Telecommunications connectivity via the Internet, cellular data networks and other systems is available in many parts of the world. However, there are locations where such connectivity is unavailable, unreliable or subject to outages from natural disasters. Some systems may provide network access to remote locations or to locations with limited networking infrastructure via satellites or high altitude platforms. In the latter case, due to environmental conditions and other limitations, it is challenging to keep the platforms aloft and operational over a desired service area for long durations, such as weeks, months or longer. Such operation may require specialized platforms. However, customizing platforms prior to launch or modifying them after launch to meet operational goals can be extremely challenging or not possible with conventional architectures.
Aspects of the technology relate to a high altitude platform (HAP) that is able to remain on station or move in a particular direction toward a desired location, for instance to provide telecommunication services, video streaming or other services. The high altitude platform may be a lighter-than-air (LTA) platform such as a balloon, dirigible/airship or other LTA platform configured to operate in the stratosphere. For instance, the LTA platform may include an envelope filled with lift gas and a payload for providing telecommunication or video services, with a connection member coupling the payload with the envelope. The envelope may be a superpressure envelope, e.g., with a ballonet that can be used to aid in altitude control as part of an altitude control system (ACS). A lateral propulsion system may provide directional thrust for moving the LTA platform toward a destination or remaining on station over a location of interest (e.g., a city or regional service area). This can include a pointing mechanism that aligns a propeller assembly (or assemblies) of the lateral propulsion system such that the thrust moves the flight system along a desired heading.
The payload and lateral propulsion system may be arranged with other components on a modular bus-type chassis. In some instances, one or more components may be moveable along the chassis during flight, for instance to change the pitch of the vehicle for more effective flight operation, or otherwise improve aerodynamics and stability. The modular bus arrangement may include a truss-based chassis that can be assembled from one or more subunits. The subunits may be preassembled modules with different equipment packages that can be selected and assembled quickly on an as-needed basis. Trusses formed using sets of struts may have two or more struts terminating at the same interconnection node. Node connection elements, such as compound dovetail interconnects, can facilitate a reliable, repeatable and quick mounting method for structural interconnections, which can lead to faster assembly and disassembly times.
According to one aspect of the technology, a lighter-than-air (LTA) high altitude platform (HAP) is configured for operation in the stratosphere. The LTA HAP comprises an envelope, a modular chassis and a set of interconnection nodes. The envelope is configured to maintain pressurized lift gas therein for lighter-than-air operation in the stratosphere. The modular chassis is coupled to the envelope via a set of suspension lines. The modular chassis comprises a plurality of subunits, each subunit having a plurality of struts coupled together, at least one of the plurality of subunits having a set of photovoltaic (PV) components affixed thereto. The set of interconnection nodes is distributed along the modular chassis. One or more of the interconnection nodes of the set is configured to connect at least two struts together, and one or more of the interconnection nodes is configured to secure a first one of the plurality of subunits to a second one of the plurality of subunits.
In one example, at least one of the set of interconnection nodes comprises a compound dovetail connector. Here, the compound dovetail connector may secure a strut of the plurality of struts to one of the interconnection nodes of the set of interconnection nodes.
In another example, one or more subunits of the plurality of subunits is formed as trusses using at least some of the plurality of struts and one or more of the interconnection nodes of the set of interconnection nodes.
In a further example, the LTA HAP further comprises a pitch trim mechanism having a ballast component adjustably arranged therealong. The pitch trim mechanism may include one or more support tubes disposed between a chassis bulkhead panel on one end thereof and a lateral support member on an opposite end thereof. The ballast component may be configured to adjust a pitch of the LTA HAP by sliding along the one or more support tubes. The LTA HAP may further comprise an actuator assembly configured to move a position of the ballast component longitudinally along a given one of the plurality of subunits of the modular chassis.
In yet another example, the set of PV components comprises a set of solar panels affixed to the at least one of the plurality of subunits. In this case, the set of solar panels may be arranged along one or both sides of a truss structure of the at least one of the plurality of subunits.
In a further example, the LTA HAP further comprises a lateral propulsion system affixed to one of the plurality of subunits of the modular chassis. The lateral propulsion system may include one or more propeller assemblies affixed to the one of the plurality of subunits. In this case, the subunit having the one or more propeller assemblies affixed thereto may be a first subunit, and the at least one of the plurality of subunits having the set of PV components affixed thereto may be a second subunit different from the first subunit.
And in another example, the set of interconnection nodes distributed along the modular chassis includes a trio of nodes that are connected to a trio of the plurality of struts to form a chassis strut bulkhead.
According to another aspect of the technology, a lighter-than-air (LTA) high altitude platform (HAP) kit is provided. The kit comprises a plurality of chassis subunits each configured in a truss arrangement and a set of interconnection nodes. Each subunit has a plurality of struts coupled together. One or more of the interconnection nodes is configured to secure a first one of the plurality of chassis subunits to a second one of the plurality of chassis subunits. A first subset of the set of interconnection nodes is configured to secure the plurality of chassis subunits to a shaped envelope that is configured to maintain pressurized lift gas therein for lighter-than-air operation in the stratosphere.
In one example, a second subset of the set of interconnections includes a set of components configured for releasably coupling the plurality of chassis subunits to an assembly cart or a launch cart prior to launch of the LTA HAP into the stratosphere. In another example, at least one of the set of interconnection nodes comprises a compound dovetail connector.
According to a further aspect of the technology, a compound dovetail connector assembly is provided. The compound dovetail connector assembly comprises a tail element and a pin element releasably securable thereto. The tail element has a first end with a first dovetail connection member and a second end adapted to receive a first strut or other connector component of a high altitude platform (HAP) chassis. The first dovetail connection member has one or more through holes adapted to receive one or more fasteners. The pin element has a first end with a second dovetail connection member and a second end adapted to receive a second strut or other connector component of the HAP chassis. The second dovetail connection member has a mating geometry to the first dovetail connection member. The second dovetail connection member has one or more through holes adapted to receive the one or more fasteners to secure the pin element to the tail element.
In one example, the first dovetail connection member of the tail element has a geometry with a surface angled in a y− axis and a z− axis at the same time and mirrored to create a tail wedge along two axes; and the second dovetail connection member of the pin element has a complementary surface to the surface of the first dovetail connection member, which is angled in the y− axis and the z+ axis at the same time and mirrored to create a pin wedge along the two axes. Here, the pin and tail wedges along a first one of the two axes may be angled between 25° to 35°, and the pin and tail wedges along a second one of the two axes may be angled between 70° to 80°.
The technology relates to LTA high altitude platforms configured to operate in the stratosphere. Such platforms may provide telecommunications and other services from one or more communications modules that are part of the LTA vehicle's payload. This equipment, along with other payload devices (e.g., a control system, a power supply and a solar power generation module), is mounted along a modular bus-type chassis, for instance using truss-based submodules that allow for easy assembly and disassembly. An altitude control system and/or a lateral propulsion system can be coupled to the chassis either directly or via their placement along another part of the HAP (e.g., an air intake and venting assembly located along a base portion of a shaped envelope to effect altitude control).
Stratospheric HAPs, such as LTA platforms, may have a float altitude of between about 50,000-120,000 feet above sea level. The ambient temperature may be on the order of −10° C. to −90° C. or colder, depending on the altitude and weather conditions. These and other environmental factors in the stratosphere can be challenging for HAP operation, especially for long-duration deployment for months or longer. The architectures discussed herein are designed to effectively operate in such conditions, although they may also be used in other environments with different types of systems besides LTA-type platforms.
As explained below, an example HAP may include one or both of altitude control and/or a lateral propulsion system. Altitude control may be employed using an active altitude control system (ACS), such as with a pump and valve-type assembly coupled with an onboard ballonet. The lateral propulsion system may employ a propeller assembly to provide directional adjustments to the HAP, for instance to counteract movement due to the wind, or to otherwise cause the HAP to move along a selected heading. Such altitude and lateral adjustments can enhance operation across a fleet of HAPs. For instance, by employing a small amount of lateral propulsion and/or vertical adjustment at particular times, a given platform may stay on station over a desired service area for a longer period, or change direction to move towards a particular place of interest. The platform may also be able to return to the desired service area more quickly using lateral propulsion and/or altitude adjustments to compensate against undesired wind effects. Applying this approach for some or all of the platforms in the fleet may mean that the total number of platforms required to provide a given level of service (e.g., telecommunications coverage for a service area) may be significantly reduced as compared to a fleet that does not employ lateral propulsion.
The ACS may include a pump and valve arrangement as part of a vent and air intake assembly for a ballonet, which may be received within the shaped envelope. One or more motors can be used to actuate a lateral propulsion system of the HAP to affect the directional changes. This can include a pointing axis motor for rotating propellers to a particular heading, and a drive motor for causing a propeller assembly or other propulsion mechanism to turn on and off Powering the ACS, lateral propulsion system, communication system(s) and/or other modules of the HAP is done via an onboard power supply, such as one or more batteries that may be part of the payload assembly. The batteries may be charged using a solar power generation module, which includes solar panels or other photovoltaic (PV) components located, for example, along the chassis.
The devices in system 100 are configured to communicate with one another. As an example, the HAPs may include communication links 104 and/or 114 in order to facilitate intra-balloon communications. By way of example, links 114 may employ radio frequency (RF) signals (e.g., millimeter wave transmissions) while links 104 employ free-space optical transmission. Alternatively, all links may be RF, optical, or a hybrid that employs both RF and optical transmission. In this way balloons 102A-F may collectively function as a mesh network for data communications. At least some of the HAPs may be configured for communications with ground-based stations 106 and 112 via respective links 108 and 110, which may be RF and/or optical links.
In one scenario, a given HAP 102 may be configured to transmit an optical signal via an optical link 104. Here, the given HAP 102 may use one or more high-power light-emitting diodes (LEDs) to transmit an optical signal. Alternatively, some or all of the HAP 102 may include laser systems for free-space optical communications over the optical links 104. Other types of free-space communication are possible. Further, in order to receive an optical signal from another HAP via an optical link 104, the HAP may include one or more optical receivers.
The HAPs may also utilize one or more of various RF air-interface protocols for communication with ground-based stations via respective communication links. For instance, some or all of the HAPs 102A-F may be configured to communicate with ground-based stations 106 and 112 via RF links 108 using various protocols described in IEEE 802.11 (including any of the IEEE 802.11 revisions), cellular protocols such as GSM, CDMA, UMTS, EV-DO, WiMAX, and/or LTE, 5G and/or one or more proprietary protocols developed for long distance communication, among other possibilities.
In some examples, the links may not provide a desired link capacity for HAP-to-ground communications. For instance, increased capacity may be desirable to provide backhaul links from a ground-based gateway. Accordingly, an example network may also include downlink HAPs, which could provide a high-capacity air-ground link between the various HAPs of the network and the ground-base stations. For example, in network 100, dirigible 102A or balloon 102B operating in the stratosphere may be configured as a downlink HAP that directly communicates with station 106.
Like other HAPs in network 100, downlink HAP 102F may be operable for communication (e.g., RF or optical) with one or more other HAPs via link(s) 104. Downlink HAP 102F may also be configured for free-space optical communication with ground-based station 112 via an optical link 110. Optical link 110 may therefore serve as a high-capacity link (as compared to an RF link 108) between the network 100 and the ground-based station 112. Downlink HAP 102F may additionally be operable for RF communication with ground-based stations 106. In other cases, downlink HAP 102F may only use an optical link for balloon-to-ground communications. Further, while the arrangement shown in
A downlink HAP may be equipped with a specialized, high bandwidth RF communication system for balloon-to-ground communications, instead of, or in addition to, a free-space optical communication system. The high bandwidth RF communication system may take the form of an ultra-wideband system, which may provide an RF link with substantially the same capacity as one of the optical links 104.
In a further example, some or all of HAPs 102A-F could be configured to establish a communication link with space-based satellites and/or other types of non-LTA craft (e.g., drones, airplanes, gliders, etc.) in addition to, or as an alternative to, a ground based communication link. In some embodiments, a stratospheric HAP may communicate with a satellite or other high altitude platform via an optical or RF link. However, other types of communication arrangements are possible.
As noted above, the HAPs 102A-F may collectively function as a mesh network. More specifically, since HAPs 102A-F may communicate with one another using free-space optical links, the HAPs may collectively function as a free-space optical mesh network. In a mesh-network configuration, each HAP may function as a node of the mesh network, which is operable to receive data directed to it and to route data to other HAPs. As such, data may be routed from a source HAP to a destination HAP by determining an appropriate sequence of links between the source HAP and the destination HAP.
The network topology may change as the HAPs move relative to one another and/or relative to the ground. Accordingly, the network 100 may apply a mesh protocol to update the state of the network as the topology of the network changes. For example, to address the mobility of the HAPs 102A to 102F, the balloon network 100 may employ and/or adapt various techniques that are employed in mobile ad hoc networks (MANETs). Other examples are possible as well.
Network 100 may also implement station-keeping functions using winds and altitude control and/or lateral propulsion to help provide a desired network topology, particularly for LTA platforms. For example, station-keeping may involve some or all of HAPs 102A-F maintaining and/or moving into a certain position relative to one or more other HAPs in the network (and possibly in a certain position relative to a ground-based station or service area). As part of this process, each HAP may implement station-keeping functions to determine its desired positioning within the desired topology, and if necessary, to determine how to move to and/or maintain the desired position. Alternatively, the platforms may be moved without regard to the position of their neighbors, for instance to enhance or otherwise adjust communication coverage at a particular geographic location.
The desired topology may thus vary depending upon the particular implementation and whether or not the HAPs are continuously moving. In some cases, HAPs may implement station-keeping to provide a substantially uniform topology where the HAPs function to position themselves at substantially the same distance (or within a certain range of distances) from adjacent balloons in the network 100. Alternatively, the network 100 may have a non-uniform topology where HAPs are distributed more or less densely in certain areas, for various reasons. As an example, to help meet the higher bandwidth demands, HAPs may be clustered more densely over areas with greater demand (such as urban areas) and less densely over areas with lesser demand (such as over large bodies of water). In addition, the topology of an example HAP network may be adaptable allowing HAPs to adjust their respective positioning in accordance with a change in the desired topology of the network.
The HAPs of
In an example configuration, the HAPs include an envelope and a payload, along with various other components.
Furthermore, the shape and size of the envelope may vary depending upon the particular implementation. Additionally, the envelope may be filled with different types of gases, such as air, helium and/or hydrogen. Other types of gases, and combinations thereof, are possible as well. In some examples, an outer envelope may be filled with lift gas(es), while an inner ballonet arrangement may be configured to have ambient air pumped into and out of it for altitude control. Other ballonet configurations are possible, for instance with the ballonet forming an outer envelope, while an inner envelope holds lift gas(es).
Envelope shapes for LTA platforms may include typical balloon shapes like spheres and “pumpkins” or aerodynamic shapes that are at least partly symmetric (e.g., teardrop-shaped, such as 202 in
According to one example shown in
The data can be retrieved, stored or modified by the one or more processors 306 in accordance with the instructions. For instance, although the subject matter described herein is not limited by any particular data structure, the data can be stored in computer registers, in a relational database as a table having many different fields and records, or XML documents. The data can also be formatted in any computing device-readable format such as, but not limited to, binary values, ASCII or Unicode. Moreover, the data can comprise any information sufficient to identify the relevant information, such as numbers, descriptive text, proprietary codes, pointers, references to data stored in other memories such as at other network locations, or information that is used by a function to calculate the relevant data.
The one or more processors 306 can include any conventional processors, such as a commercially available CPU. Alternatively, each processor can be a dedicated component such as an ASIC, controller, or other hardware-based processor. Although
The payload 302 (or the flight system 300 generally) may also include various other types of equipment and systems to provide a number of different functions. For example, as shown the payload 302 includes one or more communication systems 310, which may transmit signals via RF and/or optical links as discussed above. The communication system(s) 310 include communication components such as one or more transmitters and receivers (or transceivers), one or more antennae, and a baseband processing subsystem. (not shown). In one scenario, a given communication module of the communication system operates in a directional manner. For instance, one or more high gain directional antennas may be mechanically or functionally pointed (e.g., via beamforming) in a selected direction(s) to enable uplink and/or downlink connectivity with other communications devices (e.g., other LTA platforms, ground stations, satellites in orbit or personal communication devices). In this case, it may be particularly beneficial to ensure that the given communication module is pointed at a target heading to ensure the communication link(s) (e.g., according to a determined communication bit error rate, signal-to-noise ratio, etc.).
The payload 302 is illustrated as also including a power supply 312 to supply power to the various components of the balloon. The power supply 312 could include one or more rechargeable batteries or other energy storage systems like capacitors or regenerative fuel cells. In addition, the payload 302 may include a power generation system 312 in addition to or as part of the power supply. The power generation system 314 may include solar panels or other PV components, stored energy (e.g., hot air relative to ambient air), relative wind power generation, or differential atmospheric charging (not shown), or any combination thereof, and could be used to generate power that charges and/or is distributed by the power supply 312. In some configurations, some of the PV components may be disposed along the payload or other portions of the flight system chassis while other PV components may be disposed along the envelope. In other configurations, the PV components may only be disposed along the envelope.
The payload 300 may additionally include a positioning system 316. The positioning system 316 could include, for example, a global positioning system (GPS) such as differential GPS (D-GPS), an inertial navigation system, and/or a star-tracking system. The positioning system 316 may additionally or alternatively include various motion sensors (e.g., accelerometers, magnetometers, gyroscopes, and/or compasses). The positioning system 316 may additionally or alternatively include one or more video and/or still cameras, and/or various sensors for capturing environmental data. Some or all of the components and systems within payload 302 may be implemented in a radiosonde or other probe, which may be operable to measure, e.g., pressure, altitude, geographical position (latitude and longitude), temperature, relative humidity, and/or wind speed and/or wind direction, among other information. Wind sensors may include different types of components like pitot tubes, hot wire or ultrasonic anemometers or similar, windmill or other aerodynamic pressure sensors, laser/lidar, or other methods of measuring relative velocities or distant winds.
Payload 302 may include a navigation system 318 separate from, or partially or fully incorporated into control system 304. The navigation system 318 may implement station-keeping functions to maintain position within and/or move to a position in accordance with a desired topology or other service requirement. In particular, the navigation system 318 may use wind data (e.g., from onboard and/or remote sensors) to determine altitudinal and/or lateral positional adjustments that result in the wind carrying the balloon in a desired direction and/or to a desired location. Lateral positional adjustments may also be handled directly by a lateral positioning system that is separate from the payload, which is discussed further below. Alternatively, the altitudinal and/or lateral adjustments may be computed by a central control location and transmitted by a ground based, air based, or satellite based system and communicated to the HAP. In other embodiments, specific HAPs may be configured to compute altitudinal and/or lateral adjustments for other HAPs and transmit the adjustment commands to those other HAPs. In some examples, part or all of the navigation system may be implemented by the lateral propulsion system 340.
In one configuration, one or more components of the flight system may be moveable along the chassis. A pitch control module 319 can be employed, for instance, to slide such components forward or aft (or side to side) along the chassis, to adjust the pitch of the HAP. The moveable components may include, by way of example only, batteries of the power supply, electronics modules, ballast, or other components which may be part of the flight system generally or of the payload. In another configuration, the entire flight system may be adjustable with respect to the lifting body of the envelope.
As illustrated in
In order to affect lateral positions or velocities, the platform includes lateral propulsion system 340. As shown in
A block diagram of an exemplary electronics module 350 is illustrated in
The control subsystem may include a navigation controller 366 that is configured to employ data obtained from onboard navigation sensors 368, including an inertial measurement unit (IMU) and/or differential GPS, received data (e.g., weather information), and/or other sensors such as health and performance sensors 370 (e.g., a force torque sensor) to manage operation of the LTA vehicle's systems. The navigation controller 366 may be separate from or part of the processor(s) 352, and may operate independently or in conjunction with navigation system 318. The navigation controller 366 works with system software, ground controller commands, and health & safety objectives of the system (e.g., battery power, temperature management, electrical activity, etc.) and helps decide courses of action. The decisions based on the sensors and software may be to save power, improve system safety (e.g., increase heater power to avoid systems from getting too cold during stratospheric operation) or divert power to altitude control or divert power to lateral propulsion.
When decisions are made to activate the lateral propulsion system, the navigation controller then leverages sensors for position, wind direction, altitude and power availability to properly point the propeller and to provide a specific thrust condition for a specific duration or until a specific condition is reached (a specific velocity or position is reached, while monitoring and reporting overall system health, temperature, vibration, and other performance parameters). In this way, the navigation controller can continually optimize the use of the lateral propulsion systems for performance, safety and system health. Upon termination of a flight, the navigation controller can engage the safety systems (for example a propeller braking mechanism) to prepare the system to descend, land, and be recovered safely. Similarly, the ACS may be controlled to start or increase airflow into a ballonet or to pump air out from the ballonet. This can include actuating a compressor, pump, impeller or other mechanism to effect the desired amount of airflow or otherwise adjust the vertical position of the HAP in the stratosphere.
Lateral propulsion controller 372 is configured to control the propeller's pointing direction (e.g., via a worm gear mechanism), manage speed of rotation, power levels, and determine when to turn on the propeller or off, and for how long. The lateral propulsion controller 372 thus oversees thruster pointing direction 374, thruster power level 376 and thruster on-time 378 modules. The lateral propulsion controller 372 may be separate from or part of the processor(s) 352. Processor software or received human controller decisions may set priorities on what power is available for lateral propulsion functions (e.g., using lateral propulsion power 364). The navigation controller then decides how much of that power to apply to the lateral propulsion motors and when (e.g., using thruster power level 376). In this way, power optimizations occur at the overall system level as well as at the lateral propulsion subsystem level. This optimization may occur in a datacenter on the ground or locally onboard the balloon platform.
The lateral propulsion controller 372 is able to control the drive motor of the propeller motor assembly so that the propeller assembly may operate in different modes. Two example operational modes are: constant power control or constant rotational velocity control. The electronics module may store data for both modes and the processor(s) of the control assembly may manage operation of the drive motor in accordance with such data. For instance, the processor(s) may use the stored data to calculate or control the amount of power or the rotational propeller velocity needed to achieve a given lateral speed. The electronics module may store data for the operational modes and the processor(s) of the control assembly may manage operation of the drive motor in accordance with such data. For instance, the processor(s) may use the stored data to calculate the amount of current needed to achieve a given lateral speed. The processor(s) may also correlate the amount of torque required to yield a particular speed in view of the altitude of the balloon platform. The processor(s) may control the drive motor continuously for a certain period of time, or may cycle the drive motor on and off for selected periods of time. This latter approach may be done for thermal regulation of the drive motor. For instance, the propeller may be actuated for anywhere from 1 second to 5 minutes (or more), and then turned off to allow for motor cooling. This may be dependent on the thermal mass available to dissipate heat from the motor. All of the components of the electronics module 350 and the overall flight system 300 may be powered by power supply 312, which is operatively coupled to the solar power generation module 314.
Modular chassis 410 including the payload is configured to couple the envelope 402 via suspension lines such as spars (or woven cables, ropes, struts, etc.) 412. One or more solar panel assemblies 414 may be coupled to the payload or another part of the chassis 410. Example 400 also illustrates a lateral propulsion system 416 using, for instance, one or more propeller assemblies. While the illustrated placement of the lateral propulsion system 416 is one possibility, the location could be either fore or aft of the payload on either the front or rear of the chassis 410. In other configurations, the lateral propulsion system may be affixed to one or more of the spars or other suspension lines 412, or to the envelope 402 itself.
Also shown in
View 620 omits the suspension lines and the solar panels on one side of the chassis. In this view, truss shapes can be seen, including triangular-shaped chassis strut bulkheads 612 and a chassis panel bulkhead 614. Also illustrated here is a pitch trim mechanism 616, with a ballast component 618, such as a battery module arranged therealong. These features are discussed in detail below.
As noted above, the chassis may be modular, which permits rapid assembly and disassembly.
As seen in the close-up perspective view of
The interconnections at the nodes of the chassis can take on different forms, depending on how many struts, bulkheads, sensors and/or other devices are to be coupled together, their relative size, placement, angle, etc. For instance,
Another connector configuration is shown in views 1200 of
The compound dovetail connector may be used with struts and other components to secure them at nodes along the chassis. For instance, the compound dovetail connector could have one side (e.g., the tail-side or the pin-side) affixed to an end of the strut (e.g., end 1014), while the complementary side (e.g., the pin-side or the tail-side) is part of a truss node (or another strut element, a solar panel, or other equipment).
The foregoing examples are not mutually exclusive and may be implemented in various combinations to achieve unique advantages. As these and other variations and combinations of the features discussed above can be utilized without departing from the subject matter defined by the claims, the foregoing description of the embodiments should be taken by way of illustration rather than by way of limitation of the subject matter defined by the claims. In addition, the provision of the examples described herein, as well as clauses phrased as “such as,” “including” and the like, should not be interpreted as limiting the subject matter of the claims to the specific examples; rather, the examples are intended to illustrate only one of many possible embodiments. Further, the same reference numbers in different drawings can identify the same or similar elements.