119-670: A multiple independently targetable reentry vehicle ( MIRV ) is an exoatmospheric ballistic missile payload containing several warheads , each capable of being aimed to hit a different target. The concept is almost invariably associated with intercontinental ballistic missiles carrying thermonuclear warheads , even if not strictly being limited to them. An intermediate case is the multiple reentry vehicle (MRV) missile which carries several warheads which are dispersed but not individually aimed. All nuclear-weapon states except Pakistan and North Korea are currently confirmed to have deployed MIRV missile systems. The first true MIRV design
238-438: A ballistic missile deploys multiple warheads above a single aimpoint which then drift apart, producing a cluster bomb-like effect. These warheads are not individually targetable. The advantage of an MRV over a single warhead is the increased effectiveness due to the greater coverage; this increases the overall damage produced within the center of the pattern, making it far greater than the damage possible from any single warhead in
357-414: A nuclear warhead and allows a single launched missile to strike several targets. Submarine-launched ballistic missiles operate in a different way from submarine-launched cruise missiles . Modern submarine-launched ballistic missiles are closely related to intercontinental ballistic missiles (ICBMs), with ranges of over 5,500 kilometres (3,000 nmi), and in many cases SLBMs and ICBMs may be part of
476-545: A 19-species model. 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
595-471: 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
714-739: A Polaris A-1 on 20 July 1960. Fifty-two days later, the Soviet Union made its first successful underwater launch of a submarine ballistic missile in the White Sea, on 10 September 1960 from the same converted Project 611 ( NATO reporting name Zulu-IV class) submarine that first launched the R-11FM. The Soviets were only a year behind the US with their first SSBN, the ill-fated K-19 of Project 658 (Hotel class), commissioned in November 1960. However,
833-499: 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
952-459: 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
1071-435: 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
1190-488: A covert purpose to map mass concentrations and determine local gravity anomalies , in order to improve accuracies of ballistic missiles. Accuracy is expressed as circular error probable (CEP). This is the radius of the circle that the warhead has a 50 percent chance of falling into when aimed at the center. CEP is about 90–100 m for the Trident II and Peacekeeper missiles. A multiple re-entry vehicle (MRV) system for
1309-489: A different target. Although the US did not commission any new SSBNs from 1967 through 1981, it did introduce two new SLBMs. Thirty-one of the 41 original US SSBNs were built with larger diameter launch tubes with future missiles in mind. In the early 1970s the Poseidon (C-3) missile entered service, and those 31 SSBNs were backfitted with it. Poseidon offered a massive MIRV capability of up to 14 warheads per missile. Like
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#17327724501671428-455: 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
1547-572: A gas that are important to aeronautical engineers who design heat shields: 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. The perfect gas theory
1666-574: A heat shield designer must use a real gas model . 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
1785-752: A lone Typhoon used as a testbed for new missiles (the R-39s unique to the Typhoons were reportedly scrapped in 2012). Upgraded missiles such as the R-29RMU Sineva (SS-N-23 Sineva) were developed for the Deltas. In 2013 the Russians commissioned the first Borei-class submarine , also called the Dolgorukiy class after the lead vessel. By 2015 two others had entered service. This class is intended to replace
1904-430: A major change in the strategic balance. Previously, with one warhead per missile, it was conceivable that one could build a defense that used missiles to attack individual warheads. Any increase in missile fleet by the enemy could be countered by a similar increase in interceptors. With MIRV, a single new enemy missile meant that multiple interceptors would have to be built, meaning that it was much less expensive to increase
2023-621: A miniaturized physics package and a lower mass re-entry vehicle, both of which are highly advanced technologies. As a result, single-warhead missiles are more attractive for nations with less advanced or less productive nuclear technology. The United States first deployed MRV warheads on the Polaris A-3 SLBM in 1964 on the USS Daniel Webster . The Polaris A-3 missile carried three warheads each having an approximate yield of 200 kilotonnes of TNT (840 TJ). This system
2142-656: 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. 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. The thermal conductivity of
2261-455: A new Oreshnik intermediate-range ballistic missile , striking Dnipro . Analysts stated the missile used a multiple independently targetable reentry vehicle (MIRV), likely marking their first use in combat. The night attack was reported to see six sequential vertical flashes, each comprising a cluster of up to six individual projectiles. Ukraine's air force initially claimed an intercontinental ballistic missile (range greater than 5,500 km)
2380-454: 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
2499-402: 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. AMaRV's attitude
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#17327724501672618-461: 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. The NASA Galileo Probe used carbon phenolic for its TPS material. 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
2737-421: 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
2856-742: A range of 7,700 kilometres (4,200 nmi), entered service on the first Delta-I boat in 1972, before the Yankee class was even completed. A total of 43 Delta-class boats of all types entered service 1972–90, with the SS-N-18 on the Delta III class and the R-29RM Shtil (SS-N-23) on the Delta IV class. The new missiles had increased range and eventually multiple independently targetable reentry vehicles ( MIRV ), multiple warheads that could each hit
2975-515: A single reentry vehicle system, as part of its obligations under the New START treaty. The military purpose of a MIRV is fourfold: MIRV land-based ICBMs were considered destabilizing because they tended to put a premium on striking first . The world's first MIRV—US Minuteman III missile of 1970—threatened to rapidly increase the US's deployable nuclear arsenal and thus the possibility that it would have enough bombs to destroy virtually all of
3094-428: 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. There are several basic shapes used in designing entry vehicles: The simplest axisymmetric shape is the sphere or spherical section. This can either be
3213-407: 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
3332-521: 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. 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
3451-411: 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. A thermal protection system , or TPS,
3570-531: Is another entry vehicle geometry and was used with the X-23 PRIME (Precision Recovery Including Maneuvering Entry) vehicle. 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: As velocity increases, both convective and radiative heating increase, but at different rates. At very high speeds, radiative heating will dominate
3689-465: Is at 400,000 feet (122 km), the main heating during controlled entry takes place at altitudes of 65 to 35 kilometres (213,000 to 115,000 ft), peaking at 58 kilometres (190,000 ft). 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
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3808-506: 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 7.8 km/s (28,000 km/h; 17,000 mph). For lunar return entry of 11 km/s,
3927-566: Is because of their first-strike capability that land-based MIRVs were banned under the START II agreement. START II was ratified by the Russian Duma on 14 April 2000, but Russia withdrew from the treaty in 2002 after the US withdrew from the ABM treaty . In a MIRV, the main rocket motor (or booster ) pushes a "bus" into a free-flight suborbital ballistic flight path. After the boost phase,
4046-408: Is crucial because doubling the accuracy decreases the needed warhead energy by a factor of four for radiation damage and by a factor of eight for blast damage. Navigation system accuracy and the available geophysical information limits the warhead target accuracy. Some writers believe that government-supported geophysical mapping initiatives and ocean satellite altitude systems such as Seasat may have
4165-448: 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 (277 °C; 530 °F) 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 (1,730 °C; 3,140 °F). For temperatures greater than 2,000 K,
4284-466: Is lower than other high-heat-flux-ablative materials, such as conventional carbon phenolics. 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 28,000 mph (ca. 12.5 km/s) at 135 km altitude. This was faster than
4403-528: Is pre-bonded to the aeroshell's structure thus enabling construction of a large heat shield. 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
4522-446: 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. 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
4641-457: Is the barrier that protects a spacecraft during the searing heat of atmospheric reentry. Multiple approaches for the thermal protection of spacecraft are in use, among them ablative heat shields, passive cooling, and active cooling of spacecraft surfaces. In general they can be divided into two categories: ablative TPS and reusable TPS. Ablative TPS are required when space craft reach a relatively low altitude before slowing down. Spacecraft like
4760-447: 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
4879-453: 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.) The original American sphere-cone aeroshell
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4998-490: 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. 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
5117-541: The Cold War , as they can hide from reconnaissance satellites and fire their nuclear weapons with virtual impunity. This makes them immune to a first strike directed against nuclear forces, allowing each side to maintain the capability to launch a devastating retaliatory strike , even if all land-based missiles have been destroyed. This relieves each side of the necessity to adopt a launch on warning posture, with its attendant risk of accidental nuclear war. Additionally,
5236-642: The G77 Fortran compiler. 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 2 = N + N and N + N = N 2 (dissociation and recombination). Because of its simplicity,
5355-592: 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 . 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
5474-791: The Naval Submarine Base King's Bay in Georgia was built for the Trident I-equipped force. Both the United States and the Soviet Union commissioned larger SSBNs designed for new missiles in 1981. The American large SSBN was the Ohio class , also called the "Trident submarine", with the largest SSBN armament ever of 24 missiles, initially Trident I but built with much larger tubes for the Trident II (D-5) missile , which entered service in 1990. The entire class
5593-626: The Soviet Union's nuclear weapons and negate any significant retaliation. Later on the US feared the Soviet's MIRVs because Soviet missiles had a greater throw-weight and could thus put more warheads on each missile than the US could. For example, the US MIRVs might have increased their warhead per missile count by a factor of 6 while the Soviets increased theirs by a factor of 10. Furthermore,
5712-480: 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
5831-610: The Stardust probe. Crewed space vehicles must be slowed to subsonic speeds before parachutes or air brakes may be deployed. Such vehicles have high kinetic energies, and atmospheric dissipation is the only way of expending this, as it is highly impractical to use retrorockets for the entire reentry procedure. 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 high-altitude parachute jumps from balloons do not require heat shielding because
5950-566: The Strategic Air Command 's (SAC) arsenal and replace them with the new Minuteman IIIs outfitted with a MIRV payload, increasing their overall effectiveness. The smaller power of the warheads used (W62, W78 and W87) was offset by increasing the accuracy of the system, allowing it to attack the same hard targets as the larger, less accurate, W56. The MMIII was introduced specifically to address the Soviet construction of an anti-ballistic missile (ABM) system around Moscow; MIRV allowed
6069-611: 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 1,200-kilometer (650-nautical-mile) 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 8,000 to 12,000 km (4,300 to 6,500 nmi), were only possible with
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#17327724501676188-408: The giant planets . 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 30 miles (48 km) 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
6307-419: 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
6426-455: The nuclear test series Operation Dominic . The first Soviet SSBN with 16 missiles was the Project 667A (Yankee class), which first entered service in 1967 with 32 boats completed by 1974. By the time the first Yankee was commissioned the US had built 41 SSBNs, nicknamed the " 41 for Freedom ". The short range of the early SLBMs dictated basing and deployment locations. By the late 1960s
6545-548: 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
6664-634: 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 . An improved and easier to produce version called PICA-X
6783-787: 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,
6902-676: The DC-X also served as the basis for an unsuccessful proposal for what eventually became the Lockheed Martin X-33 . 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
7021-504: 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.,
7140-513: The Hotel class carried only three R-13 missiles (NATO reporting name SS-N-4) each and had to surface and raise the missile to launch. Submerged launch was not an operational capability for the Soviets until 1963, when the R-21 missile (SS-N-5) was first backfitted to Project 658 (Hotel class) and Project 629 (Golf class) submarines. The Soviet Union was able to beat the U.S. in launching and testing
7259-533: The Lighthill-Freeman model is a useful pedagogical tool, but is 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 2 , O 2 , NO, N, and O. The five species model assumes no ionization and ignores trace species like carbon dioxide. When running
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#17327724501677378-500: The MRV cluster; this makes for an efficient area-attack weapon and makes interception by anti-ballistic missiles more challenging due to the number of warheads being deployed at once. Improved warhead designs allow smaller warheads for a given yield, while better electronics and guidance systems allow greater accuracy. As a result, MIRV technology has proven more attractive than MRV for advanced nations. Multiple-warhead missiles require both
7497-843: The Navy, beginning in late 1955. However, at the Project Nobska submarine warfare conference in 1956, physicist Edward Teller stated that a physically small one-megaton warhead could be produced for the relatively small, solid-fueled Polaris missile , and this prompted the Navy to leave the Jupiter program in December of that year. Soon Chief of Naval Operations Admiral Arleigh Burke concentrated all Navy strategic research on Polaris , still under Admiral Raborn's Special Project Office. All US SLBMs have been solid-fueled while all Soviet and Russian SLBMs have been liquid-fueled except for
7616-568: The Polaris A-3 was deployed on all US SSBNs with a range of 4,600 kilometres (2,500 nmi), a great improvement on the 1,900 kilometres (1,000 nmi) range of Polaris A-1. The A-3 also had three warheads that landed in a pattern around a single target. The Yankee class was initially equipped with the R-27 Zyb missile (SS-N-6) with a range of 2,400 kilometres (1,300 nmi). The US was much more fortunate in its basing arrangements than
7735-499: The Russian RSM-56 Bulava , which entered service in 2014. The world's first operational nuclear-powered ballistic missile submarine (SSBN) was USS George Washington (SSBN-598) with 16 Polaris A-1 missiles, which entered service in December 1959 and conducted the first SSBN deterrent patrol November 1960 – January 1961. George Washington also conducted the first successful submerged SLBM launch with
7854-585: The Soviets, the US also desired a longer-range missile that would allow SSBNs to be based in CONUS. In the late 1970s the Trident I (C-4) missile with a range of 7,400 kilometres (4,000 nmi) and eight MIRV warheads was backfitted to 12 of the Poseidon-equipped submarines. The SSBN facilities (primarily a submarine tender and floating dry dock ) of the base at Rota, Spain were disestablished and
7973-651: The Soviets. Thanks to NATO and the US possession of Guam , US SSBNs were permanently forward deployed at Advanced Refit Sites in Holy Loch , Scotland, Rota, Spain , and Guam by the middle 1960s, resulting in short transit times to patrol areas near the Soviet Union. The SSBN facilities at the Advanced Refit Sites were austere, with only a submarine tender and floating dry dock . Converted merchant ships designated T-AKs ( Military Sealift Command cargo ships) were provided to ferry missiles and supplies to
8092-488: 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: 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
8211-517: The US had a much smaller proportion of its nuclear arsenal in ICBMs than the Soviets. Bombers could not be outfitted with MIRVs so their capacity would not be multiplied. Thus the US did not seem to have as much potential for MIRV usage as the Soviets. However, the US had a larger number of submarine-launched ballistic missiles , which could be outfitted with MIRVs, and helped offset the ICBM disadvantage. It
8330-440: The US to overwhelm any conceivable ABM system without increasing the size of their own missile fleet. The Soviets responded by adding MIRV to their R-36 design, first with three warheads in 1975, and eventually up to ten in later versions. While the United States phased out the use of MIRVs in ICBMs in 2014 to comply with New START , Russia continues to develop new ICBM designs using the technology. The introduction of MIRV led to
8449-607: The US with the collapse of the Soviet Union and the end of the Cold War in 1991. The US rapidly decommissioned its remaining 31 older SSBNs, with a few converted to other roles, and the base at Holy Loch was disestablished. Most of the former Soviet SSBN force was gradually scrapped under the provisions of the Nunn–Lugar Cooperative Threat Reduction agreement through 2012. By that time the Russian SSBN force stood at six Delta-IVs, three Delta-IIIs, and
8568-565: The United States ( Operation Paperclip ) and for the Soviet Union on their SLBM programs. These and other early SLBM systems required vessels to be surfaced when they fired missiles, but launch systems were adapted to allow underwater launching in the 1950-1960s. A converted Project 611 (Zulu-IV class) submarine launched the world's first SLBM, an R-11FM (SS-N-1 Scud-A, naval variant of the SS-1 Scud ) on 16 September 1955. Five additional Project V611 and AV611 (Zulu-V class) submarines became
8687-487: The aging Deltas, and carries 16 solid-fuel RSM-56 Bulava missiles, with a reported range of 10,000 kilometres (5,400 nmi) and six MIRV warheads. The US is building a replacement for the Ohio class ; however, the first of the class wasn't laid down until October 2020. Ballistic missile submarines have been of great strategic importance for the United States, Russia, and other nuclear powers since they entered service in
8806-442: 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." Practical development of reentry systems began as the range, and reentry velocity of ballistic missiles increased. For early short-range missiles, like
8925-422: 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). 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
9044-413: The attack than the defense. This cost-exchange ratio was so heavily biased towards the attacker that the concept of mutual assured destruction became the leading concept in strategic planning and ABM systems were severely limited in the 1972 Anti-Ballistic Missile Treaty in order to avoid a massive arms race . In June 2017 the United States finished converting its Minuteman III missiles back to using
9163-530: The bus maneuvers using small on-board rocket motors and a computerized inertial guidance system . It takes up a ballistic trajectory that will deliver a re-entry vehicle containing a warhead to a target and then releases a warhead on that trajectory. It then maneuvers to a different trajectory, releasing another warhead, and repeats the process for all warheads. The precise technical details are closely guarded military secrets , to hinder any development of enemy counter-measures. The bus's on-board propellant limits
9282-469: 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). Determining the thermodynamic state of the stagnation point is more difficult under an equilibrium gas model than a perfect gas model. Under
9401-402: 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
9520-551: The continental United States ( CONUS ) at risk. This resulted in only a small percentage of the Soviet force occupying patrol areas at any time, and was a great motivation for longer-range Soviet SLBMs, which would allow them to patrol close to their bases, in areas sometimes referred to as "deep bastions". These missiles were the R-29 Vysota series (SS-N-8, SS-N-18, SS-N-23), equipped on Projects 667B, 667BD, 667BDR, and 667BDRM (Delta-I through Delta-IV classes). The SS-N-8, with
9639-598: The controlled atmospheric entry, descent, and landing of spacecraft are collectively termed as EDL . 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. Reentry has been achieved with speeds ranging from 7.8 km/s for low Earth orbit to around 12.5 km/s for
9758-418: 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. During certain intensity of ionization, a radio-blackout with the spacecraft is produced. While NASA's Earth entry interface
9877-596: The deployment of highly accurate missiles on ultra-quiet submarines allows an attacker to sneak up close to the enemy coast and launch a missile on a depressed trajectory (a non-optimal ballistic trajectory which trades off reduced throw-weight for a faster and lower path, effectively reducing the time between launch and impact), thus opening the possibility of a decapitation strike . Specific types of SLBMs (current, past and under development) include: Some former Russian SLBMs have been converted into Volna and Shtil' launch vehicles to launch satellites – either from
9996-524: The development of modern ablative heat shields and blunt-shaped vehicles. 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
10115-468: The distances between targets of individual warheads to perhaps a few hundred kilometers. Some warheads may use small hypersonic airfoils during the descent to gain additional cross-range distance. Additionally, some buses (e.g. the British Chevaline system) can release decoys to confuse interception devices and radars , such as aluminized balloons or electronic noisemakers. Accuracy
10234-517: The end of 1982. These were all in the Pacific, and the Guam SSBN base was disestablished; the first several Ohio -class boats used new Trident facilities at Naval Submarine Base Bangor , Washington . Eighteen Ohio -class boats were commissioned by 1997, four of which were converted as cruise missile submarines (SSGN) in the 2000s to comply with START I treaty requirements. The Soviet large SSBN
10353-625: The first SLBM with a live nuclear warhead, an R-13 that detonated in the Novaya Zemlya Test Range in the Arctic Ocean, doing so on 20 October 1961, just ten days before the gigantic 50 Mt Tsar Bomba 's detonation in the same general area. The United States eventually conducted a similar test in the Pacific Ocean on 6 May 1962, with a Polaris A-2 launched from USS Ethan Allen (SSBN-608) as part of
10472-447: 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
10591-432: 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
10710-648: 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. For Earth, atmospheric entry occurs by convention at the Kármán line at an altitude of 100 km (62 miles; 54 nautical miles) above the surface, while at Venus atmospheric entry occurs at 250 km (160 mi; 130 nmi) and at Mars atmospheric entry at about 80 km (50 mi; 43 nmi). Uncontrolled objects reach high velocities while accelerating through space toward
10829-408: 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
10948-444: 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:
11067-593: 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. Submarine-launched ballistic missile A submarine-launched ballistic missile ( SLBM ) is a ballistic missile capable of being launched from submarines . Modern variants usually deliver multiple independently targetable reentry vehicles (MIRVs), each of which carries
11186-438: 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
11305-481: 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
11424-463: The same family of weapons. The first practical design of a submarine -based launch platform was developed by the Germans near the end of World War II involving a launch tube which contained a V-2 ballistic missile variant and was towed behind a submarine, known by the code-name Prüfstand XII . The war ended before it could be tested, but the engineers who had worked on it were taken to work for
11543-451: 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
11662-430: 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
11781-447: 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. Atmospheric entry interface velocities on a Mars–Earth trajectory are on the order of 12 km/s (43,000 km/h; 27,000 mph). Modeling high-speed Mars atmospheric entry—which involves a carbon dioxide, nitrogen and argon atmosphere—is even more complex requiring
11900-589: 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). 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
12019-399: 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
12138-703: The sites. With two rotating crews per boat, about one-third of the total US force could be in a patrol area at any time. The Soviet bases, in Severomorsk (near Murmansk ) for the Arctic - Atlantic theater in Petropavlovsk-Kamchatsky for the Pacific theater, required their SSBNs to make a long transit (e.g., through NATO-monitored waters in the Atlantic) to their mid-ocean patrol areas to hold
12257-408: The space shuttle are designed to slow down at high altitude so that they can use reuseable TPS. (see: Space Shuttle thermal protection system ). Thermal protection systems are tested in high enthalpy ground testing or plasma wind tunnels that reproduce the combination of high enthalpy and high stagnation pressure using Induction plasma or DC plasma. The ablative heat shield functions by lifting
12376-471: 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. The sphere-cone is a spherical section with a frustum or blunted cone attached. The sphere-cone's dynamic stability
12495-483: 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. 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
12614-455: The vehicle, the heat energy would stay in the shocked gas and simply move around the vehicle to later dissipate into the atmosphere. The Allen and Eggers discovery, though initially treated as a military secret, was eventually published in 1958. 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
12733-484: The world's first operational ballistic missile submarines (SSBs) with two R-11FM missiles each, entering service in 1956–57. The United States Navy initially worked on a sea-based variant of the US Army Jupiter intermediate-range ballistic missile , projecting four of the large, liquid-fueled missiles per submarine. Rear Admiral W. F. "Red" Raborn headed a Special Project Office to develop Jupiter for
12852-402: 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
12971-798: Was also used by the Royal Navy who also retained MRV with the Chevaline upgrade, though the number of warheads in Chevaline was reduced to two due to the ABM counter-measures carried. The Soviet Union deployed 3 MRVs on the R-27U SLBM and 3 MRVs on the R-36P ICBM. Refer to atmospheric re-entry for more details. On November 21, 2024, as part of the Russian invasion of Ukraine , Russia launched
13090-418: 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
13209-459: Was converted to use Trident II by the early 2000s. Trident II offered a range of over 8,000 kilometres (4,300 nmi) with eight larger MIRV warheads than Trident I. When the USS ; Ohio (SSBN-726) commenced sea trials in 1980, two of the first ten US SSBNs had their missiles removed to comply with SALT treaty requirements; the remaining eight were converted to attack submarines (SSN) by
13328-657: 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. PICA-X is ten times less expensive to manufacture than the NASA PICA heat shield material. A second enhanced version of PICA—called PICA-3—was developed by SpaceX during
13447-544: 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. 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
13566-498: 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° and 11°. Reconnaissance satellite RVs (recovery vehicles) also used
13685-602: Was the Minuteman III , first successfully tested in 1968 and introduced into actual use in 1970. The Minuteman III held three smaller W62 warheads, with yields of about 170 kilotons of TNT (710 TJ) each in place of the single 1.2 megatons of TNT (5.0 PJ) W56 used on the Minuteman II. From 1970 to 1975, the United States would remove approximately 550 earlier versions of the Minuteman ICBM in
13804-608: Was the Project 941 Akula , famous as the Typhoon-class (and not to be confused with the Project 971 Shchuka attack submarine , called "Akula" by NATO). The Typhoons were the largest submarines ever built at 48,000 tons submerged. They were armed with 20 of the new R-39 Rif (SS-N-20) missiles with a range of 8,300 kilometres (4,500 nmi) and 10 MIRV warheads. Six Typhoons were commissioned in 1981–89. New SSBN construction terminated for over 10 years in Russia and slowed in
13923-604: 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
14042-663: Was used, and Ukrainian media initially reported it was an RS-26 Rubezh ICBM with range 5,800 km. The US and Russia confirmed it was intermediate-range (3,000–5,500 km), but the Pentagon stated it was based on the RS-26 ICBM. It was fired from the Astrakhan region 700 km away. UN spokesperson Stéphane Dujarric called the use of the intermediate-range weapon "concerning and worrying". Atmospheric entry Atmospheric entry (sometimes listed as V impact or V entry )
14161-483: 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
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