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153-531: Huygens ( / ˈ h ɔɪ ɡ ən z / HOY -gənz ) was an atmospheric entry robotic space probe that landed successfully on Saturn 's moon Titan in 2005. Built and operated by the European Space Agency (ESA), launched by NASA, it was part of the Cassini–Huygens mission and became the first spacecraft to land on Titan and the farthest landing from Earth a spacecraft has ever made. The probe

306-536: A crème brûlée (that is, a hard surface covering a sticky mud-like subsurface). Subsequent analysis of the data suggests that surface consistency readings were likely caused by Huygens pushing a large pebble into the ground as it landed, and that the surface is better described as a "sand" made of ice grains or snow that has been frozen on top. The images taken after the probe's landing show a flat plain covered in pebbles. The pebbles, which may be made of hydrocarbon-coated water ice, are somewhat rounded, which may indicate

459-576: A 10-meter radio telescope Spektr-R , was launched in July 2011 and made observations until January 2019. It was placed into a highly elliptical orbit, ranging from a perigee of 10,652 km to an apogee of 338,541 km, making RadioAstron, the SVLBI program incorporating the satellite and ground arrays, the biggest radio interferometer to date. The resolution of the system reached 8 microarcseconds . The International VLBI Service for Geodesy and Astrometry ( IVS )

612-545: 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

765-484: A GPS time standard. Alongside the astronomical data samples, the output of this clock is recorded. The recorded media are then transported to a central location. More recent experiments have been conducted with "electronic" VLBI (e-VLBI) where the data are sent by fibre-optics (e.g., 10 Gbit/s fiber-optic paths in the European GEANT2 research network) and not recorded at the telescopes, speeding up and simplifying

918-471: 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

1071-492: 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

1224-459: 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

1377-435: 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

1530-414: A depth of at least 1 m (3 ft)). The likely supplier in dry desert areas is probably underground aquifers ; in other words, the arid equatorial regions of Titan contain " oases ". The surface was initially reported to be a clay -like "material which might have a thin crust followed by a region of relative uniform consistency." One ESA scientist compared the texture and colour of Titan's surface to

1683-493: A few metres per second, roughly in line with expectations. As Huygens was primarily an atmospheric mission, the DISR instrument was optimized to study the radiation balance inside Titan's atmosphere. Its visible and infrared spectrometers and violet photometers measured the up- and downward radiant flux from an altitude of 145 km (90 mi) down to the surface. Solar aureole cameras measured how scattering by aerosols varies

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1836-415: A fully instrumented robotic laboratory to the surface. When the mission was planned, it was not yet certain whether the landing site would be a mountain range, a flat plain , an ocean , or something else, and it was thought that analysis of data from Cassini would help to answer these questions. Based on pictures taken by Cassini 1,200 km (750 mi) above Titan, the landing site appeared to be

1989-451: 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

2142-566: 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

2295-404: A global network of antennas over a period of time. In VLBI, the digitized antenna data are usually recorded at each of the telescopes (in the past this was done on large magnetic tapes, but nowadays it is usually done on large arrays of computer disk drives). The antenna signal is sampled with an extremely precise and stable atomic clock (usually a hydrogen maser ) that is additionally locked onto

2448-563: 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

2601-451: A liquid surface, its motion due to waves would also have been measurable. Temperature and pressure sensors measured the thermal properties of the atmosphere. The Permittivity and Electromagnetic Wave Analyzer component measured the electron and ion (i.e., positively charged particle) conductivities of the atmosphere and searched for electromagnetic wave activity. On the surface of Titan, the electrical conductivity and permittivity (i.e.,

2754-633: 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

2907-477: A moon other than Earth's. Huygens touched down on land, although the possibility that it would touch down in an ocean was also taken into account in its design. The probe was designed to gather data for a few hours in the atmosphere , and possibly a short time at the surface. It continued to send data for about 90 minutes after touchdown. Huygens was designed to enter and brake in Titan's atmosphere and parachute

3060-454: 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

3213-402: 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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3366-409: A number of sensors designed to determine the physical properties of Titan's surface at the point of impact, whether the surface was solid or liquid. An acoustic sounder , activated during the last 100 m (300 ft) of the descent, continuously determined the distance to the surface, measuring the rate of descent and the surface roughness (e.g., due to waves). The instrument was designed so that if

3519-458: 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

3672-421: 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

3825-643: A radio interferometer, but it only became widely used for long-baseline radio interferometry in 1974. At least three antennas are required. This method was used for the first VLBI measurements, and a modified form of this approach ("Self-Calibration") is still used today. Some of the scientific results derived from VLBI include: There are several VLBI arrays located in Europe , Canada , the United States , Chile , Russia , China , South Korea , Japan , Mexico , Australia and Thailand . The most sensitive VLBI array in

3978-462: A shadow bar, which would tell DISR when the Sun had passed through the field of view. Unfortunately, this scheme was upset by the fact that Huygens rotated in a direction opposite to that expected. Just before landing a lamp was switched on to illuminate the surface, which enabled measurements of the surface reflectance at wavelengths which are completely blocked out by atmospheric methane absorption. DISR

4131-428: A shoreline. Assuming the landing site could be non-solid, Huygens was designed to survive the impact, splash down on a liquid surface on Titan, and send back data for several minutes under these conditions. If that occurred it was expected to be the first time a human-made probe would land in an extraterrestrial ocean. The spacecraft had no more than three hours of battery life, most of which was planned to be used during

4284-428: 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

4437-407: 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

4590-513: 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

4743-401: A suite of sensors that measured the physical and electrical properties of Titan's atmosphere. Accelerometers measured forces in all three axes as the probe descended through the atmosphere. With the aerodynamic properties of the probe already known, it was possible to determine the density of Titan's atmosphere and to detect wind gusts. The probe was designed so that in the event of a landing on

Huygens (spacecraft) - Misplaced Pages Continue

4896-411: 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,

5049-538: A very-long-baseline interferometer the symmetry of the corresponding contribution to the source brightness distributions is not known. Roger Clifton Jennison developed a novel technique for obtaining information about visibility phases when delay errors are present, using an observable called the closure phase . Although his initial laboratory measurements of closure phase had been done at optical wavelengths, he foresaw greater potential for his technique in radio interferometry. In 1958 he demonstrated its effectiveness with

5202-537: A very-long-baseline interferometer. Temperature variations at VLBI sites can deform the structure of the antennas and affect the baseline measurements. Neglecting atmospheric pressure and hydrological loading corrections at the observation level can also contaminate the VLBI measurements by introducing annual and seasonal signals, like in the Global Navigation Satellite System time series. The phase of

5355-525: 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

5508-465: 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

5661-506: 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,

5814-448: 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,

5967-463: Is expected to feature torrential downpours causing flash floods, interspersed by decades or centuries of drought. Huygens found the brightness of the surface of Titan (at time of landing) to be about one thousand times dimmer than full solar illumination on Earth (or 500 times brighter than illumination by full moonlight)—that is, the illumination level experienced about ten minutes after sunset on Earth, approximately late civil twilight . The color of

6120-461: 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

6273-528: 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

Huygens (spacecraft) - Misplaced Pages Continue

6426-446: 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

6579-457: 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

6732-506: Is the largest VLBI array that operates all year round as both an astronomical and geodesy instrument. The combination of the EVN and VLBA is known as Global VLBI . When one or both of these arrays are combined with space-based VLBI antennas such as HALCA or Spektr-R , the resolution obtained is higher than any other astronomical instrument, capable of imaging the sky with a level of detail measured in microarcseconds . VLBI generally benefits from

6885-447: 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

7038-453: 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

7191-485: 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

7344-674: The Doppler Effect . The wind-induced horizontal motion from Huygens would have been derived from the measured Doppler shift measurements, corrected for all known orbit and propagation effects. The swinging motion of the probe beneath its parachute due to atmospheric properties may also have been detected. Failure of ground controllers to turn on the receiver in the Cassini orbiter caused the loss of this data. Earth-based radio telescopes were able to reconstruct some of it. Measurements started 150 km (93 mi) above Titan's surface, where Huygens

7497-628: 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,

7650-581: 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

7803-633: The Huygens DISR data for several months until virtually all images with recognizable structures could be assigned to their correct position, resulting in comprehensive mosaics and panoramas. A surface panorama from this citizen science project was finally published in the context of a Nature review by Joseph Burns. The probe landed on the surface of Titan at 10°34′23″S 192°20′06″W  /  10.573°S 192.335°W  / -10.573; -192.335 . Atmospheric entry Atmospheric entry (sometimes listed as V impact or V entry )

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7956-576: The Huygens landing site. Further data from the Cassini Mission, however, definitely confirmed the existence of permanent liquid hydrocarbon lakes in the polar regions of Titan (see Lakes of Titan ). Long-standing tropical hydrocarbon lakes were also discovered in 2012 (including one not far from the Huygens landing site in the Shangri-La region which is about half the size of Utah's Great Salt Lake , with

8109-464: The Huygens mission, and that it was executed by Cassini as delivered. Because Channel A was not used, only 350 pictures were received instead of the 700 planned. All Doppler radio measurements between Cassini and Huygens were lost as well. Doppler radio measurements of Huygens from Earth were made, although they were not as accurate as the lost measurements that Cassini made. The use of accelerometer sensors on Huygens and VLBI tracking of

8262-554: The Huygens signal. The signal strength received on Earth from Huygens was comparable to that from the Galileo probe (the Jupiter atmospheric descent probe) as received by the VLA , and was therefore too weak to detect in real time because of the signal modulation by the (then) unknown telemetry . Instead, wide-band recordings of the probe signal were made throughout the three-hour descent. After

8415-741: The Robert C. Byrd Green Bank Telescope (GBT) in West Virginia detected the carrier signal from Huygens . The GBT continued to detect the carrier signal well after Cassini stopped listening to the incoming data stream. In addition to the GBT, eight of the ten telescopes of the continent-wide VLBA in North America, located at Pie Town and Los Alamos, New Mexico ; Fort Davis, Texas ; North Liberty, Iowa ; Kitt Peak, Arizona ; Brewster, Washington ; Owens Valley, California ; and Mauna Kea, Hawaii , also listened for

8568-476: 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

8721-610: 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

8874-602: 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

9027-408: 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

9180-419: 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

9333-534: 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

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9486-586: The Aerosol Collector Pyrolyser. Finally, the GC/MS measured the composition of Titan's surface. This investigation was made possible by heating the GC/MS instrument just prior to impact in order to vaporize the surface material upon contact. The GC/MS was developed by Goddard Space Flight Center and the University of Michigan 's Space Physics Research Lab. The ACP experiment drew in aerosol particles from

9639-619: 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

9792-754: 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,

9945-647: 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

10098-500: 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.,

10251-525: 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

10404-483: 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

10557-408: The action of fluids on them. The rocks appear to be rounded, size-selected and size-layered as though located in the bed of a stream within a dark lakebed, which consists of finer-grained material. No pebbles larger than 15 cm (5.9 in) across were spotted, while rocks smaller than 5 cm (2.0 in) are rare on the Huygens landing site. This implies large pebbles cannot be transported to

10710-442: 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

10863-440: The atmosphere for about four seconds by the impact. At the landing site there were indications of pebbles of water ice scattered over an orange surface, the majority of which is covered by a thin haze of methane . Early aerial imaging of Titan from Huygens was consistent with the presence of large bodies of liquid on the surface. The initial photos of Titan before landing showed what appeared to be large drainage channels crossing

11016-588: The atmosphere through filters, then heated the trapped samples in ovens (using the process of pyrolysis ) to vaporize volatiles and decompose the complex organic materials. The products were flushed along a pipe to the GC/MS instrument for analysis. Two filters were provided to collect samples at different altitudes. The ACP was developed by a (French) ESA team at the Laboratoire Inter-Universitaire des Systèmes Atmosphériques (LISA). The SSP contained

11169-422: 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

11322-411: The bottom of the Huygens descent module, was used to create a penetrometer trace as Huygens landed on the surface. This was done by measuring the force exerted on the instrument by the body's surface as it broke through and was pushed down into the body by the landing. The trace shows this force as a function of time over a period of about 400 ms. The trace has an initial spike which suggests that

11475-416: 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

11628-402: 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

11781-470: The complex visibility depends on the symmetry of the source brightness distribution. Any brightness distribution can be written as the sum of a symmetric component and an anti-symmetric component . The symmetric component of the brightness distribution only contributes to the real part of the complex visibility, while the anti-symmetric component only contributes to the imaginary part. As the phase of each complex visibility measurement cannot be determined with

11934-598: 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

12087-418: 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

12240-444: The descent and was also designed to indicate the probe's attitude after landing and show any motion due to waves. If the surface had been liquid, other sensors would also have measured its density , temperature, thermal conductivity , heat capacity, electrical properties ( permittivity and conductivity) and refractive index (using a critical angle refractometer). A penetrometer instrument, that protruded 55 mm (2.2 in) past

12393-492: The descent imager were split, with each channel carrying 350 pictures. Cassini never listened to channel A because of an error in the sequence of commands sent to the spacecraft. The receiver on the orbiter was never commanded to turn on, according to officials with the European Space Agency. ESA announced that the error was a mistake on their part, the missing command was part of a command sequence developed by ESA for

12546-408: The descent. Engineers expected to get at most only 30 minutes of data from the surface. The Huygens probe system consists of the 318 kg (701 lb) probe itself, which descended to Titan, and the 30 kg (66 lb) probe support equipment (PSE), which remained attached to the orbiting spacecraft. Huygens ' heat shield was 2.7 m (8.9 ft) in diameter. After ejecting the shield,

12699-569: 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

12852-706: The development of the closure phase imaging technique by Roger Jennison in the 1950s, allowing VLBI to produce images with superior resolution. VLBI is best known for imaging distant cosmic radio sources, spacecraft tracking, and for applications in astrometry . However, since the VLBI technique measures the time differences between the arrival of radio waves at separate antennas, it can also be used "in reverse" to perform Earth rotation studies, map movements of tectonic plates very precisely (within millimetres), and perform other types of geodesy . Using VLBI in this manner requires large numbers of time difference measurements from distant sources (such as quasars ) observed with

13005-428: The estimated times of arrival of the radio signal at each of the telescopes. A range of playback timings over a range of nanoseconds are usually tested until the correct timing is found. Each antenna will be a different distance from the radio source, and as with the short baseline radio interferometer the delays incurred by the extra distance to one antenna must be added artificially to the signals received at each of

13158-729: The first science produced by the European VLBI Network using e-VLBI. The data from each of the telescopes were routed through the GÉANT2 network and on through SURFnet to be the processed in real time at the European Data Processing centre at JIVE . In the quest for even greater angular resolution, dedicated VLBI satellites have been placed in Earth orbit to provide greatly extended baselines. Experiments incorporating such space-borne array elements are termed Space Very Long Baseline Interferometry (SVLBI). The first SVLBI experiment

13311-447: 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

13464-432: 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

13617-644: 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

13770-411: The ground must have been damp, and one image shows light reflected by a dewdrop as it falls across the camera's field of view. On Titan, the feeble sunlight allows only about one centimeter of evaporation per year (versus one metre of water on Earth), but the atmosphere can hold the equivalent of about 10 m (30 ft) of liquid before rain forms vs. only a few centimeters on Earth. So Titan's weather

13923-451: The hardware of Cassini' s receiver was designed to be able to receive over a range of shifted frequencies. However, the firmware failed to take into account that the Doppler shift would have changed not only the carrier frequency, but also the timing of the payload bits , coded by phase-shift keying at 8192 bits per second . Reprogramming the firmware was impossible, and as a solution

14076-408: 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

14229-444: 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:

14382-557: The illumination comes from the sky. There was a transit of the Earth and Moon across the Sun as seen from Saturn/Titan just hours before the landing. Huygens entered the upper layer of Titan's atmosphere 2.7 hours after the end of the transit of the Earth, or only one or two minutes after the end of the transit of the Moon. However, the transit did not interfere with the Cassini orbiter or Huygens probe, for two reasons. First, although they could not receive any signal from Earth because it

14535-499: The information from one of the two radio channels was lost due to an unrelated error. Huygens was programmed to transmit telemetry and scientific data to the Cassini orbiter for relay to Earth using two redundant S-band radio systems, referred to as Channel A and B, or Chain A and B. Channel A was the sole path for an experiment to measure wind speeds by studying tiny frequency changes caused by Huygens 's motion. In one other deliberate departure from full redundancy, pictures from

14688-661: The instrument hit one of the icy pebbles on the surface photographed by the DISR camera. The Huygens SSP was developed by the Space Sciences Department of the University of Kent and the Rutherford Appleton Laboratory Space Science Department (now RAL Space) under the direction of Professor John Zarnecki . The SSP research and responsibility transferred to the Open University when John Zarnecki transferred in 2000. Huygens

14841-409: The intensity directly around the Sun. Three imagers, sharing the same CCD , periodically imaged a swath of around 30 degrees wide, ranging from almost nadir to just above the horizon. Aided by the slowly spinning probe they would build up a full mosaic of the landing site, which, surprisingly, became clearly visible only below 25 km (16 mi) altitude. All measurements were timed by aid of

14994-465: The lakebed, while small rocks are quickly removed from the surface. The temperature at the landing site was 93.8  K (−179.3 °C; −290.8 °F) and pressure of 1,467.6 mbar (1.4484 atm), implying a methane abundance of 5 ± 1% and methane relative humidity of 50% near the surface. Therefore, ground fogs caused by methane in the neighborhood of the landing site are unlikely. Thermometers indicated that heat left Huygens so quickly that

15147-447: The lighter colored mainland into a dark sea. Some of the photos suggested islands and a mist shrouded coastline. Subsequent analysis of the probe's trajectory indicated that, in fact, Huygens had landed within the dark 'sea' region in the photos. The photos from the surface of a dry lakebed like landscape suggest that while there is evidence of liquid acting on the surface recently, hydrocarbon lakes and/or seas might not currently exist at

15300-524: The local time references of the VLBI technique, in a technique known as e-VLBI. In Europe, six radio telescopes of the European VLBI Network (EVN) were connected with Gigabit per second links via their National Research Networks and the Pan-European research network GEANT2 , and the first astronomical experiments using this new technique were successfully conducted. The image to the right shows

15453-690: The longer baselines afforded by international collaboration, with a notable early example in 1976, when radio telescopes in the United States, USSR and Australia were linked to observe hydroxyl - maser sources. This technique is currently being used by the Event Horizon Telescope , whose goal is to observe the supermassive black holes at the centers of the Milky Way Galaxy and Messier 87 . NASAs Deep Space Network uses its larger antennas (normally used for spacecraft communication) for VLBI, in order to construct radio reference frames for

15606-551: 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. Very long baseline interferometry Data received at each antenna in the array include arrival times from a local atomic clock , such as a hydrogen maser . At a later time, the data are correlated with data from other antennas that recorded

15759-438: 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

15912-455: The next three hours, including the descent phase, and the first thirty minutes after touchdown. Not long after the end of this three-hour communication window, Cassini 's high-gain antenna (HGA) was turned away from Titan and towards Earth. Very large radio telescopes on Earth were also listening to Huygens 's 10-watt transmission using the technique of very long baseline interferometry and aperture synthesis mode. At 11:25 CET on 14 January,

16065-400: The observing process significantly. Even though the data rates are very high, the data can be sent over normal Internet connections taking advantage of the fact that many of the international high speed networks have significant spare capacity at present. At the location of the correlator, the data is played back. The timing of the playback is adjusted according to the atomic clock signals, and

16218-440: The other antennas. The approximate delay required can be calculated from the geometry of the problem. The tape playback is synchronized using the recorded signals from the atomic clocks as time references, as shown in the drawing on the right. If the position of the antennas is not known to sufficient accuracy or atmospheric effects are significant, fine adjustments to the delays must be made until interference fringes are detected. If

16371-481: 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

16524-412: The position of the Huygens probe from Earth allowed reasonably accurate wind speed and direction calculations to be made. The fact that Huygens rotated in the opposite direction than planned delayed the creation of surface mosaics from the raw data by the project team for many months. On the other hand, this provided an opportunity for some citizen science projects to attempt the task of assembling

16677-496: The probe telemetry was finished being relayed from Cassini to Earth, the now-known data modulation was stripped off the recorded signal, leaving a pure carrier that could be integrated over several seconds to determine the probe frequency. It was expected that through analysis of the Doppler shifting of Huygens 's signal as it descended through the atmosphere of Titan, wind speed and direction could be determined with some degree of accuracy. A position of Huygens's landing site on Titan

16830-483: The probe was 1.3 m (4.3 ft) in diameter. The PSE included the electronics necessary to track the probe, to recover the data gathered during its descent, and to process and deliver the data to the orbiter, from where it was transmitted or "downlinked" to the Earth. The probe remained dormant throughout the 6.7-year interplanetary cruise, except for semiannual health checks. These checkouts followed preprogrammed descent scenario sequences as closely as possible, and

16983-461: The probe's descent onto Titan. IRVIN-GQ was responsible for the definition of the structure of each of Huygens ' parachutes. Irvin worked on the probe's descent control sub-system under contract to Martin-Baker Space Systems . Long after launch, a few persistent engineers discovered that the communication equipment on Cassini had a potentially fatal design flaw, which would have caused the loss of all data transmitted by Huygens . Since Huygens

17136-486: The purpose of spacecraft navigation. The inclusion of the ESA station at Malargue, Argentina, adds baselines that allow much better coverage of the southern hemisphere. VLBI has traditionally operated by recording the signal at each telescope on magnetic tapes or disks , and shipping those to the correlation center for replay. In 2004 it became possible to connect VLBI radio telescopes in close to real-time, while still employing

17289-498: The ratio of electric displacement field to its electric field ) of the surface material was measured. The HASI subsystem also contains a microphone, which was used to record any acoustic events during probe's descent and landing; This experiment used an ultra-stable oscillator which provided a precise S-band carrier frequency that allowed the Cassini orbiter to accurately determine Huygens's radial velocity with respect to Cassini via

17442-507: The results were relayed to Earth for examination by system and payload experts. Prior to the probe's separation from the orbiter on 25 December 2004, a final health check was performed. The "coast" timer was loaded with the precise time necessary to turn on the probe systems (15 minutes before its encounter with Titan's atmosphere), then the probe detached from the orbiter and coasted in free space to Titan in 22 days with no systems active except for its wake-up timer. The main mission phase

17595-479: The same radio signal, to produce the resulting image. The resolution achievable using interferometry is proportional to the observing frequency. The VLBI technique enables the distance between telescopes to be much greater than that possible with conventional interferometry , which requires antennas to be physically connected by coaxial cable , waveguide , optical fiber , or other type of transmission line . The greater telescope separations are possible in VLBI due to

17748-451: 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

17901-430: 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

18054-447: 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

18207-578: 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

18360-399: 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

18513-433: The signal from antenna A is taken as the reference, inaccuracies in the delay will lead to errors ϵ B {\displaystyle \epsilon _{B}} and ϵ C {\displaystyle \epsilon _{C}} in the phases of the signals from tapes B and C respectively (see drawing on right). As a result of these errors the phase of the complex visibility cannot be measured with

18666-461: The size, shape, vertical distribution, optical properties, sources and sinks of aerosols in Titan’s atmosphere; and (4) measurements of the spectrum of downward solar flux to study the composition of the atmosphere, especially the mixing ratio profile of methane throughout the descent." This instrument is a gas chemical analyzer that was designed to identify and measure chemicals in Titan's atmosphere. It

18819-458: The sky and the scene on Titan is mainly orange due to the much greater attenuation of blue light by Titan's haze relative to red light. The Sun (which was comparatively high in the sky when Huygens landed) would be visible as a small, bright spot, one tenth the size of the solar disk seen from Earth, and comparable in size and brightness to a car headlight seen from about 150 m (500 ft). It casts sharp shadows, but of low contrast as 90% of

18972-408: 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

19125-471: 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

19278-477: 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

19431-427: The story of amateurs outperforming the professionals, most of the participants understood themselves as citizen scientists, and the driving force behind their work was a desire to find out and show as much as possible of the hitherto unknown surface of Titan. Some enthusiasts projects were the first at all to publish surface mosaics and panoramas of Titan already the day after Huygens landed, another project worked with

19584-420: The surface for studies of the composition, topography, and physical processes which form the surface as well as for direct measurements of the wind profile during the descent; (3) measurements of the brightness and degree of linear polarization of scattered sunlight including the solar aureole together with measurements of the extinction optical depth of the aerosols as a function of wavelength and altitude to study

19737-400: The surface mosaics. This was possible, because the European Space Agency approved the publication of the DISR raw images and gave the permission for citizen scientists to present their results on the internet. Some of these citizen science projects have received a lot of attention in the scientific community, in popular scientific journals and in the public media. While the media liked to present

19890-418: The surface were liquid, the sounder would measure the speed of sound in the "ocean" and possibly also the subsurface structure (depth). During descent, measurements of the speed of sound gave information on atmospheric composition and temperature, and an accelerometer recorded the deceleration profile at impact, indicating the hardness and structure of the surface. A tilt sensor measured pendulum motion during

20043-412: The surface. It slowed due to friction with the surface and, upon coming to its final resting place, wobbled back and forth five times. Huygens ' sensors continued to detect small vibrations for another two seconds, until motion subsided about ten seconds after touchdown. The probe kicked up a cloud of dust (most likely organic aerosols which drizzle out of the atmosphere) which remained suspended in

20196-404: The trajectory had to be changed. Huygens detached a month later than originally planned (December 2004 instead of November) and approached Titan in such a way that its transmissions travelled perpendicular to its direction of motion relative to Cassini , greatly reducing the Doppler shift. The trajectory change overcame the design flaw for the most part, and data transmission succeeded, although

20349-455: 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

20502-580: The world is the European VLBI Network (EVN). This is a part-time array that brings together the largest European radiotelescopes and some others outside of Europe for typically weeklong sessions, with the data being processed at the Joint Institute for VLBI in Europe (JIVE). The Very Long Baseline Array (VLBA), which uses ten dedicated, 25-meter telescopes spanning 5351 miles across the United States,

20655-402: 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

20808-406: Was a parachute descent through Titan's atmosphere. The batteries and all other resources were sized for a Huygens mission duration of 153 minutes, corresponding to a maximum descent time of 2.5 hours plus at least 3 additional minutes (and possibly a half-hour or more) on Titan's surface. The probe's radio link was activated early in the descent phase, and the orbiter "listened" to the probe for

20961-489: Was blown eastwards at more than 400 km/h (250 mph), agreeing with earlier measurements of the winds at 200 km (120 mi) altitude, made over the past few years using telescopes . Between 60 and 80 km (37 and 50 mi), Huygens was buffeted by rapidly fluctuating winds, which are thought to be vertical wind shear. At ground level, the Earth-based doppler shift and VLBI measurements show gentle winds of

21114-487: Was built under the Prime Contractorship of Aérospatiale in its Cannes Mandelieu Space Center , France, now part of Thales Alenia Space . The heat shield system was built under the responsibility of Aérospatiale near Bordeaux, now part of Airbus Defence and Space . Martin-Baker Space Systems was responsible for Huygens' parachute systems and the structural components, mechanisms and pyrotechnics that control

21267-477: Was carried out on Salyut-6 orbital station with KRT-10, a 10-meter radio telescope, which was launched in July 1978. The first dedicated SVLBI satellite was HALCA , an 8-meter radio telescope , which was launched in February 1997 and made observations until October 2003. Due to the small size of the dish, only very strong radio sources could be observed with SVLBI arrays incorporating it. Another SVLBI satellite,

21420-418: 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

21573-501: Was developed at the Lunar and Planetary Laboratory at the University of Arizona under the direction of Martin Tomasko, with several European institutes contributing to the hardware. "The scientific objectives of the experiment fall into four areas including (1) measurement of the solar heating profile for studies of the thermal balance of Titan; (2) imaging and spectral reflection measurements of

21726-643: 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

21879-419: Was equipped with samplers that were filled at high altitude for analysis. The mass spectrometer , a high-voltage quadrupole, collected data to build a model of the molecular masses of each gas, and a more powerful separation of molecular and isotopic species was accomplished by the gas chromatograph . During descent, the GC/MS also analyzed pyrolysis products (i.e., samples altered by heating) passed to it from

22032-413: Was found with precision (within one km – one km on Titan measures 1.3 arcminutes of latitude and longitude at the equator) using the Doppler data at a distance from Earth of about 1.2 billion kilometers. The probe landed on the surface of the moon at 10°34′23″S 192°20′06″W  /  10.573°S 192.335°W  / -10.573; -192.335  ( Huygens probe ) . A similar technique

22185-454: Was in flight. In early 2000, he sent simulated telemetry data at varying power and Doppler shift levels from Earth to Cassini . It turned out that Cassini was unable to relay the data correctly. This was because under the original flight plan, when Huygens was to descend to Titan, it would have accelerated relative to Cassini , causing the Doppler shift of its signal to vary. Consequently,

22338-415: Was in front of the Sun, Earth could still listen to them. Second, Huygens did not send any readable data directly to Earth. Rather, it transmitted data to the Cassini orbiter, which later relayed to Earth the data received. Huygens had six instruments aboard that took in a wide range of scientific data as the probe descended through Titan's atmosphere. The six instruments are: This instrument contains

22491-544: 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

22644-468: Was named after the 17th-century Dutch astronomer Christiaan Huygens , who discovered Titan in 1655. The combined Cassini–Huygens spacecraft was launched from Earth on 15 October 1997. Huygens separated from the Cassini orbiter on 25 December 2004, and landed on Titan on 14 January 2005 near the Adiri region . Huygens ' s landing is so far the only one accomplished in the outer Solar System or on

22797-498: 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

22950-590: 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

23103-601: Was too small to transmit directly to Earth, it was designed to transmit the telemetry data obtained while descending through Titan's atmosphere by radio to Cassini , which would in turn relay it to Earth using its large 4 m (13 ft) diameter main antenna. Some engineers, most notably ESA ESOC employees Claudio Sollazzo and Boris Smeds , felt uneasy about the fact that, in their opinion, this feature had not been tested before launch under sufficiently realistic conditions. Smeds managed, with some difficulty, to persuade superiors to perform additional tests while Cassini

23256-454: Was used to determine the landing site of the Mars exploration rovers by listening to their telemetry alone. Huygens landed at around 12:43 UTC on January 14, 2005 with an impact speed similar to dropping a ball on Earth from a height of about 1 m (3 ft). It made a dent 12 cm (4.7 in) deep, before bouncing onto a flat surface, and sliding 30 to 40 cm (12 to 16 in) across

23409-478: 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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