Patent Application
20140266955
Commercial geostationary satellites typically employ shaped reflector antennas to produce directivity patterns contoured to desired coverage areas. For example, commercial satellites may have reflectors designed to produce antenna pattern contours that mimic the borders of the continental United States (CONUS), Europe, or northern Africa, as projected from orbit, thereby minimizing directivity to unserved regions. Shaped reflector antennas have the advantages of using transponder power more efficiently and having significantly lower mass than other antenna technologies producing similar results, such as phased array antennas. Shaped reflectors also have excellent pattern characteristics (particularly cross-polar discrimination, sidelobe suppression, and other pattern characteristics required for regulatory compliance and inter-operator coordination), high power handling capability, simple deployability on-orbit, and proven on-orbit reliability. These shaped reflectors have continuous, fixed, and doubly-curved surfaces, typically molded with carbon composite materials.
One disadvantage with conventional shaped reflectors is that their shape cannot be altered after manufacture. Geostationary satellites are typically built to have a lifetime of 15 years or more. Over the course of a satellite's lifetime, its operator may want to change its orbital slot or coverage area. However, because shaped reflectors are fixed to a particular orbital slot and coverage area at manufacturing, a satellite that is moved to a different orbital slot and/or is re-oriented to serve a different region would not efficiently illuminate the new coverage area. Another disadvantage with conventional shaped reflectors is that it is often difficult to repair reflector surface errors or mis-shaping after manufacturing, which can cause significant cost and schedule impacts late in satellite production.
Further, satellite manufacturers may need to design antenna systems before a satellite's orbital slot has been assigned or its intended coverage area has been defined. For example, a satellite may have a 100 degree longitudinal range within which its orbital slot will be assigned. The optimal antenna configuration for a particular coverage area depends on the orbital slot since the projected contour of a region of the earth can be dramatically different in size and shape from the vantage point of differing orbital slots. So, when the actual orbital slot is unknown, it is impossible to design an optimal antenna system. When the orbital slot is yet to be determined, the satellite manufacturer may design the reflector for a mid-range position, by averaging the footprint of the two ends of the possible range, or by enveloping all possible patterns across the entire range of projected contours. In any case, the reflector would not have been optimized for the final orbital slot, leading to suboptimal performance.
In another case, a satellite may be re-tasked by the operator in response to changing market demands to an entirely different region from its initially designated deployment, with markedly different contours (for example, moving a satellite designed for CONUS to cover Africa). In that case, the operator is forced to accept partial coverage, tolerate directivity wasted on unserved areas, and coordinate potential interference issues with adjacent satellite operators.
Furthermore, shaped reflector antennas are long-lead, pacing items in the critical path of satellite manufacturing flow and must have the definition of their surfaces finalized over a year before launch, during which time the desired coverage area might change. However, no flexibility currently exists to alter the reflector surface after fabrication.
Lastly, fixed shaped reflectors cannot compensate for one-time and dynamic on-orbit effects, such as hygroscopic distortion, diurnal and seasonal thermal distortion, and various sources of mis-alignments. In addition, fixed reflectors cannot be adjusted to address deterioration in dynamic link conditions such as regional rain fading, uplink interference, and inclined orbit operations during extended satellite life.
Therefore, there is a need in the art for a reflector that can be reconfigured dynamically on orbit. A reflector that can be reconfigured on orbit would allow the satellite operators to repurpose the satellites for different orbital positions and coverage areas while still achieving optimal or high performance. If an operator's orbital slot and coverage goals change, being able to reconfigure an in-orbit satellite provides a superior result to moving a satellite whose reflectors are optimized for a different coverage area and orbital slot. Reconfiguring an in-orbit satellite is also far more efficient than building and launching in-orbit spares, or designing and launching new satellites as coverage areas or orbital slots change.
Once on orbit, a reconfigurable reflector surface, under closed-loop or open-loop control, would allow adaptive compensation for dynamic effects such as diurnal and seasonal thermal distortion, regional rain fades, spacecraft attitude mis-alignments, and non-static footprints during inclined-orbit operations. Furthermore, other innovative uses of dynamic pattern adjustment capability are possible such as auto-tracking for spot-beam applications, geolocation, and interference/anti-jam nulling.
Additionally, there is a need in the art for a reflector that can be reconfigured on the ground prior to launch. Such a reflector would not require final pattern coverage definition until late in satellite manufacturing flow, providing significant flexibility to the operator during the acquisition phase. Unlike fixed reflectors, this reconfigurable reflector can easily compensate for manufacturing errors, damage, and misalignments detected prior to launch at minimal cost and schedule impact.
A reconfigurable reflector may be composed of a number of independent reflector facets, some or all of which may have independently adjustable positions and/or orientations. These adjustable positions and/or orientations may be fixed prior to launch or driven by commandable actuators, allowing reconfiguration on orbit. By independently adjusting the positions and/or orientations of the reflector facets, the reconfigurable reflector can be re-shaped to create a virtually infinite number of coverage footprints and beam shapes. Sufficient pattern control may be achievable by a single degree-of-freedom through linear translation of the facet, greatly simplifying mechanical implementation and reducing size and mass of the antenna system. For static applications, the facet positions can be set and fixed late in manufacturing flow using a common antenna platform across an entire product line, eliminating unique reflector manufacturing for each satellite antenna. For dynamic, on-orbit control, each facet (or a subset of facets) can be integrated with an independent, controllable, actuating mechanism. The facets have rigid surfaces and can be fabricated from common space-qualified materials with significant flight heritage, obviating the need for novel materials such as continuous flexible membranes that continuous adjustable surfaces would require. Similarly, the actuators can be implemented with existing space-qualified materials and designs. The reconfigurable reflector can be a main reflector, subreflector, or both. A reconfigurable reflector can be used in commercial communication satellites, military communication satellites (e.g., Global Broadcast Service), or other applications.
Some embodiments include a reconfigurable faceted reflector for producing a plurality of antenna patterns. The reconfigurable reflector includes a backing structure, a plurality of adjusting mechanisms mounted to the backing structure, and a plurality of reflector facets. Each of the plurality of reflector facets is coupled to a respective one of the plurality of adjusting mechanisms for adjusting the position of the reflector facet with which it is coupled. The reflector facets are arranged to produce a first antenna pattern of the plurality of antenna patterns. By adjusting the plurality of adjusting mechanisms, the position of each of the reflector facets coupled to the respective one of the plurality of adjusting mechanisms is adjusted so that the reflector facets are arranged to produce a second antenna pattern of the plurality of antenna patterns.
In some embodiments, one or more of the adjusting mechanisms are mechanical adjusting mechanisms. In other embodiments, one or more of the adjusting mechanisms are actuators, such as linear actuators. If the adjusting mechanisms are linear actuators, each of the linear actuator may have a corresponding range, and the ranges of the plurality of linear actuators may allow the linear positions of the first number of reflector facets to be optimized for at least two different coverage areas. The linear actuators may be oriented to translate all facets in the same direction, such as towards the feed, towards the aperture, or along another common axis. Alternatively, the linear actuators may independently translate each facet in different directions.
The reflector facets may be substantially flat or curved. The reflector facets may be equally or unequally sized. The shapes of the reflector facets can be, for example, circular, hexagonal, rectangular, square, super-elliptical, trapezoidal, or triangular. In some embodiments, the reconfigurable reflector includes a plurality of fixed reflector facets that are mounted to the backing structure and are not coupled to an adjusting mechanism. The backing structure profile can be, for example, parabolic, ellipsoidal, flat, hyperbolic, or spherical.
In some embodiments, the reconfigurable reflector includes a plurality of tilting mechanisms. Each of the plurality of tilting mechanisms may be coupled to a corresponding one of the plurality of reflector facets to tilt the corresponding one of the plurality of reflector facets relative to the backing structure. In some embodiments, the reconfigurable reflector includes a plurality of translating mechanisms. Each of the plurality of translating mechanisms may be coupled to a corresponding one of the plurality of reflector facets to tilt the corresponding one of the plurality of reflector facets relative to the backing structure. With a plurality of tilting and translating mechanisms, up to 6 degrees of freedom can be provided to each facet's position and orientation.
Another aspect includes a method for antenna pattern shaping with a reconfigurable faceted reflector. The method involves receiving data describing a coverage area and/or a beam shape of a desired antenna pattern and determining, based on the desired coverage area and/or beam shape of the desired antenna pattern, optimal positions for a plurality of reflector facets for radiating the desired antenna pattern. The plurality of reflector facets are coupled to a plurality of adjusting mechanisms for adjusting the positions of the plurality of reflector facets, and the plurality of adjusting mechanisms are mounted to a backing structure. The method further includes adjusting, using the plurality of adjusting mechanisms, the positions and/or orientations of the plurality of reflector facets to the determined optimal positions for the plurality of reflector facets.
In some embodiments, the optimal positions of the plurality of reflector facets minimize antenna directivity to directions and areas outside of the desired coverage area. In some embodiments, one or more of the adjusting mechanisms are mechanical adjusting mechanisms. In such embodiments, the positions of the plurality of reflector facets may be adjusted to the determined optimal positions on the ground.
In other embodiments, one or more of the adjusting mechanisms are actuators, such as linear actuators. In such embodiments, commands for adjusting the positions of the plurality of reflector facets may be transmitted to the actuators. The method may also include receiving a failure condition of at least one of the at least one actuator. In this case, determining the optimal positions of the plurality of reflector facets may be further based on the failure condition of the at least one of the at least one actuator.
In some embodiments, the actuators are linear actuators, and the commands for adjusting the plurality of reflector facet positions are commands for independently adjusting each of the at least one linear actuator to move each of the plurality of reflector facets towards or away from the backing structure.
In some embodiments, the optimal positions of the plurality of reflector facets may be further based on the orbital position of the spacecraft. In other embodiments, the optimal positions of the plurality of reflector facets may be further based on the range of available positions of each of the plurality of reflector facets.
In some embodiments, the plurality of reflector facets, the plurality of adjusting mechanisms, and the backing structure form a main reflector. In such embodiments, the method may involve determining optimal positions of a second plurality of reflector facets coupled to a second plurality of adjusting mechanisms and mounted to a second backing structure. In this case, the second plurality of reflector facets, the second plurality of adjusting mechanisms, and the second backing structure may form a sub-reflector.
In some embodiments, the method involves receiving a second desired coverage area that is different from a first desired coverage area and determining, based on the second desired coverage area, second optimal positions for the plurality of reflector facets for radiating the second desired coverage area. Commands for adjusting the plurality of reflector facet positions to the determined second optimal positions of the plurality of reflector facets for radiating the second desired coverage area may then be transmitted to the adjusting mechanisms.
To provide an overall understanding of the invention, certain illustrative embodiments will now be described, including systems and methods for reconfigurable faceted reflectors for producing multiple radiation patterns. However, it will be understood by one of ordinary skill in the art that the systems and methods described herein may be adapted and modified as is appropriate for the application being addressed and that the systems and methods described herein may be employed in other suitable applications, and that such other additions and modifications will not depart from the scope thereof.
A reconfigurable reflector that can be used to produce multiple different radiation patterns can be composed of multiple reflector facets that are independently movable, with suitable results achievable through a single linear axis of translation.
The backing structure 102 may be any backing structure suitable for supporting multiple actuators 106 and multiple reflector facets 104. The backing structure 102 may be convex, as shown, or flat or concave. The backing structure 102 may have a parabolic, ellipsoidal, flat, hyperbolic, or spherical profile. The reflector facets 104 may be made of any material for reflecting electromagnetic waves, such as a carbon composite or aluminum. The individual reflector facets 104 may be flat, as shown, or curved. Flat reflector facets 104 are easier to produce than curved reflector facets because flat reflector production does not involve the creation and use of curved molds. Common facet shapes and/or surface profiles reduce production cost and schedule risk. The actuators 106 may be linear actuators, which come in various types, such as electromechanical and piezo-electrical devices. Linear actuators with space-flight heritage are available. If, for example, the actuators 106 are electromechanical actuators, they each may include a screw-nut pair and a stepper motor; the screw-nut pair translates the rotary motion of the stepper motor to linear output motion.
The actuators 106 may be connected to one or more controllers (not shown) for providing an input signal. An actuator 106 adjusts the position of its connected reflector facet 104 via the connecting rod 112 based on the input signal. The controller may receive a control signal via on-board processing or ground command indicating the desired positions of the reflector facets, and the controller may send input signals to the actuators 106 according to these positions. Alternatively, the control signals may indicate relative adjustments to be made to each reflector facet's position, e.g., a first reflector facet 104 should be moved, for example, 0.50 inches further from the backing structure 102 from its current position, a second reflector facet 104 should be moved 0.25 inches toward the backing structure 102 from its current position, and so forth. Alternatively, the spacecraft may store the optimal actuator settings for one or more coverage patterns; in this case, the ground signal transmits a control signal indicating the coverage pattern to be used. Alternatively, the spacecraft controller may run an algorithm for determining actuator settings for a given coverage pattern, which may be supplied by the ground station.
In some embodiments, an on-board processor may provide autonomous, closed-loop control of the reconfigurable reflector by using on-orbit measurement of facet positions and/or orientations. These measurements may be performed using photogrammetry if optical targets are placed on the facet surfaces. Alternatively, when using a stepper motor, the positions of each of the reflectors may be stored. On-board receivers may provide additional input signals to the facet-positioning algorithms to allow adaptive pattern adjustment, mitigating dynamic, temporal link degradation due to effects such as uplink interference and regional rain fading.
After launch, there may be a risk that one or more actuators 106 fail. In this case, the actuator's failure condition (i.e., the position at which the reflector facet 104 attached to the actuator 106 is fixed, the range of positions now available to the reflector facet 104, or the loss of or damage to a reflector facet 104) can be transmitted to the ground station or accounted for in on-board processing. Based on the failure condition, the configuration of the reflector 100 can be re-optimized, and calculation of future configurations can take into account the failure position to mitigate the impact of the failure.
Additional conditions may also be taken into account when optimizing the configuration of the reflector facets. For example, the reflector configuration may be adjusted to compensate for hygroscopic and diurnal/seasonal temperature distortions. The reflector configuration may additionally, or alternatively, be designed to reduce interference with other satellites, e.g., by on-orbit adjustment of sidelobe and roll-off characteristics. Further, the reconfigurable reflector may be used for dynamic beam-pointing to compensate for misalignments in an antenna system. Beam-pointing may reduce or eliminate the need to use gimbals for repositioning antennas, and can improve coverage in inclined or degraded orbits. Any of these or other conditions and considerations may be taken into account by an on-board controller or ground controller for optimizing the actuator settings and, thus, the reflector configuration.
The reconfigurable reflector can also be used for controlling interference and counteracting intentional jamming, e.g., in military applications. In this case, uplink receivers (not shown) and an on-board or ground controller are used to determine the presence of intentional or unintentional interference. Geolocation of the uplink interferer may be achieved through dynamic beam steering via the reconfigurable reflector in a manner similar to monopulse tracking. Then, the controller can determine an adjustment to the reflector facet positions to produce a pattern null in the direction of the interference. These adjustments are made by the actuators 106. In a similar manner, tracking the received signal strengths of uplink beacons or carriers from different regions of the coverage area can be used to implement on-board or ground-based pattern adjustments to compensate for propagation impairments, primarily rain fading.
As shown in
An exemplary arrangement of the reflector facets 104 is shown in
In
The reflector 100 can include any number of reflector facets 104 and actuators 106, depending on the desired size of the reflector 100, the desired size of the reflector facets 104, the desired weight of the reflector 100, and other factors. In some embodiments, the reflector facets 104 are on the order of several inches in diameter, and the reflector 100 is on the order of several meters in diameter. As shown in
An exemplary reflector 200 made up of differently sized and shaped reflector facets is shown in
The varying sizes and shapes of reflector facets 204 are also shown in
While
In some embodiments, the reconfigurable reflector may not be reconfigurable on-orbit but instead is only reconfigurable on the ground prior to launch. In such embodiments, the on-orbit controls discussed above are not needed. In addition, the actuators 106 may be replaced by a simple mechanical adjusting mechanism, such as a screw or other mechanical device. The positions of the facets 104 can be set late in the satellite manufacturing process, providing greater flexibility over fixed reflectors by allowing the operator or acquirer to configure the reflector before launch, after the final orbital slot and coverage region, for example, have been selected. Furthermore, if any manufacturing errors, damage, and/or misalignments are detected before launch, adjustments to the positions of facets 104 can be made to minimize the effects of such errors.
The reflectors 100 and 200 described above may be implemented as main reflectors and/or sub-reflectors in various implementations. Four possible reconfigurable antenna configurations are shown in
When the reflector 400 is illuminated by the feed 402 shown in
When the reflector 420 is illuminated by the feed 422 shown in
Based on this information, a ground-based or on-orbit processor determines the optimal positions for the reflector facets to achieve the desired directivity pattern (step 506). The desired directivity pattern may be contoured to the desired coverage area and may minimize antenna directivity to directions and areas outside of the desired coverage area. The optimal positions may be constrained by the range of motion and types of motion (e.g., linear motion perpendicular to the backing structure, pivot motion, other degrees of translation) available to the reflector facets, and may take into account that different reflector facets have different ranges and types of motion available, as discussed above. The positions may also be constrained by actuator or reflector facet failures, as discussed above. The algorithm for determining the optimal position may be similar to algorithms used for designing fixed-shaped continuous reflectors. The algorithm may also consider the diffraction or scattering effects created by discontinuities in the reflector surface.
The processor also retrieves the current facet positions (step 508). This could be telemetered directly from the individual actuators or determined via on-board photogrammetry of optical targets placed on the surfaces of the facets, as discussed above. Based on the optimal reflector facet positions determined in step 506 and the current reflector facet positions, the processor determines the adjustments to be made from the current reflector facet positions to obtain the optimal reflector facet positions (step 510). The processor then outputs these adjustments and, in the case of ground-based processing, they are transmitted by the ground station to the spacecraft (step 512). The spacecraft's command and data-handling subsystem relays signals to the actuators, causing the actuators to adjust the reflector facet positions according to the received commands (step 514).
One or more of the steps preceding step 512 may be performed on the spacecraft rather than at a ground station. For example, the spacecraft may store the current reflector facet positions and, based on these positions, determine the adjustments from the current reflector facet positions (step 510). As another example, anti jamming adjustments described in relation to
Based on this information, a processor determines the optimal positions for the reflector facets to achieve the desired radiation pattern (step 506). The desired directivity pattern may be contoured to the desired coverage area and may minimize antenna directivity to directions and areas outside of the desired coverage area. The optimal positions may be constrained by the range of motion and types of motion (e.g., linear motion perpendicular to the backing structure, pivot motion, other degrees of translation) available to the reflector facets, and may take into account that different reflector facets have different ranges and types of motion available, as discussed above. The positions may also be constrained by any manufacturing errors, damage, or misalignments, as discussed above. The algorithm for determining the optimal position may be similar to algorithms used for designing fixed-shaped continuous reflectors. The algorithm may also consider the diffraction or scattering effects created by discontinuities in the reflector surface.
After calculating the optimal reflector facet positions, the processor then outputs the optimal reflector facet positions to the manufacturer, who sets the facets at their optimal positions (step 558). In some embodiments, the facet positions may be manually set by the manufacturer using one or more manual mechanical adjustors coupled to each facet. In other embodiments, the facets may be automatically set at their optimal positions using actuators as described in relation to
While preferable embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.
