Variable volume altitude control system for super pressure balloons

Abstract

An example super pressure balloon system with a variable volume altitude control mechanism includes a balloon envelope and a winch assembly. The balloon envelope has an interior volume that is sealed off from an external environment. The winch assembly includes a winch cord and a winch spool at a location internal to the balloon envelope. The winch assembly is operated to apply an adjustable tension that pulls a first end of the balloon envelope toward and a second opposing end of the balloon envelope. The super pressure balloon system further includes an electrical control system that drives a motor to gradually invert the balloon envelope by increasing the adjustable tension.

Description

VARIABLE VOLUME ALTITUDE CONTROL SYSTEM FOR SUPER PRESSURE BALLOONSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Patent Application No. 63 / 517,748, titled “Variable Volume Super Pressure Altitude Control System for High Altitude Balloons,” and filed on August 4th, 2023, which is hereby incorporated by reference for all that it discloses or teaches.Background

[0002] High-altitude balloons are used in diverse scientific and technological applications, including meteorology, astronomy, telecommunications, atmospheric sciences, and remote sensing. While high-altitude balloons can typically be built and operated at a lower cost than alternative types of flight vehicles, such as satellites, standard high-altitude balloons are driven by wind, making navigation and flight control a fundamental challenge.

[0003] Many balloon systems achieve functional navigation using altitude control. By adjusting altitude, a balloon can access different wind layers, or airstreams, that may flow in different directions at various heights. As a balloon ascends or descends through these layers, it can “catch” different winds that propel the balloon system in various earth-lateral directions. When planning a flight path for a balloon system, a flight operator commonly references wind data (from weather forecasts, meteorological models, or real-time measurements) to understand the wind profiles at different altitudes. During balloon flight, the flight operator then dynamically controls the altitude of the balloon system to cause ascension or descension into the layer(s) where the wind is moving in the desired direction.

[0004] The above-described use of altitude changes to access different wind layers has enabled long-distance travel, precise positioning, and functional navigation of high-altitude balloons without requiring propulsion systems or complex mechanical steering devices, thus making high- altitude balloon operations more feasible and cost-effective. However, existing methods of altitude control have shortcomings. Some rely on finite resources, while others add significant technical complexity, weight, and / or power needs to the balloon system. Consequently, these existing methods of altitude control are not well suited for small, lightweight systems designed to fly continuously foran extended period of time (e g., months or years).Summary

[0005] According to one implementation, an altitude control system controllably varies the altitude of a super pressure balloon system by using a winch assembly to vary an effective volume of an inflated balloon envelope. The balloon envelope has an interior volume that is sealed off from an external environment. Ends of the balloon envelope are sealed, gathered, and attached to a winch assembly. The winch assembly supplies an adjustable tension that pulls the ends of balloon envelope toward one another at a location internal to the balloon envelope. The altitude control system further includes an electrical control system that drives a motor to gradually invert the balloon envelope by increasing the adjustable tension.

[0006] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. These and various other features and advantages will be apparent from a reading of the following Detailed Description.Brief Descriptions of the Drawings

[0007] FIG. 1 illustrates an example super pressure balloon system that includes a winch assembly that provides altitude control during flight by varying the effective volume of a balloon envelope.

[0008] FIG. 2 illustrates another example super pressure balloon system implementing a variable volume altitude control system.

[0009] FIG. 3 illustrates a cross-sectional view of a balloon envelope that is part of a system that includes a variable volume altitude control system implementing the herein-disclosed technology.

[0010] FIG. 4 illustrates a winch assembly suitable for implementation within the variable volume altitude control systems described herein.

[0011] FIG. 5 illustrates another example balloon envelope of a system that includes a variable volume altitude control system that offers multiple volume states, each of whichcorresponds to a different theoretical altitude during flight.

[0012] FIG. 6 illustrates another super pressure balloon system implementing the herein- disclosed variable volume altitude control system.

[0013] FIG. 7 illustrates an example balloon envelope, filled with lift gas, suitable for use in a system that implements the herein-disclosed variable volume altitude control system technology.

[0014] FIG. 8 illustrates example operations of a variable volume altitude control system that is part of a super pressure balloon system.Detailed Description

[0015] In some high-altitude balloon systems, altitude control is achieved by using a valve and ballast system that is controlled to vary the buoyancy and mass of the balloon and thereby dynamically alter flight altitude. Opening the valve allows the escape of lift gas, which causes the balloon system to lose buoyancy and descend. A reverse effect is achieved by dropping ballast, typically in the form of sand or other small particles, to reduce the system’s mass and decrease the relative force due to gravity, which causes the balloon system to ascend. This approach suffers from an inherent limitation in that the available ballast and lift gas are finite resources, limiting the duration of controlled flight and carrying a heavy media that could otherwise be used for more payload mass.

[0016] Other altitude control measures have been developed for use in super pressure balloon systems designed to operate at relatively constant volume. Within a super pressure balloon system, the balloon envelope remains sealed from the external environment during flight. Because the air density outside the balloon goes down as the balloon ascends and the density of the gas inside the balloon envelope does not change once the envelope initially becomes full, the density of the system and the air outside the balloon approach equilibrium during ascent. As the balloon envelope rises, the buoyancy force on the balloon system reduces with the external air density until it eventually equals the gravitational force on the system. At this time, internal pressure stops building, allowing the balloon to fly potentially indefinitely or until the lift gas leaks out or the envelope otherwise fails. These super pressure balloon systems commonly include a balloon-internal pressure control mechanism that is used to adjust the pressure and mass within the balloon envelope by pumping air into the balloon that is contained by an internal bladder. According to one approach, thisballoon-internal pressure control system includes a flexible, air-filled space called a “ballonet” coupled to a compressor with bi-directional flow control capability. The compressor is driven to pump outside air into or out of the ballonet, similar to inflating or deflating a balloon within the larger balloon. This manipulation of the volume and density of the lift gas internal to the ballonet and the larger balloon (e.g., by compression / decompression) can be changed, causing the system to descend when the ballonet pressure is increased and to ascend when the ballonet pressure is decreased.[00171 While the above-described ballonet-type altitude control system extends the possible duration of flights in super pressure balloon systems, ballonet-type systems are complex to construct due, in part, to compressor fan speed and impeller shape changes that need to be tailored for operation at different altitudes and the high speeds required to move low-density high-altitude air. Moreover, the compressors in these types of systems are heavy and require significant power, making them impractical for use in lightweight, lower-power super pressure balloon systems.

[0018] Still another approach to altitude control in super pressure balloon systems is to use an external air-filled ballast tank. These systems allow for altitude control by altering the overall weight of the balloon system. Air can be pumped into these tanks or allowed to vent out to increase or decrease the overall system's weight, respectively, thus controlling the balloon's descent or ascent. However, this method also tends to involve more complex mechanisms, including a compressor similar to those used in ballonet-type systems, and can add considerable weight to the overall system.

[0019] The herein-disclosed technology includes a simple, low-cost, lightweight, and low- power approach to achieving altitude control in super pressure balloon systems. In contrast to the above-described systems that achieve altitude control using a compressor to change the mass of gas within the sealed balloon envelope to change the density of the overall system, the herein-proposed altitude control system employs a simple mechanical mechanism to vary the size and volume of a sealed balloon envelope, thereby changing the density of the gas within the envelope and - as a result - the altitude at which the system will float. The disclosed altitude control methodology does not rely on a consumable except for a relatively small amount of power that can be stored onboard or generated in-flight with solar panels, a generator powered by the expansion of the envelope, or a combination of the two.

[0020] The herein-disclosed altitude control technology for super-pressure balloon systemscould be employed to facilitate controlled ascent and descent across a large range of altitudes. Furthermore, the herein-described approach also provides an operator with a finer granularity of altitude control than existing altitude control systems by facilitating altitude adjustments that allow the balloon system to access different wind layers at different altitudes, thereby providing unprecedented control over the flight path and destination of the balloon system. The herein- disclosed altitude control system provides the foregoing advantages while consuming significantly less power than existing altitude control mechanisms while adding less weight to the overall system. Due to all of the above, the disclosed technology represents a significant advancement in the field of high-altitude balloon systems.

[0021] According to one implementation, an altitude control system for a super pressure balloon system employs mechanical compression to vary the volume and transient pressure within a balloon envelope. The mechanical compression can be remotely operated to actively control the ascension and descension of a balloon system, thereby enabling the balloon to fly at any altitude within its altitude control range.

[0022] In one implementation, the altitude control system is implemented within a cylindrical balloon envelope with opposing ends that are gathered and sealed (or otherwise designed to converge) and pulled internally. These gathered, sealed, opposing ends of the balloon envelope are attached to an electronically controlled winch system that uses mechanical power to controllably vary an inward tension applied to the opposing ends of the balloon envelope by allowing the opposing ends to be drawn closer together by adding tension or further apart by releasing tension. This, in turn, provides control over the overall volume of the balloon.

[0023] FIG. 1 illustrates an example super pressure balloon system 100 that includes a winch assembly 102 that provides altitude control during flight by varying the effective volume of a balloon envelope 104. As used herein, “effective volume” refers to the volume of a balloon envelope that is occupied by lift gas at a given point in time. The effective volume of the balloon envelope correlates with the externally-facing surface area of the balloon envelope. “Externally-facing surface area” is defined herein as referring to surface area on the balloon envelope that faces away from the balloon system and not toward any other portion of the balloon envelope. In contrast to externally- facing surface area, “internally-facing surface area” refers to surface area on the balloon envelope that faces toward the balloon system - e.g., toward some other portion of the balloon envelope. While in flight, the balloon envelope 104 is sealed off from an external environment such that liftgas can neither enter nor exit the balloon envelope 104. The effective volume of the balloon envelope 104 can be altered by contorting and manipulating the shape of the balloon envelope 104.

[0024] Although other shapes are contemplated, the balloon envelope 104 is shown to be cylindrical in FIG.1. The cylindrical body of the balloon envelope serves as the primary container for lift gas that is less dense than the surrounding atmosphere at equivalent pressures (e.g., air if flying in Earth’s stratosphere). For example, the lift gas contains helium or hydrogen. In Opposing ends 110 and 112 of the balloon envelope 104 are gathered, sealed, and tensioned toward one another (e.g., pulled internally) by the winch assembly 102. The winch assembly 102 includes a winch cord 114 at least partially wound about a winch spool (not shown). This tensioning contorts the opposing ends 110 and 112 of the balloon envelope to form an elongated toroid-like shape.

[0025] In the implementation of FIG. 1, the balloon envelop is constructed as a cylinder. However, in other implementations, the balloon envelope 104 is designed with converging ends, which may take on conical or toroidal shapes when inflated. In these configurations, the inflated balloon envelope may have a true “hole” in the center of the toroid that is permeable to gas external to the sealed balloon envelope 104.

[0026] In one embodiment of the invention, the opposing ends 110, 112 of the balloon envelope 104 are allowed to pop out to the outside of the balloon body when the winch cord 108 is released to a maximum-supported length. In this case, one or both of the opposing ends 110 and 112 create a sloping shoulder, such that the corresponding end of the balloon envelope assumes a winebottle-like shape. This shape is not shown.

[0027] Due to being located on an inner portion of the elongated toroid-like shape of the balloon envelope 104, the winch assembly 102 and opposing ends 110 and 112 of the balloon envelope are not visible from the exterior of the super pressure balloon system 100. However, FIG. 1 illustrates both the opposing ends 110 and 112 and the aspects of the winch assembly 102 in dotted lines to better convey their relative shapes, locations, and functions with respect to the overall system.

[0028] When the balloon envelope 104 is manipulated in shape as shown (e.g., by pulling the opposing ends 110, 112 of the balloon envelope 104 inward via attachment to the winch assembly 102), the exposed top and bottom surfaces of the balloon envelope take on a toroidal (doughnut-shaped) form and are thus referred to herein as toroidal end caps 116, 118. In one implementation, the toroidal end caps 116 and 118 are strategically designed to be less material-intensive when it comes to gathering and sealing while also providing an efficient mechanical attachment point for the winch assembly 102.

[0029] During ascent, the sealed balloon envelope 104 is filled with a lift gas (e.g., via a fill port that subsequently closed prior to ascent). Once the super pressure balloon system 100 is released, the lift gas within the balloon envelope 104 expands as the balloon ascends until the lift gas reaches the maximum volume contained by balloon envelope 104. From this point forward, internal absolute pressure stabilizes within the balloon envelope 104, and the external air pressure continues to decrease as the balloon continues to rise, effectively causing the gas inside the envelope to pressurize relative to the external air pressure. Eventually, the external air density equals the system density, causing the balloon to float at a constant altitude (e.g., a “target float altitude”).

[0030] After the super pressure balloon system 100 reaches the target float altitude, a ground-based system operator may selectively command the winch assembly 102 to increase or decrease tension that is applied to the opposing ends 110 and 112 of the balloon envelope. This tensioning contorts the shape of the balloon envelope 104 and changes its effective volume. This change in the effective volume of the balloon envelope 104 causes the super pressure balloon system 100 to ascend or descend to a new (different) target float altitude.

[0031] The winch assembly 102 includes a winch spool 106 and a winch cord 108 that is at least partially wound about the winch spool 106. In various implementations, the winch cord 108 may be either a single cord or multiple cords where the multiple cords could be configured as a pulley. The first end of the winch cord 108 is secured to the winch spool 106, and a second opposite end of the winch cord 108 is attached to one of the ends (e.g., the end 110 or the end 112) of balloon envelope 104 that have been gathered, sealed, and pulled inward as described above. An adjustable length of the winch cord 108, referred to as the “effective winch cord length LI,” extends between the winch spool 106 and the end 110 of the balloon envelope 104. The effective winch cord length LI is adjustable by rotating the winch spool 106 to release or retract additional quantities of the winch cord 108.

[0032] The function of the winch assembly 102 is to alter the effective volume of the balloon envelope 104 by changing the effective winch cord length LI and, consequently, the separation between the opposing ends 110 and 112 of the balloon envelope 104. In one implementation, the winch assembly 102 includes an integrated pulley system designed to reduce the amount of torque required to retract the winch cord 108, thereby decreasing the size and torquedemands on the winch assembly 102.

[0033] Although not shown in FIG. 1, the winch assembly 102 additionally includes an electrical control system (not shown) that leverages mechanical power to controllably vary an inward tension applied by the winch assembly 102 on the opposing ends 110 and 112 of the balloon envelope 104. This allows the opposing ends to be drawn closer together by adding tension or further apart by releasing tension.

[0034] When the winch spool 106 is rotated in a first direction, additional cord is released, thereby extending the effective winch cord length LI. This increase in the effective winch cord length LI relaxes tension on the opposing ends 110 and 112 of the balloon envelope, which causes a corresponding increase in the length of the balloon envelope 104 that is occupied by the lift gas (“effective balloon envelope length L2”). This increase in the effective balloon envelope length L2 has the effect of increasing the effective volume of the balloon envelope 104, which in turn reduces the pressure and, therefore, the gas density within the balloon envelope 104. This translates to an increase in buoyancy, causing the super pressure balloon system 100 to ascend until equilibrium is re-established at a higher altitude.

[0035] When the electrical control system drives a motor (not shown) to rotate the winch spool 106 in a second opposite direction, a length of the winch cord 108 is retracted into the winch spool 106, thereby reducing the effective winch cord length LI, increasing the inward tension on the opposing ends 110, 112 of the balloon envelope 104. This increase in the inward tension decreases the effective balloon envelope length L2, and the effective volume of the balloon envelope 104, increasing the density of the internal lift gas and thereby increasing the density of the total system. This increase in the density of the system causes the super pressure balloon system 100 to descend until it reaches an altitude where the system density once again equals the external air density, at which point the balloon would again float at a roughly constant altitude.

[0036] The above-described method of altitude control eliminates the need for high-speed compressors and circumvents reliance on consumables that, once depleted, would prevent further altitude control. Additionally, the method presents a super-pressure configuration that could passively stay aloft through a diurnal cycle (because the density of the gas in the balloon is unchanging, even if the temperature changes), which eliminates the need to use power or a different consumable to keep a balloon aloft through the night. Thus, the presently-disclosed technology presents a sustainable and more efficient means of controlling the altitude of high-altitude balloonsthan those currently known in the industry.

[0037] FIG. 2 illustrates another super pressure balloon system 200 implementing an example variable volume altitude control system. The super pressure balloon system 200 includes a balloon envelope 204 with opposing ends that are gathered, sealed, and attached to opposing ends of a winch assembly. Notably, FIG. 2 does not illustrate the winch assembly or the opposing ends of the balloon envelope, as these components are located within the balloon envelope 204 and not visible when the balloon envelope 204 is inflated and viewed as shown in FIG. 2.

[0038] The variable volume altitude control system includes a winch cord that is retractable into and releasable from the spool of the winch, which is suspended between and attached to the opposing (inwardly-tensioned) ends of the balloon envelope as generally shown and described with respect to FIG. 1. The winch assembly includes an electrical control system controllable (e.g., via ground-based command or autopilot algorithm) to retract or release additional cord from the winch, thereby increasing or decreasing separation between the opposing ends of the balloon envelope 204. The above-described inward tension applied to the opposite ends of the balloon envelope 204 manipulates the shape of the balloon, creating toroidal end caps 206, 208.

[0039] FIG. 3 illustrates a cross-sectional view 300 of a balloon envelope 302 that is part of a system that includes a variable volume altitude control system implementing the herein- disclosed technology.

[0040] The balloon envelope 302 has a cylindrically-shaped mid-section defined by a first length (L) and a first diameter (D). The balloon envelope 302 includes a first end 308 and a second opposite end 310 that are sealed, gathered, and pulled inward toward the center of the balloon envelope 302, where they are attached to opposite ends of a winch assembly 312.

[0041] In contrast to FIG. 1 that shows a single winch cord that retracts into and releases from a winch spool, the winch assembly 312 of FIG. 3 is shown to include a pair of winch cords 314 and 316, each retractable into and releasable from a corresponding winch spool (not shown) in the winch assembly 312. In one implementation, the winch assembly 312 is configured to release and retract the winch cords 314 and 316 in unison (e.g., by retracting or releasing both winch cords by identical amounts). For example, a single crank mechanism may be configured to control both spools of cord such that rotation of the crank mechanism releases or retracts the winch cords 314 and 316 by an identical amount.

[0042] FIG. 3 further illustrates an effective winch cord length (C), which corresponds to atotal combined length of the winch cords 314, 316 that is released from the winch assembly 312 at a given point in time. The effective winch cord length (C) also represents the separation between the first end 308 and the second opposite end 310 of the balloon envelope 304. In implementations that utilize a single winch cord, the effective winch cord length is defined as generally described with respect to FIG. 1.

[0043] In addition to the above, FIG. 3 also illustrates a length Al of the gathered balloon material proximal to the first end 308 that is inverted. Likewise, a length A2 corresponds to the length of gathered balloon material on the second end 310 that is inverted into the balloon’s interior. As used herein, “inversion” of the balloon envelope refers to a positional change that causes an initially externally-facing portion of the balloon envelope to be pulled inward and become internally facing (as defined above). The first end 308 of the balloon envelope 302 is said to become more and more “inverted” as the fabric of an externally-facing portion of the first end 308 is pulled inside of a volume (e.g., outer cylinder) created by the balloon fabric, where the volume has an externally- facing portion that does not face any other portion of the system. An example of this inversion is shown in FIG. 3.

[0044] In the system shown in FIG. 3, the lengths Al and A2 are fixed to equal one another and the winch cords 314 and 316 are retracted and released in unison, by identical amounts, such that Al is always equal to A2 regardless of the effective winch cord length (C). This symmetric winching of the two winch cords 314 and 316, with the winch assembly 312 positioned at the center - e.g., coinciding with the system’s center of gravity - ensures that the system’s center of gravity remains unchanged, which prevents undesirable asymmetric contortions and / or rotation of the balloon envelope 302 at different effective winch cord lengths.

[0045] Since Al and A2 are equal regardless of the effective winch cord length (C), Al and A2 are referred to as merely “A” in the following description.

[0046] In the illustrated implementation, the diameter of the balloon cylinder (D) is a known (fixed) value, determined during the construction of the balloon envelope 304. In contrast, the effective winch cord length (C) is variable and is controlled either by an operator of the balloon system or an automated control algorithm. In this configuration, the two undetermined variables are length L of the cylindrically shaped portion of the balloon envelope 304 and the length A of the bunched material at either end of the balloon envelope. Here, the variables L and A share an interdependent relationship, and changes in one will correspondingly affect the other. Understandingthis relationship facilitates the calculation of a volume internal to the balloon envelope 304 as a function of the effective winch cord length C. In addition, understanding the relationship between L and A makes it possible to determine the maximum achievable variability in the effective volume of the balloon envelope 304 under different geometries and winch conditions and, hence, the range of altitude control achievable with a given geometry.[0047J The cylindrical design with toroidal end caps, e.g., as generally shown in FIG. 1-3, represents one of many possible embodiments that could implement a variable volume altitude control system that relies on the same principles of operation. For instance, non-cylindrical variants, where the ends of the balloon flare outward akin to an hourglass shape with the winch in the middle, could provide substantial volume change ratios, thereby offering a broad altitude control range. Different geometries of the balloon envelope 304 carry advantages and disadvantages. Factors for consideration could include the simplicity and ease of construction, achievable compression ratio, overall envelope size and weight, the magnitude of critical dimensions (such as length), and the force or speed requirements of the winching system. Balancing these considerations will allow for the design and implementation of an optimized balloon system that satisfies the specific needs of each application.

[0048] Since the winch assembly 312 may apply thousands of pounds of force on the balloon envelope during flight, the balloon envelope 302 is particularly vulnerable to tearing. The design of the herein-disclosed variable volume altitude control system mitigates this risk of tearing by evenly distributing the load between the two opposing, tensioned ends 308 and 310 of the balloon envelope 302. This even load distribution is attributable to the fact that the balloon envelope is symmetrical about a midpoint 322 of its longitudinal axis 320 and also attributable, at least in part, to the winch assembly 312 being located internal to the balloon envelope 104, e.g., between the ends 110 and 112. This placement of the winch assembly 312 equally distributes the applied load between the opposing, tensioned ends, thereby mitigating both tearing of the balloon envelope.

[0049] FIG. 4 illustrates a winch assembly 400 suitable for implementation within the variable volume altitude control systems described herein. The winch assembly 400 includes a housing 406 that encases a winch spool 402. In FIG. 2, the housing of the winch assembly 400 is shown transparent to illustrate the relative position of the winch spool 402, which is internal to the housing. In addition to the winch spool 402, the winch assembly 400 further includes a winch cord 404 with a first end secured by and at least partially coiling about the winch spool 402.

[0050] In one implementation, a free end 426 of the winch cord 404 is coupled to a first end of a balloon envelope (not shown) and a slot 428 in the winch assembly 400 serves as a coupling point that attaches to a second opposite end of the balloon envelope. The winch assembly 400 tensions the first and second opposite ends of the balloon system toward one another, as generally shown and described with respect to FIG. 1. In this way, varying the length of the winch cord 404 external to the winch spool 402 varies the separation between the ends of the balloon system as generally described with respect to FIG. 1.

[0051] The winch spool 402 is selectably rotated in a first direction by a motor-generator 408, which is controlled by an electronic control system 411 housed within an electronics box 412. The electronic control system 411 includes at least memory and a processor that executes instructions (firmware) stored in the memory to generate control signals that drive the motorgenerator 408. In some implementations, the electronics box 412 further includes a long-range communication system capable of receiving commands that originate external to the winch assembly 400. The communication system may be adapted for either short-range communications or long- range communications. For example, altitude control commands that initiate on the ground (on Earth) may be transmitted to the electronic control system 411 within the winch assembly 400 or, alternatively, to a long-range communication system located elsewhere within the balloon system that, in turn, relays the commands to the winch assembly 400 via suitable short-range communication system and protocol. The winch assembly 400 further includes a power supply 410 that supplies power to the electronic control system 411, which drives the motor-generator 408. The power supply 410 includes at least one or more batteries that are, in some implementations, charged by solar panels (not shown). For example, solar panels may be located on the winch assembly 400 or elsewhere in a same balloon system, either inside or outside of the envelope.

[0052] The motor-generator 408 rotates a crankshaft 422 that rotates gear(s) within a gearbox 414 to turn the winch spool 402. The gearbox 414 functions to translate a relatively small torque applied to the crankshaft 422 to a much larger torque that is transferred to the winch spool 402 to retract the winch cord 404, which may be under thousands of pounds of tension during nominal use scenarios. Cross-sectional view 420 illustrates a cross-section of the gearbox 418, e.g., taken along an axis labeled (X), that shows a simplified arrangement of gears. The crankshaft 422 rotates to turn a first, smaller gear (A). Teeth of the smaller gear interface with teeth of a larger gear (B) such that first angular rotation of the smaller gear (A) imparts a corresponding but lesser degreeof angular rotation upon the larger gear (B). The winch spool 402 is rotationally coupled to the larger gear (B) either directly or through one or more additional gears. In some implementations, the smaller gear (A) is configured to selectively engage with gears of variable size to generate different respective degrees of torque. For example, gear A can be rotatably coupled to gear B and then decoupled from gear B and rotatably coupled to another gear C (not shown), where both gears B and C are rotatably coupled to the winch spool 402.

[0053] The gearbox 414 is coupled to the motor-generator 408 through a clutch 416, which allows the motor 408 and gearbox 414 to lock when the motor-generator 408 is not energized to conserve power. As tension on the winch cord 404 increases, the electronic control system 411 may selectively shift to larger and larger gears to further increase torque applied when rotating the winch spool 402. This gear changing could also be facilitated by the clutch 416, which would allow the motor to disengage from the tensioned line while changing gears.

[0054] In addition to the above, the motor 408 is further coupled to an encoder 419 that is configured to read the position of the winch spool 402 (e.g., and thereby determine the rotation of the winch spool 402 that is achieved between discrete points in time). For example, the encoder 419 is a hall effects sensor that can be used to verify the number of rotations of the winch spool 402 that have been made. This number of rotations can, in turn, be used to calculate the length LI 108. The encoder 419 provides a feedback signal to the electronic control system 411 that is, in turn, processed to determine when to “stop” rotation of the crankshaft - e.g., when the length of the cord has been extended or retracted by a target amount that mathematically corresponding to a fractional rotation of the winch spool 402.

[0055] To rotate the winch spool 402 in a first direction that adds tension to the winch cord 404, the electronic control system 411 drives the motor-generator 408, which rotates the crankshaft 422 to turn the winch spool 402. To rotate the winch spool 402 in the opposite direction (e.g., to release tension from the winch cord 404), the motor-generator 408 is engaged and driven in the opposite direction using power to control the rate of release. For certain motors power can be generated during this process where the motor is driven in the same direction it is turning. In this case, the control system 411 disengages the clutch 416 to decouple the gearbox 414 and motorgenerator 408 from the winch spool 402 and then uses the motor-generator 408 to controllably let out the line. Additionally, the clutch 416 could be used like a brake to slowly let out the line by applying a partial breaking force that will allow a clutch plate to slip against the clutch 416 atcontrollable rates. This functionality is akin to that of a brake consisting of a disk that is engaged by brake pads to controllably resist rotary motion. The control system 411 uses a feedback signal from the encoder 419 to determine when the winch spool 402 has rotated by a target amount and, at that time, engages the clutch 416 to secure the winch spool 402 in place.

[0056] Notably, some implementations of the herein-disclosed altitude adjustment system may include a motor that lacks a generator in place of the motor-generator 408. However, the motor-generator 408 includes a motor (with functionality as described above) that can be operated as a generator. The motor-generator 408 drives the motor when operated in one direction and generates power when operated in the opposite direction - specifically, when the torque applied to the winch spool 402 by the motor-generator 408 is in the same direction as the direction of rotation of the winch spool 402. This operational principle is similar to that of regenerative braking in electric and hybrid vehicles. In a regenerative braking system, a generator in the motor charges a battery when the operator engages the brake, thereby applying a torque on the motor shaft that counteracts the rotation of the motor shaft that propels the vehicle forward.

[0057] In one implementation of the disclosed technology, the variable volume altitude control systems described herein are operated to strategically translate decreases in lift gas pressure to power that is, in turn, captured by the motor-generator 408. Notably, lift gas temperatures tend to be lower at night and higher during the day. It, therefore, requires more power to reduce the effective volume of the balloon envelope by a fixed quantity during the day (at higher temperatures) than at night. This night / day delta in power needed to reduce the effective volume by a fixed amount is equal to a power surplus that can be recaptured by expanding the effective volume during the day than at night.

[0058] The above-described phenomena are, in one implementation, leveraged by a balloon system operator to operate the variable volume altitude control system in a manner that yields a net positive capture of power during a given balloon flight - meaning, the altitude control system generates more power than it utilizes. This positive net power yield is realized by strategically commanding the balloon system to perform ascent maneuvers during the day and descent maneuvers at night.

[0059] As described with respect to FIG. 1, descent maneuvers are achieved by adding tension to the winch cord (not shown) to reduce the effective volume of the balloon envelope. Descent maneuvers are driven by the motor in the winch assembly (e.g., the winch assembly 400 ofFIG. 4). Since the gas inside of the balloon envelope is more pressurized during the day when temperatures are warmer, the motor-generator 408 consumes more power when retracting the winch cord by a fixed length during the day than when retracting the winch cord by the identical fixed length at night when the air is less pressurized. Therefore, performing all descent maneuvers during the night instead of during the day can result in some overall power savings.[0060J The same phenomenon responsible for the above-described power savings is responsible for a net power “gain” that is realized as a result of performing ascent maneuvers during the day and descent maneuvers at night. As described elsewhere herein, ascent maneuvers are achieved by releasing tension in the winch cord to increase the effective volume of the balloon envelope. Further, as described above, the motor-generator 408 translates the energy released from the winch cord during ascent maneuvers to electrical power that is stored on-board the balloon system and re-used. Since the air inside of the balloon is more pressurized during the day when air is warmer, more power is captured by the motor-generator 408 when a fixed length of the winch cord is released from the winch spool 402 during the day than when the same fixed length of the winch cord is released from the winch spool 402 at night.

[0061] Due to the above-described phenomena, it becomes possible to operate the winch assembly (e.g., of FIG. 4) in a manner that results in a net yield (increase) in power for the variable volume altitude control system as a whole. Assume, for example, a balloon flight includes three descent maneuvers totaling 600 meters of descent and two ascent maneuvers totaling 600 meters of climb. If all descent maneuvers and ascent maneuvers were performed at equal ambient temperature (e.g., all during the day or all during the night), then the descent maneuvers would collectively consume approximately the same quantity of power that is returned to the motor-generator 408 by the ascent maneuvers. When, however, the descent maneuvers are performed at night, and the ascent maneuvers are performed during the day, more power is captured by the motor-generator 408 during the ascent maneuvers than is expended during the descent maneuvers.

[0062] This net positive power yield can extend the duration of balloon flights by compensating for wear and tear on solar panels that otherwise reduce nominal daily power yields over time. In some implementations, the net power gains of the variable volume altitude control system are exported to other subsystems on the same balloon system.

[0063] FIG. 5 illustrates another example balloon envelope 501 of a system that includes variable volume altitude control system that offers multiple volume states (e.g., 502, 504, 506, 508,510, and 512), each of which corresponds to a different theoretical altitude during flight. Although not shown, the super pressure balloon system includes a winch assembly on the interior of the balloon envelope 501 that applies an adjustable inward tension on opposing ends 503, 505 of the balloon envelope 501 to vary the separation between the opposing ends 503, 505 and, consequently the effective volume of the balloon envelope 501. The different volume states 502, 504, 506, 508, 510, and 512 correspond to different effective volumes of the balloon envelope 501 at various degrees of extension and retraction of one or more winch cords (not shown), effectively demonstrating the balloon's variable volume capabilities.

[0064] A first volume state 502 illustrates the balloon envelope 501 when the winch assembly has completely retracted the winch cord (e.g., the effective winch cord length is zero), resulting in the balloon contracting to its minimum possible volume for this embodiment. This contracted state represents the balloon's lowest achievable flight altitude.

[0065] A second volume state 504 illustrates the balloon envelope 501 at a time when the winch assembly has let out approximately one-fifth of the effective winch cord length, leading to an intermediate volume. In this state, the balloon system would be capable of floating at an intermediate altitude that lies above its minimum but below its maximum achievable altitude.

[0066] A third volume state 506, fourth volume state 508, and fifth volume state 510 represent conditions where the effective winch cord length has been extended to lengths of approximately two-fifths, three-fifths, and four-fifths of its maximum length, respectively. Each of these states would enable the balloon to float at progressively higher altitudes, demonstrating the balloon's incremental altitude adjustment capabilities.

[0067] Finally, a sixth volume state 512 represents the state where the effective winch cord length is at its maximum value, allowing the balloon to expand to its maximum effective volume. This expanded state corresponds to the highest possible flight altitude achievable by this configuration. In other slightly different configurations, the ends could be allowed to pop out so the system could achieve a slightly larger volume than what is shown in 512.

[0068] FIG. 6 illustrates another super pressure balloon system 600 implementing the herein-disclosed variable volume altitude control system. The super pressure balloon system 600 includes a balloon envelope 604 with a cylindrical midsection attached to a payload 606. However, in contrast to the orientation of the balloon envelope shown in FIG. 1, the balloon envelope 604 is rotated 90 degrees - that is, the cylindrical mid-section is turned on its side such that toroidalendcaps 608, 610 of the balloon envelope 604 are aligned along a winch cord axis “A” that does not intersect the payload 606. In this horizontal setup, the positioning and attachment points of the winch assembly (not shown) play a crucial role in maintaining the balance of the super pressure balloon system 600 during the altitude adjustments. To preserve the equilibrium of the payload 606 and ensure that the payload 606 remains approximately centered throughout the altitude change maneuvers, the winch cord needs to attach to the remainder of the winch assembly in a way that enables the balloon to invert symmetrically from both sides. The winch assembly shown and described above with respect to FIG. 3 (e.g., with two winch cords that retract and release in unison) is one example way of achieving symmetrical or near-symmetrical winching. This balanced inversion mechanism prevents any shifts in the center of mass during volume changes, facilitating a stable payload even when the system's volume is being actively adjusted. Notably, symmetrical winching is much more important in the horizontal setup of FIG. 6 than in the other vertical setups disclosed herein since the horizontal setup is more likely to be prone to rotation at the effective winch cord length is reduced.

[0069] FIG. 7 illustrates an example balloon envelope 700, fdled with lift gas, suitable for use in a system that implements the herein-disclosed variable volume altitude control system technology. The balloon envelope 700 has a cylindrical shape. Opposite ends of the balloon envelope 700 are sealed, gathered, and pulled inward toward one another via attachment to opposite ends of a winch assembly (not shown), as generally shown or described with respect to any of FIG. 1-6. FIG. 7 additionally illustrates reinforcement seams 702 that provide symmetrical reinforcement of the balloon envelope 700 to mitigate tearing of the balloon envelope under the thousands of pounds of force potentially applied by the winch assembly.

[0070] The reinforcement seams 702 extend in a direction substantially parallel to the longitudinal axis (axis Y) of the balloon envelope 700 that intersects a center of each of the toroidal endcaps 704, 706. The reinforcement seams 702 are also distributed symmetrically - both about the longitudinal axis (axis Y) and about the lateral perpendicular axis (axis X), which intersects a midpoint between opposite ends of the balloon envelope 700.

[0071] Although not shown in FIG. 7, the reinforcement seams 702 extend from end-to- end of the balloon envelope 700 between contact points, on opposing ends of the balloon envelope, that physically couple to winch assembly. This symmetrical reinforcement around the contact points, parallel to the direction of force applied by the winch assembly, ensures that the load applied by thewinch assembly is symmetrically dispersed equally around the balloon envelope 700, so there is no tearing or tilting of the balloon envelope 700 during flight.

[0072] FIG. 8 illustrates example operations 800 of a variable volume altitude control system that is part of a super pressure balloon system. The operations 800 leverage temperature shifts between day and night to reduce or mitigate power consumed when driving a descent maneuver and to increase or maximize a quantity of power that is returned to an on-board power supply during each ascent maneuver. According to one implementation, the operations 800 are executable to realize a net power gain of the variable volume altitude control system over the course of a nominal flight for the super pressure balloon system.

[0073] The operations 800 include a first command receipt operation 802 that receives a first command that instructs an on-onboard control system to initiate a nighttime descent maneuver- e.g., at a time that is after sunset and before sunrise at a location of the super pressure balloon system. In response to the first command receipt operation 802, a descent maneuver operation 804 initiates the rotation of a winch spool in a winch assembly in a first direction. The rotation of the winch spool in the first direction increases an inward tension that is imparted by the winch assembly on the first and second opposite ends of a balloon envelope, such as a balloon envelope that is attached to the winch assembly as generally described with respect to any of FIG. 1-4.

[0074] Because lift gas temperatures are generally warmer during the day than at night, the gas inside of the balloon envelope is more pressurized during the day than at night. Consequently, less power is consumed when a motor is driven to retract the winch cord by a fixed length during the night than when the same motor is driven to retract the winch cord by an identical fixed length during the day. Thus, a power savings is realized by selectively performing the descent maneuver at night instead of during the day.

[0075] The operations 800 additionally includes a second command receipt operation 806 that receives a second command that instructs the on-onboard control system to initiate a daytime ascent - e.g., at a time that is after sunrise and before sunset at a location of the super pressure balloon system.

[0076] In response to the second command receipt operation 806, an ascent maneuver operation 808 initiates the rotation of a winch spool in a winch assembly in a second opposite direction. The rotation of the winch spool in the second opposite direction decreases the inward tension on the first and second opposite ends of the balloon envelope, which translates to a release ofenergy from the winch spool.

[0077] An energy convert and capture operation 810 uses a motor-generator to convert the energy that is released by the rotation of the winch spool in the second opposite direction to electrical energy that is stored on-board the super pressure balloon system. Since the air inside of the balloon is more pressurized during the day when air is warmer, more power is captured by the generator when a fixed length of the winch cord is released from the winch spool during the day than when the same fixed length of the winch cord is released from the winch spool at night. Thus, a power gain can be realized by selectively performing ascent maneuvers of the super pressure balloon system during the day and by storing the energy released from the winch spool on-board for later use.

[0078] In one implementation, the variable volume altitude control system is commanded to perform several ascent and descent maneuvers during a single flight of the super pressure balloon system. The first command receipt operation 802 serves as the trigger for each descent maneuver and the second command receipt operation 806 serves as the trigger for each ascent operation.

[0079] The above specification, examples, and data provide a complete description of the structure and use of exemplary embodiments of the disclosed technology. Since many embodiments of the disclosed technology can be made without departing from the spirit and scope of the disclosed technology, the disclosed technology resides in the claims hereinafter appended. Furthermore, structural features of the different embodiments may be combined in yet another embodiment without departing from the recited claims.

Claims

ClaimsWHAT IS CLAIMED IS:

1. A balloon system comprising: a balloon envelope having an interior volume that is sealed off from an external environment; a winch assembly including: a winch cord and a winch spool positioned to apply an adjustable tension that pulls a first end of the balloon envelope toward a second opposing end of the balloon envelope; and an electrical control system that drives a motor to gradually invert the balloon envelope by increasing the adjustable tension.

2. The balloon system of claim 1, wherein the electrical control system further comprises: a clutch that locks the winch cord in place without consuming power while the winch cord is tensioned between the winch assembly and the balloon envelope.

3. The balloon system of claim 1, wherein the winch spool is positioned within the interior volume of the balloon envelope.

4. The balloon system of claim 1, wherein the balloon envelope includes a first contact point and a second contact point attached to opposing ends of the winch assembly, wherein the first contact point and the second contact point are symmetrically reinforced to distribute a load created by the winch assembly evenly around the first contact point and the second contact point.

5. The balloon system of claim 4, wherein the winch assembly includes two winch cords that retract and release in unison, each of the winch cords being attached to a different end of the balloon envelope.

6. The balloon system of claim 1, wherein the winch assembly applies the adjustable tension along a first axis of the balloon envelope that extends between the first end and the second opposing end.

7. The balloon system of claim 6, wherein the balloon envelope is cylindrical and symmetrical across the first axis and across a second axis perpendicular to the first axis.

8. The balloon system of claim 1, wherein the balloon system further comprises: a generator that converts energy released from the winch assembly to electrical energy stored on-board the balloon system.

9. The balloon system of claim 1, wherein the winch assembly applies a tension along a first axis extending between the first end of the balloon envelope and a second opposing end of the balloon envelope and wherein retracting the winch cord inverts a first portion of the balloon envelope proximal to the first end and a second portion of the balloon envelope proximal to the second opposing end.

10. The balloon system of claim 1, wherein the interior volume of the balloon envelope is filled with a lift gas that is less dense than surrounding atmosphere at equivalent pressures.

11. A method of performing an altitude maneuver for a super pressure balloon system, the method comprises: initiating a descent maneuver by transmitting a first electrical control signal to a motor, the first electrical control signal driving a motor to turn a winch spool in a winch assembly and thereby increase an applied tension that causes inversion of first and second opposing ends of a sealed balloon envelope; receiving a first feedback signal indicating that the winch spool has rotated by a first target amount in a first direction, the first target amount corresponding to a target decrease in separation between the first and second opposing ends of the sealed balloon envelope; andin response to receipt of the first feedback signal, transmitting a second electrical control signal that causes the motor to stop turning the winch spool.

12. The method of claim 11, further comprising: prior or simultaneous to transmitting the first electrical control signal, transmitting a third electrical control signal that unlocks a clutch from the winch spool; and in response to the first feedback signal, transmitting a fourth electrical control signal that engages the clutch to secure the winch spool, wherein the clutch consumes power when unlocked from the winch spool and the clutch does not consume power when locking the winch spool in place.

13. The method of claim 11, further comprising: initiating an ascent maneuver by transmitting a third electrical control signal that disengages a clutch from the winch spool; receiving a second feedback signal indicating that the winch spool has rotated by a second target amount in a second direction opposing the first direction, the second target amount corresponding to a target increase in separation between the first and second opposing ends of the sealed balloon envelope; and in response to the second feedback signal, transmitting a fourth control signal that engages the clutch to prevent further rotation of the winch spool.

14. The method of claim 13, wherein the super pressure balloon system includes a generator and the method further comprises: converting, by the generator, energy released by rotating the winch spool during the ascent maneuver into to electrical energy stored on-board the super pressure balloon system15. The method of claim 11, wherein the winch assembly is located internal to a sealed balloon envelope.

16. The method of claim 11 , wherein the sealed balloon envelope includes a first contact point and a second contact point attached to opposing ends of the winch assembly, wherein the first contact point and the second contact point are symmetrically reinforced to distribute a load created by the winch assembly evenly around the first contact point and the second contact point.

17. The method of claim 11, wherein the applied tension is applied along a first axis of the sealed balloon envelope that extends between the first and second opposing ends.

18. The method of claim 17, wherein the balloon envelope is cylindrical and symmetrical across the first axis and across a second axis perpendicular to the first axis.

19. A method of efficiently operating an altitude control system in a super pressure balloon system, the method comprising: receiving a first command instructing initiation of a descent maneuver at a time that is after sunset and before sunrise at a location of the super pressure balloon system; in response to receipt of the first command, executing one or more control actions that initiate rotation of a winch spool in a winch assembly in a first direction, the rotation in the first direction increasing an inward tension that is imparted, by the winch assembly, on first and second opposing ends of a balloon envelope; receiving a second command instructing initiation of an ascent maneuver at a time that is after sunrise and before sunset at a location of the super pressure balloon system; in response to receipt of the second command, executing one or more control actions that initiate rotation of the winch spool in a second opposing direction, the rotation in the second opposing direction decreasing the inward tension on the first and second opposing ends of the balloon envelope; and converting, at a generator of the super pressure balloon system, energy released during the rotation of the winch spool in the second opposing direction into electrical energy that is stored in an on-board power supply.

20. The method of claim 19, wherein the winch assembly is located internal to the balloonenvelope.

21. The method of claim 19, wherein the rotation in the first direction inverts a first end of the balloon envelope.

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