Systems and methods for automated, lighter-than-air airborne platform

Embodiments disclosed herein enable routine autonomous execution of at least some major phases of aerostat operation in response to commands from human or automated external operators, a built-in decision-making capacity, or both. Various embodiments combine one or more actively controlled tethers, aerodynamic aerostat control surfaces, mechanical assistive devices (e.g., jointed arms attached to a ground station), and/or active propulsors attached to the aerostat to govern aerostat behavior during launch, flight, and landing phases of operation. Some embodiments enable automatic autonomous performance of all phases of routine post-commissioning aerostat operation, including launch, flight, and landing, without any routine need for availability of a human crew.

FIELD OF INVENTION

Embodiments of the present invention relate to aerostats, aerostat ground stations, aerostat control systems, and methods of controlling tethered aerostats.

DISCUSSION OF THE RELATED ART

Moored (i.e., tethered) lighter-than-air craft, i.e., aerostats, have had widespread use in several actual and potential applications, such as surveillance, advertising, telecommunications, and weather monitoring. There has also been increased interest in employing tethered aerostats or kite-based systems for lofting relatively small wind turbines, as such arrangements to deliver wind energy at lower cost than traditional tower-mounted turbines of comparable size and altitude, and can easily access higher altitudes (and thus steadier, stronger winds) than any practical tower system.

That aerostats can easily achieve altitudes comparable to or higher than traditional fixed towers is advantageous for several reasons, including greater coverage of earth surface at favorable angles of view from higher altitudes, greater maximum line-of-sight, and the like. Aerostat altitude is easily adjustable, while traditional tower height is not. Aerostat deployment requires little or no ground site preparation, and aerostat location is easily changed, as opposed to laborious assembly and disassembly of a tower. Given appropriate technology development, and especially for short-term applications, the capital cost of deploying an aerostat system can be much lower than that of constructing a tower. Kites offer some of the advantages of aerostats, but aerostat-based systems have the intrinsic advantage that their well-established core technology uses a lighter-than-air (e.g., helium-filled) lifting body to provide support even in the absence of wind.

SUMMARY

To more fully realize the advantages of aerostats, reliable control of aerostat launch, flight, and landing are required. For example, in various applications it is desirable that the altitude of the aerostat be controlled and that the aerostat remain approximately steady during operation. Early systems concentrated on altitude control for tethered aerostats, providing a configuration for which the aerostat is controlled to a particular altitude. An approach employing two or more actuators originating from a single actuator platform on the ground to control aerostat altitude and at least one independent attitude variable was shown and described in U.S. Pat. No. 9,187,165 B2, “SYSTEMS AND METHODS FOR ATTITUDE CONTROL OF TETHERED AEROSTATS,” the entire disclosure of which is incorporated herein by reference.

However, even advanced prior methods for altitude and attitude control have not overcome certain disadvantages of aerostat systems. Most notably, human crews are still required for the launch and landing of aerostats. Because aerostats may be damaged or destroyed by severe weather or other circumstances, crews must be ready to lower and dock them on short notice at any time of day or night. Re-launch when conditions are again favorable also requires a human crew. Such operations may be necessary at any time, mandating round-the-clock availability of a human crew. This raises aerostat operating costs. Moreover, docking operations can be hazardous for human crew members, especially in extreme weather conditions, precisely when aerostat landing is most desirable.

There is therefore a need for an aerostat system and method of operating a tethered lighter-than-air craft that eliminates the need for continual human crew availability while also realizing all the advantages of aerostats over towers and kites for various payloads.

Embodiments of the present invention may address some of the limitations of the prior art by providing an aerostat system that enables one or more of automated launching, flying, and landing. Various embodiments of the aerostat system comprise one or more of (1) a lighter-than-air craft (e.g, an aerostat) that may carry one or more payloads, (2) a ground station, which may be relocatable in some embodiments, that anchors the aerostat, typically powers, controls, and communicates with the aerostat, and communicates with various users, observers, or operators, both human and computer, (3) one or more tethers that connect the aerostat to the ground station and may comprise load-bearing cables, conductors, data transmission lines, beacons, sensors, and other components, (4) actuators influencing the position and/or attitude of the aerostat by acting upon tethers, altering aerodynamic or other properties of the aerostat, or applying forces to the aerostat via propulsors, (5) actuators influencing other attributes of the aerostat or ground station, such as blowers and/or valves affecting the aerostat pressure or heaters affecting the temperature of the enclosed gas or other components, (6) various sensors, which may be located on the aerostat, the ground station, and/or elsewhere, (7) a computerized aerostat flight controller that may be located on board the aerostat, on board the ground station, or elsewhere, and that is in communication with the aerostat and/or the ground station and with various sensors and actuators relevant to operating the aerostat system, and (8) a computerized automated dispatch controller, located near the ground station in some embodiments or elsewhere in some other embodiments, that communicates with the aerostat flight controller, that exchanges information with various external entities, such as sensors, system operators, clients, and weather forecasting systems, and that comprises a built-in decision engine for accommodating aerostat operations to operator requests, fault conditions, weather conditions and forecasts, and other factors.

Embodiments of the invention enable routine autonomous execution of at least some major phases of aerostat operation in response to commands from human or automated external operators, a built-in decision-making capacity, or both. Various embodiments combine one or more actively controlled tethers, aerodynamic aerostat control surfaces, mechanical assistive devices (e.g., jointed arms attached to a ground station), and/or active propulsors attached to the aerostat to govern aerostat behavior during launch, flight, and landing phases of operation. Some embodiments of the invention enable automatic autonomous performance of all phases of routine aerostat operation, including launch, flight, and landing, without any routine need for availability of a human crew.

In one embodiment, a system for control of an aerostat includes a ground station and a first tether to connect a lighter-than-air balloon to the ground station. The system includes one or more sensors to determine an orientation of the balloon, one or more sensors to determine a location of the balloon, and one or more actuators to affect the orientation and/or location of the balloon. A flight controller is configured to receive information from the one or more orientation sensors, the one or more location sensors, and further configured to control the one or more actuators. An automated dispatch controller is configured to receive inputs from a source which is external to both the system and the balloon.

According to another embodiment, a method of controlling landing of an aerostat is disclosed. The aerostat is attached to a ground station with one or more tethers, and the method includes retracting the one or more tethers to bring the aerostat toward the ground station during a descend phase. The method also includes, upon the aerostat reaching a specified altitude, automatically transitioning to a capture mode during which the ground station makes physical contact with the aerostat and/or bridles attached to the aerostat. Further included is verifying physical contact of the ground station with the aerostat and/or bridles attached to the aerostat. Upon verified initial contact of the ground station with the aerostat and/or bridles attached to the aerostat, the method includes automatically transitioning to a dock mode during which the aerostat moves from an initial ground station contact position to a docked position on a cradle of the ground station or other docking surface.

In yet another embodiment, a method of determining a risk of a failure associated with an aerostat is disclosed. The method includes receiving a present measurement of each of one or more current wind conditions from a sensor positioned on an aerostat, receiving a value of each of one or more physical attributes of the aerostat, and receiving a value of each of one or more target physical set points of the aerostat. The method further includes determining an estimated risk of a failure based on at least: the present measurement of each of the one or more current wind conditions; the value of each of the one or more physical attributes of the aerostat; and the value of each of the one or more target physical set points of the aerostat.

According to a further embodiment, a bridle capture system for an aerostat bridle includes a bridle block having a plurality of bridles attached to the bridle block, and a tether attached to the bridle block. The bridle portion has higher portion and a lower portion, wherein the higher portion has a larger width than the lower portion, and the bridle block includes at least two side faces which are angled outwardly from a center of the block in the direction from the lower portion to the higher portion. The system also includes a bridle block catch positioned on a landing platform, the bridle block catch having a top opening with a width that is larger than the width of the bridle block at the lower portion.

These and other aspects of embodiments of the invention will be clarified with reference to the figures.

DETAILED DESCRIPTION

FIG. 1is a schematic diagram depicting two cross-sectional views of major mechanical components of an illustrative automated aerostat system100in a first state of operation according to an embodiment of the invention. The assembly100comprises an aerostat102, here depicted in a docked or grounded state of operation, and a ground platform104. The ground platform104comprises a fixed ground contactor or base106, a bearing mechanism or rotator108that rotates around its vertical axis with respect to the base106, a main platform110that rotates upon the rotator108, and a cradle112within which the aerostat102rests when in a docked state. The cradle112may comprise a soft pad or pads possessing or possessing together a concavity or groove on its upper surface, or may comprise flat plates, nose cones, inflated tubes, bars, or other structures meant to interface with the aerostat while in the docked position. The aerostat102is connected to the main platform110by a number of tethers, e.g., tethers114and116. The illustrative embodiment ofFIG. 1comprises three tethers (two fore, one aft); various embodiments comprise one, two, or more tethers. The tethers can be payed out or reeled in by mechanisms (e.g., winches), not depicted inFIG. 1, that are comprised by the main platform110. The main platform110is substantially aligned with the aerostat102when the aerostat102is nested in the cradle112and is preferably approximately aligned with the aerostat102when the aerostat102is not in contact with the cradle112(i.e., when the aerostat102is launching, landing, or at flying altitude). In some embodiments, the main platform110is precisely aligned with the aerostat102when the aerostat102is nested in the cradle112. Also, the assembly100points approximately into the wind at all times to minimize wind forces not acting along the long axis of the aerostat, thus minimizing total wind force on the system as well as system stability. Alignment is maintained by having the rotator108turn so that the main platform110and aerostat102point approximately into the wind at all times. Wind alignment can be maintained by an active system that detects the direction of incident wind and commands a motor to rotate the rotator108correspondingly; or, by a passive weather-vane-type system in which the torque exerted by non-axial wind forces on the linked system of aerostat102, tethers (e.g., tethers114,116), and main platform110rotates the upper portions of the assembly100upon the rotator108to minimize this torque; or by a combination of these and/or active and passive alignment mechanisms.

The ground station104can also comprise various components not depicted inFIG. 1in this and other embodiments, including electronic controllers, sensors, telecommunications devices, a power source or power-source connections, wheels, rails/tracks and associated carriage mechanisms, a multiplicity of pads rather than the single pad depicted inFIG. 1, an aerostat catch-and-release mechanism, a docking nose cone, and other components.

FIG. 2Ais a side-view schematic of the assembly100ofFIG. 1in a second state of operation. InFIG. 2A, the aerostat102is at a low altitude, where “low” signifies that the aerostat is below a defined minimum flying altitude200. The minimum flying altitude is an altitude above which the aerostat may fly and implement its automated flight processes, and may for example be equal to two to four times the length of the aerostat in some embodiments. In some embodiments, the minimum flying altitude may be three times the length of the aerostat. In some embodiments, the minimum flying altitude may not be related to the length of the aerostat. The minimum flying altitude may be outside the range of two to four times the aerostat length in some embodiments. A functional or mission requirement may be part of determining a minimum flying altitude in some embodiments, while in other embodiments a selection of a minimum flying altitude may be made without reference to aerostat characteristics, functional or mission requirements, or environmental circumstances. For example, a minimum flying altitude may be selected simply as a convenient altitude at which to transition control logic from launch control to flight control and/or flight control to land control. The state of operation depicted inFIG. 2Acan occur during a landing process, whereby the aerostat102is drawn down from a higher altitude to the ground station104by reeling in the one or more tethers (e.g., tethers114,116), or during a launch process, whereby the aerostat102is released from the ground station104and flown to a higher altitude by paying out the tethers. Various embodiments provide for autonomous performance of landing and/or launching processes, where “autonomous” signifies that physical human presence on the site of the aerostat system100(to, for example, grab handling lines dangling from the aerostat102) is not, in general, required. Though a human may be present during autonomous modes.

FIG. 2Bis a side-view schematic of the assembly100ofFIG. 1in a third state of operation. InFIG. 2B, the aerostat102is at a flying altitude, i.e., the aerostat102is above the minimum flying altitude200.

InFIGS. 2A and 2Ba nonzero wind condition is depicted, with the aerostat102displaced downwind with respect to the ground station104; in a zero wind condition, the aerostat102would fly directly above the ground station104.

FIG. 3is a schematic diagram depicting some components of an automated aerostat system300according to an illustrative embodiment of the invention. The system300comprises an aerostat system100(aerostat, ground station, tethers, sensors, actuators, and other components), an aerostat Flight Controller304which exchanges data (e.g., commands, telemetry) with the aerostat system100, and an Automated Dispatch System306. All information exchanges between components depicted inFIG. 3and in other figures herein may take place in a wired manner, a wireless manner, or both: e.g., communications between the Flight System306and the aerostat system100may take place via a fiber-optic cable, or via a low-power radio link, or by other means. All information exchanges between components depicted inFIG. 3, whether wired or wireless, direct or networked, may be encrypted and otherwise secured (e.g., with passwords for command users) to protect system security. Moreover, all computational capabilities depicted inFIG. 3and other figures herein may be entirely on-site with the aerostat system100, entirely off-site, partially both, partially in the Cloud or other distributed computing system, and/or in a customer or other operating center. The unit's computational capacity depicted inFIG. 3and elsewhere herein are illustrative, not restrictive.

The aerostat Flight Controller304directly receives data from sensors on board the aerostat system100and directly transmits operational commands to actuators on board the aerostat system100. The Flight Controller304may be located on board the aerostat or the ground platform, or its functions may be divided between hardware units located on both the aerostat and ground platform.

The Automated Dispatch System306comprises a device having a programmable computational capability, the Dispatch Controller308. The Dispatch Controller308may also receive data inputs from dedicated environmental sensors310comprised by the Dispatch System306. The Dispatch Controller308will be understood to include memory, communications, machine-human-interface, and other capabilities (not depicted) as well as a computational capability. The environmental sensors310are co-located with the aerostat system100(e.g., as a component of the ground station). Some portions of the Dispatch Controller308(e.g., data store, devices enabling communication with the Flight Controller304) may also be co-located with the aerostat system100. The computational capability of the Dispatch Controller308may be co-located, remotely located, or partially both. A co-located computational capability may be backed up by a remote capability in case of failure. The environmental sensors310may be of any type, as for example LIDAR or RADAR for sensing of wind speeds, airborne debris, and approaching airborne vehicles or birds; thermometers; cameras; anemometers; ground intruder detectors; and other.

The Dispatch System306may comprise one or more human-machine or machine-machine interface elements. An interface element may be on-site with the aerostat system100, or remotely located (e.g., communicating with the Dispatch System306via the Internet), or both. Where more than one interface is implemented, a predetermined hierarchy excludes simultaneous control by more than one user in some embodiments. An on-site, password-protected human-machine interface provides control override capability in some embodiments.

The Dispatch System306may also interface with external entities or organizations, e.g., entity312. An appropriate interface protocol (e.g., TCP-IP or UDP) may be employed for communications between the Dispatch Controller308and an external entity312such as a customer operating center.

An appropriate interface protocol (e.g., OPC, OPC-UA, or Profibus) may be used for communications between the Dispatch Controller308and the Flight Controller304. Manufacturer-specific or other protocols, including real-time communications protocols, may be used for communication of data and commands between the aerostat Flight Controller304and the various actuators and sensors comprised by the aerostat system100with which the Flight Controller304is in communication.

The automated aerostat system300performs storage of sensor data, flight telemetry, system state changes, commands issued, alarms and faults, and other system states in some embodiments. Such data storage may be implemented both by an on-site memory capacity (e.g., a capacity of the Dispatch Controller308) and by an off-site memory capacity (e.g., a memory capacity which the aerostat system300is in communication via the Internet). By these means, system records are likely to preserved even when the system's network connection is down or in the event that the memory capacity of the Dispatch Controller308fails.

The Dispatch Controller308can receive inputs from any number of external sources, e.g., a weather forecast source314. Other possible inputs include specifications of aerostat operational parameters (e.g., priority parameters specifying the value of system availability vs. system safety) originating from one or more external organizations312such as a customer operating center, municipal or government agency (e.g., FAA), manufacturer's operating center, or other. Such inputs will inform operational decisions made by a decision capability of the dispatch system306. The Dispatch Controller308also receives aerostat system feedback and status and sensor data from the aerostat Flight Controller304in some embodiments.

The Dispatch Controller308can transmit outputs to any number of external receivers, e.g., one or more external organizations or the aerostat Flight Controller304. Data transmitted to external organizations can include summary status feedback on the aerostat system300and/or detailed telemetry, system state, or sensor data, stored or real-time. Data transmitted to the aerostat Flight Controller304can include commands such as “launch” and “land” and set points such as an altitude set point.

FIG. 4is a schematic depiction of portions of the illustrative system300ofFIG. 3detailing internal portions of the Dispatch Controller308according to an embodiment of the invention. In particular, in the illustrative embodiment ofFIG. 3andFIG. 4, several subsystems of the computational capability of the Dispatch Controller308are depicted. These subsystems include a Data Store416, a Decision Engine418, an Adaptive Learning Unit420, and a Dynamic Risk Assessment Unit422. In various embodiments, these subsystems, as well as additional subsystems (e.g., an operating system) not depicted inFIG. 3, may be implemented as separate hardware units, or as units of software functionality in a single computational device, or in multiple computational devices (e.g., both on-site and in the Cloud), or in some combination of these manners. In the illustrative embodiment ofFIG. 4, the Data Store416is a distinctive device (e.g., hard drive) comprised by the Dispatch Controller308, and the Decision Engine418, Adaptive Learning Unit420, and Dynamic Risk Assessment Unit422are implemented as bodies of instruction code stored in the Data Store416and executed by a processor comprised by the Dispatch Controller308.

In the illustrative embodiment ofFIG. 4, the Dispatch Controller308implements methods of an automated dispatch system. These methods include the code by which the functional subunits Decision Engine418, Adaptive Learning Unit420, and Dynamic Risk Assessment422are implemented. The Data Store416facilitates communication with external interfaces of the Dispatch Controller308and between the functional subunits. In schematic representations of various other embodiments, the functional subunits and flows of command and data indicated by arrows inFIG. 4may differ in number and arrangement while accomplishing tasks essentially similar to those described herein, as well be readily apparent to persons familiar with computer design and control systems.

The functions ascribed hereinbelow to the functional subunits of the Dispatch Controller308can in various embodiments be realized in software and executed on hardware according to methods well known to persons familiar with computer science and systems control theory.

Reference is now made to the functionality of the Decision Engine418ofFIG. 4. As will be clear to persons familiar with computer science, the functionalities about to be described for the Decision Engine418and other functional subunits can be implemented using tools (e.g., programming languages, hardware) readily available from existing sources, although not hitherto employed by aerostat control systems, to enable the advantages described herein.

The Decision Engine418may make use of weather forecast data, sensor and telemetric data from the aerostat system, site geographical data, default or user-specified operational targets and parameters, and potentially other inputs to calculate optimal set points (e.g. altitude or attitude) to which to command the aerostat and to otherwise command the aerostat and its payload (not depicted). The Decision Engine418includes software and hardware for formatting and transmitting the chosen set points and other commands to the aerostat Flight Controller304and the aerostat payload. Illustrative commands that may be issued by the decision engine to the aerostat and its payload are commands to change aerostat altitude and/or attitude, commands to land or launch the aerostat, commands to turn capabilities of the payload on and off, commands to change the orientation of the payload, and the like. In an example, if the payload of the autonomous airborne platform is agriculture monitoring equipment, then the Decision Engine418calculates, with help from external inputs (e.g., user commands specifying what areas of a farm or field to be monitored), the preferred orientation of the agriculture monitoring equipment (which may differ from the orientation of the aerostat). In another example, if the payload is telecommunication equipment, then the Decision Engine418may know the regions of greater population or customer density and use that information to inform the decision of output commands and set points.

The Decision Engine418may also make use of weather-forecast data and dedicated environmental sensors310comprised by the Dispatch Controller308to determine when the aerostat should launch or land, or set appropriate altitude, attitude and/or other set points, based on aerostat flight wind limits, docking wind limits, operational considerations, or other preprogrammed terms. There are three primary aspects to the launch-land decision:1) Response to immediate sensed conditions (weather, aerostat telemetry, user demand inputs, etc.)2) Response to predicted conditions (weather, user demand, etc.)3) Tolerable risk level or other inputs from the Dynamic Risk Assessment unit422(to be described further below).

The Decision Engine418also incorporates an adaptive weighting of the relative importance of a possible response to immediate conditions and a possible response to predicted conditions, and weighs or averages those responses accordingly. This adaptive weighting is calculated by the Adaptive Learning Unit420, to be described further below.

The Decision Engine418may be constructed to incorporate the concept of flight envelopes. Herein, a “flight envelope” is defined as a surface in an N-dimensional flight space (N≥1) whose N dimensions are physical, environmental, and/or control variables pertinent to the flight behavior of an aerostat. With a subregion of the flight space bounded by one or more flight envelopes, the flight behavior of the aerostat has a certain most-probable character, as for example the character of passive stable flight, of stable flight achievable with active control, of unstable flight with or without active control, or of flight failure. A flight envelope may in part or whole be a region of gradation rather than an abrupt edge or surface; also, flight envelopes may have various topologies (e.g., simply connected, multiply connected). Examples of variables that can define a flight space include wind angle of attack, wind sideslip, wind variability, average wind speed, wind elevation angle, rate of wind heading change, rate of wind elevation angle change, aerostat attitude (pitch, roll, yaw), aerostat altitude, aerostat location with respect to ground station, tether tension(s), mean tether tension vector, aerostat center of mass with respect to center of buoyancy, aerostat buoyancy, aerostat center of mass with respect to center of pressure, precipitation, lightning proximity, or other variables. As these examples show, variables of a flight space can include both observed, uncontrolled variables such as wind characteristics and settable variables such as aerostat altitude. Other possible variables include aerostat fin angle of attack, aerostat fin anhedral angle, aerostat fin surface area relative to the aerostat body size, control surface settings, and any number of other variables. The number of flight-space dimensions may vary with time, installation, aerostat type, and other conditions.

Flight envelopes typically define nested, continuous subregions of the flight space. A conceptual cartoon of nested flight envelopes is shown inFIG. 5. This drawing is illustrative, not a strict depiction of any actual geometry. The flight space500ofFIG. 5is defined by N=6 dimensions whereof the 6 axes are depicted as dashed arrows (e.g., axis502). A first flight envelope504bounds an ellipsoid wherein passive stable flight of the aerostat occurs. The first envelope504and a second envelope506together bound a region wherein stable flight is possible, but only with active control (e.g., of tether lengths and aerostat control surfaces). The second envelope506and a third envelope508together bound a region wherein flight is unstable, even with active control. Outside the third flight envelope508, safe flight may not be possible. In other embodiments, more or fewer flight envelopes and corresponding subregions of flight space could be defined.

The Decision Engine418ofFIG. 4may be cognizant of the flight envelope structure in N-dimensional flight space for a given aerostat, ground platform, and control system. At any given moment, a given aerostat occupies a single point in the flight space. In an example, if axis502is the axis of wind speed, starting at zero wind speed and moving solely along axis502will eventually take the aerostat outside the third envelope508into the region of no flight: that is, above a certain absolutely velocity, wind will destroy the aerostat system no matter what other conditions prevail. Typically, the goal of the Decision Engine418is to maintain the aerostat in flight, which means maintaining the aerostat within the passive-stable region or stable-with-active-control region of the flight space. Exceptions can occur, e.g., if flight failure is highly probable the controller may precipitate a failure mode to limit damage to person or property.

Aerostat flight behavior in any region of the flight space is probabilistic, not certain: thus, some level of risk is associated with every point in the flight space, where “risk” can be conceived as a probability density function over the performance space of the aerostat system (i.e., that space whose dimensions comprise aspects of aerostat condition and behavior, payload condition and behavior, etc.). In an example, the “risk” associated with a certain point in the flight space includes both (a) a relatively high risk of failure to perform a payload task, such as delivering telecommunication signal, and (b) a relatively low probability of damage to the aerostat. (The aerostat is safer, but the job may not get done.) Moreover, risk is typically nonuniform within subregions of the flight space: in an example, within the region of stable flight with active control, risk is higher near the unstable-flight envelope508and lower near the passive-stable-flight envelope504. Risk is also typically nonstationary in the statistical sense, that is, the risk assigned to each point of flight space may vary in response to environmental variables, command inputs, time of day, or other factors.

The Decision Engine418ofFIG. 4may be cognizant of the risk or risk distribution assigned to each point in the flight space, however this is assigned. In general, the Decision Engine418seeks to achieve user-specified goals or set points (e.g., time aloft, altitude, and the like) while minimizing overall risk. The determination of command outputs by the Decision Engine418is shaped by settable weights or functions that parameterize the decision-making algorithm: in an example, deployment of a telecommunications payload may be given a relatively high or low priority compared to non-fatal damage to the aerostat, depending on the criticality of the payload service. Also, the Decision Engine418can use the likely time-course of upcoming weather as based on forecasts or internal predictive algorithms, along with information about rates at which the system can in the future progress through the flight envelope (e.g., how long it takes to launch, adjust flight variables, land), in order to determine real-time risk and to inform the command and set point outputs of the automated Dispatch Controller308. For purposes herein, “real-time risk” refers to a risk which has been determined based on data that is sufficiently current to provide a reasonably reliable estimate of the immediately present state of the data. In some embodiments, all of the wind condition data used in assessing real-time risk may be no more than five seconds old. In some embodiments, all of the wind condition data may be no more than thirty seconds old. In some embodiments, all of the wind condition data may be no more than one minute old. The particular amount of time that has passed for data to still be considered real-time may vary relative to the particular value being measured or received. For example, the buoyancy of the aerostat may vary over time due to air temperature, but twenty minute-old data may be relevant for a real-time risk assessment. Whereas for a wind heading, data may be limited to measurements taken less than five seconds ago. Similarly, a “present measurement” includes measurements which have been taken sufficiently recently to provide a reasonably reliable estimate of the immediately present value of a condition. For purposes herein, determining a risk is meant to include determining an estimated risk, or estimating a risk.

The Decision Engine418also may reference settable criteria for setting alarm conditions that are transmitted to one or more control systems and/or human operators in some embodiments, e.g., by text message, alarm sounding, and/or other forms of alerting. The Decision Engine418may control one or more aerostats, either co-located or in diverse locations.

Reference is now made to the functionality of the Dynamic Risk Assessment unit422ofFIG. 4. In one embodiment, the Dynamic Risk Assessment unit422sends a value for tolerated risk to the Decision Engine which the Decision Engine418may use to determine commands and set points. Here, a “value for tolerated risk” may be a single scalar number or a vector specifying tolerable risk for a number of variables. Moreover, “risk” may comprise estimates of both event probability and event cost, or may be calculated as a function of these. Risk values may be attached to damage to particular aerostat components, damage to particular ground platform components, payload damage, failure to perform payload function, loss of aerostat and/or ground platform, collision with an airborne vehicle, and any other event that may be construed as undesirable by system programmers.

The algorithm employed by the Dynamic Risk Assessment Unit422determines and updates tolerable risk values either continuously (e.g., at a rate limited by computational capability) or at fixed intervals, and bases its determinations upon a number of factors. These factors may include the following, as well as others not specified herein:Input from an external entity (e.g., customer(s) operating center, municipal or governmental agencies) on the importance of having the payload remain in a particular position and orientation at a particular time.Knowledge of aerostat system maintenance status or predictive maintenance system status (service recently done, service overdue, upcoming service needs, system health status) and its impact on risk on continued flight and mission performance.Customer desired performance metrics (e.g., up-time, platform stability, platform orientation and altitude).Knowledge of the system's current (e.g., monthly) up-time status.

In an example, the algorithm employed by the Dynamic Risk Assessment Unit422determines the probability and cost of payload up-time loss and of damage if the aerostat remains flying, and communicates these risk assessments to the Decision Engine418.

The Dynamic Risk Assessment Unit422may assess risk for one or more aerostats, either co-located or in diverse locations. Assessed risk may be a system-wide risk as opposed to an agglomerate of individual risks.

Reference is now made to the functionality of the Adaptive Learning Unit420ofFIG. 4. The Adaptive Learning Unit420logs and evaluates historic system aerostat launch, flight, and landing operations and responses under recorded environmental conditions (e.g., temperature, wind). The goal of such evaluation is to adapt operational parameters for launch, flight, and landing to achieve better performance according to defined metrics (e.g., rapidity of response, reduction of risk, expanding stable flight envelope, minimizing power consumption, minimizing transient motion or attitude offsets, etc.). The output of the Adaptive Learning Unit420is communicated to both the Dynamic Risk Assessment Unit422and the Decision Engine418as an input to their own algorithms. In an example, one output of the Adaptive Learning Unit420is a set of adjusted flight envelopes. The Adaptive Learning Unit420can be implemented using a variety of techniques known to persons familiar with the field of machine learning. In various embodiments the Adaptive Learning Unit420is implemented as a neural network, plant model and Kalman filter, or genetic algorithm.

The Adaptive Learning Unit420may perform Adaptive Learning for one or more aerostats, either co-located or in diverse locations, and may work in conjunction with other Adaptive Learning Units to leverage a larger pool of historic data.

The system and method of various embodiments comprises an autonomous flight sequence, where “autonomous” signifies a lessened need for human presence at the aerostat operational site and/or for human control intervention either locally or remotely, possibly to include no need for human presence or intervention. The autonomous flight sequence is implemented by the Flight Controller304ofFIGS. 3 and 4to enable the advantages of autonomous aerostat operation to be realized. The autonomous flight sequence may comprise a sequence of system modes of operation of the various components of an aerostat system (e.g., the assembly100ofFIG. 1) which enable the aerostat to transition from a secured state (i.e., aerostat firmly coupled to ground station) to a docked state (i.e., aerostat is in contact with the ground station but not secured thereto) through launching (i.e., aerostat is attached to the ground station only by one or more tethers and is ascending but has not yet achieved the minimum operational flying altitude) to a flying state. From the flying state, the autonomous flight sequence can be reversed to enable the aerostat to transition through the modes of flying, landing (i.e., aerostat is attached to the ground station only by one or more tethers, is descending, and has passed below the minimum operational flying altitude), docked, and secured. In prior art, on-site human presence is mandatory for the accomplishment of these sequences. Modes may comprise sub-modes: in an example, the flying mode has sub-modes of ascent, steady-state flight, and descent.

Each operating mode has a corresponding set of control laws. The control laws define the operation of settable or controllable components of the aerostat system, such as tether winches, aerostat control surfaces, aerostat propulsors, ground station slew systems, and the like. Transitions between the modes and their sub-modes are managed in part by commands from the decision engine (which is informed in part by commands from an external entity), programmed operational set points, inputs from airborne and/or ground-based sensors, and possibly other factors. In an example, a remote operator commands retrieval of the aerostat and the decision engine of the dispatch controller issues a command to dock. The flight controller, upon receiving the command to dock, manages transition through steady-state flying submode, descent submode, landing mode, docking mode, to docked mode. In another example, the decision engine of the dispatch controller detects unacceptably risky weather conditions in a near-term forecast and autonomously manages retrieval of the aerostat by issuing a command to dock; when weather again permits aerostat flight, the decision engine autonomously re-launches the aerostat by issuing a command to launch.

FIG. 6is a state diagram depicting an illustrative set of operational modes and submodes of an autonomous flight sequence600and the transitions between the modes. Five modes are defined, namely (1) Docked602, (2) Autonomous Launch604, (3) Autonomous Flight606, (4) Autonomous Land608, and (5) Autonomous Secure610. The number, identity, and transitional relationships of modes comprised by an autonomous flight sequence may differ in various embodiments from the modes depicted inFIG. 6. In some embodiments, one, more than one, or all of the modes need not necessarily be fully autonomous or even partially autonomous. For example, in some embodiments, the launch mode may be performed entirely manually while the launch, flight, land, and secure modes may be autonomous.

For purposes herein, the term “mode” denotes a mode of operation which may include inventive methods and control of physical devices. In some embodiments, some or all of the physical devices may be known devices. In some embodiments, new device arrangements may be operationally controlled by the system during a given mode of operation. A “mode” is also referred to as a “process” or equivalent terms herein.

Below, five modes of the autonomous flight sequence600are as follows:

1) Docked602. The nominal starting point for the system is in the Docked position602. In the Docked position602, the tether or tethers are pulled all the way in and the aerostat is held in its cradle (which may comprise pads or other supports) by the tethers and potentially by the bridles and other mechanisms, e.g., a nose cone, belts, latches, magnets, or the like. However, the aerostat is not fully secured to the ground station.

2) Autonomous Launch604. The Autonomous Launch mode604comprises two sub-modes, Release (undock) and Ascend, which are described in more detail hereinbelow. During Autonomous Launch604, the aerostat and its bridle(s) are disengaged from the ground station and the one or more tethers are spooled out, allowing the aerostat to rise to the minimum flying altitude.

3) Autonomous Flight606. During Autonomous Flight606, described in more detail hereinbelow, the automated Flight Controller304ofFIGS. 3 and 4receives sensor readings and generates commands to actuators of the ground station and/or aerostat in order to substantially achieve the attitude and altitude set-points received from the automated Dispatch Controller308.

4) Autonomous Land608. The Autonomous Land mode608comprises three sub-modes, Descend, Capture, and Dock, described in more detail hereinbelow. During Autonomous Land608, the ground station reels in the one or more tethers and/or bridle lines or handling lines, causing the aerostat to descend until positive contact with the ground station is made and the aerostat is pulled into its final position in its cradle.

5) Autonomous Secure610. The Autonomous Secure mode610comprises a sequence of sub-states (Securing, Secured, and Un-securing) that mediate between the Docked state602and a fully secured condition. During the Autonomous Secure process610, which typically makes use of sensors and actuators additional to those used in other modes, the ground station brings the aerostat into a secured state that is resistant to weather conditions more severe than those tolerated while the aerostat is in the normal, docked position and in which the aerostat may, in an some embodiments, be transported. The un-securing process reverses the securing process. The purpose of the secured state is to allow the system to “hunker down” and weather more extreme conditions (e.g. hurricane force winds) and/or transport.

InFIG. 6, transitions between modes are denoted by single- or double-headed arrows. The allowed transitions between the five modes of the autonomous flight sequence600are as follows:

1) Transition Between Docked and Autonomous Launch612. The transition from docked to autonomous launch occurs upon a “launch” command from the automated Dispatch Controller308ofFIGS. 3 and 4. In some embodiments, the system may transition back from Autonomous Launch604to Docked602upon an “abort launch” command from the Dispatch Controller308if the launch process has not substantially begun.

2) Transitions Between Autonomous Launch and Autonomous Flight614. The transition614from Autonomous Launch604to Autonomous Flight606occurs upon the aerostat reaching a minimum flying altitude, as determined by the altitude sensors or estimators.

3) Transitions Between Autonomous Flight and Autonomous Land616. The transition from Autonomous Flight606to Autonomous Land608occurs upon a “land” command from the automated Dispatch Controller308. In some embodiments, the system may transition back from Autonomous Land608to Autonomous Flight606upon an “abort land” command from the automated Dispatch Controller308if the land process has not substantially descended the aerostat below the minimum flight altitude.

4) Transitions Between Autonomous Land and Autonomous Launch618. The transition from Autonomous Land608to Autonomous Launch604occurs upon an “abort land” command (if the aerostat is substantially below the minimum flying altitude) or a “launch” command from the automated Dispatch Controller308. The transition from Autonomous Launch604to Autonomous Land608occurs upon an “abort launch” command (if the launch process has already begun) or upon a “land” command from the automated Dispatch Controller308.

5) Transitions Between Autonomous Land and Docked620. The transition [0080] from Autonomous Land608to Docked602occurs once the Autonomous Land process608is complete (as determined by the sensors used during the autonomous land process) and the aerostat is in the final docked position in its cradle.

6) Transitions between Docked and Autonomous Secure622. The transition from Docked602to Autonomous Secure610occurs upon a “secure” command from the automated Dispatch Controller308. Similarly, the transition from Autonomous Secure610to Docked602occurs upon an “unsecure” command from the automated Dispatch Controller308.

Reference is now made toFIG. 7, which further clarifies the Autonomous Land mode608ofFIG. 6. The submodes of Autonomous Land608and transitions between Autonomous Land608and the other modes of the illustrative autonomous flight sequence600ofFIG. 6are partially depicted inFIG. 7. The Autonomous Land mode608comprises autonomous submodes or processes Descend702, Capture704, and Dock706. In other embodiments, additional or different submodes may be included. The autonomous Capture and Dock submodes704,706, also referred to herein jointly as “autoland,” bring the aerostat down from a flying condition to the ground station and capture it into a docked position without the need for manual intervention (e.g., line handling or issuing of commands by a human operator). In traditional aerostat systems, in contrast, a ground crew of at least several persons is needed to capture handling lines and aid in guiding the aerostat down to the docked position. The crew is similarly needed for launch to control handling lines and aid in releasing the aerostat from the docked position. The need for a large ground crew for docking in traditional systems greatly increases the cost of docking and launching procedures. Moreover, since weather conditions may mandate aerostat landing at any time, a crew must be on call to the aerostat site around the clock to assure system operability. Moreover, delay can be entailed by crew travel to the site. Although launch timing is not as constrained, it is preferable in many applications to have launch capability at any time of day or night: e.g., after a storm passes it is desirable to have a telecommunications capability restored as quickly as possible. Embodiments of the present invention enable an aerostat system that dispenses with the costs, hazards, and delays associated with hands-on human operation. In particular, some embodiments provide the systems and methods necessary to autonomously land, capture, and dock. As mentioned above, the embodiments disclosed herein are described with reference to autonomous modes, but one, some, or all of the modes may not be autonomous in some embodiments. In some embodiments, a given mode may include sub-modes, and one of the sub-modes may be autonomous while another of the sub-modes may be manually controlled.

The Autonomous Land process608brings the aerostat from its minimum flying altitude down to its final docked position on the ground station. Descend702, the first stage of Autonomous Land608, is triggered by a “land” command from the automated Dispatch Controller308ofFIG. 3: the transition from Autonomous Flight606to Descend702is depicted as a first transition708inFIG. 7. An “abort land” command or a “launch” command from the automated Dispatch Controller308may transition the system back to Autonomous Flight606, so long as the aerostat has not substantially descended below the minimum flying altitude: the transition from Descend702to Autonomous Flight606is depicted as a second transition710inFIG. 7. If the aerostat is below the minimum flying altitude, or partially captured or docked, an “abort land” command or a “launch” command will transition the system back to Autonomous Launch mode604: the transition from Autonomous Land702to Autonomous Launch604is depicted as a third transition712inFIG. 7.

During the Descend702process, one or more winches or other tether-retracting devices pull the aerostat and its bridles from its starting flight altitude down to a selected altitude threshold or altitude range. For example, in some embodiments, a selected threshold may be 0.5 meters. In some embodiments, the altitude range may be between 0.1 meters and ten meters. Any other suitable threshold or altitude range may be used. During Descend702, the aerostat Flight Controller304ofFIG. 3performs a sequence of maneuvers to control aerostat attitude and prevent undesired behavior as the aerostat is decreasing altitude. An example of an undesired behavior due to decreased tether length is increased angular oscillation, caused essentially by conservation of angular momentum as moment arm is decreased.

The system transitions from Descend702to Capture704based at least in part upon aerostat altitude, with this transition occurring when the aerostat and its bridles are at a predetermined distance above the ground station. Capture begins with the aerostat at the aforementioned predetermined distance above the ground station. During the capture process, the ground station makes initial, verified physical contact with the aerostat and/or its bridles and then begins the process of pulling the aerostat down into its cradle (which may include holding pads, nose cone, etc.). Pulldown into the cradle continues until the aerostat proper makes first contact with the cradle. Specific actuators may be used as part of the capture process (e.g., mobile guide arms).

The system transitions from Capture704to Dock706upon initial physical contact of the aerostat with the cradle. Initial contact is detected by sensors whose data may include, for example, tether tension estimates, forces on cradle components, and laser position measurements. During Dock706, the ground station pulls the aerostat down from an initial cradle contact position to a final cradle contact position. This may include relatively small release and pull-in motions of tether(s) in order to allow the aerostat to shift on or within the cradle. Final docking of the aerostat typically involves the positive closure of latches or other mechanisms that maximally constrain aerostat movement with respect to the ground station.

Throughout Autonomous Land608, operational tasks that are handled by the Flight Controller304ofFIG. 3include but are not limited to determination of contact status, command of various adjustive maneuvers during docking, evaluation of response to such commands, some decisions to transition between modes, and confirmation of mode transitions.

The system transitions from Dock process706to Docked mode602upon positive indication of docked configuration, that is, secured (e.g., latched) positioning of the aerostat in the cradle as opposed to mere touch contact: the transition from Dock706to Docked602is depicted as a fourth transition714inFIG. 7. Such positive indication of docked status may be had via tether tension measurements, aerostat to cradle contact force measurements, laser position indicators, electrical contacts, or other means.

The system may transition from Autonomous Launch604to Autonomous Land608upon receiving an “abort launch” command or “land” command from the automated Dispatch Controller308ofFIG. 3: the transition from Autonomous Launch604to Autonomous Land608is depicted as a fifth transition716inFIG. 7. In this case, the aerostat Flight Controller304will determine the sub-mode of automated land (descend, capture, dock) into which the system transitions based upon previous automated launch sub-mode, current docking actuator positions, and sensor readings. The latter may include cradle force sensors, tether tensions, laser position sensors, aerostat altitude sensing or estimation, or other means.

FIG. 8Ais a schematic depicting an aspect of a method of control comprised by various embodiments that enables autonomous landing of an aerostat. InFIG. 8A, this aspect of control method is clarified with reference to the illustrative assembly100ofFIG. 1. A volume of space800having approximately the shape of an inverted cone is centered over the ground station104. This conoid volume is herein termed the “cone of comfort”800and is indicated in frontal vertical cross-section by dashed lines802,804. The upper end of the cone of comfort800terminates at the minimum flying altitude200and the lower end terminates approximately at the level of the ground station104. In the state of operation of assembly100depicted inFIG. 8A, the aerostat102floats in a stationary manner directly above the ground station104. In various embodiments, the angular extent of cone of comfort in any vertical cross-sectional plane is defined by a cone-of-comfort angle θ806. In general, the cone-of-comfort angle θ806varies with orientation, that is, with respect to a horizontal angle of rotation ϕ, and is thus definable as a function θ(ϕ). Typically, the cone of comfort will have an approximately elliptical cross-section, be symmetrical with respect to a plane aligned with the ground station104and aligned therewith (i.e., a plane perpendicular to the plane ofFIG. 8Aand passing through the center of the ground station104), and be asymmetrical with respect to other planes. For example, the cone of comfort800will typically extend equally to left and right of the ground station104(in the view ofFIG. 8a) but extend further downwind than upwind at any given altitude.

The foregoing description of an illustrative cone of comfort800assumes that the conoid volume is bounded by a ruled surface (i.e., a surface that can be generated by translating and rotating a straight line). In various embodiments, however, the conoid is bounded in a more complex manner, e.g., a manner determined by features of the specific mechanical character of the assembly100(e.g., aerostat flying properties, locations of tethers) and/or by dynamic factors such as wind gustiness. In general, the bounds of the cone of comfort800are known and/or dynamically calculated by the Flight Controller304ofFIG. 3. In brief, the operational goal of the Flight Controller304is to maintain the position of the aerostat102within the cone of comfort at all times during a descent or launch process. Straying outside the cone of comfort800entails a level of risk that has been deemed unacceptable (e.g., by a human operator or designer or by software executed by the Dispatch Controller308ofFIG. 1); the bounding surface of the cone of comfort800is, then, determined by a combination of system mechanical properties and acceptable risk. Risk is acceptable inside the cone, unacceptable outside.

FIG. 8Bschematically depicts an illustrative trajectory of the aerostat102during a Descend process702such as that described with reference toFIG. 7. In the depicted case, the aerostat102is presumed to begin its descent from above the minimum flying altitude200and to possess some initial oscillatory motion, or to have an oscillatory motion imparted by wind forces during descent, or both. In the descent depicted inFIG. 8B, the path808, although oscillatory, is such as to keep the position of the aerostat102within the cone of comfort800. Here, aerostat “position” is defined as the location of the center of gravity of the aerostat102: in various other embodiments, position may be defined otherwise, e.g., as the extent of the main body of the aerostat102, or of its fins.

By the conservation of angular momentum, in the absence of sufficient damping, the amplitude of a pendulum's swing increases if the pendulum's length is progressively shortened; similarly, the tendency of an aerostat102having oscillatory motion is for the oscillations to increase as the aerostat is drawn down. This tendency is depicted inFIG. 8C, where an illustrative descent trajectory810features increasing oscillations that, at least one time, place the aerostat102outside the cone of comfort800. By definition, excursion of the aerostat102outside the cone of comfort800raises risk (e.g., of aerostat damage) to an unacceptable level. In response to the detection of such a condition, the Flight Controller304ofFIG. 1can make one or more responses. A first possible response is to pause drawdown of the aerostat102and allow the oscillations to damp spontaneously to an acceptable magnitude. A second possible response is to pay out the tethers in a manner that increases aerostat altitude and, by conservation of angular momentum, decreases oscillation magnitude. A third possible response is to differentially pay out and reel in tethers in a manner that damps the oscillations. A fourth possible response is to activate propulsors or control surfaces on the aerostat in a manner that damps the oscillation. Any two or more of these responses may be made simultaneously. Other suitable responses or combinations of responses may be made as this list is not intended to be comprehensive.

Unacceptable motions or oscillations of the aerostat102, i.e. motions that take it outside the cone of comfort800, may occur not only as a result of the increasing-oscillations process depicted inFIG. 8C, but as a result of wind gusts impinging on the aerostat102during descent. In general, the goal of the Flight Controller304is to first restore the aerostat to a flight condition having acceptably low risk, and then to proceed with whatever procedure had been previously commanded by the Dispatch Controller308ofFIG. 3, e.g., launching or landing.

FIG. 9schematically depicts portions of an automated docking system for an aerostat system900according to an illustrative embodiment in which an aerostat102is anchored by a single primary tether910and a bridle. Herein, the term “bridle” refers to a group of two or more cables or lines (“bridle lines”), e.g., bridle line906, each of which is attached at one end to the aerostat102and at the other to a bridle block908. Bridle line906may also include split or branching lines, in which a bridle line may connect to a group of two or more lines, each of which may be attached to further branching bridle lines or to the aerostat, and so on. Typically, the bridle lines converge from points of attachment on the aerostat102to the bridle block908. From the bottom of the bridle block908a single or primary tether runs to the ground station. In a typical single-primary-tether aerostat system, M bridle lines converge to a bridle block908and a single tether910leads from the bridle block908to the ground station912, where the tether910is payed out or reeled in by a winch or other mechanism (not depicted inFIG. 9).

The bridle-capture system of the illustrative embodiment ofFIG. 9comprises two complementary subsystems: (1) a bridle block908comprising one or more sensor-detectable orientation tags (e.g., tag914) and other features to be described hereinbelow; and (2) a ground-station capture system comprising a bridle catch port916, bridle-line capturer (e.g., hooks918,920), bridle-line actuators (e.g., rails922,924,926), orientation-tag sensors (e.g., sensor928), and cradles930,932. The components and operation of one embodiment of a bridle-capture system comprised by assembly900will be clarified in following figures. Other bridle-line capturers may include snatch blocks, articulated rollers, actuated or passive pinch rollers, capstans, spools, windlasses, bobbins, or other suitable capturer.

InFIG. 9, the aerostat102is depicted as being partway through an automated launch or landing process; that is, the aerostat is below the minimum flying altitude and is relatively close to the ground station912. Specifically for the Autonomous Land process608ofFIG. 7,FIG. 9depicts the Aerostat102as substantially through the Descend process702ofFIG. 7and nearing the transition to Capture704.

FIG. 10depicts the two complementary subsystems of the bridle-capture system ofFIG. 9in more detail:

1) Bridle block subsystem1000: In the illustrative embodiment, the bridle block908is structured as follows: Four bridle lines (e.g., line906) converge from the aerostat to the bridle block908. The bridle catch block908has a characteristic, nonisotropic shape which in this embodiment approximates an inverted, truncated, square pyramid. The four bridle lines are attached to the four corners of the upper surface of the bridle block908. The primary tether910is attached to the center of the base of the block908. The block908also comprises one or more distinguishable, sensor-detectable components (e.g., near-field communications tags, magnets of specific orientations), e.g., tag914, with one or more such tags located near one or more edges of the bridle block908.

2) Block capture subsystem1002: A bridle catch port916comprises a concavity or receptacle whose shape is complementary to the anisotropic shape of the bridle block908; that is, the bridle block908fits the catch port916in a lock-and-key manner. Because of the anisotropic shapes of the block908and port916, the block908can fit into the port916only in a limited number of orientations: e.g., a symmetric four-sided truncated pyramid can be fully fitted into a four-sided pyramidal receiver in only four orientations. In some embodiments, the bridle block and the port may be arranged such that only one relative orientation results in a fit. Further, in some embodiments, the bridle block may not have discrete faces, but instead have a smooth surface without edges. For example, the bridle block may be shaped as an approximate ellipse with one or more irregular bumps along an outside wall such that the block fits into a complementary port in only one possible orientation. The ground-station capture system may also comprise a plurality of sensors (e.g., sensor928), arranged around the perimeter of the catch port916. The plurality of sensors (e.g., A, B, C, and D) are capable of sensing or identifying the proximity of the orientation tag914and of producing an electronic output signal that reports which sensor the tag914is most proximate to when the block908is fitted into the catch port916. Thus, for example, upon block fitting, sensor A may report that the tag914is proximate. The sensor reports will uniquely determine which of the finite number of fitted orientations the block908has assumed. In various other embodiments, other numbers of sensors and/or tags are employed and/or other mechanisms (e.g., electrical contacts, an overall magnetic field of the block908) are employed to detect the orientation of the snugged bridle block908with respect to the catch port916. The primary tether910is threaded through an eye or port1004or otherwise attached at the nethermost point of the catch port and is conducted thence to a winch or other mechanism (not depicted) capable of reeling in and paying out the tether910. The block capture system1002may also comprise a plurality of bridle spreaders, each of which is configured to capture and actuate one or more bridle lines. In one embodiment, an exemplary bridle spreader may take the form of openable and closeable hook assemblies, each bridle spreader comprising a hinged hook (e.g., hook920) and a hook base1006. Other exemplary bridle spreaders may take the form of snatch blocks, articulated rollers, actuated or passive pinch rollers, capstans, spools, windlasses, bobbins, or any other suitable mechanism or combination of mechanisms suitable for the capture and actuation of bridle lines. Each of these mechanisms may further comprise various sensors to measure and ensure the successful capture of bridle lines. The capture mechanism may also comprise a plurality of bridle spreader translators configured to induce translational motion to the bridle spreader and associated captured bridle lines. In one embodiment, an exemplary bridle spreader translator may take the form of one or more rails (e.g., rail922) that radiate from points near the perimeter of the catch port916. In some embodiments, the rails may radiate from the port916opening in the plane of the port opening or at some declivity with respect to the plane of the port opening. The rails (or other suitable actuator) may be oriented and positioned in any suitable manner and are not limited to radiating from the port. In some embodiments, the orientation and/or position of one or more rails may be actively changed during operation. In some embodiments, a controller may control the orientation and/or position of one or more rails. In one embodiment, each hook base1006moves along its associated rail922and each hook920is controllably driven to positions along the rail922. In other embodiments, the bridle spreader translator may take the form of a twing, barber hauler, or any other mechanism or combination of mechanisms suitable for the translation of the bridle spreader distally from the capture block. Various mechanisms well-known to mechanical engineers (e.g., pulley-and-cable mechanisms, screws, linear actuators, motors, etc.) can be used to actuate bridle spreader assemblies and bridle spreader translators in any number of manners to achieve their intended purpose. In brief, the function of the bridle block and catch port are to align the bridles into known positions and the function of the combination of bridle spreaders and bridle spreader translators is to capture the bridle lines and actuate the bridle lines so as to draw down the aerostat in a controllable fashion.

It should be appreciated that the aforementioned mechanisms may be utilized to actuate one or more bridle lines, and that it may not be necessary for all bridle lines to be so actuated in order to achieve the objective of docking or otherwise controlling an aerostat. It should be further appreciated that in some embodiments, one, several, or all of the bridle lines may be detached from the bridle block upon capture by the bridle spreader, and may be, prior to or following detachment from the bridle block, attached to a portion of the bridle spreader.

In the illustrated embodiment, the positioning of hook assemblies along their rails, as well as hook closure and opening, are controlled by the Flight Controller304ofFIG. 3. Data from the sensors (e.g., A, B, C, and D) as well as from various other sensors comprised by the ground station912are reported to the Flight Controller304. As discussed above, other bridle spreaders and bridle actuators may be used.

FIG. 11depicts the illustrative system900ofFIG. 9in a second state of operation that occurs during an automated landing process, specifically at the end of the capture process704ofFIG. 7. In the state of operation ofFIG. 11, the block908has been drawn down fully into the catch port by retracting the primary tether (port and tether not depicted inFIG. 11) through the port eye1004ofFIG. 10. The bridle lines (e.g., line906) have not been drawn down, so the aerostat102hovers some distance above the ground station912. The orientation tag914has aligned with a sensor928(in this case, sensor B ofFIG. 10). The four bridle spreader hooks (e.g., hook920) have been positioned on their respective rails (e.g., rail922) proximately to the block908.

FIGS. 12A and 12Bclarify the dock process706ofFIG. 7whereby the aerostat102is drawn down from the position ofFIG. 11into contact with the ground station912.FIG. 12Adepicts in side view portions of the system900in the state of operation already shown inFIG. 11. A hook assembly1200is shown in proximate position on its rail1202. Bridle lines (e.g., line906) diverge upward from the corners of the bridle block, which is fitted into the catch port (block and port not depicted inFIG. 12A).FIG. 12Bdepicts the system900in a state where the bridle lines have been captured by the hook assemblies and the hook assemblies have retracted to drawn down the aerostat102. That is, hook assembly1200has captured bridle line906and retracted along rail1202from the proximate position ofFIG. 12Ato a distal position. An aerostat Flight Controller304ofFIG. 3may independently control the rate that each bridle line is retracted so as to control the altitude and attitude (e.g., pitch and roll angles) of the aerostat during the retraction process. The aerostat102has been drawn down into contact with the fore and aft cradles930,932. As the hook assemblies further retract along their rails and pull the aerostat102firmly down into cradles930,932, force sensors within cradles930,932transmit force data to Flight Controller304ofFIG. 3, which transitions the system from Dock706ofFIG. 7to Docked602upon detection of sufficient contact between the aerostat and the cradles.

A typical sequence of operational states of the illustrative system900ofFIG. 9during an automated landing process is as follows:1) The four hooks of the block-capture subsystem are at distal positions on their respective rails.2) The primary tether is reeled in through the eye of the catch port until the catch block is immediately above (e.g. 0.5 m) the catch port (descend process702ofFIG. 7)3) The primary tether is reeled in through the eye of the catch port until the catch block fits into the catch port (capture process704ofFIG. 7) and has registered in the correct orientation.4) When correctly oriented block-in-port fit is determined by the Flight Controller304ofFIG. 3based on sensor reports of orientation tag proximity (beginning of Dock706ofFIG. 7), the hook assemblies are moved to proximal positions on their respective rails with their hooks in an Open state. This hook arrangement is herein termed Bridle Catching Position.5) The four hooks close on the four bridle lines. The hooks are sized, positioned, and hinged so that when they are in Bridle Catching Position and go from Open to Closed each hook will capture one of the bridle lines. Hook opening is sufficiently large so that the hook does not grip the line, i.e., the hook can slip lengthwise along the line. Each hook in its Closed state achieves closure with its hook base, disallowing escape of the bridle line. The state where the hooks have closed on the bridle lines is herein termed Bridle Caught Position.6) The four hooks move toward distal positions, sliding along their captured lines and drawing down the bridle lines and the aerostat with them.7) The four hooks cease to move distally when the aerostat makes contact with the cradles (End of Dock706ofFIG. 7).

The foregoing description assumes of correct block-in-port fit orientation, which is achieved during the Capture phase704ofFIG. 7. Correct fit is defined herein as the fit position that most closely aligns the aerostat with the cradles when the bridle line assembly is minimally twisted with respect to the aerostat and ground station. Since either the aerostat, the bridle block, or both are free to rotate unless the bridle block is fitted to the catch port and the aerostat is in contact with the cradles, the aerostat and bridle block will tend to spontaneously approximate to a state of least mutual twist: thus, correct bridle-block fit assures correct aerostat alignment with the ground station. Correct block-in-port fit is achieved as follows, where reference is again made toFIG. 10:

Upon the fitting of the block908into the port916, each sensor (e.g., A, B, C, and D) reports to the Flight Controller304whether the orientation tag914is proximate to the sensor. The Flight Controller304can readily determine from this information the orientation of the bridle block908with respect to the catch port916, and thus the orientation of the aerostat to the ground station (given a state of non-extreme bridle twist, i.e., less than 90 degrees). In an example, if the tag914is placed so that it is proximate to sensor A when the aerostat and block908are in correct alignment with the ground station912, but sensor D detects proximity of the tag914, the catch block is 90 degrees out of correct fit. In this case, the primary tether910may be payed out by the Flight Controller304ofFIG. 3by some amount to allow for free and/or forced rotation of the bridle block and aerostat toward the correct position.

If the ground platform912is oriented with wind direction during docking, the aerostat102and thus the bridle block908will tend spontaneously to be aligned with the ground platform912and catch port916. However, in general, upon first contact the bridle block908will be at least partly out of alignment with the catch port916, both in and out of the plane of the port opening.FIG. 13Adepicts a state of operation of the mechanism ofFIG. 10upon an initial, misaligned contact. Upon such contact, one or more edges of the bridle block908will contact one or more edges of the opening of port916. Unless misalignment is such as to produce forces perfectly orthogonal to all points of edge contact (a case that in in various embodiments is rendered impossible by employing a non-rectangular shape for the block908), there will be a component of force acting along the block edge at the point of contact and an equal and opposite force acting along the port edge. (Tension on the primary tether is the effective source of these forces.) These along-edge forces will be directed off-center of the bridle block908and will therefore exert a torque on the block908that will (if the forces are strong enough to overcome friction) cause it to rotate. (The port916will not rotate significantly if the ground station912is rigidly attached to the earth; or, if the upper portion of the ground station912is free to rotate, both the ground station912and bridle block908will rotate toward alignment in proportion to their respective moments of inertia.) As the block908rotates it will tend to rotate into one of its possible states of alignment with the port916. In short, continued retraction of the primary tether tends to force the bridle block908to rotate until it is aligned with and enters the port916. Rotation of the block908will tend to twist the bridle lines and transmit torque to the aerostat, rotating it as well. After the bridle block908is fitted into the catch port916, no further retraction of the primary tether is attempted.FIG. 13Bdepicts the state of the mechanism ofFIG. 10after the block908has aligned with and fitted into the port916.

Upon the achievement of block-into-port fitting, the sensors (e.g., A, B, C, and D) ofFIG. 10each report the proximity of the orientation tag914. The Flight Controller304ofFIG. 3determines from this information the orientation of the bridle block908with respect to the catch port916, and thus the approximate orientation of the aerostat to the ground station. If the bridle block908is out of correct orientation, the primary tether may be payed out by the Flight Controller304by a sufficient amount to allow for rotation (e.g., free or actuated) of the bridle block908(and aerostat) toward correct alignment. If the ground platform is oriented with wind direction during automated landing, the bridle block908and aerostat will tend spontaneously to align correctly with the ground platform912and catch port916. Capture phase704ofFIG. 7is complete when sensors (e.g., A, B, C, and D) ofFIG. 10report that correct orientation of bridle block908within catch port916has been achieved.

FIGS. 14A, 14B, and 14Cdepict in more detail the dock process706ofFIG. 7wherein the bridle-lines are caught by the hooks.FIG. 14Adepicts the mechanism ofFIG. 10in a state of operation where the block908is fitted into the port916and the hook assemblies (e.g., hook920, hook base1006) have been moved to proximal positions by the corners of the block908. That is, the hooks are in Bridle Catching Position. The hooks are sized and positioned so that their reach is ample to encircle the bridle lines (e.g., line906) near the lines' points of attachment to the block908over the full feasible range of bridle-line angular position.FIG. 14Bdepicts the mechanism ofFIG. 14Awith the hooks (e.g., hook920) closed over the bridle lines (Bridle Caught Position).

After bridle-line capture by all of the bridle spreaders, the bridle spreader assemblies are moved distally along their respective rails. This results in a portion of each bridle line being drawn down and aligned between its point of connection to a corner of the catch block and the hook assembly. Retreat of bridle spreader assemblies from the catch block thus produces drawn-down of the bridle lines and approximation of the aerostat to the ground station. Bridle spreader assembly withdrawal and bridle lines are proportioned in length to enable sufficient draw-down of the aerostat to produce firm contact with the cradle, which may comprise pads, a nose cone, and/or other ground-station components that constrain aerostat motion and enable transition to a finally secured state. It should be noted that other methods and mechanisms for retracting the bridle lines may be used to achieve substantially the same result of drawing down the aerostat to produce firm contact with the cradle. Other such mechanisms may include bridle line spools, winches, capstans, bobbins, twings, barber haulers, pinch rollers or other mechanisms or combinations of mechanisms that may have various advantages over rail systems, such as compactness.

FIG. 14Cdepicts the mechanism ofFIG. 14Awith the hook assemblies withdrawn distally from the block908: in this state of operation the aerostat is in the process of final draw-down.FIG. 14Cmakes clear that the hooks slide over the lines, lengthening the portion of each line extending from the hook to the block908(e.g., portion1400) and shortening the portion of the line that stretches between the hook and the aerostat (e.g., portion1402, only partially shown).

It will be clear that launch can be accomplished by, in essence, reversing the foregoing sequence of steps, minus any need for bridle-block orientation adjustment: e.g., the bridle spreader assemblies approach the catch port, the bridle spreaders release the bridle lines, and the primary tether is payed out until launch is aborted or a flying altitude is achieved.

An illustrative docking process for an embodiment in which an aerostat is anchored by multiple tethers is now described with reference toFIGS. 1, 2A, and 2B. The aerostat102ofFIG. 1is connected to the ground station104by three tethers, namely an aft tether116(visible in side view ofFIG. 1) and two fore tethers (e.g., tether114; both fore tethers are visible in the Front View ofFIG. 1). In various multiple-tether embodiments, the number of tethers varies from 2 to any larger number; however, the illustrative docking process here described may be readily adapted to such embodiments. A docking process for the three-tether aerostat102is as follows:1) The aerostat102begins at flying altitude, as depicted inFIG. 2B.2) Under the control of the Flight Controller304ofFIG. 3, all of the tethers are reeled in simultaneously, descend phase702ofFIG. 7. Reel-in of the tethers is not necessarily carried out uniformly: for example, if windspeed changes during drawdown of the aerostat102, the aerostat will tend to shift farther upwind or downwind with respect to the ground station104, and the lengths of the fore and aft tethers required to keep the aerostat within a desired range of pitch angles may vary accordingly. Thus, the software executing on the Flight Controller304implements a control algorithm that takes into account sensor readings of wind velocity and magnitude, aerostat attitude, estimated or measured tether length, and other inputs such as attitude set points, altitude set points or rate set points. The Flight Controller304may temporarily slow the retraction or pay out of one or more tethers during the drawdown process, and may also adjust aerostat control surfaces, activate propulsors aboard the aerostat, and take other measures, in order to achieve preferred aerostat flight behavior. This descent continues until the aerostat102is immediately above (e.g. 0.5 m) the ground station cradle112.3) During the capture phase704ofFIG. 7, all the tethers are reeled in under the control of the Flight Controller until the aerostat makes initial contact with the cradle112of ground station104. (In various embodiments, the cradle comprises two or more pads or other support mechanisms that enable the aerostat102to be in contact the ground station102without sustaining damage.) Initial contact is confirmed via sensors on one or more of the aerostat or ground station. Sensing may include force sensors in the cradle, tension sensors in the tether path, current sensors on the winch motor, laser distance sensors, or other means.4) During the dock phase706ofFIG. 7, the tethers are payed out and reeled in by a small amount as determined by the Flight Controller304in order to allow the aerostat102to settle from its initial cradle contact position into a final cradle contact position if the initial cradle contact position is not within acceptable final cradle contact position bounds. In some embodiments, predetermined sequences may be used to pay out and/or reel in tethers during the dock phase. The dock process concludes by pulling the aerostat102snuggly into the cradle112. Force, optical, electrical, and/or other sensors confirm adequate contact to the Flight Controller304, which ceases to reel in the tethers.5) With the aerostat102in contact with its cradle, additional securing mechanisms such as a nose cone, gripper arms, latches, or the like may be activated (Autonomous Secure610ofFIG. 6), if the Flight Controller's instructions or innate programming mandate that the aerostat be fully secured.

Reference is now made to the Autonomous Launch mode604ofFIG. 6. The submodes of Autonomous Launch604and transitions between Autonomous Launch604and the other modes of the illustrative autonomous flight sequence600ofFIG. 6are partially depicted inFIG. 15. Autonomous Launch604brings the aerostat from its docked position on the ground station up to its minimum flying altitude. The autonomous launch mode includes two sub-modes, i.e., Release1502and Ascend1504.

The Release process1502, the first stage of Autonomous Launch604, is triggered by a “launch” command from the automated Dispatch Controller308ofFIG. 3(transition1508). An “abort launch” command or a “land” command from the Automated Dispatch Controller308may transition the system back to Docked mode602, so long as the aerostat has not substantially begun Release1502(transition1510). Once Release1502has substantially begun, an “abort launch” command or a “land” command will transition the system to Autonomous Land mode608(transition716).

During Release1502, the aerostat and its bridle(s), if any, are disengaged from the ground station so that the only remaining connection between the aerostat and the ground station is the one or more primary tethers. In an illustrative three-tether embodiment, Release1502comprises sufficient payout of the three tethers so that the aerostat disengages from the ground station cradle (e.g. all ground station pads) and remains connected to the ground station only via the three tethers. In an illustrative single-tether-with-bridle embodiment, Release1502comprises convergence of the bridle spreaders discussed hereinabove with reference toFIGS. 9-14Cso that the aerostat rises up and disengages the cradles, followed by release of the bridle lines from the bridle spreaders, followed by disengagement of the bridle catch block from the catch port, with the end result being that the aerostat and its bridle assembly (including bridle block) are both fully disengaged from the ground station except through the single-tether connection. In various multiple-tether embodiments (e.g., that ofFIG. 1), Release1502comprises the un-setting of any winch brakes or other mechanisms that prevent payout of the multiple tethers, followed by payout of the tethers under the control of the Flight Controller304ofFIG. 3. The principles of aerostat control during ascent are, in an example, similar to those described for descent hereinabove with reference toFIGS. 1, 2A, and 2B.

The system transitions from Release1502to Ascend1504once the aerostat and bridle (if any) are disengaged from the ground station and the aerostat is at a certain distance above the ground station. For example, the transition could be set to occur when the aerostat is 0.5 meters above the ground station. Other suitable distances may be used, and the distance may be calculated or revised based on various data, situations, or equipment being used. This transition may occur at a certain height so that engaging the attitude-control algorithms employed during the Ascend phase1504avoids aerostat impact (e.g., fin impact) on the ground or ground station, e.g., by increasing aerostat pitch at an angle that causes ground conflict.

During Ascend1504, the one or more primary tethers are payed out, allowing the aerostat to ascend to its minimum flying altitude. During ascent, tether, aerostat surface, and other actuators perform a sequence of maneuvers under the control of the Flight Controller304in order to increase altitude while effecting stable flight and preventing undesired behaviors.

The system transitions from the Ascend1504to Autonomous Flight606upon the aerostat reaching minimum flying altitude: the transition from Ascend1504to Autonomous Flight606is depicted as transition1506inFIG. 15. Aerostat altitude may be measured or estimated based upon a variety of sensors, including but not limited to GPS, inertial navigation, and tether payout estimates.

The system may transition into Autonomous Launch604from Autonomous Land608(transition712) upon an “abort land” command or “launch” command from the automated dispatch controller. In this case, the aerostat Flight Controller304will determine the sub-mode of autonomous launch (Release1502or Ascend1504) into which the system transitions based upon the previous automated land submode, current docking actuator positions, and sensor readings. The latter may include cradle force sensors, tether tensions, laser position sensors, aerostat altitude sensing or estimation, or other means.

The foregoing has been a detailed description of illustrative embodiments of the invention. Various modifications and additions can be made without departing from the spirit and scope of this invention. Each of the various embodiments described above may be combined with other described embodiments in order to provide multiple features. Furthermore, while the foregoing describes a number of separate

embodiments of the apparatus and method of the present invention, what has been described herein is merely illustrative of the application of the principles of embodiments of the present invention. For example, the teachings herein are applicable to a wide range, size and type of aerostats without departing from the scope of the present invention. Shape and contour of the aerostat, number of tethers, specific actuators and docking mechanisms, and other mechanical and computational specifics are highly variable across embodiments of the invention. Accordingly, this description is meant to be taken only by way of example, and not to limit the scope of this invention.