An orbital spaceflight (or orbital flight) is a spaceflight in which a spacecraft is placed on a trajectory where it could remain in space for at least one orbit. Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar. Events 636 - Battle of Yarmouk: Arab forces led by Khalid ibn al-Walid take control of Syria and Palestine Spaceflight is the use of Space technology to fly a Spacecraft into and through Outer space. A spacecraft is a Vehicle or machine designed for Spaceflight. Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. To do this around the Earth, it must be on a free trajectory which has an altitude at perigee (altitude at closest approach) above 100 kilometers (62 mi) (this is by convention the boundary of space). To remain in orbit at this altitude requires an orbital speed of ~7. The orbital speed of a body generally a Planet, a Natural satellite, an artificial satellite, or a Multiple star, is the speed at which it 8km/s. Orbital speed is slower for higher orbits, but attaining them requires higher delta-v. In Astrodynamics, the term delta-v, literally "change in velocity" (see symbol delta) has a specific meaning it is a Scalar which takes
The expression "orbital spaceflight" is mostly used to distinguish from sub-orbital spaceflights, which are flights where apogee of a spacecraft reaches space but perigee is too low. A sub-orbital spaceflight (or sub-orbital flight is a Spaceflight in which the Spacecraft reaches space, but its Trajectory intersects In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from
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Orbital launch
Orbital spaceflight from Earth has only been achieved by launch vehicles that use rocket engines for propulsion. In Spaceflight, a launch vehicle or carrier rocket is a Rocket used to carry a payload from the Earth's surface into Outer space. A rocket engine is a Jet engine that uses only Propellant mass for forming its high speed propulsive jet. To reach orbit, the rocket must impart to the payload a delta-v of about 9. In Astrodynamics, the term delta-v, literally "change in velocity" (see symbol delta) has a specific meaning it is a Scalar which takes 3-10 km/s. This figure allows for atmospheric drag (approximately 300 m/s with the ballistic coefficient of a 20 m long dense fuelled vehicle), gravity losses (depending on burn time and details of the trajectory and launch vehicle), gaining altitude, and the horizontal acceleration needed to reach orbital speed. The ballistic coefficient ( BC) of a body is a measure of its ability to overcome air resistance in flight In Astrodynamics and Rocketry, gravity drag (or gravity losses) is the difference between the Delta-v expended and the actual change in speed
The only proven technique involves launching nearly vertically for a few kilometers while performing a gravity turn, and then progressively flattening the trajectory out at an altitude of 170+ km and accelerating on a horizontal trajectory (with the rocket angled upwards to fight gravity and maintain altitude) for a 5-8 minute burn until orbital velocity is achieved. A gravity turn or zero-lift turn is a maneuver (see Trajectory optimization) used in launching a spacecraft into or descending from an Orbit around a Frequently 2-3 stages are needed to achieve the required delta-v.
Other techniques, such as use of a launch loop, have been proposed for non-rocket spacelaunch. A launch loop or Lofstrom loop is a design for a belt based Maglev Orbital launch system that would be around 2000 km long and maintained at Non-rocket spacelaunch (NRS is the idea of reaching outer space specifically from the Earth's surface predominately without the use of conventional chemical rockets which today These techniques are theoretical: no attempts have been made to orbit a vehicle using any of them.
Stability
An object in orbit at an altitude of less than roughly 200 km is considered unstable due to atmospheric drag. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a For a satellite to be in a stable orbit (i. e. sustainable for more than a few months), 350 km is a more standard altitude for low Earth orbit. A Low Earth Orbit (LEO is generally defined as an Orbit within the locus extending from the Earth’s surface up to an altitude of 2000 km For example, on 1958-02-01 the Explorer 1 satellite was launched into an orbit with a perigee of 358 kilometers (222 mi). Year 1958 ( MCMLVIII) was a Common year starting on Wednesday (link will display full calendar of the Gregorian calendar. Events 1327 - Teenaged Edward III is crowned King of England, but the country is ruled by his mother Queen Explorer 1 (officially titled at NASA as satellite 1958 Alpha) was the first Earth Satellite of the United States, launched on February 1 [1] It remained in orbit for more than 12 years before its atmospheric reentry over the Pacific Ocean on 1970-03-31. Year 1970 ( MCMLXX) was a Common year starting on Thursday (link shows full calendar of the Gregorian calendar. Events 307 - After divorcing his wife Minervina, Constantine marries Fausta, the daughter of the retired Roman Emperor
However, the exact behaviour of objects in orbit depends on altitude, their ballistic coefficient, and details of space weather which can affect the height of the upper atmosphere. Altitude is the Elevation of a point or object from a known level or datum (plural data The ballistic coefficient ( BC) of a body is a measure of its ability to overcome air resistance in flight Space weather is the concept of changing environmental conditions in Outer space.
Orbits
There are three main 'bands' of orbit around the Earth: low Earth orbit, intermediate circular orbit and geostationary orbit. A Low Earth Orbit (LEO is generally defined as an Orbit within the locus extending from the Earth’s surface up to an altitude of 2000 km Medium Earth Orbit (MEO, sometimes called Intermediate Circular Orbit (ICO is the region of space around the Earth above low Earth orbit ( and below Geostationary orbit A geostationary orbit (GEO is a Geosynchronous orbit directly above the Earth 's Equator (0° Latitude) with a period equal to the Earth's
Due to Orbital mechanics orbits are in a particular, largely fixed plane around the Earth, which coincides with the center of the Earth, and may be tilted with respect to the equator. Orbital mechanics or astrodynamics is the application of Celestial mechanics to the practical problems concerning the motion of Rockets and other Spacecraft The Earth rotates about its axis within this orbit, and the relative motion of the spacecraft and the movement of the Earths surface determines the position that the spacecraft appears in the sky from the ground, and which parts of the Earth are visible from the spacecraft.
By dropping a vertical down to the Earth's surface it is possible to calculate a ground track which shows which part of the Earth a spacecraft is immediately above, and this is useful for helping to visualise the orbit. A ground track or ground trace is the projection of a Satellite 's Orbit onto the surface of the Earth (or whatever body the satellite is orbiting
Re-entry
Due to the high speeds of orbital spaceflight, atmospheric reentry is much more difficult compared to sub-orbital flights.
Even if the vehicle is a satellite that is ultimately expendable, most space authorities are pushing towards controlled re-entry techniques to avoid issues of space debris reaching the ground and causing a hazard to lives and property. Space debris or orbital debris, also called space junk and space waste are the objects in Orbit around Earth created by humans that no In addition, this minimises the creation of orbital space junk.
Returning craft though (including all potentially manned craft), have to find a way of slowing down as much as possible while still in higher atmospheric layers and avoid hitting the ground (lithobraking) or burning up. Lithobraking is a technique of descent by an unmanned space vehicle (usually a probe to the surface of a body by which the vehicle is slowed by impact with the body's surface The problem of deceleration from orbital speeds is solved through using atmospheric drag (aerobraking) to lose nearly all of the speed. Aerobraking is a Spaceflight maneuver that reduces the high point of an Elliptical orbit ( Apoapsis) by flying the vehicle through the Atmosphere On an orbital space flight initial deceleration is provided by the retrofiring of the craft's rocket engines, perturbing the orbit (by lowering perigee down into the atmosphere) onto a suborbital trajectory.
Aerobraking is achieved by orienting the returning space craft to fly so as to present the heat shields forwards towards the atmosphere so as to protect against the high temperatures generated by atmospheric compression and friction caused by passing through the atmosphere at hypersonic speeds. In Aerodynamics, hypersonic speeds are speeds that are highly Supersonic. The thermal energy is dissipated mainly by compression heating the air in a shockwave ahead of the vehicle using a blunt heat shield shape, with the aim of minimising the heat entering the vehicle. Sub-orbital space flights, being at a much lower speed, do not generate anywhere near as much heat upon re-entry.
See also
- Orbit
- List of orbits
- Ground track
- Orbital mechanics
- Project HARP was a failed attempt, and a ram accelerator is another design, to launch an object into orbit with a gun
- Rocket launch
- Non-rocket spacelaunch
- Spacecraft
- Spaceflight
References
- ^ Explorer 1 - NSSDC ID: 1958-001A. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star The following is a list of types of orbits Centric classifications Galactocentric orbit: An orbit about the center of a Galaxy A ground track or ground trace is the projection of a Satellite 's Orbit onto the surface of the Earth (or whatever body the satellite is orbiting Orbital mechanics or astrodynamics is the application of Celestial mechanics to the practical problems concerning the motion of Rockets and other Spacecraft Project HARP, short for High Altitude Research Project, was a joint project of the United States Department of Defense and Canada 's Department A ram accelerator has the same function as a Gun; ie it is a device for accelerating projectiles however it is entirely different in that jet-engine-like propulsion cycles A gun is a particular Weapon that propels Projectiles The projectile is generally fired through a hollow tube known as the gun's barrel. A rocket launch is the first phase of the flight of a Rocket. Non-rocket spacelaunch (NRS is the idea of reaching outer space specifically from the Earth's surface predominately without the use of conventional chemical rockets which today A spacecraft is a Vehicle or machine designed for Spaceflight. Spaceflight is the use of Space technology to fly a Spacecraft into and through Outer space. NASA.
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