Dzz in the use of navigation systems. Orbital Pilgrims
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1 Topic 2.3. Application of remote sensing of the Earth and satellite navigation in the oil and gas industry Method of remote sensing of the Earth: characteristics and advantages Obtaining and processing data for GIS is the most important and laborious stage of creating such information systems. Currently, the most promising and economically feasible method is considered to be the method of obtaining data on objects based on Earth remote sensing (ERS) data and GPS measurements. In a broad sense, remote sensing is the receipt by any non-contact methods of information about the Earth's surface, objects on it or in its depths. Traditionally, remote sensing data includes only those methods that make it possible to obtain an image of the earth's surface from space or from the air in any part of the electromagnetic spectrum. There are several types of surveys that use the specific properties of radiation at different wavelengths. When conducting geographic analysis, in addition to the remote sensing itself, spatial data from other sources are necessarily used, digital topographic and thematic maps, infrastructure schemes, external databases. Pictures allow not only to identify various phenomena and objects, but also to evaluate them quantitatively. The advantages of the Earth remote sensing method are as follows: the relevance of the data at the time of the survey (most of the cartographic materials are hopelessly outdated); high efficiency of data acquisition; high accuracy of data processing due to the use of GPS technologies; high information content (the use of multispectral, infrared and radar surveys allows you to see details that are not distinguishable in ordinary images); economic feasibility (the cost of obtaining information through remote sensing is significantly lower than ground field work); the ability to obtain a three-dimensional terrain model (relief matrix) through the use of stereo mode or lidar sensing methods and, as a result, the ability to carry out three-dimensional modeling of a section of the earth's surface (virtual reality systems). Remote methods are characterized by the fact that the recording device is significantly removed from the object under study. In such studies of phenomena and processes on the earth's surface, distances to objects can be measured from units to thousands of kilometers. This circumstance provides the necessary overview of the surface and allows obtaining the most generalized images. There are various classifications of remote sensing. Let's mark the most important from the point of view of practical data collection in the oil and gas industry. Own radiation of objects and reflected radiation of other sources can be registered. These sources can be the Sun or the imaging equipment itself. In the latter case, coherent radiation (radars, sonars and lasers) is used, which allows recording not only the radiation intensity, but also its polarization, phase and Doppler shift, which provides additional information. It is clear that the operation of self-emitting (active) sensors does not depend on the time of day, but it requires significant energy consumption. Thus, the types of sounding by the signal source: active (stimulated emission of objects, initiated by an artificial source of directional action); passive (own, natural reflected or secondary thermal radiation of objects on the Earth's surface, due to solar activity). The filming equipment can be placed on various platforms. The platform can be a spacecraft (SC, satellite), an airplane, a helicopter and even a simple tripod. In po 1
In the latter case, we are dealing with ground shooting of the sides of objects (for example, for architectural and restoration tasks) or oblique shooting from natural or artificial high-altitude objects. The third type of platform is not considered due to the fact that it belongs to specialties far from the one for which these lectures are written. One platform can house several imaging devices, called instruments or sensors, which is typical for spacecraft. For example, Resurs-O1 satellites carry MSU-E and MSU-SK sensors, and SPOT satellites have two identical HRV sensors (SPOT-4 HRVIR). It is clear that the farther the platform with the sensor is from the object under study, the greater the coverage and the less detail the resulting images will have. Therefore, at present, the following types of surveying are distinguished for obtaining remote sensing data: 1. Space survey (photographic or optoelectronic): panchromatic (more often in one wide visible part of the spectrum), the simplest example is black and white photography; color (shooting in several, more often real colors on one medium); multi-zone (simultaneous but separate image capture in different zones of the spectrum); radar (radar); 2. Aerial photography (photographic or optoelectronic): the same types of remote sensing data as in space imagery; lidar (laser). Both types of survey are widely used in the oil and gas industry when creating a GIS enterprise, and each of them occupies its own niche. Space imagery (CS) has a lower resolution (from 30 to 1 m, depending on the type of survey and the type of spacecraft), but due to this it covers large areas. Space imagery is used to survey large areas in order to obtain operational and up-to-date information about the area of prospective geological exploration, a basic framework for creating a global GIS for the mining area, environmental monitoring of oil spills, etc. In this case, both conventional monochrome (black and white photography) and multispectral are used. Aerial photography (AFS) allows you to obtain a higher resolution image (from 1-2 m to 5-7 cm). Aerial photography is used to obtain highly detailed materials for solving land cadastre problems in relation to leased areas of mining, accounting and property management. In addition, the use of aerial photography today seems to be the best option for obtaining data for creating GIS for linearly extended objects (oil, gas pipelines, etc. ) due to the possibility of using "corridor" shooting. The characteristics of the images obtained (both APS and CS), i.e. the ability to detect and measure a particular phenomenon, object or process depends on the characteristics of the sensors, respectively. The main characteristic is the resolution. Remote sensing systems are characterized by several types of resolutions: spatial, spectral, radiometric and temporal. The term “resolution” usually refers to spatial resolution. Spatial resolution (Figure 1) characterizes the size of the smallest objects visible in the image. Depending on the tasks to be solved, data of low (more than 100 m), medium (m) and high (less than 10 m) resolutions can be used. Low spatial resolution images are general and allow one-time coverage of large areas up to the whole hemisphere. Such data are used most often in meteorology, in monitoring forest fires and other large-scale natural disasters. Images of medium spatial resolution are currently the main source of data for monitoring the natural environment. Satellites with imaging equipment operating in this range of spatial resolutions have been launched and are being launched by many countries such as Russia, the USA, France, and others, which ensures the consistency and continuity of observation. Shooting you- 2
3 high resolution from space until recently was conducted almost exclusively in the interests of military intelligence, and from the air for the purpose of topographic mapping. However, today there are already several commercially available high-resolution space sensors (KVR-1000, IRS, IKONOS), which make it possible to conduct spatial analysis with greater accuracy or refine the analysis results at medium or low resolution. Figure 1. Examples of aerial photographs with different spatial resolution: 0.6 m (top), 2 and 6 m (bottom) Spectral resolution indicates which parts of the electromagnetic wave (EMW) spectrum are recorded by the sensor. When analyzing the natural environment, for example, for environmental monitoring, this parameter is the most important. Conventionally, the entire range of wavelengths used in remote sensing can be divided into three sections of radio waves, thermal radiation (IR radiation) and visible light. This division is due to the difference in the interaction of electromagnetic waves and the earth's surface, the difference in the processes that determine the reflection and emission of EMW. The most commonly used EMW range is visible light and adjacent shortwave infrared radiation. In this range, the reflected solar radiation carries information mainly about the chemical composition of the surface. Just as the human eye distinguishes substances by color, a remote sensing sensor captures "color" in the broader sense of the word. While the human eye registers only three sections (zones) of the electromagnetic spectrum, modern sensors are capable of distinguishing tens and hundreds of such zones, which makes it possible to reliably detect objects and phenomena from their previously known spectrograms. For many practical tasks, such detail is not always necessary. If objects of interest are known in advance, you can select a small number of spectral zones in which they will be most noticeable. So, for example, the near-infrared range is very effective in assessing the state of vegetation, determining the degree of its suppression. For most applications, a sufficient amount of information is provided by multispectral imagery from LANDSAT (USA), SPOT (France), Resurs-O (Russia) satellites. Sunlight and clear weather are essential for successful surveying in this wavelength range. Usually, optical shooting is carried out either at once in the entire visible range (panchromatic), or in several narrower zones of the spectrum (multi-zone). All other things being equal, 3
4 conditions, panchromatic images have higher spatial resolution. They are most suitable for topographic tasks and for clarifying the boundaries of objects, which are highlighted on multi-zone images of lower spatial resolution. Thermal infrared radiation (Figure 2) carries information mainly about the surface temperature. In addition to directly determining the temperature regimes of visible objects and phenomena (both natural and artificial), thermal images allow you to indirectly reveal what is hidden underground underground rivers, pipelines, etc. Since the thermal radiation is generated by the objects themselves, sunlight is not required to take pictures (it even gets in the way). Such images allow tracking the dynamics of forest fires, oil and gas flares, and underground erosion processes. It should be noted that it is technically difficult to obtain space-based thermal images of high spatial resolution, therefore, images with a resolution of about 100 m are available today. Thermal imaging from airplanes also provides a lot of useful information. Figure 2. Aerial photograph of a tank farm in the range of visible light (left) and a night thermal image in the infrared range of the same area (right) The centimeter range of radio waves is used for radar photography. The most important advantage of this class of images is their all-weather performance. Since the radar registers its own radiation reflected by the earth's surface, it does not require sunlight to operate. In addition, radio waves in this range freely pass through continuous clouds and are even able to penetrate to some depth into the soil. The reflection of centimeter radio waves from the surface is determined by its texture ("roughness") and the presence of all kinds of films on it. For example, radars are capable of detecting the presence of an oil film with a thickness of 50 microns (Figure 3) and more on the surface of water bodies even with significant waves. In principle, airborne radar is capable of detecting underground objects such as pipelines and leaks from them. Figure 3. Radar image of an oil slick on the water surface 4
5 Radiometric resolution defines the range of brightness perceptible in the image. Most sensors have a radiometric resolution of 6 or 8 bits, which is closest to the instantaneous dynamic range of human vision. But there are sensors with a higher radiometric resolution (10-bit for AVHRR and 11-bit for IKONOS), allowing you to see more detail in very bright or very dark areas of the image. This is important when shooting objects in the shade, as well as when there are large water surfaces and land in the picture at the same time. In addition, sensors such as the AVHRR are radiometric calibrated to allow accurate quantitative measurements. Finally, the temporal resolution determines how often the same sensor can capture a certain area of the earth's surface. This parameter is very important for monitoring emergencies and other rapidly evolving events. Most satellites (more precisely, their families) provide re-imaging in a few days, some in a few hours. In critical cases, images from various satellites can be used for daily observation, however, it must be borne in mind that ordering and delivery itself can take a lot of time. One of the solution options is to purchase a receiving station that allows you to receive data directly from the satellite. This convenient solution for continuous monitoring is used by some organizations in Russia that have receiving stations for data from Resurs-O satellites. To track changes in any territory, it is also important to be able to obtain archival (retrospective) images. Table 1 shows brief characteristics of the main types of spacecraft for remote sensing of the Earth for commercial use, the use of which is possible for solving problems of creating and updating GIS for oil and gas enterprises. Table 1 Brief characteristics of spacecraft for obtaining remote sensing data of the Earth for commercial use Spacecraft name Resolution Multi-zonal frame size Country panchromatic QuickBird 2 0.61 m 2.44 m 16 x 16 km USA Iconos 2 1 m 4 m 11 x 11 km USA EROS A1 1.8 m - 12.5 х 12.5 km USA CWR m - 40 х 40 km Russia Spot 5 5 m (2.5 m) 10 m 60 х 60 km France TC m х 300 km Russia Landsat 7 15 m 30 m 170 x 185 km USA In addition, ERS can be classified by different types of resolution and coverage, by the type of data carrier (photographic and digital), by the principle of the sensor (photoelectric effect, pyroelectric effect, etc. ), by the method of forming (scanning) the image, by special features (stereo mode, complex geometry of the survey), by the type of orbit from which the survey is carried out, etc. To receive and process ERS data from spacecraft, ground-based data reception and processing complexes (NKPOD) are used. The basic configuration of NKPOD includes (Figure 4): antenna complex; reception complex; complex of synchronization, registration and structural restoration; software package. five
6 Figure 4. The composition of the ground complex for receiving and processing data NKPOD provides: the formation of applications for planning the survey of the earth's surface and receiving data; unpacking of information with sorting by routes and allocation of arrays of video information and service information; restoration of the line-line structure of video information, decoding, radiometric correction, filtering, transformation of the dynamic range, the formation of an overview image and the execution of other operations of digital primary processing; analysis of the quality of the images obtained using expert and software methods; cataloging and archiving information; geometric correction and georeferencing of images using data on the parameters of the angular and linear motion of spacecraft and / or ground control points; licensed access to data received from many foreign ERS satellites. The hardware component of NKPOD works in close relationship with the software complex. The software for controlling the antenna and receiving complex performs the following main functions: automatic check of the functioning of the NKPOD hardware part; calculation of the schedule of communication sessions, i.e., the passage of the satellite through the NKPOD visibility zone; automatic activation of NKPOD and data reception in accordance with the schedule; calculation of the satellite trajectory and control of the antenna complex for tracking the satellite; formatting the received information stream and writing it to the hard disk; indication of the current state of the system and information flow; automatic maintenance of work logs. The software makes it possible to control NKPOD from a remote terminal via a local network or the Internet. 6
7 The NKPOD software, as a rule, includes tools for maintaining an electronic catalog of images and archiving. The search for images in the catalog is performed according to the following main criteria: the name of the satellite, the type of imaging equipment and its mode of operation, the date and time of the survey, the territory (geographical coordinates). Additionally, software for visualization, photogrammetric and thematic processing of remote sensing data can be installed, such as: INPHO (company INPHO, Germany) full-function photogrammetric system; ENVI (ITT Visual Information Solutions Corporation, USA) software package for processing remote sensing data and their integration with GIS data; ArcGIS (ESRI company, USA) software solution for building corporate, industry, regional, state GIS. To ensure the maximum radius of view, the antenna complex should be installed so that the horizon is open from elevation angles 2 and higher in any azimuth direction. For high-quality reception, it is essential that there is no radio interference in the range from 8.0 to 8.4 GHz (transmitting devices for radio relay, tropospheric and other communication lines). It should also be noted that, according to experts, in the near future, remote sensing data will become the main source of information for GIS, while traditional maps will be used only at the initial stage as a source of static information (relief, hydrography, main roads, settlements, Administrative division). Currently in the oil and gas industry there is a rapid surge in the use of satellite navigation systems designed to determine the parameters of the spatial position of objects. Today, two second-generation systems are used, the American GPS (Global Positioning System), also called NAVSTAR, and the Russian GLONASS (Global Navigation Satellite System). Design and application of satellite global positioning systems in the oil and gas industry The main areas of application of satellite global positioning systems in geoinformation support of oil and gas sector enterprises are as follows: development of geodetic reference networks at all levels from global to survey, as well as leveling work in order to geodetic support of enterprises; ensuring the extraction of minerals (opencast mining, drilling, etc.); geodetic support of construction, laying of pipelines, cables, overpasses, power lines, etc. engineering and applied works; land surveying work; rescue and preventive work (geodetic support in case of disasters and catastrophes); environmental studies: coordinate referencing of oil spills, assessment of the areas of oil spills and determination of the direction of their movement; survey and mapping of all types of topographic, special, thematic; integration with GIS; application in dispatching services; all types of navigation are air, sea, land. Global positioning satellite systems (GPSS) data are used in various (monitoring, prospecting, research, etc.) systems that require 7
8 rigid spatio-temporal reference of measurement results. The main advantages of the SGSP are: globality, efficiency, all-weather, accuracy, efficiency. The trends in the development of these systems can be judged by the sales volume of GPS / GLONASS satellite receivers, which doubles every 2-3 years. Both systems have a dual purpose military and civil, therefore they emit two types of signals: one with a reduced accuracy of determining the coordinates (~ 100 m) L1 for civilian use and the other high accuracy (~ 10-15 m and more precisely) L2 for military use. To restrict access to accurate navigation information, special interference is introduced, which can be taken into account after receiving the keys from the relevant military department (USA for NAVSTAR and Russia for GLONASS). For NAVSTAR L1 = 1575.42 MHz and L2 = 1227.6 MHz. GLONASS uses frequency division of signals, that is, each satellite operates at its own frequency and, accordingly, L1 is in the range from 1602.56 to 1615.5 MHz and L2 from 1246.43 to 1256.53 MHz. The signal in L1 is available to all users, the signal in L2 is only available to the military (that is, it cannot be decrypted without a special secret key). Currently, this interference has been canceled, and the accurate signal is available to civilian receivers, however, if the state authorities of the owner countries decide accordingly, the military code can be blocked again (in the NAVSTAR system this restriction was lifted only in May 2000 and can be restored at any time. ). Three components can be distinguished as part of global satellite positioning systems: a ground-based monitoring and control system; spacecraft systems; user equipment. The monitoring and control system consists of satellite tracking stations, an accurate time service, a main station with a computing center and stations for downloading data on board spacecraft. Satellites pass over checkpoints twice a day. The collected orbital information is processed and the coordinates of the satellites (ephemeris) are predicted. An almanac is compiled from these data. These and other data from ground stations are loaded on board each satellite. The principle of operation of satellite navigation systems is based on measuring the distance from the antenna on the object (the coordinates of which must be obtained) to the satellites, the position of which is known with great accuracy. The table of the positions of all satellites is called an almanac, which must be located by any satellite receiver before starting measurements. Typically, the receiver stores the almanac in memory since the last shutdown and if it is not out of date immediately uses it. Each satellite transmits the entire almanac in its signal. Thus, knowing the distances to several satellites of the system, using conventional geometric constructions, based on the almanac, it is possible to calculate the position of the object in space, since in the global satellite positioning system, each satellite plays the role of a separate geodetic control point with known coordinates at the current time. The coordinates of the measured object, on which the navigation receiver is located, are determined by the method of linear intersections. The measured parameters define the surface of the position, at the point of intersection of which the desired object is located. The method for measuring the distance from the satellite to the receiver antenna is based on the certainty of the propagation speed of radio waves. To implement the possibility of measuring the time of the propagated radio signal, each satellite of the navigation system emits precise time signals, as part of its signal, using atomic clocks precisely synchronized with the system time. When the satellite receiver is operating, its clock is synchronized with the system time, and upon further reception of signals, the delay between the emission time contained in the signal itself and the time of signal reception is calculated. With this information, the navigation receiver calculates the coordinates of the antenna. Additionally, accumulating and processing this data for a certain period of time, it becomes possible to calculate such parameters of movement as speed (current, maximum, average), passed 8
9 path, etc. Measurements are carried out in the so-called non-demand mode, when the transmitter on the satellite works continuously, and the navigation receiver is turned on as needed. Let us consider the composition of the spacecraft system. NAVSTAR satellites are located in six planes at an altitude of about km. GLONASS satellites (code "Hurricane") are located in three planes at an altitude of about km. The nominal number of satellites in both systems is 24. The NAVSTAR constellation was fully staffed in April 1994 and has been maintained since then, the GLONASS constellation was fully deployed in December 1995, but then significantly degraded and only in September 2010 was staffed to the nominal number of 24 ( as well as two backup satellites). Figure 5 shows the navigation satellites Navstar-2 and Glonass-M. Figure 5. Satellites of the GPS (left) and GLONASS (right) navigation systems 24 satellites provide 100% system performance anywhere in the world, but they cannot always provide reliable reception and good position calculation. Therefore, in order to increase positioning accuracy and reserve in case of failures, the total number of satellites in orbit is maintained in a larger number. For GPS, this number is 30 (6 reserve), and for GLONASS 26 (2 reserve). Also, the low inclination of the satellite orbits (about 55 for GPS and 64.8 for GLONASS) seriously degrades the accuracy in the circumpolar regions of the Earth, since the satellites are not high above the horizon. Both systems use signals based on the so-called. "Pseudo-noise sequences", the use of which gives them high noise immunity and reliability at a low radiation power of transmitters. Each satellite of the system, in addition to the basic information, also transmits auxiliary information necessary for the continuous operation of the receiving equipment. This category includes the complete almanac of the entire satellite constellation, transmitted sequentially over several minutes. Thus, the start of the receiving device can be fast enough if it contains an up-to-date almanac (about one minute), i.e. has been turned off for less than 3-4 hours this is called a "warm start" (the receiver receives only satellite ephemeris), but it can take up to 30 minutes if the receiver is forced to receive a complete almanac, so-called. Cold start. The need for a "cold start" usually arises when the receiver is turned on for the first time, or if it has not been used for a long time (more than 70 hours) or has been moved a considerable distance. There is also a “hot start” (the receiver is off for less than 30 minutes), where the receiver starts immediately with a small error corrected during the position measurement. A common disadvantage of using any radio navigation system is that, under certain conditions, the signal may not reach the receiver, or arrive with significant distortion or delays. For example, it is almost impossible to determine your exact location deep inside a reinforced concrete building, in a basement or in a tunnel. Since the operating frequency of GPS lies in the decimeter range of radio waves, the signal reception from satellites can seriously deteriorate under dense foliage of trees or due to very high 9
10 clouds. Normal GPS signal reception can be damaged by interference from many terrestrial radio sources as well as magnetic storms. Active jamming transmitters are used to artificially suppress signals from satellite navigation systems. For the first time to the general public, the transmitters developed by the Russian company Aviakonversiya were presented in 1997 at the MAKS air show. The accuracy of determining coordinates can vary widely from several tens of meters to tens of centimeters and depends on the measurement methods, which are divided into: absolute methods of determining geocentric coordinates (autonomous , differential); relative methods for determining the spatial vectors of baselines (static, kinematic). Differential and relative static methods provide the highest accuracy. They are based on a method of measuring coordinates from two stations located at a relatively small distance from each other (up to 30 km). It is assumed that at such distances, measurements from two stations to satellites are equally distorted. Such measurement methods allow professional geodetic navigation receivers of such companies as Leica (Switzerland), Ashtech (USA), Trimble (USA) and some others. In the differential mode, the receivers must be able to implement the differential mode. The essence of this method is as follows. One receiver is placed at a point with previously known coordinates (for example, a control point of a geodetic network). At the same time, it is called a basic reference station or control correcting station. Another successor, movable, is placed at the designated point. Since the coordinates of the base station are known, they can be used for comparison with newly determined ones and, on this basis, corrections for the mobile station can be found, which are transmitted to the mobile station via a radio channel by means of a special transmitter. The mobile station, having received differential corrections, corrects its measured coordinates, thereby increasing the measurement accuracy. The most tangible benefits from the introduction of the idea of eliminating errors have been achieved in methods of relative static measurements. As in the differential mode, the equipment is installed at two stations, for example, A and B. In statics, using the differences free from many distortions, the space vector D connecting these stations is calculated: D = (X B X A, Y B Y A, Z B Z A). The base station must have exact coordinates so that the measured increments can be used to calculate the coordinates of the remaining points of the geodetic network with the required accuracy. Thanks to the measurement of coordinate increments and the use of the phase method, errors in the results of determining the coordinates of points are reduced to several tens of centimeters. These methods are basic in geodynamic and most important geodetic works. There are entire networks that generate differential corrections for navigation devices according to the principles described above. They are described below. The use of certain types of navigation receivers and measurement methods depends on the requirements for the accuracy of determining the coordinates of control points. There is no point in using expensive geodetic receivers and long-term measurement methods to obtain the coordinates of the control point for the purpose of referencing, for example, Landsat images with a resolution of 15 (30) m.In this case, it is sufficient to use the simplest inexpensive navigation receivers that provide an acceptable accuracy of 5 -20 m.It is important to emphasize that the accuracy of all navigation receivers depends not only on the duration of individual measurements and the measurement method, but also on the number of visible satellites above the horizon, as well as the nature and openness of the terrain (plain or built-up area), which affects signal re-reflection ... The accuracy of the GLONASS system is currently slightly lower than GPS, 4.46-8.38 m when using an average of 7-8 spacecraft (depending on the receiving point). Then 10
11, the GPS error time is 2.00-8.76 m when using an average of 6-11 spacecraft (depending on the receiving point). When both navigation systems are used together, the errors are 2.37-4.65 m when using spacecraft on average (depending on the receiving point). According to statements by the head of Roscosmos, Anatoly Perminov, measures are being taken to increase accuracy. By the end of 2010, the accuracy of the calculation of ephemeris and the drift of the onboard clock will increase, which will lead to an increase in the accuracy of navigation determinations up to 5.5 meters. This will be done due to the modernization of the ground segment at 7 points of the ground control complex, a new measuring system with high accuracy characteristics is being installed. In 2011, the number of satellites in the constellation is planned to be increased to 30. In parallel, the replacement of Glonass-M satellites with more advanced Glonass-K will take place (they support new CDMA signals in the GPS / Galileo / Compass format, which will greatly facilitate the development of multisystem navigation devices) and Glonass-K2 (transmits signals with code division: two signals in the L1 and L2 frequency ranges and an open signal in the L3 range), which will increase the accuracy up to 2.8 m. To increase the navigation accuracy, systems are used that send clarifying information ("differential correction to the coordinates "DGPS, the theoretical aspects of the formation of which were discussed above), which makes it possible to increase the accuracy of measuring the coordinates of the receiver up to several meters and even up to several tens of centimeters when using complex differential modes. Derivative correction is based on geostationary satellites and ground base stations. Each of the stations is equipped with GPS equipment and special software designed to receive GPS signals, analyze the obtained measurements, calculate ionospheric errors, deviations of trajectories and satellite clocks. This data is transmitted to the central control station (Master Station WMS), where it is re-processed and analyzed taking into account the measurements obtained from all base stations of the network. Then the correction information is transmitted to geostationary satellites and from there is relayed to users. The signal from the geostationary satellites is received similarly to the signal from the satellites of the navigation system through one or more channels. DGPS can be paid (signal decryption is possible only by one specific receiver after paying for the "service subscription") or free. Currently, there are free American WAAS system, European EGNOS system, Japanese MSAS system based on several transmitting corrections from geostationary satellites, which allow obtaining high accuracy (up to 30 cm). In Russia, only in the Kaliningrad region is it possible to fully use the signals from the EGNOS system. In the rest of the territory, reception of the differential correction is impossible. The key issue in the organization of satellite navigation is the choice of devices for signal reception, i.e. user equipment. Consumers are offered various devices and software products that allow them to see their location on an electronic map; having the ability to lay routes taking into account the terrain; search for specific objects on the map by coordinates or address, etc. In this case, the navigation receiver can be made as a separate device, or the navigation chip is embedded in other equipment, for example, mobile phones, smartphones, PDAs or onborders (on-board computers). Figure 6 shows examples of navigators: at the top, without map support (on the left, the Magellan Blazer 12 GPS navigator in a shock-resistant waterproof case, on the right, navigation using a cell phone (iphone) fixed to the bicycle handlebars), below the Glospace auto navigator with map support. Comparing equipment for GPS and GLONASS, we can say that all GLONASS receivers allow working with GPS, but not vice versa. Simultaneous reception of signals from both navigation systems is possible, giving more accurate coordinates. Combined GLONASS / GPS equipment of a professional level is manufactured by many manufacturers, including foreign firms Topcon, Javad, Trimble, Septentrio, Ashtech, NovAtel, SkyWave Mobile Communications. The main reason why GLONASS is not used in its pure form is the lack of high-quality digital maps, as well as the bulkiness and too high power consumption of the receivers themselves (for these reasons, GLONASS chips are not built into 11
12 mobile equipment). However, there is a gradual decrease in these parameters, and at the moment there are fully functional chips with support for GLONASS / GPS systems, as well as GALILEO / COMPASS. Figure 6. Navigators In the oil and gas industry, GPS trackers and GPS loggers have become widespread, which record and transmit coordinates to the server center and are used for satellite monitoring of cars, people, assets, etc. This data is used by dispatching services to organize effective transport and personnel management. The GPS tracker records location data and at regular intervals transmits them via radio, GPRS or GSM connections, satellite modem to the server monitoring center or just a computer with special software via USB, RS-232, PS / 2. The tracker user, or the dispatcher monitoring the object, can connect to the system server using the client program or the web interface under his username and password. The system displays the location of the object and the history of its movement track on the map (Figure 7). Tracker movements can be analyzed either in real time or later. GPS trackers do not have their own displays and, due to this, are cheaper than their fellow navigators. Personal trackers (small size) are used to monitor personnel, and automobile trackers are used to monitor transport. Auto trackers allow you to connect various sensors (fuel level, axle load, etc.) and are themselves connected to the on-board network. An external antenna connection is also provided for vehicle trackers. 12
13 Figure 7. Track GPS-loggers not only do not have a display, but also do not contain data transmission modules (GSM-modules), therefore they are not suitable for real-time monitoring. Logger information is recorded while driving in the built-in memory and becomes available after connecting to a computer for its analysis. In cases where it is necessary to provide additional capabilities besides simply entering the coordinates into the receiver's memory, navigators themselves are used (almost always, GPS navigators). They have a wide range of possibilities, an overview of which is beyond the scope of our presentation. The main ones for the oil and gas industry are the ability to display maps of various profiles, lay routes on the ground, search and determine the coordinates of objects, etc. For example, specialists from BG Transco, a company that maintains more than a kilometer of underground gas pipelines, used these capabilities to locate structures that fall into a potentially dangerous area near the pipeline in case of critical situations. For this, a panchromatic satellite image with a resolution of 1 m on the ground was used to analyze buffer zones in areas with a high population density. The image was snapped to ground control points obtained using a GPS receiver. The gas pipeline route was superimposed on the image using the analytical method (by coordinates), and as a result of spatial analysis, a 200-meter buffer zone of potential risk and all objects located in it were calculated. Another example is the construction of a 450 km long oil trunk pipeline in the Nenets Autonomous District of RAO Rosneftegazstroy. As the main source of information, Landsat images were used, which made it possible to obtain the most reliable and timely information about the terrain in the area of the proposed laying of the oil pipeline. On the basis of the digital elevation model, digital models of the territory of the planned object were created, the angles of rotation, the magnitude and direction of the slopes along the pipeline route were calculated. Professional GPS navigators are distinguished by the quality of components (especially antennas), the software used, the supported operating modes (for example, RTK, binary data output), operating frequencies (L1 + L2), algorithms for suppressing interference dependences, solar activity (influence of the ionosphere ) supported by navigation systems (for example, NAVSTAR GPS, GLONASS, Galileo, Beidou), increased power supply and, of course, the price. It should be noted that currently there is a tendency towards close integration of GPS technologies and methods of obtaining and processing Earth remote sensing data, which is manifested mainly in the field of aerial photography. For quite a long time, aerial cameras of some manufacturers, integrated with GPS receivers (Figure 8), have been used during surveying work (Figure 8), which, when photographing the terrain, fix the spatial three-dimensional coordinates of the center of the projection of each frame. Using this technology 13
14, according to experts, it allows one to reduce the number of control points required for photogrammetric processing of flyover materials by times, which significantly increases the productivity of work and reduces the total cost of costs for obtaining the initial data. Figure 8. Aerial photo complex integrated with a GPS receiver Thus, when creating a GIS, combined sources of information are used: a combination of methods for remote sensing of the Earth by spacecraft of different detail, GPS measurements, laser and stereo photography, data from topographic maps, etc. It all depends only on the requirements for the system. It can be argued that the combination of information obtained using various means of remote sensing of the Earth and GPS measurement data will allow obtaining complete and comprehensive information about any object most quickly and reliably, and will also fully meet all the needs for information support of any project, any system. any enterprise. The steady growth in the use of geoinformation technologies at the enterprises of the oil and gas complex, which has emerged recently, is due not only to the development of the capabilities of the GIS themselves, but also to the close integration of information systems data with GPS technologies and technologies for obtaining and processing Earth remote sensing data. fourteen
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Perhaps, there is not a single branch of the economy where satellite navigation technologies have not already been used - from all types of transport to agriculture. And the application areas are constantly expanding. Moreover, for the most part, receiving devices receive signals from at least two global navigation systems - GPS and GLONASS.
State of the issue
It just so happened that the use of GLONASS in the space industry in Russia is not as great as one might expect, given the fact that the main developer of the GLONASS system is Roskosmos. Yes, already many of our spacecraft, launch vehicles, upper stages have GLONASS receivers as part of onboard equipment. But so far they are either auxiliary means or are used as part of the payload. Until now, to carry out trajectory measurements, to determine the orbits of near-earth spacecraft, synchronization, in most cases, ground-based means of the command-measuring complex are used, many of which have long been used up. In addition, the measuring instruments are located on the territory of the Russian Federation, which does not allow providing a global coverage of the entire trajectory of spacecraft, which affects the accuracy of the orbit. The use of GLONASS navigation receivers as part of the standard on-board equipment for trajectory measurements will make it possible to obtain the orbit accuracy of low-orbit spacecraft (which constitute the bulk of the orbital constellation) at the level of 10 centimeters at any point of the orbit in real time. At the same time, there is no need to involve the means of the command-measuring complex in carrying out trajectory measurements, to spend funds to ensure their operability and the maintenance of personnel. It is enough to have one or two stations for receiving navigation information from the aircraft and transmitting it to the flight control center for solving planning problems. This approach changes the entire strategy of ballistic and navigation support. But, nevertheless, this technology is already well developed in the world and does not present any particular difficulty. It only requires making a decision on the transition to such a technology.
A significant number of low-orbit spacecraft are satellites for remote sensing of the Earth and solving scientific problems. With the development of technologies and means of observation, increasing the resolution, the requirements for the accuracy of binding the received target information to the coordinates of the satellite at the time of the survey are increasing. In a posteriori mode, to process images and scientific data, in many cases, the orbit accuracy needs to be known at the centimeter level.
For special spacecraft of a geodetic class (such as Lageos, Etalon), which are specially designed to solve fundamental problems of studying the Earth and refining models of spacecraft motion, centimeter accuracy of orbits has already been achieved. But it should be borne in mind that these vehicles fly outside the atmosphere and are spherical in order to minimize the uncertainty of solar pressure disturbances. For trajectory measurements, a global international network of laser rangefinders is used, which is not cheap, and the operation of the tools is highly dependent on weather conditions.
ERS and science spacecraft mainly fly at altitudes up to 2000 km, have a complex geometric shape, and are fully disturbed by the atmosphere and solar pressure. It is not always possible to use laser facilities of international services. Therefore, the task of obtaining the orbits of such satellites with centimeter accuracy is very difficult. The use of special motion models and information processing methods is required. Over the past 10-15 years, significant progress has been made in world practice to solve such problems using on-board high-precision GNSS navigation receivers (mainly GPS). The pioneer in this area was the Topex-Poseidon satellite (joint NASA-CNES project, 1992-2005, altitude 1,336 km, inclination 66), the orbital accuracy of which was provided 20 years ago at a level of 10 cm (2.5 cm in radius).
In the next decade in the Russian Federation, it is planned to launch a lot of ERS spacecraft for solving applied problems for various purposes. In particular, for a number of space systems, the binding of target information with very high accuracy is required. These are the tasks of reconnaissance, mapping, monitoring of ice conditions, emergency situations, meteorology, as well as a number of fundamental scientific tasks in the field of studying the Earth and the World Ocean, building a high-precision dynamic geoid model, high-precision dynamic models of the ionosphere and atmosphere. The accuracy of the position of the spacecraft is already required to know at the level of centimeters throughout the entire orbit. It's about posterior precision.
This is no longer an easy task for space ballistics. Perhaps the only way that can provide a solution to this problem is the use of measurements from the onboard GNSS navigation receiver and the corresponding means of high-precision processing of navigation information on the ground. In most cases, this is a combined GPS and GLONASS receiver. In some cases, requirements may be put forward to use only the GLONASS system.
Experiment on high-precision determination of orbits using GLONASS
In our country, the technology for obtaining high-precision coordinates using geodetic-class navigation receivers has been quite well developed for solving geodetic and geodynamic problems on the Earth's surface. This is a so-called precise point positioning technology. A feature of the technology is the following:
* for processing the measurements of the navigation receiver, the coordinates of which must be specified, information from the navigation frames of the GNSS signals is not used. Navigation signals are used only for range measurements, primarily based on measurements of the carrier phase of the signal;
* High-precision orbits and onboard clock corrections, which are obtained on the basis of continuous processing of measurements of the global network of GNSS navigation signals receiving stations, are used as ephemeris-time information of navigation spacecraft. Most of the solutions are now used by the International GNSS Service (IGS);
* measurements of the navigation receiver, the coordinates of which need to be determined, are processed together with high-precision ephemeris-time information using special processing methods.
As a result, the coordinates of the receiver (the phase center of the receiver antenna) can be obtained with an accuracy of a few centimeters.
For solving scientific problems, as well as for the tasks of land management, cadastre, construction in Russia, for several years now, such means have existed and are widely used. At the same time, the author has not yet had information about the means that can solve the problems of high-precision determination of the orbits of low-orbit spacecraft.
An initiative experiment conducted a few months ago showed that we have prototypes of such means, and they can be used to create standard industry-specific means of high-precision ballistic and navigation support for low-orbit spacecraft.
As a result of the experiment, the possibility of using existing prototypes for high-precision determination of the orbit of LEO spacecraft at a level of several centimeters was confirmed.
For the experiment, a flying domestic ERS "Resurs-P" No. 1 (near-circular sun-synchronous orbit with an average altitude of 475 km) was chosen, equipped with a combined navigation receiver GLONASS / GPS. To confirm the result, the data processing was repeated for geodetic spacecraft of the GRACE system (joint project of NASA and DLR, 2002-2016, altitude 500 km, inclination 90), on board of which GPS receivers were installed. The features of the experiment are as follows:
* in order to assess the capabilities of the GLONASS system for determining the orbit of the Resurs-P spacecraft (general view is shown in Fig. 1), only GLONASS measurements were used (4 sets of onboard navigation receivers developed by JSC RIRV);
* to obtain the orbit of the spacecraft of the GRACE system (general view is shown in Fig. 2), only GPS measurements were used (measurements are freely available);
* High-precision ephemeris and corrections of the on-board clocks of the navigation satellites of the GLONASS and GPS systems, which were obtained at the IAC KVNO TsNIIMash on the basis of processing the measurements of the stations of the IGS global network (data are freely available), were used as assistance information. The IGS estimate of the accuracy of this data is shown in Fig. 3 and is about 2.5 cm. The location of the global network of GLONASS / GPS stations of the IGS service is shown in Fig. four;
* a prototype of the hardware and software complex, providing high-precision determination of the orbit of low-orbit spacecraft (initiative development of JSC "GEO-MCC"). The sample also provides decoding of measurements of the onboard receivers of the Resurs-P spacecraft using high-precision ephemeris-time information and taking into account the peculiarities of the session operation of the onboard receivers. The prototype was tested according to the measurements of the spacecraft of the GRACE system.
Fig. 1. General view of the Resurs-P spacecraft.
Fig. 2. General view of the spacecraft of the GRACE system.
Fig. 3. Evaluation of the accuracy of the IAC KVNO TsNIIMash ephemeris by the IGS service. The accuracy of the assisting ephemeris information of the GLONASS navigation spacecraft (designation - IAC, dark blue dots on the graph) is 2.5 cm.
Fig. 4. Location of the global network of GLONASS / GPS stations of the international IGS service (source - http://igscb.jpl.nasa.gov/network/iglos.html).
As a result of the experiment, an unprecedented result was obtained for the domestic ballistic and navigation support of low-orbit spacecraft:
* Taking into account the assisting information and real measurements of the onboard navigation receivers of the Resurs-P spacecraft, a high-precision orbit of this spacecraft with an accuracy of 8-10 cm was obtained only from GLONASS measurements (see Fig. 5).
* In order to confirm the result during the experiment, similar calculations were carried out for geodetic spacecraft of the GRACE system, but using GPS measurements (see Fig. 6). The orbital accuracy of these spacecraft was obtained at a level of 3-5 cm, which fully coincides with the results of the leading analysis centers of the IGS service.
Fig. 5. The accuracy of the "Resurs-P" spacecraft orbit obtained from GLONASS measurements only with the use of assisting information, estimated from measurements of four sets of onboard navigation receivers.
Fig. 6. Accuracy of the orbit of the GRACE-B spacecraft, obtained from GPS measurements only with the use of assisting information.
ANNKA system of the first stage
Based on the results of the experiment, the following conclusions objectively follow:
In Russia, there is a significant backlog of domestic development for solving the problems of high-precision determination of the orbits of LEO spacecraft at a competitive level with foreign information processing centers. On the basis of this groundwork, the creation of a permanent industry ballistic center for solving such problems will not require large expenditures. This center will be able to provide all interested organizations that require binding to the coordinates of information from remote sensing satellites, services for high-precision determination of the orbits of any remote sensing satellites equipped with GLONASS and / or GLONASS / GPS satellite navigation equipment. In the future, the measurements of the Chinese system BeiDou and the European Galileo can also be used.
It is shown for the first time that the GLONASS system measurements when solving high-precision problems can provide the solution accuracy practically no worse than the GPS measurements. The final accuracy depends mainly on the accuracy of the assisting ephemeris information and the accuracy of knowledge of the low-orbit spacecraft motion model.
Presentation of the results of domestic remote sensing systems with high-precision referencing to coordinates will dramatically increase its importance and competitiveness (taking into account growth and market prices) in the world market for the results of remote sensing of the Earth.
Thus, for the creation of the first stage of the Assisted Navigation system for LEO spacecraft (code name - ANNKA system), all the components are available (or are under construction) in the Russian Federation:
* there is its own basic special software that allows, independently of the GLONASS and GPS operators, to receive high-precision ephemeris-time information;
* there is a prototype of special software, on the basis of which a standard hardware and software complex for determining the orbits of LEO spacecraft with an accuracy of centimeters can be created in the shortest possible time;
* there are domestic samples of on-board navigation receivers that allow solving the problem with such accuracy;
* Roscosmos is creating its own global network of GNSS navigation signal receiving stations.
The architecture of the ANNKA system for the implementation of the first stage (a posteriori mode) is shown in Fig. 7.
The system functions are as follows:
* receiving measurements from the global network to the information processing center of the ANNKA system;
* formation of high-precision ephemeris for navigation satellites of GLONASS and GPS systems (in the future - for BeiDou and Galileo systems) at the ANNKA center;
* obtaining measurements of on-board satellite navigation equipment installed on board the low-orbit ERS satellite and transferring it to the ANNKA center;
* calculation of the high-precision orbit of the remote sensing spacecraft in the center of ANNKA;
* transfer of the high-precision orbit of the remote sensing spacecraft to the data processing center of the ground-based special complex of the remote sensing system.
The system can be created in the shortest possible time, even within the framework of the existing measures of the federal target program for the maintenance, development and use of the GLONASS system.
Fig. 7. The architecture of the ANNKA system at the first stage (a posteriori mode), which ensures the determination of the orbits of LEO spacecraft at a level of 3-5 cm.
Further development
Further development of the ANNKA system in the direction of implementing the mode of high-precision determination and prediction of the orbit of low-orbit spacecraft in real time on board can radically change the entire ideology of ballistic and navigation support of such satellites and completely abandon the use of measurements of ground-based means of the command and measurement complex. It is difficult to say how much, but the operational costs of ballistic and navigation support will be reduced significantly, taking into account the payment for the work of ground assets and personnel.
In the USA, NASA created such a system more than 10 years ago on the basis of a communication satellite system to control TDRSS spacecraft and the GDGPS global high-precision navigation system created earlier. The system was named TASS. It provides assisting information to all scientific spacecraft and remote sensing satellites in low orbits in order to solve onboard orbit determination tasks in real time at a level of 10-30 cm.
The architecture of the ANNKA system at the second stage, which provides the solution of onboard orbit determination problems with an accuracy of 10-30 cm in real time, is shown in Fig. eight:
The functions of the ANNKA system at the second stage are as follows:
* receiving measurements from stations for receiving GNSS navigation signals of the global network in real time to the ANNKA data processing center;
* formation of high-precision ephemeris for navigation spacecraft of GLONASS and GPS systems (in the future - for BeiDou and Galileo systems) in the ANNKA center in real time;
* tab of high-precision ephemeris on the SC-relay of communication systems (constantly, in real time);
* relaying of high-precision ephemeris (assisting information) by satellites-repeaters for low-orbit ERS spacecraft;
* obtaining a high-precision position of the remote sensing spacecraft on board using special satellite navigation equipment capable of processing received GNSS navigation signals together with assistance information;
* transmission of target information with high-precision referencing to the data processing center of a special ground-based remote sensing complex.
Fig. 8. The architecture of the ANNKA system at the second stage (real-time mode), which provides the determination of the orbits of LEO spacecraft at the level of 10-30 cm in real time on board.
The analysis of existing capabilities, experimental results show that the Russian Federation has a good groundwork for creating a high-precision assisted navigation system for low-orbit spacecraft, which will significantly reduce the cost of controlling these vehicles and reduce the lag behind the leading space powers in the field of high-precision spacecraft navigation in solving urgent scientific and applied problems. In order to take the necessary step in the evolution of LEO SC control technology, it is only necessary to make an appropriate decision.
The ANNKA system of the first stage can be created as soon as possible with minimal costs.
To proceed to the second stage, it will be necessary to implement a set of measures that should be provided for within the framework of state or federal targeted programs:
* creation of a special communication satellite system to ensure continuous control of near-earth spacecraft, either in geostationary orbit, or in inclined geosynchronous orbits;
* modernization of the hardware and software complex for the formation of assisting ephemeris information in real time;
* completion of the creation of the Russian global network of stations for receiving navigation signals from GNSS;
* development and organization of production of on-board navigation receivers capable of processing GNSS navigation signals together with assistance information in real time.
The implementation of these measures is serious, but quite realizable work. It can be carried out by the URSC enterprises taking into account the already planned activities within the framework of the Federal Space Program and within the framework of the Federal Target Program for the maintenance, development and use of the GLONASS system, taking into account the corresponding adjustments. Assessment of the costs of its creation and the economic effect is a necessary stage, which must be done taking into account the planned projects for the creation of space systems of complexes for remote sensing of the Earth, satellite communication systems, space systems and scientific complexes. There is absolute confidence that these costs will pay off.
In conclusion, the author expresses his sincere gratitude to the leading specialists in the field of domestic satellite navigation Arkady Tyulyakov, Vladimir Mitrikas, Dmitry Fedorov, Ivan Skakun for organizing the experiment and providing materials for this article, the IGS international service and its leaders - Urs Hugentoble and Ruth Nilan - for the opportunity to make full use of the measurements of the global network of stations for receiving navigation signals, as well as to all those who helped and did not interfere.
B.A. Dvorkin
The active introduction of information satellite technologies as an integral part of the rapidly developing informatization of society radically changes the living conditions and activities of people, their culture, stereotype of behavior, way of thinking. A few years ago, household or car navigators were looked upon as a miracle. High-resolution space images on Internet services, such as Google Earth, people looked at and did not cease to admire. Now, not a single motorist (if there is no navigator in the car yet) will leave the house without first selecting the optimal route in the navigation portal, taking into account traffic jams. Navigation equipment is installed on the rolling stock of public transport, including for control purposes. Space images are used to obtain operational information in areas of natural disasters and for solving various problems, for example, municipal administration. Examples can be multiplied and they all confirm the fact that the results of space activities have become an integral part of modern life. It is also not surprising that various space technologies are often used together. Hence, of course, the idea of integrating technologies and creating unified end-to-end technological chains lies on the surface. In this sense, the technology of remote sensing of the Earth (ERS) from space and global navigation satellite systems (GNSS) is not an exception. But first things first…
GLOBAL NAVIGATION SATELLITE SYSTEMS
The Global Navigation Satellite System (GNSS) is a complex of hardware and software that allows you to get your coordinates at any point on the earth's surface by processing satellite signals. The main elements of any GNSS are:
- orbital constellation of satellites;
- ground control system;
- receiving equipment.
Satellites constantly transmit information about their position in orbit, ground stationary stations provide monitoring and control of the position of satellites, as well as their technical condition. The receiving equipment is a variety of satellite navigators that are used by people in their professional activities or everyday life.
The principle of operation of GNSS is based on measuring the distance from the antenna of the receiving device to the satellites, the position of which is known with great accuracy. The distance is calculated from the propagation delay time of the signal transmitted by the satellite to the receiver. To determine the coordinates of the receiver, it is enough to know the position of the three satellites. In fact, signals from four (or more) satellites are used to eliminate the error caused by the difference between the clock of the satellite and the receiver. Knowing the distances to several satellites of the system, using conventional geometric constructions, the program "wired" into the navigator calculates its position in space, thus GNSS allows you to quickly determine the location with high accuracy at any point on the earth's surface, at any time, in any weather conditions ... Each satellite of the system, in addition to the basic information, also transmits auxiliary information necessary for the continuous operation of the receiving equipment, including a complete table of the position of the entire satellite constellation, transmitted sequentially for several minutes. This is necessary to speed up the operation of the receiving devices. It should be noted an important characteristic of the main GNSS - for users with satellite receivers (navigators), receiving signals for free.
A common disadvantage of using any navigation system is that under certain conditions the signal may not reach the receiver, or arrive with significant distortions or delays. For example, it is almost impossible to determine your exact location inside a reinforced concrete building, in a tunnel, in a dense forest. To solve this problem, additional navigation services are used, such as, for example, A-GPS.
Today, several GNSSs operate in space (Table 1), which are at different stages of their development:
- Gps(or NAVSTAR) - operated by the US Department of Defense; currently the only fully deployed GNSS available 24/7 to users around the world;
- GLONASS- Russian GNSS; is in the final stage of full deployment;
- Galileo- European GNSS, which is at the stage of creating a satellite constellation.
We also mention the national regional GNSS of China and India, respectively - Beidou and IRNSS, which are under development and deployment; distinguished by a small number of satellites and nationally oriented.
Characteristics of the main GNSS as of March 2010
Let's consider some of the features of each GNSS.
Gps
The basis of the American GPS system are satellites (Fig. 2) that orbit the Earth along 6 circular orbital trajectories (4 satellites in each), at an altitude of about 20 180 km. Satellites transmit signals in the ranges: L1 = 1575.42 MHz and L2 = 1227.60 MHz, the latest models also in the L5 = 1176.45 MHz range. The system is fully operational with 24 satellites, however, in order to increase positioning accuracy and reserve in case of failures, the total number of satellites in orbit is currently 31 satellites.
Fig. 1 GPS Block II-F spacecraft
GPS was originally intended for military use only. The first satellite was launched into orbit on July 14, 1974, and the last of all 24 satellites required to fully cover the earth's surface, was launched into orbit in 1993. It became possible to use GPS to accurately target rockets to stationary, and then to mobile objects in the air and on the ground. To restrict access to accurate navigation information for civilian users, special interference was introduced, however, they were canceled since 2000, after which the accuracy of determining coordinates using the simplest civilian GPS navigator ranges from 5-15 m (the height is determined with an accuracy of 10 m) and depends on the conditions for receiving signals at a particular point, the number of visible satellites and a number of other reasons. The use of the global WAAS correction distribution system improves the GPS positioning accuracy for North America to 1–2 m.
GLONASS
The first satellite of the Russian satellite navigation system GLONASS was launched into orbit back in Soviet times - on October 12, 1982. The system was partially put into operation in 1993 and consisted of 12 satellites. The basis of the system should be 24 satellites moving above the Earth's surface in three orbital planes with an inclination of 64.8 ° and an altitude of 19,100 km. The measuring principle and signal transmission ranges are similar to the American GPS GLONASS system.
fig. 2 Spacecraft GLONASS-M Currently, there are 23 GLONASS satellites in orbit (Fig. 2). The last three spacecraft were launched into orbit on March 2, 2010. Now they are used for their intended purpose - 18 satellites. This ensures continuous navigation throughout almost the entire territory of Russia, and the European part is provided with a signal by almost 100%. According to plans, the entire GLONASS system will be deployed by the end of 2010.
At present, the accuracy of determining coordinates by the GLONASS system is slightly lower than similar indicators for GPS (does not exceed 10 m), while it should be noted that the joint use of both navigation systems significantly increases the positioning accuracy. The European Geostationary Navigation Coverage Service (EGNOS) serves to improve the performance of GPS, GLONASS and Galileo systems in Europe and to increase their accuracy.
Galileo
The European GNSS Galileo is designed to solve navigation problems for any mobile objects with an accuracy of less than 1 m. Unlike the American GPS and Russian GLONASS, Galileo is not controlled by the military departments. Its development is carried out by the European Space Agency. Currently, there are 2 test satellites in orbit, GIOVE-A (Fig. 3) and GIOVE-B, launched in 2005 and 2008, respectively. The Galileo navigation system is planned to be fully deployed in 2013 and will consist of 30 satellites.
fig. 3 Spacecraft GIOVE-A SATELLITE NAVIGATORS
As already noted, receiving equipment is an integral part of any satellite navigation system. The modern market for navigation receivers (navigators) is as diverse as the market for any other electronic and telecommunication products. All navigators can be divided into professional receivers and receivers used by a wide range of users. Let us dwell on the latter in more detail. Various names are used for them: GPS navigators, GPS trackers, GPS receivers, satellite navigators, etc. Recently, navigators built into other devices (PDAs, mobile phones, communicators, watches, etc.) have become popular. .). Among the actual satellite navigators, a special large class is made up of car navigators. Navigators designed for hiking, water, etc. trips are also becoming widespread (they are often called simply GPS navigators, despite the fact that they can also receive GLONASS signals).
A mandatory accessory for almost all personal navigators is a GPS chipset (or receiver), a processor, RAM and a monitor for displaying information.
Modern car navigators are able to plot a route taking into account the traffic organization and carry out address search. A feature of personal navigators for tourists is, as a rule, the ability to receive a satellite signal in difficult conditions, such as a dense forest or mountainous terrain. Some models have a waterproof case with increased shock resistance.
The main manufacturers of personal satellite navigators are:
- Garmin (USA; navigators for air, automobile, motor and water transport, as well as for tourists and athletes)
- GlobalSat (Taiwan; navigation equipment for various purposes, including GPS receivers)
- Ashtech (formerly Magellan) (USA; personal and professional navigation receivers)
- MiTac (Taiwan; car and travel navigators, pocket personal computers and communicators with built-in GPS-receiver under the brands Mio, Navman, Magellan)
- ThinkWare (Korea; personal navigation devices under the I-Navi brand)
- TomTom (Netherlands; car navigators), etc.
Professional navigation equipment, including for engineering, geodetic and mine surveying, is produced by such companies as Trimble, Javad (USA), Topcon (Japan), Leica Geosystems (Switzerland), etc.
As already noted, a large number of personal navigation devices are currently being produced, differing in their capabilities and price. As an illustration, we will describe the features of only one sufficiently "advanced" device in order to characterize the capabilities of the entire class of modern GPS navigators. This is one of the latest innovations in the popular series of car navigators - TomTom GO 930 (description taken from the GPS-Club website - http://gps-club.ru).
The TomTom GO 930 (Fig. 6) combines the latest trends in car navigation - maps of several continents, wireless headset and unique Map Share ™ technology
fig. 4 TomTom GO 930 Car Navigator All TomTom devices are developed in-house and are completely plug & play, which means they can be simply taken out of the box and used without having to read long instructions. An intuitive interface and "icons" in Russian will allow drivers to easily plan a route. Clear voice instructions in Russian help motorists reach their destination easily and stress-free. The navigator supports wireless control and Enhanced Positioning Technology (EPT), designed for uninterrupted navigation even in tunnels or densely built-up areas.
The TomTom navigation map provider is Tele Atlas, part of the TomTom Group. In addition to the fact that TomTom has fully Russified maps, it is the only navigation solution provider that offers maps of Europe and the United States on select models of navigators.
The world's road infrastructure changes by 15% annually. Therefore, TomTom gives its users the opportunity to download the latest map version free of charge within 30 days of using the navigation device for the first time, as well as access to the unique Map Share ™ technology. TomTom navigation users can download a new map through the TomTom HOME service. Thus, the latest version of the map can be accessed at any time. What's more, motorists can use Map Share ™ technology, a free manual map update right on the navigator as soon as traffic changes become known, with just a few taps on the touchscreen. Users can make changes to street names, speed limits on certain sections of the road, driving directions, blocked roads, and changes to POIs (points of interest).
TomTom's unique map sharing technology enhances navigation by allowing users to instantly make changes directly to their map. In addition, the user can receive information about similar changes made by the entire TomTom community.
This card sharing feature allows you to:
- change the maps of your TomTom device daily and immediately;
- gain access to the world's largest community of users of navigation devices;
- share updates daily with other TomTom users;
- get full control over downloaded updates;
- use the best and most accurate maps in any location.
CARDS FOR PERSONAL SATELLITE NAVIGATORS
Modern navigators are unthinkable without the presence of full-fledged large-scale maps in them, which show objects not only along the route of movement, but also throughout the survey area (Fig. 7).
fig. 5 Sample small-scale navigation chart Both raster and vector maps can be loaded into navigators. We will talk about one of the types of raster information in particular, but here we will note that paper maps scanned and loaded into GPS receivers are not the best way to display spatial information. In addition to the low positioning accuracy, there is also the problem of binding the map coordinates to the coordinates issued by the receiver.
Vector digital maps, especially in GIS formats, are actually a database that stores information about the coordinates of objects in the form of, for example, "shapefiles" and, separately, qualitative and quantitative characteristics. With this approach, the information takes up much less space in the memory of navigators and it becomes possible to download a large amount of useful reference information: gas stations, hotels, cafes and restaurants, parking lots, attractions, etc.
As mentioned above, there are navigation systems that allow the user to supplement the navigator maps with their own objects.
In some personal navigation devices, especially those intended for tourists, it is possible to put objects on your own (that is, in fact, make your own maps and diagrams). For these purposes, a special simple graphic editor is provided.
Special attention should be paid to regime issues. As you know, in Russia, there are still restrictions on the use of large-scale topographic maps. This is quite a hindrance to the development of navigational cartography. However, it should be noted that at present the Federal Service for State Registration, Cadastre and Cartography (Rosrestr) has set the task by 2011 to have full coverage of the Russian Federation (economically developed regions and cities) with digital navigation maps of 1:10 000, 1:25 scales. 000, 1:50 000. These maps will display navigation information represented by a road graph, digital cartographic background and thematic information (roadside infrastructure and service facilities).
NAVIGATION SERVICES
The development and improvement of satellite navigation systems and receiving equipment, as well as all the active implementation of WEB-technologies and WEB-services, gave rise to the emergence of various navigation services. Many models of navigators are able to receive and take into account information about the traffic situation when planning a route, avoiding traffic congestion as much as possible. Traffic data (traffic jams) are provided by specialized services and services, via the GPRS protocol or from the radio on the air via the RDS channels of the FM band.
SPACE IMAGES IN NAVIGATORS
Any navigational maps become outdated quickly enough. The advent of ultra-high spatial resolution space imagery (currently WorldView-1, WorldView-2, GeoEye-1 spacecraft provide up to 50 cm resolution) provide cartography with a powerful tool for updating map content. However, after updating the map and before its release and the possibility of "loading" into the navigation device, a lot of time passes. Space images provide an opportunity to immediately receive the most relevant information in the navigator.
Of particular interest from the point of view of using space images are the so-called. LBS services. LBS (Location-based service) is a service based on determining the location of a mobile phone. Taking into account the widespread development of mobile communications and the expansion of services provided by cellular operators, it is difficult to overestimate the potential of the LBS market. LBSs do not necessarily use GPS technology to determine their location. Location can also be determined using base stations of GSM and UMT cellular networks.
fig. 6 Space shot in Nokia mobile phone Manufacturers of mobile phones and navigation devices, providing LBS services, pay more and more attention to space imagery. Let's take as an example Nokia (Finland), which signed an agreement in 2009 with DigitalGlobe, operator of super-high-resolution satellites WorldView-1, WorldView-2 and QuickBird, to provide Ovi Maps users with access to space imagery (note that Ovi - Nokia's new brand for Internet services).
In addition to clarity when navigating urban areas (Fig. 8), it is very useful to have a background in the form of space images, traveling through an underexplored territory for which there are no fresh and detailed maps. Ovi Maps can be downloaded to almost all Nokia devices.
The integration of ultra-high resolution satellite imagery into LBS services makes it possible to increase their functionality by an order of magnitude.
One of the promising possibilities of using Earth remote sensing data from space is the creation of three-dimensional models based on them. Three-dimensional maps are highly visual, and allow you to better navigate, especially in urban areas (Fig. 9).
fig. 7 3D navigation chart In conclusion, we note the great promise of using ultra-high resolution orthorectified images in satellite navigators and LBS services. The Sovzond company produces ORTOREGION and ORTO10 products, which are based on orthorectified images from the ALOS (ORTOREGION) and WorldView-1, WorldView-2 (ORTO10) spacecraft. Orthorectification of individual scenes is performed using the rational polynomial coefficients (RPC) method without using ground control points, which significantly reduces the cost of work. The studies have shown that, according to their characteristics, the ORTOREGION and ORTO10 products may well serve as a basis for updating navigation maps, respectively, in scales of 1:25 000 and 1:10 000. Orthophoto mosaics, which are actually photo maps, supplemented with captions, can also be directly loaded into navigators.
The integration of high-resolution satellite imagery into navigation systems and LBS-services allows an order of magnitude increase in their functionality, convenience and efficiency of use.
The word "satellite" in the meaning of an aircraft appeared in our language thanks to Fyodor Mikhailovich Dostoevsky, who reasoned about "what will become in space with an ax? .. If he gets somewhere far, then I think he will start flying around the Earth without knowing why, in the form of a satellite ... ". It is difficult to say today what prompted the writer to such reasoning, but a century later - at the beginning of October 1957 - it was not even an ax that began to fly around our planet, but a device that was the most complicated at that time, which became the first artificial satellite sent into space with very specific goals ... And others followed him.
Features of "behavior"
Today everyone has long been accustomed to satellites - violators of the calm picture of the night sky. Created at factories and launched into orbit, they continue to "circle" for the good of mankind, remaining invariably interesting only to a narrow circle of specialists. What are artificial satellites and what benefit does a person get from them?
As you know, one of the main conditions for a satellite to enter orbit is its speed - 7.9 km / s for low-orbit satellites. It is at this speed that dynamic equilibrium occurs and the centrifugal force balances the force of gravity. In other words, the satellite flies so fast that it does not have time to fall to the earth's surface, since the Earth literally leaves from under its feet due to the fact that it is round. The higher the initial velocity reported to the satellite, the higher its orbit will be. However, with distance from the Earth, the speed in a circular orbit decreases and geostationary satellites move in their orbits at a speed of only 2.5 km / s. When solving the problem of a long and even eternal existence of a spacecraft (SC) in a near-earth orbit, it is necessary to raise it to an ever greater height. It should be noted that the Earth's atmosphere also significantly affects the spacecraft motion: even being super-rarefied at altitudes above 100 km from sea level (the conditional boundary of the atmosphere), it noticeably slows them down. So, over time, all spacecraft lose their flight altitude and the duration of their stay in orbit directly depends on this altitude.
From the Earth, satellites are visible only at night and at those times when they are illuminated by the Sun, that is, they do not fall into the region of the earth's shadow. The need for all of the above factors to coincide leads to the fact that the duration of observation of most LEO satellites is, on average, 10 minutes before entering and the same amount after leaving the Earth's shadow. If desired, terrestrial observers can systematize satellites by brightness (the International Space Station (ISS) is in the first place here - its brightness is approaching the first magnitude), by the frequency of blinking (determined by forced or specially set rotation), by the direction of movement (through the pole or in the other direction). The conditions for observing satellites are significantly influenced by the color of its coverage, the presence and range of solar panels, as well as the flight altitude - the higher it is, the slower the satellite moves and the less bright and noticeable it becomes.
The high altitude of flight (the minimum distance to the Earth is 180-200 km) conceals the size of even such relatively large spacecraft as the Mir orbital complexes (de-orbited in 2001) or the ISS - all of them are visible as luminous points, more or less brightness. With rare exceptions, it is impossible to identify a satellite with a simple eye. For the purpose of accurate identification of spacecraft, various optical means are used - from binoculars to telescopes, which is not always accessible to a simple observer, as well as calculations of their trajectories. The Internet helps the amateur astronomer to identify individual spacecraft, where information on the location of satellites in near-earth orbit is published. In particular, anyone can enter the NASA website, which displays the current location of the ISS in real time.
As for the practical use of satellites, starting from the very first launches, they immediately began to solve specific problems. So, the flight of the first satellite was used to study the Earth's magnetic field from space, and its radio signal carried data on the temperature inside the sealed satellite body. Since the launch of a spacecraft is a rather expensive pleasure, and besides, it is very difficult to implement, then several tasks are assigned to each of the launches at once.
First of all, technological problems are solved: development of new designs, control systems, data transmission, and the like. The experience gained allows us to create the next copies of satellites more advanced and gradually move on to solving complicated target tasks that justify the costs of their creation. After all, the ultimate goal of this production, like any other, is to make a profit (commercial launches) or the most efficient use of satellites during operation for defense purposes, solving geopolitical and many other tasks.
It should be recalled that cosmonautics as a whole was born as a result of the military-political confrontation between the USSR and the USA. And, of course, as soon as the first satellite appeared, the defense departments of both countries, having established control over outer space, have since then kept a constant record of all objects in the immediate vicinity of the Earth. So, probably, only they know the exact number of spacecraft, one way or another functioning at the moment. At the same time, not only the spacecraft themselves are monitored, but also the last stages of the rockets, transition compartments and other elements that delivered them into orbit. That is, strictly speaking, a satellite is considered not only something that has "intelligence" - its own control, observation and communication system - but also a simple bolt that separated from the spacecraft during the next phase of the flight.
According to the catalog of the US Space Command, as of December 31, 2003, there were 28,140 such satellites in near-earth orbit, and their number is steadily growing (objects larger than 10 cm are taken into account). Over time, due to natural reasons, some of the satellites fall to Earth in the form of fused remnants, but many remain in orbits for decades. When spacecraft work out their resource and cease to obey commands from the Earth, while continuing to fly, it becomes not only cramped in near-Earth space, but sometimes even dangerous. Therefore, when launching a new spacecraft into orbit, in order to avoid collisions and disasters, it is necessary to constantly be aware of where the “old” one is.
The classification of spacecraft is a rather laborious task, since each spacecraft is unique, and the range of tasks solved by new spacecraft is constantly expanding. However, if we consider spacecraft from the point of view of practical use, then we can distinguish the main categories determined by their intended purpose. The most in demand today are communication satellites, navigation, remote sensing of the Earth and scientific. Military satellites and reconnaissance satellites constitute a separate class, but in essence they solve the same problems as their "peaceful" counterparts.
Communication satellites
Signalers were among the first to benefit from the launch of satellites in practice. The launching of transponder satellites into near-earth orbit made it possible in the shortest possible time to solve the problem of stable all-weather communication in most of the inhabited territory. The first commercial satellite was the communications satellite, Echo-2, launched by the United States in 1964 and which made it possible to organize the transmission of television programs from America to Europe without using cable communication lines.
At the same time, its own communications satellite "Molniya-1" was created in the Soviet Union. After the deployment of the ground network of Orbita stations, all regions of our large country gained access to Central Television, and in addition, the problem of organizing reliable and high-quality telephone communications was resolved. The communication satellites "Molniya" were located in highly elliptical orbits with an apogee of 39,000 km. For the purposes of continuous broadcasting, a whole constellation of Molniya satellites was deployed, flying in different orbital planes. The ground stations of the Orbita network were equipped with rather large antennas, which, with the help of servo drives, tracked the movement of the satellite in orbit, periodically switching to the one that was in the field of view. Over time, in the process of improving the element base and improving the technical parameters of onboard and ground systems, several generations of such satellites have changed. But to this day constellations of satellites of the Molniya-3 family provide information transmission throughout Russia and beyond.
The creation of powerful launch vehicles of the "Proton" and "Delta" types made it possible to ensure the delivery of communication satellites to a geostationary circular orbit. Its peculiarity lies in the fact that at an altitude of 35,800 km, the angular velocity of rotation of the satellite around the Earth is equal to the angular velocity of rotation of the Earth itself. Therefore, a satellite in such an orbit in the plane of the earth's equator seems to hang over one point, and 3 geostationary satellites located at an angle of 120 ° provide an overview of the entire surface of the Earth, with the exception of only the polar regions. Since the task of maintaining its given position in orbit is assigned to the satellite itself, the use of geostationary spacecraft has made it possible to significantly simplify ground-based means of receiving and transmitting information. The need to supply the antennas with drives has disappeared - they have become static, and to organize a communication channel, it is enough to set them only once, during the initial setup. As a result, the terrestrial network of users was significantly expanded, and information began to flow directly to the consumer. Evidence of this is the multitude of parabolic dish antennas located on residential buildings both in large cities and in rural areas.
At first, when space was "available" only to the USSR and the USA, each of the countries cared exclusively about meeting their own needs and ambitions, but over time it became clear that everyone needed satellites, and as a result, international projects gradually began to appear. One of them is the publicly accessible global communications system INMARSAT, created in the late 1970s. Its main purpose was to provide ships with stable communications while on the high seas and coordinate actions during rescue operations. Now mobile communication through the INMARSAT satellite communication system is provided by means of a portable terminal the size of a small case. When you open the lid of the "suitcase" with a flat antenna mounted in it and aim this antenna at the supposed location of the satellite, two-way voice communication is established, and data exchange occurs at a speed of up to 64 kilobits per second. Moreover, today four modern satellites provide communication not only at sea, but also on land, covering a huge territory stretching from the Northern to the Southern Arctic Circle.
Further miniaturization of communication facilities and the use of high-performance antennas on spacecraft led to the fact that the satellite phone acquired a "pocket" format, not much different from the usual cellular one.
In the 1990s, the deployment of several mobile personal satellite communications systems began almost simultaneously. First appeared low-orbit - IRIDIUM ("Iridium") and GLOBAL STAR ("Global Star"), and then geostationary - THURAYA ("Thuraya").
The Thuraya satellite communications system has so far 2 geostationary satellites, which allow communication over most of the African continent, the Arabian Peninsula, the Middle East and Europe.
The Iridium and Global Star systems, which are similar in structure, use constellations of a large number of LEO satellites. Spacecraft alternately fly over the subscriber, replacing each other, thereby maintaining continuous communication.
The "Iridium" includes 66 satellites rotating in circular orbits (altitude 780 km from the Earth's surface, inclination 86.4 °), located in six orbital planes, 11 vehicles in each. This system provides 100% coverage of our planet.
Global Star includes 48 satellites flying in eight orbital planes (altitude 1,414 km from the Earth's surface, inclination 52 °), 6 vehicles each, providing 80% coverage, excluding the circumpolar regions.
There is a fundamental difference between these two satellite communication systems. In Iridium, a telephone signal arriving at a satellite from Earth is transmitted through a chain to the next satellite until it reaches the one that is currently in the visibility range of one of the ground receiving stations (gateway stations). This arrangement makes it possible to start operating it as soon as possible after the deployment of the orbital component at a minimum cost of creating a ground infrastructure. In "Global Star" broadcasting of a signal from satellite to satellite is not provided, therefore this system requires a denser network of ground receiving stations. And since they are absent in a number of regions of the planet, there is no continuous global coverage.
The practical benefits of the use of personal satellite communications have become obvious today. Thus, in the process of climbing Mount Everest in June 2004, Russian climbers had the opportunity to use telephone communication via Iridium, which significantly reduced the intensity of the anxiety of all those who followed the fate of climbers during this difficult and dangerous event.
An emergency with the crew of the SoyuzTM-1 spacecraft in May 2003, when, after returning to Earth, the rescuers could not find the cosmonauts in the Kazakh steppe for 3 hours, also prompted the ISS program managers to supply the cosmonauts with the Iridium satellite phone.
Navigation satellites
Another achievement of modern astronautics is the receiver of the global positioning system. The creation of the currently existing satellite systems of global positioning - the American GPS (NAVSTAR) and the Russian "GLONASS" - began 40 years ago, during the Cold War, to accurately determine the coordinates of ballistic missiles. For these purposes, as a supplement to satellites - rocket launch recorders, a system of navigation satellites was deployed in space, the task of which was to communicate their exact coordinates in space. Having received the necessary data from several satellites simultaneously, the navigation receiver also determined its own position.
The “protracted” peacetime forced the owners of the systems to start sharing information with civilian users, first in the air and on the water, and then on land, although it reserved the right to coarse the binding of navigation parameters in certain “special” periods. This is how military systems became civilian.
Various types and modifications of GPS receivers are widely used in sea and air vehicles, in mobile and satellite communication systems. Moreover, the GPS receiver, like the transmitter of the Cospas-Sarsat system, is a must-have equipment for any floating craft going to the open sea. The cargo spacecraft ATV, which is to fly to the ISS in 2005, being created by the European Space Agency, will also correct its trajectory with the station according to GPS and GLONASS data.
Both navigation satellite systems are approximately the same. GPS has 24 satellites, located in circular orbits of 4 in six orbital planes (altitude 20,000 km from the Earth's surface, inclination 52 °), as well as 5 spare vehicles. GLONASS also has 24 satellites, 8 each in three planes (altitude 19,000 km from the Earth's surface, inclination 65 °). In order for the navigation systems to work with the required accuracy, atomic clocks are installed on the satellites, information is regularly transmitted from the Earth, specifying the nature of the movement of each of them in orbit, as well as the conditions for the propagation of radio waves.
Despite the seeming complexity and scale of the global positioning system, a compact GPS receiver today can be purchased by anyone. According to signals from satellites, this device allows not only to determine the location of a person with an accuracy of 5-10 meters, but also to provide him with all the necessary data: geographical coordinates indicating the location on the map, current world time, movement speed, altitude, position of the sides light, as well as a number of service functions derived from primary information.
The advantages of space navigation systems are so indisputable that the United Europe, despite the huge costs, plans to create its own navigation system GALILEO ("Galileo"). China also plans to deploy a system of its navigation satellites.
Earth remote sensing satellites
The use of miniature GPS receivers has made it possible to significantly improve the operation of another category of spacecraft - the so-called Earth remote sensing satellites (ERS). If earlier images of the Earth taken from space were difficult enough to associate with certain geographic points, now this process does not present any problems. And since our planet is constantly changing, its photos from space, never repeated, will always be in demand, providing irreplaceable information for studying the most diverse aspects of life on earth.
Remote sensing satellites have a fairly large number, and nevertheless, their group is constantly replenished with new, more and more advanced devices. Modern satellites for remote sensing, unlike those that operated in the 1960s and 1970s, do not need to return to Earth the films captured in space in special capsules - they are equipped with super-light optical telescopes and miniature photodetectors based on CCD matrices, as well as high-speed data lines with a bandwidth of hundreds of megabits per second. In addition to the efficiency of data acquisition, it becomes possible to fully automate the processing of the received images on Earth. Digitized information is no longer just an image, but the most valuable information for ecologists, foresters, land surveyors and many other interested structures.
In particular, multispectral photographs obtained in the spring make it possible to predict the harvest based on the moisture reserve in the soil, during the growing season of plants - to detect the places where narcotic crops are grown and take timely measures to destroy them.
In addition, current commercial systems for selling video images of the Earth's surface (photographs) to consumers must be taken into account. The first such systems were first the grouping of American civilian satellites LANDSAT, and then French ones - SPOT. Under certain restrictions and in accordance with certain prices, consumers around the world can acquire images of areas of interest on the Earth with a resolution of 30 and 10 meters. The current, much more advanced civilian satellites - ICONOS-2, QUICK BIRD-2 (USA) and EROS-AI (Israel-USA) - after the removal of restrictions by the American government, allow you to buy photographs of the earth's surface with a resolution of up to 0.5 meters - in panchromatic mode and up to 1 meter - in multispectral mode.
Close to the remote sensing satellites are meteorological spacecraft. The development of their network in near-earth orbits has significantly increased the reliability of weather forecasting and made it possible to do without extensive networks of ground-based weather stations. And the news releases published today all over the world, accompanied by animated images of cyclones, cloud paths, typhoons and other phenomena, which are created on the basis of data from meteorological satellites, allow each of us to personally verify the reality of natural processes occurring on Earth.
Satellites - "scientists"
By and large, each of the artificial satellites is an instrument of cognition of the surrounding world taken out of the Earth. Scientific satellites, on the other hand, can be called a kind of testing grounds for testing new ideas and designs and obtaining unique information that cannot be obtained in any other way.
In the mid-1980s, NASA adopted a program to create four astronomical observatories in space. With some delays or other, all four telescopes were launched into orbit. The first to start its work was "HUBBL" (1990), designed to study the Universe in the visible wavelength range, followed by "COMPTON" (1991), which studied space using gamma rays, the third was "CHANDRA" (1999 ), which used X-rays, and completed this extensive program SPITZER (2003), which accounted for the infrared range. All four observatories were named after prominent American scientists.
HUBBL, which has been operating in near-Earth orbit for 15 years, delivers unique images of distant stars and galaxies to Earth. For such a long service life, the telescope was repaired several times during shuttle flights, but after the sinking of Columbia on February 1, 2003, the launches of space shuttles were suspended. It is planned that the HUBBL will remain in orbit until 2010, after which, having exhausted its resource, it will be destroyed. KOMPTON, which transmitted images of gamma-ray sources to Earth, ceased to exist in 1999. CHANDRA continues to supply information about X-ray sources on a regular basis. All three of these telescopes were designed by scientists to work in highly elliptical orbits in order to reduce the influence of the Earth's magnetosphere on them.
As for the "SPITZER", which is capable of capturing the weakest thermal radiation emanating from cold distant objects, unlike its counterparts revolving around our planet, it is in solar orbit, gradually moving away from the Earth by 7 ° per year. In order to perceive extremely weak thermal signals emanating from the depths of space, SPITZER cools its sensors to a temperature that exceeds absolute zero by only 3 °.
For scientific purposes, not only bulky and complex scientific laboratories are launched into space, but also small spherical satellites equipped with glass windows and containing corner reflectors inside. The parameters of the flight trajectory of such miniature satellites are tracked with a high degree of accuracy using laser radiation directed at them, which makes it possible to obtain information about the slightest changes in the state of the Earth's gravitational field.
Immediate prospects
Space engineering, which received such rapid development at the end of the 20th century, does not stop progressing for a single year. Satellites, which seemed to be the height of technical thought some 5-10 years ago, are replacing new generations of spacecraft in orbit. And although the evolution of artificial earth satellites is becoming more and more fleeting, looking into the near future, one can try to see the main prospects for the development of unmanned astronautics.
X-ray and optical telescopes flying in space have already presented scientists with many discoveries. Now, entire orbital complexes equipped with these devices are being prepared for launch. Such systems will make it possible to conduct a massive study of the stars in our Galaxy for the presence of planets in them.
It's no secret that modern earth-based radio telescopes receive pictures of the starry sky with a resolution that is orders of magnitude higher than that achieved in the optical range. Today it is time for this kind of research instruments to be launched into space. These radio telescopes will be launched into high elliptical orbits with a maximum distance of 350 thousand km from the Earth, which will make it possible to improve the quality of the radio emission of the starry sky obtained with their help by at least 100 times.
The day is not far off when factories for the production of highly pure crystals will be built in space. And this applies not only to biocrystalline structures, so necessary for medicine, but also materials for the semiconductor and laser industries. It is unlikely that these will be satellites - here you will most likely need visited or robotic complexes, as well as transport ships docked to them, delivering the initial products and bringing the fruits of extraterrestrial technology to Earth.
The colonization of other planets is not far off. On such long flights, you cannot do without creating a closed ecosystem. And biological satellites (flying greenhouses), simulating long-distance space flights, will appear in near-earth orbit in the very near future.
One of the most fantastic tasks, while already today from a technical point of view is absolutely real, is the creation of a space system for global navigation and observation of the earth's surface with an accuracy of centimeters. This positioning accuracy will find applications in a wide variety of areas of life. First of all, seismologists need this, hoping, by tracking the slightest vibrations of the earth's crust, to learn how to predict earthquakes.
At the moment, the most economical way to launch satellites into orbit are disposable launch vehicles, and the closer to the equator the cosmodrome is, the cheaper the launch is, and the larger the payload to be launched into space. And although floating and aircraft launchers have already been created and are successfully operating, the well-developed infrastructure around the cosmodrome will be the basis for the successful activities of earthlings in the development of near-earth space for a long time to come.
Alexander Spirin, Maria Pobedinskaya
The editors are grateful to Alexander Kuznetsov for his help in preparing the material.
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