satelliteFlyinglevelSpeed callFirst cosmic velocity, i.eOrbit speed。As long as the satellite obtains the speed in this horizontal direction, it does not need to increasepowerYou can fly around the earth.Then the satellite flewtrajectoryIt's called satellite orbit.
If we regard the earth as a homogeneous sphere, its gravitational field is the central force field, and its center of mass is the gravitational center.Then, to make the artificial earth satellite (hereinafter referred to as satellite) move in a circle in this central force field, in general, it is to make the force (centrifugal inertia) formed by the force acceleration of satellite flight just offset (balance)Gravity。satelliteTrack planeThrough the center of the earth.If the speed is slightly higher, it will form an elliptical orbit. If it reaches the escape speed, it will be a parabolic orbit. At that time, it will fly around the sunArtificial planet；If it reachesThird cosmic speed, is a hyperbolic orbit, andsunlightSame but windingGalactic centerFlying.[1]
characteristic
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As far as man-made earth satellites are concerned, their orbits are divided into low orbits and high orbits according to height, and into forward orbits and retrograde orbits according to the direction of earth rotation.There are some orbits of special significance, such as the equatorial orbitGeosynchronous orbit、Geostationary orbit、Polar orbitandSun synchronous orbitEtc.
The shape and size of satellite orbit are determined bythe major axisAnd the minor axis, while the intersection angle Ω, the argument angle of the near earth point ω and the orbital inclination i determine the orientation of the orbit in space.These five parameters are called satellitesOrbital elements(Number of pieces).Sometimes the perigee time tp is added, which is collectively referred to as the six elements.With these six elements, we can know the position of the satellite in space at any time.
Six elements of satellite orbit: major axis, minor axis, intersection angle Ω, argument angle of perigee ω, orbit inclination i, passing perigee time tp.
There is no clear demarcation between high and low orbits. Generally speaking, satellite orbits hundreds of kilometers above the ground are called low orbitsEarth orbit。
Track heightAt 35786 km, the operation period of the satellite is the same as the rotation period of the earth. This orbit is called geosynchronous orbit;If the inclination angle of the geosynchronous orbit is zero, the satellite will fly around the earth at the same angular speed as the earth's rotation just above the earth's equator. Seen from the ground, it seems to be stationary. This satellite orbit is called geostationary orbit, which is a special case of geosynchronous orbit.There is only one geostationary orbit.
When the orbital inclination is 90 degrees, the orbital plane passes through the earth's polestrackIt's called polar orbit.
If the rotation direction, angular velocity andThe earth revolves around the sunIf its direction and angular velocity are the same, its orbit is called sun synchronous orbit.The sun synchronous orbit isRetrograde orbit, the inclination is greater than 90 degrees.[2]
classification
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According to the inclination of the orbit, the orbit of the satellite can be divided into equatorial orbit, polar orbit and inclined orbit (including forward orbit and reverse orbit).
1. Equatorial orbit: the inclination is 0 degrees, the satellite orbit plane coincides with the Earth's equatorial plane, and the satellite always flies over the equator.
2. Polar orbit: the inclination is 90 degrees, the satellite orbit plane is perpendicular to the earth equator plane, and the satellite flies over the north and south poles.Its sub satellite point track can cover the whole world, and is the most suitable orbit for observing the whole earth.Meteorological satellite, resource satelliteReconnaissance satelliteThis kind of track is often used.
3. Inclined orbit: the inclination of the orbit is neither 0 degrees nor 90 degrees, which is collectively referred to as inclined orbit, and is divided into forward and reverse orbits.
Forward orbit: when the inclination is greater than 0 degrees but less than 90 degrees, the satellite moves in the direction of the earth's rotation from west to east.
Retrograde orbit: when the inclination is greater than 90 degrees but less than 180 degrees, the satellite moves from east to west against the direction of earth rotation.
Satellite orbit parameters
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Satellite orbit parameters are various parameters used to describe the position, shape and orientation of satellites in space.The satellite in space makes periodic motion under the action of gravity and other forces, and the first order approximation is a Kepler elliptical orbit.Due to the existence of other forces (such as the shape of the earth, atmospheric resistance, gravity of other planets, etc.), the actual orbit deviates from the ideal Kepler orbit, which is called "orbit perturbation" in aerospace.
Synonym: number of satellite orbit elements.
dip angle: The included angle between the equatorial plane and the satellite orbital plane. The specific calculation is the included angle from the equatorial plane to the orbital plane counterclockwise during the satellite orbital upgrade.
height: The distance from the satellite to the earth's surface.
Substellar pointThe intersection of the satellite and the earth center line on the earth's surface.
Ascending intersection: The intersection of the satellite's flight path from south to north on the equator.
cycle: The time required for the satellite to circle the earth.
intercept: The satellite orbits the earth, and the earth rotatesdegrees。
Eccentricity: The ratio of the focal length to the semi major axis of the track.
Perigee angle: The included angle between the ascending intersection point and the perigee and the geocentric line in the orbital plane.
Average near point angle: If the time when the satellite passes through the perigee is tp, and the average angular velocity of the satellite is n, then the average perigee angle at any time M=n (t-tp).[3]
Satellite orbit management
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With the development of the times, mankind has entered the neighborhood of space resources development.The number of man-made satellites is increasing year by year.As long as the satellite gets the speed in this horizontal direction, it can fly around the earth without additional power. Each satellite has its own specific orbit. In order to prevent collisions in space, it is necessary to manage and divide the satellite orbit.
