Simplified inter-satellite link communications using orbital plane crossings to optimize inter-satellite data transfer
阅读说明:本技术 使用轨道平面交叉来优化卫星间数据传送的简化的卫星间链路通信 (Simplified inter-satellite link communications using orbital plane crossings to optimize inter-satellite data transfer ) 是由 泰盖·罗伯特·斯派德尔 安德鲁·J·格伯 于 2018-03-02 设计创作,主要内容包括:在一种用于卫星间通信的方法和设备中,卫星和共享轨道平面的相邻卫星之间的发射经由后置天线或前置天线发生,且所述卫星和不共享轨道平面的相邻卫星之间的发射经由在轨道平面交叉期间定时的所述后置天线或所述前置天线发生。即使总路径长度和链路数目高于使用边到边传送的卫星间通信时,也发生这种情形。(In a method and apparatus for inter-satellite communication, transmissions between a satellite and an adjacent satellite sharing an orbital plane occur via a rear antenna or a front antenna, and transmissions between the satellite and an adjacent satellite not sharing an orbital plane occur via the rear antenna or the front antenna timed during orbital plane crossings. This situation occurs even when the total path length and number of links are higher than when inter-satellite communication using edge-to-edge transmission is used.)
1. A method of operating a communication system to transmit a message from a source device to a destination device, the method comprising:
obtaining a message at a satellite;
obtaining a message path for the message at the satellite, wherein the message path accounts for orbital motion of the satellite and other satellites in a constellation;
determining, at the satellite, a next satellite in the constellation based on the message path, the next satellite selected from a back satellite, a front satellite, a west cross-plane satellite, or an east cross-plane satellite; and
sending the message from the satellite to the next satellite, wherein the message path indicates the next satellite.
2. The method of claim 1, wherein obtaining the message path comprises computing the message path on the satellite.
3. The method of claim 1, wherein obtaining the message path comprises computing the message path at a surface location, the method further comprising including a representation of the message path with the message.
4. The method of claim 1, further comprising:
causing the message to be communicated from a downlink satellite to a ground station; and
if the message path includes the ground station, causing the message to be communicated from the ground station to an uplink satellite.
5. The method of claim 1, further comprising:
storing the message at the satellite for a predetermined time period before sending the message to the next satellite.
6. The method of claim 5, wherein the predetermined time period is specified in the representation of the message path.
7. The method of claim 5, wherein the predetermined time period is determined in accordance with orbital parameters and corresponds to one pass in a beam path of a cross-plane satellite in the satellite.
8. The method of claim 1, wherein each satellite in the constellation has a distinct orbital plane and the constellation is arranged in a spiral.
9. The method of claim 1, wherein the message path contains only links between cross-plane satellites when in-plane antennas are available to communicate the message.
10. A system for delivering a message from a source device to a destination device, comprising:
a processor for calculating a message path for a message;
a plurality of satellites in a constellation, wherein a satellite is configured to receive and transmit messages to other satellites in the constellation;
storage means for a message path for the message, wherein the message path takes into account the orbital motion of the satellite and other satellites in the constellation;
a first antenna for transmitting and receiving messages between the satellite and a back-mounted in-plane satellite or a back-mounted cross-plane satellite;
a second antenna for transmitting and receiving messages between the satellite and a pre-planar or pre-cross-planar satellite;
logic for determining, at the satellite, a next satellite in the constellation based on the message path, the next satellite selected from a postpositional in-plane satellite, a prepositioned in-plane satellite, a postpositional cross-plane satellite, or a prepositioned cross-plane satellite; and
and a radio frequency transmission system for transmitting or receiving the message between the satellite and the next satellite based on the message path.
11. The system of claim 10, further comprising a program code memory.
12. The system of claim 10, wherein obtaining the message path comprises calculating the message path at a surface location and including a representation of the message path with the message.
13. The system of claim 10, further comprising:
causing the message to be communicated from a downlink satellite to a ground station; and
if the message path includes the ground station, causing the message to be communicated from the ground station to an uplink satellite.
14. The system of claim 10, further comprising:
a clock for at least timing storage of messages as indicated by the representation of the predetermined period specified by the message path.
15. The system of claim 14, wherein the representation of the predetermined time period for timing the transmission of the message is specified in the representation of the message path.
16. The system of claim 14, wherein a representation of a predetermined period of time for timing message transmissions is determined from orbital parameters and corresponds to one pass across a planar satellite in a beam path of the satellite.
17. The system of claim 10, wherein each satellite in the constellation has a distinct orbital plane and the constellation is arranged in a spiral.
18. The system of claim 10, wherein the message comprises a representation of an SMS message, a data packet, or at least a portion of a digitized audio signal.
19. The system of claim 18, wherein the digitized audio signal comprises a voice signal.
20. A satellite for use in a constellation of satellites, capable of inter-satellite message forwarding and having an orbital plane, the satellite comprising:
a processor;
memory storage for messages;
memory storage for a representation of at least a portion of a message path, wherein the message path indicates a plurality of satellites in the constellation via which the message is to be forwarded, wherein at least two of the plurality of satellites indicated in the message path are in distinct orbital planes and thus are cross-plane satellites with respect to each other;
a rear-mounted antenna for transmitting and receiving messages between the satellite and a rear in-plane satellite or a rear cross-plane satellite;
a front-mounted antenna for transmitting and receiving messages between the satellite and a front-mounted in-plane satellite or a front-mounted cross-plane satellite;
a radio frequency transmission system for receiving the message from the satellite via the back antenna or the front antenna and sending the message to a next satellite;
program code stored in a memory accessible by the processor, wherein the program code is executable by the processor and comprises:
a) program code for initiating receipt of the message;
b) program code for initiating transmission of the message;
c) program code for calculating, obtaining, or extracting the representation of at least a portion of the message path, wherein calculation of the representation of at least a portion of the message path takes into account orbital motion of the satellite and other satellites in the constellation; and
d) program code for determining, at the satellite, which of the satellites in the constellation will be the next satellite based on the message path, the next satellite selected from the group consisting of the back in-plane satellite, the front in-plane satellite, the back cross-plane satellite, or the front cross-plane satellite, wherein the determination takes into account orbital plane crossings.
Technical Field
The present disclosure relates generally to inter-satellite communication between satellites in orbit. The present disclosure more particularly relates to apparatus and techniques for performing multilink data transfers over multiple satellites, some of which may be in different orbital planes.
CROSS-REFERENCE TO PRIORITY AND RELATED APPLICATIONS
The present application claims priority of and non-provisional patent application No. 62/465,945 entitled "Method for Low Cost and Low Complexity Inter-Satellite Link Communications within a Satellite constellation Network for Near Real Time, Continuous and Global Connectivity (Method for Low-Cost and Low-Complexity Inter-Satellite Communications with a Satellite constellation networking for Near Real Time, Continuous and Global Connectivity)" filed on 3/2 of 2017. The entire disclosure of this application is hereby incorporated by reference for all purposes as if fully set forth herein.
United states patent application No. 15/857,073 entitled Method and Apparatus for Handling Communications Between a spacecraft operating in an Orbital Environment and a Terrestrial telecommunications device communicating using Terrestrial Base stations (Method and Apparatus for Handling Communications Between a spacecraft operating in an Orbital Environment and a Terrestrial telecommunications device using Terrestrial Base Station) filed 2017, 12, 28 is also incorporated by reference for all purposes as if fully set forth in this document.
Background
Communications using satellites provide advantages not available with terrestrial-based communications alone, but may also be subject to more constraints than terrestrial-based communications. For example, the satellites must remain in orbit a certain distance above the surface of the earth, one satellite cannot cover the entire surface of the earth at the same time, and the satellites move relative to the surface of the earth except for geostationary satellites. Thus, it is often necessary to use a constellation of satellites, and inter-satellite communication may be required where one ground-based user device needs to communicate with another ground-based user device, but they are not all within the coverage of one satellite. Geostationary satellites may have a coverage large enough that the entire earth surface may be covered by four satellite coverage, but in the case of Low Earth Orbit (LEO) satellites, the coverage may be approximately circular with a diameter of about 1,000 km. In this case, a constellation of about 1,000 to 2,000 satellites may be required in order to have a coverage that continuously covers the entire earth's surface in distinct orbital planes. Even in the case of geostationary satellites that orbit approximately in a plane containing the equator of the earth, full coverage is not easily achieved, since poles are not well covered by a geostationary satellite and it may be necessary to use constellations of dissimilar orbital planes, such as those of geostationary and polar satellites.
If the source device and the destination device are both within the coverage of one satellite, the source device may send data to the satellite by transmitting signals received by the satellite, and the satellite may send data to the destination device by transmitting signals received by the destination device. More conditions are needed if the source device and the destination device are not both within the coverage of one satellite. In this case, the data must be obtained from one overlay to another. More specifically, the link path from the source device to the destination device is more than the path from the source device to the satellite to the destination device.
In some approaches, the constellation includes multiple orbital planes and the arrangement of data communication satellites is done in a grid fashion, with data being transmitted from one satellite to another in front of the transmitter (referred to as north, but which may not be in the same direction as north on the surface of the earth below the transmitter), one satellite behind the transmitter (south), one side of the transmitter (west) or the other side (east). Although the rear and front receivers may be in a stable orientation with respect to the transmitter, the east and west satellites are in different orbital planes and therefore their orientation with respect to the transmitter varies. This may require a wideband antenna, which may be inefficient, expensive, and increase link, weight, and power budgets.
Satellite communication systems are often required to provide global or near-global coverage of the planet so that individuals and businesses can remain connected and receive/send information (i.e., telephone calls, messages, data, etc.) in near real-time or otherwise at any time.
Improved inter-satellite link communications may overcome some of the limitations described above.
Disclosure of Invention
In a method and apparatus for inter-satellite communication, transmissions between a satellite and an adjacent satellite sharing an orbital plane occur via a rear antenna or a front antenna, and transmissions between the satellite and an adjacent satellite not sharing an orbital plane occur via the rear antenna or the front antenna timed during orbital plane crossings. This situation occurs even when the total path length and number of links are higher than when inter-satellite communication using edge-to-edge transmission is used.
A method of operating a communication system to transmit a message from a source device to a destination device may comprise: obtaining a message at a satellite; obtaining a message path for the message at the satellite, wherein the message path accounts for orbital motion of the satellite and other satellites in a constellation; determining, at the satellite, a next satellite in a constellation selected from a back-facing satellite, a front-facing satellite, a west-crossing cross-plane satellite, or an east-crossing cross-plane satellite based on a message path; and sending the message from the satellite to the next satellite, wherein a message path indicates the next satellite. The message path may be computed at a satellite or at a terrestrial location, the method further comprising including with the message a representation of the message path.
If the message path includes a ground station, the method may include passing the message from the downlink satellite to the ground station and passing the message from the ground station to the uplink satellite. The message may be stored at the satellite for a predetermined period of time before being sent to the next satellite. The predetermined time period may be specified in a representation of the message path and/or determined in terms of orbital parameters and corresponds to one pass in the beam path of the satellite across the planar satellite, and the satellite will use the representation of the predetermined time period to time the message transmission.
In some variations, each satellite in the constellation has a distinct orbital plane, and the constellation is arranged in a spiral.
When in-plane antennas may be used to communicate messages, the message path may be explicitly limited to only links for cross-plane satellites.
A system for delivering a message from a source device to a destination device may comprise: a processor for calculating a message path for a message; a plurality of satellites in a constellation, wherein a satellite is configured to receive and transmit messages to other satellites in the constellation; storage means for a message path for a message, wherein the message path takes into account the orbital motion of the satellite and other satellites in the constellation; a first antenna for transmitting and receiving messages between the satellite and a back-mounted in-plane satellite or a back-mounted cross-plane satellite; a second antenna for transmitting and receiving messages between the satellite and a pre-planar or pre-cross-planar satellite; logic for determining, at the satellite, a next satellite in a constellation based on a message path, the next satellite selected from a postpositional in-plane satellite, a prepositioned in-plane satellite, a postpositional cross-plane satellite, or a prepositioned cross-plane satellite; and a radio frequency transmission system for transmitting or receiving messages between the satellite and the next satellite based on a message path.
The system may include one or more ground stations for repeating the message. The system may include a clock for use at least in timing the storage of messages as indicated by the representation of the predetermined period specified by the message path. The representation of the predetermined time period may be specified in the representation of the message path and/or determined in accordance with the orbital parameters and correspond to one pass in the beam path of the satellite across the planar satellite.
The message may comprise a representation of at least a portion of an SMS message, a data packet, or a digitized audio signal (e.g., a voice signal).
In some aspects, a satellite for use in a constellation of satellites capable of inter-satellite message forwarding and having an orbital plane is described, the satellite comprising: a processor; memory storage for messages; memory storage for a representation of at least a portion of a message path, wherein the message path indicates a plurality of satellites in a constellation via which to forward the message, wherein at least two of the plurality of satellites indicated in the message path are in dissimilar orbital planes and are thus cross-planar satellites with respect to one another; a rear-mounted antenna for transmitting and receiving messages between the satellite and a rear in-plane satellite or a rear cross-plane satellite; a front-mounted antenna for transmitting and receiving messages between the satellite and a front-mounted in-plane satellite or a front-mounted cross-plane satellite; a radio frequency transmission system for receiving the message from the satellite via a back antenna or a front antenna and sending the message to a next satellite; and program code stored in a program code memory accessible by the processor.
The program code may be executable by a processor and include: a) program code for initiating receipt of a message; b) program code for initiating transmission of a message; c) program code for calculating, obtaining or extracting the representation of at least a portion of a message path, wherein calculation of the representation of at least a portion of a message path takes into account orbital motion of the satellite and other satellites in the constellation; and d) program code for determining at the satellite which satellites in the constellation will be the next satellite based on the message path, the next satellite selected from a postpositional in-plane satellite, a prepositioned in-plane satellite, a postpositional cross-plane satellite, or a prepositioned cross-plane satellite, wherein the determination takes into account orbital plane crossings.
The following detailed description together with the accompanying drawings will provide a better understanding of the nature and advantages of the present invention.
Drawings
Various embodiments according to the present disclosure will be described with reference to the figures, in which:
fig. 1 shows a constellation of satellites in an orbital plane that may be used with aspects of the present invention.
Fig. 2 shows the relevant reference frames of the satellites.
FIG. 3 shows an example of device-to-satellite communications that may be used with aspects of the present invention.
Fig. 4 shows a constellation of satellites similar to the woker Delta Pattern constellation.
Fig. 5 shows a conventional message path on a wacker constellation.
Fig. 6 shows a satellite that may be used as one of the satellites in the constellation shown in fig. 5.
Fig. 7 illustrates an improved satellite that can handle inter-satellite communications in a constellation having a wobbe constellation arrangement or other multi-planar constellation.
Fig. 8 is a block diagram of elements of the satellite shown in fig. 7.
Fig. 9 shows an example of a message path following the plane of the track until cross-plane transmission using a front/rear antenna.
Fig. 10 shows the cross-plane transport in more detail.
Fig. 11 shows an example of a message path using a bent-tube link.
Fig. 12 shows an example of store-and-forward, which may also be used with the bent-pipe approach of fig. 11, with timed track plane crossings.
Fig. 13 shows the orbital mechanism of the spacecraft in the constellation.
Figure 14 illustrates neighboring satellite motion in a reference frame for a reference satellite of the same hypothetical satellite constellation of figure 13.
Figure 15 shows the juxtaposition of adjacent satellite positions within one period of their relative orbits.
Fig. 16 shows the timing resulting from the tracks shown in fig. 15 and 9.
Fig. 17 is a flow chart of a process that may be performed by a satellite handling a message.
Fig. 18 shows the geometry of the orbital mechanism of the spiral constellation.
Fig. 19 shows the geometry of the anterior and posterior directions relative to a reference satellite in a spiral constellation.
Fig. 20 shows a multiple pass spiral arrangement.
Fig. 21 is a flow chart of a process that may be performed on this spiral constellation by handling messages through satellites.
Fig. 22 is an illustration of the arrangement of helical satellites.
Detailed Description
In the following description, various embodiments will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the embodiments. However, it will also be apparent to one skilled in the art that the embodiments may be practiced without the specific details. Furthermore, well-known features may be omitted or simplified in order not to obscure the described embodiments.
The technology described and presented herein includes novel arrangements for inter-satellite communications and terrestrial-to-satellite communications. In many examples herein, communication involves the transfer of data from one device to another device via one or more other devices or systems. In this disclosure, a path may be described using parentheses (e.g., "{ }") such as {
Mobile communications involve sending signals between a Mobile Station (MS) and a transceiver, which may provide an interface for the MS to communicate to and from other network resources, such as a telecommunications network, the internet, etc., to carry voice and data communications, and possibly a location finding feature, possibly for eventual communication between two mobile stations. Examples of mobile stations include mobile telephones, cellular telephones, smart phones, and other devices equipped to communicate wirelessly. Although the mobile station is referred to by this name herein, it should be understood that the operation, function, or characteristic of the mobile station may also be that of a station that is actually or functionally the mobile station, but is not currently mobile. In some examples, a mobile station may actually be considered a portable station that can move from one place to another but is stationary in operation, such as a laptop computer with several connected peripherals and with a cellular connection; or the mobile station may be stationary, such as a cellular device embedded in an installed home security system. It is only necessary that the mobile station be capable of or configured to communicate in at least one mode in a wireless manner.
For simplicity of explanation, in many examples herein, communication is described as between a first device and a second device, but it is understood that interaction may be from the first device to the first device or a device attached to the first device's wireless circuitry, to the first device's antenna (each implemented in hardware, firmware, and/or software), and a corresponding path at the second device end. In some variations, there are more than one first device and/or more than one second device, so the examples herein may be extended to broadcast mode.
The apparatus may use GSM (global system for mobile communications; registered trademark by GSM alliance) 2G + protocol with Gaussian Minimum Shift Keying (GMSK), EDGE protocol with GMSK, 8-PSK keying, etc. With the spectral band logically divided into a spectrum of carriers, a device may use a channel that communicates using one (or more) of those carrier frequencies. Other variations of communication are possible.
Generally, as described herein, the communication path between a first device and a second device is {
Communication refers to communicating a signal by propagating electromagnetic energy, e.g., within a frequency range for antenna-to-antenna transfer, optical transmission, etc., of the signal, where the signal communicates or transfers data from a source device to a destination device. As used herein, "data" may represent binary data, voice, image, video, or other forms of data, possibly including information and redundant data for error detection and correction. The source device and/or destination device may be mobile devices (designed to be easily carried and used in motion), portable devices (designed to be easily moved, but typically used while stationary), or stationary devices used at the site of installation. The size of the source device and/or destination device may vary from a smartphone to a building having an antenna attached or otherwise connected to electronics in or around the building. In the examples herein, at least one satellite (i.e., a man-made object in orbit around a celestial body capable of electronic communication) is in a path from a source device to a destination device.
A "message," as used herein, may be represented by a data structure that is communicated from a source device or system to a destination device or system. In some cases, the source and destination of the message are ground-based, such as a mobile device or a communications gateway to other terrestrial destinations. In other cases, the message is a control message, which is a message to or from a satellite. The data structure represents data to be communicated. In one example, the message comprises a sequence of 160 characters, like an SMS message. Some communications may include multiple messages intended for reintegration, such as packet-based communications. In some terms, a message having more than one source and/or more than one destination may be considered multiple messages each having one source and one destination.
The satellite runs in an orbit, which is a path in space of the satellite around a celestial body that can be at least approximatelyIs determined from the initial position and velocity of the satellite, and from the propulsive or other forces applied to or impinging on the satellite, and may be maintained, at least approximately and over a period of time, in a balance between the gravitational force of the celestial body and the tangential motion of the satellite along the orbital path. The trajectory may be specified by a small number of parameters, such as a set of kepler roots: inclination (i), longitude (omega) of ascending node, argument of near arch (omega), eccentricity (e), semi-major axis (a) and true nearing angle of duration (M)0). In general, the orbit may be considered planar, and satellites that are not under propulsive force or that are affected by forces other than gravity may be considered orbiting in a plane with a predictable path, orbital period, etc. The satellite may be equipped with a rocket or other propulsion means to allow the satellite to maintain its position in its orbit in its orbital plane.
In the case where the orbit of the satellite defines a curve in space that is a plane curve, the orbital plane is a plane in some reference frame in which the satellite operates. In some cases, the orbital plane may drift slightly, and the satellite may change slightly with respect to its path and still be considered to be traveling in the orbital plane. In earth orbit, the orbital plane may correspond to a great circle and may be determined entirely from the two parameters of inclination and longitude of the orbiting satellite in the orbital plane.
Examples of orbits include Low Earth Orbit (LEO), in which a satellite traveling at 7.45 to 7.61 km/sec relative to the earth's surface follows an elliptical path about 500 to 700km above the earth's surface; a Medium Earth Orbit (MEO) in which satellites traveling at 5.78 to 6.33 km/sec relative to the earth's surface follow an elliptical path about 4,000 to 5,000km above the earth's surface; or geosynchronous orbit, in which a satellite traveling at about 3.1 km/sec relative to the surface of the earth follows an elliptical path about 35,800km above the surface of the earth.
At a particular time and/or orbital location, there is a region on the surface where mobile devices or other devices or systems can communicate with the satellite, provided they are within a particular range of the satellite (and possibly in line of sight as needed) and meet other requirements. The area on the ground where such devices are present is called the "footprint" of the satellite. This definition need not be exact, and there may be situations where the terrestrial device is in the coverage plane in some cases and out of the coverage plane in other cases for the same terrestrial location, satellite location, and other factors. There may also be different coverage levels, for example, higher speed data communications may be achieved when the satellite is overhead, lower speed data communications may be achieved when the satellite is at a lower angle relative to the surface plane, and no communications may be achieved when the satellite is below the horizon, in which case there will be "high speed coverage" and "low speed coverage", the latter presumably being greater than the former. The coverage of a satellite is said to cover an area or device if the satellite is in a position where direct communication between the ground-based device and the satellite is possible.
A group of two or more satellites in orbit and positioned to provide a greater communication range than a single satellite is often referred to as a constellation. The relative positions and positions over time and velocities of the individual satellites in the constellation may be based on a constellation coverage plan that provides a larger constellation coverage than one satellite can provide. For example, if coverage is required to enable continuous communication between 20 degrees north to 20 degrees south of latitude with a ground device having a fixed directional antenna, a constellation coverage plan may require a constellation of six geostationary satellites. One example of a constellation used herein for purposes of explanation is a wobbe triangle pattern constellation. After reading this disclosure, it should be apparent how an example referring to one constellation may be implemented in a similar constellation. The constellation may be optimized for imaging, communications, exploration, or other tasks, and may be oriented in polar orbits, equatorial orbits, oblique orbits, low orbits, high orbits, eccentric orbits, and the like.
Fig. 1 shows a constellation of sixteen song satellites 102 (numbered 1 through 16) all in one orbital plane that may be used with aspects of the present invention. If each satellite has a
However, if source device S106 and destination device D108 are both within the constellation coverage plane, the communication path may be { device S,
Satellite-based terrestrial communications may involve data transmissions from a source device on the ground to a satellite system in orbit that receives the data transmissions, may process the received data, and transmit the data to a destination device. The source device may not be the original source of the data and the destination device may not be the final destination of the data because there may be additional ground-based communication elements present before the source device and/or after the destination device. Communications via a satellite system may include multiple links between satellites and/or terrestrial repeaters, which are ground-based devices that receive data transmissions from one satellite and forward them to another satellite.
It is often useful to consider the reference frame of the satellite, for example when positioning the satellite using directional antennas, navigation, etc. A reference frame is a coordinate space defined relative to a physical object or aspect of a physical object, where the object or aspect is stationary (i.e., the coordinates of various points on the object or aspect do not substantially change over a relevant time period), such as a geocentric reference frame, where the center of mass of the earth is stationary in the coordinate space of the geocentric reference frame and the angle between the earth and a remote star is constant (although the earth's surface is of course not stationary in the reference frame); a frame of reference of the earth's surface, wherein the earth's surface is substantially stationary; or a satellite reference frame, wherein the main structural elements of the satellite are stationary in the coordinate space of the satellite reference frame.
Fig. 2 shows the
In designing an antenna for a satellite, the reference frame may be used to determine antenna requirements. In the reference frame of the satellite, other satellites in the same orbital plane in the same orbit but advanced or delayed in time/position will appear more or less stationary, while satellites in east/west orbits will appear to move in figure-8 in the reference frame of the satellite. Typically, for east/west orbits, this would require a wide angle antenna or steerable antenna.
FIG. 3 shows an example of device-to-satellite communications that may be used with aspects of the present invention. As shown here,
Fig. 4 shows a constellation of satellites similar to the wobbe triangle pattern constellation. The satellite is represented by a point on a line that crosses the sphere, and the line represents the orbital path of the satellite. Satellites on one orbital path are said to be in-plane because the orbital paths shared by the satellites (even though spaced apart in time) at least approximately form an orbital plane. For purposes of explanation, only four
In the reference frame of a given satellite, two adjacent satellites in the same orbital plane may be referred to as the "front satellite" and the "back satellite" (or the "north satellite" and the "south satellite," respectively), while adjacent satellites in adjacent or nearby orbital planes may be referred to as the east satellite and the west satellite. As is known from orbital mechanisms, east and west satellites that are in different orbital planes than a given satellite will not appear stationary in the reference frame of the given satellite. In fact, if in stable orbit, the east and west satellites will appear to travel in a wide "figure 8" pattern on the course of the orbit in the reference frame of a given satellite, while the leading and trailing neighboring satellites in the same orbital plane will be more or less at the same position in the reference frame of the given satellite.
Fig. 5 shows a conventional message path on a wacker constellation. As in fig. 4, the visible satellites are shown as points on a line representing the orbital plane. The corresponding coverage of the satellite is also shown in fig. 5. Because the satellite coverage areas overlap, continuous coverage can be implemented on the surface of the earth.
As shown, source device 502 is within
In this illustration, the message path follows a sequence of links, and the inter-satellite links are to adjacent or neighboring satellites. For a constellation of satellites all in one orbital plane, it is possible that their common coverage provides good coverage for the surface strips and for a given satellite, neighboring satellites being in the same orbital plane and thus they remain stationary in the reference frame of the given satellite. Thus, a simple, highly directional antenna may be used for satellite-to-satellite transmissions. To obtain further coverage, a satellite in one orbital plane may need to transmit to a satellite in another orbital plane, for example if the destination device is outside the common coverage area of the satellites in the orbital plane that covers the source device. This is shown in fig. 5. In the method of fig. 5, a side (in this example, eastward) wide angle antenna to a second satellite in a different orbital plane is required.
Fig. 6 shows a satellite 602 that may be used as one of the satellites in the constellation shown in fig. 5. The satellite 602 includes various antennas in addition to electronics, solar power generation, propulsion, maintenance, and other satellite details not shown. Fig. 6(a) shows the front antenna 604 facing in the direction of travel of the satellite 602 (i.e., more or less in the direction of the velocity vector of the satellite 602). The rear antenna 606 faces in the opposite direction of the operation of the satellite 602. East antenna 608 (i.e., an antenna that faces more or less in a direction perpendicular to a radial vector of satellite 602 and perpendicular to a velocity vector of satellite 602, which is conventionally referred to as "east," but may not be correlated with the east-facing direction on the surface of the earth) is shown, and satellite 602 also has a west antenna 610, not shown. Fig. 6(B) shows a view from below at satellite 602, where west antenna 610 is shown. Terrestrial antenna 612 is used for communication between satellite 602 and ground devices or ground stations (e.g., stations 622 on the surface of the earth 620), while front antenna 604, rear antenna 606, east antenna 608, and west antenna 610 are used for inter-satellite communication within the constellation.
Inter-satellite communication between a satellite and its west and east neighbors in different orbital planes can be cumbersome because the positions of the neighbors change relative to the reference frame of the satellite. The inter-plane connection typically uses multiple low-gain wide beam width antennas for east 608 and west 610 antennas to handle relative motion to the west and east neighbors. This may limit the data rate and/or increase the power requirements in the inter-plane link budget. The data rate may be increased via increased transmit power, but this may complicate the power budget requirements. The satellite 602 may use a higher gain, narrower beamwidth steerable antenna to steer west and east neighbors in the current direction and change the orientation as those neighbors travel in the reference frame of the satellite 602. The pointing of such antennas may be controlled in an active feedback loop or pointed in a direction determined by the predicted position of the neighbors predicted from the orbital mechanism. Phased array antennas may be used to steer the antenna beam digitally to reduce the risk of mechanical failure on the spacecraft, but still result in increased complexity and quality on the satellite 602 because high-gain narrow beam-width antennas are larger than low-gain wide beam-width antennas.
Unlike east antenna 608 and west antenna 610, front antenna 604 and rear antenna 606 are simpler to implement. With a suitable attitude control system, the front and back satellite neighbors remain approximately static in the reference frame of the satellite 602, and thus very high gain and very narrow beam width antennas can be used without requiring complex steering capabilities, and they can provide a high data rate link in both directions. At high enough frequencies, very high gain patch antennas may still be small enough to fit on the surface of even 1U-sized nano-satellites (i.e., 35dB gain V-band, or 60GHz antennas, which may have a diameter of about 10 cm).
Fig. 7 illustrates an
Fig. 8 is a block diagram of elements of a
As shown,
Other elements, such as a control system, may be handled by
One aspect of the operation of
Each message may have a message path, and the path of the message may be provided explicitly with the message, or may be determined by program steps performed on the satellite or elsewhere. Regardless of how calculated, the message path follows the orbital plane until appropriate cross-plane transmission can be achieved using the front/rear antennas. The message path may be stored at the satellite and used to determine which antenna to use to retransmit and thus forward the received message.
Fig. 9 shows an example. As shown, the source device S902 is within the
Depending on design considerations, inter-plane transfer may be limited to adjacent planes. For example, a message path may require a link from a satellite in orbital plane 920(1) to a satellite in orbital plane 920(2), then to a satellite in orbital plane 920(3), then to a satellite in orbital plane 920 (4). Alternatively, the message path may skip one or more adjacent track planes. In some cases, it may be preferable to limit the link to one orbital plane at a time, as the closer the orbital planes are, the longer the cross-plane satellite may remain in range. In some variations, the message path may skip adjacent orbital planes, and may also skip adjacent satellites in the same orbital plane as desired.
The
The
Fig. 10 shows the cross-plane transport in more detail. As shown here,
In combination with other link types
As described above, a message path may follow an uplink from a source device on the ground to a satellite, through one or more inter-satellite links intersecting an orbital plane as needed, and follow a downlink from the satellite to a destination device. Inter-satellite links may also be combined in the message path with "bent pipe" links and "store and forward" links.
Using the bent-tube path, the satellite receives data from the source device and forwards the data to a terrestrial repeater within the coverage of the satellite. The terrestrial repeater used will be a terrestrial repeater that is also in the coverage of the second satellite and that forwards the data to the second satellite. The second satellite may transmit data to the destination device if the destination device is within a coverage area of the second satellite. If the destination device is not within the coverage of the second satellite (and the coverage of any satellites in which the source and destination devices are located do not overlap), the second satellite may send data to another ground station, which would then forward to a third satellite, and so on, until the satellite with the coverage enclosing the destination device is reached. This may involve appropriately placed terrestrial repeater sites. The message path may be { source device,
Fig. 11 shows an example of a message path using a bent-tube link. There is shown a source device S1102, a
In this example, the source device S1102 sends a message to the destination device D1116, and those devices are located at transmission time for some reason or other, making it more desirable to use the ground station 1108 as compared to a full satellite-based link set. In this case, the message path is { source device S1102,
It is possible that the ground station 1108 does not bridge the track path. For example,
Another approach is the "store and forward" approach. This method takes into account that the coverage of the satellite is running over the surface (excluding geostationary satellites of course) and thus at one point in time the coverage of the satellite may cover the source device but not the destination device, but at a later point in time the satellite already running in its orbit may cover the destination device while the source device is outside the coverage of the satellite. In this scenario, the transmission of data is from the source device to the satellite while the source device is within the coverage area of the satellite, the satellite stores the data for a period of time, and then later when the destination device is within the coverage area of the satellite, the satellite sends the data to the destination device. This can result in large latencies in the transmission process due to the time it takes for the satellite to travel in its orbit to a new position. The particular store-and-forward delay period between reception from the source device and transmission to the destination device may be determined by a computer process executed by the device, satellite, or elsewhere and communicated to the device/satellite that needs to know the link path in order to properly time the forwarding or transmission of the data. The computer process may run in real-time or may run in advance to derive a data table for determining message paths and storage time requirements based on device/satellite locations. In this approach, the message path may be { source device,
Fig. 12 shows an example of using store-and-forward, which may also be used with the bent-pipe approach of fig. 11, with timed track plane crossings. This may be useful in keeping messages more cost effective than transmitting messages across many links in the orbital plane. As illustrated herein,
With store-and-forward, the satellite may also store/hold messages to allow time for better alignment across the planar satellite. It is possible that a first satellite in one orbital plane will transmit a message to a second satellite in another orbital plane and the first satellite will hold the message for a short period until the second satellite is close to the orbital plane of the first satellite. In the more general case of the message path, there is an intervening delay, e.g., message path { source device,
Inter-satellite link geometry
When using inter-satellite links, the geometry of the communication link is driven by the orbital mechanism of the spacecraft in the constellation. In the reference frame of a certain reference satellite (referred to herein as a "reference satellite") in the constellation, the forward, rearward, eastward and westward neighboring satellites actually orbit around the reference satellite, completing one revolution around the reference satellite for each orbit around the earth.
This is illustrated in fig. 13, which shows adjacent satellites in the reference frame of a reference satellite in a hypothetical constellation of satellites tilted 51.6 degrees in motion. Typically, spacecraft are equipped to maintain a particular orientation in space when they are operating in orbit. In the reference frame of an orbiting spacecraft, the axis of the spacecraft body frame is maintained in alignment with the spacecraft velocity vector, the nadir vector (toward the earth's surface, in the opposite direction to the radial vector), and the orbital angular momentum vector. The nadir vector does not always differ from the radial vector by exactly 180 degrees, but upon reading this disclosure it should be apparent that one of the reference frame axes may be parallel to the nadir vector or parallel to the radial vector, as long as a non-identical correspondence thereof is observed.
In this reference frame, the relative positions of the forward, rearward, east-ward and west-ward neighbors orbit around the reference satellite, with the forward and rearward neighbors remaining in near-static positions forward and rearward of the reference satellite, respectively. East and west neighboring satellites travel in figure-8 motion-following a four-quarter bean loop-where they travel cyclically and almost completely in the direction of the orbital angular momentum vector of the reference satellite.
Figure 14 shows adjacent satellites in the reference frame of a reference satellite of the same hypothetical satellite constellation tilted 51.6 degrees in motion. This cyclic motion forms trajectories for east (E) and west (W) neighboring satellites to pass above and below the velocity vector of the reference satellite, crossing the velocity vector in front of and behind the reference satellite, respectively. The front (F) and back (a) neighbors remain relatively stationary in the reference frame. In other configurations and possibly elsewhere in the constellation, satellites that are considered east-bound neighbor satellites may be figure-8 in the backward direction, and satellites that are considered west-bound neighbor satellites may be figure-8 in the forward direction.
Figure 15 shows the juxtaposition of adjacent satellite positions within one period (cycle) of their relative orbits. The left column shows the geocentric reference frame locations of the reference satellite and the forward, rearward, eastward and westward neighbors. The second column shows the same satellite positions, but in the reference frame of the reference satellite. The rows indicate the relative positions of the satellites over time, where fig. 15(a) represents the time that the reference satellite is at the rising node, fig. 15(B) represents the time that the reference satellite has elapsed 90 degrees from the rising node, fig. 15(C) represents the time that the reference satellite is at the falling node, and fig. 15(D) represents the time that the reference satellite has elapsed 90 degrees from the falling node.
Fig. 16 shows the timing resulting from the tracks shown in fig. 15 and 9. The transmission of messages between satellites need only be in the forward and backward directions. Cross-plane communication occurs at a cross-plane location in the constellation, which may be a point in the satellite orbit approximately 90 degrees before both its rising and its falling nodes. These points in space are graphically illustrated in fig. 15(B) and 15(D), and are also shown in fig. 16(B) and 16 (D). Thus, messages or signals to be routed via inter-plane communications pass forward or backward to a satellite in its plane that is flying 90 degrees before its ascending (or descending) node. This satellite is in a position such that its front antenna points in the direction to the east and front adjacent satellites, and the rear antenna points in the direction to the west and rear adjacent satellites. Depending on the required change in plane, the satellite will route its messages forward to the eastern satellite or backward to the western satellite. If more than one plane change is required, the satellite receiving the inter-plane communication may then pass the message to another plane using its front or rear antenna. Once the message has been routed to the destination plane, the message can be delivered within the plane using the forward and reverse links in that plane until the message reaches the satellite intended to transmit the message down the downlink to the device of the recipient.
Fig. 17 is a flow chart of a process that may be performed by a satellite handling a message. In
In
The satellite then waits for another message, and/or performs other tasks, at
Spiral constellation
Instead of distinct orbital planes, the satellites may be arranged such that each satellite is in a separate plane, but adjacent satellites are stationary in the reference frame of the satellite, albeit slightly to one side. The satellites in this constellation thus form a spiral such that each other satellite can arrive from the originating satellite using only the forward and reverse links.
Each satellite in the spiral may be considered to be in its own "plane" because it is similar to winding around a sphere, with each successive winding/spiral being slightly offset from the previous winding/spiral. Although the true proximal angles of the satellites in the orbital spiral are equally spaced across 360 degrees, the elevation node of each satellite is shifted west as the true proximal angle increases (i.e., continuously wraps around the ball). The result is that the last satellite in any spiral is approximately directly behind (in the direction of the velocity vector) the first satellite in the next spiral.
Fig. 18 shows the geometry of the orbital mechanism of this constellation configuration. It should be noted that this orbital configuration may be reversed such that as the true anomaly increases, the elevation node of each satellite is shifted east within each spiral. In other words, the continuous wrapping around the ball may be east or west facing and achieve a similar goal.
This orbital architecture is advantageous because it creates a satellite system in which all satellite nodes are connected in a single global string. With this design, each satellite orbits the earth in its own unique plane in inertial space, and thus, any messages passing in the forward direction are also passed in the westward direction, and any messages passing in the backward direction are also passed in the eastward direction. This fact means that the satellite network is never required to efficiently decide whether it has to pass messages between planes to deliver the data payload to the intended recipient on the earth's surface. In practice, the only satellite that needs to transmit the data payload down the downlink to the recipient is a certain number of forward or backward passes in the satellite network, or a certain number of outward spirals.
This also has a beneficial effect on the ground system requirements. With a globally connected satellite string, individual global ground segments are not required to provide connectivity between satellite orbital planes. In fact, a minimum of one ground station (possibly two, for redundancy) is required to connect to all the satellites in the network to reach the ground. Of course, in some configurations, there are also satellites that share an orbital plane and are used in the manner described herein.
Fig. 19 shows the geometry in the forward and backward directions relative to the reference satellite. Although the front and back satellites in this architecture operate in different planes of inertia than the reference satellite (much like eastern and westward satellites in typical wacker configurations), the offset of the true proximal angle is sufficient so that the quarternary bean shape of the flight path in the reference frame of the reference satellite is still very narrow. Redundancy can be provided in this design because satellites in front of the forward neighbor satellite can fall within the communication cone of the forward high gain antenna of the reference satellite. The communication link can be easily closed, although the distance to this satellite is approximately twice the distance to the forward neighbor relative to the reference satellite. Tradeoffs can be made to optimize transmit power and antenna design depending on the number of satellites in the network to manage variability in data rate performance and network throughput. For example, it is possible to use a phased antenna array, wherein when a spacecraft in front of a reference satellite fails, the antenna beam can be digitally commanded to point to the satellite in front of the failed satellite, thereby maintaining a spiral link around the sphere for the entire satellite constellation.
This link may also be allowed to close using an RF communication design in the event that a second failure causes the reference satellite to need to connect to a satellite in the spiral two slots ahead of it. However, if this distance is too far to close a meaningful link, in this case, it can be noted that the backward direction can actually be used to serve any communication that would normally need to be sent in the forward direction, because the system is actually one long chain of communication around the sphere. This comes at the expense of increased latency and reduced network throughput, but will at least accomplish the task of delivering data without the need for store and forward activity.
The neighboring satellites do operate in the reference frame of the reference satellite, but the amount of operation is small. In the spiral, the back satellite is behind the reference satellite and only slightly to one side, and in one orbit it does follow a figure 8, but with a small angular deviation with respect to the reference satellite, well within the beam width of the back antenna of the reference satellite.
Fig. 20 shows a multiple pass spiral arrangement.
Fig. 21 is a flow chart of a process that may be performed on this spiral constellation by handling messages through satellites. In
In
It is possible that each satellite does not fully compute the message path. It may be that the satellite only needs to determine whether it will send a message in the proceed path (i.e., if the satellite receives a message at its back antenna, it transmits the message using its front antenna, and if the satellite receives a message at its front antenna, it transmits the message using its back antenna), or whether it sends it to the ground. The satellite that first receives the message may calculate the entire message path for the message and attach the message path to the message. The path may not need to be fully specified except to indicate which satellite in the spiral will be sending the message in the downlink.
In one variation, the determination of the message path is on the ground, and the calculation at one satellite or at multiple places takes into account the likelihood of "wormholes" in the spiral, where the satellite (or other path determiner) determines that it is preferable to send the message to a ground station that can transmit the message up-link to another location in the spiral. For example, if a ground station is within the coverage of a first satellite and also within the coverage of a second satellite that is 60 links out of phase with the first satellite, the first satellite sends a message to the ground that is picked up by the ground station and transmitted along an uplink to the second satellite, potentially speeding up the delivery of the message. In another variant, the ground station obtaining the downlink is geographically separated from the second ground station forming the uplink, and neither need be in the coverage of both satellites at the same time.
Fig. 22 is an illustration of the arrangement of helical satellites. As will be described herein in greater detail,vthe forward beam from the front antenna in the vector direction will cover the front adjacent satellite in the helix throughout its orbit, and similarly for the rear adjacent satellite. In practice, as shown, the next adjacent rear and front antennas are also within the beam.
Benefits of embodiments described herein may include a reduction in the technical complexity, cost, quality, and power requirements of the spacecraft in the satellite network required to maintain connectivity between each satellite in the network and the ground at any point in time. By effectively creating a continuous but operationally and technically simple string of communication connections between each node in the satellite network, global knowledge can be delivered at low cost throughout segments of space and globally dispersed ground nodes (devices, systems, users, etc.). The cost of a segment of space may be reduced by two to three times, considering the savings in quality, power, and link budget, and how those savings propagate through design, integration, testing, startup, and operation, etc. Further operational and financial benefits may be obtained by not requiring many ground stations for network operation and TT & C. Thus, when using the teachings herein, the cost associated with the terrestrial system portion of the satellite network may be reduced by an order of magnitude or more.
As has now been described, in the novel method, the message path (which may be a list of links that messages will take and the time that a message will likely travel on those links) need not be calculated and assigned to the shortest path, but rather follows the message path of the satellites in the constellation along the orbital plane until the point at which the other orbital plane intersects the first orbital plane, at which point the satellite can transmit using its front or rear antenna to another satellite (albeit then in front of or behind the transmitting satellite) that is actually in a different orbital plane. This allows inter-satellite links to occur without the need to use side antennas or wide lobe antennas. This can be done without latency that cannot work (even if signal transmission times are taken into account) because there is a calculable maximum time of flight for the message. In one example, the satellite forwards the data to a preceding satellite, which in turn sends the data forward until the orbital planes intersect, and then the satellite sends the data forward or backward on the new orbital plane, depending on which is the closest route to the satellite with the coverage of the coverage destination device.
In a variation of the novel method, each satellite operates in its own orbital plane and the other satellites in the constellation operate in intersecting orbital planes. In this arrangement the emission can be directed in one direction, e.g. in a spiral, each time slightly changing the track plane. While this may involve the data transmission navigating the earth more than once, the resulting latency of about 140 milliseconds/navigation may be acceptable. Messages can hop from one part of the spiral to another using strategically placed terrestrial repeater sites.
The novel techniques may be used in combination with existing techniques where appropriate. In one embodiment, the satellites may be configured to use some techniques, including conventional techniques, until enough satellites fill the constellation and implement novel techniques.
In a computer process for determining a message path, this may be done at one location by entering source location, time of transmission, destination location and other parameters, and then including the message path with the source message so that each receiving satellite knows how to route each data transmission. This satellite will be programmed to direct transmissions after reading the message path data fields from the transmissions, where the message path data fields are calculated according to the novel method described herein. Alternatively, the satellite may be programmed to calculate a message path or portion thereof with the time of transmission, the destination location, and other parameters, and use the message path or portion thereof to determine how to route the data transmission. Where the message path includes timing targets, the satellite may hold messages for delayed transmission in order to meet those timing targets. Timing targets may be used to provide closer alignment across planar satellites or to account for dynamic satellite coverage.
The operations of the processes described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The processes described herein (or variations and/or combinations thereof) may be performed under the control of one or more computer systems configured with executable instructions, and may be implemented as code (e.g., executable instructions, one or more computer programs, or one or more applications) that are executed collectively by hardware or combinations thereof on one or more processors. The code may be stored on a computer-readable storage medium, for example in the form of a computer program comprising a plurality of instructions executable by one or more processors. The computer readable storage medium may be non-transitory.
Unless otherwise expressly stated or otherwise clearly contradicted by context, conjunctive language such as phrases in the form of "A, B, and at least one of C" or "A, B and at least one of C" are otherwise understood by context to be used generically to refer to items, terms, etc., which may be any non-empty subset of the set of A or B or C, or A and B and C. For example, in an illustrative example of a set having three components, the conjunctive phrases "A, B, and at least one of C" and "A, B and at least one of C" refer to any of the following sets: { A }, { B }, { C }, { A, B }, { A, C }, { B, C }, and { A, B, C }. Thus, such conjunctive language is generally not intended to imply that certain embodiments require at least one A, at least one B, and at least one C to be present.
The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate embodiments of the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense. The sole and exclusive indicator of the scope of the invention, and what is intended by the applicants to be the scope of the invention, is the literal and equivalent scope of such claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction.
Other embodiments may be envisioned by one of ordinary skill in the art after reading this disclosure. In other embodiments, combinations or sub-combinations of the above disclosed invention may be advantageously made. Example configurations of components are shown for illustrative purposes, and it is understood that combinations, additions, rearrangements, and the like are contemplated in alternative embodiments of the invention. Thus, while the invention has been described with respect to exemplary embodiments, those skilled in the art will recognize that numerous modifications are possible.
For example, the processes described herein may be implemented using hardware components, software components, and/or any combination thereof. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims, and the invention is intended to cover all modifications and equivalents within the scope of the appended claims.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
- 上一篇:一种医用注射器针头装配设备
- 下一篇:具有无线链路的卫星终端系统