Patent Application
20210016866
Telecommunications connectivity via the Internet, cellular data networks and other systems is available in many parts of the world. However, there are many 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 located in the stratosphere. 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 days, weeks or more.
Aspects of the technology provide lateral propulsion based systems that enable high altitude balloon platforms to spend more time over a desired region, reduce the return time to the desired region, and reduce fleet size.
According to one aspect, a propeller assembly is provided for use with a lighter-than-air craft for operation in the stratosphere. The propeller assembly comprises at least two propeller blades and a hub assembly. Each propeller blade has a connection end and a blade end remote from the connection end. The hub assembly includes a central hub element and a plurality of fasteners. The central hub element has a central opening configured to receive a rotatable shaft of a propeller motor assembly, and receives a first side of the connection end of each of the propeller blades. A set of the plurality of fasteners secures the propeller blades to the central hub element.
In one example, the propeller blades provide a propeller diameter of between 1-5 m, for instance where the propeller diameter is on the order of 2 m. In another example, the central hub is machined aluminum or die cast. Here, a die cast central hub may be formed of aluminum. The blades and the hub assembly may have a combined mass of between 1.0-3.0 Kg.
In a further example, each propeller blade has a plastic shell, which comprises a pair of mating shell sides. A first one of the shell sides forms a first side of the propeller blade and a second one of the shell sides forms a second side of the propeller blade. Each propeller blade may further include a stiffening spar member disposed between the first and second shell sides. Here, the stiffening spar member may be a carbon fiber spar.
In yet another example, the plastic shell of each propeller blade is formed of polycarbonate. The polycarbonate may a glass fiber reinforced polycarbonate.
In another example, the propeller assembly also includes the shaft of the propeller assembly. The propeller assembly may further comprising the propeller motor assembly coupled to the shaft, in which the propeller motor assembly is configured to rotatably actuate the shaft. The propeller assembly may further include a temperature sensor coupled to the propeller motor assembly. The propeller motor assembly may be configured to actuate the propeller assembly in either a rotational velocity operating mode or a power control operating mode. A pointing direction of the propeller assembly may be adjustable about an axis of the lighter-than-air craft in response to a control signal received from a lateral propulsion controller of the lighter-than-air craft. The propeller motor assembly may be configured to receive power from a lateral propulsion controller of the lighter-than-air craft to manage a speed of rotation of the propeller assembly and to determine when to turn the propeller assembly on or off.
In another example, the at least two propeller blades are three propeller blades. Each propeller blade may be shaped for operation at stratospheric air densities. And the propeller assembly may be constructed in a manner that if broken, blade parts resist separation from the hub assembly.
The technology relates to lateral propulsion systems for balloon platforms designed to operate in the stratosphere. As explained below, example lateral propulsion systems employ a multi-bladed propeller arrangement to provide directional adjustments to the balloons movement with the wind. Such adjustments enhance the coverage and safety capabilities for the platforms in a fleet of balloon platforms. For instance, by employing a small amount of lateral propulsion at particular times, a given platform may stay on station over a desired service area for a longer period, or, if engaged early enough, may avoid undesired airspaces. The given platform may also be able to return to the desired service area more quickly using lateral propulsion to compensate against undesired wind effects. Using 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 may be significantly reduced as compared to a fleet that does not employ lateral propulsion.
Stratospheric high altitude balloon platforms may have a float altitude of between about 50,000-120,000 feet above sea level. At such heights, the density of the air is very low compared to ground level. For example, while the pressure at ground level is around 1,000 mb, the pressure in the lower stratosphere may be on the order of 100 mb and the pressure in the upper stratosphere may be on the order of 1 mb. The temperature in the stratosphere varies with altitude, generally increasing with height. For instance, in the lower stratosphere the average temperature may be on the order of −40° C. to −50° C. or colder, while the average temperature in the upper stratosphere may be on the order of −15° C. to −5° C. or warmer. These and other environmental conditions in the stratosphere can be challenging for propulsion systems. The systems and arrangements discussed below are configured to effectively operate in such conditions.
The devices in system 100 are configured to communicate with one another. As an example, the balloons 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 balloons 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 balloon 102 may be configured to transmit an optical signal via an optical link 104. Here, the given balloon 102 may use one or more high-power light-emitting diodes (LEDs) to transmit an optical signal. Alternatively, some or all of the balloons 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 balloon via an optical link 104, the balloon may include one or more optical receivers.
The balloons 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 balloons 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 balloon-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 balloons, which could provide a high-capacity air-ground link between the various balloons of the network and the ground-base stations. For example, in balloon network 100, balloon 102F may be configured as a downlink balloon that directly communicates with station 112.
Like other balloons in network 100, downlink balloon 102F may be operable for communication (e.g., RF or optical) with one or more other balloons via link(s) 104. Downlink balloon 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 balloon network 100 and the ground-based station 112. Downlink balloon 102F may additionally be operable for RF communication with ground-based stations 106. In other cases, downlink balloon 102F may only use an optical link for balloon-to-ground communications. Further, while the arrangement shown in
A downlink balloon 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 balloons 102A-F could be configured to establish a communication link with space-based satellites and/or other types of high altitude platforms (e.g., drones, airplanes, airships, etc.) in addition to, or as an alternative to, a ground based communication link. In some embodiments, a balloon may communicate with a satellite or a high altitude platform via an optical or RF link. However, other types of communication arrangements are possible.
As noted above, the balloons 102A-F may collectively function as a mesh network. More specifically, since balloons 102A-F may communicate with one another using free-space optical links, the balloons may collectively function as a free-space optical mesh network. In a mesh-network configuration, each balloon may function as a node of the mesh network, which is operable to receive data directed to it and to route data to other balloons. As such, data may be routed from a source balloon to a destination balloon by determining an appropriate sequence of links between the source balloon and the destination balloon.
The network topology may change as the balloons move relative to one another and/or relative to the ground. Accordingly, the balloon 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 balloons 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.
Balloon network 100 may also implement station-keeping functions using winds and altitude control or lateral propulsion to help provide a desired network topology. For example, station-keeping may involve some or all of balloons 102A-F maintaining and/or moving into a certain position relative to one or more other balloons in the network (and possibly in a certain position relative to a ground-based station or service area). As part of this process, each balloon 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.
The desired topology may vary depending upon the particular implementation and whether or not the balloons are continuously moving. In some cases, balloons may implement station-keeping to provide a substantially uniform topology where the balloons function to position themselves at substantially the same distance (or within a certain range of distances) from adjacent balloons in the balloon network 100. Alternatively, the balloon network 100 may have a non-uniform topology where balloons are distributed more or less densely in certain areas, for various reasons. As an example, to help meet the higher bandwidth demands, balloons 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 balloon network may be adaptable allowing balloons to adjust their respective positioning in accordance with a change in the desired topology of the network.
The balloons of
In an example configuration, the high altitude balloon platforms include an envelope and a payload, along with various other components.
The envelope 202 may take various shapes and forms. For instance, the envelope 202 may be made of materials such as polyethylene, mylar, FEP, rubber, latex or other thin film materials or composite laminates of those materials with fiber reinforcements imbedded inside or outside. Other materials or combinations thereof or laminations may also be employed to deliver required strength, gas barrier, RF and thermal properties. Furthermore, the shape and size of the envelope 202 may vary depending upon the particular implementation. Additionally, the envelope 202 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. Shapes may include typical balloon shapes like spheres and “pumpkins”, or aerodynamic shapes that are symmetric, provide shaped lift, or are changeable in shape. Lift may come from lift gasses (e.g., helium, hydrogen), electrostatic charging of conductive surfaces, aerodynamic lift (wing shapes), air moving devices (propellers, flapping wings, electrostatic propulsion, etc.) or any hybrid combination of lifting techniques.
According to one example shown in
The one or more processors 304 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 300 may also include various other types of equipment and systems to provide a number of different functions. For example, as shown the payload 300 includes one or more communication systems 308, which may transmit signals via RF and/or optical links as discussed above. The communication system(s) 308 include communication components such as one or more transmitters and receivers (or transceivers), one or more antennae, and a baseband processing subsystem. (not shown)
The payload 300 is illustrated as also including a power supply 310 to supply power to the various components of balloon. The power supply 310 could include one or more rechargeable batteries or other energy storage systems like capacitors or regenerative fuel cells. In addition, the balloon 300 may include a power generation system 312 in addition to or as part of the power supply. The power generation system 312 may include solar panels, stored energy (hot 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 310.
The payload 300 may additionally include a positioning system 314. The positioning system 314 could include, for example, a global positioning system (GPS), an inertial navigation system, and/or a star-tracking system. The positioning system 314 may additionally or alternatively include various motion sensors (e.g., accelerometers, magnetometers, gyroscopes, and/or compasses). The positioning system 314 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 300 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 300 may include a navigation system 316 separate from, or partially or fully incorporated into control system 302. The navigation system 316 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 316 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. 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 high-altitude balloon. In other embodiments, specific balloons may be configured to compute altitudinal and/or lateral adjustments for other balloons and transmit the adjustment commands to those other balloons.
In order to effect lateral positions or velocities, the platform includes a lateral propulsion system.
While this configuration or other similar configurations gives the lateral propulsion system 410 two degrees of operational freedom, additional degrees of freedom are possible with other pointing mechanisms or air-ducting mechanisms. This flexible thrusting approach may be used to help counteract continually changing wind effects. Rotation of the control assembly 504 and propeller assembly 502 about the down connect member 406 is desirably independent of rotation of the solar panel assemblies (and/or payload) about the down connect member 406.
The coupling member 602 is configured to enable unrestricted and continuous 360° rotation of the propeller and the entire lateral propulsion system 410. Other configurations besides a slip ring are possible for providing power and data across a moving interface, for example a series of flexible wires in a helix with fixed hard stops beyond 360 degrees (or more or less). Periodic unwinding of a helix-wire system may become necessary.
An exemplary block diagram of electronics module 800 is illustrated in
A navigation controller 816 is configured to employ data obtained from onboard navigation sensors 818, 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 820 (e.g., a force torque sensor) to manage operation of the balloon's systems. The navigation controller 816 may be separate from or part of the processor(s) 802. The navigation controller works with system software (e.g., Machine Learning algorithms), 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 controls or divert power to lateral propulsion systems. 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 optimized 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 propeller brake) to prepare the system to descend, land, and be recovered safely.
Lateral propulsion controller 822 is configured to continuously control the propeller's pointing direction, manage speed of rotation, power levels, and determine when to turn on the propeller or off, and for how long. The lateral propulsion controller 822 thus oversees thruster pointing direction 824, thruster power level 826 and thruster on-time 828 modules. The lateral propulsion controller 822 may be separate from or part of the processor(s) 802. Processor software or received human controller decisions may set priority on what power is available for lateral propulsion functions (e.g., using lateral propulsion power 814). 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 826). 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 822 is able to control the propeller motor 604 (
The processor(s) may control the propeller motor 604 continuously for a certain period of time, or may cycle the propeller motor 604 on and off for selected periods of time, e.g., using pulse width modulation (PWM). This latter approach may be done for thermal regulation of the propeller motor 604. 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.
The power required to generate a given lateral speed is proportional to the speed cubed. High altitude vehicles may have limited power availability, resulting in a tradeoff between speed and power consumption. Lower power consumption is desirable, because it enables the lateral propulsion system to be used for longer durations. One approach is to use a larger diameter propeller, which is generally more power efficient for the lateral velocities achievable with a balloon platform.
A temperature sensor (not shown) may also be included with the propeller motor 604, for instance as one of the health and performance sensors, because as noted above this component can generate significant heat. The processor(s) may employ the temperature sensor to cease actuation or reduce operation of the propeller when the detected heat exceeds a threshold level. The temperature sensor can also be used by the processor(s) when driving the propeller motor 604 via PWM or another technique.
The lateral propulsion system may also employ one or more safety tethers to secure components in case of failure or damage. For instance,
According to one approach, the propeller assembly would have as large a blade diameter as possible to maximize power efficiency and thrust. However, the size and weight of the propeller assembly may impact not only maximum float altitude but also launch of the balloon platform. In view of this, in some examples the overall propeller diameter may be on the order of 1-5 m, for instance 2 m or more or less. Configurations using multiple propeller blade assemblies are possible to help with performance, vibrations, controls, reliability, etc.
While a two blade propeller arrangement may be used, a three or more blade configuration 1000 as shown in
The blades may be formed of different materials. For instance, a carbon fiber or other composite outer shell with a lightweight or hollow core could be used for each blade. However, this type of configuration can be cost prohibitive. Thus, a less expensive alternative may be desirable. One such alternative is to employ injection molded blades. At operational altitudes (e.g., 60 k feet or higher), low thrust is required so stiffness of the blades is not a significant issue and there are many inexpensive materials like plastics and fiber reinforced plastics that could be employed. Also, the centrifugal force resists bending of the blades. One or more weights could be added along each blade to balance it. For a longer blade, a carbon fiber or similar spar could be included for stiffness. The length of the spar would depend on the loads to be handled. In one example, the spar length is about ⅔ the length of the blade. The spar may be glued or otherwise bonded inside the two halves of the blade shell.
The type(s) of plastics employed for the blades may depend on the loads and speeds to be handled by the propeller assembly. For instance, the blades may be polycarbonate, or a glass fiber reinforced polycarbonate, e.g., a 50% long glass fiber reinforced polycarbonate. Given the example above in which the diameter of the propeller is approximately 1.5 m, the weight of the propeller assembly may be on the order of 1.0-1.5 Kg (e.g., +/−25%). In another example, when the diameter is approximately 2.25 m, the weight of the propeller assembly may be on the order of 3 Kg (e.g., +/−25%). In further examples, the weight may exceed 3 Kg.
While the propeller assembly may include the blades in a unitary configuration (e.g., a single carbon fiber arrangement), the plastic blade configuration or other approach could employ separate blades. Here, the blades would be attached to a central hub.
This type of propulsion architecture may be used to provide an aerodynamically efficient balloon platform with upwards of 15 m/s lateral velocity vector adjustment. However, drag and maximum speed can be highly dependent on balloon tilt, shape, and size of the balloon. As the balloon envelope tilts, the drag increases, which may adversely impact system operation. Ligaments or tethers from the balloon envelope to the down connect member or other controls may help to counteract the drag.
Notwithstanding any concerns regarding drag, small to moderate amounts of lateral propulsion can provide significant benefits for station-keeping, time to return to station and safety cases. For instance,
Most of the foregoing examples are not mutually exclusive, but 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.
This application is related to co-pending application Ser. No. ______, entitled Lateral Propulsion Systems and Architectures for High Altitude Balloons attorney docket No. LOON 3.0F-2153 I [8463], filed concurrently herewith, the entire disclosure of which is incorporated herein by reference.
