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A geostationary orbit, also referred to as a geosynchronous equatorial orbit (GEO), is a circular geosynchronous orbit 35,786 km (22,236 mi) in altitude above Earth's equator, 42,164 km (26,199 mi) in radius from Earth's center, and following the direction of Earth's rotation.
An Earth observation satellite or Earth remote sensing satellite is a satellite used or designed for Earth observation (EO) from orbit, including spy satellites and similar ones intended for non-military uses such as environmental monitoring, meteorology, cartography and others. The most common type are Earth imaging satellites, that take satellite images, analogous to aerial photographs; some EO satellites may perform remote sensing without forming pictures, such as in GNSS radio occultation.
A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never more than about one-third of the radius of Earth.
Apparent retrograde motion is the apparent motion of a planet in a direction opposite to that of other bodies within its system, as observed from a particular vantage point. Direct motion or prograde motion is motion in the same direction as other bodies.
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object.
A polar orbit is one in which a satellite passes above or nearly above both poles of the body being orbited on each revolution. It has an inclination of about 60–90 degrees to the body's equator.
A geocentric orbit, Earth-centered orbit, or Earth orbit involves any object orbiting Earth, such as the Moon or artificial satellites. In 1997, NASA estimated there were approximately 2,465 artificial satellite payloads orbiting Earth and 6,216 pieces of space debris as tracked by the Goddard Space Flight Center. More than 16,291 objects previously launched have undergone orbital decay and entered Earth's atmosphere.
Shavit 2 is a small lift launch vehicle produced by Israel from 1982 onwards, to launch satellites into low Earth orbit. It was first launched on 19 September 1988, making Israel the eighth nation to have an orbital launch capability after the USSR, United States, France, Japan, People's Republic of China, United Kingdom, and India.
A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is an orbit arranged so that it precesses through one complete revolution each year, so it always maintains the same relationship with the Sun.
In astrodynamics, orbital station-keeping is keeping a spacecraft at a fixed distance from another spacecraft or celestial body. It requires a series of orbital maneuvers made with thruster burns to keep the active craft in the same orbit as its target. For many low Earth orbit satellites, the effects of non-Keplerian forces, i.e. the deviations of the gravitational force of the Earth from that of a homogeneous sphere, gravitational forces from Sun/Moon, solar radiation pressure and air drag, must be counteracted.
Ofeq, also spelled Offek or Ofek is the designation of a series of Israeli reconnaissance satellites first launched in 1988. Most Ofeq satellites have been carried on top of Shavit 2 launch vehicles from Palmachim Airbase in Israel, on the Mediterranean coast. The low Earth orbit satellites complete one Earth orbit every 90 minutes.
A momentum exchange tether is a kind of space tether that could theoretically be used as a launch system, or to change spacecraft orbits. Momentum exchange tethers create a controlled force on the end-masses of the system due to the pseudo-force known as centrifugal force. While the tether system rotates, the objects on either end of the tether will experience continuous acceleration; the magnitude of the acceleration depends on the length of the tether and the rotation rate. Momentum exchange occurs when an end body is released during the rotation. The transfer of momentum to the released object will cause the rotating tether to lose energy, and thus lose velocity and altitude. However, using electrodynamic tether thrusting, or ion propulsion the system can then re-boost itself with little or no expenditure of consumable reaction mass.
A supersynchronous orbit is either an orbit with a period greater than that of a synchronous orbit, or just an orbit whose major axis is larger than that of a synchronous orbit. A synchronous orbit has a period equal to the rotational period of the body which contains the barycenter of the orbit.
The Israel Space Agency is a governmental body, a part of Israel's Ministry of Science and Technology, that coordinates all Israeli space research programs with scientific and commercial goals.
A near-equatorial orbit is an orbit that lies close to the equatorial plane of the object orbited. Such an orbit has an inclination near 0°. On Earth, such orbits lie on the celestial equator, the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. A geostationary orbit is a particular type of equatorial orbit, one which is geosynchronous. A satellite in a geostationary orbit appears stationary, always at the same point in the sky, to observers on the surface of the Earth.
A ground track or ground trace is the path on the surface of a planet directly below an aircraft's or satellite's trajectory. In the case of satellites, it is also known as a suborbital track or subsatellite track, and is the vertical projection of the satellite's orbit onto the surface of the Earth.
Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object. It may also describe other motions such as precession or nutation of an object's rotational axis. Prograde or direct motion is more normal motion in the same direction as the primary rotates. However, "retrograde" and "prograde" can also refer to an object other than the primary if so described. The direction of rotation is determined by an inertial frame of reference, such as distant fixed stars.
Nodal precession is the precession of the orbital plane of a satellite around the rotational axis of an astronomical body such as Earth. This precession is due to the non-spherical nature of a rotating body, which creates a non-uniform gravitational field. The following discussion relates to low Earth orbit of artificial satellites, which have no measurable effect on the motion of Earth. The nodal precession of more massive, natural satellites like the Moon is more complex.
PSLV-C42 was the 44th mission of the Indian Polar Satellite Launch Vehicle (PSLV) program and its 12th mission in the Core Alone (CA) configuration. PSLV-C42 successfully carried and deployed 2 Earth observation satellites in Sun-synchronous orbits at an altitude of 588 kilometres (365 mi). It was launched on 16 September 2018 by the Indian Space Research Organisation (ISRO) from the first launch pad of the Satish Dhawan Space Centre at Sriharikota, Andhra Pradesh. The two international satellites were launched as part of a commercial arrangement between Surrey Satellite Technology Limited (SSTL) and ISRO's commercial arm Antrix Corporation Limited, run under the auspices of the Indian Government's Department of Space.
References
- ↑ http://www.wseas.us/e-library/conferences/2009/istanbul/TELE-INFO/TELE-INFO-08.pdf "Most satellites are launched in a prograde orbit because the Earth's rotational velocity provides part of the orbital velocity with a consequent saving "
- ↑ Ippolito, L.J. (2008). Satellite Communications Systems Engineering: Atmospheric Effects, Satellite Link Design and System Performance. Wiley. p. 23. ISBN 9780470754450 . Retrieved 2014-11-30.
- 1 2 Allen Thomson. "SeeSat-L Oct-10 : Reason for FIA Radar 1/USA 215 retrograde orb". satobs.org. SeeSat-L . Retrieved 2014-11-30.
- ↑ http://www.ioccg.org/training/turkey/DrLynch_lectures2.pdf "Most Earth observing satellites are launched so as to have retrograde orbits."
- ↑ http://www.sac.gov.in/Satcom_Overview.doc%5B%5D "Orbits of almost all communication satellites are prograde orbits, as it takes less propellant to achieve the final velocity of the satellite in prograde orbit by taking advantage of the earth's rotational"
- ↑ "Shavit (Israeli launch vehicle) -- Encyclopædia Britannica". britannica.com. Retrieved 2014-11-30.
- ↑ "Shavit". deagel.com. Retrieved 2014-11-30.
- ↑ Timothy A Warner; Giles M Foody; M Duane Nellis (2009). The SAGE Handbook of Remote Sensing. SAGE Publications. p. 109. ISBN 9781412936163 . Retrieved 2014-11-30.