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65-721: The J-2X was intended to be based on the J-2 used on the S-II and S-IVB stages of the Saturn rockets used during the Apollo program , but as required thrust for the Ares I increased due to weight problems it became a clean-sheet design. It entered development in 2007 as part of the now-cancelled Constellation program . Originally planned for use on the upper stages of the Ares I and Ares V rockets,

130-570: A domino effect known as Kessler syndrome . NASA's Orbital Debris Program tracks over 25,000 objects larger than 10 cm diameter in LEO, while the estimated number between 1 and 10 cm is 500,000, and the number of particles bigger than 1 mm exceeds 100 million. The particles travel at speeds up to 7.8 km/s (28,000 km/h; 17,500 mph), so even a small impact can severely damage a spacecraft. [REDACTED]  This article incorporates public domain material from websites or documents of

195-505: A channel-walled combustion chamber versus the tube-welded chamber of the J-2, a redesign of all the electronics, a gas generator and supersonic main injector based on the RS-68 , and the use of 21st-century joining techniques. On 16 July 2007 NASA officially announced the award to Pratt & Whitney Rocketdyne (PWR) of a $ 1.2 billion contract "for design, development, testing and evaluation of

260-682: A flurry of activity as different means of reaching the Moon were evaluated. Both the Nova and Saturn rockets, which shared a similar design and could share some parts, were evaluated for the mission. However, it was judged that the Saturn would be easier to get into production, since many of the components were designed to be air-transportable. Nova would require new factories for all the major stages, and there were serious concerns that they could not be completed in time. Saturn required only one new factory, for

325-660: A goal of building a crewed lunar outpost. Like NASA, Lunex favored the direct ascent mode, and therefore required much larger boosters. As part of the project, they designed an entirely new rocket series known as the Space Launcher System , or SLS (not to be confused with the Space Launch System part of the Artemis program ), which combined a number of solid-fuel boosters with either the Titan missile or

390-630: A hitch, starting in December 1956, and a launch was planned for late 1957. On October 4, 1957, the Soviet Union surprised the world with the launch of Sputnik I . Although there had been some indications that the Soviets were working towards this goal, few in the U.S. military and scientific establishment considered these efforts seriously. When asked in November 1954 about the possibility of

455-549: A large spacecraft, a new booster with much greater power would be needed; even the Saturn was not nearly large enough. NASA started examining a number of potential rocket designs under their Nova program. NASA was not alone in studying crewed lunar missions. Von Braun had always expressed an interest in this goal, and had been studying what would be required for a lunar mission for some time. ABMA's Project Horizon proposed using fifteen Saturn launches to carry up spacecraft components and fuel that would be assembled in orbit to build

520-515: A launcher capable of placing loads up to 8,500 lb (3,900 kg) into low Earth orbit. The Centaur was based on the same "balloon tank" concept as the Atlas, and built on the same jigs at the same 120-inch (3,000 mm) diameter. As the Titan was deliberately built at the same size as well, this meant the Centaur could be used with either missile. Given that the Atlas was the higher priority of

585-590: A memorandum stripping the Army of offensive missiles with a range of 200 miles (320 km) or greater, and turning their Jupiter missiles over to the Air Force. From that point on, the Air Force would be the primary missile developer, especially for dual-use missiles that could also be used as space launch vehicles . In late 1956, the Department of Defense released a requirement for a heavy-lift vehicle to orbit

650-462: A new class of communications and "other" satellites (the spy satellite program was top secret ). The requirements, drawn up by the then-unofficial Advanced Research Projects Agency (ARPA), called for a vehicle capable of putting 9,000 to 18,000 kilograms into orbit, or accelerating 2,700 to 5,400 kg to escape velocity. Since the Wilson memorandum covered only weapons, not space vehicles,

715-454: A new custom booster stage to address a wide variety of launch weights. The smallest SLS vehicle consisted of a Titan and two strap-on solids, giving it performance similar to Titan C, allowing it to act as a launcher for Dyna-Soar. The largest used much larger solid-rockets and a much-enlarged booster for their direct ascent mission. Combinations in-between these extremes would be used for other satellite launching duties. A government commission,

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780-543: A satellite into a LEO, and a satellite there needs less powerful amplifiers for successful transmission, LEO is used for many communication applications, such as the Iridium phone system . Some communication satellites use much higher geostationary orbits and move at the same angular velocity as the Earth as to appear stationary above one location on the planet. Unlike geosynchronous satellites , satellites in low orbit have

845-484: A second round of successful gas generator tests was announced on 21 September 2010. Starting in 2011, the full J-2X engine, derived from heritage and new designs, has undergone hot-fire tests. In October 2013, it was reported that work on the J-2X would pause following development testing in 2014, due to funding limitations, an expected delayed need for the engine's capabilities for piloted missions to Mars, and selection of

910-477: A single larger booster; using existing designs they looked at combining tankage from one Jupiter as a central core, with eight Redstone diameter tanks attached to it. This relatively cheap configuration allowed existing fabrication and design facilities to be used to produce this "quick and dirty" design. Two approaches to building the Super-Jupiter were considered; the first used multiple engines to reach

975-433: A single very large lunar craft. This Earth orbit rendezvous mission profile required the least amount of booster capacity per launch , and was thus able to be carried out using the existing rocket design. This would be the first step towards a small crewed base on the moon, which would require several additional Saturn launches every month to supply it. The Air Force had also started their Lunex Project in 1958, also with

1040-441: A small field of view and can only observe and communicate with a fraction of the Earth at a given time. This means that a large network (or constellation ) of satellites is required to provide continuous coverage. Satellites at lower altitudes of orbit are in the atmosphere and suffer from rapid orbital decay , requiring either periodic re-boosting to maintain stable orbits, or the launching of replacements for those that re-enter

1105-433: A subset of LEO. These orbits, with low orbital inclination , allow rapid revisit times over low-latitude locations on Earth. Prograde equatorial LEOs also have lower delta-v launch requirements because they take advantage of the Earth's rotation. Other useful LEO orbits including polar orbits and Sun-synchronous orbits have a higher inclinations to the equator and provide coverage for higher latitudes on Earth. Some of

1170-457: A test vehicle, since its lower stage was based on existing technology ( Redstone and Jupiter tankage) and its upper stage was already in development. This would provide valuable testing for the S-IV as well as a launch platform for capsules and other components in low earth orbit. The members of the Saturn family that were actually built were: Low Earth orbit A low Earth orbit ( LEO )

1235-431: A thrust plate at the bottom, and four Rocketdyne E-1 engines, each having 380,000 lbf (1,700 kN) of thrust. The ABMA team also left the design open to future expansion with a single 1,500,000 lbf (6,700 kN) engine, which would require relatively minor changes to the design. The upper stage was the lengthened Titan, with the Centaur on top. The result was a very tall and skinny rocket, quite different from

1300-421: Is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, peaking in number at an altitude around 800 km (500 mi), while the farthest in LEO, before medium Earth orbit (MEO), have an altitude of 2,000 kilometers, about one-third of the radius of Earth and near

1365-496: Is only slightly less than on the Earth's surface. This is because the distance to LEO from the Earth's surface is much less than the Earth's radius. However, an object in orbit is in a permanent free fall around Earth, because in orbit the gravitational force and the centrifugal force balance each other out. As a result, spacecraft in orbit continue to stay in orbit, and people inside or outside such craft continuously experience weightlessness . Objects in LEO orbit Earth between

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1430-751: The Army Ballistic Missile Agency (ABMA) saw this as a way to continue the development of their own large-rocket projects. In April 1957, von Braun directed Heinz-Hermann Koelle , chief of the Future Projects design branch, to study dedicated launch vehicle designs that could be built as quickly as possible. Koelle evaluated a variety of designs for missile-derived launchers that could place a maximum of about 1,400 kg in orbit, but might be expanded to as much as 4,500 kg with new high-energy upper stages. In any event, these upper stages would not be available until 1961 or 1962 at

1495-531: The RL10 powered Exploration Upper Stage for SLS. In September 2022, the components of the J-2X were put up for auction on GSA Auctions, likely confirming the cancellation of the program. Saturn (rocket family) The Saturn family of American rockets was developed by a team of former German rocket engineers and scientists led by Wernher von Braun to launch heavy payloads to Earth orbit and beyond. The Saturn family used liquid hydrogen as fuel in

1560-566: The lunar orbit rendezvous method reduced the launch weight requirements below those of the Nova, into the C-5's range. At this point, however, all three stages existed only on paper, and it was realized that it was very likely that the actual lunar spacecraft would be developed and ready for testing long before the booster. NASA, therefore, decided to also continue development of the C-1 (later Saturn I ) as

1625-429: The oblateness of Earth's spheroid figure and local topography . While definitions based on altitude are inherently ambiguous, most of them fall within the range specified by an orbit period of 128 minutes because, according to Kepler's third law , this corresponds to a semi-major axis of 8,413 km (5,228 mi). For circular orbits, this in turn corresponds to an altitude of 2,042 km (1,269 mi) above

1690-571: The upper stages . Originally proposed as a military satellite launcher, they were adopted as the launch vehicles for the Apollo Moon program . Three versions were built and flown: the medium-lift Saturn I , the heavy-lift Saturn IB , and the super heavy-lift Saturn V . The Saturn name was proposed by von Braun in October 1958 as a logical successor to the Jupiter series as well as

1755-580: The "Saturn Vehicle Evaluation Committee" (better known as the Silverstein Committee ), was assembled to recommend specific directions that NASA could take with the existing Army program. The committee recommended the development of new, hydrogen-burning upper stages for the Saturn, and outlined eight different configurations for heavy-lift boosters ranging from very low-risk solutions making heavy use of existing technology, to designs that relied on hardware that had not been developed yet, including

1820-601: The 1,500,000 lbf (6,700 kN) mark, the second used a single much larger engine. Both approaches had their own advantages and disadvantages. Building a smaller engine for clustered use would be a relatively low-risk path from existing systems, but required duplication of systems and made the possibility of a stage failure much higher (adding engines generally reduces reliability, as per Lusser's law ). A single larger engine would be more reliable, and would offer higher performance because it eliminated duplication of "dead weight" like propellant plumbing and hydraulics for steering

1885-635: The ABMA group were already referring to the design as Saturn, as von Braun explained it as a reference to the planet after Jupiter. The name change became official in February 1959. In addition to ARPA, various groups within the US government had been considering the formation of a civilian agency to handle space exploration. After the Sputnik launch, these efforts gained urgency and were quickly moved forward. NASA

1950-459: The DoD studied the problem and concluded that it was primarily bureaucratic. As all of the branches of the military had their own research and development programs, there was considerable duplication and inter-service fighting for resources. Making matters worse, the DoD imposed its own Byzantine procurement and contracting rules, adding considerable overhead. To address these concerns, the DoD initiated

2015-437: The J-2X engine", and began construction of a new test stand for altitude testing of J-2X engines at Stennis Space Center on 23 August 2007. Component testing was undertaken between December 2007 and May 2008, with nine tests of heritage J-2 engine components at SSC in preparation for the design of the J-2X engine. and on 8 September 2008 PWR announced successful testing of the initial J-2X gas generator design. The completion of

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2080-691: The J-2X was later intended for use in the Earth Departure Stage of the Block 2 Space Launch System , the successor to the Constellation program. The engine is intended to be more efficient and simpler to build than its J-2 ancestor, and cost less than the RS-25 engine. Differences in the new engine include the removal of beryllium , a centrifugal turbo pump versus the axial turbo pump of the J-2, different chamber and nozzle expansion ratios,

2145-498: The LEO region but are not in a LEO orbit because they re-enter the atmosphere . The distinction between LEO orbits and the LEO region is especially important for analysis of possible collisions between objects which may not themselves be in LEO but could collide with satellites or debris in LEO orbits. The mean orbital velocity needed to maintain a stable low Earth orbit is about 7.8 km/s (4.8 mi/s), which translates to 28,000 km/h (17,000 mph). However, this depends on

2210-555: The Moon in the four years spanning December 1968 through December 1972. No Saturn rocket failed catastrophically in flight. All the Saturn family rockets are listed here by date of introduction. In the early 1950s, the US Navy and US Army actively developed long-range missiles with the help of German rocket engineers who were involved in developing the successful V-2 during the Second World War. These missiles included

2275-593: The Navy's Viking , and the Army's Corporal , Jupiter and Redstone . Meanwhile, the US Air Force developed its Atlas and Titan missiles, relying more on American engineers. Infighting among the various branches was constant, with the United States Department of Defense (DoD) deciding which projects to fund for development. On November 26, 1956, Defense Secretary Charles E. Wilson issued

2340-658: The Roman god 's powerful position. In 1963, President John F. Kennedy identified the Saturn I SA-5 launch as being the point where US lift capability would surpass the Soviets , after having been behind since Sputnik . He last mentioned this in a speech given at Brooks Air Force Base in San Antonio on the day before he was assassinated. To date, the Saturn V is the only launch vehicle to transport human beings beyond low Earth orbit . A total of 24 humans were flown to

2405-456: The Saturn that eventually emerged. Specific uses were forecast for each of the military services, including navigation satellites for the Navy; reconnaissance, communications, and meteorological satellites for the Army and Air Force; support for Air Force crewed missions; and surface-to-surface logistics supply for the Army at distances up to 6400 km. Development and testing of the lower stage stack were projected to be completed by 1963, about

2470-400: The Soviets launching a satellite, Defense Secretary Wilson replied: "I wouldn't care if they did." The public did not see it the same way, however, and the event was a major public relations disaster for the US. Vanguard was planned to launch shortly after Sputnik, but a series of delays pushed this into December, when the rocket exploded in spectacular fashion. The press was harsh, referring to

2535-507: The Super-Jupiter design was based on off-the-shelf components, with the exception of the E-1 engines. Although it too relied on the Centaur for high-altitude missions, the rocket was usable for low-Earth orbit without Centaur, which offered some flexibility in case Centaur ran into problems. ARPA agreed that the Juno proposal was more likely to meet the timeframes required, although they felt that there

2600-433: The atmosphere. The effects of adding such quantities of vaporized metals to Earth's stratosphere are potentially of concern but currently unknown. The LEO environment is becoming congested with space debris because of the frequency of object launches. This has caused growing concern in recent years, since collisions at orbital velocities can be dangerous or deadly. Collisions can produce additional space debris, creating

2665-433: The beginning of the inner Van Allen radiation belt . The term LEO region is used for the area of space below an altitude of 2,000 km (1,200 mi) (about one-third of Earth's radius). Objects in orbits that pass through this zone, even if they have an apogee further out or are sub-orbital , are carefully tracked since they present a collision risk to the many LEO satellites. No human spaceflights other than

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2730-455: The denser part of the atmosphere and below the inner Van Allen radiation belt . They encounter atmospheric drag from gases in the thermosphere (approximately 80–600 km above the surface) or exosphere (approximately 600 km or 400 mi and higher), depending on orbit height. Satellites in orbits that reach altitudes below 300 km (190 mi) decay quickly due to atmospheric drag. Equatorial low Earth orbits ( ELEO ) are

2795-450: The earliest, and the launchers would still not meet the DoD requirements for heavy loads. In order to fill the projected need for loads of 10,000 kg or greater, the ABMA team calculated that a booster (first stage) with a thrust of about 1,500,000 lbf (6,700 kN) thrust would be needed, far greater than any existing or planned missile. For this role they proposed using a number of existing missiles clustered together to produce

2860-419: The engines. On the downside, an engine of this size had never been built before and development would be expensive and risky. The Air Force had recently expressed an interest in such an engine, which would develop into the famed F-1 , but at the time they were aiming for 1,000,000 lbf (4,400 kN) and the engines would not be ready until the mid-1960s. The engine-cluster appeared to be the only way to meet

2925-403: The exact altitude of the orbit. Calculated for a circular orbit of 200 km (120 mi) the orbital velocity is 7.79 km/s (4.84 mi/s), but for a higher 1,500 km (930 mi) orbit the velocity is reduced to 7.12 km/s (4.42 mi/s). The launch vehicle's delta-v needed to achieve low Earth orbit starts around 9.4 km/s (5.8 mi/s). The pull of gravity in LEO

2990-647: The first generation of Starlink satellites used polar orbits which provide coverage everywhere on Earth. Later Starlink constellations orbit at a lower inclination and provide more coverage for populated areas. Higher orbits include medium Earth orbit (MEO), sometimes called intermediate circular orbit (ICO), and further above, geostationary orbit (GEO). Orbits higher than low orbit can lead to early failure of electronic components due to intense radiation and charge accumulation. In 2017, " very low Earth orbits " ( VLEO ) began to be seen in regulatory filings. These orbits, below about 450 km (280 mi), require

3055-413: The formation of a new research and development group focused on launch vehicles and given wide discretionary powers that cut across traditional Army/Navy/Air Force lines. The group was given the job of catching up to the Soviets in space technology as quickly as possible, using whatever technology it could, regardless of the origin. Formalized as Advanced Research Projects Agency (ARPA) on February 7, 1958,

3120-601: The group examined the DoD launcher requirements and compared the various approaches that were currently available. At the same time that ABMA was drawing up the Super-Jupiter proposal, the Air Force was in the midst of working on their Titan C concept. The Air Force had gained valuable experience working with liquid hydrogen on the Lockheed CL-400 Suntan spy plane project and felt confident in their ability to use this volatile fuel for rockets. They had already accepted Krafft Ehricke 's arguments that hydrogen

3185-482: The largest of the proposed lower stages, and was selected primarily for that reason. The Saturn C-5 (later given the name Saturn V ), the most powerful of the Silverstein Committee's configurations, was selected as the most suitable design. At the time the mission mode had not been selected, so they chose the most powerful booster design in order to ensure that there would be ample power. Selection of

3250-474: The lunar missions of the Apollo program (1968-1972) and the 2024 Polaris Dawn have taken place beyond LEO. All space stations to date have operated geocentric within LEO. A wide variety of sources define LEO in terms of altitude . The altitude of an object in an elliptic orbit can vary significantly along the orbit. Even for circular orbits , the altitude above ground can vary by as much as 30 km (19 mi) (especially for polar orbits ) due to

3315-455: The mean radius of Earth, which is consistent with some of the upper altitude limits in some LEO definitions. The LEO region is defined by some sources as a region in space that LEO orbits occupy. Some highly elliptical orbits may pass through the LEO region near their lowest altitude (or perigee ) but are not in a LEO orbit because their highest altitude (or apogee ) exceeds 2,000 km (1,243 mi). Sub-orbital objects can also reach

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3380-451: The program had been given to the US Navy under Project Vanguard . The Vanguard launcher consisted of a Viking lower stage combined with new uppers adapted from sounding rockets . ABMA provided valuable support on Viking and Vanguard, both with their first-hand knowledge of the V-2, as well as developing its guidance system. The first three Vanguard suborbital test flights had gone off without

3445-515: The project as "Kaputnik" or "Project Rearguard". As Time magazine noted at the time: Von Braun responded to Sputnik I's launch by claiming he could have a satellite in orbit within 90 days of being given a go-ahead. His plan was to combine the existing Jupiter C rocket (confusingly, a Redstone adaptation, not a Jupiter) with the solid-fuel engines from the Vanguard, producing the Juno I . There

3510-579: The proposed new upper stage. The configurations were: Contracts for the development of a new hydrogen-burning engine were given to Rocketdyne in 1960 and for the development of the Saturn IV stage to Douglas the same year. The challenge that President John F. Kennedy put to NASA in May 1961 to put an astronaut on the Moon by the end of the decade put a sudden new urgency on the Saturn program. That year saw

3575-423: The requirements on time and budget. Super-Jupiter was the first-stage booster only; to place payloads in orbit, additional upper stages would be needed. ABMA proposed using either the Titan or Atlas as a second stage, optionally with the new Centaur upper-stage. The Centaur had been proposed by General Dynamics (Astronautics Corp.) as an upper stage for the Atlas (also their design) in order to quickly produce

3640-497: The same time that the Centaur should become available for testing in combination. The total development cost of $ 850 million during the years 1958-1963 covered 30 research and development flights. While the Super-Jupiter program was being drawn up, preparations were underway for the first satellite launch as the US contribution to the International Geophysical Year in 1957. For complex political reasons,

3705-400: The scope of the program, stating "In addition to the captive dynamic firing..., it is hereby agreed that this program should now be extended to provide for a propulsion flight test of this booster by approximately September 1960". Further, they wanted ABMA to produce three additional boosters, the last two of which would be "capable of placing limited payloads in orbit." By this point, many in

3770-465: The two ICBM projects and its production was fully accounted for, ABMA focused on "backup" design, Titan, although they proposed extending it in length in order to carry additional fuel. In December 1957, ABMA delivered Proposal: A National Integrated Missile and Space Vehicle Development Program to the DoD, detailing their clustered approach. They proposed a booster consisting of a Jupiter missile airframe surrounded by eight Redstones acting as tankage,

3835-429: The upper stage would have to be fairly large in order to hold enough fuel. As the Atlas and Titan were both built at 120" diameters it would make sense to build Titan C at this diameter as well, but this would result in an unwieldy tall and skinny rocket with dubious strength and stability. Instead, Titan C proposed building the new stage at a larger 160" diameter, meaning it would be an entirely new rocket. In comparison,

3900-412: The use of novel technologies for orbit raising because they operate in orbits that would ordinarily decay too soon to be economically useful. A low Earth orbit requires the lowest amount of energy for satellite placement. It provides high bandwidth and low communication latency . Satellites and space stations in LEO are more accessible for crew and servicing. Since it requires less energy to place

3965-600: Was estimated that this approach would save as much as $ 60 million in development and cut as much as two years of R&D time. Happy with the results of the redesign, on August 15, 1958, ARPA issued Order Number 14-59 that called on ABMA to: This was followed on September 11, 1958, with another contract with Rocketdyne to start work on the H-1. On September 23, 1958, ARPA and the Army Ordnance Missile Command (AOMC) drew up an additional agreement enlarging

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4030-503: Was formed on July 29, 1958, and immediately set about studying the problem of crewed space flight, and the launchers needed to work in this field. One goal, even in this early stage, was a crewed lunar mission. At the time, the NASA panels felt that the direct ascent mission profile was the best approach; this placed a single very large spacecraft in orbit, which was capable of flying to the Moon , landing and returning to Earth. To launch such

4095-457: Was no immediate response while everyone waited for Vanguard to launch, but the continued delays in Vanguard and the November launch of Sputnik II resulted in the go-ahead being given that month. Von Braun kept his promise with the successful launch of Explorer I on 1 February 1958. Vanguard was finally successful on March 17, 1958. Concerned that the Soviets continued to surprise the U.S. with technologies that seemed beyond their capabilities,

4160-550: Was no strong reason to use the E-1, and recommended a lower-risk approach here as well. ABMA responded with a new design, the Juno V (as a continuation of the Juno I and Juno II series of rockets, while Juno III and IV were unbuilt Atlas- and Titan-derived concepts), which replaced the four E-1 engines with eight H-1s , a much more modest upgrade of the existing S-3D already used on the Thor and Jupiter missiles, raising thrust from 150,000 to 188,000 lbf (670 to 840 kN). It

4225-421: Was the only practical fuel for upper stages, and started the Centaur project based on the strength of these arguments. Titan C was a hydrogen-burning intermediate stage that would normally sit between the Titan lower and Centaur upper, or could be used without the Centaur for low-Earth orbit missiles like Dyna-Soar . However, as hydrogen is much less dense than "traditional" fuels then in use, especially kerosene ,

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