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    • 专利摘要:
    METHOD AND SATELLITE SYSTEM FOR CIRCUMPOLAR LATITUDES. The present invention relates to satellite systems and, more specifically, the provision of a satellite system for monitoring climate and weather, communications applications and scientific research at higher altitudes, referred to as a circumpolar region and defined here as the area with latitudes greater than 60 °, whether in the northern hemisphere or the southern hemisphere. Contrary to the teachings in the technique it was discovered that a satellite system and method can be provided using satellites in 24-hour sidereal orbits (geosynchronous) with correct inclinations (70 ° to 90 °), orbital planes, ascents and eccentricities (0.2750 , 45) chosen to optimize the coverage of a specific service area located at high latitudes. A constellation of two satellites can provide continuous coverage of the circumpolar region. Satellites in this orbit avoid most Van Allen belts.
    公开号:BR112013007565B1
    申请号:R112013007565-1
    申请日:2011-09-30
    公开日:2021-03-09
    发明作者:Andre E. Bigras；Jack Rigley；Alireza Shoamanesh；Paul Ng；Surinder Pal Singh；Peter Megyeri
    申请人:Telesat Canada；
    IPC主号:
    专利说明:

    Field of the Invention
    [001] The present invention relates to satellite systems and, more specifically, to the provision of a satellite system and method for monitoring climate and weather, communication applications, scientific research and similar tasks at higher latitudes, whether in the northern hemisphere or in the southern hemisphere. Description of the Prior Art
    [002] Meteorological monitoring satellites and communication satellites are usually located in the Geostationary Earth Orbit - (GEO) or Low Earth Orbit (LEO). GEO satellites appear to be motionless in the sky, providing the satellite with a continuous view of a particular area on the Earth's surface. Unfortunately, such an orbit can only be obtained by placing the satellite directly above the Earth's equator (0 ° latitude), with a period equal to the Earth's rotation period, an orbital eccentricity of approximately zero and at an altitude of 35,789 km. Although such orbits are useful in many applications, they are very deficient in covering higher latitudes (not very useful above 60 ° latitude for weather and weather monitoring nor above 70 ° latitude for secure mobile communications). Optical sensors on a GEO meteorological monitoring satellite, for example, would see higher latitudes at an insufficient angle (that is, a low “elevation angle”) that it would not be able to collect useful data. Links from GEO communications satellites become insecure or flawed as the elevation angle for the satellite decreases with increasing latitude.
    [003] Low Earth Orbit (LEO) satellites are placed in circular orbits at low altitudes (less than 2,000 km) and can provide continuous coverage of the circumpolar region, but this requires many satellites since each of them is over the region for a relatively short period of time. An operational example is the Iridium system which uses a constellation of 66 satellites. Although practical for relatively small bandwidth communications, it is not cost-effective for broadband communications or for monitoring weather and weather which requires large and expensive payloads to be placed on each satellite. Due to the cost of building, launching and maintaining each satellite this is a very expensive way to provide continuous satellite coverage for a specific geographic area.
    [004] Highly Elliptical Orbits (HEO) such as the Molniya orbit and the classic Tundra orbit can provide better coverage of high latitudes with a smaller number of satellites, but the two orbits are problematic.
    [005] Highly Elliptical Orbits (HEO) are those in which one of the foci of the orbit is the center of the Earth. The speed of a satellite in an elliptical orbit is a declining function of the distance from the focus. Having the satellite to move close to Earth during part of its orbit (the perigee) will make it move very quickly each time, while at the other end of the orbit (the apogee), it will move very slowly. A satellite placed in these orbits spends most of its time on a chosen area of the Earth, a phenomenon known as "permanence in apogee". The satellite travels relatively slowly over areas of interest, and quickly over areas that are not of interest.
    [006] The orbital plane of a HEO is tilted with respect to the Earth's equator. An inclination of close to 63.4 ° is chosen to minimize the requirement for the propulsion system on board the satellite to maintain the peak above the service area.
    [007] The Molniya orbit is a HEO with an orbital period of approximately 12 hours. The attitude at the perigee of a Molniya orbit is low (on the order of 500 km above the Earth's surface) and the orbit passes through the Van Allen belt. Van Allen's belts are belts of charged energy particles (plasma) around the Earth, which are held in place by the Earth's magnetic field. Solar cells, integrated circuits and sensors are damaged by radiation levels in these belts, even if they are "hardened" or other security measures are implemented, for example, by turning off sensors when passing through regions of intense radiation. Despite these efforts, satellites that might otherwise have an expected life of 15 years will only have approximately 5 years of useful life if they have to travel regularly through the interior of the high-energy proton Van Allen belt (the outer belt of electrons is less of a problem). This reduced satellite life makes Molniya systems very expensive.
    [008] The classic Tundra orbit is also a highly elliptical orbit, with the same inclination as Molniya (63.4 °). It is also a geosynchronous orbit with an orbital period of one sidereal day (approximately 24 hours). The only operating system in Tundra orbit is Sirius Satellite Radio, which operates a constellation of three satellites on different planes, each satellite plane shifted by 120 °, to provide the coverage they want for their radio broadcast system. Two satellites in classic Tundra orbit could not provide continuous coverage of a circumpolar region.
    [009] Even due to the problems with Molniya (short expected life) and the classic Tundra systems (requiring more than two satellites for circumpolar coverage), those skilled in the art support the use of these systems in such applications. For example: • A current NASA document ("The case for launching a meteorological imager in a Molniya orbit" by Lars Peter Riishojgaard, Global Modeling and Assimilation Office), ensures that the most effective way to provide a satellite system for meteorological monitoring at high latitudes is to use a Molniya system: http://www.wmo.int/pages/progwww/OSY/Meetings/ODRRGOS- 7 / Doc7-5 (1) .pdf • A document from the European Space Agency (" HEO for ATM; SATCOM for AIR TRAFFIC MANAGEMENT by HEO satellites ", Final Report, 2007) concludes that a Tundra orbit would need more satellites than Molniya, to cover northern latitudes for Air Traffic Management (ATM) applications; and • A presentation at the International Communications, Navigations and Surveillance Conference, 2009, "SATCOM for ATM in High Latitudes", Jan Erik Hakegard, Trond Bakken, Tor Andre Myrvoll, concludes that three satellites in the Tundra orbit would be required for ATM at high latitudes. See: http: // icns. org / media / 2009/05 / presentations / Session K C0mmu nications FCS / 01-Hakegard.pdf
    [0010] There is, therefore, a need for an improved satellite system and methods to provide high latitude coverage, particularly for meteorological monitoring and communication applications.
    [0011] Summary of the Invention
    [0012] An objective of the invention is to provide improved satellite systems and methods to provide continuous coverage of the circumpolar region, which alleviate the problems described above.
    [0013] Contrary to the teachings in the technique it was determined that a satellite system and method can be provided using satellites in 24 sidereal time orbits (geosynchronous) with correct inclinations, orbital planes, ascents and eccentricities chosen to optimize the coverage of a specific service area located at high latitudes. A constellation of two satellites can provide continuous coverage of the circumpolar region. Satellite orbits avoid Van Allen's inner belt of high-energy protons and can reach an expected lifespan of 15 years or more.
    [0014] In one embodiment of the invention, a satellite system for Earth observation and communications is provided, comprising: a constellation of two satellites, which together provide continuous coverage of approximately 20 ° of elevation or more throughout an entire geographic service area above 60 ° latitude; each satellite having an orbital inclination between approximately 70 ° and 90 ° and an orbital eccentricity between approximately 0.275 and 0.45; and a base station for transmitting to, and receiving signals from, the constellation of two satellites.
    [0015] In another embodiment of the invention a method of operation is provided for a satellite system for Earth observation and communications, comprising: providing a constellation of two satellites, which together provide continuous coverage of approximately 20 ° of elevation or more over a geographic service area above 60 ° latitude, each satellite having an orbital inclination between approximately 70 ° and 90 ° and an orbital eccentricity between approximately 0.275 and 0.45; and providing a base station for transmitting to and receiving signals from the constellation of two satellites.
    [0016] In a further embodiment of the invention, a satellite base station is provided, comprising: communication mechanisms for transmitting and receiving signals to and from a constellation of two satellites, which together provide continuous coverage of approximately 20 ° of elevation or more across a geographic service area above approximately 60 ° latitude; and flight control mechanisms to control the orbits of the constellation of two satellites, each satellite having an orbital inclination between approximately 70 ° and 90 ° and an orbital eccentricity between approximately 0.275 and 0.45.
    [0017] Still in a further embodiment of the invention, a satellite is provided comprising: communication mechanisms for transmitting and receiving signals to and from a base station; an Earth observation and communication payload to serve a geographic service area above 60 ° latitude, with an elevation of approximately 20 ° or greater; and flight control mechanisms to control an orbit to have an orbital inclination between approximately 70 ° and 90 ° and an orbital eccentricity between approximately 0.275 and 0.45.
    [0018] Other aspects and characteristics of the present invention will be evident to those skilled in the art from an analysis of the detailed description below when considered in conjunction with the drawings. Brief Description of Drawings
    [0019] These and other characteristics of the invention will become evident from the following description in which reference is made to the accompanying drawings in which:
    [0020] Figure 1 presents a map of the geographical area to be covered, in this example for the northern hemisphere, the area above 60 ° to the north.
    [0021] Figure 2 shows the output graph of a satellite orbit software tool, indicating the percentage of time in which the criterion of a minimum elevation angle of 20 ° is found throughout the area. In this example, the northern hemisphere above 50 ° north latitude is shown to have slightly less than 100% coverage. The graph of the percentage coverage of the area above 60 ° indicates 100% coverage.
    [0022] Figure 3 shows two satellites in an exemplary 24-hour elliptical orbit, tilted 90 °. The satellites are on the same plane separated by approximately 12 hours.
    [0023] Figure 4 is a simplified diagram of Van Allen's radiation belts, indicating the inner proton belt and the outer electron belt.
    [0024] Figure 5 shows the terrestrial layout of two satellites in the same orbital plane, in an embodiment of the invention. The land plot is repeated daily.
    [0025] Figure 6 presents an exemplary network architecture to implement the invention.
    [0026] Figures 7 and 8 are graphs showing the Total Ionization Dose (TID) so that the orbit of the invention is smaller than those of the geostationary and Molniya orbits.
    [0027] Figure 9 shows an exemplary payload arrangement for a launch vehicle.
    [0028] Figure 10 presents a flow chart of an exemplary method of implementing the invention.
    [0029] Figure 11 shows a block diagram of an exemplary Gateway in an embodiment of the invention.
    [0030] Figure 12 shows a block diagram of an exemplary satellite in an embodiment of the invention.
    [0031] Similar reference numerals are used in different figures to denote similar components. Detailed Description of the Invention
    [0032] Contrary to the teachings in the technique it was determined that a satellite system and method can be provided using satellites in 24-hour sidereal orbits (geosynchronous) with correct inclinations, orbital planes, ascents and eccentricities chosen to optimize the coverage of a specific service area located at high latitudes. A constellation of two satellites can provide continuous coverage of the circumpolar region, which is defined as the area with more than 60 ° latitude whether in the northern hemisphere or the southern hemisphere (see Figure 1, which identifies the 60 latitude area ° of the northern hemisphere). Satellites in this orbit avoid Van Allen's inner belt of high-energy protons.
    [0033] For example, as shown in Figure 2, a constellation of two satellites at an inclination of 90 ° and 0.3 eccentricities, will provide a minimum elevation angle of 20 ° for the entire area above 50 ° to the north, most of the time with the percentage coverage of the area at an elevation angle of at least 20 ° never less than 96.5%. The “elevation angle” refers to the line of sight angle between the ground and the satellite as measured from the horizon. The minimum elevation angle that climate and weather monitoring instruments should have for accurate data is typically in the vicinity of 20 °. Other exemplary embodiments of the invention are described below.
    [0034] The classic Tundra system does not provide continuous coverage of the circumpolar region. By increasing the eccentricity, causing a higher peak, the coverage requirement can be satisfied. However, higher altitude above the coverage area requires larger antennas and sensors on the satellite. More importantly, the perigee is lowered by causing satellites to pass through a larger portion of Van Allen's belts, reducing their operational life. Only by modifying both the eccentricity and the inclination can the desired coverage of the circumpolar region be provided at a reasonable altitude, with minimal exposure to the Van Allen belts. Other system parameters are as follows:
    [0035] Inclination: The inclination is the angle between the orbital plane of the satellites, and the plane that passes through the Earth's equator. The slope may be only slightly greater than 63.4 ° in some embodiments, but it is between 80 ° and 90 ° for most applications that require circumpolar coverage. Figure 3 shows a simplified diagram of two satellites, separated by 180 °, in a HEO orbit with a 90 ° inclination. One satellite 300 is at the height of orbit, passing through axis 310 of Earth 320 in the northern hemisphere, while the second satellite 330 is at perigee passing through axis 310 in the southern hemisphere.
    [0036] Eccentricity: the eccentricity is the shape of the elliptical trajectory of the satellites, which determines the height of the apogee (the highest altitude) and the perigee (the lowest altitude). The eccentricity is chosen to have a sufficiently high peak over the service area so that the satellites are able to provide the necessary coverage for the required period of their orbit. Higher eccentricity increases the height of the apogee, which must be overcome with greater energy, gain of antenna or greater optics on the satellite. Higher eccentricities (above approximately 0.34) also increase exposure to Van Allen belts.
    [0037] Altitude: It is desirable to have as low an apex as possible above the coverage area since the increased range negatively affects the required energy and / or the sensitivity of the satellite instruments. In perigee, of course, a sufficiently high altitude must be reached to minimize exposure to Van Allen belts. As shown in Figure 4, Van Allen belts comprise a torus of fields around Earth 320. The belts of greatest interest are the 410 inner proton belts. As will be explained, the 420 outer electron belts are of secondary interest. .
    [0038] Location / Number of Satellites: An orbital plane with two or more satellites is the preferred implementation. This allows for multiple satellites launched from a single launch vehicle, or increasing the number of satellites in the same plane for redundancy and / or improved performance. For example, although only two satellites are required, it may be convenient to launch a third redundant satellite in case a satellite fails. Since all three satellites are on the same plane, it is easier to place them in the appropriate position and activate the third satellite when required. This type of redundancy cannot be performed on systems that use different orbital planes for their satellites.
    [0039] Argument from Perigee: The Argument from Perigee describes the orientation of an elliptical orbit with respect to the equatorial plane of the Earth. For service to the northern circumpolar region (for example, latitudes greater than 60 ° to the north), the perigee argument is close to 270 ° so the apogee is in the northern hemisphere and the perigee is in the southern hemisphere. For service to the southern circumpolar region (for example, latitudes greater than 60 ° south), the perigee argument is close to 90 ° so the apogee is in the southern hemisphere and the perigee is in the northern hemisphere.
    [0040] Ascending Node Longitude: In simple terms, the Ascending Node Longitude describes where the orbital plane crosses the Earth's equator. The Longitude of the Ascending Node becomes a factor in specifying the orbit if it is desired to shift (bias) the cover towards a subset of the circumpolar region, or to optimize Earth observation by the satellite for a situation with better sunlight illumination, such as examples.
    [0041] Orbital Period: The orbital period is preferably approximately 24 hours, but this orbit can be adjusted to provide the coverage required in periods above and below 24 hours and still obtain continuous coverage of the circumpolar region.
    [0042] Terrestrial layout: In the preferred mode, the two satellites are in the same orbital plane and each of them repeatedly follows a different terrestrial layout. For a constellation of two satellites, the phasing or spacing of the satellites in the orbital plane is such that the time between their respective heights is approximately half the orbital period. See Figure 5 that shows the terrestrial traces for an exemplary modality of two satellites in the same plane, with a 90 ° inclination and an eccentricity of 0.3.
    [0043] Orbit Control: Satellite constellations of the invention experience changes in the previously mentioned orbital parameters over time due to the flattening of the Earth, gravitational forces of the sun and moon, and pressure from solar radiation. These can be compensated by the propulsion system on board the satellite. The way in which this is done is described below.
    [0044] Base Stations: As shown in Figure 6, the system includes a communications network based on Earth 620, satellites 300, 330 with communications functionality, Earth observation and / or scientific payloads, and at least one base station or Gateway 610. The base station or Gateway 610 is required to obtain data from satellite 300, 330 and to perform Telemetry, Tracking & Control (TTC). Directional antennas would be used due to their greater efficiency, requiring base station (s) 610 to track satellites 300, 330 across the sky. The tracking technology is well known in the art, although it had to be modified to accommodate the invention's two-satellite system. The handoff from one satellite to the next as they move across the sky would not require any interaction for the user. The handoff can be affected using known techniques, although they had to be optimized for this implementation.
    [0045] Two-way communications, in real time, are possible only when the satellite is mutually visible to both, a Gateway 610 and an element of the Earth 620-based communication network. This 620 network consists of the satellite terminals, fixed and that communicate with the satellite. The transfer of data generated by the satellite payloads is possible only when the satellite is visible to a Gateway 610. It is possible to increase the number of Gateways 610 strategically placed to obtain continuous links between a satellite 300, 330 and at least one Gateway 610. Satellites 300, 330 may also have “store and send” functionality allowing the satellite to store SOE and other data when communications to a Gateway infrastructure are not possible. The stored data can then be retransmitted to the terrestrial segment when communications are possible between the satellite and the Gateway.
    [0046] Avoiding a large part of the Van Allen belts increases the expected life of the satellites. Using this invention, less frequent launches are required to reestablish the satellite constellation and there are fewer restrictions on the model and operation of communications, scientific payloads and Earth observation.
    [0047] The flight dynamics (that is, adjustments required to keep the satellite in the desired orbit) of satellites in such a system would be different from that of other satellite systems, but the way in which these problems are dealt with would be largely the same . That is, the flight path of the satellite could be hindered, for example, by the gravitational attraction of the moon and sun, solar radiation pressure and flattening of the Earth. Computer software systems for managing other satellite flight systems are known and could easily be modified to accommodate the orbits described here.
    [0048] It is intended that the system be used initially in a two-way communication mode, in these satellite bands: Zona-L (1-3 GHz); Zone X (approximately 7-8 GHz); Ku band (approximately 11-15 GHz), and Ka band (approximately 17-31 GHz). Error correction, encoding and retransmission of lost / corrupted packets would also be used.
    [0049] The advantages of the system include at least the following: • only two satellites are required, unlike the three satellites required by classic Tundra systems, and many more required by LEO systems for complete circumpolar coverage; • this system minimizes exposure to Van Allen belts, providing satellites with a minimum useful life of 15 years instead of the expected 5 years for the satellite in a Molniya system; • the necessary continuous coverage of the circumpolar region for Earth observation and broadband communications can be provided, unlike GEO systems that cannot provide such coverage; and • the altitude at the perigee would be approximately 24,000 km, and non-continuous communications and Earth observation are possible in the other circumpolar region. Various Modalities
    [0050] The main drivers for this invention can be summarized as follows: • Earth and Scientific Observation (SEO) and Communication / Diffusion (COM) applications • Coverage area required by the SEO and / or COM payload • Angle minimum lift required by the SEO and / or COM payload • Coverage in percentage of time required from the SEO and COM payload.
    [0051] As shown in Table 1, the parameters for some exemplary embodiments of the invention would be as follows: TABLE 1 - APPLICATIONS OF THE INVENTION


    [0052] Sub-application 1 is for Satellites for “communication only” services for the two Polar regions. Note that the eccentricity in this application has been relaxed from 0.3 to 0.275. This is permissible because the COM application can accommodate a lower elevation angle than the SEO application. Advantages of the parameters for this modality include the following: o With a satellite dedicated only for communications (ie, no SEO payload), a greater communication payload would be possible, allowing, as examples: greater capacity, redundancy, larger antennas more frequency bands; o The size of the satellite can be reduced, reducing total costs; o Possibility of a single launch for multiple satellites; and o Possibility to load more fuel, therefore a longer satellite life cycle.
    [0053] Sub-application 2 is the same as the Main application except that the heyday is placed over the South Pole which becomes the main service area.
    [0054] Sub-application 3 is the same as Sub-application 1 except that the heyday is placed on the South Pole that becomes the main service area. Of course, this application has the same advantages as Sub-application 1.
    [0055] Although an inclination of 90 ° was considered to be advantageous, this parameter can be relaxed to an inclination range of approximately 70 ° to 90 ° as shown in Subplications 4 and 5. Even with the relaxation of this parameter, this application still provides the following advantages: o Coverage of the entire circumpolar region above 60 ° is possible, but the apogee should increase with decreasing slope; for example, an increase in heyday from 48,100 km to 50,100 km results from a decrease in inclination from 90 ° to 80 °. Although 2,000 km is a small percentage difference, it is significant enough to make 90 ° orbit preferable. The closest altitude will result in more accurate scientific data and better resolution from Earth observation equipment; and Satellites not tilted at 90 ° can operate in different orbital planes making a single ground tracking possible.
    [0056] Table 2 below shows the minimum eccentricity (ie minimum height of apogee) required to meet the requirement for circumpolar coverage indicated for a range of slopes in orbital plane in accordance with Sub-applications 4 and 5, and slopes in general.
    [0057] For this table, the circumpolar coverage requirement is defined as 100% coverage for 100% of the time in the circumpolar region above 60 ° north (or below 60 ° south for the southern circumpolar region) in a minimum elevation angle of 20 ° (equivalent to a maximum incidence angle of 70 °). TABLE 2 - HIGH SLOPE ANALYSIS

    [0058] The decrease in inclination increases the required eccentricity. However, this results in a height of Apogee that will increase the loss of trajectory for a communication payload and will reduce the resolution obtained by an Earth observation payload. Therefore, for such applications, an inclination range of approximately 80 to 90 ° is preferred.
    [0059] Increasing the eccentricity above a minimum required for a given slope will increase the area that can be covered continuously, in this case even below the 60 ° latitude contour. Orbit Control
    [0060] The satellite constellations of this invention will experience changes in the previously mentioned orbital parameters over time due to the flattening of the Earth, gravitational forces of the sun and moon, and pressure from solar radiation. These can be compensated by carrying out periodic orbit correction maneuvers using the propulsion system on board the satellite. The main parameter of interest is the Argument from Perigee.
    [0061] For orbit inclinations greater than 63.4 °, the perigee argument will tend to change (decrease) at a reasonably constant rate, due (mainly) to the flattening of the Earth. As the inclination increases from 63.4 ° to 90 °, the rate of change of the perigee argument (w) increases. In order to maintain service for the north polar cap, the orbital apogee must be maintained close to the most northerly point of the terrestrial trail (corresponding to w = 270 °); therefore, “station maintenance” maneuvers will be carried out to control the danger argument. These maneuvers will be similar to the east-west double-burn maneuvers that are carried out to control the eccentricity of a geostationary satellite, but they will be considerably larger.
    [0062] The rate at which the perigee argument is changed is a complete function of the orbital inclination, eccentricity, semi-main axis and direct ascension of the ascending node (RAAN). Note that the classic Molniya orbit with an inclination of 63.4 ° is not exempt from changes in the perigee argument due to the gravitational effects of the sun and moon; the perilee argument Molniya may decrease by 2 ° / year, depending on the RAAN. For the orbit of the invention, the magnitude of the perigee argument rate is greater. At a slope of 63.4 ° the rate may exceed 6 ° / y, and at a slope of 90 ° the rate is 8.3 ° / y.
    [0063] A single correction to the perigee argument can be applied by performing two “delta-v” maneuvers on opposite sides of the orbit approximately halfway between the apogee and the perigee (“delta-v” is simply an aerospace term for a change in speed). With the maneuver that is performed as the satellite moves south towards the perigee, propellants will be fired to provide a retrograde delta-v to reduce the orbital speed, causing the danger argument to increase. With the maneuver that is carried out as the satellite moves north towards the apogee, the propellants will be fired to provide a progressive delta-v to increase the orbital speed, which will also increase the perigee argument. The two maneuvers will be carried out with half orbit separation; the order in which the maneuvers are performed will not matter. The speed changes of the two maneuvers will be approximately equal to avoid unwanted changes for the orbital period.
    [0064] The size of each perigee argument correction will be determined by the propulsion and duration of the two maneuvers. As longer maneuvers are less efficient, it will be preferable to perform frequent short-term maneuvers instead of less frequent long-term maneuvers. For satellites equipped with chemical propulsion systems (bi-explosive), the propulsion that can be obtained will be large enough to allow several days or even weeks between maneuver pairs. For satellites using high-efficiency, low-propulsion ion thrusters, maneuvers can be performed during each orbital turn.
    [0065] Over time, if left out of control, the other orbit parameters will start to deviate from their nominal values due to the disturbing forces of the flattening of the Earth and lunar / solar gravity. The remaining two classic “flat” orbital elements, semi-main axis and eccentricity, will tend to move very slowly and irregularly, and can be controlled with an additional explosion virtually zero by slightly adjusting the locations and difference in magnitudes of the maneuvers double firing that are carried out to control the perigee argument.
    [0066] Of the two classic elements "out of plane", the inclination will also tend to change very slowly, and as it is not a crucial parameter, it will not need to be controlled. RAAN, like the perigee argument, will tend to change at a reasonably constant rate, resulting in a slow but stationary precession of the orbital plane over the North Pole. The signal and magnitude of the RAAN rate will be determined by the slope and the initial RAAN value. For the preferred configuration with two or more satellites in the same orbital plane, the precession of the orbital plane will not affect the coverage of the polar region, so that no maneuver will be required to control the RAAN. (Note that the effect of a small, constant rate in the RAAN on coverage at any point on the ground can be easily offset by the slight shift in the average orbit period from exactly one sidereal day to maintain a fixed terrestrial trail.) For a constellation in which satellites are kept in two or more orbital planes, infrequent “cross-track” maneuvers can be performed in the orbital apogee to maintain nodal separation between the planes. Radiation
    [0067] The orbits selected for this invention allow satellites to avoid the inner Van Allen radiation belt of high energy protons. Satellites in this orbit will still pass through the less severe external electron radiation belt. Proton particles are much heavier than electron particles so they can create a lot more damage. It is difficult if not impossible to protect against high energy protons.
    [0068] As the satellite passes through these radiation zones, there is a cumulative absorption of radiation by the satellite components. This cumulative absorption is a factor in determining the expected useful life of a satellite. The second factor, which occurs as a result of the proton belt, but not the electron belt, is called the Single Event Effect (SEE) caused by a single energetic particle. The particle can cause a temporary interruption in the electronic media or permanent damage. The orbits of the invention were specially designed to obtain circumpolar coverage with two satellites, while avoiding Van Allen's proton radiation belts.
    [0069] Figures 7 and 8 show dose-depth curves comparing three orbits: a 90 ° inclination or eccentricity 0.3 in the manner of the invention, a 160 W GEO orbit (ie, a geosynchronous orbit established in 160 ° west) and a classical Molniya orbit (inclination of 63.4 °, eccentricity of 0.74). During an expected useful life of 15 years for a typical GEO satellite, the total accumulated radiation that is expected to be absorbed is 500 krads. As shown in Figure 7, a satellite in the Molniya orbit would require a protective thickness of 11.5 mm to satisfy this requirement, while a 160 W GEO would require 8 mm of aluminum protection. In comparison, the orbit of the invention would require only 6.5 mm. There is a significant advantage in using an orbit like that of the invention, which can use components and subsystems with GEO flight inheritance, and can reach or exceed the expected life of GEO satellites.
    [0070] It is preferable to use "ready to use" components to minimize costs and optimize reliability. Although the invention can be implemented with new components having 6.5 mm protection, 8 mm protection would typically be used because GEO satellites and components are the most common. As shown in Figure 8, if it is intended to maintain the protection and the total radiation absorbed for a GEO as a reference (ie, an 8 mm shield and 500 krad radiation dose), a satellite in the Molniya orbit will absorb that dose of total radiation in 8 years, a satellite in the GEO orbit in 15 years and a satellite in a 90 ° tilt orbit of the invention in 36 years. Thus, the system of the invention would be much safer and would have a much longer expected durability than a system in the Molniya orbit.
    [0071] Figure 10 illustrates a flow chart of an exemplary method of operating the satellite system. The method starts at block 1010, by launching the constellation of satellites and installing the satellites in orbits having the desired orbital parameters. Satellites can be launched one at a time (for example, one satellite per launch vehicle) or with multiple satellites on the same launch vehicle. In the preferred mode, it is desirable to have all satellites in the same orbital plane; in such a configuration, it is more efficient to launch all satellites with a single launch vehicle.
    [0072] Figure 9 shows a cross-sectional view of an exemplary payload 900 for a launch vehicle (not shown) containing three satellites 300, 330, 910. The launch vehicle will include a sufficient number of propulsion stages, from sufficient capacity to charge the satellites to the desired orbit, or to a position from which the satellites can reach their operational orbits (ie, two stages of propulsion, three stages, etc.). The launch vehicle can load multiple satellites into a low-altitude parking orbit, from which the satellites have their own propulsion for the operational orbit, or it can launch the satellites directly into its operational orbit.
    [0073] Figure 9 shows three satellites 300, 330, 910 stacked on a 920 payload adapter within the 930 payload aerodynamic shell. Although only two satellites are required to provide coverage of the circumpolar region, it may be desirable to launch a third redundant satellite in orbit at the same time as the two main satellites. Thus, the third redundant satellite could be authorized if any of the main satellites failed for some reason. Of course, a greater or lesser number of satellites than three could be arranged within the aerodynamic payload shell.
    [0074] As will be described with reference to Figure 12, each satellite 300, 330, 910 will include a communications system, a control system and a propulsion system. Regardless of which launch vehicle configuration is used, these systems allow satellites 300, 330, 910 to communicate with Gateway 610, and position themselves in their final operating orbits, with the desired nodal separation. In the case of a constellation of two satellites with the satellites in the same plane, the two satellites will have a 180 ° nodal separation.
    [0075] Referring again to Figure 10, once the constellation of satellites has been launched by the launch vehicle, the satellites can be activated and an authorization / testing procedure for the basic systems would be performed 1020. This authorization / testing procedure may include installing antennas and rotating satellites 300, 330, 910 so that the antenna is pointed in the appropriate direction, installing solar panels, energizing processors and electronic systems, starting software systems, and verifying the operation of all basic systems and subsystems. As part of this procedure, it may also be necessary to perform troubleshooting and / or corrective measures.
    [0076] Once the basic systems and subsystems have been activated and their operation verified, satellites 300, 330, 910 can be moved to their final orbital positions 1030. As described above, this can comprise satellites 300, 330, 910 simply performing self-propulsion for the correct nodal separations, if they were launched in the same operational orbit. Alternatively, if satellites 300, 330, 910 were launched into a parking orbit, they might have to consume a much larger amount of self-propelling fuel for their operational orbit and nodal separation.
    [0077] With satellites 300, 330, 910 now in their final orbital positions, payloads can be activated, authorized and tested 1040. This would be done in a very identical way as the activation, testing and authorization of basic satellite systems described above, that is, installing any necessary antennas or sensors, powering processors and electronic systems, initializing software systems and verifying the operation of all payload systems and subsystems. Of course, problem solving and / or corrective measures could also be carried out as part of the payload authorization procedure.
    [0078] Satellites 300, 330, 910 are now in an operational mode. The operation of the payload will be determined entirely by the nature of the payload. In the case of an Earth observation payload such as a weather monitoring system, this may comprise the operation of imaging instruments, and the transmission of observation data from the satellite to the Gateway.
    [0079] With all satellite systems and operational payload, the only remaining concern is to maintain satellite position 300, 330, 910 in the orbit of interest 1050. This can be done as described above under the heading “ Orbital Control ”. Satellite position information can be determined by satellite 300, 330, 910, a Gateway 610 or some other control center. Typically, satellite position information can be calculated from global positioning system (GPS) data and / or from other satellite telemetry.
    [0080] Optionally, certain systems and subsystems can be deactivated in the course of the satellite's orbits, for example, to save energy or to protect the instrumentation. If, for example, the payload comprises scientific instruments to monitor the weather in the northern circumpolar region, it may be desirable to disable the payload systems while satellite 300, 330, 910 is in the southern hemisphere, reactivating it when it re-enters in the region of interest. It may be desirable to keep basic satellite subsystems operational at all times, so that it will continue to receive and transmit data related to its health, status and control.
    [0081] Figure 11 illustrates a simplified block diagram of an exemplary Gateway system 1100 for communication with satellites 300, 330, 910. Communication signals can include operational / control signals and signals related to payload. In the case of a scientific payload, signals related to the payload may include control signals transmitted to the instruments, and observation / monitoring data received from the instruments. The Gateway 1100 system can be modified to receive and present other types of information, and can be used in conjunction with one or more computers, servers, networks and other related devices.
    [0082] As shown in Figure 11, the Gateway 610 system can include an antenna 1110, a transceiver 1120, a processing unit or system 1130, and a network communication system 1140.
    [0083] The 1110 antenna is designed to receive and transmit signals at the desired communication frequencies. Typically, the 1110 antenna will be a highly directional tracking antenna, known for the high altitudes of the satellites and the low signal levels involved. Other antenna models such as non-tracking antennas can be used if the application is changed.
    [0084] The Gateway 1120 transceiver consists of a receiver portion for receiving data from the satellites and preparing them for CPU 1130, and a transmission portion for processing data from CPU 1130, preparing them for transmission to satellites 300, 330, 910 via antenna 1110. The transmission portion of transmitter 1120 can, for example, multiplex, encode and compress the data to be transmitted to satellites 300, 330, 910 then modulate the data for the transmission frequency and amplify them for transmission. Multiple channels can be used, error correction coding and the like. In a complementary manner, the receiver portion of transceiver 1120 demodulates the received signals and performs any necessary demultiplexing, decoding, decompression, error correction and formatting of the signals from the antenna, for use by the 1130 CPU. The antenna and / or the receiver can also include any other desired switches, filters, low-noise amplifiers, drop converters (for example, for an intermediate frequency), and other components.
    [0085] A local 1150 user interface is also shown in Figure 11. The geographic positions of the Gateway (s) 610 can be chosen to minimize the number of Gateways required. As a result, the 610 Gateway (s) may not be in a geographical location that is convenient for satellite operators and / or parties receiving payload data. Thus, Gateway (s) 610 will typically be provided with network communication facilities 1140 so that remote computers 1160 can be used to access the system via the Internet or similar 1170 networks.
    [0086] Figure 12 illustrates a simplified block diagram of a satellite 300, 330, 910 which can be used in an exemplary embodiment of the invention. As shown, satellite 300, 330, 910 can include a station maintenance system 1210, a propulsion system 1220, a power system 1230, a communication system, a computer processing system 1240 and a payload 1250. The communication system will typically consist of a 1260 transceiver and a 1270 antenna. Of course, other components and arrangements can be used to implement the invention including, for example, redundant and auxiliary components.
    [0087] The maintenance subsystem of station 1210 is responsible for maintaining the satellite's orbit. Consequently, the state maintenance subsystem 1210 can calculate and / or receive attitude and / or orbit adjustment information, and can trigger the propulsion system to adjust the attitude and / or orbit of the satellite. Maintaining the orbit can also include maintaining the desired nodal separations between itself and the other satellites within the satellite constellation. The propulsion system 1220 may include, for example, a fuel source (i.e., fuel and oxidizer tanks) and the liquid fuel rocket, or an ion propellant system.
    [0088] The 1230 energy subsystem provides electrical energy to all satellite systems and subsystems. The 1230 power subsystem can, for example, include one or more solar panels and a support structure, and one or more batteries.
    [0089] The 1270 satellite antenna would be designed to accommodate the required communication frequencies and systems. Due to the physical size and weight limitations of the satellite, it would be much smaller than the 1110 antenna of the Gateway 610. The direction of the 1270 antenna beam is controlled by either mechanical antenna guidance or electronic antenna beam guidance. Alternatively, the satellite attitude can be controlled to orient the antenna.
    [0090] Similarly, the satellite transceiver 1280 is designed to be complementary to that of Gateway 610, consisting of a receiver portion to receive data from Gateway 610 and prepare it for CPU 1240, and a transmission portion to process data at from CPU 1240, preparing them for transmission to Gateway 610 via antenna 1270. The transmission portion of transceiver 1260 can, for example, multiplex, encode and compress the data to be transmitted, then modulate the data to the frequency desired transmission and amplify them for transmission. Multiple channels can be used, error correction coding, and the like. The receiving portion of transceiver 1260 demodulates received signals and performs any necessary demultiplexing, decoding, decompression, error correction and signal formatting from antenna 1270, for use by the 1240 satellite CPU. The antenna and / or receiver may also include any other computers, filters, low-noise amplifiers, drop converters (for example, for an intermediate frequency and / or baseband), and other components.
    [0091] The CPU system 1240 of the satellite 300, 330, 910 typically receives signals used for operation of the attitude and orbit control systems. It also receives control signals for 1250 payload operation, and processes payload data for transmission to Gateway 610. It can also manage the activation and deactivation of the various subsystems as the satellite 300, 330, 910 passes into and out of the geographic region of interest. OPTIONS and ALTERNATIVES
    [0092] In addition to the meteorological implementations described above, the system of the invention can be applied at least to the following applications: 1. Military UAVs: the current requirement for Military UAVs specifies that an uplink rate of 10-20 Mbps (megabits per second) is supported. This can be accommodated by the system of the invention throughout the circumpolar region. The classic Tundra system requires more than two satellites to have continuous coverage of that area; 2. Polar cross air traffic must shift from geostationary communications to HF (high frequency) radio communications as it passes over the poles. The system of the invention could support broadband communications, navigation and surveillance with aircraft crossing the pole. There are currently 700 aircraft per month using polar routes and continuous coverage over the northern circumpolar region is required to improve the safety and efficiency of air traffic in the area; 3. Increase in satellite-based navigation: accuracy, integrity and reliability of satellite-based navigation systems (for example, GPS) can be improved by increasing or overlapping their signals with those from other satellites that disseminate error corrections and integrity information. This is particularly important for air traffic. Two such systems are in place, one in the United States (Remote Area Increase System) and one in Europe (European Geostationary Navigation Overlay System). Both are based on geostationary satellite systems and neither covers the entire circumpolar region where there is a recognized need for improved navigation; 4. Earth observation: In addition to meteorological observations, other Earth observation payloads can perform well in the described orbits and provide monitoring of any of the circumpolar regions including hyperspectral soundings and ocean color radiometry; 5. Situational Space Awareness: These payloads can detect space hazards such as fragments and asteroids as well as other satellites that can be considered dangerous; 6. Spatial Climatic Conditions: The orbits of the invention can withstand payloads of spatial climatic conditions that measure factors such as solar radiation, Van Allen belt radiation, and the Earth's ionosphere; 7. Link Between Satellites (ISL): ISL links are a feature derived from this invention. The satellite will be able to provide ISL links to other satellites that will behave as a relay station for communication with the terrestrial infrastructure; 8. Two Orbital Planes: For inclines below 90 ° the satellites will be able to operate in a dual orbital plane. With a dual orbital plane, a single terrestrial trail is possible which can improve the coverage of a specific area and provide flexibility in the placement of the terrestrial infrastructure; and 9. Minor Circumpolar Regions: The parameters of the invention can be easily optimized for smaller geographic regions such as latitudes above 65 ° or 70 °. It would be preferable to reduce orbital eccentricity to accommodate such changes in coverage. CONCLUSIONS
    [0093] One or more currently preferred modalities have been described as an example. It will be apparent to those skilled in the art that some variations and modifications can be made without departing from the scope of the invention as defined in the claims. For example, the selection of the slope depends on the balance between the required service area, the amount of fuel in the spacecraft and the launch mass of the payload. These parameters can be optimized to accommodate different priorities, without departing from the concept of the invention.
    [0094] The method steps of the invention can be incorporated into sets of machine executable codes stored in a variety of formats such as object code or source code. Such code can be described generically as programming code, software or a computer program for simplification. The modalities of the invention can be performed by a computer processor or similar device programmed in the manner of method steps, or they can be performed by an electronic system that is provided with mechanisms to perform these steps. Similarly, an electronic memory medium such as computer diskettes, hard drives, thumb drives, CD-ROMs, Random Access Memory (RAM), Read-Only Memory (ROM) or similar computer software storage medium, known in the technique, can be programmed to perform such method steps.
    [0095] All citations are incorporated by reference.
    权利要求:
    Claims (15)
    [0001]
    1. Satellite system for Earth observation and communications, characterized by the fact that it comprises: a constellation of two satellites (300, 330), which together provide continuous coverage with 20 ° of elevation or greater throughout a geographic area of service above 60 ° latitude; each satellite (300, 330) having an orbital inclination between 70 ° and 90 ° and an orbital eccentricity between 0.275 and 0.45; and a base station (610) for transmitting to, and receiving signals from the constellation of two satellites (300, 330); in which the orbital eccentricity and orbital inclination are calculated to obtain an apogee over a polar region of interest, and a perigee which minimizes exposure to the Van Allen proton belt.
    [0002]
    2. System, according to claim 1, characterized by the fact that the orbital inclination is between 80 ° and 90 °.
    [0003]
    3. System, according to claims 1 and 2, characterized by the fact that the orbital eccentricity is chosen to have a high enough peak over the geographic service area to provide coverage for the required period of its orbit.
    [0004]
    4. System according to any one of claims 1 to 3, characterized by the fact that the orbital eccentricity is between 0.30 and 0.34.
    [0005]
    5. System according to any one of claims 1 to 4, characterized by the fact that it also comprises a third satellite (910).
    [0006]
    6. System according to any one of claims 1 to 5, characterized by the fact that the satellites (300, 330) have an orbital period of 24 hours.
    [0007]
    7. System according to any one of claims 1 to 6, characterized by the fact that directional antennas are used for communications between satellites (300, 330) and the base station (610).
    [0008]
    8. System according to any one of claims 1 to 7, characterized in that the base station (610) is operable to track satellites (300, 330) across the sky, and the base station (610) is operable for carry out communications handoff between satellites (300, 330) as they move across the sky.
    [0009]
    9. System according to any one of claims 1 to 8, characterized by the fact that the satellites (300, 330) move in the same orbital plane.
    [0010]
    10. System according to any one of claims 1 to 9, characterized by the fact that the perigee's argument is 270 °.
    [0011]
    11. System according to any one of claims 1 to 9, characterized by the fact that the perigee argument is 90 ° so that the apogee is in the southern hemisphere and the perigee is in the northern hemisphere.
    [0012]
    12. Method of operation for a satellite system for Earth observation and communications, characterized by the fact that it comprises: providing a constellation of two satellites (300, 330), which together provide continuous coverage of 20 ° of elevation or greater across a geographic service area above 60 ° latitude, each satellite (300, 330) having an orbital inclination between 70 ° and 90 ° and an orbital eccentricity between 0.275 and 0.45; and providing a base station (610) for transmitting to, and receiving signals from, the constellation of two satellites.
    [0013]
    13. Satellite base station (610), characterized by the fact that it comprises: communication mechanisms (1110, 1120) to transmit and receive signals to and from a constellation of two satellites (300, 330), which together provide coverage continuous elevation of 20 ° or more across a geographic service area above 60 ° latitude; and flight control mechanisms to control the orbits of the constellation of two satellites (300, 330), each satellite (300, 330) having an orbital inclination between 70 ° and 90 ° and an orbital eccentricity between 0.275 and 0.45.
    [0014]
    14. Satellite, comprising: communication mechanisms (1260, 1270) to transmit and receive signals to and from a base station (610); the satellite characterized by the fact that it additionally comprises: a payload of communication and observation of the Earth (1250) to serve a geographic service area above 60 ° latitude, with an elevation of 20 ° or greater; and flight control mechanisms (1210, 1220) to control an orbit to have an orbital inclination between 70 ° and 90 ° and an orbital eccentricity between 0.275 and 0.45.
    [0015]
    15. Launch vehicle comprising: an aerodynamic payload casing (930) the vehicle characterized by the fact that it additionally comprises: two or more satellites (300, 330) configured as defined in claim 19, positioned within the aerodynamic payload casing (930); and propulsion mechanisms to launch the two or more satellites (300, 330) into an orbit in the same orbital plane.
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    同族专利:
    公开号 | 公开日
    AU2011308037A1|2013-05-23|
    CA2716174C|2019-11-26|
    US9344182B2|2016-05-17|
    US20160137317A1|2016-05-19|
    CN103298695A|2013-09-11|
    JP2013540639A|2013-11-07|
    EA025745B1|2017-01-30|
    US20140017992A1|2014-01-16|
    JP6391650B2|2018-09-19|
    EP2621813A1|2013-08-07|
    EP2621813B1|2018-07-25|
    ZA201302774B|2018-12-19|
    JP2016222246A|2016-12-28|
    CA2834926C|2018-11-06|
    ES2692181T3|2018-11-30|
    CN103298695B|2016-10-19|
    ES2871080T3|2021-10-28|
    BR112013007565A2|2016-08-02|
    AU2011308037B2|2016-10-06|
    NZ608940A|2015-06-26|
    US10875668B2|2020-12-29|
    CA2834926A1|2012-04-05|
    WO2012040828A1|2012-04-05|
    CL2013000845A1|2014-04-11|
    EP2621813A4|2016-10-12|
    CA2716174A1|2012-04-01|
    EA201390511A1|2013-07-30|
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    法律状态:
    2018-12-26| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2019-11-12| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2020-12-22| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2021-03-09| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 30/09/2011, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    CA2716174A|CA2716174C|2010-10-01|2010-10-01|Satellite system|
    CA2,716,174|2010-10-01|
    PCT/CA2011/001093|WO2012040828A1|2010-10-01|2011-09-30|Satellite system and method for circumpolar latitudes|
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