# Patent

## Title
Drag plate for controlled descent of balloon

## Abstract

A balloon is provided having a balloon envelope, a payload positioned beneath the balloon envelope, and a drag plate positioned beneath the balloon envelope and attached to the payload, and a control system configured to initiate a process to cause the balloon envelope to no longer provide lift to the payload, wherein the drag plate serves to slow the descent of the payload to the earth.

## Background
BACKGROUND
Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Computing devices such as personal computers, laptop computers, tablet computers, cellular phones, and countless types of Internet-capable devices are increasingly prevalent in numerous aspects of modern life. As such, the demand for data connectivity via the Internet, cellular data networks, and other such networks, is growing. However, there are many areas of the world where data connectivity is still unavailable, or if available, is unreliable and/or costly. Accordingly, additional network infrastructure is desirable.
SUMMARY
In one aspect, a balloon is provided having a balloon envelope, a payload positioned beneath the balloon envelope, and a drag plate positioned beneath the balloon envelope and attached to the payload, and a control system configured to initiate a process to cause the balloon envelope to no longer provide lift to the payload, wherein the drag plate serves to slow the descent of the payload to the earth. In addition, the balloon may further include a drag plate where the outer surface of the drag plate extends as far as the diameter of the balloon envelope when the balloon envelope is inflated, or even extends beyond the diameter of the balloon envelope when the balloon envelope is inflated.
In another aspect, a computer-implemented method is provided, comprising the steps of slowing the descent of a payload attached to a balloon, wherein the balloon is comprised of a balloon envelope, a payload positioned beneath the balloon envelope, and a drag plate positioned beneath the balloon envelope and attached to the payload, and operating a control system to initiate a process to cause the balloon envelope to no longer provide lift to the payload, wherein the drag plate serves to slow the descent of the payload to the earth.
In another aspect, a non-transitory computer readable medium has stored therein instructions that are executable by a computing device to cause the computing device to perform functions comprising slowing the descent of a payload attached to a balloon, wherein the balloon is comprised of a balloon envelope, a payload positioned beneath the balloon envelope, and a drag plate positioned beneath the balloon envelope and attached to the payload, and operating a control system to cause the balloon envelope to be no longer provide lift to the balloon envelope, wherein the drag plate serves to slow the descent of the payload to the earth.
In another aspect, a balloon is provided having a balloon envelope, a payload positioned beneath the balloon envelope, and a drag plate positioned beneath the balloon envelope and attached to the payload, wherein an outer surface of the drag plate extends beyond sides of the payload and the drag plate serves to slow the rate of ascent or descent of the balloon when the altitude of the balloon is being controlled.
These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified block diagram illustrating a balloon network, according to an example embodiment.
FIG. 2 is a block diagram illustrating a balloon-network control system, according to an example embodiment.
FIG. 3 is a simplified block diagram illustrating a high-altitude balloon, according to an example embodiment.
FIG. 4 shows a balloon network that includes super-nodes and sub-nodes, according to an example embodiment.
FIG. 5 shows an expanded balloon 20 positioned above payload 30 with a concave drag plate 40 positioned therebetween, according to an example embodiment.
FIG. 5A shows a deflated balloon 20 positioned above payload 30 with a concave drag plate 40 positioned therebetween, and drag forces acting upon the payload 30 and drag plate 40 upon balloon descent, according to an example embodiment.
FIG. 6 shows an expanded balloon 20 positioned above payload 30 with an inverted concave drag plate 40 positioned therebetween, according to an example embodiment.
FIG. 6A shows a deflated balloon 20 positioned above payload 30 with an inverted concave drag plate 40 positioned therebetween, and drag forces acting upon the payload 30 and drag plate 40 upon balloon descent, according to an example embodiment.
FIG. 6B shows a payload 30 with an inverted concave drag plate 40 with drag forces acting upon the payload 30 and drag plate 40 upon balloon descent, according to an example embodiment.
FIG. 7 shows an expanded balloon 20 positioned above payload 30 with a flat drag plate 40 positioned therebetween, according to an example embodiment.
FIG. 7A shows a deflated balloon 20 positioned above payload 30 with a flat drag plate 40 positioned therebetween, and drag forces acting upon the payload 30 and drag plate 40 upon balloon descent, according to an example embodiment.
FIG. 7B shows a payload 30 with a flat drag plate 40 with drag forces acting upon the payload 30 and drag plate 40 upon balloon descent, according to an example embodiment.
FIG. 8A shows a top view of drag plate 40 shown in FIGS. 5-7.
FIG. 8B shows a top view of an alternate geometry of drag plate 40 shown in FIGS. 5-7.
FIG. 9 is a method, according to an example embodiment.



DETAILED DESCRIPTION
Example methods and systems are described herein. Any example embodiment or feature described herein is not necessarily to be construed as preferred or advantageous over other embodiments or features. The example embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.
Furthermore, the particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an example embodiment may include elements that are not illustrated in the Figures.
1. Overview
Example embodiments help to provide a data network that includes a plurality of balloons; for example, a mesh network formed by high-altitude balloons deployed in the stratosphere. Since winds in the stratosphere may affect the locations of the balloons in a differential manner, each balloon in an example network may be configured to change its horizontal position by adjusting its vertical position (i.e., altitude). For instance, by adjusting its altitude, a balloon may be able find winds that will carry it horizontally (e.g., latitudinally and/or longitudinally) to a desired horizontal location.
Further, in an example balloon network, the balloons may communicate with one another using free-space optical communications. For instance, the balloons may be configured for optical communications using lasers and/or ultra-bright LEDs (which are also referred to as “high-power” or “high-output” LEDs). In addition, the balloons may communicate with ground-based station(s) using radio-frequency (RF) communications.
In some embodiments, a high-altitude-balloon network may be homogenous. That is, the balloons in a high-altitude-balloon network could be substantially similar to each other in one or more ways. More specifically, in a homogenous high-altitude-balloon network, each balloon is configured to communicate with one or more other balloons via free-space optical links. Further, some or all of the balloons in such a network, may additionally be configured to communicate with ground-based and/or satellite-based station(s) using RF and/or optical communications. Thus, in some embodiments, the balloons may be homogenous in so far as each balloon is configured for free-space optical communication with other balloons, but heterogeneous with regard to RF communications with ground-based stations.
In other embodiments, a high-altitude-balloon network may be heterogeneous, and thus may include two or more different types of balloons. For example, some balloons in a heterogeneous network may be configured as super-nodes, while other balloons may be configured as sub-nodes. It is also possible that some balloons in a heterogeneous network may be configured to function as both a super-node and a sub-node. Such balloons may function as either a super-node or a sub-node at a particular time, or, alternatively, act as both simultaneously depending on the context. For instance, an example balloon could aggregate search requests of a first type to transmit to a ground-based station. The example balloon could also send search requests of a second type to another balloon, which could act as a super-node in that context. Further, some balloons, which may be super-nodes in an example embodiment, can be configured to communicate via optical links with ground-based stations and/or satellites.
In an example configuration, the super-node balloons may be configured to communicate with nearby super-node balloons via free-space optical links. However, the sub-node balloons may not be configured for free-space optical communication, and may instead be configured for some other type of communication, such as RF communications. In that case, a super-node may be further configured to communicate with sub-nodes using RF communications. Thus, the sub-nodes may relay communications between the super-nodes and one or more ground-based stations using RF communications. In this way, the super-nodes may collectively function as backhaul for the balloon network, while the sub-nodes function to relay communications from the super-nodes to ground-based stations.
Instruments and electronic equipment may be positioned within a payload of a balloon that may be kept aloft in the upper atmosphere. The instruments or electronic devices may be used to record various data and information. After a period of time, it may be desirable to have the payload return to the surface of the earth to retrieve the information obtained from the instruments and electronic devices positioned in the payload. There may be other, perhaps more important, reasons to bring the payload down to the earth's surface. For example, the balloon payload may be brought down to provide necessary upgrades to the electronic equipment within the payload. Or, the payload may be brought down to prevent the payload from entering into unauthorized air space.
The balloon envelope may be deflated or collapsed, or disconnected from the payload, to allow the payload to descend to the surface of the earth. For example, the balloon envelope may be caused to rip, opening a hole in the envelope to deflate the balloon; or if a cord is used to attach the payload to the balloon envelope, the cord may be severed, using for example mechanical, electromagnetic, or explosive devices. Once the balloon is deflated, or the payload is severed from the balloon envelope, the payload is allowed to descend to the earth.
It may be desirable to slow the rate of descent of the payload to the earth so that the instruments or electronic devices are not damaged upon impact, and so that the data and information that has been obtained may be retrieved, as well as to reduce the risk of injury to people or property beneath payload. A parachute could be deployed from the payload to slow the rate of descent, although the remote deployment of a parachute may be unreliable. If the parachute fails to deploy, an undesirable, uncontrolled descent of the payload may occur.
Example embodiments may be directed to a balloon having a drag plate attached to the payload that may serve to slow the descent of the payload after the balloon envelope has been deflated or disconnected from the payload. The drag plate may be attached to the payload, either beneath the payload, or above the payload between the payload and the balloon envelope, or may be formed integral with the payload. The drag plate has a surface area that creates a drag force as the payload descends towards the earth. The larger the surface of the drag plate facing the earth, the larger the drag forces that are created slowing the descent of the payload.
An advantage of using a drag plate is that it does not need to be deployed, like a parachute would be, to slow the descent of the payload because the drag plate is already in place. Thus, the use of a drag plate to control the descent of the payload eliminates any issues or risks that may arise when a means for slowing the descent must be deployed, e.g., when using a parachute that must properly deploy.
The drag plate may be a downward facing concave plate where the payload is positioned within at least a portion of the downward facing concave section of the drag plate. The use of a downward facing concave plate may be advantageous because the geometry of the drag plate serves to reduce the amount of air that may be displaced from beneath the drag plate, thus increasing the drag forces that may be used to slow the descent of the payload.
The drag plate could also be an upward facing concave plate that is attached to the balloon envelope (and the payload) such that the balloon envelope is positioned within at least a portion of the upward facing concave section of the drag plate. Of course, the drag plate could also have other geometries, including a flat plate. Viewed from the top, the drag plate may also have a number of different geometries, including square, round, polygonal, etc.
The drag plate may advantageously have a surface area that extends beyond the outer surface of the payload, and may extend as far as the diameter of the balloon envelope when the balloon envelope is inflated. The outer surface of the drag plate may also extend beyond the diameter of the balloon envelope when the balloon envelope is inflated to provide even greater drag resistance to slow the descent of the payload.
The drag plate may be made from a solid material so that air and wind do not pass through the drag plate during descent, although some porosity or air flow through the drag plate may be tolerated, and may serve to stabilize the drag plate during descent. The drag plate may be comprised of a lightweight material, such as a carbon fiber or plastic material, or other composite material that is not too heavy so as to negatively impact achieving or maintaining a desired balloon altitude, prior to the descent of the payload.
2. Example Balloon Networks
FIG. 1 is a simplified block diagram illustrating a balloon network 100, according to an example embodiment. As shown, balloon network 100 includes balloons 102A to 102F, which are configured to communicate with one another via free-space optical links 104. Balloons 102A to 102F could additionally or alternatively be configured to communicate with one another via RF links 114. Balloons 102A to 102F may collectively function as a mesh network for packet-data communications. Further, at least some of balloons 102A and 102B may be configured for RF communications with ground-based stations 106 and 112 via respective RF links 108. Further, some balloons, such as balloon 102F, could be configured to communicate via optical link 110 with ground-based station 112.
In an example embodiment, balloons 102A to 102F are high-altitude balloons, which are deployed in the stratosphere. At moderate latitudes, the stratosphere includes altitudes between approximately 10 kilometers (km) and 50 km altitude above the surface. At the poles, the stratosphere starts at an altitude of approximately 8 km. In an example embodiment, high-altitude balloons may be generally configured to operate in an altitude range within the stratosphere that has relatively low wind speed (e.g., between 5 and 20 miles per hour (mph)).
More specifically, in a high-altitude-balloon network, balloons 102A to 102F may generally be configured to operate at altitudes between 18 km and 25 km (although other altitudes are possible). This altitude range may be advantageous for several reasons. In particular, this layer of the stratosphere generally has relatively low wind speeds (e.g., winds between 5 and 20 mph) and relatively little turbulence. Further, while the winds between 18 km and 25 km may vary with latitude and by season, the variations can be modeled in a reasonably accurate manner. Additionally, altitudes above 18 km are typically above the maximum flight level designated for commercial air traffic. Therefore, interference with commercial flights is not a concern when balloons are deployed between 18 km and 25 km.
To transmit data to another balloon, a given balloon 102A to 102F may be configured to transmit an optical signal via an optical link 104. In an example embodiment, a given balloon 102A to 102F may use one or more high-power light-emitting diodes (LEDs) to transmit an optical signal. Alternatively, some or all of balloons 102A to 102F may include laser systems for free-space optical communications over optical links 104. Other types of free-space optical communication are possible. Further, in order to receive an optical signal from another balloon via an optical link 104, a given balloon 102A to 102F may include one or more optical receivers. Additional details of example balloons are discussed in greater detail below, with reference to FIG. 3.
In a further aspect, balloons 102A to 102F may utilize one or more of various different RF air-interface protocols for communication with ground-based stations 106 and 112 via respective RF links 108. For instance, some or all of balloons 102A to 102F may be configured to communicate with ground-based stations 106 and 112 using protocols described in IEEE 802.11 (including any of the IEEE 802.11 revisions), various cellular protocols such as GSM, CDMA, UMTS, EV-DO, WiMAX, and/or LTE, and/or one or more propriety protocols developed for balloon-ground RF communication, among other possibilities.
In a further aspect, there may be scenarios where RF links 108 do not provide a desired link capacity for balloon-to-ground communications. For instance, increased capacity may be desirable to provide backhaul links from a ground-based gateway, and in other scenarios as well. Accordingly, an example network may also include downlink balloons, which could provide a high-capacity air-ground link.
For example, in balloon network 100, balloon 102F is configured as a downlink balloon. Like other balloons in an example network, a downlink balloon 102F may be operable for optical communication with other balloons via optical links 104. However, a downlink balloon 102F may also be configured for free-space optical communication with a ground-based station 112 via an optical link 110. Optical link 110 may therefore serve as a high-capacity link (as compared to an RF link 108) between the balloon network 100 and the ground-based station 112.
Note that in some implementations, a downlink balloon 102F may additionally be operable for RF communication with ground-based stations 106. In other cases, a downlink balloon 102F may only use an optical link for balloon-to-ground communications. Further, while the arrangement shown in FIG. 1 includes just one downlink balloon 102F, an example balloon network can also include multiple downlink balloons. On the other hand, a balloon network can also be implemented without any downlink balloons.
In other implementations, a downlink balloon may be equipped with a specialized, high-bandwidth RF communication system for balloon-to-ground communications, instead of, or in addition to, a free-space optical communication system. The high-bandwidth RF communication system may take the form of an ultra-wideband system, which may provide an RF link with substantially the same capacity as one of the optical links 104. Other forms are also possible.
Ground-based stations, such as ground-based stations 106 and/or 112, may take various forms. Generally, a ground-based station may include components such as transceivers, transmitters, and/or receivers for communication via RF links and/or optical links with a balloon network. Further, a ground-based station may use various air-interface protocols in order to communicate with a balloon 102A to 102F over an RF link 108. As such, ground-based stations 106 and 112 may be configured as an access point via which various devices can connect to balloon network 100. Ground-based stations 106 and 112 may have other configurations and/or serve other purposes without departing from the scope of the invention.
In a further aspect, some or all of balloons 102A to 102F could be configured to establish a communication link with space-based satellites in addition to, or as an alternative to, a ground-based communication link. In some embodiments, a balloon may communicate with a satellite via an optical link. However, other types of satellite communications are possible.
Further, some ground-based stations, such as ground-based stations 106 and 112, may be configured as gateways between balloon network 100 and one or more other networks. Such ground-based stations 106 and 112 may thus serve as an interface between the balloon network and the Internet, a cellular service provider's network, and/or other types of networks.
Variations on this configuration and other configurations of ground-based stations 106 and 112 are also possible.
2a) Mesh Network Functionality
As noted, balloons 102A to 102F may collectively function as a mesh network. More specifically, since balloons 102A to 102F may communicate with one another using free-space optical links, the balloons may collectively function as a free-space optical mesh network.
In a mesh-network configuration, each balloon 102A to 102F may function as a node of the mesh network, which is operable to receive data directed to it and to route data to other balloons. As such, data may be routed from a source balloon to a destination balloon by determining an appropriate sequence of optical links between the source balloon and the destination balloon. These optical links may be collectively referred to as a “lightpath” for the connection between the source and destination balloons. Further, each of the optical links may be referred to as a “hop” on the lightpath.
To operate as a mesh network, balloons 102A to 102F may employ various routing techniques and self-healing algorithms. In some embodiments, a balloon network 100 may employ adaptive or dynamic routing, where a lightpath between a source and destination balloon is determined and set-up when the connection is needed, and released at a later time. Further, when adaptive routing is used, the lightpath may be determined dynamically depending upon the current state, past state, and/or predicted state of the balloon network.
In addition, the network topology may change as the balloons 102A to 102F move relative to one another and/or relative to the ground. Accordingly, an example balloon network 100 may apply a mesh protocol to update the state of the network as the topology of the network changes. For example, to address the mobility of the balloons 102A to 102F, balloon network 100 may employ and/or adapt various techniques that are employed in mobile ad hoc networks (MANETs). Other examples are possible as well.
In some implementations, a balloon network 100 may be configured as a transparent mesh network. More specifically, in a transparent balloon network, the balloons may include components for physical switching that is entirely optical, without any electrical components involved in the physical routing of optical signals. Thus, in a transparent configuration with optical switching, signals travel through a multi-hop lightpath that is entirely optical.
In other implementations, the balloon network 100 may implement a free-space optical mesh network that is opaque. In an opaque configuration, some or all balloons 102A to 102F may implement optical-electrical-optical (OEO) switching. For example, some or all balloons may include optical cross-connects (OXCs) for OEO conversion of optical signals. Other opaque configurations are also possible. Additionally, network configurations are possible that include routing paths with both transparent and opaque sections.
In a further aspect, balloons in an example balloon network 100 may implement wavelength division multiplexing (WDM), which may help to increase link capacity. When WDM is implemented with transparent switching, physical lightpaths through the balloon network may be subject to the “wavelength continuity constraint.” More specifically, because the switching in a transparent network is entirely optical, it may be necessary to assign the same wavelength for all optical links on a given lightpath.
An opaque configuration, on the other hand, may avoid the wavelength continuity constraint. In particular, balloons in an opaque balloon network may include the OEO switching systems operable for wavelength conversion. As a result, balloons can convert the wavelength of an optical signal at each hop along a lightpath. Alternatively, optical wavelength conversion could take place at only selected hops along the lightpath.
Further, various routing algorithms may be employed in an opaque configuration. For example, to determine a primary lightpath and/or one or more diverse backup lightpaths for a given connection, example balloons may apply or consider shortest-path routing techniques such as Dijkstra's algorithm and k-shortest path, and/or edge and node-diverse or disjoint routing such as Suurballe's algorithm, among others. Additionally or alternatively, techniques for maintaining a particular quality of service (QoS) may be employed when determining a lightpath. Other techniques are also possible.
2b) Station-Keeping Functionality
In an example embodiment, a balloon network 100 may implement station-keeping functions to help provide a desired network topology. For example, station-keeping may involve each balloon 102A to 102F maintaining and/or moving into a certain position relative to one or more other balloons in the network (and possibly in a certain position relative to the ground). As part of this process, each balloon 102A to 102F may implement station-keeping functions to determine its desired positioning within the desired topology, and if necessary, to determine how to move to the desired position.
The desired topology may vary depending upon the particular implementation. In some cases, balloons may implement station-keeping to provide a substantially uniform topology. In such cases, a given balloon 102A to 102F may implement station-keeping functions to position itself at substantially the same distance (or within a certain range of distances) from adjacent balloons in the balloon network 100.
In other cases, a balloon network 100 may have a non-uniform topology. For instance, example embodiments may involve topologies where balloons are distributed more or less densely in certain areas, for various reasons. As an example, to help meet the higher bandwidth demands that are typical in urban areas, balloons may be clustered more densely over urban areas. For similar reasons, the distribution of balloons may be denser over land than over large bodies of water. Many other examples of non-uniform topologies are possible.
In a further aspect, the topology of an example balloon network may be adaptable. In particular, station-keeping functionality of example balloons may allow the balloons to adjust their respective positioning in accordance with a change in the desired topology of the network. For example, one or more balloons could move to new positions to increase or decrease the density of balloons in a given area. Other examples are possible.
In some embodiments, a balloon network 100 may employ an energy function to determine if and/or how balloons should move to provide a desired topology. In particular, the state of a given balloon and the states of some or all nearby balloons may be input to an energy function. The energy function may apply the current states of the given balloon and the nearby balloons to a desired network state (e.g., a state corresponding to the desired topology). A vector indicating a desired movement of the given balloon may then be determined by determining the gradient of the energy function. The given balloon may then determine appropriate actions to take in order to effectuate the desired movement. For example, a balloon may determine an altitude adjustment or adjustments such that winds will move the balloon in the desired manner.
2c) Control of Balloons in a Balloon Network
In some embodiments, mesh networking and/or station-keeping functions may be centralized. For example, FIG. 2 is a block diagram illustrating a balloon-network control system, according to an example embodiment. In particular, FIG. 2 shows a distributed control system, which includes a central control system 200 and a number of regional control-systems 202A to 202B. Such a control system may be configured to coordinate certain functionality for balloon network 204, and as such, may be configured to control and/or coordinate certain functions for balloons 206A to 206I.
In the illustrated embodiment, central control system 200 may be configured to communicate with balloons 206A to 206I via a number of regional control systems 202A to 202C. These regional control systems 202A to 202C may be configured to receive communications and/or aggregate data from balloons in the respective geographic areas that they cover, and to relay the communications and/or data to central control system 200. Further, regional control systems 202A to 202C may be configured to route communications from central control system 200 to the balloons in their respective geographic areas. For instance, as shown in FIG. 2, regional control system 202A may relay communications and/or data between balloons 206A to 206C and central control system 200, regional control system 202B may relay communications and/or data between balloons 206D to 206F and central control system 200, and regional control system 202C may relay communications and/or data between balloons 206G to 206I and central control system 200.
In order to facilitate communications between the central control system 200 and balloons 206A to 206I, certain balloons may be configured as downlink balloons, which are operable to communicate with regional control systems 202A to 202C. Accordingly, each regional control system 202A to 202C may be configured to communicate with the downlink balloon or balloons in the respective geographic area it covers. For example, in the illustrated embodiment, balloons 206A, 206F, and 206I are configured as downlink balloons. As such, regional control systems 202A to 202C may respectively communicate with balloons 206A, 206F, and 206I via optical links 206, 208, and 210, respectively.
In the illustrated configuration, only some of balloons 206A to 206I are configured as downlink balloons. The balloons 206A, 206F, and 206I that are configured as downlink balloons may relay communications from central control system 200 to other balloons in the balloon network, such as balloons 206B to 206E, 206G, and 206H. However, it should be understood that in some implementations, it is possible that all balloons may function as downlink balloons. Further, while FIG. 2 shows multiple balloons configured as downlink balloons, it is also possible for a balloon network to include only one downlink balloon, or possibly even no downlink balloons.
Note that a regional control system 202A to 202C may in fact just be a particular type of ground-based station that is configured to communicate with downlink balloons (e.g., such as ground-based station 112 of FIG. 1). Thus, while not shown in FIG. 2, a control system may be implemented in conjunction with other types of ground-based stations (e.g., access points, gateways, etc.).
In a centralized control arrangement, such as that shown in FIG. 2, the central control system 200 (and possibly regional control systems 202A to 202C as well) may coordinate certain mesh-networking functions for balloon network 204. For example, balloons 206A to 206I may send the central control system 200 certain state information, which the central control system 200 may utilize to determine the state of balloon network 204. The state information from a given balloon may include location data, optical-link information (e.g., the identity of other balloons with which the balloon has established an optical link, the bandwidth of the link, wavelength usage and/or availability on a link, etc.), wind data collected by the balloon, and/or other types of information. Accordingly, the central control system 200 may aggregate state information from some or all of the balloons 206A to 206I in order to determine an overall state of the network.
The overall state of the network may then be used to coordinate and/or facilitate certain mesh-networking functions such as determining lightpaths for connections. For example, the central control system 200 may determine a current topology based on the aggregate state information from some or all of the balloons 206A to 206I. The topology may provide a picture of the current optical links that are available in balloon network and/or the wavelength availability on the links. This topology may then be sent to some or all of the balloons so that a routing technique may be employed to select appropriate lightpaths (and possibly backup lightpaths) for communications through the balloon network 204.
In a further aspect, the central control system 200 (and possibly regional control systems 202A to 202C as well) may also coordinate certain station-keeping functions for balloon network 204. For example, the central control system 200 may input state information that is received from balloons 206A to 206I to an energy function, which may effectively compare the current topology of the network to a desired topology, and provide a vector indicating a direction of movement (if any) for each balloon, such that the balloons can move towards the desired topology. Further, the central control system 200 may use altitudinal wind data to determine respective altitude adjustments that may be initiated to achieve the movement towards the desired topology. The central control system 200 may provide and/or support other station-keeping functions as well.
FIG. 2 shows a distributed arrangement that provides centralized control, with regional control systems 202A to 202C coordinating communications between a central control system 200 and a balloon network 204. Such an arrangement may be useful to provide centralized control for a balloon network that covers a large geographic area. In some embodiments, a distributed arrangement may even support a global balloon network that provides coverage everywhere on earth. Of course, a distributed-control arrangement may be useful in other scenarios as well.
Further, it should be understood that other control-system arrangements are also possible. For instance, some implementations may involve a centralized control system with additional layers (e.g., sub-region systems within the regional control systems, and so on). Alternatively, control functions may be provided by a single, centralized, control system, which communicates directly with one or more downlink balloons.
In some embodiments, control and coordination of a balloon network may be shared by a ground-based control system and a balloon network to varying degrees, depending upon the implementation. In fact, in some embodiments, there may be no ground-based control systems. In such an embodiment, all network control and coordination functions may be implemented by the balloon network itself. For example, certain balloons may be configured to provide the same or similar functions as central control system 200 and/or regional control systems 202A to 202C. Other examples are also possible.
Furthermore, control and/or coordination of a balloon network may be de-centralized. For example, each balloon may relay state information to, and receive state information from, some or all nearby balloons. Further, each balloon may relay state information that it receives from a nearby balloon to some or all nearby balloons. When all balloons do so, each balloon may be able to individually determine the state of the network. Alternatively, certain balloons may be designated to aggregate state information for a given portion of the network. These balloons may then coordinate with one another to determine the overall state of the network.
Further, in some aspects, control of a balloon network may be partially or entirely localized, such that it is not dependent on the overall state of the network. For example, individual balloons may implement station-keeping functions that only consider nearby balloons. In particular, each balloon may implement an energy function that takes into account its own state and the states of nearby balloons. The energy function may be used to maintain and/or move to a desired position with respect to the nearby balloons, without necessarily considering the desired topology of the network as a whole. However, when each balloon implements such an energy function for station-keeping, the balloon network as a whole may maintain and/or move towards the desired topology.
As an example, each balloon A may receive distance information dl to dk with respect to each of its k closest neighbors. Each balloon A may treat the distance to each of the k balloons as a virtual spring with vector representing a force direction from the first nearest neighbor balloon i toward balloon A and with force magnitude proportional to di. The balloon A may sum each of the k vectors and the summed vector is the vector of desired movement for balloon A. Balloon A may attempt to achieve the desired movement by controlling its altitude.
Alternatively, this process could assign the force magnitude of each of these virtual forces equal to di×di, for instance. Other algorithms for assigning force magnitudes for respective balloons in a mesh network are possible.
In another embodiment, a similar process could be carried out for each of the k balloons and each balloon could transmit its planned movement vector to its local neighbors. Further rounds of refinement to each balloon's planned movement vector can be made based on the corresponding planned movement vectors of its neighbors. It will be evident to those skilled in the art that other algorithms could be implemented in a balloon network in an effort to maintain a set of balloon spacings and/or a specific network capacity level over a given geographic location.
2d) Example Balloon Configuration
Various types of balloon systems may be incorporated in an example balloon network. As noted above, an example embodiment may utilize high-altitude balloons, which could typically operate in an altitude range between 18 km and 25 km. FIG. 3 shows a high-altitude balloon 300, according to an example embodiment. As shown, the balloon 300 includes an envelope 302, a skirt 304, a payload 306, and a cut-down system 308, which is attached between the balloon 302 and payload 304.
The envelope 302 and skirt 304 may take various forms, which may be currently well-known or yet to be developed. For instance, the envelope 302 and/or skirt 304 may be made of materials including metalized Mylar or BoPet. Additionally or alternatively, some or all of the envelope 302 and/or skirt 304 may be constructed from a highly-flexible latex material or a rubber material such as chloroprene. Other materials are also possible. Further, the shape and size of the envelope 302 and skirt 304 may vary depending upon the particular implementation. Additionally, the envelope 302 may be filled with various different types of gases, such as helium and/or hydrogen. Other types of gases are possible as well.
The payload 306 of balloon 300 may include a processor 312 and on-board data storage, such as memory 314. The memory 314 may take the form of or include a non-transitory computer-readable medium. The non-transitory computer-readable medium may have instructions stored thereon, which can be accessed and executed by the processor 312 in order to carry out the balloon functions described herein. Thus, processor 312, in conjunction with instructions stored in memory 314, and/or other components, may function as a controller of balloon 300.
The payload 306 of balloon 300 may also include various other types of equipment and systems to provide a number of different functions. For example, payload 306 may include an optical communication system 316, which may transmit optical signals via an ultra-bright LED system 320, and which may receive optical signals via an optical-communication receiver 322 (e.g., a photodiode receiver system). Further, payload 306 may include an RF communication system 318, which may transmit and/or receive RF communications via an antenna system 340.
The payload 306 may also include a power supply 326 to supply power to the various components of balloon 300. The power supply 326 could include a rechargeable battery. In other embodiments, the power supply 326 may additionally or alternatively represent other means known in the art for producing power. In addition, the balloon 300 may include a solar power generation system 327. The solar power generation system 327 may include solar panels and could be used to generate power that charges and/or is distributed by the power supply 326.
The payload 306 may additionally include a positioning system 324. The positioning system 324 could include, for example, a global positioning system (GPS), an inertial navigation system, and/or a star-tracking system. The positioning system 324 may additionally or alternatively include various motion sensors (e.g., accelerometers, magnetometers, gyroscopes, and/or compasses).
The positioning system 324 may additionally or alternatively include one or more video and/or still cameras, and/or various sensors for capturing environmental data.
Some or all of the components and systems within payload 306 may be implemented in a radiosonde or other probe, which may be operable to measure, e.g., pressure, altitude, geographical position (latitude and longitude), temperature, relative humidity, and/or wind speed and/or wind direction, among other information.
As noted, balloon 300 includes an ultra-bright LED system 320 for free-space optical communication with other balloons. As such, optical communication system 316 may be configured to transmit a free-space optical signal by modulating the ultra-bright LED system 320. The optical communication system 316 may be implemented with mechanical systems and/or with hardware, firmware, and/or software. Generally, the manner in which an optical communication system is implemented may vary, depending upon the particular application. The optical communication system 316 and other associated components are described in further detail below.
In a further aspect, balloon 300 may be configured for altitude control. For instance, balloon 300 may include a variable buoyancy system, which is configured to change the altitude of the balloon 300 by adjusting the volume and/or density of the gas in the balloon 300. A variable buoyancy system may take various forms, and may generally be any system that can change the volume and/or density of gas in the envelope 302.
In an example embodiment, a variable buoyancy system may include a bladder 310 that is located inside of envelope 302. The bladder 310 could be an elastic chamber configured to hold liquid and/or gas. Alternatively, the bladder 310 need not be inside the envelope 302. For instance, the bladder 310 could be a rigid bladder that could be pressurized well beyond neutral pressure. The buoyancy of the balloon 300 may therefore be adjusted by changing the density and/or volume of the gas in bladder 310. To change the density in bladder 310, balloon 300 may be configured with systems and/or mechanisms for heating and/or cooling the gas in bladder 310. Further, to change the volume, balloon 300 may include pumps or other features for adding gas to and/or removing gas from bladder 310. Additionally or alternatively, to change the volume of bladder 310, balloon 300 may include release valves or other features that are controllable to allow gas to escape from bladder 310. Multiple bladders 310 could be implemented within the scope of this disclosure. For instance, multiple bladders could be used to improve balloon stability.
In an example embodiment, the envelope 302 could be filled with helium, hydrogen or other lighter-than-air material. The envelope 302 could thus have an associated upward buoyancy force. In such an embodiment, air in the bladder 310 could be considered a ballast tank that may have an associated downward ballast force. In another example embodiment, the amount of air in the bladder 310 could be changed by pumping air (e.g., with an air compressor) into and out of the bladder 310. By adjusting the amount of air in the bladder 310, the ballast force may be controlled. In some embodiments, the ballast force may be used, in part, to counteract the buoyancy force and/or to provide altitude stability.
In other embodiments, the envelope 302 could be substantially rigid and include an enclosed volume. Air could be evacuated from envelope 302 while the enclosed volume is substantially maintained. In other words, at least a partial vacuum could be created and maintained within the enclosed volume. Thus, the envelope 302 and the enclosed volume could become lighter-than-air and provide a buoyancy force. In yet other embodiments, air or another material could be controllably introduced into the partial vacuum of the enclosed volume in an effort to adjust the overall buoyancy force and/or to provide altitude control.
In another embodiment, a portion of the envelope 302 could be a first color (e.g., black) and/or a first material from the rest of envelope 302, which may have a second color (e.g., white) and/or a second material. For instance, the first color and/or first material could be configured to absorb a relatively larger amount of solar energy than the second color and/or second material. Thus, rotating the balloon such that the first material is facing the sun may act to heat the envelope 302 as well as the gas inside the envelope 302. In this way, the buoyancy force of the envelope 302 may increase. By rotating the balloon such that the second material is facing the sun, the temperature of gas inside the envelope 302 may decrease. Accordingly, the buoyancy force may decrease. In this manner, the buoyancy force of the balloon could be adjusted by changing the temperature/volume of gas inside the envelope 302 using solar energy. In such embodiments, it is possible that a bladder 310 may not be a necessary element of balloon 300. Thus, in various contemplated embodiments, altitude control of balloon 300 could be achieved, at least in part, by adjusting the rotation of the balloon with respect to the sun.
Further, a balloon 306 may include a navigation system (not shown). The navigation system may implement station-keeping functions to maintain position within and/or move to a position in accordance with a desired topology. In particular, the navigation system may use altitudinal wind data to determine altitudinal adjustments that result in the wind carrying the balloon in a desired direction and/or to a desired location. The altitude-control system may then make adjustments to the density of the balloon chamber in order to effectuate the determined altitudinal adjustments and cause the balloon to move laterally to the desired direction and/or to the desired location. Alternatively, the altitudinal adjustments may be computed by a ground-based or satellite-based control system and communicated to the high-altitude balloon. In other embodiments, specific balloons in a heterogeneous balloon network may be configured to compute altitudinal adjustments for other balloons and transmit the adjustment commands to those other balloons.
As shown, the balloon 300 also includes a cut-down system 308. The cut-down system 308 may be activated to separate the payload 306 from the rest of balloon 300. The cut-down system 308 could include at least a connector, such as a balloon cord, connecting the payload 306 to the envelope 302 and a means for severing the connector (e.g., a shearing mechanism or an explosive bolt). In an example embodiment, the balloon cord, which may be nylon, is wrapped with a nichrome wire. A current could be passed through the nichrome wire to heat it and melt the cord, cutting the payload 306 away from the envelope 302.
The cut-down functionality may be utilized anytime the payload needs to be accessed on the ground, such as when it is time to remove balloon 300 from a balloon network, when maintenance is due on systems within payload 306, and/or when power supply 326 needs to be recharged or replaced.
In an alternative arrangement, a balloon may not include a cut-down system. In such an arrangement, the navigation system may be operable to navigate the balloon to a landing location, in the event the balloon needs to be removed from the network and/or accessed on the ground. Further, it is possible that a balloon may be self-sustaining, such that it does not need to be accessed on the ground. In yet other embodiments, in-flight balloons may be serviced by specific service balloons or another type of service aerostat or service aircraft.
3. Balloon Network with Optical and RF Links Between Balloons
In some embodiments, a high-altitude-balloon network may include super-node balloons, which communicate with one another via optical links, as well as sub-node balloons, which communicate with super-node balloons via RF links. Generally, the optical links between super-node balloons may be configured to have more bandwidth than the RF links between super-node and sub-node balloons. As such, the super-node balloons may function as the backbone of the balloon network, while the sub-nodes may provide sub-networks providing access to the balloon network and/or connecting the balloon network to other networks.
FIG. 4 is a simplified block diagram illustrating a balloon network that includes super-nodes and sub-nodes, according to an example embodiment. More specifically, FIG. 4 illustrates a portion of a balloon network 400 that includes super-node balloons 410A to 410C (which may also be referred to as “super-nodes”) and sub-node balloons 420 (which may also be referred to as “sub-nodes”).
Each super-node balloon 410A to 410C may include a free-space optical communication system that is operable for packet-data communication with other super-node balloons. As such, super-nodes may communicate with one another over optical links. For example, in the illustrated embodiment, super-node 410A and super-node 401B may communicate with one another over optical link 402, and super-node 410A and super-node 401C may communicate with one another over optical link 404.
Each of the sub-node balloons 420 may include a radio-frequency (RF) communication system that is operable for packet-data communication over one or more RF air interfaces. Accordingly, each super-node balloon 410A to 410C may include an RF communication system that is operable to route packet data to one or more nearby sub-node balloons 420. When a sub-node 420 receives packet data from a super-node 410, the sub-node 420 may use its RF communication system to route the packet data to a ground-based station 430 via an RF air interface.
As noted above, the super-nodes 410A to 410C may be configured for both longer-range optical communication with other super-nodes and shorter-range RF communications with nearby sub-nodes 420. For example, super-nodes 410A to 410C may use using high-power or ultra-bright LEDs to transmit optical signals over optical links 402, 404, which may extend for as much as 100 miles, or possibly more. Configured as such, the super-nodes 410A to 410C may be capable of optical communications at data rates of 10 to 50 GBit/sec or more.
A larger number of high-altitude balloons may then be configured as sub-nodes, which may communicate with ground-based Internet nodes at data rates on the order of approximately 10 Mbit/sec. For instance, in the illustrated implementation, the sub-nodes 420 may be configured to connect the super-nodes 410 to other networks and/or directly to client devices.
Note that the data speeds and link distances described in the above example and elsewhere herein are provided for illustrative purposes and should not be considered limiting; other data speeds and link distances are possible.
In some embodiments, the super-nodes 410A to 410C may function as a core network, while the sub-nodes 420 function as one or more access networks to the core network. In such an embodiment, some or all of the sub-nodes 420 may also function as gateways to the balloon network 400. Additionally or alternatively, some or all of ground-based stations 430 may function as gateways to the balloon network 400.
4. Providing a Payload Positioned Beneath a Balloon Envelope and a Drag Plate Attached to the Payload Wherein when the Balloon Envelope is Deflated, or Disconnected from the Payload, the Drag Plate Serves to Slow the Descent of the Payload to the Earth
As noted above, instruments or electronic devices may be positioned within a payload attached to a high atmosphere balloon. The instruments or electronic devices may be used to record various data and information. After a period of time, it may be desirable to have the payload return to the surface of the earth to retrieve the information obtained from the instruments and electronic devices positioned in the payload.
The balloon envelope may be deflated or collapsed, or disconnected from the payload, to allow the payload to descend to the surface of the earth. For example, the balloon envelope may be caused to rip, opening a hole in the envelope to deflate the balloon; or if a cord is used to attach the payload to the balloon envelope, the cord may be severed, using for example mechanical or explosive devices. Once the balloon is deflated, or the payload is severed from the balloon envelope, the payload is allowed to descend to the earth.
It is desirable to slow the rate of descent of the payload to the earth so that the instruments or electronic devices are not damaged upon impact, and so that the data and information that has been obtained may be retrieved. A parachute could be deployed from the payload to slow the rate of descent, although the remote deployment of a parachute may be unreliable. If the parachute fails to deploy, an undesirable, uncontrolled descent of the payload may occur.
Example embodiments may be directed to a balloon having a drag plate attached to the payload that may serve to slow the descent of the payload after the balloon envelope has been deflated or disconnected from the payload. As shown in FIGS. 5 and 5A, a drag plate 40 may be attached to the payload 30, where drag plate 40 is shown positioned above payload 30 and beneath balloon envelope 20. Of course, the drag plate could also be positioned beneath the payload, or may even be formed integral with the payload. In FIGS. 5 and 5A, the drag plate 40 is also shown attached to balloon envelope 20. Alternately, the payload 30 could be tethered to the balloon envelope via a cord, as an example.
FIG. 5A shows balloon envelope 20 after it has been deflated. The drag plate 40 has a surface area that creates a drag force (depicted by the arrows) as the payload 30 descends towards the earth and is forced through the air in the atmosphere. The larger the surface of the drag plate 40 facing the earth, the larger the drag forces that are created slowing the descent of the payload. In this example the drag plate 40 is concave with an upward facing concave surface. The drag plate 40 is positioned about balloon envelope 20 so that the balloon envelope is positioned in at least a portion of the concave section of the drag plate 40 such that the outer edges of the drag plate 40 extend adjacent the balloon envelope 20.
Furthermore, outer edges of the drag plate 40 may extend beyond the outer surface of the payload 30. Moreover, the outer edges of drag plate 40 may extend as far as the diameter of the balloon envelope 20 when balloon envelope 20 is inflated. The outer surface or outer edges of drag plate 40 may even extend further than the diameter of balloon envelope 20 when balloon envelope 20 is inflated to create even larger drag forces to slow the descent of the payload if desired.
An advantage of using a drag plate is that it does not need to be deployed, like a parachute would, to slow the descent of the payload because the drag plate is already in place. Thus, the use of a drag plate to control the descent of the payload eliminates any issues or risks that may arise when a means for slowing the descent must be deployed, e.g., when using a parachute that must properly deploy.
As shown in FIGS. 6, 6A, and 6B, the drag plate 40 may be a downward facing concave plate where the payload 30 is positioned within at least a portion of the downward facing concave section of the drag plate 40. The use of a downward facing concave drag plate may be advantageous because the geometry of the drag plate 40 serves to reduce the amount of air that may be displaced from beneath the drag plate 40 during descent, thus increasing the drag forces that may be used to slow the descent of the payload 30. Drag plate 40 and/or payload 30 may be tethered to balloon envelope via cord 50. Alternately, the drag plate 40 could be attached to the balloon envelope directly as shown in FIG. 5.
FIG. 6A shows balloon envelope 20 after it has been deflated. The drag plate 40 has a surface area that creates a drag force (depicted by the arrows) as the payload 30 descends towards the earth and is forced through the air in the atmosphere. The larger the surface of the drag plate 30 facing the earth, the larger the drag forces that are created slowing the descent of the payload. In FIG. 6A, the deflated balloon envelope 20 is shown remaining attached to drag plate 40. In FIG. 6B, the drag plate 40 and payload 30 are shown descending after balloon envelope 20 has been disconnected from the drag plate 40 by severing cord 50. Cord 50 may be severed using mechanical, electromagnetic, or explosive devices, or other suitable means for severing or disconnecting the balloon envelope 20 from the drag plate 40.
In FIG. 6, the drag plate 40 is shown having outer edges that extend past a top of the payload 30 and are adjacent the side of the payload. The outer edges could also extend past a bottom of the payload 30 as well. It should also be understand that the drag plate 40 could also have other geometries, including a flat plate. In fact, FIGS. 7, 7A, and 7B show drag plate 40 as a flat plate. Drag plate 40 and/or payload 30 may be tethered to balloon envelope via cord 50. Alternately, the drag plate 40 could be attached to the balloon envelope directly as shown in FIG. 5.
FIG. 7A shows balloon envelope 20 after it has been deflated. The drag plate 40 has a surface area that creates a drag force as the payload 30 descends towards the earth and is forced through the air in the atmosphere. The larger the surface of the drag plate 40 facing the earth, the larger the drag forces that are created slowing the descent of the payload. In FIG. 7A, the deflated balloon envelope 20 is shown remaining attached to drag plate 40. In FIG. 7B, the drag plate 40 and payload 30 are shown descending after balloon envelope 20 has been disconnected from the drag plate 40 by severing cord 50. Cord 50 may be severed using mechanical, electromagnetic, or explosive devices, or other suitable means for severing or disconnecting the balloon envelope 20 from the drag plate 40.
Viewed from the top, the drag plate 40 shown in FIGS. 5-7 may also have a number of different geometries, including square, round, polygonal, etc. For example, FIG. 8A shows drag plate 40 as a circular plate whereas FIG. 8B shows drag plate 40 as a square plate.
The drag plate 40 shown in FIGS. 5-8B above may advantageously have a surface area that extends beyond the outer surface of the payload 30, and may extend as far as the diameter of the balloon envelope 20 when the balloon envelope 20 is inflated. The outer surface of the drag plate 40 may also extend beyond the diameter of the balloon envelope 20 when the balloon envelope is inflated to provide even greater drag resistance to slow the descent of the payload 30.
In addition to slowing the descent of the payload after the balloon envelope has been deflated or disconnected from the payload, the drag plate may also help to control the rate of ascent or descent of the balloon when the balloon envelope is inflated, and the balloon is operating normally as part of the balloon network. The drag plate may inhibit the speed with which the balloon can change its altitude, when the balloon is operating normally as part of the balloon network. As a result, by slowing the rate of ascent or descent of the balloon, the drag plate may allow for greater accuracy is controlling the altitude of the balloon.
FIG. 9 shows a method 1200 that is provided that includes the step 1202 of slowing the descent of a payload attached to a balloon, wherein the balloon is comprised of a balloon envelope, a payload positioned beneath the balloon envelope, and a drag plate positioned beneath the balloon envelope and attached to the payload. The method 1200 further includes the step 1204 of operating a control system to cause the balloon envelope to be deflated, or to be disconnected from the payload, wherein when the balloon envelope is deflated, or disconnected from the payload, the drag plate serves to slow the descent of the payload to the earth.
5. A Non-Transitory Computer Readable Medium with Instructions to Cause the Balloon Envelope to be Deflated, or to be Disconnected from the Payload, Wherein when the Balloon Envelope is Deflated, or Disconnected from the Payload, a Drag Plate Serves to Slow the Descent of the Payload to the Earth.
Some or all of the functions described above and illustrated in FIGS. 5-8B may be performed by a computing device in response to the execution of instructions stored in a non-transitory computer readable medium. The non-transitory computer readable medium could be, for example, a random access memory (RAM), a read-only memory (ROM), a flash memory, a cache memory, one or more magnetically encoded discs, one or more optically encoded discs, or any other form of non-transitory data storage. The non-transitory computer readable medium could also be distributed among multiple data storage elements, which could be remotely located from each other. The computing device that executes the stored instructions could be a computing device, such as the processor 312 illustrated in FIG. 3. Alternatively, the computing device that executes the stored instructions could be another computing device, such as a server in a server network, or a ground-based station.
The non-transitory computer readable medium may store instructions executable by the processor 312 to perform various functions. The functions could include the controlling the descent of a balloon by causing the balloon envelope to be deflated, or to be disconnected from the payload, wherein when the balloon envelope is deflated, or disconnected from the payload, a drag plate serves to slow the descent of the payload to the earth.
CONCLUSION
The above detailed description describes various features and functions of the disclosed systems, devices, and methods with reference to the accompanying figures. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

## Claims

1. A balloon, comprising:
a balloon envelope;
a payload positioned beneath the balloon envelope, wherein the balloon envelope is adapted to be filled with a lift gas to provide a buoyant upward force acting on the payload;
a drag plate positioned beneath the balloon envelope and attached to the payload;
a control system configured to initiate a process to cause the balloon envelope to no longer provide lift to the payload; and
wherein the drag plate serves to slow the descent of the payload through an atmosphere above a surface of the earth.

2. The balloon of claim 1, wherein the drag plate is attached directly to the balloon envelope.

3. The balloon of claim 1, wherein the balloon envelope is attached to the drag plate by a cord.

4. The balloon of claim 1, wherein the process to cause the balloon envelope to no longer provide lift to the payload involves deflating the balloon envelope.

5. The balloon of claim 1, wherein the drag plate is flat and extends as far as the diameter of the balloon envelope when the balloon envelope is inflated.

6. The balloon of claim 1, wherein the outer surface of the drag plate is circular and extends as far as the diameter of the balloon envelope when the balloon envelope is inflated.

7. The balloon of claim 1, wherein the outer surface of the drag plate extends as far as the diameter of the balloon envelope when the balloon envelope is inflated.

8. The balloon of claim 7, wherein the outer surface of the drag plate extends beyond the diameter of the balloon envelope when the balloon envelope is inflated.

9. The balloon of claim 1, wherein the drag plate comprises a downward-facing concave portion, wherein the payload is positioned beneath the drag plate, and wherein the payload is at least partially within the downward-facing concave portion of the drag plate such that outer edges of the drag plate extend past a top of the payload and extend at least to the side of the payload.

10. The balloon of claim 9, wherein the outer surface of the drag plate extends as far as the diameter of the balloon envelope when the balloon envelope is inflated.

11. The balloon of claim 9, wherein the outer surface of the drag plate extends beyond the diameter of the balloon envelope when the balloon envelope is inflated.

12. The balloon of claim 1, wherein the drag plate comprises an upward-facing concave portion, wherein and the envelope is positioned above the drag plate, and wherein the envelope is at least partially within an upward-facing concave portion of the drag plate such that outer edges of the drag plate extend adjacent the balloon envelope.

13. The balloon of claim 12, wherein the outer surface of the drag plate extends as far as the diameter of the balloon envelope when the balloon envelope is inflated.

14. The balloon of claim 12, wherein the outer surface of the drag plate extends beyond the diameter of the balloon envelope when the balloon envelope is inflated.

15. A computer-implemented method, comprising:
slowing the descent of a payload attached to a balloon, wherein the balloon is comprised of a balloon envelope, a payload positioned beneath the balloon envelope, and a drag plate positioned beneath the balloon envelope and attached to the payload; and
operating a control system to initiate a process to cause the balloon envelope to no longer provide lift to the payload, wherein the drag plate serves to slow the descent of the payload to the earth.

16. The method of claim 15, wherein the outer surface of the drag plate is circular and extends as far as the diameter of the balloon envelope when the balloon envelope is inflated.

17. The method of claim 15, wherein the outer surface of the drag plate extends as far as the diameter of the balloon envelope when the balloon envelope is inflated.

18. The method of claim 17, wherein the outer surface of the drag plate extends beyond the diameter of the balloon envelope when the balloon envelope is inflated.

19. The method claim 15, wherein the drag plate is concave and the payload is positioned beneath the drag plate and is at least partially within a downward facing concave portion of the drag plate such that outer edges of the drag plate extend past a top of the payload and extend at least to the side of the payload.

20. The method of claim 19, wherein the outer surface of the drag plate extends as far as the diameter of the balloon envelope when the balloon envelope is inflated.

21. The method of claim 19, wherein the outer surface of the drag plate extends beyond the diameter of the balloon envelope when the balloon envelope is inflated.

22. The method of claim 15, wherein the drag plate is concave and the balloon envelope is positioned above the drag plate and is at least partially within an upward facing concave portion of the drag plate such that outer edges of the drag plate extend adjacent the balloon envelope.

23. The method of claim 22, wherein the outer surface of the drag plate extends as far as the diameter of the balloon envelope when the balloon envelope is inflated.

24. The method of claim 22, wherein the outer surface of the drag plate extends beyond the diameter of the balloon envelope when the balloon envelope is inflated.

25. A non-transitory computer readable medium having stored therein instructions executable by a computing device to cause the computing device to perform functions comprising:
slowing the descent of a payload attached to a balloon, wherein the balloon is comprised of a balloon envelope, a payload positioned beneath the balloon envelope, and a drag plate positioned beneath the balloon envelope and attached to the payload; and
operating a control system to cause the balloon envelope to be no longer provide lift to the balloon envelope, wherein the drag plate serves to slow the descent of the payload to the earth.

26. The non-transitory computer readable medium of claim 25, wherein the outer surface of the drag plate extends as far as the diameter of the balloon envelope when the balloon envelope is inflated.

27. The non-transitory computer readable medium of claim 25, wherein the outer surface of the drag plate extends beyond the diameter of the balloon envelope when the balloon envelope is inflated.

28. The non-transitory computer readable medium of claim 25, wherein the drag plate is concave and the payload is positioned beneath the drag plate and is at least partially within a downward facing concave portion of the drag plate such that outer edges of the drag plate extend past a top of the payload and extend at least to the side of the payload.

29. The non-transitory computer readable medium of claim 28, wherein the outer surface of the drag plate extends as far as the diameter of the balloon envelope when the balloon envelope is inflated such that outer edges of the drag plate extend adjacent the balloon envelope.

30. The non-transitory computer readable medium of claim 29, wherein the outer surface of the drag plate extends beyond the diameter of the balloon envelope when the balloon envelope is inflated.

31. A balloon, comprising:
a balloon envelope;
a payload positioned beneath the balloon envelope wherein the balloon envelope is adapted to be filled with a lift gas to provide a buoyant upward force acting on the payload; and
a drag plate positioned beneath the balloon envelope and attached to the payload, wherein an outer surface of the drag plate extends beyond sides of the payload and the drag plate serves to slow the rate of ascent or descent of the balloon through an atmosphere above a surface of the earth when the altitude of the balloon is being controlled.