Two bodies of different orbiting a common. The relative sizes and type of orbit are similar to the – system. In, an orbit is the curved of an, such as the trajectory of a around a star or a around a planet. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. To a close approximation, planets and satellites follow, with the being orbited at a focal point of the ellipse, as described. Current understanding of the mechanics of orbital motion is based on 's, which accounts for gravity as due to curvature of, with orbits following. For ease of calculation, in most situations, orbital motion is adequately approximated by, which explains as a force obeying an. • • • Historically, the apparent motions of the planets were described by European and Arabic philosophers using the idea of. This model posited the existence of perfect moving spheres or rings to which the stars and planets were attached. It assumed the heavens were fixed apart from the motion of the spheres, and was developed without any understanding of gravity. After the planets' motions were more accurately measured, theoretical mechanisms such as were added. Although the model was capable of reasonably accurately predicting the planets' positions in the sky, more and more epicycles were required as the measurements became more accurate, hence the model became increasingly unwieldy. Originally it was modified by to place the sun at the centre to help simplify the model. The model was further challenged during the 16th century, as comets were observed traversing the spheres. The basis for the modern understanding of orbits was first formulated by whose results are summarised in his three laws of planetary motion. First, he found that the orbits of the planets in our solar system are elliptical, not (or ), as had previously been believed, and that the Sun is not located at the center of the orbits, but rather at one. Second, he found that the orbital speed of each planet is not constant, as had previously been thought, but rather that the speed depends on the planet's distance from the Sun. Third, Kepler found a universal relationship between the orbital properties of all the planets orbiting the Sun. For the planets, the cubes of their distances from the Sun are proportional to the squares of their orbital periods. Jupiter and Venus, for example, are respectively about 5.2 and 0.723 distant from the Sun, their orbital periods respectively about 11.86 and 0.615 years. The proportionality is seen by the fact that the ratio for Jupiter, 5.2 3/11.86 2, is practically equal to that for Venus, 0.723 3/0.615 2, in accord with the relationship. Idealised orbits meeting these rules are known as. This image shows the four trajectory categories with the of the central mass's field of potential energy shown in black and the height of the kinetic energy of the moving body shown in red extending above that, correlating to changes in speed as distance changes according to Kepler's laws. Demonstrated that Kepler's laws were derivable from his theory of and that, in general, the orbits of bodies subject to gravity were (this assumes that the force of gravity propagates instantaneously). Newton showed that, for a pair of bodies, the orbits' sizes are in inverse proportion to their, and that those bodies orbit their common. Where one body is much more massive than the other (as is the case of an artificial satellite orbiting a planet), it is a convenient approximation to take the center of mass as coinciding with the center of the more massive body. Advances in Newtonian mechanics were then used to explore variations from the simple assumptions behind Kepler orbits, such as the perturbations due to other bodies, or the impact of spheroidal rather than spherical bodies. (1736–1813) developed a to Newtonian mechanics emphasizing energy more than force, and made progress on the three body problem, discovering the. In a dramatic vindication of classical mechanics, in 1846 was able to predict the position of based on unexplained perturbations in the orbit of. (1879-1955) in his 1916 paper The Foundation of the General Theory of Relativity explained that gravity was due to curvature of and removed Newton's assumption that changes propagate instantaneously. This led astronomers to recognize that did not provide the highest accuracy in understanding orbits. In, orbits follow geodesic trajectories which are usually approximated very well by the Newtonian predictions (except where there are very strong gravity fields and very high speeds) but the differences are measurable. Essentially all the experimental evidence that can distinguish between the theories agrees with relativity theory to within experimental measurement accuracy. The original vindication of general relativity is that it was able to account for the remaining unexplained amount in first noted by Le Verrier. Dec 13, 2017 Use Smart Applock function to lock apps to prevent intrusion. Protect your private information by hiding photos&videos and important files in our private zone. Anti piracy solution in VC++ and PHP codes with IPN via PayPal. More LeoGuard images. However, Newton's solution is still used for most short term purposes since it is significantly easier to use and sufficiently accurate. Planetary orbits [ ] Within a, planets,, and other,, and orbit the system's in. A comet in a or orbit about a barycenter is not gravitationally bound to the star and therefore is not considered part of the star's planetary system. Bodies which are gravitationally bound to one of the planets in a planetary system, either or, follow orbits about a barycenter near or within that planet. Owing to mutual, the of the planetary orbits vary over time., the smallest planet in the Solar System, has the most eccentric orbit. At the present, has the next largest eccentricity while the smallest orbital eccentricities are seen with and. As two objects orbit each other, the is that point at which the two objects are closest to each other and the is that point at which they are the farthest. (More specific terms are used for specific bodies. For example, perigee and apogee are the lowest and highest parts of an orbit around Earth, while perihelion and aphelion are the closest and farthest points of an orbit around the Sun.) In the case of planets orbiting a star, the mass of the star and all its satellites are calculated to be at a single point called the barycenter. The paths of all the star's satellites are elliptical orbits about that barycenter. Each satellite in that system will have its own elliptical orbit with the barycenter at one focal point of that ellipse. At any point along its orbit, any satellite will have a certain value of kinetic and potential energy with respect to the barycenter, and that energy is a constant value at every point along its orbit. As a result, as a planet approaches, the planet will increase in speed as its potential energy decreases; as a planet approaches, its velocity will decrease as its potential energy increases. Understanding orbits [ ] There are a few common ways of understanding orbits: • A force, such as gravity, pulls an object into a curved path as it attempts to fly off in a straight line. • As the object is pulled toward the massive body, it falls toward that body. However, if it has enough it will not fall into the body but will instead continue to follow the curved trajectory caused by that body indefinitely. The object is then said to be orbiting the body. As an illustration of an orbit around a planet, the model may prove useful (see image below). This is a ', in which a cannon on top of a tall mountain is able to fire a cannonball horizontally at any chosen muzzle speed. The effects of air friction on the cannonball are ignored (or perhaps the mountain is high enough that the cannon will be above the Earth's atmosphere, which comes to the same thing). Conic sections describe the possible orbits (yellow) of small objects around the Earth. A projection of these orbits onto the gravitational potential (blue) of the Earth makes it possible to determine the orbital energy at each point in space. If the cannon fires its ball with a low initial speed, the trajectory of the ball curves downward and hits the ground (A). As the firing speed is increased, the cannonball hits the ground farther (B) away from the cannon, because while the ball is still falling towards the ground, the ground is increasingly curving away from it (see first point, above). All these motions are actually 'orbits' in a technical sense – they are describing a portion of an elliptical path around the center of gravity – but the orbits are interrupted by striking the Earth. If the cannonball is fired with sufficient speed, the ground curves away from the ball at least as much as the ball falls – so the ball never strikes the ground. It is now in what could be called a non-interrupted, or circumnavigating, orbit. For any specific combination of height above the center of gravity and mass of the planet, there is one specific firing speed (unaffected by the mass of the ball, which is assumed to be very small relative to the Earth's mass) that produces a, as shown in (C). As the firing speed is increased beyond this, non-interrupted elliptic orbits are produced; one is shown in (D). If the initial firing is above the surface of the Earth as shown, there will also be non-interrupted elliptical orbits at slower firing speed; these will come closest to the Earth at the point half an orbit beyond, and directly opposite the firing point, below the circular orbit. At a specific horizontal firing speed called, dependent on the mass of the planet, an open orbit (E) is achieved that has a. At even greater speeds the object will follow a range of. In a practical sense, both of these trajectory types mean the object is 'breaking free' of the planet's gravity, and 'going off into space' never to return. See also: Six parameters are required to specify a about a body. For example, the three numbers that specify the body's initial position, and the three values that specify its velocity will define a unique orbit that can be calculated forwards (or backwards) in time. However, traditionally the parameters used are slightly different. The traditionally used set of orbital elements is called the set of, after Johannes Kepler and his laws. The Keplerian elements are six: • ( i) • (Ω) • (ω) • ( e) • ( a) • at ( M 0). In principle once the orbital elements are known for a body, its position can be calculated forward and backwards indefinitely in time. However, in practice, orbits are affected or, by other forces than simple gravity from an assumed point source (see the next section), and thus the orbital elements change over time. Orbital perturbations [ ] An orbital perturbation is when a force or impulse which is much smaller than the overall force or average impulse of the main gravitating body and which is external to the two orbiting bodies causes an acceleration, which changes the parameters of the orbit over time. Radial, prograde and transverse perturbations [ ] A small radial impulse given to a body in orbit changes the, but not the (to first order). A or impulse (i.e. An impulse applied along the orbital motion) changes both the eccentricity and the. Notably, a prograde impulse at raises the altitude at, and vice versa, and a retrograde impulse does the opposite. A transverse impulse (out of the orbital plane) causes rotation of the without changing the or eccentricity. In all instances, a closed orbit will still intersect the perturbation point. Orbital decay [ ]. Main article: If an orbit is about a planetary body with significant atmosphere, its orbit can decay because of. Particularly at each, the object experiences atmospheric drag, losing energy. Each time, the orbit grows less eccentric (more circular) because the object loses kinetic energy precisely when that energy is at its maximum. This is similar to the effect of slowing a pendulum at its lowest point; the highest point of the pendulum's swing becomes lower. With each successive slowing more of the orbit's path is affected by the atmosphere and the effect becomes more pronounced. Eventually, the effect becomes so great that the maximum kinetic energy is not enough to return the orbit above the limits of the atmospheric drag effect. When this happens the body will rapidly spiral down and intersect the central body. The bounds of an atmosphere vary wildly. During a, the Earth's atmosphere causes drag up to a hundred kilometres higher than during a solar minimum. Some satellites with long conductive tethers can also experience orbital decay because of electromagnetic drag from the. As the wire cuts the magnetic field it acts as a generator, moving electrons from one end to the other. The orbital energy is converted to heat in the wire. Orbits can be artificially influenced through the use of rocket engines which change the kinetic energy of the body at some point in its path. This is the conversion of chemical or electrical energy to kinetic energy. In this way changes in the orbit shape or orientation can be facilitated. Another method of artificially influencing an orbit is through the use of. These forms of propulsion require no propellant or energy input other than that of the Sun, and so can be used indefinitely. See for one such proposed use. Orbital decay can occur due to for objects below the for the body they're orbiting. The gravity of the orbiting object raises in the primary, and since below the synchronous orbit the orbiting object is moving faster than the body's surface the bulges lag a short angle behind it. The gravity of the bulges is slightly off of the primary-satellite axis and thus has a component along the satellite's motion. The near bulge slows the object more than the far bulge speeds it up, and as a result the orbit decays. Conversely, the gravity of the satellite on the bulges applies on the primary and speeds up its rotation. Artificial satellites are too small to have an appreciable tidal effect on the planets they orbit, but several moons in the solar system are undergoing orbital decay by this mechanism. Mars' innermost moon is a prime example, and is expected to either impact Mars' surface or break up into a ring within 50 million years. Orbits can decay via the emission of. This mechanism is extremely weak for most stellar objects, only becoming significant in cases where there is a combination of extreme mass and extreme acceleration, such as with or that are orbiting each other closely. Oblateness [ ] The standard analysis of orbiting bodies assumes that all bodies consist of uniform spheres, or more generally, concentric shells each of uniform density. It can be shown that such bodies are gravitationally equivalent to point sources. However, in the real world, many bodies rotate, and this introduces and distorts the gravity field, and gives a moment to the gravitational field which is significant at distances comparable to the radius of the body. In the general case, the gravitational potential of a rotating body such as, e.g., a planet is usually expanded in multipoles accounting for the departures of it from spherical symmetry. From the point of view of satellite dynamics, of particular relevance are the so-called even zonal harmonic coefficients, or even zonals, since they induce secular orbital perturbations which are cumulative over time spans longer than the orbital period. They do depend on the orientation of the body's symmetry axis in the space, affecting, in general, the whole orbit, with the exception of the semimajor axis. Multiple gravitating bodies [ ]. Main article: The effects of other gravitating bodies can be significant. For example, the cannot be accurately described without allowing for the action of the Sun's gravity as well as the Earth's. One approximate result is that bodies will usually have reasonably stable orbits around a heavier planet or moon, in spite of these perturbations, provided they are orbiting well within the heavier body's. When there are more than two gravitating bodies it is referred to as an. Most n-body problems have no, although some special cases have been formulated. Light radiation and stellar wind [ ] For smaller bodies particularly, light and can cause significant perturbations to the attitude and direction of motion of the body, and over time can be significant. Of the planetary bodies, the motion of is particularly affected over large periods when the asteroids are rotating relative to the Sun. Strange orbits [ ] Mathematicians have discovered that it is possible in principle to have multiple bodies in non-elliptical orbits that repeat periodically, although most such orbits are not stable regarding small perturbations in mass, position, or velocity. However, some special stable cases have been identified, including a planar figure-eight orbit occupied. Further studies have discovered that nonplanar orbits are also possible, including one involving 12 masses moving in 4 roughly circular, interlocking orbits equivalent to the edges of a. Finding such orbits naturally occurring in the universe is thought to be extremely unlikely, because of the improbability of the required conditions occurring by chance. Astrodynamics [ ]. Main article: Orbital mechanics or astrodynamics is the application of and to the practical problems concerning the motion of and other. The motion of these objects is usually calculated from and. It is a core discipline within space mission design and control. Celestial mechanics treats more broadly the orbital dynamics of systems under the influence of, including spacecraft and natural astronomical bodies such as star systems,,, and. Orbital mechanics focuses on spacecraft, including, orbit plane changes, and interplanetary transfers, and is used by mission planners to predict the results of. Is a more exact theory than Newton's laws for calculating orbits, and is sometimes necessary for greater accuracy or in high-gravity situations (such as orbits close to the Sun). Earth orbits [ ]. • • • Kuhn, The Copernican Revolution, pp. 238, 246–252 • Encyclopædia Britannica, 1968, vol. 645 • M Caspar, Kepler (1959, Abelard-Schuman), at pp.131–140; A Koyré, The Astronomical Revolution: Copernicus, Kepler, Borelli (1973, Methuen), pp. 277–279 • Jones, Andrew... Retrieved 2008-06-01. • See (written 1685, translated into English 1728, see ), for the original version of this 'cannonball' thought-experiment. • Fitzpatrick, Richard (2006-02-02).. Classical Mechanics – an introductory course. The University of Texas at Austin. From the original on 3 March 2001. Retrieved 2009-01-14. • Pogge, Richard W.;. Retrieved 25 January 2008. 'Perturbed stellar motions around the rotating black hole in Sgr A* for a generic orientation of its spin axis'.. 84 (12): 124001.:... • Renzetti, G. 'Satellite Orbital Precessions Caused by the Octupolar Mass Moment of a Non-Spherical Body Arbitrarily Oriented in Space'.. 34 (4): 341–348... • Renzetti, G. 'Satellite orbital precessions caused by the first odd zonal J3 multipole of a non-spherical body arbitrarily oriented in space'.. 352 (2): 493–496... • ^ Peterson, Ivars (23 September 2013).. Science News. Retrieved 2017-07-21. Office of Safety and Mission Assurance. 1 August 1995. Archived from (PDF) on 15 February 2013., pages 37-38 (6-1,6-2); figure 6-1. Ancillary Description Writer's Guide, 2013. National Aeronautics and Space Administration (NASA) Global Change Master Directory. Archived from on 11 May 2013. Retrieved 29 April 2013. • Vallado, David A. Fundamentals of Astrodynamics and Applications. Hawthorne, CA: Microcosm Press. • Further reading [ ] • Abell; Morrison & Wolff (1987). Exploration of the Universe (fifth ed.). Saunders College Publishing. • Linton, Christopher (2004).. Cambridge: University Press. • Swetz, Frank; et al. Mathematical Association of America. • Andrea Milani and Giovanni F. Theory of Orbit Determination (Cambridge University Press; 378 pages; 2010). Discusses new algorithms for determining the orbits of both natural and artificial celestial bodies. External links [ ] Look up in Wiktionary, the free dictionary. Wikimedia Commons has media related to. Has wide choice of units. Requires JavaScript. Requires Java. • includes (calculated) data on Earth orbit variations over the last 50 million years and for the coming 20 million years •. Requires JavaScript. • (Rocket and Space Technology) • provide another, slightly different series for Earth orbit eccentricity, and also a series for orbital inclination. Orbits for the other planets were also calculated, by F. 'Successive Refinements in Long-Term Integrations of Planetary Orbits'. The Astrophysical Journal. 592: 620–630..., but only the are available online. Requires JavaScript and Macromedia • Merrifield, Michael.. Sixty Symbols. 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TechWriter has the unique feature of allowing your tech writers to enhance the generated doc with additional information that is NOT overwritten on subsequent revisions. The was a proposed SSTO spaceplane. A single-stage-to-orbit (or SSTO) vehicle reaches from the surface of a body without jettisoning hardware, expending only propellants and fluids. The term usually, but not exclusively, refers to. No Earth-launched SSTO launch vehicles have ever been constructed. To date, orbital launches have been performed either by fully or partially, the having both attributes. Launch costs for (LEO) range from $10,000 to $19,000 per kg of ($4,500–$8,500 / pound). Reusable SSTO vehicles offer the promise of reduced launch expenses by eliminating recurring costs associated with hardware replacement inherent in expendable launch systems. However, the nonrecurring costs associated with design, development, research and engineering (DDR&E) of reusable SSTO systems are much higher than expendable systems due to the substantial technical challenges of SSTO. It is considered to be marginally possible to launch a single-stage-to-orbit spacecraft from Earth. The principal complicating factors for SSTO from Earth are: high orbital velocity of over 7,400 metres per second (27,000 km/h; 17,000 mph); the need to overcome Earth's gravity, especially in the early stages of flight; and flight within, which limits speed in the early stages of flight and influences engine performance. Notable single stage to orbit research spacecraft include, the, the, and the. However, despite showing some promise, none of them has come close to achieving orbit yet due to problems with finding the most efficient propulsion system. Single-stage-to-orbit is much easier to achieve on extraterrestrial bodies such as the Moon and Mars, which have weaker gravitational fields and lower atmospheric pressure than Earth, and has been achieved from the by both the 's and several robotic spacecraft of the Soviet. ROMBUS concept art For a long time before the second half of the twentieth century, the concept of a single stage to orbit vehicle was rarely considered, and when it was it was generally considered to be impractical and therefore very little research was conducted into the concept. However, advancements in flight technology led to the idea becoming more plausible, and during the 1960s some of the first concept designs for this kind of craft began to emerge. One of the earliest was the One stage Orbital Space Truck (OOST) designed by, an engineer for, which was a concept for an expendable booster stage which could deliver a payload to orbit in one stage. A reusable version named ROOST was also proposed. Another early SSTO design was a reusable launch vehicle named which was designed by in the early 1960s. It was one of the largest space craft ever conceptualized with a diameter of over fifty metres and the capability to lift up to two thousand short tons into Earth orbit, intended for missions to further out locations in the solar system such as. The North American Air Augmented VTOVL from 1963 was a similarly large craft which would have used external burning ramjets to decrease the liftoff mass of the vehicle by removing the need for large amounts of liquid oxygen while travelling through the atmosphere. From 1965, Robert Salked investigated various single stage to orbit spaceplane concepts, which would include wings. He proposed a vehicle which would burn hydrocarbon fuel while in the atmosphere and then switch to hydrogen fuel for increasing efficiency once in space. This was around the same time as the development of the. Further examples of Bono's early concepts (prior to the 1990s) which were never constructed include: • ROMBUS (Reusable Orbital Module, Booster, and Utility Shuttle), another design from Philip Bono. This wasn't technically single stage since it dropped some of its initial hydrogen tanks, but it came very close. • Ithacus, an adapted ROMBUS concept which was designed to carry soldiers and military equipment to other continents via a sub-orbital trajectory. • Pegasus, another adapted ROMBUS concept designed to carry passengers and payloads long distances in short amounts of time via space. • SASSTO, another launch vehicle concept. • Hyperion, yet another Philip Bono concept which used a sled to build up speed before liftoff to save on the amount of fuel which had to be lifted into the air. Around 1985 the project was intended to create a scramjet vehicle to reach orbit, but this had its funding stopped and was cancelled. At around the same time, the tried to use technology, but failed to show significant advantages over rocket technology. DC-X Technology [ ]. Main article: The DC-X, short for Delta Clipper Experimental, was an unmanned one third scale SSTO vehicle which was too small to actually achieve orbit but was instead built to demonstrate vertical takeoff and landing. It is one of only a few prototype SSTO vehicles ever built. Several other prototypes of this design were proposed, including the DC-X2 (a half-scale prototype) and the DC-Y, a full scale vehicle which would be capable of single stage insertion into orbit. Neither of these were built, but the project was taken over by in 1995, and they built the DC-XA, an upgraded one third scale prototype. This vehicle was lost when it landed with only three of its four landing pads deployed, which caused it to tip over on its side and explode. The project has not been continued since. Despite this failure, several future proposals have been based on the DC-X design. Main article: From 1999 to 2001 Rotary Rocket attempted to build a SSTO vehicle called the Roton. It received a large amount of media attention and a working sub-scale prototype was completed, but the design was largely impractical. Approaches [ ] There have been various approaches to SSTO, including pure rockets that are launched and land vertically, air-breathing -powered vehicles that are launched and land horizontally, vehicles, and even -powered vehicles that can fly into orbit and return landing like an airliner, completely intact. For rocket-powered SSTO, the main challenge is achieving a high enough mass-ratio to carry sufficient to achieve, plus a meaningful weight. [ ] One possibility is to give the rocket an initial speed with a, as planned in the project. For air-breathing SSTO, the main challenge is system complexity and associated costs,, and construction techniques necessary for surviving sustained high-speed flight within the atmosphere, and achieving a high enough mass-ratio to carry sufficient propellant to achieve orbit, plus a meaningful payload weight. Air-breathing designs typically fly at or speeds, and usually include a rocket engine for the final burn for orbit. Whether rocket-powered or air-breathing, a reusable vehicle must be rugged enough to survive multiple round trips into space without adding excessive weight or maintenance. In addition a reusable vehicle must be able to reenter without damage, and land safely. While single-stage rockets were once thought to be beyond reach, advances in materials technology and construction techniques have shown them to be possible. For example, calculations show that the first stage, launched on its own, would have a 25-to-1 ratio of fuel to vehicle hardware. It has a sufficiently efficient engine to achieve orbit, but without carrying much payload. Design challenges inherent in SSTO [ ] The design space constraints of SSTO vehicles were described by rocket design engineer. This section does not any. Unsourced material may be challenged and. (December 2017) () Some SSTO vehicles use the same engine for all altitudes, which is a problem for traditional engines with a bell-shaped. Depending on the atmospheric pressure, different bell shapes are optimal. Engines operating in the lower atmosphere have shorter bells than those designed to work in vacuum. Having a bell that is only optimal at a single altitude lowers the overall engine efficiency. One possible solution would be to use an, which can be effective in a wide range of ambient pressures. In fact, a linear aerospike engine was used in the X-33 design. Other solutions involve using multiple engines and other such as double-mu bells. Still, at very high altitudes, the extremely large engine bells tend to expand the exhaust gases down to near vacuum pressures. As a result, these engine bells are counterproductive [ – ] due to their excess weight. Some SSTO vehicles simply use very high pressure engines which permit high ratios to be used from ground level. This gives good performance, negating the need for more complex solutions. Airbreathing SSTO [ ] Some designs for SSTO attempt to use that collect oxidizer and reaction mass from the atmosphere to reduce the take-off weight of the vehicle. Some of the issues with this approach are: • No known air breathing engine is capable of operating at orbital speed within the atmosphere (for example hydrogen fueled seem to have a top speed of about Mach 17). This means that rockets must be used for the final orbital insertion. • Rocket thrust needs the orbital mass to be as small as possible to minimize propellant weight. • The thrust-to-weight ratio of rockets that rely on on-board oxygen increases dramatically as fuel is expended, because the oxidizer fuel tank has about 1% of the mass as the oxidizer it carries, whereas air-breathing engines traditionally have a poor thrust/weight ratio which is relatively fixed during the air-breathing ascent. • Very high speeds in the atmosphere necessitate very heavy thermal protection systems, which makes reaching orbit even harder. • While at lower speeds, air-breathing engines are very efficient, but the efficiency () and thrust levels of air-breathing jet engines drop considerably at high speed (above Mach 5–10 depending on the engine) and begin to approach that of rocket engines or worse. • of vehicles at hypersonic speeds are poor whereas since acceleration is a vector, the effective lift to drag ratios of rocket vehicles at high g is. Thus with for example scramjet designs (e.g. ) the mass budgets do not seem to close for orbital launch. Similar issues occur with single-stage vehicles attempting to carry conventional jet engines to orbit—the weight of the jet engines is not compensated sufficiently by the reduction in propellant. On the other hand, LACE-like designs such as the (and ) which transition to rocket thrust at rather lower speeds (Mach 5.5) do seem to give, on paper at least, an improved orbital over pure rockets (even multistage rockets) sufficiently to hold out the possibility of full reusability with better payload fraction. It is important to note that mass fraction is an important concept in the engineering of a rocket. However, mass fraction may have little to do with the costs of a rocket, as the costs of fuel are very small when compared to the costs of the engineering program as a whole. As a result, a cheap rocket with a poor mass fraction may be able to deliver more payload to orbit with a given amount of money than a more complicated, more efficient rocket. Launch assists [ ] Many vehicles are only narrowly suborbital, so practically anything that gives a relatively small delta-v increase can be helpful, and outside assistance for a vehicle is therefore desirable. Proposed launch assists include: • (rail, maglev including, and, etc.) • • in-flight fueling • / And on-orbit resources such as: • • tugs Nuclear propulsion [ ]. Main article: Due to weight issues such as shielding, many nuclear propulsion systems are unable to lift their own weight, and hence are unsuitable for launching to orbit. However some designs such as the and some designs do have a in excess of 1, enabling them to lift off. Clearly one of the main issues with nuclear propulsion would be safety, both during a launch for the passengers, but also in case of a failure during launch. No current program is attempting nuclear propulsion from Earth's surface. Beam-powered propulsion [ ]. Main article: Because they can be more energetic than the potential energy that chemical fuel allows for, some laser or microwave powered rocket concepts have the potential to launch vehicles into orbit, single stage. In practice, this area is relatively undeveloped, and current technology falls far short of this. Comparison with the Shuttle [ ] The high cost per launch of the sparked interest throughout the 1980s in designing a cheaper successor vehicle. Several official design studies were done, but most were basically smaller versions of the existing Shuttle concept. Most cost analysis studies of the Space Shuttle have shown that workforce is by far the single greatest expense. Early shuttle discussions speculated airliner-type operation, with a two-week turnaround. However, senior NASA planners envisioned no more than 10 to 12 flights per year for the entire shuttle fleet. The absolute maximum flights per year for the entire fleet was limited by external tank manufacturing capacity to 24 per year. Very efficient (hence complex and sophisticated) were required to fit within the available vehicle space. Likewise the only known suitable lightweight was delicate, maintenance-intensive tiles. These and other design decisions resulted in a vehicle that requires great maintenance after every mission. The engines are removed and inspected, and prior to the new 'block II' main engines, the were removed, disassembled and rebuilt. While was refurbished and relaunched in 53 days between missions and, generally months were required to repair an orbiter for a new mission. Many in the aerospace community [ ] concluded that an entirely self-contained, reusable single-stage vehicle could solve these problems. The idea behind such a vehicle is to reduce the processing requirements from those of the Shuttle. Examples [ ] It is easier to achieve SSTO from a body with lower gravitational pull than Earth, such as the. The ascended from the lunar surface to lunar orbit in a single stage. A detailed study into SSTO vehicles was prepared by 's Space Division in 1970–1971 under NASA contract NAS8-26341. Their proposal () was an enormous vehicle with more than 50,000 kilograms (110,000 lb) of payload, utilizing for (vertical) landing. While the technical problems seemed to be solvable, the required a winged design that led to the Shuttle as we know it today. The unmanned technology demonstrator, originally developed by for the (SDI) program office, was an attempt to build a vehicle that could lead to an SSTO vehicle. The one-third-size test craft was operated and maintained by a small team of three people based out of a trailer, and the craft was once relaunched less than 24 hours after landing. Although the test program was not without mishap (including a minor explosion), the DC-X demonstrated that the maintenance aspects of the concept were sound. That project was cancelled when it landed with three of four legs deployed, tipped over, and exploded on the fourth flight after transferring management from the to NASA. The was designed to bring bulk materials to orbit as cheaply as possible. Current development [ ] Current and previous SSTO projects include the Japanese project, the,, and the Indian spaceplane. Main article: The British Government partnered with the in 2010 to promote a concept called. This design was pioneered by, a company founded by after was canceled. The Skylon spaceplane has been positively received by the British government, and the. Following a successful propulsion system test that was audited by ESA's propulsion division in mid-2012, REL announced that it would begin a three-and-a-half-year project to develop and build a test jig of the to prove the engines performance across its air-breathing and rocket modes. In November 2012, it was announced that a key test of the engine precooler had been successfully completed, and that ESA had verified the precooler's design. The project's development is now allowed to advance to its next phase, which involves the construction and testing of a full-scale prototype engine. Alternative approaches to inexpensive spaceflight [ ] Many studies have shown that regardless of selected technology, the most effective cost reduction technique is. [ ] Merely launching a large total quantity reduces the manufacturing costs per vehicle, similar to how the of automobiles brought about great increases in affordability. Using this concept, some aerospace analysts believe the way to lower launch costs is the exact opposite of SSTO. Whereas reusable SSTOs would reduce per launch costs by making a reusable high-tech vehicle that launches frequently with low maintenance, the 'mass production' approach views the technical advances as a source of the cost problem in the first place. By simply building and launching large quantities of rockets, and hence launching a large volume of payload, costs can be brought down. This approach was attempted in the late 1970s, early 1980s in with the -based. A related idea is to obtain economies of scale from building simple, massive, multi-stage rockets using cheap, off-the-shelf parts. The vehicles would be dumped into the ocean after use. This strategy is known as the ' approach. This is somewhat similar to the approach some previous systems have taken, using simple engine systems with 'low-tech' fuels, as the and still do. These nations' launches are significantly cheaper than their Western counterparts. An alternative to scale is to make the discarded stages practically reusable: this is the goal of the and its Falcon 9, Falcon Heavy and Interplanetary Transport System vehicles. A similar approach is being pursued. See also [ ] • • • • • • • • • • • • • • • • • • • Further reading [ ] • Andrew J. Butrica: Single Stage to Orbit - Politics, Space Technology, and the Quest for Reusable Rocketry. The Johns Hopkins University Press, Baltimore 2004,. References [ ]. • ^ Richard Varvill & Alan Bond (2003). Archived from (PDF) on 15 June 2011. Retrieved 5 March 2011. • 'Space Transportation Costs: Trends in Price Per Pound to Orbit 1990-2000', Futron, 2002. • Dick, Stephen and Lannius, R., 'Critical Issues in the History of Spaceflight,' NASA Publication SP-2006-4702, 2006. • Philip Bono & Kenneth William Gatland, Frontiers Of Space, • Wade, Mark.. Encyclopedia Astronautica. Archived from on 10 October 2011. Retrieved 18 October 2015. NASA History. Retrieved 18 October 2015. Retrieved 18 October 2015. Retrieved 13 June 2015. Retrieved 13 June 2015. Retrieved 13 June 2015. • Bono, Philip (June 1963).. AIAA (AIAA-1963-271). • • Bono, Philip (June 1963).. AIAA (AIAA-1964-280). • • • • • • Flight international 1 March 1986 •. Retrieved 13 June 2015. Retrieved 2009-09-14. • Mitchell Burnside-Clapp (February 1997).. Retrieved 2009-09-14. • Truax, Robert C., “One Stage to Orbit-Or Two” Unpublished paper, Truax Engineering, Inc., 2614 Temple Heights Drive, Oceanside, Calif., 5 March 1992. • London III, Lt Col John R., 'LEO on the Cheap', Air University (AFMC) Research Report No. AU-ARI-93-8, October 1994. • Hale, Francis, 'Introduction to Space Flight,' Prentice Hall, 1994. • Mossman, Jason, 'Investigation of Advanced Propellants to Enable Single Stage to Orbit Launch Vehicles,' Master’s Thesis, California State University, Fresno, 2006. • Livington, J.W., 'Comparative Analysis of Rocket and Air-Breathing Launch Vehicle Systems,' Space 2004 Conference and Exhibit, San Diego, California, 2004. • Curtis, Howard,, Third Edition, Oxford: Elsevier, 2010. Bruce Dunn (1996).. Retrieved 2007-11-15. Retrieved 13 June 2015. • Mark Wade (2007).. Archived from on 2002-08-29. Retrieved 2007-11-15. • Richard Varvill & Alan Bond (2003). Archived from (PDF) on 28 June 2012. Retrieved 15 November 2007. • Cimino, P.; Drake, J.; Jones, J.; Strayer, D.; Venetoklis, P.:, AIAA, Joint Propulsion Conference, 21st, Monterey, CA, July 8–11, 1985. Research supported by the Rensselaer Polytechnic Institute., 07/1985 •.. 23 April 2003. Archived from on 12 August 2006. Retrieved 15 November 2007. • Mark Wade (2007).. Retrieved 2010-04-01. Retrieved 13 June 2015. Archived from on 2 June 2015. Retrieved 13 June 2015. Archived from on 26 September 2010. Retrieved 1 March 2011. Retrieved 13 June 2015. • Robert Parkinson (22 February 2011).. Space:The Development of Single Stage Flight. The Global Herald. Archived from on 23 February 2011. Retrieved 28 February 2011. 28 November 2012. Retrieved 28 November 2012. • Thomson, Ian.. The Register. 29 November 2012. External links [ ] Wikimedia Commons has media related to. • •, an analysis of space launch costs, with a section critiquing SSTO • A critique of SSTO by Jeffrey F.
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