Further information: Re-Entry (Marley Marl album) and Re-Entry (Big Brovaz album)

Atmospheric reentry refers to the movement of human-made or natural objects as they enter the atmosphere of a planet from outer space, in the case of Earth from an altitude above the "edge of space. Re-entry is a 2001 studio album by Marley Marl, released on on Barely Breaking Even Records "Re-Entry" was the second album released by UK R&B / Hip Hop collective Big Brovaz. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is Altitude is the Elevation of a point or object from a known level or datum (plural data " This article primarily addresses the process of controlled reentry of vehicles which are intended to reach the planetary surface intact, but the topic also includes uncontrolled (or minimally controlled) cases, such as the intentionally or circumstantially occurring, destructive deorbiting of satellites and the falling back to the planet of "space junk" due to orbital decay. This article is about artificial satellites For natural satellites also known as moons see Natural satellite. Space debris or orbital debris, also called space junk and space waste are the objects in Orbit around Earth created by humans that no Orbital decay is the process of prolonged reduction in the height of a satellite's Orbit.

Vehicles that typically undergo this process include ones returning from orbit (spacecraft) and ones on exo-orbital (suborbital) trajectories (ICBM reentry vehicles, some spacecraft. A spacecraft is a Vehicle or machine designed for Spaceflight. A sub-orbital spaceflight (or sub-orbital flight is a Spaceflight in which the Spacecraft reaches space, but its Trajectory intersects ) Typically this process requires special methods to protect against aerodynamic heating. Aerodynamic heating is the heating of a solid body produced by the passage of fluid (such as air over a body such as a Meteor, Missile, or Airplane. Various advanced technologies have been developed to enable atmospheric reentry and flight at extreme velocities.

Contents 1 History 2 Terminology, definitions and jargon 3 Blunt body entry vehicles 4 Entry vehicle shapes 4.1 Sphere or spherical section 4.2 Sphere-cone 4.3 Biconic 4.4 Non-axisymmetric shapes 5 Shock layer gas physics 5.1 Perfect gas model 5.2 Real (equilibrium) gas model 5.3 Real (non-equilibrium) gas model 5.4 Frozen gas model 6 Thermal protection systems 6.1 Ablative 6.1.1 SLA-561V 6.1.2 PICA 6.1.3 SIRCA 6.2 Thermal soak 6.3 Passively cooled 6.4 Actively cooled 7 Feathered reentry 8 Entry vehicle design considerations 9 History's most difficult atmospheric entry 10 Notable atmospheric entry mishaps 11 Uncontrolled and unprotected reentries 11.1 Deorbit disposal 12 Research into atmospheric entry 13 Further reading 14 Notes and references 15 See also 16 External links

History

The technology of atmospheric reentry was a consequence of the Cold War. Cold War is the state of conflict tension and competition that existed between the United States and the Soviet Union (USSR and their respective allies from the Ballistic missiles and nuclear weapons were legacies of World War II left to both the Soviet Union and the United States. A ballistic missile is a Missile that follows a Sub-orbital ballistic flightpath with the objective of delivering a warhead to a predetermined target A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including The Union of Soviet Socialist Republics (USSR was a constitutionally Socialist state that existed in Eurasia from 1922 to 1991 The United States of America —commonly referred to as the Both nations initiated massive research and development programs to further the military capability of those technologies. However before a missile-delivered nuclear weapon could be practical they lacked an essential ingredient: an atmospheric reentry technology. A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. In theory, the nation first developing reentry technology had a decisive military advantage, yet it was unclear whether the technology was physically possible. Basic calculations showed the kinetic energy of a nuclear warhead returning from orbit was sufficient to completely vaporize the warhead. Despite these calculations, the military stakes were so high that simply assuming atmospheric reentry's impossibility was unacceptable, and it was known that meteorites were able to successfully reach ground level. Consequently a high-priority program was initiated to develop reentry technology. Atmospheric reentry was successfully developed, which made possible nuclear-armed intercontinental ballistic missiles.

The technology was further pushed forward for human use by another consequence of the Cold War. The Soviet Union saw a propaganda and military advantage in pursuing space exploration. Propaganda is a concerted set of messages aimed at influencing the opinions or behaviors of large numbers of people History First orbital flights The first successful orbital launch was of the Soviet unmanned Sputnik To the embarrassment of the United States, the Soviet Union orbited an artificial satellite, followed by a series of other technological firsts that culminated with a Soviet cosmonaut orbiting the Earth and returning safely to Earth. This article is about artificial satellites For natural satellites also known as moons see Natural satellite. Vostok 1 (Восток-1 meaning Orient -1 or East-1 was the first Human spaceflight. Many of these achievements were enabled through atmospheric reentry technology. The United States saw the Soviet Union's achievements as a challenge to its national pride as well as a threat to national security. Consequently, the United States followed the Soviet Union's initiative and increased its nascent Space Program, thus beginning the Space Race. The Space Race was a competition of space exploration between the Soviet Union and the United States, which lasted roughly from 1957 to 1975

Terminology, definitions and jargon

Over the decades since the 1950s, a rich technical jargon has grown around the engineering of vehicles designed to enter planetary atmospheres. It is recommended that the reader review the jargon glossary before continuing with this article on atmospheric reentry.

Blunt body entry vehicles

These four shadowgraph images represent early reentry-vehicle concepts. Schlieren photography is a visual process that is used to photograph the flow of fluids of varying density A shadowgraph is a process that makes visible the disturbances that occur in a fluid flow at high velocity, in which light passing through a flowing fluid is refracted by the density gradients in the fluid resulting in bright and dark areas on a screen placed behind the fluid. Density gradient is a variation in density over an area The term is used in the natural sciences to describe varying density of matter but can apply to any quantity whose density can

H. Julian Allen and A. J. Eggers, Jr. of the National Advisory Committee for Aeronautics (NACA) made the counterintuitive discovery in 1951^[1] that a blunt shape (high drag) made the most effective heat shield. Harry Julian Allen ( 1 April 1910 - 29 January 1977) also known as Harvey Allen, was an Aeronautical engineer and Alfred J Eggers Jr (June 24 1922 - September 22 2006 was NASA 's Assistant Administrator for Policy and devoted efforts to determine the influence of aviation technology 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. Through making the reentry vehicle blunt, air can't "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.

The Allen and Eggers discovery, though initially treated as a military secret, was eventually published in 1958. ^[2] The Blunt Body Theory made possible the heat shield designs that were embodied in the Mercury, Gemini and Apollo space capsules, enabling astronauts to survive the fiery reentry into Earth's atmosphere. Team The Gemini program was managed by the Manned Spacecraft Center Houston Texas under direction of the Office of Manned Space Flight NASA Headquarters Washington

Entry vehicle shapes

There are several basic shapes used in designing entry vehicles:

Sphere or spherical section

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 sphere or spherical section's aerodynamics 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. ^[3] 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 CFD was still embryonic. Computational fluid dynamics (CFD is one of the branches of Fluid mechanics that uses Numerical methods and algorithms to solve and analyze problems that involve Because the spherical section was amenable to closed-form analysis, that geometry became the default for conservative design. Consequently, manned capsules of that era were based upon the spherical section. Pure spherical entry vehicles were used in the early Soviet Vostok. The Vostok programme (Восто́к translated as "East") was a Soviet Human spaceflight project that succeeded in putting a person into The most famous example of a spherical section entry vehicle was the Apollo Command Module (Apollo-CM), using a spherical section forebody heatshield with a converging conical afterbody. The Apollo-CM (AS-501) flew a lifting entry with a hypersonic trim angle of attack of −27° (0° is blunt-end first) to yield an average L/D of 0. 368. ^[4] This angle of attack was achieved by precisely offsetting the vehicle's center of mass from its axis of symmetry. Other examples of the spherical section geometry in manned capsules are Soyuz/Zond, Gemini and Mercury. The Soyuz programme (Союз saˈjus English: Union) is a Human spaceflight programme that was initiated by the Soviet Union in Zond ( Зонд; meaning "probe" was the name given to two series of Soviet Unmanned space missions undertaken from 1964 to 1970 to gather information Team The Gemini program was managed by the Manned Spacecraft Center Houston Texas under direction of the Office of Manned Space Flight NASA Headquarters Washington

Sphere-cone

The sphere-cone is a spherical section with a frustum or blunted cone attached. Elements special cases and related concepts Each plane section is a base of the frustum The sphere-cone's dynamic stability is typically better than that of a spherical section. 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 was the Mk-2 RV 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.

This new RV was the Mk-6 which used a non-metallic ablative TPS (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 3360 kg, a length of 3. 1 meters 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°.

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). A spy satellite (officially referred to as a reconnaissance satellite) is an Earth observation satellite or Communications satellite deployed for The sphere-cone was later used for space exploration missions to other celestial bodies or for return from open space, e. g. , Stardust probe. Stardust is an American interplanetary mission of the NASA Jet Propulsion Laboratory, whose primary purpose was to investigate the makeup of the 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°. Galileo was an Unmanned spacecraft sent by NASA to study the Planet Jupiter and its moons Named after the Astronomer NASA 's Viking program consisted of a pair of space probes sent to Mars, Viking 1 and Viking 2. Space exploration sphere-cone entry vehicles have landed on the surface or entered the atmospheres of Mars, Venus, Jupiter and Titan. The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University TemplateInfobox Planet.--> Titan (ˈtaɪtən, or as

Biconic

The biconic is a sphere-cone with an additional frustum attached. Many shapes have metaphorical names, ie their names are Metaphors these Shapes are named after a most common object that has it 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 quantum leap in RV sophistication. McDonnell Douglas was a major American Aerospace manufacturer and Defense contractor, producing a number of famous commercial and military aircraft Three of the AMaRVs were launched by Minuteman-1 ICBMs on 20 December 1979, 8 October 1980 and 4 October 1981. The LGM-30 Minuteman is a United States nuclear Missile, a land-based Intercontinental ballistic missile (ICBM 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. ^[5]

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. Hydraulic machinery are machines and tools which use Fluid power to do work AMaRV was guided by a fully autonomous navigation system designed for evading anti-ballistic missile (ABM) interception. An anti-ballistic missile (ABM is a Missile designed to counter Ballistic missiles (a missile for Missile defense) The McDonnell Douglas DC-X (also a biconic) was essentially a scaled up version of AMaRV. The DC-X, short for Delta Clipper or Delta Clipper Experimental, was an unmanned prototype of a reusable Single stage to orbit launch vehicle built AMaRV and the DC-X also served as the basis for an unsuccessful proposal for what eventually became the Lockheed Martin X-33. The X-33 was an unmanned sub-scale technology demonstrator for the VentureStar under the Space Launch Initiative. Amongst aerospace engineers, AMaRV has achieved legendary status alongside such technological marvels as the SR-71 Blackbird and the N-1 rocket. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout N1 or N-1 was the secret Soviet Rocket intended to send Soviet Cosmonauts to the Moon.

Non-axisymmetric shapes

Non-axisymmetric shapes have been used for manned entry vehicles. One example is the winged orbit vehicle that uses a delta wing for maneuvering during descent much like a conventional glider. The delta wing is a Wing Planform in the form of a triangle named after the Greek uppercase delta which is a triangle (Δ This approach has been used by the American Space Shuttle and the Soviet Buran. NASA 's Space Shuttle, officially called the Space Transportation System ( STS) is the Spacecraft currently used by the United States The Buran spacecraft ( Буран "Snowstorm" or "Blizzard") GRAU index 11F35 K1, was the only fully completed and operational The lifting body is another entry vehicle geometry and was used with the X-23 PRIME (Precision Recovery Including Maneuvering Entry) vehicle. The lifting body is an Aircraft configuration where the body itself produces lift. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout

The FIRST (Fabrication of Inflatable Re-entry Structures for Test) system was an Aerojet proposal for an inflated-spar Rogallo wing made up from Inconel wire cloth impregnated with silicone rubber and Silicon Carbide dust. Aerojet is a major Rocket and missile propulsion manufacturer based primarily in Sacramento California with divisions in Redmond WA; Orange VA rogalloarp750pixjpg|thumb|right|200px| Paresev, tested by NASA for spacecraft landing research Inconel is a registered Trademark of Special Metals Corporation that refers to a family of Austenitic Nickel -based Superalloys Inconel FIRST was proposed in both one-man and six man versions, used for emergency escape and reentry of stranded space station crews, and was based on an earlier unmanned test program that resulted in a partially successful reentry flight from space (the launcher nose cone fairing hung up on the material, dragging it too low and fast for the TPS, but otherwise it appears the concept would have worked, even with the fairing dragging it, the test article flew stably on reentry until burn-through).

The proposed MOOSE system would have used a one-man inflatable ballistic capsule as an emergency astronaut entry vehicle. The moose (North America or elk (Europe Alces alces, is the largest extant Species in the Deer family. This concept was carried further by the Douglas Paracone project. An Atmospheric reentry concept using an inflatable cone While these concepts were unusual, the inflated shape on reentry was in fact axisymmetric.

Shock layer gas physics

An approximate rule-of-thumb used by heat shield designers for estimating peak shock layer temperature is to assume the air temperature in kelvins to be equal to the entry speed in meters per second - a mathematical coincidence. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic For example, a spacecraft entering the atmosphere at 7. 8 km/s would experience a peak shock layer temperature of 7800 K. This is unexpected, since the kinetic energy increases with the square of the velocity, and can only occur because the specific heat of the gas increases greatly with temperature (unlike the nearly constant specific heat assumed for solids under ordinary conditions).

At typical reentry temperatures, the air in the shock layer is both ionized and dissociated. Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons Dissociation in Chemistry and Biochemistry is a general process in which ionic compounds ( complexes, Molecules, or Salts) separate 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:

Perfect gas model

Almost all aeronautical engineers are taught the perfect (ideal) gas model during their undergraduate education. These four properties that constitute an ideal gas can be easily remembered by the acronym RIPE which stands for - R andom Motion (molecules are in constant random motion Most of the important perfect gas equations along with their corresponding tables and graphs are shown in NACA Report 1135. ^[6] Excerpts from NACA Report 1135 often appear in the appendices of thermodynamics textbooks and are familiar to most aeronautical engineers who design supersonic aircraft.

Perfect gas theory is elegant and extremely useful for designing aircraft but assumes 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. Perfect gas theory begins to break down at 550 K and is not usable at temperatures greater than 2000 K. For temperatures greater than 2000 K, a heat shield designer must use a real gas model.

Real (equilibrium) gas model

The real gas equilibrium model is normally taught to aeronautical engineers studying towards a master's degree. Not surprisingly, it is a common error for a bachelor's-level engineer to incorrectly use perfect-gas theory on a hypersonic design. An entry vehicle's pitching moment can be significantly influenced by real-gas effects. Both the Apollo-CM and the Space Shuttle were designed using incorrect pitching moments determined through inaccurate real-gas modeling. 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. Space Shuttle Columbia ( NASA Orbiter Vehicle Designation: OV-102) was the first spaceworthy Space shuttle in NASA 's On Columbia’s maiden flight (STS-1), astronauts John W. Young and Robert Crippen had some anxious moments during reentry when there was concern about losing control of the vehicle. The first Space Shuttle mission STS (Space Transportation System-1, was launched April 12 1981, and returned April 14. John Young may refer to John Young (actor (1916–1996 Scottish actor John Young, (1909–1997 American (Hawaiian painter Robert Laurel Crippen (born September 11, 1937 in Beaumont Texas) ( Captain, United States Navy, retired is a former USN and

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 (contrary to popular belief, friction is not the main cause of shock-layer heating). The distance from the shock wave to the stagnation point on the entry vehicle's leading edge is called shock wave stand off. The stagnation point is a point on the surface of a body submerged in a fluid flow where the fluid Velocity is zero 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. In a Chemical process, chemical equilibrium is the state in which the chemical activities or Concentrations of the reactants and products have no net change 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. It should be emphasized that 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).

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. Ideal gas relations For an ideal gas the heat capacity is constant with temperature Relationship with the Boltzmann constant The Boltzmann constant kB (often abbreviated k) may be used in place of the gas constant by working 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. In Thermodynamics, the Gibbs free energy ( IUPAC recommended name Gibbs energy or Gibbs function) is a Thermodynamic potential which In Thermodynamics and molecular chemistry, the enthalpy (denoted as H, h, or rarely as χ) is a quotient or description of In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy 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). In Numerical analysis, Newton's method (also known as the Newton–Raphson method, named after Isaac Newton and Joseph Raphson) is perhaps the The data base for a Gibbs free energy program comes from spectroscopic data used in defining partition functions. In Statistical mechanics, the partition function Z is an important quantity that encodes the statistical properties of a system in Thermodynamic 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 modeled). CEA can be downloaded from the Internet along with full documentation and will compile on Linux under the G77 Fortran compiler.

Real (non-equilibrium) gas model

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. ^[7][8] 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. N₂ → N + N and N + N → N₂ (dissociation and recombination). Because of its simplicity, the Lighthill-Freeman model is a useful pedagogical tool but is unfortunately too simple for modeling 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 N₂, O₂, NO, N and O. The five species model assumes no ionization and ignores trace species like carbon dioxide.

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 loosely 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. A Low Earth Orbit (LEO is generally defined as an Orbit within the locus extending from the Earth’s surface up to an altitude of 2000 km 8 km/s. 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. High speed Mars entry which involves a carbon dioxide, nitrogen and argon atmosphere is even more complex requiring a 19 species model.

An important aspect of modeling 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 unsymmetric diatomic molecules, e. g. cyanogen (CN), carbon monoxide, nitric oxide (NO), single ionized molecular nitrogen, et cetera. Cyanogen is the Chemical compound with the formula ( C[[nitrogen N]]2 Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. Nitric oxide or nitrogen monoxide is a Chemical compound with Chemical formula N[[Oxygen O]] 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. Diatomic molecules are molecules made only of two Atoms of either the same or different Chemical elements The prefix di- means two in Greek A quantum vibration is a Vibration of a Chemical bond in a molecule that must be treated quantum mechanically e. radiative heat flux. The whole process takes place in less than a millisecond which makes modeling 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. In Physics, especially Quantum mechanics, the Schrödinger equation is an equation that describes how the Quantum state of a Physical system 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 insure Apollo's success. However radiative heat flux in carbon dioxide (Mars entry) is still barely understood and will require major research.

Frozen gas model

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.

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, et cetera) for the same thermodynamic state, e. Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. 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 modeling the flow in the wake of an entry vehicle is very difficult. 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.

Thermal protection systems

Ablative

The type of heat shield that best protects against high heat flux is the ablative heat shield. 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) through blowing. In Physics and Fluid mechanics, a boundary layer is that layer of Fluid in the immediate vicinity of a bounding surface The overall process of reducing the heat flux experienced by the heat shield's outer wall is called blockage. Ablation causes the TPS layer to char, melt, and sublime through the process of pyrolysis. Sublimation of an element or compound is a transition from the Solid to Gas phase with no intermediate liquid stage Pyrolysis is the Chemical decomposition of organic materials by heating in the absence of Oxygen or any other reagents except possibly Steam 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. Pyrolysis is the Chemical decomposition of organic materials by heating in the absence of Oxygen or any other reagents except possibly Steam Thermogravimetric Analysis or TGA is a type of testing that is performed on samples to determine changes in Weight in relation to change in Temperature ^[9] 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 RV nose tips. The Space Shuttle Solid Rocket Boosters (SRBs are the pair of large solid rockets used by the Space Shuttle during the first two minutes of powered flight Thermal protection can also be enhanced in some TPS materials through coking. Coke is a solid Carbonaceous material derived from Destructive distillation of low-ash low-sulfur Bituminous coal. Coking is the process of forming solid carbon on the outer char layer of the TPS. TPS coking was discovered accidentally during development of the Apollo-CM TPS material (Avcoat 5026-39).

The thermal conductivity of a TPS material is proportional to the material's density. In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. 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:

SLA-561V

"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 degree sphere-cone entry vehicles sent by NASA to Mars. Lockheed Martin ( is a large multinational Aerospace manufacturer and advanced technology Company formed in 1995 by the merger of SLA-561V begins significant ablation at a heat flux of approximately 110 W/cm² but will fail for heat fluxes greater than 300 W/cm². The Mars Science Laboratory (MSL) aeroshell TPS is currently designed to withstand a peak heat flux of 234 W/cm². The Mars Science Laboratory ( MSL) is a NASA rover scheduled to be launched on September 15, 2009 and perform the first ever The peak heat flux experienced by the Viking-1 aeroshell which landed on Mars was 21 W/cm². Viking 1 was the first of two spacecraft sent to Mars as part of NASA 's Viking program, and holds the record for the longest Mars surface mission 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 yet used on Mars). 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.

PICA

Phenolic Impregnated Carbon Ablator (PICA) was developed by NASA Ames Research Center and was the primary TPS material for the Stardust aeroshell. Stardust is an American interplanetary mission of the NASA Jet Propulsion Laboratory, whose primary purpose was to investigate the makeup of the ^[10] Because the Stardust sample-return capsule was the fastest man-made object to reenter Earth's atmosphere (12. 4 km/s or 28,000 mph relative velocity at 135 km altitude), PICA was an enabling technology for the Stardust mission. (For reference, the Stardust reentry was faster than the Apollo Mission capsules and 70% faster than the reentry velocity of the Shuttle. ) PICA is a modern TPS material and has the advantages of low density (much lighter than carbon phenolic) coupled with efficient ablative capability at high heat flux. Stardust's heat shield (0. 81 m base diameter) was manufactured from a single monolithic piece sized to withstand a nominal peak heating rate of 1200 W/cm². PICA 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.

SIRCA

Silicone Impregnated Reuseable 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 Deep Space 2 mission which launched in January 1999 as part of NASA 's New Millennium Program, consisted of two highly advanced miniature Space probes The Mars Pathfinder was launched on December 4, 1996 by NASA aboard a Delta II just a month after the Mars Global Surveyor NASA 's Mars Exploration Rover ( MER) Mission is an ongoing robotic mission of exploring Mars, that began in 2003 with the sending of 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 probes with their 0. The Deep Space 2 mission which launched in January 1999 as part of NASA 's New Millennium Program, consisted of two highly advanced miniature Space probes 35 m base diameter aeroshells. SIRCA is a monolithic, insulative 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 current 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 has been demonstrated in BIP applications but not yet as a forebody TPS material. ^[11]

Early research on ablation technology in the USA was centered at NASA's Ames Research Center located at Moffett Field, California. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program NASA Ames Research Center (ARC is a NASA facility located at Moffett Federal Airfield, which covers 43 acres at the borders of the cities of Mountain View Moffett Federal Airfield, also known as Moffett Field, is a joint civil-military Airport located 3 miles (5 km north of Mountain View, in Santa Ames Research Center was ideal, since it had numerous wind tunnels capable of generating varying wind velocities. NASA Ames Research Center (ARC is a NASA facility located at Moffett Federal Airfield, which covers 43 acres at the borders of the cities of Mountain View A wind tunnel is a research tool developed to assist with studying the effects of air moving over or around solid objects Initial experiments typically mounted a mock-up of the ablative material to be analyzed within a hypersonic wind tunnel. In Aerodynamics, hypersonic speeds are speeds that are highly Supersonic. ^[12]

Thermal soak

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 soaks into the heat shield's outer wall and would eventually convect to the payload. This outcome is prevented by ejecting the heat shield (with its heat soak) prior to the heat convecting to the inner wall.

Thermal soak TPS is intended to shield mainly against heat load and not against a high peak heat flux (a long duration heat pulse of low intensity is assumed for the TPS design). The Space Shuttle orbit vehicle was designed with a reusable heat shield based upon a thermal soak TPS. NASA 's Space Shuttle, officially called the Space Transportation System ( STS) is the Spacecraft currently used by the United States It should be emphasized that the tradeoff for TPS reusability is an inability to withstand a high heat flux, e. g. a Space Shuttle TPS would not be practical as a primary thermal protection for lunar return. A Space Shuttle's underside is coated with thousands of tiles made of silica foam, which are intended to survive multiple reentries with only minor repairs between missions. Fabric sheets known as gap fillers are inserted between the tiles where necessary. These gap fillers provide for a snug fit between separate tiles while allowing for thermal expansion. Thermal Expansion is the tendency of matter to change in Volume in response to a change in temperature When a Space Shuttle lands, a significant amount of heat is stored in the TPS. Shortly after landing, a ground-support cooling unit connects to the Space Shuttle's internal Freon coolant loop to remove heat soaked in the TPS and orbiter structure.

Typical Space Shuttle's TPS tiles (LI-900) have remarkable thermal protection properties but are relatively brittle and break easily, and cannot survive in-flight rain. An LI-900 tile exposed to a temperature of 1000 K on one side will remain merely warm to the touch on the other side. An impressive stunt that can be performed with a cube of LI-900 is to remove it glowing white hot from a furnace and then hold it with one's bare fingers without discomfort along the cube's edges.

Passively cooled

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. A sub-orbital spaceflight (or sub-orbital flight is a Spaceflight in which the Spacecraft reaches space, but its Trajectory intersects Unfortunately, the earlier version of this technique required a considerable quantity of metal TPS (e. g. titanium, beryllium, copper, et cetera). Titanium (taɪˈteɪniəm is a Chemical element with the symbol Ti and Atomic number 22 Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Modern designers prefer to avoid this added mass by using ablative and thermal soak TPS instead.

Radiatively cooled TPS can still be found on modern entry vehicles but Reinforced Carbon-Carbon (also called RCC or carbon-carbon) is normally used instead of metal. Reinforced Carbon-Carbon ( carbon-carbon or RCC) is a Composite material consisting of Carbon fiber reinforcement in a matrix of Graphite RCC is the TPS material on the nose cone and leading edges of the Space Shuttle's wings. RCC was also proposed as the leading edge material for the X-33. The X-33 was an unmanned sub-scale technology demonstrator for the VentureStar under the Space Launch Initiative. Carbon is the most refractory material known with a one atmosphere sublimation temperature of 3825 °C for graphite. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 This high temperature made carbon an obvious choice as a radiatively cooled TPS material. Disadvantages of RCC are that it is currently very expensive to manufacture and lacks impact resistance.

Some high-velocity aircraft, such as the SR-71 Blackbird and Concorde, had to deal with heating similar to that experienced by spacecraft at much lower intensity, but for hours at a time. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout Studies of the SR-71's titanium skin revealed the metal structure was restored to its original strength through annealing due to aerodynamic heating. Annealing, in Metallurgy and Materials science, is a Heat treatment wherein a material is altered causing changes in its properties such as strength In the case of Concorde the aluminium nose was permitted to reach a maximum operating temperature of 127 °C (typically 180 °C warmer than the sub-zero ambient air); the metallurgical implications (loss of temper) that would be associated with a higher peak temperature was the most significant factor determining the top speed of the aircraft. Tempering is a Heat treatment technique for metals and Alloys In Steels tempering is done to "toughen" the metal by transforming brittle

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 titanium shingles. Unfortunately the earlier Shuttle TPS concept was rejected because it was incorrectly believed a silica tile based TPS offered less expensive development and manufacturing costs. A titanium shingle TPS was again proposed for the unsuccessful X-33 Single-Stage to Orbit (SSTO) prototype. The X-33 was an unmanned sub-scale technology demonstrator for the VentureStar under the Space Launch Initiative. A single-stage-to-orbit (or SSTO) vehicle reaches Orbit from the surface of a body without jettisoning hardware expending only propellants and fluids

Recently, newer radiatively cooled TPS materials have been developed that could be superior to RCC. Referred to by their prototype vehicle "SHARP" (Slender Hypervelocity Aerothermodynamic Research Probe), these TPS materials have been based upon substances such as zirconium diboride and hafnium diboride. Hafnium diboride is an ultra-high temperature Ceramic composed of Hafnium and Boron. SHARP TPS have suggested performance improvements allowing for sustained Mach 7 flight at sea level, Mach 11 flight at 100,000 ft 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 air breathing combined cycle propelled space planes and lifting bodies. SHARP materials have exhibited effective TPS characteristics from zero to more than 2000 °C, with melting points over 3500 °C . They are structurally stronger than RCC thus not requiring structural reinforcement with materials such as Inconel. SHARP materials are extremely efficient at re-radiating absorbed heat thus eliminating the need for additional TPS behind and between 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. The University of Montana is a State university located in Missoula Montana, U ^[13][14]

Actively cooled

Various advanced reusable spacecraft and hypersonic aircraft designs have been proposed to employ heat shields made from temperature-resistant metal alloys that incorporated a refrigerant or cryogenic fuel circulating through them. An alloy is a Solid solution or Homogeneous mixture of two or more elements, at least one of which is a Metal, which itself has Such a TPS concept was proposed for the X-30 National Aerospace Plane (NASP). The X-30 National Aero-Space Plane (NASP was an attempt by the United States to create a viable Single stage to orbit (SSTO Spacecraft. The NASP was supposed to have been a scramjet powered hypersonic aircraft but failed in development. A scramjet ( s upersonic c ombustion ramjet) is a variation of a Ramjet with the distinction being that some or all of the combustion process

In the early 1960s various TPS systems were proposed to use water or other cooling liquid sprayed into the shock layer. Such concepts never got past the proposal phase since ordinary ablative TPS is much more reliable and efficient.

Feathered reentry

In 2004, aircraft designer Burt Rutan demonstrated the feasibility of a shape changing airfoil for reentry with the suborbital SpaceShipOne. Elbert Leander "Burt" Rutan (born June 17, 1943 in Estacada Oregon) is an American aerospace engineer noted for his originality SpaceShipOne is a Spaceplane that completed the first privately funded Human spaceflight on June 21, 2004. The wings on this craft rotate to provide a shuttlecock effect. A shuttlecock' is a high- drag Projectile used in the sport of Badminton. Notably, SpaceShipOne, does not experience significant thermal loads on reentry.

This increases drag, as the craft is now less streamlined. This 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 very key to efficient reentry, see above). It should also be noted that SpaceShipOne, in its "wings flipped" configuration, will automatically orient itself to a high drag attitude. Rutan has compared this to a falling shuttlecock. A shuttlecock' is a high- drag Projectile used in the sport of Badminton. However, it is important to realize that the velocity obtained by SpaceShipOne prior to reentry is much lower than of an orbital spacecraft, and most engineers (including Rutan) do not consider the shuttlecock reentry technique viable for return from orbit.

The feathered or shuttlecock reentry was first described by Dean Chapman of NACA in 1958. ^[15] In the section of his report on Composite Entry, Chapman described a solution to the problem using a high-drag device:

"It may be desirable to combine lifting and nonlifting entry in order to achieve some advantages… For landing maneuverability it obviously is advantageous to employ a lifting vehicle. The total heat absorbed by a lifting vehicle, however, is much higher than for a nonlifting vehicle… Nonlifting vehicles can more easily be constructed… by employing, for example, a large, light drag device… The larger the device, the smaller is the heating rate"

Chapman noted that:

"Nonlifting vehicles with shuttlecock stability are advantageous also from the viewpoint of minimum control requirements during entry. "

Finally, Chapman said:

"an evident composite type of entry, which combines some of the desirable features of lifting and nonlifting trajectories, would be to enter first without lift but with a… drag device; then, when the velocity is reduced to a certain value… the device is jettisoned or retracted, leaving a lifting vehicle… for the remainder of the descent".

Entry vehicle design considerations

There are four critical parameters considered when designing a vehicle for atmospheric entry:

1. Peak heat flux
2. Heat load
3. Peak deceleration
4. Peak dynamic pressure

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 manned missions. The upper limit for manned return to Earth from Low Earth Orbit (LEO) or lunar return is 10 Gs. For Martian atmospheric entry after long exposure to zero gravity, the upper limit is 4 Gs. Peak dynamic pressure can also influence the selection of the outermost TPS material if spallation is an issue.

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 manned 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). ^[16] 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 adverse designer).

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). A free falling object achieves its terminal velocity when the downward force of gravity ( Fg)equals the upward force of drag ( Fd) 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). The Huygens probe, supplied by the European Space Agency (ESA and named after the Dutch 17th century astronomer Christiaan Huygens, is an atmospheric entry Beagle 2 was an unsuccessful British landing spacecraft that formed part of the European Space Agency 's 2003 Mars Express mission After being abandoned, the Soviet Mars lander program achieved no successful landings (no useful data returned) after multiple attempts. This article is for the Russian (Soviet series of space probes for the moon designated as Mars II see Deimos (moon; for all missions to Mars see Exploration The Soviet Mars landers were based upon a 60° half-angle aeroshell design. In the early 1960s, it was incorrectly believed the Martian atmosphere was mostly nitrogen, (actual Martian atmospheric mole fractions are carbon dioxide 0. 9550, nitrogen 0. 0270 and argon 0. 0160). The Soviet aeroshells were probably(?) based upon an incorrect Martian atmospheric model and then not revised when new data became available.

A 45 degree 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 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 landers and Pioneer Venus Probes. The Pioneer mission to Venus consisted of two components launched separately

History's most difficult atmospheric entry

The highest speed controlled entry so far achieved was by the Galileo Probe. Galileo was an Unmanned spacecraft sent by NASA to study the Planet Jupiter and its moons Named after the Astronomer The Galileo Probe was a 45° sphere-cone that entered Jupiter's atmosphere at 47. 4 km/s (atmosphere relative speed at 450 km above the 1 bar reference altitude). The peak deceleration experienced was 230 g (2. g-force (also G-force, g-load) is a measurement of an object's Acceleration expressed in g s 3 km/s²). Peak stagnation point pressure before aeroshell jettison was 9 bars (900 kPa). The peak shock layer temperature was approximately 16000 K (the solar photosphere is merely 5800 K). Approximately 26% of the Galileo Probe's original entry mass of 338. 93 kg was vaporized during the 70 second heat pulse. Total blocked heat flux peaked at approximately 15000 W/cm². By way of comparison, the peak total heat flux experienced by the Mars Pathfinder aeroshell, the highest experienced by a successful Mars lander, was 106 W/cm², and the Apollo-4 (AS-501) command module, re-entering at 10. 77 km/s (atmosphere relative speed at 121. 9 km altitude) experienced a peak total heat flux of 497 W/cm².

Conservative design was used in creating the Galileo Probe. Due to the extreme state of the Galileo Probe's entry conditions, the radiative heat flux and turbulence of the shock layer along with the TPS material response were barely understood. Carbon Phenolic was used for the Galileo Probe TPS. Carbon phenolic was earlier used for the Pioneer Venus Probes which were the design ancestors to the Galileo Probe. The Pioneer mission to Venus consisted of two components launched separately The Galileo Probe experienced far greater TPS recession near the base of its frustum than expected. Despite a safety-factor of two in TPS thickness, the Galileo Probe's heatshield almost failed. The precise mechanism for this higher TPS recession is still unknown and currently beyond definitive theoretical analysis.

After successfully completing its mission, the Galileo Probe continued descending into Jupiter's atmosphere where the ambient temperature grew with greater depth due to isentropic compression. In Thermodynamics, an isentropic process ( iso = "equal" (Greek Entropy = "disorder" is one during which the entropy of the system In the depths of Jupiter's atmosphere, the ambient atmospheric gas temperature became so hot that the entire probe, including its jettisoned heat shield, were vaporized into monatomic gas. In Physics and Chemistry, monatomic is a combination of the words "mono" and "atomic" and means "single Atom.

Notable atmospheric entry mishaps

Not all atmospheric re-entries have been successful and some have led to significant disasters.

• Vostok 1 — The service module failed to detach for 10 minutes. Vostok 1 (Восток-1 meaning Orient -1 or East-1 was the first Human spaceflight. Lone cosmonaut Yuri Gagarin survived.
• Mercury 6 — Instrument readings show that the heat shield and landing bag were not locked. The Mercury-Atlas 6 mission was the first attempt by the US and Mercury program to place an astronaut in orbit The decision was made to leave the retrorocket pack in position during reentry. A retrorocket (short for retrograde rocket) is a Rocket engine used to provide Thrust opposing the motion of a Spacecraft, thereby causing it Lone astronaut John Glenn survived. John Herschel Glenn Jr (born July 18 1921 in Cambridge Ohio) is a former United States Senator who first rose to fame as the first American to Orbit The instrument readings were later found to be erroneous.
• Voskhod 2 — The service module failed to detach for some time, but the crew survived. Voskhod 2 (Восход 2 "Dawn 2" was a Soviet manned space mission in March 1965
• Soyuz 1 — Different accounts exist. Soyuz 1 ( Russian Союз 1 Union 1) was part of the Soviet Union 's space program and was launched into orbit on April 23, 1967 Either the attitude control system failed while still in orbit and/or parachutes got entangled during the landing sequence (entry, descent and landing (EDL) failure). Lone cosmonaut Vladimir Mikhailovich Komarov died. Vladimir Komarov redirects here for the botanist see Vladimir Leontyevich Komarov.
• Soyuz 5 — The service module failed to detach, but the crew survived. The Soyuz 5 was a Soyuz spacecraft launched by the Soviet Union on January 15 1969 that docked with Soyuz 4 in orbit
• Soyuz 11 — Early depressurization led to the death of all three crew. Soyuz 11 was the first successful visit to the world's first Space station, Salyut 1. Cabin pressurization is the active pumping of compressed Air into an Aircraft cabin when flying at altitude to maintain a safe and comfortable environment for crew
• Mars Polar Lander — Failed during EDL. The Mars Polar Lander was part of the NASA Mars Surveyor '98 program, which consisted of two spacecraft launched separately the Mars Climate The failure was believed to be the consequence of a software error. The precise cause is unknown due to lack of real time telemetry.

• Space Shuttle Columbia disaster — The failure of an RCC tile on a wing leading edge led to breakup of the orbit vehicle at hypersonic speed resulting in the loss of all seven crew members. The Space Shuttle Columbia disaster occurred on February 1, 2003, when the Space Shuttle ''Columbia'' disintegrated over Texas
• Genesis — The parachute failed to deploy due to a G-switch being installed backwards (a similar error delayed parachute deployment for the Galileo Probe). The Genesis spacecraft was the first ever attempt to collect a sample of Solar wind, and the first " Sample return mission " to return from beyond the Consequently, the Genesis entry vehicle crashed into the desert floor. The payload was damaged but it was later claimed that some scientific data was recoverable.

Uncontrolled and unprotected reentries

More than 100 metric tons of man-made objects reenter in an uncontrolled fashion each year. This article is about the tonne or metric ton For other tons see Ton. Of satellites that reenter, approximately 10-40% of the mass of the object is likely to reach the surface of the Earth. ^[17] On average, about one catalogued object reenters per day. Approximately a quarter of all objects are of U. S. origin.

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 person will get hit and injured is around 1 in a trillion. ^[18]

In 1978, Cosmos 954 reentered uncontrolled and crashed near Great Slave Lake in the Northwest Territories of Canada. Year 1978 ( MCMLXXVIII) was a Common year starting on Sunday (link displays the 1978 Gregorian calendar) Cosmos 954 was a Soviet Radar Ocean Reconnaissance Satellite ( RORSAT) with an onboard nuclear reactor. Great Slave Lake (French Grand lac des Esclaves) is the second-largest Lake in the Northwest Territories of Canada (behind Great Bear The Northwest Territories (ˌnɔrθˌwɛstˈtɛrɨtɔriz ( NWT or NT; French, les Territoires du Nord-Ouest) is a territory Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page Cosmos 954 was nuclear powered, using a nuclear fission reactor, and spread radioactive debris across northern Canada.

In 1979, Skylab reentered uncontrolled and parts of it crashed into Esperance, Western Australia, damaging several buildings. Year 1979 ( MCMLXXIX) was a Common year starting on Monday (link displays the 1979 Gregorian calendar) Skylab was the first Space station the United States launched into orbit and the second space station ever visited by a human crew Esperance is a town in Western Australia, located on the south coast around half-way between Albany and the South Australian border Local authorities issued a fine for littering to the United States, but the fine was never settled. Litter is Waste disposed in the wrong place by Unlawful human action and can vary in size of incident occurrence or items The United States of America —commonly referred to as the ^[19]

Deorbit disposal

In 2001, the Russian Mir space station was deliberately de-orbited, and broke apart during atmospheric re-entry. Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar. Mir (Мир which can mean both Peace and World, and was the name given to peasant communes in pre-revolutionary Russia was a Soviet (and Mir entered the Earth's atmosphere on March 23, 2001, near Nadi, Fiji, and fell into the South Pacific Ocean. Events 1174 - Jocelin, Abbot of Melrose, is elected Bishop of Glasgow. Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar. Fiji (Matanitu ko Viti फ़िजी officially the Republic of the Fiji Islands (Matanitu Tu-Vaka-i-koya ko Viti फ़िजी द्वीप समूह गणराज्य The Pacific Ocean is the largest of the Earth 's Oceanic divisions Previously, its two predecessors, Salyut 6 and Salyut 7, were deorbited in a controlled manner as well. Salyut 6 (Салют-6 lit  Salute 6) was a Soviet orbital space station, the eighth flown as part of the Salyut programme. Salyut 7 (Салют-7 Salute 7 was the final Space station launched into Low Earth orbit as part of the Soviet Union 's Salyut Program

On February 21, 2008, a disabled U.S. spy satellite, USA 193, was successfully intercepted and destroyed, at an altitude of approximately 246 kilometers (153 miles) above the Earth, by a U.S. Navy cruiser off the coast of Hawaii, which fired an SM-3 missile. Events 362 - Athanasius returns to Alexandria. 1245 - Thomas, the first known Bishop of Finland 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common The United States of America —commonly referred to as the A spy satellite (officially referred to as a reconnaissance satellite) is an Earth observation satellite or Communications satellite deployed for USA 193, also known as NRO launch 21 ( NROL-21 or simply L-21) was an American military Spy satellite launched on December 14 2006 Altitude is the Elevation of a point or object from a known level or datum (plural data The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand A mile is a unit of Length, usually used to measure Distance, in a number of different systems including Imperial units United States EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 A cruiser is a large type of Warship, which had its prime period from the late 19th century to the end of the Cold War. The State of Hawaii ( or həˈwaɪʔiː Hawaiian: Mokuāina o Hawaii) is a state in the United States located on an Archipelago in the A missile (see also pronunciation differences) is a self-propelled explosive Projectile used as a weapon towards a target The satellite had been inoperative upon its launch in 2006, and had never reached its designated orbit, but was in a rapidly deteriorating Low Earth orbit, and destined for an uncontrolled reentry within a month. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star A Low Earth Orbit (LEO is generally defined as an Orbit within the locus extending from the Earth’s surface up to an altitude of 2000 km United States Department of Defense expressed concern that the debris, including a 1000-pound (450-kilogram) highly toxic hydrazine fuel tank, might reach the Earth’s surface. The United States Department of Defense ( DOD or DoD) is the federal department charged with coordinating and supervising all agencies and functions of the government The pound or pound-mass (abbreviation lb, lbm, or sometimes in the United States #) is a unit of Mass Toxicity is the degree to which a substance is able to damage an exposed organism Hydrazine is a Chemical compound with the formula N2H4 It has an Ammonia -like odor and is derived from the same industrial chemistry A fuel tank is safe container for flammable liquids and typically part of an Engine system in which the Fuel is stored and propelled (fuel pump or released (pressurized In Mathematics, specifically in Topology, a surface is a Two-dimensional Manifold. Several governments including those of Russia, China, and Belarus protested the US action. Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National Belarus ( Belarusian Беларусь / Biełaruś is a Landlocked country in Eastern Europe, bordered by Russia to the north and east They were claiming that the operation may have been a disguised test of a new space weapons system. Space weapons are Weapons used in Space warfare. They include weapons that can attack space systems in orbit (i ^[20]

Research into atmospheric entry

Aerospace technologies can be used for civilian or military purposes (known as dual use). Dual-use is a term often used in Politics and Diplomacy to refer to Technology which can be used for both Peaceful and Military aims Atmospheric entry technology owes its origins to the development of ballistic missiles during the Cold War. A ballistic missile is a Missile that follows a Sub-orbital ballistic flightpath with the objective of delivering a warhead to a predetermined target Given the enormous expense required in developing this technology, it is doubtful it could have appeared as quickly as it did without the military incentive. Mankind's survival beyond its planet of origin could be dependent upon atmospheric entry technology. It is ironic that the same technology enabling destructive nuclear-tipped missiles also enables this exploration and development of outer space. Aerospace technology is needed for civilian space exploration, yet certain aspects are and will remain restricted to impede military proliferation of the technology. This basic dilemma is present throughout the literature on atmospheric entry. There is a glass wall between pedagogical and practical information. For example, in the text books referenced in this article, a topic thread will proceed as long as the information is nonspecific but almost always stops at the point of practical application. To go beyond pedagogical information, one must search the technical literature (NACA/NASA Technical Reports, declassified technical reports and peer reviewed archive literature). Declassified technical reports are a frustrating information source since many of the reports were destroyed prior to going through the legally required declassification process. It is almost always true that significant documents referred to in declassified technical reports no longer exist (technical information costing many millions of dollars has simply vanished).

Further reading

• Martin, John J. (1966). John Joseph Martin (1922 &ndash) was educated as a mechanical engineer receiving a Ph Atmospheric Entry - An Introduction to Its Science and Engineering. Old Tappan, NJ: Prentice-Hall.  ^[21]
• Regan, Frank J. (1984). Re-Entry Vehicle Dynamics (AIAA Education Series). New York: American Institute of Aeronautics and Astronautics, Inc. . ISBN 0-915928-78-7.  ^[22]
• Etkin, Bernard (1972). Bernard Etkin, CM (born 1918 is a Canadian academic and one of the world's recognized authorities on aircraft guidance and control Dynamics of Atmospheric Flight. New York: John Wiley & Sons, Inc. . ISBN 0-471-24620-4.  ^[23]
• Vincenti, Walter G. ; Kruger, Jr. , Charles H. (1986). Introduction to Physical Gas Dynamics. Malabar, Florida: Robert E. Krieger Publishing Co. . ISBN 0-88275-309-6.  ^[24]
• Hansen, C. Frederick (1976). Molecular Physics of Equilibrium Gases, A Handbook for Engineers. NASA. NASA SP-3096.  ^[25]
• Hayes, Wallace D. ; Probstein, Ronald F. (1959). Hypersonic Flow Theory. New York and London: Academic Press.   A revised version of this classic text has been reissued as an inexpensive paperback: Hayes, Wallace D. (1966, reissued in 2004). Hypersonic Inviscid Flow. Mineola, New York: Dover Publications. ISBN 0-486-43281-5.  
• Anderson, Jr. , John D. (1989). Hypersonic and High Temperature Gas Dynamics. New York: McGraw-Hill, Inc. . ISBN 0-07-001671-2.  

Notes and references

See also

• Aerocapture
• Landing footprint
• Ballistic reentry
• Decelerated micrometeorites

External links

• Early Reentry Vehicles: Blunt Bodies and Ablatives
• Buran's heat shield
• Encyclopedia Astronautica article on the history of space rescue crafts, including some re-entry craft designs. Aerocapture is a technique used to reduce Velocity of a spacecraft arriving at a Celestial body with a Hyperbolic trajectory, in order to bring it After Atmospheric reentry, a non powered Spacecraft will land on an area depending upon entry angle entry mass atmosphere and drag A ballistic Reentry is a re-entry of an atmosphere that relies solely on drag within the atmosphere to slow the vehicle The interplanetary dust cloud is Cosmic dust (small particles floating in space which pervade the space between Planets in the Solar System and in

---

© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic