in the appendices of thermodynamics textbooks and are familiar to most aeronautical engineers who design supersonic aircraft.


title: Atmospheric entry

text: The perfect gas theory is elegant and extremely useful for designing aircraft but assumes that the gas is chemically inert. From the standpoint of aircraft design, air can be assumed to be inert for temperatures less than 550 K at one atmosphere pressure. The perfect gas theory begins to break down at 550 K and is not usable at temperatures greater than 2,000 K. For temperatures greater than 2,000 K, a heat shield designer must use a "real gas model".


title: Atmospheric entry

text: An entry vehicle's pitching moment can be significantly influenced by real-gas effects. Both the Apollo command module and the Space Shuttle were designed using incorrect pitching moments determined through inaccurate real-gas modelling. The Apollo-CM's trim-angle angle of attack was higher than originally estimated, resulting in a narrower lunar return entry corridor. The actual aerodynamic center of the "Columbia" was upstream from the calculated value due to real-gas effects. On "Columbia"s maiden flight (STS-1), astronauts John Young and Robert Crippen had some anxious moments during reentry when there was concern about losing control of the vehicle.


title: Atmospheric entry

text: An equilibrium real-gas model assumes that a gas is chemically reactive, but also assumes all chemical reactions have had time to complete and all components of the gas have the same temperature (this is called "thermodynamic equilibrium"). When air is processed by a shock wave, it is superheated by compression and chemically dissociates through many different reactions. Direct friction upon the reentry object is not the main cause of shock-layer heating. It is caused mainly from isentropic heating of the air molecules within the compression wave. Friction based entropy increases of the molecules within the wave also account for some heating. The distance from the shock wave to the stagnation point on the entry vehicle's leading edge is called "shock wave stand off". An approximate rule of thumb for shock wave standoff distance is 0.14 times the nose radius. One can estimate the time of travel for a gas molecule from the shock wave to the stagnation point by assuming a free stream velocity of 7.8 km/s and a nose radius of 1 meter, i.e., time of travel is about 18 microseconds. This is roughly the time required for shock-wave-initiated chemical dissociation to approach chemical equilibrium in a shock layer for a 7.8 km/s entry into air during peak heat flux. Consequently, as air approaches the entry vehicle's stagnation point, the air effectively reaches chemical equilibrium thus enabling an equilibrium model to be usable. For this case, most of the shock layer between the shock wave and leading edge of an entry vehicle is chemically reacting and "not" in a state of equilibrium. The Fay–Riddell equation, which is of extreme importance towards modeling heat flux, owes its validity to the stagnation point being in chemical equilibrium. The time required for the shock layer gas to reach equilibrium is strongly dependent upon the shock layer's pressure. For example, in the case of the "Galileo" probe's entry into Jupiter's atmosphere, the shock layer was mostly in equilibrium during peak heat flux due to the very high pressures experienced (this is counterintuitive given the free stream velocity was 39 km/s during peak heat flux).


title: Atmospheric entry

text: Determining the thermodynamic state of the stagnation point is more difficult under an equilibrium gas model than a perfect gas model. Under a perfect gas model, the "ratio of specific heats" (also called "isentropic exponent", adiabatic index, "gamma", or "kappa") is assumed to be constant along with the gas constant. For a real gas, the ratio of specific heats can wildly oscillate as a function of temperature. Under a perfect gas model there is an elegant set of equations for determining thermodynamic state along a constant entropy stream line called the "isentropic chain". For a real gas, the isentropic chain is unusable and a "Mollier diagram" would be used instead for manual calculation. However, graphical solution with a Mollier diagram is now considered obsolete with modern heat shield designers using computer programs based upon a digital lookup table (another form of Mollier diagram) or a chemistry based thermodynamics program. The chemical composition of a gas in equilibrium with fixed pressure and temperature can be determined through the "Gibbs free energy method". Gibbs free energy is simply the total enthalpy of the gas minus its total entropy times temperature. A chemical equilibrium program normally does not require chemical formulas or reaction-rate equations. The program works by preserving the original elemental abundances specified for the gas and varying the different molecular combinations of the elements through numerical iteration until the lowest possible Gibbs free energy is calculated (a Newton–Raphson method is the usual numerical scheme). The data base for a Gibbs free energy program comes from spectroscopic data used in defining partition functions. Among the best equilibrium codes in existence is the program "Chemical Equilibrium with Applications" (CEA) which was written by Bonnie J. McBride and Sanford Gordon at NASA Lewis (now renamed "NASA Glenn Research Center"). Other names for CEA are the "Gordon and McBride Code" and the "Lewis Code". CEA is quite accurate up to 10,000 K for planetary atmospheric gases, but unusable beyond 20,000 K (double ionization is not modelled). CEA can be downloaded from the Internet along with full documentation and will compile on Linux under the G77 Fortran compiler.


title: Atmospheric entry

text: A non-equilibrium real gas model is the most accurate model of a shock layer's gas physics, but is more difficult to solve than an equilibrium model. The simplest non-equilibrium model is the "Lighthill-Freeman model" developed in 1958. The Lighthill-Freeman model initially assumes a gas made up of a single diatomic species susceptible to only one chemical formula and its reverse; e.g., N ? N + N and N + N ? N (dissociation and recombination). Because of its simplicity, the Lighthill-Freeman model is a useful pedagogical tool, but is unfortunately too simple for modelling non-equilibrium air. Air is typically assumed to have a mole fraction composition of 0.7812 molecular nitrogen, 0.2095 molecular oxygen and 0.0093 argon. The simplest real gas model for air is the "five species model", which is based upon N, O, NO, N, and O. The five species model assumes no ionization and ignores trace species like carbon dioxide.


title: Atmospheric entry

text: When running a Gibbs free energy equilibrium program, the iterative process from the originally specified molecular composition to the final calculated equilibrium composition is essentially random and not time accurate. With a non-equilibrium program, the computation process is time accurate and follows a solution path dictated by chemical and reaction rate formulas. The five species model has 17 chemical formulas (34 when counting reverse formulas). The Lighthill-Freeman model is based upon a single ordinary differential equation and one algebraic equation. The five species model is based upon 5 ordinary differential equations and 17 algebraic equations. Because the 5 ordinary differential equations are tightly coupled, the system is numerically "stiff" and difficult to solve. The five species model is only usable for entry from low Earth orbit where entry velocity is approximately . For lunar return entry of 11 km/s, the shock layer contains a significant amount of ionized nitrogen and oxygen. The five-species model is no longer accurate and a twelve-species model must be used instead.


title: Atmospheric entry

text: Modeling high-speed Mars atmospheric entry—which involves a carbon dioxide, nitrogen and argon atmosphere—is even more complex requiring a 19-species model.


title: Atmospheric entry

text: An important aspect of modelling non-equilibrium real gas effects is radiative heat flux. If a vehicle is entering an atmosphere at very high speed (hyperbolic trajectory, lunar return) and has a large nose radius then radiative heat flux can dominate TPS heating. Radiative heat flux during entry into an air or carbon dioxide atmosphere typically comes from asymmetric diatomic molecules; e.g., cyanogen (CN), carbon monoxide, nitric oxide (NO), single ionized molecular nitrogen etc. These molecules are formed by the shock wave dissociating ambient atmospheric gas followed by recombination within the shock layer into new molecular species. The newly formed diatomic molecules initially have a very high vibrational temperature that efficiently transforms the vibrational energy into radiant energy; i.e., radiative heat flux. The whole process takes place in less than a millisecond which makes modelling a challenge. The experimental measurement of radiative heat flux (typically done with shock tubes) along with theoretical calculation through the unsteady Schrödinger equation are among the more esoteric aspects of aerospace engineering. Most of the aerospace research work related to understanding radiative heat flux was done in the 1960s, but largely discontinued after conclusion of the Apollo Program. Radiative heat flux in air was just sufficiently understood to ensure Apollo's success. However, radiative heat flux in carbon dioxide (Mars entry) is still barely understood and will require major research.


title: Atmospheric entry

text: The frozen gas model describes a special case of a gas that is not in equilibrium. The name "frozen gas" can be misleading. A frozen gas is not "frozen" like ice is frozen water. Rather a frozen gas is "frozen" in time (all chemical reactions are assumed to have stopped). Chemical reactions are normally driven by collisions between molecules. If gas pressure is slowly reduced such that chemical reactions can continue then the gas can remain in equilibrium. However, it is possible for gas pressure to be so suddenly reduced that almost all chemical reactions stop. For that situation the gas is considered frozen.


title: Atmospheric entry

text: The distinction between equilibrium and frozen is important because it is possible for a gas such as air to have significantly different properties (speed-of-sound, viscosity etc.) for the same thermodynamic state; e.g., pressure and temperature. Frozen gas can be a significant issue in the wake behind an entry vehicle. During reentry, free stream air is compressed to high temperature and pressure by the entry vehicle's shock wave. Non-equilibrium air in the shock layer is then transported past the entry vehicle's leading side into a region of rapidly expanding flow that causes freezing. The frozen air can then be entrained into a trailing vortex behind the entry vehicle. Correctly modelling the flow in the wake of an entry vehicle is very difficult. Thermal protection shield (TPS) heating in the vehicle's afterbody is usually not very high, but the geometry and unsteadiness of the vehicle's wake can significantly influence aerodynamics (pitching moment) and particularly dynamic stability.


title: Atmospheric entry

text: A thermal protection system, or TPS, is the barrier that protects a spacecraft during the searing heat of atmospheric reentry. A secondary goal may be to protect the spacecraft from the heat and cold of space while in orbit. Multiple approaches for the thermal protection of spacecraft are in use, among them ablative heat shields, passive cooling, and active cooling of spacecraft surfaces.


title: Atmospheric entry

text: The ablative heat shield functions by lifting the hot shock layer gas away from the heat shield's outer wall (creating a cooler boundary layer). The boundary layer comes from "blowing" of gaseous reaction products from the heat shield material and provides protection against all forms of heat flux. The overall process of reducing the heat flux experienced by the heat shield's outer wall by way of a boundary layer is called "blockage". Ablation occurs at two levels in an ablative TPS: the outer surface of the TPS material chars, melts, and sublimes, while the bulk of the TPS material undergoes pyrolysis and expels product gases. The gas produced by pyrolysis is what drives blowing and causes blockage of convective and catalytic heat flux. Pyrolysis can be measured in real time using thermogravimetric analysis, so that the ablative performance can be evaluated. Ablation can also provide blockage against radiative heat flux by introducing carbon into the shock layer thus making it optically opaque. Radiative heat flux blockage was the primary thermal protection mechanism of the Galileo Probe TPS material (carbon phenolic). Carbon phenolic was originally developed as a rocket nozzle throat material (used in the Space Shuttle Solid Rocket Booster) and for reentry-vehicle nose tips.


title: Atmospheric entry

text: Early research on ablation technology in the USA was centered at NASA's Ames Research Center located at Moffett Field, California. Ames Research Center was ideal, since it had numerous wind tunnels capable of generating varying wind velocities. Initial experiments typically mounted a mock-up of the ablative material to be analyzed within a hypersonic wind tunnel. Testing of ablative materials occurs at the Ames Arc Jet Complex. Many spacecraft thermal protection systems have been tested in this facility, including the Apollo, space shuttle, and Orion heat shield materials.


title: Atmospheric entry

text: The thermal conductivity of a particular TPS material is usually proportional to the material's density. Carbon phenolic is a very effective ablative material, but also has high density which is undesirable. If the heat flux experienced by an entry vehicle is insufficient to cause pyrolysis then the TPS material's conductivity could allow heat flux conduction into the TPS bondline material thus leading to TPS failure. Consequently, for entry trajectories causing lower heat flux, carbon phenolic is sometimes inappropriate and lower-density TPS materials such as the following examples can be better design choices:


title: Atmospheric entry

text: "SLA" in "SLA-561V" stands for "super light-weight ablator". SLA-561V is a proprietary ablative made by Lockheed Martin that has been used as the primary TPS material on all of the 70° sphere-cone entry vehicles sent by NASA to Mars other than the Mars Science Laboratory (MSL). SLA-561V begins significant ablation at a heat flux of approximately 110 W/cm, but will fail for heat fluxes greater than 300 W/cm. The MSL aeroshell TPS is currently designed to withstand a peak heat flux of 234 W/cm. The peak heat flux experienced by the "Viking 1" aeroshell which landed on Mars was 21 W/cm. For "Viking 1", the TPS acted as a charred thermal insulator and never experienced significant ablation. "Viking 1" was the first Mars lander and based upon a very conservative design. The Viking aeroshell had a base diameter of 3.54 meters (the largest used on Mars until Mars Science Laboratory). SLA-561V is applied by packing the ablative material into a honeycomb core that is pre-bonded to the aeroshell's structure thus enabling construction of a large heat shield.


title: Atmospheric entry

text: "Phenolic-impregnated carbon ablator" (PICA), a carbon fiber preform impregnated in phenolic resin, is a modern TPS material and has the advantages of low density (much lighter than carbon phenolic) coupled with efficient ablative ability at high heat flux. It is a good choice for ablative applications such as high-peak-heating conditions found on sample-return missions or lunar-return missions. PICA's thermal conductivity is lower than other high-heat-flux-ablative materials, such as conventional carbon phenolics.


title: Atmospheric entry

text: PICA was patented by NASA Ames Research Center in the 1990s and was the primary TPS material for the Stardust aeroshell. The Stardust sample-return capsule was the fastest man-made object ever to reenter Earth's atmosphere ( at 135 km altitude). This was faster than the Apollo mission capsules and 70% faster than the Shuttle. PICA was critical for the viability of the Stardust mission, which returned to Earth in 2006. Stardust's heat shield (0.81 m base diameter) was made of one monolithic piece sized to withstand a nominal peak heating rate of 1.2 kW/cm. A PICA heat shield was also used for the Mars Science Laboratory entry into the Martian atmosphere.


title: Atmospheric entry

text: An improved and easier to produce version called PICA-X was developed by SpaceX in 2006–2010 for the Dragon space capsule. The first reentry test of a PICA-X heat shield was on the Dragon C1 mission on 8 December 2010. The PICA-X heat shield was designed, developed and fully qualified by a small team of a dozen engineers and technicians in less than four years.


title: Atmospheric entry

text: A second enhanced version of PICA—called PICA-3—was developed by SpaceX during the mid-2010s. It was first flight tested on the Crew Dragon spacecraft in 2019 during the flight demonstration mission, in April 2019, and put into regular service on that spacecraft in 2020.


title: Atmospheric entry

text: Silicone-impregnated reusable ceramic ablator (SIRCA) was also developed at NASA Ames Research Center and was used on the Backshell Interface Plate (BIP) of the "Mars Pathfinder" and Mars Exploration Rover (MER) aeroshells. The BIP was at the attachment points between the aeroshell's backshell (also called the afterbody or aft cover) and the cruise ring (also called the cruise stage). SIRCA was also the primary TPS material for the unsuccessful Deep Space 2 (DS/2) Mars impactor probes with their aeroshells. SIRCA is a monolithic, insulating material that can provide thermal protection through ablation. It is the only TPS material that can be machined to custom shapes and then applied directly to the spacecraft. There is no post-processing, heat treating, or additional coatings required (unlike Space Shuttle tiles). Since SIRCA can be machined to precise shapes, it can be applied as tiles, leading edge sections, full nose caps, or in any number of custom shapes or sizes. , SIRCA had been demonstrated in backshell interface applications, but not yet as a forebody TPS material.


title: Atmospheric entry

text: NASA originally used it for the Apollo command module in the 1960s, and then utilized the material for its next-generation beyond low-Earth-orbit Orion crew module, which first flew in a December 2014 test and then operationally in November 2022. The Avcoat to be used on Orion has been reformulated to meet environmental legislation that has been passed since the end of Apollo.


title: Atmospheric entry

text: Thermal soak is a part of almost all TPS schemes. For example, an ablative heat shield loses most of its thermal protection effectiveness when the outer wall temperature drops below the minimum necessary for pyrolysis. From that time to the end of the heat pulse, heat from the shock layer convects into the heat shield's outer wall and would eventually conduct to the payload. This outcome can be prevented by ejecting the heat shield (with its heat soak) prior to the heat conducting to the inner wall.


title: Atmospheric entry

text: Refractory insulation keeps the heat in the outermost layer of the spacecraft surface, where it is conducted away by the air. The temperature of the surface rises to incandescent levels, so the material must have a very high melting point, and the material must also exhibit very low thermal conductivity. Materials with these properties tend to be brittle, delicate, and difficult to fabricate in large sizes, so they are generally fabricated as relatively small tiles that are then attached to the structural skin of the spacecraft. There is a tradeoff between toughness and thermal conductivity: less conductive materials are generally more brittle. The space shuttle used multiple types of tiles. Tiles are also used on the Boeing X-37 and in the Dream Chaser and SpaceX Starship designs.


title: Atmospheric entry

text: Because insulation cannot be perfect, some heat energy is stored in the insulation and in the underlying material ("thermal soaking") and must be dissipated after the spacecraft exits the high-temperature flight regime. Some of this heat will re-radiate through the surface or will be carried off the surface by convection, but some will heat the spacecraft structure and interior, which may require active cooling after landing.


title: Atmospheric entry

text: Typical Space Shuttle TPS tiles (LI-900) have remarkable thermal protection properties. An LI-900 tile exposed to a temperature of 1,000 K on one side will remain merely warm to the touch on the other side. However, they are relatively brittle and break easily, and cannot survive in-flight rain.


title: Atmospheric entry

text: In some early ballistic missile RVs (e.g., the Mk-2 and the sub-orbital Mercury spacecraft), "radiatively cooled TPS" were used to initially absorb heat flux during the heat pulse, and, then, after the heat pulse, radiate and convect the stored heat back into the atmosphere. However, the earlier version of this technique required a considerable quantity of metal TPS (e.g., titanium, beryllium, copper, etc.). Modern designers prefer to avoid this added mass by using ablative and thermal-soak TPS instead.


title: Atmospheric entry

text: Thermal protection systems relying on emissivity use high emissivity coatings (HECs) to facilitate radiative cooling, while an underlying porous ceramic layer serves to protect the structure from high surface temperatures. High thermally stable emissivity values coupled with low thermal conductivity are key to the functionality of such systems.


title: Atmospheric entry

text: Radiatively cooled TPS can be found on modern entry vehicles, but reinforced carbon–carbon (RCC) (also called "carbon–carbon") is normally used instead of metal. RCC was the TPS material on the Space Shuttle's nose cone and wing leading edges, and was also proposed as the leading-edge material for the X-33. Carbon is the most refractory material known, with a one-atmosphere sublimation temperature of for graphite. This high temperature made carbon an obvious choice as a radiatively cooled TPS material. Disadvantages of RCC are that it is currently expensive to manufacture, is heavy, and lacks robust impact resistance.


title: Atmospheric entry

text: Some high-velocity aircraft, such as the SR-71 Blackbird and Concorde, deal with heating similar to that experienced by spacecraft, but at much lower intensity, and for hours at a time. Studies of the SR-71's titanium skin revealed that the metal structure was restored to its original strength through annealing due to aerodynamic heating. In the case of the Concorde, the aluminium nose was permitted to reach a maximum operating temperature of (approximately warmer than the normally sub-zero, ambient air); the metallurgical implications (loss of temper) that would be associated with a higher peak temperature were the most significant factors determining the top speed of the aircraft.


title: Atmospheric entry

text: A radiatively cooled TPS for an entry vehicle is often called a "hot-metal TPS". Early TPS designs for the Space Shuttle called for a hot-metal TPS based upon a nickel superalloy (dubbed René 41) and titanium shingles. This Shuttle TPS concept was rejected, because it was believed a silica tile-based TPS would involve lower development and manufacturing costs. A nickel superalloy-shingle TPS was again proposed for the unsuccessful X-33 single-stage-to-orbit (SSTO) prototype.


title: Atmospheric entry

text: Recently, newer radiatively cooled TPS materials have been developed that could be superior to RCC. Known as Ultra-High Temperature Ceramics, they were developed for the prototype vehicle Slender Hypervelocity Aerothermodynamic Research Probe (SHARP). These TPS materials are based on zirconium diboride and hafnium diboride. SHARP TPS have suggested performance improvements allowing for sustained Mach 7 flight at sea level, Mach 11 flight at altitudes, and significant improvements for vehicles designed for continuous hypersonic flight. SHARP TPS materials enable sharp leading edges and nose cones to greatly reduce drag for airbreathing combined-cycle-propelled spaceplanes and lifting bodies. SHARP materials have exhibited effective TPS characteristics from zero to more than , with melting points over . They are structurally stronger than RCC, and, thus, do not require structural reinforcement with materials such as Inconel. SHARP materials are extremely efficient at reradiating absorbed heat, thus eliminating the need for additional TPS behind and between the SHARP materials and conventional vehicle structure. NASA initially funded (and discontinued) a multi-phase R&D program through the University of Montana in 2001 to test SHARP materials on test vehicles.


title: Atmospheric entry

text: Various advanced reusable spacecraft and hypersonic aircraft designs have been proposed to employ heat shields made from temperature-resistant metal alloys that incorporate a refrigerant or cryogenic fuel circulating through them.


title: Atmospheric entry

text: Such a TPS concept was proposed for the X-30 National Aerospace Plane (NASP) in the mid-80s. The NASP was supposed to have been a scramjet powered hypersonic aircraft, but failed in development.


title: Atmospheric entry

text: In 2005 and 2012, two unmanned lifting body craft with actively cooled hulls were launched as a part of the German Sharp Edge Flight Experiment (SHEFEX).


title: Atmospheric entry

text: In early 2019, SpaceX was developing an actively cooled heat shield for its Starship spacecraft where a part of the thermal protection system will be a transpirationally cooled outer-skin design for the reentering spaceship. However, SpaceX abandoned this approach in favor of a modern version of heat shield tiles later in 2019.


title: Atmospheric entry

text: In the early 1960s various TPS systems were proposed to use water or other cooling liquid sprayed into the shock layer, or passed through channels in the heat shield. Advantages included the possibility of more all-metal designs which would be cheaper to develop, be more rugged, and eliminate the need for classified and unknown technology. The disadvantages are increased weight and complexity, and lower reliability. The concept has never been flown, but a similar technology (the plug nozzle) did undergo extensive ground testing.


title: Atmospheric entry

text: Fuel permitting, nothing prevents a vehicle from entering the atmosphere with a retrograde engine burn, which has the double effect of slowing the vehicle down much faster than atmospheric drag alone would, and forcing the compressed hot air away from the vehicle's body. During reentry, the first stage of the SpaceX Falcon 9 performs an entry burn to rapidly decelerate from its initial hypersonic speed.


title: Atmospheric entry

text: In 2004, aircraft designer Burt Rutan demonstrated the feasibility of a shape-changing airfoil for reentry with the sub-orbital SpaceShipOne. The wings on this craft rotate upward into the "feathered configuration" that provides a shuttlecock effect. Thus SpaceShipOne achieves much more aerodynamic drag on reentry while not experiencing significant thermal loads.


title: Atmospheric entry

text: The configuration increases drag, as the craft is now less streamlined and results in more atmospheric gas particles hitting the spacecraft at higher altitudes than otherwise. The aircraft thus slows down more in higher atmospheric layers which is the key to efficient reentry. Secondly, the aircraft will "automatically" orient itself in this state to a high drag attitude.


title: Atmospheric entry

text: However, the velocity attained by SpaceShipOne prior to reentry is much lower than that of an orbital spacecraft, and engineers, including Rutan, recognize that a feathered reentry technique is not suitable for return from orbit.


title: Atmospheric entry

text: On 4 May 2011, the first test on the SpaceShipTwo of the feathering mechanism was made during a glideflight after release


title: Atmospheric entry

text: from the White Knight Two. Premature deployment of the feathering system was responsible for the 2014 VSS "Enterprise" crash, in which the aircraft disintegrated, killing the co-pilot.


title: Atmospheric entry

text: The feathered reentry was first described by Dean Chapman of NACA in 1958. In the section of his report on "Composite Entry", Chapman described a solution to the problem using a high-drag device:


title: Atmospheric entry

text: Deceleration for atmospheric reentry, especially for higher-speed Mars-return missions, benefits from maximizing "the drag area of the entry system. The larger the diameter of the aeroshell, the bigger the payload can be." An inflatable aeroshell provides one alternative for enlarging the drag area with a low-mass design.


title: Atmospheric entry

text: Such an inflatable shield/aerobrake was designed for the penetrators of Mars 96 mission. Since the mission failed due to the launcher malfunction, the NPO Lavochkin and DASA/ESA have designed a mission for Earth orbit. The Inflatable Reentry and Descent Technology (IRDT) demonstrator was launched on Soyuz-Fregat on 8 February 2000. The inflatable shield was designed as a cone with two stages of inflation. Although the second stage of the shield failed to inflate, the demonstrator survived the orbital reentry and was recovered. The subsequent missions flown on the Volna rocket failed due to launcher failure.


title: Atmospheric entry

text: NASA launched an inflatable heat shield experimental spacecraft on 17 August 2009 with the successful first test flight of the Inflatable Re-entry Vehicle Experiment (IRVE). The heat shield had been vacuum-packed into a payload shroud and launched on a Black Brant 9 sounding rocket from NASA's Wallops Flight Facility on Wallops Island, Virginia. "Nitrogen inflated the heat shield, made of several layers of silicone-coated <nowiki>[</nowiki>Kevlar<nowiki>]</nowiki> fabric, to a mushroom shape in space several minutes after liftoff." The rocket apogee was at an altitude of where it began its descent to supersonic speed. Less than a minute later the shield was released from its cover to inflate at an altitude of . The inflation of the shield took less than 90 seconds.


title: Atmospheric entry

text: Following the success of the initial IRVE experiments, NASA developed the concept into the more ambitious Hypersonic Inflatable Aerodynamic Decelerator (HIAD). The current design is shaped like a shallow cone, with the structure built up as a stack of circular inflated tubes of gradually increasing major diameter. The forward (convex) face of the cone is covered with a flexible thermal protection system robust enough to withstand the stresses of atmospheric entry (or reentry).


title: Atmospheric entry

text: In 2012, a HIAD was tested as Inflatable Reentry Vehicle Experiment 3 (IRVE-3) using a sub-orbital sounding rocket, and worked.


title: Atmospheric entry

text: See also Low-Density Supersonic Decelerator, a NASA project with tests in 2014 & 2015 of a 6m diameter SIAD-R.


title: Atmospheric entry

text: A inflatable reentry vehicle, "Low-Earth Orbit Flight Test of an Inflatable Decelerator" (LOFTID), was launched in Nov 2022, inflated in orbit, reentered faster than Mach 25, and was successfully recovered on November 10.


title: Atmospheric entry

text: Peak heat flux and dynamic pressure selects the TPS material. Heat load selects the thickness of the TPS material stack. Peak deceleration is of major importance for crewed missions. The upper limit for crewed return to Earth from low Earth orbit (LEO) or lunar return is 10"g". For Martian atmospheric entry after long exposure to zero gravity, the upper limit is 4"g". Peak dynamic pressure can also influence the selection of the outermost TPS material if spallation is an issue.


title: Atmospheric entry

text: Starting from the principle of "conservative design", the engineer typically considers two worst-case trajectories, the undershoot and overshoot trajectories. The overshoot trajectory is typically defined as the shallowest-allowable entry velocity angle prior to atmospheric skip-off. The overshoot trajectory has the highest heat load and sets the TPS thickness. The undershoot trajectory is defined by the steepest allowable trajectory. For crewed missions the steepest entry angle is limited by the peak deceleration. The undershoot trajectory also has the highest peak heat flux and dynamic pressure. Consequently, the undershoot trajectory is the basis for selecting the TPS material. There is no "one size fits all" TPS material. A TPS material that is ideal for high heat flux may be too conductive (too dense) for a long duration heat load. A low-density TPS material might lack the tensile strength to resist spallation if the dynamic pressure is too high. A TPS material can perform well for a specific peak heat flux, but fail catastrophically for the same peak heat flux if the wall pressure is significantly increased (this happened with NASA's R-4 test spacecraft). Older TPS materials tend to be more labor-intensive and expensive to manufacture compared to modern materials. However, modern TPS materials often lack the flight history of the older materials (an important consideration for a risk-averse designer).


title: Atmospheric entry

text: Based upon Allen and Eggers discovery, maximum aeroshell bluntness (maximum drag) yields minimum TPS mass. Maximum bluntness (minimum ballistic coefficient) also yields a minimal terminal velocity at maximum altitude (very important for Mars EDL, but detrimental for military RVs). However, there is an upper limit to bluntness imposed by aerodynamic stability considerations based upon "shock wave detachment". A shock wave will remain attached to the tip of a sharp cone if the cone's half-angle is below a critical value. This critical half-angle can be estimated using perfect gas theory (this specific aerodynamic instability occurs below hypersonic speeds). For a nitrogen atmosphere (Earth or Titan), the maximum allowed half-angle is approximately 60°. For a carbon dioxide atmosphere (Mars or Venus), the maximum-allowed half-angle is approximately 70°. After shock wave detachment, an entry vehicle must carry significantly more shocklayer gas around the leading edge stagnation point (the subsonic cap). Consequently, the aerodynamic center moves upstream thus causing aerodynamic instability. It is incorrect to reapply an aeroshell design intended for Titan entry ("Huygens" probe in a nitrogen atmosphere) for Mars entry ("Beagle 2" in a carbon dioxide atmosphere). Prior to being abandoned, the Soviet Mars lander program achieved one successful landing (Mars 3), on the second of three entry attempts (the others were Mars 2 and Mars 6). The Soviet Mars landers were based upon a 60° half-angle aeroshell design.


title: Atmospheric entry

text: A 45° half-angle sphere-cone is typically used for atmospheric probes (surface landing not intended) even though TPS mass is not minimized. The rationale for a 45° half-angle is to have either aerodynamic stability from entry-to-impact (the heat shield is not jettisoned) or a short-and-sharp heat pulse followed by prompt heat shield jettison. A 45° sphere-cone design was used with the DS/2 Mars impactor and Pioneer Venus probes.


title: Atmospheric entry

text: Of satellites that reenter, approximately 10–40% of the mass of the object is likely to reach the surface of the Earth. On average, about one catalogued object reenters per day.


title: Atmospheric entry

text: Due to the Earth's surface being primarily water, most objects that survive reentry land in one of the world's oceans. The estimated chances that a given person will get hit and injured during their lifetime is around 1 in a trillion.


title: Atmospheric entry

text: On January 24, 1978, the Soviet Kosmos 954 () reentered and crashed near Great Slave Lake in the Northwest Territories of Canada. The satellite was nuclear-powered and left radioactive debris near its impact site.


title: Atmospheric entry

text: On July 11, 1979, the US Skylab space station () reentered and spread debris across the Australian Outback. The reentry was a major media event largely due to the Cosmos 954 incident, but not viewed as much as a potential disaster since it did not carry toxic nuclear or hydrazine fuel. NASA had originally hoped to use a Space Shuttle mission to either extend its life or enable a controlled reentry, but delays in the Shuttle program, plus unexpectedly high solar activity, made this impossible.


title: Atmospheric entry

text: On February 7, 1991, the Soviet Salyut 7 space station (), with the Kosmos 1686 module () attached, reentered and scattered debris over the town of Capitán Bermúdez, Argentina. The station had been boosted to a higher orbit in August 1986 in an attempt to keep it up until 1994, but in a scenario similar to Skylab, the planned Buran shuttle was cancelled and high solar activity caused it to come down sooner than expected.


title: Atmospheric entry

text: On September 7, 2011, NASA announced the impending uncontrolled reentry of the Upper Atmosphere Research Satellite () and noted that there was a small risk to the public. The decommissioned satellite reentered the atmosphere on September 24, 2011, and some pieces are presumed to have crashed into the South Pacific Ocean over a debris field long.


title: Atmospheric entry

text: On April 1, 2018, the Chinese Tiangong-1 space station () reentered over the Pacific Ocean, halfway between Australia and South America. The China Manned Space Engineering Office had intended to control the reentry, but lost telemetry and control in March 2017.


title: Atmospheric entry

text: On May 11, 2020, the core stage of Chinese Long March 5B (COSPAR ID 2020-027C) weighing roughly ) made an uncontrolled reentry over the Atlantic Ocean, near West African coast. Few pieces of rocket debris reportedly survived reentry and fell over at least two villages in Ivory Coast.


title: Atmospheric entry

text: On May 8, 2021, the core stage of Chinese Long March 5B (COSPAR ID 2021-0035B) weighing ) made an uncontrolled reentry, just west of the Maldives in the Indian Ocean (approximately 72.47°E longitude and 2.65°N latitude). Witnesses reported rocket debris as far away as the Arabian peninsula.


title: Atmospheric entry

text: It is expected that the Cruise Mass Balance Devices (CMBDs) from the Mars 2020 mission, which are ejected prior to the spacecraft entering the atmosphere, will survive re-entry and impact the surface on Thursday 18 February 2021. The CMBDs are 77 kg tungsten blocks used to adjust the spacecraft's trajectory prior to entry. The Science Team of another NASA mission, InSight, announced in early 2021 that they would attempt to detect the seismic waves from this impact event.


title: Atmospheric entry

text: In 2022 it was confirmed that space debris that had landed in New South Wales Australia were from a SpaceX craft that had launched in 2020.


title: Atmospheric entry

text: Salyut 1, the world's first space station, was deliberately de-orbited into the Pacific Ocean in 1971 following the Soyuz 11 accident. Its successor, Salyut 6, was de-orbited in a controlled manner as well.


title: Atmospheric entry

text: On June 4, 2000 the Compton Gamma Ray Observatory was deliberately de-orbited after one of its gyroscopes failed. The debris that did not burn up fell harmlessly into the Pacific Ocean. The observatory was still operational, but the failure of another gyroscope would have made de-orbiting much more difficult and dangerous. With some controversy, NASA decided in the interest of public safety that a controlled crash was preferable to letting the craft come down at random.


title: Atmospheric entry

text: In 2001, the Russian "Mir" space station was deliberately de-orbited, and broke apart in the fashion expected by the command center during atmospheric reentry. Mir entered the Earth's atmosphere on March 23, 2001, near Nadi, Fiji, and fell into the South Pacific Ocean.


title: Atmospheric entry

text: On February 21, 2008, a disabled U.S. spy satellite, USA-193, was hit at an altitude of approximately with an SM-3 missile fired from the U.S. Navy cruiser off the coast of Hawaii. The satellite was inoperative, having failed to reach its intended orbit when it was launched in 2006. Due to its rapidly deteriorating orbit it was destined for uncontrolled reentry within a month. U.S. Department of Defense expressed concern that the fuel tank containing highly toxic hydrazine might survive reentry to reach the Earth's surface intact. Several governments including those of Russia, China, and Belarus protested the action as a thinly-veiled demonstration of US anti-satellite capabilities. China had previously caused an international incident when it tested an anti-satellite missile in 2007.


title: Atmospheric entry

text: This list includes some notable atmospheric entries in which the spacecraft was not intended to be recovered, but was destroyed in the atmosphere.


title: Nordic Council

text: The Nordic Council is the official body for formal inter-parliamentary Nordic cooperation among the Nordic countries. Formed in 1952, it has 87 representatives from Denmark, Finland, Iceland, Norway, and Sweden as well as from the autonomous areas of the Faroe Islands, Greenland, and Åland. The representatives are members of parliament in their respective countries or areas and are elected by those parliaments. The Council holds ordinary sessions each year in October/November and usually one extra session per year with a specific theme. The council's official languages are Danish, Finnish, Icelandic, Norwegian, and Swedish, though it uses only the mutually intelligible Scandinavian languages—Danish, Norwegian, and Swedish—as its working languages. These three comprise the first language of around 80% of the region's population and are learned as a second or foreign language by the remaining 20%.


title: Nordic Council

text: In 1971, the Nordic Council of Ministers, an intergovernmental forum, was established to complement the council. The Council and the Council of Ministers are involved in various forms of cooperation with neighbouring areas in Northern Europe, including the German state of Schleswig-Holstein, the Benelux countries, the Baltic states and Russia.


title: Nordic Council

text: During World War II, Denmark and Norway were occupied by Germany; Finland was under assault by the Soviet Union; while Sweden, though neutral, still felt the war's effects. Following the war, the Nordic countries pursued the idea of a Scandinavian defence union to ensure their mutual defence. However, Finland, due to its Paasikivi-Kekkonen policy of neutrality and FCMA treaty with the USSR, could not participate.


title: Nordic Council

text: It was proposed that the Nordic countries would unify their foreign policy and defence, remain neutral in the event of a conflict and not ally with NATO, which some were planning at the time. The United States, keen on getting access to bases in Scandinavia and believing the Nordic countries incapable of defending themselves, stated it would not ensure military support for Scandinavia if they did not join NATO. As Denmark and Norway sought US aid for their post-war reconstruction, the project collapsed, with Denmark, Norway and Iceland joining NATO.


title: Nordic Council

text: Further Nordic co-operation, such as an economic customs union, also failed. This led Danish Prime Minister Hans Hedtoft to propose, in 1951, a consultative inter-parliamentary body. This proposal was agreed by Denmark, Iceland, Norway, and Sweden in 1952. The council's first session was held in the Danish Parliament on 13 February 1953 and it elected Hans Hedtoft as its president. When Finnish-Soviet relations thawed following the death of Joseph Stalin, Finland joined the council in 1955.


title: Nordic Council

text: On 2 July 1954, the Nordic labour market was created and in 1958, building upon a 1952 passport-free travel area, the Nordic Passport Union was created. These two measures helped ensure Nordic citizens' free movement around the area. A Nordic Convention on Social Security was implemented in 1955. There were also plans for a single market but they were abandoned in 1959 shortly before Denmark, Norway, and Sweden joined the European Free Trade Area (EFTA). Finland became an associated member of EFTA in 1961 and Denmark and Norway applied to join the European Economic Community (EEC).


title: Nordic Council

text: This move towards the EEC led to desire for a formal Nordic treaty. The Helsinki Treaty outlined the workings of the council and came into force on 24 March 1962. Further advancements on Nordic cooperation were made in the following years: a Nordic School of Public Health, a Nordic Cultural Fund, and Nordic House in Reykjavík were created. Danish Prime Minister Hilmar Baunsgaard proposed full economic cooperation ("Nordek") in 1968. Nordek was agreed in 1970, but Finland then backtracked, stating that its ties with the Soviet Union meant it could not form close economic ties with potential members of the EEC (Denmark and Norway). Nordek was then abandoned.


title: Nordic Council

text: As a consequence, Denmark and Norway applied to join the EEC and the Nordic Council of Ministers was set up in 1971 to ensure continued Nordic cooperation. In 1970 representatives of the Faroe Islands and Åland were allowed to take part in the Nordic Council as part of the Danish and Finnish delegations. Norway turned down EEC membership in 1972 while Denmark acted as a bridge builder between the EEC and the Nordics. Also in 1973, although it did not opt for full membership of the EEC, Finland negotiated a free trade treaty with the EEC that in practice removed customs duties from 1977 on, although there were transition periods up to 1985 for some products. Sweden did not apply due to its non-alliance policy, which was aimed at preserving neutrality. Greenland subsequently left the EEC and has since sought a more active role in circumpolar affairs.


title: Nordic Council

text: In the 1970s, the Nordic Council founded the Nordic Industrial Fund, Nordtest and the Nordic Investment Bank. The council's remit was also expanded to include environmental protection and, in order to clean up the pollution in the Baltic Sea and the North Atlantic, a joint energy network was established. The Nordic Science Policy Council was set up in 1983 and, in 1984, representatives from Greenland were allowed to join the Danish delegation.


title: Nordic Council

text: Following the collapse of the Soviet Union in 1991, the Nordic Council began to cooperate more with the Baltic states and new Baltic Sea organisations. Sweden and Finland joined the European Union (EU), the EEC's successor, in 1995. Norway had also applied, but once again voted against membership. However, Norway and Iceland did join the European Economic Area (EEA) which integrated them economically with the EU. The Nordic Passport Union was also subsumed into the EU's Schengen Area in 1996.


title: Nordic Council

text: The Nordic Council became more outward-looking, to the Arctic, Baltic, Europe, and Canada. The Øresund Bridge linking Sweden and Denmark led to a large amount of cross-border travel, which in turn led to further efforts to reduce barriers. However, the initially envisioned tasks and functions of the Nordic Council have become partially dormant due to the significant overlap with the EU and EEA. In 2008 Iceland began EU membership talks, but decided to annul these in 2015. Unlike the Benelux, there is no explicit provision in the Treaty on European Union that takes into account Nordic co-operation. However, the Treaties provide that international agreements concluded by the Member States before they become members of the Union remain valid, even if they are contrary to the provisions of Union law. However, each Member State must take all necessary measures to eliminate any discrepancies as quickly as possible. Nordic co-operation can therefore in practice only be designed to the extent that it complies with Union law.


title: Nordic Council

text: The Nordic Council consists of 87 representatives, elected from its members' parliaments and reflecting the relative representation of the political parties in those parliaments. It holds its main session in the autumn, while a so-called "theme session" is arranged in the spring. Each of the national delegations has its own secretariat in the national parliament. The autonomous territoriesGreenland, the Faroe Islands, and Ålandalso have Nordic secretariats.


title: Nordic Council

text: The Council does not have any formal power on its own, but each government has to implement any decisions through its national legislature. With Denmark, Norway, and Iceland being members of NATO and Finland and Sweden being neutral, the Nordic Council has not been involved in any military cooperation.


title: Nordic Council

text: The original Nordic Council concentrates on inter-parliamentary cooperation. The "Nordic Council of Ministers", founded in 1971, is responsible for intergovernmental cooperation. Prime Ministers have ultimate responsibility but this is usually delegated to the Minister for Nordic Cooperation and the Nordic Committee for Co-operation, which coordinates the day-to-day work. The autonomous territories have the same representation as states. The Nordic Council of Ministers has offices in the Baltic countries.


title: Nordic Council

text: The Nordic Council uses the three Continental Scandinavian languages (Danish, Norwegian, and Swedish) as its official working languages, while interpretation and translation service is arranged for Finnish and Icelandic (but never between the Scandinavian languages). The council also publishes material in English for information purposes. The Council refers to Danish, Norwegian, and Swedish collectively as Scandinavian and considers them to be different forms of the same language forming a common language community. Since 1987, under the Nordic Language Convention, citizens of the Nordic countries have the opportunity to use their native language when interacting with official bodies in other Nordic countries without being liable to any interpretation or translation costs. The Convention covers visits to hospitals, job centres, the police, and social security offices. The languages included are Danish, Finnish, Icelandic, Norwegian, and Swedish.


title: Nordic Council

text: On 31 October 2018, the council established it has five official languages, giving Finnish and Icelandic equal status with Danish, Norwegian, and Swedish from 1 January 2020 onward. While the working languages of the council's secretariat remain the three Scandinavian languages, the Council emphasised that the secretariat must include personnel with comprehensive understanding of Finnish and Icelandic as well. The then-President of the Council Michael Tetzschner thought the compromise good but also expressed concern over the change's expenses and hoped they would not increase so much that there would be pressure to switch over to using English.


title: Nordic Council

text: The Nordic Council and the Nordic Council of Ministers have a particular focus on strengthening the Nordic language community; the main focus of their work to promote language understanding in the Nordic countries is on children and young people's understanding of written and oral Danish, Norwegian, and Swedish, the three mutually intelligible Scandinavian languages.


title: Nordic Council

text: The Nordic Council and the Council of Ministers have their headquarters in Copenhagen and various installations in each separate country, as well as many offices in neighbouring countries. The headquarters are located at Ved Stranden No. 18, close to Slotsholmen.


title: Nordic Council

text: The Nordic Council has five full members (which are sovereign states) and three associate members (which are self-governing regions of full member states).


title: Nordic Council

text: In accordance with § 13 of the Rules of Procedure for the Nordic Council the Sámi Parliamentary Council is the only institution with observer status with the Nordic Council. In accordance with § 14, the Nordic Youth Council has the status of "guest" on a permanent basis, and the Presidium "may invite representatives of popularly elected bodies and other persons to a session and grant them speaking rights" as guests. According to the council, "within the last couple of years, guests from other international and Nordic organisations have been able to take part in the debates at the Sessions. Visitors from the Baltic States and Northwest Russia are those who mostly take up this opportunity. Guests who have a connection to the theme under discussion are invited to the Theme Session."


title: Nordic Council

text: The Nordic Council of Ministers has established four "Offices outside the Nordic Region": In Estonia, Latvia, Lithuania and the German state of Schleswig-Holstein. The offices form part of the secretariat of the Nordic Council of Ministers; according to the Council of Ministers their primary mission is to promote cooperation between the Nordic countries and the Baltic states and to promote the Nordic countries in cooperation with their embassies within the Baltic states.


title: Nordic Council

text: The Nordic Council and the Council of Ministers also define Estonia, Latvia, Lithuania, and Russia as "Adjacent Areas" and has formal cooperation with them under the Adjacent Areas policies framework; in recent years the cooperation has focused increasingly on Russia.


title: Nordic Council

text: The Nordic Council had historically been a strong supporter of Baltic independence from the Soviet Union. During the move towards independence in the Baltic States in 1991, Denmark and Iceland pressed for the Observer Status in the Nordic Council for the then-nonsovereign Estonia, Latvia, and Lithuania. The move in 1991 was opposed by Norway and Finland. The move was heavily opposed by the Soviet Union, accusing the Nordic Council of getting involved in its internal affairs. In the same year, the Nordic Council refused to give observer status for the three, at the time nonsovereign, Baltic states.


title: Nordic Council

text: While the Nordic Council rejected the Baltic states' application for formal observer status, the council nevertheless has extensive cooperation on different levels with all neighbouring countries, including the Baltic states and Germany, especially the state of Schleswig-Holstein. Representatives of Schleswig-Holstein were present as informal guests during a session for the first time in 2016. The state has historical ties to Denmark and cross-border cooperation with Denmark and has a Danish minority population. As parliamentary representatives from Schleswig-Holstein, a member of the South Schleswig Voter Federation and a member of the Social Democrats with ties to the Danish minority were elected.


title: Nordic Council

text: The Sámi political structures long desired formal representation in the Nordic Council's structures, and were eventually granted observer status through the Sámi Parliamentary Council. In addition, representatives of the Sámi people are de facto included in activities touching upon their interests. In addition, the Faroe Islands have expressed their wishes for full membership in the Nordic Council instead of the current associate membership.


title: Nordic Council

text: Three of the members of the Nordic Council (Sweden, Denmark, and Finland, all EU-member states), the Baltic Assembly, and the Benelux sought intensifying cooperation in the Digital Single Market, as well as discussing social matters, the Economic and Monetary Union of the European Union, the European migrant crisis and defense cooperation. Foreign relations in the wake of Russia's annexation of Crimea and the 2017 Turkish constitutional referendum were also on the agenda.


title: Nordic Council

text: Following the 2021 Scottish Parliament election, the Finnish member of Parliament Mikko Kärnä announced he would launch an initiative at the Nordic council to grant Scotland observer status.


title: Nordic Council

text: Some desire the Nordic Council's promotion of Nordic cooperation to go much further than at present. If the states of Iceland, Sweden, Norway, Denmark, and Finland were to merge in such an integration as some desire, it would command a gross domestic product of US$1.60 trillion, making it the twelfth largest economy in the world, larger than that of Australia, Spain, Mexico, or South Korea. Gunnar Wetterberg, a Swedish historian and economist, wrote a book entered into the Nordic Council's year book that proposes the creation of a Nordic Federation from the Council in a few decades.


title: Imperium (2016 film)

text: Imperium is a 2016 American crime thriller film written and directed by Daniel Ragussis (in his feature film debut) from a story by Michael German. The film stars Daniel Radcliffe, Toni Collette, Tracy Letts, Nestor Carbonell, and Sam Trammell. The film was released on August 19, 2016 in a limited release and through video on demand by Lionsgate Premiere.


title: Imperium (2016 film)

text: Nate Foster is a young FBI Special Agent working to uncover highly classified terrorist plots. After some illegally imported caesium-137 is stolen, Nate is recruited by Angela Zamparo, a fellow FBI Special Agent, who suspects the involvement of white supremacist groups.


title: Imperium (2016 film)

text: Through Zamparo's connections, Foster is introduced to a small group of Neo-Nazis led by Vince Sargent, a local leader who is familiar with their prime suspect, conservative talk radio host Dallas Wolf. Wolf, a figurehead in the movement for his incendiary rhetoric, assembles a gathering of the largest and most influential groups in the northeast. With Sargent's introductions, Foster becomes ingratiated in the movement and meets Andrew Blackwell, the leader of a premier white supremacist militia, as well as gaining Wolf's attention by convincing him he can fund an expansion of his radio show. Foster also becomes fast friends with Gerry Conway, a white collar engineer and family man, also a white supremacist.


title: Imperium (2016 film)

text: After earning Blackwell's trust by saving him during an attack on a white power rally by Antifa, Foster is brought to a crude military complex operated by Andrew's militia. There, Blackwell reveals that he has blueprints for the municipal water network of Washington, D.C. and is plotting an attack.


title: Imperium (2016 film)

text: The FBI begins to suspect that Wolf and Blackwell are working together after Foster meets Wolf at his home and discovers that his house sets off Foster's Geiger counter. Foster attempts to integrate himself into a possible plot by offering Wolf a substantial financial investment.


title: Imperium (2016 film)

text: Instead, Wolf becomes hostile and reports Foster to the FBI. It is revealed that he is merely an entertainer and does not believe in the cause, and that he has undergone radiation therapy for prostate cancer, which was registered by the Geiger counter. Blackwell is meanwhile also dismissed as a possible threat, as he appears to use the D.C. water network plans as a way to lure in potential recruits with promise of participating in an impending terror attack. With no further leads, the case is ordered to be closed by Foster's and Zamparo's superior. Angered at wasting his efforts, Foster prepares to have his cover identity leave the city.


title: Imperium (2016 film)

text: Foster meets Conway to make his final farewells. Sensing his genuine feelings of uselessness, Conway confides in Foster his membership in a domestic terrorist cell. It is revealed that Conway and his allies are in possession of the caesium and are plotting to detonate a dirty bomb. With Conway's introduction, Foster joins the group as supplier of the explosive (TATP). Though his cover is nearly blown several times by the paranoid terrorists, Foster manages to locate the caesium in Conway's home, leading the FBI to stop and arrest the terrorists before they are able to carry out the plot. Satisfied that he has made a difference, Foster makes one last visit to Johnny, a teenager and former member of Sargent's gang who no longer believes in the cause.


title: Imperium (2016 film)

text: Ragussis based his story on the experiences of FBI agent Michael German, who spent a year undercover with white supremacists. German wrote a book based upon his experience called "Thinking Like a Terrorist: Insights of a Former FBI Undercover Agent", and after Ragussis read the book, he reached out to German for help in creating Imperium. The two of them together then came up with the basic story for the movie.


title: Imperium (2016 film)

text: On July 30, 2015, it was announced that Radcliffe had been cast in the lead role, portraying a young FBI Special Agent who goes undercover to find and stop white supremacists trying to make a dirty bomb. The film marks the feature-length directorial debut of Daniel Ragussis. Toni Collette, Sam Trammell, and Tracy Letts joined the cast of the film on October 8, 2015.


title: Imperium (2016 film)

text: Principal photography began in late September 2015, with filming taking place in Richmond, Virginia and the nearby city of Hopewell. The first images of Radcliffe on the set, with a shaved head, were released on September 22, 2015.


title: Imperium (2016 film)

text: In September 2015, it was reported that Signature Entertainment had pre-bought the rights to the film for the United Kingdom. Lionsgate Premiere acquired the United States domestic rights in early October 2015. The film was released in a limited release and through video on demand on August 19, 2016.


title: Imperium (2016 film)

text: "Imperium" was generally well received. The review aggregator website Rotten Tomatoes gives the film an approval rating of 85%, based on 73 reviews, with an average rating of 6.50/10. The site's critical consensus reads, "The unsettling "Imperium" boasts troublingly timely themes and a talented cast led by Daniel Radcliffe as an undercover FBI agent infiltrating a ring of white supremacists." On Metacritic, which assigns a normalized rating, the film has a score of 68 out of 100, based on 17 critics, indicating "generally favorable reviews". The film was a "New York Times" Critics' Pick. The "Los Angeles Times" called it "impressively dimensional... tense, gripping and disturbing," "Slant" magazine called it "bold political cinema," and "Entertainment Weekly" said the film was "a tense, chilling thriller... Radcliffe is brilliant."


title: Joe Willock

text: Joseph George Willock (born 20 August 1999) is an English professional footballer who plays as a midfielder for Premier League club Newcastle United.


title: Joe Willock

text: A youth product of Arsenal, Willock joined Arsenal at age four-and-a-half, having been allowed to play alongside his older brothers. He made his first-team debut for the club on 20 September 2017 in the EFL Cup against Doncaster Rovers.


title: Joe Willock

text: Willock made his Premier League debut against Newcastle United on 15 April 2018. He scored his first senior goal on 29 November 2018 in a 3–0 UEFA Europa League victory away at Vorskla Poltava. He then scored his first brace in a 3–0 FA Cup victory away at Blackpool on 5 January 2019.


title: Joe Willock

text: On 12 September 2019, it was announced that Willock had signed a new long-term contract with Arsenal. On 19 September 2019, he played as Arsenal won 3–0 against Eintracht Frankfurt by scoring a deflected effort to open the scoring in the opening matchday of the 2019–20 UEFA Europa League. Willock scored his first goal at the Emirates Stadium on 24 September 2019 after tapping-in Arsenal's third goal in a 5–0 EFL Cup win over Nottingham Forest, set-up by Héctor Bellerín. On 25 June 2020, he scored his first Premier League goal in a 2–0 win over Southampton.


title: Joe Willock

text: On 1 February 2021, Willock joined Newcastle United on loan for the remainder of the 2020–21 season. On 6 February, Willock scored in the 16th minute on his debut in a 3–2 win over Southampton. After scoring in three consecutive substitute appearances against Tottenham Hotspur, West Ham United and Liverpool, Willock was rewarded with a start against Leicester City, where he was once again on target, scoring the opening goal in a 4–2 win. On 14 May, Willock scored in a 4–3 defeat against Manchester City. On 19 May, he scored in his sixth consecutive league game, becoming the youngest player in Premier League history to do so at the age of 21 years and 272 days, a record previously held by Romelu Lukaku. Four days later, on the final day of the Premier League season, he scored again to equal the club record of consecutive games scored in, set by Alan Shearer.


title: Joe Willock

text: On 13 August 2021, Newcastle confirmed the signing of Willock on a six-year contract. The fee was reported to be £25 million. On 19 February 2022, Willock scored his first goal since signing permanently for the club, in a 1–1 draw against West Ham United. The following week, he scored Newcastle's second goal in a 2–0 win over Brentford.


title: Joe Willock

text: Willock scored for the England under-16 team against Scotland in the 2014 Victory Shield. He also represented the England under-19 team but was one of a number of players withdrawn from selection for the 2018 UEFA European Under-19 Championship by their club.


title: Joe Willock

text: Willock represented the England under-20 team in the 2018–19 Under 20 Elite League and scored the winning goals in games against Italy and Germany. Willock was a member of an England Under-20 side at the 2019 Toulon Tournament and scored in group stage defeats against Portugal and Chile.


title: Joe Willock

text: On 30 August 2019, Willock was included in the England under-21 squad for the first time but had to withdraw due to injury. He eventually made his U21 debut on 11 October 2019 during a 2–2 with Slovenia in Maribor.


title: Joe Willock

text: Willock was born in Waltham Forest, Greater London. His brothers, Chris and Matty, are also footballers. All three brothers shared a pitch when Manchester United played a reserve game against Arsenal in May 2017. He is of Montserratian descent.


title: Señorita (Shawn Mendes and Camila Cabello song)

text: "Señorita" is a song by Canadian singer Shawn Mendes and Cuban-American singer Camila Cabello. It was released on June 21, 2019, through Island and Epic Records as the second single (seventh overall) from the deluxe edition of Mendes' self-titled third studio album and later included on Cabello's second studio album "Romance" (2019). The song was written by Mendes, Cabello, Charli XCX, Ali Tamposi, Jack Patterson, and its producers Andrew Watt, Benny Blanco, and Cashmere Cat.


text: The song marks Mendes and Cabello's second collaboration, following "I Know What You Did Last Summer" from Mendes' debut album, "Handwritten" (2015). "Señorita" reached number one on the US "Billboard" Hot 100, as well as topping the charts in a record setting 40 countries worldwide. It is certified multiplatinum in thirteen countries, including Diamond in France, Mexico, and Poland. "Señorita" received highly positive reviews from music critics. The single has won an American Music Award, two MTV Video Music Awards, a People's Choice Award, and received a nomination for a Grammy Award for Best Pop Duo/Group Performance. The song was the biggest song of 2019 in Malaysia and according to the International Federation of the Phonographic Industry (IFPI), it was the third best-selling single of 2019 worldwide, with combined sales and track-equivalent streams of 16.1 million units globally. As of October 2021 it is the 9th most streamed song on Spotify.


text: The song was originally conceived during a studio session between Charli XCX, Ali Tamposi, Jack Patterson of Clean Bandit, and Andrew Watt, the last of whom produced the song. Watt, prior to the studio session, created a guitar melody that he described as being reminiscent of Fleetwood Mac and José Feliciano. He played the guitar melody during the studio session where ideas for melodies and lyrics were created to accompany it. The melody and lyrics for the chorus of the song eventually formed, including what would become the opening line, "I love it when you call me señorita".


text: Watt sent the rough chorus of the song to Shawn Mendes, suggesting that the song be recorded as a duet, to which Mendes agreed and said that Camila Cabello would be "the only person" with whom he could do the song. Watt then sent the song to producers Benny Blanco and Cashmere Cat who liked it and began to work together on the production of the song, deciding to keep it simple to make room for the vocals.


text: Mendes and Cabello both made changes to the melody and lyrics to their liking. After the song's key changed and Cabello recorded some vocals, Watt flew to England and planned to record Mendes' vocals on a day off from his tour after his Manchester Arena show. However, Watt, to Mendes' amusement, accidentally blew the microphone by forgetting to change the conversion of power to 220V on the power box. This forced Watt to record Mendes' vocals at the Birmingham Arena, angering Mendes throughout the process because he wanted to preserve his voice for his then-upcoming shows at the O2 Arena.