|
Porkchop Plot
In orbital mechanics, a porkchop plot (also pork-chop plot) is a chart that shows contours of equal characteristic energy (C3) against combinations of launch date and arrival date for a particular interplanetary flight. By examining the results of the porkchop plot, engineers can determine when a launch opportunity exists (a 'launch window') that is compatible with the capabilities of a particular spacecraft. A given contour, called a porkchop curve, represents constant C3, and the center of the porkchop the optimal minimum C3. The orbital elements of the solution, where the fixed values are the departure date, the arrival date, and the length of the flight, were first solved mathematically in 1761 by Johann Heinrich Lambert, and the equation is generally known as Lambert's problem (or theorem). Math The general form of ''characteristic energy'' can be computed as: C_3 = v_\infty^2\,\! where v_\infty \, is the orbital velocity when the orbital distance tends to infinity. Not ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Porkchop Plot
In orbital mechanics, a porkchop plot (also pork-chop plot) is a chart that shows contours of equal characteristic energy (C3) against combinations of launch date and arrival date for a particular interplanetary flight. By examining the results of the porkchop plot, engineers can determine when a launch opportunity exists (a 'launch window') that is compatible with the capabilities of a particular spacecraft. A given contour, called a porkchop curve, represents constant C3, and the center of the porkchop the optimal minimum C3. The orbital elements of the solution, where the fixed values are the departure date, the arrival date, and the length of the flight, were first solved mathematically in 1761 by Johann Heinrich Lambert, and the equation is generally known as Lambert's problem (or theorem). Math The general form of ''characteristic energy'' can be computed as: C_3 = v_\infty^2\,\! where v_\infty \, is the orbital velocity when the orbital distance tends to infinity. Not ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Voyager Program
The Voyager program is an American scientific program that employs two robotic interstellar probes, ''Voyager 1'' and ''Voyager 2''. They were launched in 1977 to take advantage of a favorable alignment of Jupiter and Saturn, to Flyby (spaceflight), fly near them while collecting data for transmission back to Earth. After launch the decision was taken to send ''Voyager 2'' near Uranus and Neptune to collect data for transmission back to Earth. As of 2022, the Voyagers are still in operation past the outer boundary of the heliosphere in interstellar space. They collect and transmit useful data to Earth. , ''Voyager 1'' was moving with a velocity of , or 17 km/s, relative to the Sun, and was from the Sun reaching a distance of from Earth as of February 10, 2022. On 25 August 2012, data from ''Voyager 1'' indicated that it had entered interstellar space. , ''Voyager 2'' was moving with a velocity of , or 15 km/s, relative to the Sun, and was from the Sun reaching a distan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hyperbolic Trajectory
In astrodynamics or celestial mechanics, a hyperbolic trajectory or hyperbolic orbit is the trajectory of any object around a central body with more than enough speed to escape the central object's gravitational pull. The name derives from the fact that according to Newtonian theory such an orbit has the shape of a hyperbola. In more technical terms this can be expressed by the condition that the orbital eccentricity is greater than one. Under simplistic assumptions a body traveling along this trajectory will coast towards infinity, settling to a final excess velocity relative to the central body. Similarly to parabolic trajectories, all hyperbolic trajectories are also escape trajectories. The specific energy of a hyperbolic trajectory orbit is positive. Planetary flybys, used for gravitational slingshots, can be described within the planet's sphere of influence using hyperbolic trajectories. Parameters describing a hyperbolic trajectory Like an elliptical orbit, a hyperbol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parabolic Trajectory
In astrodynamics or celestial mechanics a parabolic trajectory is a Kepler orbit with the eccentricity equal to 1 and is an unbound orbit that is exactly on the border between elliptical and hyperbolic. When moving away from the source it is called an escape orbit, otherwise a capture orbit. It is also sometimes referred to as a C3 = 0 orbit (see Characteristic energy). Under standard assumptions a body traveling along an escape orbit will coast along a parabolic trajectory to infinity, with velocity relative to the central body tending to zero, and therefore will never return. Parabolic trajectories are minimum-energy escape trajectories, separating positive-energy hyperbolic trajectories from negative-energy elliptic orbits. Velocity The orbital velocity (v) of a body travelling along parabolic trajectory can be computed as: :v = \sqrt where: *r is the radial distance of orbiting body from central body, *\mu is the standard gravitational parameter. At any positi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a planet, moon, asteroid, or Lagrange point. 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 elliptic orbits, with the center of mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion. For most situations, orbital motion is adequately approximated by Newtonian mechanics, which explains gravity as a force obeying an inverse-square law. However, Albert Einstein's general theory of relativity, which accounts for gravity as due to curvature of spacetime, with orbits following geodesics, provides a more accurate calculation and understanding of the exact mechanics of orbi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Yale University Press
Yale University Press is the university press of Yale University. It was founded in 1908 by George Parmly Day, and became an official department of Yale University in 1961, but it remains financially and operationally autonomous. , Yale University Press publishes approximately 300 new hardcover and 150 new paperback books annually and has a backlist of about 5,000 books in print. Its books have won five National Book Awards, two National Book Critics Circle Awards and eight Pulitzer Prizes. The press maintains offices in New Haven, Connecticut and London, England. Yale is the only American university press with a full-scale publishing operation in Europe. It was a co-founder of the distributor TriLiteral LLC with MIT Press and Harvard University Press. TriLiteral was sold to LSC Communications in 2018. Series and publishing programs Yale Series of Younger Poets Since its inception in 1919, the Yale Series of Younger Poets Competition has published the first collection of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fiscal Year
A fiscal year (or financial year, or sometimes budget year) is used in government accounting, which varies between countries, and for budget purposes. It is also used for financial reporting by businesses and other organizations. Laws in many jurisdictions require company financial reports to be prepared and published on an annual basis but generally not the reporting period to align with the calendar year (1 January to 31 December). Taxation laws generally require accounting records to be maintained and taxes calculated on an annual basis, which usually corresponds to the fiscal year used for government purposes. The calculation of tax on an annual basis is especially relevant for direct taxes, such as income tax. Many annual government fees—such as council tax and license fees, are also levied on a fiscal year basis, but others are charged on an anniversary basis. Some companies, such as Cisco Systems, end their fiscal year on the same day of the week each year: the day ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Christmas
Christmas is an annual festival commemorating Nativity of Jesus, the birth of Jesus, Jesus Christ, observed primarily on December 25 as a religious and cultural celebration among billions of people Observance of Christmas by country, around the world. A Calendar of saints, feast central to the Christian liturgical year, it is preceded by the season of Advent or the Nativity Fast and initiates the season of Christmastide, which historically in the West lasts Twelve Days of Christmas, twelve days and culminates on Twelfth Night (holiday), Twelfth Night. Christmas Day is a public holiday in List of holidays by country, many countries, is celebrated religiously by a majority of Christians, as well as Christian culture, culturally by many non-Christians, and forms an integral part of the Christmas and holiday season, holiday season organized around it. The traditional Christmas narrative recounted in the New Testament, known as the Nativity of Jesus, says that Jesus was born in Bet ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thanksgiving
Thanksgiving is a national holiday celebrated on various dates in the United States, Canada, Grenada, Saint Lucia, Liberia, and unofficially in countries like Brazil and Philippines. It is also observed in the Netherlander town of Leiden and the Australian territory of Norfolk Island. It began as a day of giving thanks for the blessings of the harvest and of the preceding year. (Similarly named harvest festival holidays occur throughout the world during autumn, including in Germany and Japan). Thanksgiving is celebrated on the Thanksgiving (Canada), second Monday of October in Canada and on the Thanksgiving (United States), fourth Thursday of November in the United States and around the same part of the year in other places. Although Thanksgiving has historical roots in religious and cultural traditions, it has long been celebrated as a Secularity, secular holiday as well. History Prayers of thanks and special thanksgiving ceremonies are common among most religions after harv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Specific Orbital Energy
In the gravitational two-body problem, the specific orbital energy \varepsilon (or vis-viva energy) of two orbiting bodies is the constant sum of their mutual potential energy (\varepsilon_p) and their total kinetic energy (\varepsilon_k), divided by the reduced mass. According to the orbital energy conservation equation (also referred to as vis-viva equation), it does not vary with time: \begin \varepsilon &= \varepsilon_k + \varepsilon_p \\ &= \frac - \frac = -\frac \frac \left(1 - e^2\right) = -\frac \end where *v is the relative orbital speed; *r is the orbital distance between the bodies; *\mu = (m_1 + m_2) is the sum of the standard gravitational parameters of the bodies; *h is the specific relative angular momentum in the sense of relative angular momentum divided by the reduced mass; *e is the orbital eccentricity; *a is the semi-major axis. It is expressed in MJ/kg or \frac. For an elliptic orbit the specific orbital energy is the neg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orbital Mechanics
Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft. The motion of these objects is usually calculated from Newton's laws of motion and the law of universal gravitation. Orbital mechanics is a core discipline within space-mission design and control. Celestial mechanics treats more broadly the orbital dynamics of systems under the influence of gravity, including both spacecraft and natural astronomical bodies such as star systems, planets, moons, and comets. Orbital mechanics focuses on spacecraft trajectories, including orbital maneuvers, orbital plane changes, and interplanetary transfers, and is used by mission planners to predict the results of propulsive maneuvers. General relativity is a more exact theory than Newton's laws for calculating orbits, and it is sometimes necessary to use it for greater accuracy or in high-gravity situations (e.g. orbits ne ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orbital Speed
In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g. planet, moon, artificial satellite, spacecraft, or star) is the speed at which it orbits around either the barycenter or, if one body is much more massive than the other bodies of the system combined, its speed relative to the center of mass of the most massive body. The term can be used to refer to either the mean orbital speed (i.e. the average speed over an entire orbit) or its instantaneous speed at a particular point in its orbit. The maximum (instantaneous) orbital speed occurs at periapsis (perigee, perihelion, etc.), while the minimum speed for objects in closed orbits occurs at apoapsis (apogee, aphelion, etc.). In ideal two-body systems, objects in open orbits continue to slow down forever as their distance to the barycenter increases. When a system approximates a two-body system, instantaneous orbital speed at a given point of the orbit can be computed from its distance to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
.jpg "Click for more on -> Christmas")
