The problem of satellite orbit

If we regard the earth as a uniform sphere, its gravitational field is the central force field, and the center of mass is the center of gravity. Then, in order to make artificial earth satellites (satellites for short) do circular motion in this central force field, roughly speaking, it is necessary to make the force (centrifugal inertia) formed by the acceleration of satellite flight just offset (balance) gravity. At this time, the horizontal speed of satellite flight is called the first cosmic speed, that is, the surrounding speed. Conversely, as long as the satellite obtains this horizontal speed, it can fly around the earth without extra power. At this time, the flight path of the satellite is called satellite orbit. The orbital plane of the satellite passes through 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, and it will fly around the sun and become an artificial planet. If it reaches third cosmic velocity, it will have a hyperbolic orbit and fly around the center of the Milky Way like the sun. As far as artificial earth satellites are concerned, their orbits are divided into low orbit and high orbit according to their height, and forward orbit and retrograde orbit according to the rotation direction of the earth. There are also some special orbits, such as equatorial orbit, geosynchronous orbit, geostationary orbit, polar orbit and sun synchronous orbit. The shape and size of the satellite orbit are determined by the major axis and minor axis, while the intersection angle ω, perigee amplitude angle ω and orbit inclination angle I determine the orientation of the orbit in space. These five parameters are called satellite orbital elements. Sometimes perigee time tp is added, which is collectively called six elements. With these six elements, we can know the position of the satellite in space at any time. There is no clear boundary between high and low orbits, and satellite orbits hundreds of kilometers from the ground are generally called near-earth orbits. The orbital inclination is zero, and the orbital plane coincides with the equatorial plane of the earth. This kind of orbit is called equatorial orbit. When the orbital altitude is 35,786 kilometers, the satellite's operating period is the same as the rotation period of the earth. This orbit is called geosynchronous orbit. If the inclination of geosynchronous orbit is zero, the satellite is above the equator of the earth and flies at the same angular velocity as the rotation of the earth. Seen from the ground, it seems to be stationary. This kind of 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 poles of the earth. This orbit is called polar orbit. If the rotation direction and angular velocity of the satellite orbit plane around the earth's rotation axis are the same as those of the earth's revolution around the sun, its orbit is called sun-synchronous orbit. Sun synchronous orbit is a retrograde orbit with an inclination greater than 90 degrees. Satellite orbits are mainly divided into two types: geosynchronization and sun synchronization. Geosynchronous satellite: The orbit of this kind of satellite is the same as that of one revolution of the earth. Observing this satellite from the ground, its position relative to the ground will not change at any time. Sun-synchronous satellite: The characteristic of this orbit is that the angle of the sun relative to the orbital plane of the satellite is fixed, so the "local time" of the satellite passing through the same geographical latitude remains unchanged. Most resource exploration satellites belong to sun-synchronous satellites. B satellite height: refers to the height of the satellite from the earth's surface. Most of the resources exploration satellites are low-orbit satellites with an altitude of 400- 1000 km. C. Orbital inclination: it is the included angle between the orbital plane at the equator and the equatorial plane. The resource exploration satellite monitors the whole world, and its flight direction is near north and south. Generally, the inclination of orbit is about 95~ 100 degrees. D. Oblique observation mode: Most resource exploration satellites are designed with oblique observation, which has two main purposes: one is to provide the observation ability of satellites shooting the same place from different orbits, so as to improve the time resolution of repeated shooting; The second is to obtain stereoscopic images for stereoscopic observation or to make numerical terrain models. There are two main ways of tilt observation, one is lens rotation, and the other is satellite rotation. For example, each sensor of the SPOT satellite can change the observation direction of the satellite by changing the position of the reflector, which can be up to 27 degrees left and right, with 9 1 angular positions, and the difference between each angular position is 0.6 degrees. Therefore, SPOT satellite can select the desired target in the same orbit scanning range of about 400 kilometers from left to right, and can also take images of the same place in different orbits. Sensors of FORMOSAT-2, EROS-A, IKONOS, Quickbird and other satellites are fixed on the satellite body, so tilt observation is carried out by rotating the body. E. Orbital period: refers to the time required for a satellite to orbit the earth once. For example, the SPOT satellite orbits the earth 10 1.4 minutes, and it can orbit the earth 14 5/26 times a day, and the cycle of returning to the same orbit is 26 days. The orbital period of FORMOSAT-2 is 102.86 minutes, and it can circle the earth exactly 14 times a day, and the period of returning to the same orbit is 24 hours, that is, it will pass the same orbit twice a day. The design of this orbital period is related to the distance between two adjacent orbits. For the SPOT satellite, there are 369(= 14 x 26+5) orbits in the world, so the distance between two adjacent orbits on the equator is 108km (? 40

000/369), when shooting in dual-camera mode, its maximum image width is 1 17km at the bottom of the image. In other words, when SPOT satellite completes the shooting plan of 369 tracks in Twin mode within 26 days, its shooting area can cover the whole world. FORMOSAT-2 has only 14 tracks in the world, so the distance between two adjacent tracks on the equator is 2857 kilometers. When taking oblique photography with the maximum oblique observation angle (45 degrees), the longest observation distance is about 960 kilometers, so some areas will not be able to capture data. For the area where data can be taken, the observation angles used by satellites in different periods are almost the same, so if the terrain factors cause shielding effect, data cannot be obtained. F imaging mode: the sensors of passive spaceborne optical sensing system are mainly divided into two types: sweeping type and pushing type. For example, both Landsat MSS satellite and Landsat TM satellite use scanning frequency sensors, and the CCD arrangement direction is parallel to the flight direction. When the satellite flies, it keeps rotating the mirror and scanning back and forth from left to right. At present, most optical telemetry systems use push-broom sensors, such as SPOT, FORMOSAT-2, IKONOS, Quickbird, EROS and so on. The arrangement direction of CCD is perpendicular to the flight direction, so its imaging geometry is approximately the parallel projection of the flight direction and the perspective projection of the vertical flight direction, also referred to as semi-perspective projection. G. Sampling method: it is mainly divided into synchronous sampling and asynchronous sampling, and the main difference between them lies in whether the length of satellite flight trajectory is the same as that of shooting sampling. In asynchronous sampling, the sampling speed of the image is slower than the flying speed of the satellite, which can increase the exposure time of the sensor to the same target area, increase the radiation energy entering the sensor, and improve the signal-to-noise ratio to improve its spatial resolution. In this sampling process, for the same scanning line, the satellite must rotate the satellite body at the same time to shoot the same surface object, so it is easy to cause blur effect and reduce the image radiation quality. In synchronous sampling, the flying length of the satellite is the same as the ground length, and the observation angle of the satellite body or sensor has not changed during shooting, so the image quality obtained is relatively better than that in asynchronous sampling. For example, EROS-A adopts asynchronous sampling mode and SPOT adopts synchronous sampling mode. SPOT- 1~4 A hologram continuously scans 6000 lines in 9 seconds, so the sampling time of each scanning line is fixed at 0.00 15 seconds, while SPOT-5 scans 12000 lines in 9 seconds, so the sampling time is 0.00075 seconds. H. Stereo imaging modes: mainly divided into the same track and different tracks. For example, the SPOT- 1~4 satellite can take oblique photography at different times and in different orbits (different orbits), as shown in figure B. 19(a), and obtain left and right overlapping stereoscopic images. Its disadvantage is that the gray values of two images taken at different times are easily different due to the changes of ground objects, different positions of clouds or shadows, different atmospheric conditions and other factors, which increases the difficulty of subsequent automatic image matching. On the other hand, the stereoscopic image on the same track (as shown in figure B. 19(b)) is usually within a few minutes due to the small shooting time difference between the two images. Therefore, the gray values of images are similar, which can reduce the error rate of image matching in automatic processing and further reduce the manual editing work. Satellites that can take stereo photography in the same orbit include EROS-A, FORMOSAT-2, IKONOS, SPOT-5 HRS, Quickbird, etc. .

Peng Fei, who copied people, copied them without even understanding the landlord's problems. The quality of these people is really amazing. To answer the landlord's question again, in fact, the calculation of the track is very complicated. Foreign universities have four-year undergraduate courses specializing in orbit research, and how to calculate orbit can not be expressed in a few words. But simply put, the orbit is actually decided by anyone. As long as we know the perigee and apogee of the satellite, and then put the satellite into any of the above points at a certain speed, we can make the satellite run in space. So calculating the orbit is not the most important thing, but deciding which orbit the satellite adopts is the key. There are many kinds of orbits of satellites. In fact, there are countless orbits at any height and in any direction in the sky, which can be roughly divided into the following categories, including polar orbits, geosynchronous orbits and sun-synchronous orbits. Polar orbit means that the satellite will pass through the North Pole and the South Pole. This kind of satellite usually orbits the earth once every 90 minutes and passes through the same place on the earth twice a day (once during the day and once at night). Because of this feature, many spy satellites will use polar orbits. Geosynchronous orbit means that the satellite's running period is the same as the earth's rotation period, so it will be stationary over a place. It's only 36 degrees above the equator

This feature only exists in the orbit at an altitude of 1000 km. Because these satellites are stationary and very high in the air, many communication satellites are in that orbit. But because this feature is so useful, many countries have launched satellites into this orbit for many years, which makes this orbit very crowded now. Sun synchronous orbit is similar to polar orbit, and both satellites run in the north-south direction. It is characterized by passing through a place at the same time every day. As quoted by Peng Fei, this kind of orbit is often used by resource exploration satellites, but it is also suitable for spy satellites, so many spy satellites use this kind of orbit. In fact, in addition to these three kinds of orbits, there are infinite orbits with different inclinations and heights in apogee and perigee forms. Most satellites will use low orbits with an altitude of less than 400 kilometers, because the cost of launching into such orbits is very low. Moreover, spy satellites or meteorological satellites should carefully observe the changes in the surface, so they should not be put too high. As for navigation satellites (including GPS) and communication satellites, they will choose high orbit because it is high enough to reach a wider range. High orbit can completely avoid the friction between satellites and the upper atmosphere and the impact of space debris, so that satellites can expect to stay in the sky for a long time. Generally, the height of these satellites will be thousands to tens of thousands of kilometers. I've even heard that military communication satellites were placed at an altitude of100000 km before. The cost of launching these satellites is much higher than that of low-orbit satellites, because extra fuel is needed to put the satellites into the predetermined orbit, and extremely accurate navigation is needed to ensure the success of the orbit. Therefore, the launch of high-orbit satellites has always been the frontier field of space science, and only a few countries have this capability.

When the earth exerts a force on people to be satellites.

Equal to the centripetal force of the satellite around the earth.

The centripetal force required for the satellite to stay in orbit is mv 2/r and the gravitational force is mg, so as long as this condition is met, as long as mg = mv 2/r = > g = v 2/r.

The satellite will remain in orbit (v is the speed of 90 degrees from the center of the earth)

R is the distance from the earth to the satellite) 2007-05-09 04:37:25 Supplement: Peng Fei copied other people's D text as himself.

Well, indicate the source.

Is there any mistake?

The source of field D is big5.cast/gate/big5/app.cpst/kjmc/2002 _ 08/1029138388 2007-05-09 04: 46: 46 Supplement: Peng Fei plagiarized article D.

The source of his second half essay is csrsr.ncu.edu/chin.ver/c3t&. . S/ proper nouns 2007-05-09 04: 5 1: 29 supplement: I want to add something.

When I say R, I mean the distance from the core of the earth to the core of the satellite.

Not the distance from the surface of the earth to the surface of the satellite.