Synchronous satellite
Synchronous satellite
The run cycle is the same as the planetary self-rotation cycle or the speed of the track planar rotation angle and the planetary angle velocity is substantially equal. Satellite revolution cycles are called earth synchronous satellites as the global self-turn cycle, also known as 24-hour synchronous satellite. The rotation angular velocity of the satellite track plane is almost equal to the angular velocity of the earth around the sun, called the Sun Synchronous Satellite. It is in the same solar light in all running periods or over the same local time, over the region of the Earth's surface to complete the task given.
is usually believed that "synchronous satellite" is the province of "Earth Synchronous Satellite".
[example] The statement also said: "China delegation's distribution and use of radio frequency in International Telecom Convention (Malaga - Torremolinos, 1973) and synchronization Satellite position assignment and registration terms are retained. "(" People's Daily "October 28, 1973) | Space Solar Power Station, which is envisaged, is a huge synchronous satellite with a 10,000-tent meter, it will A few tens of square kilometers of solar cells are expanded from the land meter, and the DC electrically converted to the thus is converted into a microwave energy shot. ("People's Daily" September 24, 1978) | We call such satellite as synchronous satellites, meaning that its run is synchronized with the earth. ("People's Daily" October 13, 1978)
[Press] Use the most "synchronous satellite" to stand in place. The advantage is that it is observed on the earth to be fixed, and the user can communicate with the standard satellite without having to track the satellite.
Earth Synchronous Satellite
Definition
Earth synchronization satellite is a satellite of human launch, which is still over equally on the equator. From the ground, the satellite remains moving, so it is also known as still satellite, from the earth, satellite and the earth rotate with the same angular velocity, the angular velocity is the same as the Earth's own corner, so that the earth is synchronized. Satellite. The operating cycle is about 24 hours, and the height of the Earth's synchronous satellite is approximately 36,000 kilometers from the equator, and the line speed is approximately 3.08 kilometers per second. The direction of the solar synchronous satellite has the same direction as the global direction, the speed is also the same (ie 360 ° / year or 0.9856 ° / day), and its inclination must be greater than 90 °, form a retrograde track, a height of several hundred kilometers Between 6,000 kilometers, the tangent is slightly more than 90 °, close to the "Polar Track", overlooking the entire earth, including two levels.
Satellite Emission
Launching the earth synchronous satellite requires a high technology, generally with a multi-stage rocket, give satellite into the near-place circular track, referred to as a mooring track; When the satellite fly over the equator, the control rocket is once again ignited. The satellite will move in a short time, and the satellite will be moved by the elliptical orbit. When the satellite flew away, the satellite accelerates again, the satellite enters the opposite earth stationary track (Also known as synchronous track).
Transmitting Sun Synchronous Satellite First requires determining track six elements, satellite operational tracks are determined by the track tilt angle, near location angle, increased intensive point, eccentricity, orbital semi-axis, and satellite.
Purpose
Communication satellite
Using Earth Synchronous Satellite (Static Satellite) to forward the communication system of radio signals, called the satellite communication system, as a communication system This satellite is called synchronous communication satellite. The radio waves radiated by the antenna on the Earth's synchronization satellite, which is basically stable to the cover area of the Earth, and within this coverage area, no interworking between 24 hours can be achieved. In general, three earth synchronous satellites can basically solve global communication issues. Earth synchronous satellites in the Pacific, Atlantic and Indian Ocean, are running, providing global communications outside the poles, and his advantage is that users can communicate with the satellite without having to track satellites. Track.
Meteorological satellite
The weather is very close to human production and life relationship. Agriculture, fisheries, animal husbandry and other production, aviation, navigation, and communication business need accurate and timely weather forecasting. Before the weather satellite, people set up a weather station on the ground, observed the weather with balloons, rockets and radio probes. Most of the meteorological stations are distributed in someone living areas, oceans, mountains, deserts, two-level areas. The weather station is very rare, and the weather observation data is insufficient, and the weather cannot be accurately predicted. The emergence of meteorological satellites solves this problem, and the meteorological satellite is equipped with a TV camera and infrared radiometer, which can take cloud, measure temperature, humidity, wind speed and other weather parameters. It is possible to observe a large area to a global meteorological data, and measuring meteorological data from different heights from the ground.
Meteorological satellite usually uses two tracks. One is a polar orbit having a height of 700 to 1500 kilometers. It can observe the global weather conditions, patrol the earth every 12 hours, to the same area, close to the same area; the other is a still track, the stationary orbit meteorological satellite always stays over a certain point in the equator, can monitor 24 hours a round of monitoring Weather in large satellites in large parts of the satellite, TV photography on satellite shooting a photo of a cloud every 20 minutes.
Resource satellite
Earth resource remote sensing satellite is the most important one in many remote sensing detectors, and its goal is very clear, it is to detect Earth resources and the environment. Earth resource satellite began in 1972, the first earth resource remote sensing satellite launched in the United States. The first generation resource satellite is landster-1, 2, 3 satellite, the rails of the three satellites are near circular sun synchronous tracks, the height is about 915km, the operating cycle is 103min, 14 laps around the earth, cover the world every 18 days once. The second generation of resource satellite landsat-4, 5 covers the world every 16 days, compared to the first generation of satellites, adds the topic imager. Third generation resource satellite landsat-6,7, where Landsat-6 failed, Landsat-7 contrasts the second generation of satellites, increasing the enhanced special graphics. The fourth-generation resource satellite landsat-8 mainly carries two main loads: operational land imager and thermal infrared sensor.
Track correction
Satellite is positioned on the synchronous rail, due to the effect of the sun, the moon and other celestial gravity, as well as the influence of space "dust", it will produce different directions The drift movement deviates from the original position. Satellite deviates from the track, and the small engine on the satellite can be initiated. Due to the limited restriction of the fuel on the satellite, the correction is performed only when deviation is large.
Note problem
The cycle of earth synchronous satellite operation is the same as the Earth's own cycle, relative to the earth still does not move, there are several questions to note:
1 Earth synchronous satellite orbit why is a circle rather than an ellipse
Earth synchronous satellite is characterized by the same angular velocity of the ground shaft, the same angular speed of the earth, is stationary in the equator, and the satellite is not moving relative to the earth. This feature determines that its orbit can only be circle. Because if its track is ellipse, the earth should be in an oval, the satellite will inevitably appear near the place and the remote point during the process of running around the earth, and when the satellite runs near location, the satellite track radius will be reduced, the earth The extraction of it is getting bigger. The angular speed of the satellite also becomes large; in turn, when the satellite runs away, the satellite's track radius will become large, the earth is reduced to it, and the angular velocity of the satellite is also reduced, which is constant with the synchronous satellite constant contradiction . So the synchronous satellite track is not ellipse, but can only be circle.
2 Why is the orbit of the earth synchronous satellite and the Earth equator
Due to the center of the satellite to do the circumference of the circumference of the circumference, it can only be supplied with a force that is attractive, and the extraction force Another power of the satellite will leave the satellite to the equatorial movement unless another force is just right with f 2 balance, the satellite is transmitted above the equatorial plane (or below) At the same time, the satellite is moving around the ground shaft, also moves to the equatorial plane. Its motion will not be stable, so that the satellite cannot be synchronized with the earth, so the satellite is synchronized with the earth, and the satellite must be required to require satellite or the earth. Co cop.
If the satellite is transmitted to a point over the equator, the Earth is used to provide the center of gravity F which is used to provide the satellite to the center of movement. At this time, the satellite can be in the track. Rotate the same angular velocity with the same globe, at this time, the satellite can "stay" at a point over the equator, realize the rotation of the Earth, and the satellite is in a relative stationary state.
3 Why all the height of all Earth synchronous satellites is the same
in the equatorial satellite, the only force it receives - the extraction provides satellite winding Heart power. When the orbital radius R (or height H from the ground) takes a certain value, the satellite can be synchronized with the earth, and the cycles of the two are T = 24 h.
Establies Earth mass is m, the earth radius is R 0 , the satellite mass is M, the height of the ground is H, then there is
R 0 = 6400km, g = 6.67 × 10 -11 n · m < SUP> 2/ kg 2 , m = 6.0 × 1024kg, t = 24h = 86400s into the upper formula H = 3.6 × 10 4 km, that is, synchronization Satellite is the same height of the ground (all H = 3.6 × 10 4 km), it is inevitably positioned on the same big circle over the equator. This location over the equator is from scientists as "gold circles", which is one of the countries that are mainly competed in space in space.
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