Misplaced Pages

#996003

65-583: The beginning of the S-II came in December 1959 when a committee recommended the design and construction of a high-thrust, liquid hydrogen fueled engine. The contract for this engine was given to Rocketdyne and it would be later called the J-2 . At the same time the S-II stage design began to take shape. Initially it was to have four J-2 engines and be 74 feet (23 m) in length and 260 inches (6.6 m) in diameter. In 1961

130-423: A change in pressure at one point in a liquid is transmitted undiminished to every other part of the liquid and very little energy is lost in the form of compression. However, the negligible compressibility does lead to other phenomena. The banging of pipes, called water hammer , occurs when a valve is suddenly closed, creating a huge pressure-spike at the valve that travels backward through the system at just under

195-422: A fairly constant temperature, making a liquid suitable for blanching , boiling , or frying . Even higher rates of heat transfer can be achieved by condensing a gas into a liquid. At the liquid's boiling point, all of the heat energy is used to cause the phase change from a liquid to a gas, without an accompanying increase in temperature, and is stored as chemical potential energy . When the gas condenses back into

260-409: A gas at normal temperature and pressure. However, the liquid density is very low compared to other common fuels. Once liquefied, it can be maintained as a liquid for some time in thermally insulated containers. There are two spin isomers of hydrogen ; whereas room temperature hydrogen is mostly orthohydrogen, liquid hydrogen consists of 99.79% parahydrogen and 0.21% orthohydrogen. Hydrogen requires

325-403: A given rate, such as when it is being sheared at finite velocity. A specific example is a liquid flowing through a pipe: in this case the liquid undergoes shear deformation since it flows more slowly near the walls of the pipe than near the center. As a result, it exhibits viscous resistance to flow. In order to maintain flow, an external force must be applied, such as a pressure difference between

390-558: A lesser extent than CO 2 ). Liquid hydrogen also has a much higher specific energy than gasoline, natural gas, or diesel. The density of liquid hydrogen is only 70.85 kg/m (at 20  K ), a relative density of just 0.07. Although the specific energy is more than twice that of other fuels, this gives it a remarkably low volumetric energy density , many fold lower. Liquid hydrogen requires cryogenic storage technology such as special thermally insulated containers and requires special handling common to all cryogenic fuels . This

455-404: A limited degree of particle mobility. As the temperature increases, the increased vibrations of the molecules causes distances between the molecules to increase. When a liquid reaches its boiling point , the cohesive forces that bind the molecules closely together break, and the liquid changes to its gaseous state (unless superheating occurs). If the temperature is decreased, the distances between

520-433: A liquid this excess heat-energy is released at a constant temperature. This phenomenon is used in processes such as steaming . Since liquids often have different boiling points, mixtures or solutions of liquids or gases can typically be separated by distillation , using heat, cold, vacuum , pressure, or other means. Distillation can be found in everything from the production of alcoholic beverages , to oil refineries , to

585-490: A liquid, H 2 must be cooled below its critical point of 33  K . However, for it to be in a fully liquid state at atmospheric pressure , H 2 needs to be cooled to 20.28 K (−252.87 °C; −423.17 °F). A common method of obtaining liquid hydrogen involves a compressor resembling a jet engine in both appearance and principle. Liquid hydrogen is typically used as a concentrated form of hydrogen storage . Storing it as liquid takes less space than storing it as

650-460: A mass of about 480 t (1,060,000 lb). The hardware was only 7.6% of this—92.4% was liquid hydrogen and liquid oxygen. At the bottom was the thrust structure supporting five J-2 engines in a quincunx arrangement. The center engine was fixed, while the other four were gimballed , similar to the engines on the S-IC stage below. Instead of using an intertank (empty container between tanks) like

715-451: A mixture of otherwise immiscible liquids can be stabilized to form an emulsion , where one liquid is dispersed throughout the other as microscopic droplets. Usually this requires the presence of a surfactant in order to stabilize the droplets. A familiar example of an emulsion is mayonnaise , which consists of a mixture of water and oil that is stabilized by lecithin , a substance found in egg yolks . The microscopic structure of liquids

SECTION 10

#1732844924997

780-430: A pure oxygen environment is solely water vapor. However, the high combustion temperatures and present atmospheric nitrogen can result in the breaking of N≡N bonds, forming toxic NOx if no exhaust scrubbing is done. Since water is often considered harmless to the environment, an engine burning it can be considered "zero emissions". In aviation, however, water vapor emitted in the atmosphere contributes to global warming (to

845-409: A relatively narrow temperature/pressure range to exist. Most known matter in the universe is either gas (as interstellar clouds ) or plasma (as stars ). Liquid is one of the four primary states of matter , with the others being solid, gas and plasma . A liquid is a fluid . Unlike a solid, the molecules in a liquid have a much greater freedom to move. The forces that bind the molecules together in

910-482: A rotating liquid forms a circular paraboloid and can therefore be used as a telescope . These are known as liquid-mirror telescopes . They are significantly cheaper than conventional telescopes, but can only point straight upward ( zenith telescope ). A common choice for the liquid is mercury. Quantities of liquids are measured in units of volume . These include the SI unit cubic metre (m ) and its divisions, in particular

975-407: A solid are only temporary in a liquid, allowing a liquid to flow while a solid remains rigid. A liquid, like a gas, displays the properties of a fluid. A liquid can flow, assume the shape of a container, and, if placed in a sealed container, will distribute applied pressure evenly to every surface in the container. If liquid is placed in a bag, it can be squeezed into any shape. Unlike a gas, a liquid

1040-567: A theoretical minimum of 3.3 kWh/kg (12 MJ/kg) to liquefy, and 3.9 kWh/kg (14 MJ/kg) including converting the hydrogen to the para isomer, but practically generally takes 10–13 kWh/kg (36–47 MJ/kg) compared to a 33 kWh/kg (119 MJ/kg) heating value of hydrogen. In 1885, Zygmunt Florenty Wróblewski published hydrogen's critical temperature as 33 K (−240.2 °C; −400.3 °F); critical pressure, 13.3 standard atmospheres (195 psi); and boiling point, 23 K (−250.2 °C; −418.3 °F). Hydrogen

1105-472: Is a fixed amount of energy associated with forming a surface of a given area. This quantity is a material property called the surface tension , in units of energy per unit area (SI units: J / m ). Liquids with strong intermolecular forces tend to have large surface tensions. A practical implication of surface tension is that liquids tend to minimize their surface area, forming spherical drops and bubbles unless other constraints are present. Surface tension

1170-436: Is also used to cool neutrons to be used in neutron scattering . Since neutrons and hydrogen nuclei have similar masses, kinetic energy exchange per interaction is maximum ( elastic collision ). Finally, superheated liquid hydrogen was used in many bubble chamber experiments. The first thermonuclear bomb , Ivy Mike , used liquid deuterium , also known as hydrogen-2, for nuclear fusion. The product of hydrogen combustion in

1235-430: Is at 13.81 K and 7.042 kPa. Due to its cold temperatures, liquid hydrogen is a hazard for cold burns . Hydrogen itself is biologically inert and its only human health hazard as a vapor is displacement of oxygen, resulting in asphyxiation, and its very high flammability and ability to detonate when mixed with air. Because of its flammability, liquid hydrogen should be kept away from heat or flame unless ignition

1300-440: Is complex and historically has been the subject of intense research and debate. A few of the key ideas are explained below. Microscopically, liquids consist of a dense, disordered packing of molecules. This contrasts with the other two common phases of matter, gases and solids. Although gases are disordered, the molecules are well-separated in space and interact primarily through molecule-molecule collisions. Conversely, although

1365-436: Is considered to be a promising candidate for these applications as it is a liquid near room temperature, has low toxicity, and evaporates slowly. Liquids are sometimes used in measuring devices. A thermometer often uses the thermal expansion of liquids, such as mercury , combined with their ability to flow to indicate temperature. A manometer uses the weight of the liquid to indicate air pressure . The free surface of

SECTION 20

#1732844924997

1430-408: Is given by where: For a body of water open to the air, p 0 {\displaystyle p_{0}} would be the atmospheric pressure . Static liquids in uniform gravitational fields also exhibit the phenomenon of buoyancy , where objects immersed in the liquid experience a net force due to the pressure variation with depth. The magnitude of the force is equal to the weight of

1495-437: Is important since machinery often operate over a range of temperatures (see also viscosity index ). The viscous behavior of a liquid can be either Newtonian or non-Newtonian . A Newtonian liquid exhibits a linear strain/stress curve, meaning its viscosity is independent of time, shear rate, or shear-rate history. Examples of Newtonian liquids include water, glycerin , motor oil , honey , or mercury. A non-Newtonian liquid

1560-410: Is intended. Unlike ambient-temperature gaseous hydrogen, which is lighter than air, hydrogen recently vaporized from liquid is so cold that it is heavier than air and can form flammable heavier-than-air air–hydrogen mixtures. Liquid state A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a nearly constant volume independent of pressure. It

1625-437: Is made up of tiny vibrating particles of matter, such as atoms, held together by intermolecular bonds . Like a gas, a liquid is able to flow and take the shape of a container. Unlike a gas, a liquid maintains a fairly constant density and does not disperse to fill every space of a container. Although liquid water is abundant on Earth, this state of matter is actually the least common in the known universe, because liquids require

1690-414: Is more stable than orthohydrogen, in which the two are parallel. At room temperature, gaseous hydrogen is mostly in the ortho isomeric form due to thermal energy, but an ortho-enriched mixture is only metastable when liquified at low temperature. It slowly undergoes an exothermic reaction to become the para isomer, with enough energy released as heat to cause some of the liquid to boil. To prevent loss of

1755-451: Is nearly incompressible, meaning that it occupies nearly a constant volume over a wide range of pressures; it does not generally expand to fill available space in a container but forms its own surface, and it may not always mix readily with another liquid. These properties make a liquid suitable for applications such as hydraulics . Liquid particles are bound firmly but not rigidly. They are able to move around one another freely, resulting in

1820-473: Is no equilibrium at this transition under constant pressure, so unless supercooling occurs, the liquid will eventually completely crystallize. However, this is only true under constant pressure, so that (for example) water and ice in a closed, strong container might reach an equilibrium where both phases coexist. For the opposite transition from solid to liquid, see melting . The phase diagram explains why liquids do not exist in space or any other vacuum. Since

1885-805: Is of vital importance in chemistry and biology, and it is necessary for all known forms of life. Inorganic liquids include water, magma , inorganic nonaqueous solvents and many acids . Important everyday liquids include aqueous solutions like household bleach , other mixtures of different substances such as mineral oil and gasoline, emulsions like vinaigrette or mayonnaise , suspensions like blood, and colloids like paint and milk . Many gases can be liquefied by cooling, producing liquids such as liquid oxygen , liquid nitrogen , liquid hydrogen and liquid helium . Not all gases can be liquified at atmospheric pressure, however. Carbon dioxide , for example, can only be liquified at pressures above 5.1 atm . Some materials cannot be classified within

1950-435: Is one of the four fundamental states of matter (the others being solid , gas , and plasma ), and is the only state with a definite volume but no fixed shape. The density of a liquid is usually close to that of a solid, and much higher than that of a gas. Therefore, liquid and solid are both termed condensed matter . On the other hand, as liquids and gases share the ability to flow, they are both called fluids. A liquid

2015-435: Is one where the viscosity is not independent of these factors and either thickens (increases in viscosity) or thins (decreases in viscosity) under shear. Examples of non-Newtonian liquids include ketchup , custard , or starch solutions. The speed of sound in a liquid is given by c = K / ρ {\displaystyle c={\sqrt {K/\rho }}} where K {\displaystyle K}

S-II - Misplaced Pages Continue

2080-447: Is responsible for a range of other phenomena as well, including surface waves , capillary action , wetting , and ripples . In liquids under nanoscale confinement , surface effects can play a dominating role since – compared with a macroscopic sample of liquid – a much greater fraction of molecules are located near a surface. The surface tension of a liquid directly affects its wettability . Most common liquids have tensions ranging in

2145-442: Is similar to, but more severe than liquid oxygen . Even with thermally insulated containers it is difficult to keep such a low temperature, and the hydrogen will gradually leak away (typically at a rate of 1% per day ). It also shares many of the same safety issues as other forms of hydrogen, as well as being cold enough to liquefy, or even solidify atmospheric oxygen, which can be an explosion hazard. The triple point of hydrogen

2210-425: Is the bulk modulus of the liquid and ρ {\displaystyle \rho } the density. As an example, water has a bulk modulus of about 2.2  GPa and a density of 1000 kg/m , which gives c = 1.5 km/s. At a temperature below the boiling point , any matter in liquid form will evaporate until reaching equilibrium with the reverse process of condensation of its vapor. At this point

2275-475: Is used by NASA and the U.S. Air Force , which operate a large number of liquid hydrogen tanks with an individual capacity up to 3.8 million liters (1 million U.S. gallons). In most rocket engines fueled by liquid hydrogen, it first cools the nozzle and other parts before being mixed with the oxidizer, usually liquid oxygen , and burned to produce water with traces of ozone and hydrogen peroxide . Practical H 2 –O 2 rocket engines run fuel-rich so that

2340-432: Is very important. Initial attempts did not work well: there were bonding issues and air pockets. Initially, the stage was insulated with a honeycomb material. These panels had grooves milled in the back which were purged with helium during filling. The final method was to spray insulation on by hand and trim the excess. This change saved both weight and time and avoided the issues with air pockets entirely. The LH2 tank volume

2405-533: The DeepC , BMW H2R , and others. Due to its similarity, builders can sometimes modify and share equipment with systems designed for liquefied natural gas (LNG). Liquid hydrogen is being investigated as a zero carbon fuel for aircraft . Because of the lower volumetric energy , the hydrogen volumes needed for combustion are large. Unless direct injection is used, a severe gas-displacement effect also hampers maximum breathing and increases pumping losses. Liquid hydrogen

2470-498: The Marshall Space Flight Center began the process to find the contractor to build the stage. Out of the 30 aerospace companies invited to a conference where the initial requirements were laid out, only seven submitted proposals a month later. Three of these were eliminated after their proposals had been investigated. However it was then decided that the initial specifications for the entire rocket were too small and so it

2535-596: The S-IC , the S-II used a common bulkhead (similar to that of the S-IV and S-IVB stages) that included both the top of the LOX tank and bottom of the LH2 tank. It consisted of two aluminum sheets separated by a honeycomb structure made of phenolic resin . It insulated a 126 °F (70 °C) temperature differential between the two tanks. The use of a common bulkhead saved 3.6 tonnes in weight, both by eliminating one bulkhead and by reducing

2600-1247: The cryogenic distillation of gases such as argon , oxygen , nitrogen , neon , or xenon by liquefaction (cooling them below their individual boiling points). Liquid is the primary component of hydraulic systems, which take advantage of Pascal's law to provide fluid power . Devices such as pumps and waterwheels have been used to change liquid motion into mechanical work since ancient times. Oils are forced through hydraulic pumps , which transmit this force to hydraulic cylinders . Hydraulics can be found in many applications, such as automotive brakes and transmissions , heavy equipment , and airplane control systems. Various hydraulic presses are used extensively in repair and manufacturing, for lifting, pressing, clamping and forming. Liquid metals have several properties that are useful in sensing and actuation , particularly their electrical conductivity and ability to transmit forces (incompressibility). As freely flowing substances, liquid metals retain these bulk properties even under extreme deformation. For this reason, they have been proposed for use in soft robots and wearable healthcare devices , which must be able to operate under repeated deformation. The metal gallium

2665-709: The operating temperature range of the component. Oils are often used in engines, gear boxes , metalworking , and hydraulic systems for their good lubrication properties. Many liquids are used as solvents , to dissolve other liquids or solids. Solutions are found in a wide variety of applications, including paints , sealants , and adhesives . Naphtha and acetone are used frequently in industry to clean oil, grease, and tar from parts and machinery. Body fluids are water-based solutions. Surfactants are commonly found in soaps and detergents . Solvents like alcohol are often used as antimicrobials . They are found in cosmetics, inks , and liquid dye lasers . They are used in

S-II - Misplaced Pages Continue

2730-470: The cavities left by the bubbles with tremendous localized force, eroding any adjacent solid surface. In a gravitational field , liquids exert pressure on the sides of a container as well as on anything within the liquid itself. This pressure is transmitted in all directions and increases with depth. If a liquid is at rest in a uniform gravitational field, the pressure p {\displaystyle p} at depth z {\displaystyle z}

2795-459: The classical three states of matter. For example, liquid crystals (used in liquid-crystal displays ) possess both solid-like and liquid-like properties, and belong to their own state of matter distinct from either liquid or solid. Liquids are useful as lubricants due to their ability to form a thin, freely flowing layer between solid materials. Lubricants such as oil are chosen for viscosity and flow characteristics that are suitable throughout

2860-781: The cubic decimeter, more commonly called the litre (1 dm = 1 L = 0.001 m ), and the cubic centimetre, also called millilitre (1 cm = 1 mL = 0.001 L = 10 m ). The volume of a quantity of liquid is fixed by its temperature and pressure . Liquids generally expand when heated, and contract when cooled. Water between 0 °C and 4 °C is a notable exception. On the other hand, liquids have little compressibility . Water, for example, will compress by only 46.4 parts per million for every unit increase in atmospheric pressure (bar). At around 4000 bar (400 megapascals or 58,000 psi ) of pressure at room temperature water experiences only an 11% decrease in volume. Incompressibility makes liquids suitable for transmitting hydraulic power , because

2925-443: The ends of the pipe. The viscosity of liquids decreases with increasing temperature. Precise control of viscosity is important in many applications, particularly the lubrication industry. One way to achieve such control is by blending two or more liquids of differing viscosities in precise ratios. In addition, various additives exist which can modulate the temperature-dependence of the viscosity of lubricating oils. This capability

2990-423: The enormous variation seen in other mechanical properties, such as viscosity. The free surface of a liquid is disturbed by gravity ( flatness ) and waves ( surface roughness ). An important physical property characterizing the flow of liquids is viscosity . Intuitively, viscosity describes the resistance of a liquid to flow. More technically, viscosity measures the resistance of a liquid to deformation at

3055-539: The exhaust contains some unburned hydrogen. This reduces combustion chamber and nozzle erosion. It also reduces the molecular weight of the exhaust, which can increase specific impulse , despite the incomplete combustion. Liquid hydrogen can be used as the fuel for an internal combustion engine or fuel cell . Various submarines, including the Type 212 submarine , Type 214 submarine , and others, and concept hydrogen vehicles have been built using this form of hydrogen, such as

3120-624: The food industry, in processes such as the extraction of vegetable oil . Liquids tend to have better thermal conductivity than gases, and the ability to flow makes a liquid suitable for removing excess heat from mechanical components. The heat can be removed by channeling the liquid through a heat exchanger , such as a radiator , or the heat can be removed with the liquid during evaporation . Water or glycol coolants are used to keep engines from overheating. The coolants used in nuclear reactors include water or liquid metals, such as sodium or bismuth . Liquid propellant films are used to cool

3185-477: The individual elements are solid under the same conditions (see eutectic mixture ). An example is the sodium-potassium metal alloy NaK . Other metal alloys that are liquid at room temperature include galinstan , which is a gallium-indium-tin alloy that melts at −19 °C (−2 °F), as well as some amalgams (alloys involving mercury). Pure substances that are liquid under normal conditions include water, ethanol and many other organic solvents. Liquid water

3250-416: The liquid displaced by the object, and the direction of the force depends on the average density of the immersed object. If the density is smaller than that of the liquid, the buoyant force points upward and the object floats, whereas if the density is larger , the buoyant force points downward and the object sinks. This is known as Archimedes' principle . Unless the volume of a liquid exactly matches

3315-399: The liquid during long-term storage, it is therefore intentionally converted to the para isomer as part of the production process, typically using a catalyst such as iron(III) oxide , activated carbon , platinized asbestos, rare earth metals, uranium compounds, chromium(III) oxide , or some nickel compounds. Liquid hydrogen is a common liquid rocket fuel for rocketry application and

SECTION 50

#1732844924997

3380-475: The manufacturing plant built by the government at Seal Beach , California . 15 flight stages were to be produced. Plans were also developed to build 10 follow-on stages, S-II-16 through -25, but funding to assemble them never materialized. These stages would have supported later Apollo missions, including those of the Apollo Applications Program . When fully loaded with propellant, the S-II had

3445-594: The molecules become smaller. When the liquid reaches its freezing point the molecules will usually lock into a very specific order, called crystallizing, and the bonds between them become more rigid, changing the liquid into its solid state (unless supercooling occurs). Only two elements are liquid at standard conditions for temperature and pressure : mercury and bromine . Four more elements have melting points slightly above room temperature : francium , caesium , gallium and rubidium . In addition, certain mixtures of elements are liquid at room temperature, even if

3510-441: The overall length of the stage. The S-II's common bulkhead design was tested in 1965 on the subscale Common Bulkhead Test Tank (CBTT), made of only 2 LH2 tank cylinders. The LOX tank was an ellipsoidal container of 10 meters diameter and 6.7 meters high holding up to 83,000 US gallons (310 m) or 789,000 pounds (358 t) of oxidizer. It was formed by welding 12 gores (large triangular sections) and two circular pieces for

3575-518: The pressure is essentially zero (except on surfaces or interiors of planets and moons) water and other liquids exposed to space will either immediately boil or freeze depending on the temperature. In regions of space near the Earth, water will freeze if the sun is not shining directly on it and vaporize (sublime) as soon as it is in sunlight. If water exists as ice on the Moon, it can only exist in shadowed holes where

3640-460: The speed of sound. Another phenomenon caused by liquid's incompressibility is cavitation . Because liquids have little elasticity they can literally be pulled apart in areas of high turbulence or dramatic change in direction, such as the trailing edge of a boat propeller or a sharp corner in a pipe. A liquid in an area of low pressure (vacuum) vaporizes and forms bubbles, which then collapse as they enter high pressure areas. This causes liquid to fill

3705-626: The sun never shines and where the surrounding rock does not heat it up too much. At some point near the orbit of Saturn, the light from the Sun is too faint to sublime ice to water vapor. This is evident from the longevity of the ice that composes Saturn's rings. Liquids can form solutions with gases, solids, and other liquids. Two liquids are said to be miscible if they can form a solution in any proportion; otherwise they are immiscible. As an example, water and ethanol (drinking alcohol) are miscible whereas water and gasoline are immiscible. In some cases

3770-450: The tens of mJ/m , so droplets of oil, water, or glue can easily merge and adhere to other surfaces, whereas liquid metals such as mercury may have tensions ranging in the hundreds of mJ/m , thus droplets do not combine easily and surfaces may only wet under specific conditions. The surface tensions of common liquids occupy a relatively narrow range of values when exposed to changing conditions such as temperature, which contrasts strongly with

3835-732: The thrust chambers of rockets . In machining , water and oils are used to remove the excess heat generated, which can quickly ruin both the work piece and the tooling. During perspiration , sweat removes heat from the human body by evaporating. In the heating, ventilation, and air-conditioning industry (HVAC), liquids such as water are used to transfer heat from one area to another. Liquids are often used in cooking due to their excellent heat-transfer capabilities. In addition to thermal conduction, liquids transmit energy by convection. In particular, because warmer fluids expand and rise while cooler areas contract and sink, liquids with low kinematic viscosity tend to transfer heat through convection at

3900-478: The top and bottom. The gores were shaped by positioning in a 211,000-liter tank of water with three carefully orchestrated sets of underwater explosions to shape each gore. The LH2 tank was constructed of six cylinders: five were 2.4 meters high and the sixth was 0.69 meters high. The biggest challenge was the insulation. Liquid hydrogen must be kept colder than about 20 °C above absolute zero (−423 °F or 20.4 K or −252.8 °C) so good insulation

3965-426: The vapor will condense at the same rate as the liquid evaporates. Thus, a liquid cannot exist permanently if the evaporated liquid is continually removed. A liquid at or above its boiling point will normally boil, though superheating can prevent this in certain circumstances. At a temperature below the freezing point, a liquid will tend to crystallize , changing to its solid form. Unlike the transition to gas, there

SECTION 60

#1732844924997

4030-405: The volume of its container, one or more surfaces are observed. The presence of a surface introduces new phenomena which are not present in a bulk liquid. This is because a molecule at a surface possesses bonds with other liquid molecules only on the inner side of the surface, which implies a net force pulling surface molecules inward. Equivalently, this force can be described in terms of energy: there

4095-421: Was 260,000 US gallons (980 m) for storing 153,000 pounds (69 t) of liquid hydrogen. The S-II was constructed vertically to aid welding and keep the large circular sections in the correct shape. Download coordinates as: Liquid hydrogen Liquid hydrogen ( H 2 (l) ) is the liquid state of the element hydrogen . Hydrogen is found naturally in the molecular H 2 form. To exist as

4160-477: Was decided to increase the size of the stages used. This raised difficulties for the four remaining companies as NASA had still not yet decided on various aspects of the stage including size, and the upper stages that would be placed on top. On September 11, 1961, the contract was awarded to North American Aviation (who were also awarded the contract for the Apollo Command/Service Module ), with

4225-406: Was liquefied by James Dewar in 1898 by using regenerative cooling and his invention, the vacuum flask . The first synthesis of the stable isomer form of liquid hydrogen, parahydrogen, was achieved by Paul Harteck and Karl Friedrich Bonhoeffer in 1929. The two nuclei in a dihydrogen molecule can have two different spin states. Parahydrogen, in which the two nuclear spins are antiparallel,

#996003