Patent Publication Number: US-10322789-B2

Title: Filling apparatus for high-altitude balloons

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 15/161,613, filed May 23, 2016, which is a continuation of is a continuation of U.S. patent application Ser. No. 14/703,061, filed May 4, 2015, now issued as U.S. Pat. No. 9,371,124, which is a continuation of U.S. patent application Ser. No. 14/249,841, filed Apr. 10, 2014, now issued as U.S. Pat. No. 9,027,877, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     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 modem 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. 
     Some systems may provide network access via a balloon network operating in the stratosphere. Because of the various forces experienced by these balloons during deployment and operation, there is a balancing of needs between flexibility and stability of materials. The balloons may be made of an envelope material configured in sections or lobes to create a “pumpkin” or lobed balloon. The lobes are supported by a plurality of tendons. 
     Before a balloon can be deployed, its envelope must be inflated with lighter than air lift gas. Helium and hydrogen gases are two alternatives for lighter and air lift gases. Helium is an inert gas and thus considered generally safe. With helium, filling features can be sealed with O-rings, check vales, or caps in a manual setting. As an example, a person may remove a cap from a filling port, insert a filling hose, pull out the filing hose, and cap the filling port. When the filling hose is removed, gas can escape from the balloon. Even traditional one-way valves may allow a small amount of gas to leak. Purging after closing the valve, but prior to disconnecting the fill line can prevent leaks, but adds additional complexity to the design. However, with helium prices on the rise and reduced availability, hydrogen is becoming a more economical option. However, as hydrogen is highly explosive when combined with air, its use can present safety issues, especially during inflation. 
     BRIEF SUMMARY 
     Aspects of the present disclosure are advantageous for providing a leak free fill port that is also simple, robust and economical. For example, a high-altitude balloon including an apparatus for filling the high-altitude balloon is provided. The apparatus includes a tube configured to extend through envelope material of the balloon. A flange portion is connected to a first end of the tube. The flange portion is also situated on an interior surface of the balloon. A fitting is connected to a second end of the tube. The fitting is configured to attachment to an apparatus for filling the balloon with lift gas. 
     In one example, the tube is configured to be cold welded to seal the lift gas in the balloon. In another example, the flange portion includes a sealing O-ring configured to form a seal between the flange portion and the envelope material. In another example, high vacuum grease is applied to the sealing O-ring. In another example, the flange portion is arranged as the base of a plug having threading, and wherein the apparatus further comprises a retaining nut having threading configured to mate with the threading of the plug in order to secure the apparatus to the envelope material. In this example, the second end of the tube includes a second flange portion including at least one sealing O-ring configured to form a seal between the second flange portion and an interior of the plug. In addition, the apparatus includes a cap portion configured to secure the second flange portion to the plug. 
     Other aspects of the disclosure provide a method of manufacturing a high-altitude balloon having a balloon envelope. The method includes inserting a tube through an opening in material of an incomplete balloon envelope. The tube has a flange portion at a first end. The tube is secured to the incomplete balloon envelope. The incomplete balloon envelope is then completed such that the flange portion and the surface of the material are located within a chamber of the completed balloon envelope configured to receive lift gas. 
     In one example, the method also includes attaching a fitting to a second end of the tube, the fitting being configured to attach to a filling apparatus for filling the completed balloon envelope with the lift gas. In this example, attaching the fitting includes braze welding the fitting to the tube. In another example, the method also includes making the opening in the material. In another example, further securing the tube to the incomplete balloon envelope includes using an O-ring to clamp the balloon envelope material to the tube. 
     Further aspects of the disclosure provide a method of filling a high-altitude balloon with lift gas. The method includes connecting a filling apparatus to a fitting. The fitting is connected to a first end of a tube. The tube has a flange portion at a second end and is connected to an envelope of the balloon. The method also includes filling the envelope with the lift gas using the filling apparatus and pinching off the tube such that the tube is separated from the filling apparatus. 
     In one example, the pinching off is a cold welding process which reduces a likelihood of combustion of the lift gas. In another example, the welding prevents the lift gas from escaping from the envelope after the filling. In another example, the lift gas includes hydrogen. 
     Another aspect of the disclosure provides a method of manufacturing a high-altitude balloon having a balloon envelope and a filling port. The method includes placing a plug body having a flange portion and a threaded portion within an opening in material of an incomplete balloon envelope such that the flange portion is situated on a first side of the incomplete balloon envelope and at least some of the threaded portion is situated on a second side of the incomplete balloon envelope; attaching a retaining nut to the plug body to secure the plug body to the incomplete balloon envelope; completing the incomplete balloon envelope such that the flange portion and the surface of the material are located within a chamber of the completed balloon envelope configured to receive lift gas and the plug body and retaining nut are arranged as the part of the filling port. 
     In one example, the method also includes attaching a sealing O-ring to the plug body, the sealing O-ring being configured to form a seal between the flange portion and an interior of the plug body. In another example, the method also includes attaching a cap portion to a second flange portion at one end of a tube in order to secure the second flange portion to the plug body. In this example, the method also includes attaching a fitting to a second end of the tube, the fitting being configured to attach to a filling apparatus for filling the completed balloon envelope with the lift gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional diagram of a system in accordance with aspects of the disclosure. 
         FIG. 2  is an example of a balloon in accordance with aspects of the disclosure. 
         FIG. 3  is an example of a pinch off tube in accordance with aspects of the disclosure. 
         FIG. 4  is an example of a filling apparatus in accordance with aspects of the disclosure. 
         FIG. 5  is an example diagram of the filling apparatus of  FIG. 4  and a portion of balloon envelope material in accordance with aspects of the disclosure. 
         FIG. 6  is another example diagram of the filling apparatus of  FIG. 4  and a portion of balloon envelope material in accordance with aspects of the disclosure. 
         FIG. 7  is an example diagram of a completed balloon envelope, filling apparatus, and lift gas fill source in accordance with aspects of the disclosure. 
         FIG. 8  is an example diagram of a pinched off filling apparatus, a completed balloon envelope, and lift gas fill source in accordance with aspects of the disclosure. 
         FIG. 9  is a flow diagram in accordance with aspects of the disclosure. 
         FIG. 10  is another flow diagram in accordance with aspects of the disclosure. 
         FIG. 11  is an example of a pinch off tube assembly in accordance with aspects of the disclosure. 
         FIG. 12  is an example of a filling apparatus attached to a balloon cap in accordance with aspects of the disclosure. 
         FIG. 13  is a cross sectional view of the filling apparatus of  FIG. 12 . 
         FIG. 14  is a side view of the cross sectional view of the filling apparatus of  FIG. 13 . 
         FIG. 15  is an exploded view of the filling apparatus and balloon cap of  FIG. 12 . 
         FIG. 16  is a close up view of a portion of the cross sectional view of the filling apparatus of  FIG. 13 . 
         FIG. 17  is another close up view of a portion of the cross sectional view of the filling apparatus of  FIG. 13 . 
         FIG. 18  is another close up view of a portion of the cross sectional view of the filling apparatus of  FIG. 13 . 
         FIG. 19  is a cross sectional view of the filling apparatus of  FIG. 12  after being sealed. 
         FIG. 20  is a flow diagram in accordance with aspects of the disclosure. 
         FIG. 21  is another flow diagram in accordance with aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure generally relates to filling high altitude balloons with gas. As discussed above, such balloons may need to be filled with lighter than air lift gasses such as helium or hydrogen. As helium becomes more expensive with lesser availability, hydrogen becomes a more attractive option. However, because hydrogen is flammable, it is important to have filling features which reduce the likelihood of gas escaping, which could cause serious damage or injury to persons. 
     In one aspect, the filling apparatus may include a pinch-off tube having a threaded body and a flange portion or plate at one end and a fitting at the other end may be utilized. Pinch-off tubes are typically used to provide hermetic and leak tight for vacuum and low pressure applications. 
     Where the balloon is likely to be used for more long term flights, for example weeks or months or more, even very slow leaks can reduce the effectiveness of the balloon envelope. In such examples, the pinch-off tube may be attached to a cap and balloon envelope using a plurality of seals in order to further reduce the likelihood of even such small leaks. For instance, the filling apparatus may include a pinch off tube attached to a fitting at one end as well as a plug, a fill port body, a fill port body retaining nut, and a fill tube cap. When assembled, sealing O-rings may provide an air tight seal between the filling apparatus and the balloon envelope. 
     As noted above, a fitting may be welded to an end of the pinch off tube, for example, using braze welding. The pinch-off tube may be positioned through a hole in the balloon envelope material. The balloon envelope material may be sealed together in a completed envelope and made ready for filling. In some examples, high vacuum grease may be applied to any O-ring seals before or after the balloon is sealed together. 
     To fill the balloon, the fitting may be connected to an apparatus for providing filling gas such as hydrogen or helium. Once the filling is completed, the tubing may be cold welded shut by a scissor-like cutter. By doing so, there is no chance for the lift gas to escape and little likelihood of injury due when using a gas such as hydrogen. In addition, the cold welding does not need to be performed manually by a person, but may be done automatically by another apparatus. The pinch-off tube provides a single use, simple, and nonmoving part that is reliable, economical, and safe when using flammable filler gasses such as hydrogen. 
       FIG. 1  depicts an example system  100  in which a high altitude balloons as described above may be used. This example should not be considered as limiting the scope of the disclosure or usefulness of the features described herein. System  100  may be considered a “balloon network.” In this example, balloon network  100  includes a plurality of devices, such as of high altitude balloons  102 A-F as well as ground base stations  106  and  112 . Balloon network  100  may also include a plurality of additional devices, such as various computing devices (not shown) as discussed in more detail below. 
     As shown, the devices of system  100  are configured to communicate with one another. As an example, the balloons may include free-space optical links  104  and/or radiofrequency (RF) links  114  in order to facilitate intra-balloon communications. In this way, balloons  102 A-F may collectively function as a mesh network for packet data communications. Further, at least some of balloons  102 A-B may be configured for RF communications with ground-based stations  106  and  112  via respective RF links  108 . Some balloons, such as balloon  102 F, could be configured to communicate via optical link  110  with ground-based station  112 . 
     As noted above, to transmit data to another balloon, a given balloon  102  may be configured to transmit an optical signal via an optical link  104 . In addition, the given balloon  102  may use one or more high-power light-emitting diodes (LEDs) to transmit an optical signal. Alternatively, some or all of the balloons may include laser systems for free-space optical communications over the 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 may include one or more optical receivers. 
     The balloons  102 A-F may collectively function as a mesh network. More specifically, since balloons  102 A-F may communicate with one another using free-space optical links, the balloons may collectively function as a free-space optical mesh network where each balloon may function as a node of the mesh network. As noted above, the balloons of balloon network  100  may be high-altitude balloons, which are deployed in the stratosphere. As an example, the balloons may generally be configured to operate at altitudes between 18 km and 25 km above the Earth&#39;s surface in order to limit the balloon&#39;s exposure to high winds and interference with commercial airline flights. Additional aspects of the balloons are discussed in greater detail below, with reference to  FIG. 2 . 
       FIG. 2  is an example high-altitude balloon  200 , which may represent any of the balloons of balloon network  100 . As shown, the balloon  200  includes an envelope  210 , a payload  220  and a plurality of tendons  230 - 250  attached to the envelope  210 . 
     The high-altitude balloon envelope  210  may take various forms. In one instance, the balloon envelope  210  may be constructed from materials such as polyethylene that do not hold much load while the balloon  200  is floating in the air during flight. Additionally, or alternatively, some or all of envelope  210  may be constructed from a highly flexible latex material or rubber material such as chloroprene. Other materials or combinations thereof may also be employed. Further, the shape and size of the envelope  210  may vary depending upon the particular implementation. Additionally, the envelope  210  may be a chamber filled with various gases or mixtures thereof, such as helium, hydrogen or any other lighter-than-air gas, hereafter, lift gas. The envelope  210  is thus arranged to have an associated upward buoyancy force during deployment of the payload  220 . 
     The payload  220  of balloon  200  is affixed to the envelope by a connection  260  such as a cable. The payload  220  may include a computer system (not shown), having one or more processors and on-board data storage. The payload  220  may also include various other types of equipment and systems (not shown) to provide a number of different functions. For example, the payload  220  may include an optical communication system, a navigation system, a positioning system, a lighting system, an altitude control system and a power supply to supply power to various components of balloon  200 . 
     In view of the goal of making the balloon envelope  210  as lightweight as possible, it may be comprised of a plurality of envelope lobes or gores that have a thin film, such as polyethylene or polyethylene terephthalate, which is lightweight, yet has suitable strength properties for use as a balloon envelope deployable in the stratosphere. In this example, balloon envelope  210  is comprised of envelope gores  210 A- 210 D. 
     The individual envelope gores  210 A- 210 D may be shaped so that the length of the edge seam connecting adjacent envelope gores is greater than the length of a centerline of the envelope gores. Thus, the envelope gores  210 A- 210 D may be shaped to better optimize the strain rate experienced by the balloon envelope  210 . The pressurized lifting gas within the balloon envelope  210  may cause a force or load to be applied to the balloon  200 . 
     The tendons  230 - 250  provide strength to the balloon  200  to carrier the load created by the pressurized gas within the balloon envelope  210 . In some examples, a cage of tendons (not shown) may be created using multiple tendons that are attached vertically and horizontally. Each tendon may be formed as a fiber load tape that is adhered to a respective envelope gore. Alternately, a tubular sleeve may be adhered to the respective envelopes with the tendon positioned within the tubular sleeve. 
     Top ends of the tendons  230 ,  240  and  250  may be coupled together using an apparatus, such as top cap  201  positioned at the apex of balloon envelope  210 . Bottom ends of the tendons  230 ,  240  and  250  may also be connected to one another. For example, a corresponding apparatus, e.g., bottom cap  202 , is disposed at a base or bottom of the balloon envelope  210 . The top cap  201  at the apex may be the same size and shape as and bottom cap  202  at the bottom. Both caps include corresponding components for attaching the tendons  230 ,  240  and  250 , and may be formed from stainless steel or aluminum. 
       FIG. 3  is an example of a pinch-off tube  300  which may be used as a fill port for a high altitude balloon such as balloon  200 . In this example, pinch-off tube  300  includes a tubular portion  302  having an open first end  304  and an opposing open second end  306 . The open second end  306  is shown in dashed line to indicate that it is with threaded body  312 . The threaded body  312  has a diameter that is wider than the diameter of the open first end  304  of the tubular portion. In this regard, pinch-off tube  300  includes a passageway such that air or other gasses may flow along the general the path of arrows  308  from the open first end  304  to the opposing open second end  306  and from the open second end  306  to the open first end  304 . The arrows  308  shown in dashed line indicate that they are within the tubular portion  302 . The threaded body  312  is connected to a flattened disc or flange portion  310 . The pinch-off tube  300 , threaded body  312 , and flange portion may be made of various metals, including, for example copper. 
       FIG. 4  is an example of a filling apparatus  400  that includes a fitting  402  is attached to the open first end  304  of pinch-off tube  300 . In this regard, the fitting  402  may be fixed to the open first end  304  of the tubular portion  302  by braze welding or other connection techniques prior to or after the filling apparatus  400  is attached to a balloon envelope as described below. Fitting may be configured to connect the filling apparatus  400  with a lift gas fill source in order to fill a high altitude balloon such as balloon  200  with lift gas. 
     The filling apparatus may be attached to a balloon envelope during the manufacturing of the balloon. For example, before the balloon envelope is completed, a hole may be cut into a portion of the balloon envelope material. The filling apparatus may be placed through the hole from what will become the interior of the balloon envelope. In this regard, the second end of the filling apparatus having the fitting may be passed through the hole as well as the tubular portion of the pinch-off tube. Once the flange of the pinch-off tube is positioned below the hole, a nut or other fixation device may be used further secure the balloon envelope material to the filling apparatus and in particular, to the threaded body of the pinch-off tube. 
       FIG. 5  is an example  500  of the filling apparatus  400  being positioned relative to a portion of the balloon envelope material  502 . In this example the second open end  306 , flange  310 , the tubular portion  302 , and part of the fitting  402  are shown in dashed line as these features are located below the portion of envelope material  502  or what will become an interior of the balloon envelope. As noted above, after the filling apparatus is secured to the portion of balloon envelope material  502 , the portion of the balloon envelope material may be one of envelope gores  210 A- 210 D attached to other such envelope gores in order to form a completed balloon envelope such as balloon envelope  210 . 
     Hole  504  may be cut into the portion of balloon envelope material  502  using any conventional cutting technique. Hole  504  may be sized such that the fitting  402  and tubular portion  302  may be passed through the hole. Hole  504  may be smaller than the area of flange  310  such that the flange cannot pass through hole  504 , though larger holes may also be used. 
     In some examples, prior to inserting the filling apparatus  400  into the hole  504  or after the balloon envelope is completed, a high vacuum grease may be applied to all or a portion of the filling apparatus. Fitting  402  is then passed through the hole from a side of the portion of balloon envelope material  502  that will become the interior of the balloon envelope  210  when the envelope is completed. Thus, in the example of  FIG. 500 , fitting  402  is passed through the hole  504  in the direction of arrow  506 . 
       FIG. 6  is an example  600  of the filling apparatus  400  being secured to a portion of the balloon envelope material  502 . Once the fitting  402  passes through the hole  504  (as shown in  FIG. 5 ), the tubular portion  302  is also passed through the hole until at least a portion of the threaded body  312  is through the hole and the flange  310  meets with the portion of balloon envelope material  502  as shown in  FIG. 6 . Thus, in this example the second open end  306  and flange  310  are shown in dashed line as these features are located below the portion of envelope material  502  or what will become an interior of the balloon envelope. 
     In order to secure the pinch-off tube to the portion of balloon envelope, a fixation device such as a nut may be used. A nut  606  may be placed over the fitting  402  and moved down in the direction of arrow  608  until the clamp is positioned around the gathered material. Nut  606  includes an opening  610  wide enough to pass over the fitting  402 . The opening also includes threading  612  that is configured to mate with the threading of the threaded body  312 . The nut  606  may then be tightened around the threaded body  312  in order to secure the balloon envelope material to the filling apparatus, for example, by way of a clamping force as is shown in example  700  of  FIG. 7 . 
     Once the filling apparatus is secured to the balloon envelope material, the balloon envelope and balloon may be completed. For example, as noted above, the portion of balloon envelope material  502  may be secured to other such portions (though without the filling apparatus) using an impulse sealing process or other process in order to create a completed balloon envelope as shown in  FIG. 2 . The completed balloon envelope thus includes a chamber for receiving lift gas. The balloon envelope may then be configured with the various other features discussed above in order to produce a completed balloon. 
     The completed balloon may then be inflated using the filling apparatus. For example, the completed balloon envelope may then be attached to a lift gas fill source via the fitting in order to fill the envelope with lift gas. Thus, lift gas may progress from the lift gas fill source, through the tubular portion, and into the balloon envelope in order to inflate the chamber of the balloon envelope. Once a desired level of inflation has been reached, the filling apparatus may be pinched off, for example, using a cold welding process. For instance, while the filling apparatus is still connected to the lift gas fill source, the tubular portion of the filling apparatus may be crushed by a scissor like tool such as a pinch-off tool until the tubular portion is severed into two sections. The section having the fitting may thus still be connected to the lift gas fill source. This section may be discarded. The other section connected to the balloon envelope material may form an air tight chamber. 
       FIG. 7  is an example  700  of a completed balloon envelope  702  that includes the portion of balloon envelope material  502  having the filling apparatus  400 . Again, the second open end  306  and flange  310  are shown in dashed line as these features are located below the portion of balloon envelope material  502  and on an interior of the completed balloon envelope  702 . 
     In this example, the fitting  402  is connected to a lift gas fill source  704 . Lift gas fill source  704  may include a hose or other device that provides lift gasses such as hydrogen or helium to fill the completed balloon envelope  502 . The hose may be configured to detachably mate with fitting  403 , for example, via complementary threading. As such, tubular portion  302  connects an interior or chamber of the completed balloon envelope  702  with the lift gas fill source  704 . The tubular portion  302  extends through a hole  406  in the portion of envelope material  402 . The nut  606  again secures the filling apparatus to the portion of balloon envelope  502  and provides an air tight seal as the chamber is inflated. 
     In order to fill the balloon envelope, the lift gas fill source  704  may be connected to fitting  410  of the filling apparatus  400  as shown in  FIG. 7 . The lift gas fill source  704  may then be used to provide lift gasses to inflate the completed balloon envelope  702 . The lift gasses may flow from the lift gas fill source  704  through the fitting  410 , the tubular portion  302 , and into a chamber of the completed balloon envelope  702  along arrows  706 . 
     Once a desired inflation of the completed balloon envelope  702  is reached, the tubular portion  302  may be pinched off. For example, a scissor like tool such as a pinch-off tool may be used to cold weld the tubular portion  302  by crushing the tubular portion  302  into two sections and forming a seal on each of the two sections. Example  800  of  FIG. 8  depicts two sections  302 A and  302 B of the tubular portion which have been severed from one another using a pinch-off tool at line  708  (shown in  FIG. 7 ). In this example, the tubular portion has been crushed such that each section  302 A and  302 B has an air tight seal  802 A and  802 B, respectively. Section  302 A which is still attached to lift gas fill source  704  via the fitting  410  may be removed from lift gas fill source and discarded. Air tight seal  802 A may prevent lift gasses from escaping from the completed balloon envelope  702  during use of the balloon even in high-altitude environments as described above. 
     Flow diagram  900  of  FIG. 9  is an example flow diagram of some of the aspects described above which may be used to manufacture a high-altitude balloon having a balloon envelope. In this example, a tube is inserted through an opening in material of an incomplete balloon envelope at block  902 . The tube has a flange at a first end. The opening may be made in the material by cutting the material using an instrument having a sharp blade or a punch tool. As noted above, a fitting may also be attached to a second end of the tube via braze welding. This fitting can be configured to attach to a filling apparatus for filling a completed balloon envelope with lift gas. The tube secured to the incomplete balloon envelope at block  904 . As an example, an O-ring clamp may be used to clamp the balloon envelope material to the tube. The incomplete balloon envelope is then completed such that the flange and the surface of the material are located within a chamber of the completed balloon envelope configured to receive lift gas at block  906 . 
     Flow diagram  1000  of  FIG. 10  is an example flow diagram of some of the aspects described above which may be used to fill a high-altitude balloon with lift gas. In this example, a filling apparatus is connected to a fitting at block  1002 . The fitting is connected to a first end of a tube. The tube having a flange at a second end and being connected to an envelope of the balloon. The envelope is filled with the lift gas using the filling apparatus at block  1004 . As noted above, in some examples, the lift gas may include hydrogen. The tube is pinched off such that the tube is separated from the filling apparatus at block  1006 . The pinching off may include a cold welding process which reduces a likelihood of combustion of the lift gas. The pinching off may also prevent the lift gas from escaping from the envelope after the filling. 
     Thus, the features described above allow no chance for the lift gas to escape after inflation but before the chamber of the completed balloon envelope is sealed. This also reduces the likelihood of injury due when using a gas such as hydrogen. In addition, the cold welding does not need to be performed manually by a person using a pinch-off tool, but may be done automatically by another apparatus. The filling apparatus tube provides a single use, simple, and nonmoving part that is reliable, economical, and safe when using flammable filler gasses such as hydrogen. 
       FIG. 11  is an example of a pinch-off tube assembly  1100  which may be used as a fill port for a high altitude balloon such as balloon  200 . In this example, pinch-off tube assembly  1100  includes a tubular portion  1102  having an open first end  1104  and an opposing open second end  1106 . Pinch-off tube assembly  1100  includes a passageway such that air or other gasses may flow along the general the path of arrows  1108  from the open first end  304  to the opposing open second end  1106  (more clearly shown in  FIG. 13 ) as well as from the open second end  306  to the open first end. Second end  1106  is connected to a disc or flange portion  1110  of a plug  1112 . The flange portion  1100  includes a lip  1114  that extends outwardly from the flange portion. 
     The tubular portion  1102  may include various metals, including, for example copper. The tubular portion  1102  may be attached, for example by braze welding, to the flange portion  1110 . The plug  1112  (and the flange portion  1110 ) may be made of materials different from the tubular portion  1102 , such as stainless steel or aluminum. 
     The plug  1112  may also include one or more grooves (shown as grooves  1116  and  1118  in  FIG. 13 ). Sealing devices, such as O-rings  1126  and  1128  may be placed in such grooves. The O-rings  1126  and  1128  may be formed of flouroscilicone or other flexible materials well suited to low temperature environments as described in more detail below. 
       FIGS. 12-14  are examples of a filling apparatus  1200  for filling a balloon envelope of a balloon, such as balloon  200 , with lift gas.  FIG. 13  is a cross sectional view of  FIG. 12 , and  FIG. 14  is an offset view of the cross sectional view of  FIG. 12 .  FIG. 15  is a break out view of the components of filling apparatus  1200 . 
     Referring to  FIGS. 12 and 15 , in addition to the pinch-off tube assembly  1100 , the filling apparatus includes a fill port body  1202 , a fill port body retaining nut  1204 , and a fill tube cap  1206 . Each of the fill port body  1202 , the fill port body retaining nut  1204 , and the fill tube cap  1206  may be made of a crystallized plastic or high-performance acetal resin such as commercially available Delrin® products. 
     The fill port body  1202  includes a lower flange portion  1222  and a threaded body portion  1224  having threading. The lower flange portion has grooves  1226  and  1228  separated by a thin flexure section  1230 . A sealing device such as envelope sealing O-ring  1232  is situated in the groove  1226 . Envelope sealing O-ring may also be formed of flouroscilicone or other materials well suited to low temperature environments. However, as described in more detail below, the envelope sealing O-ring  1232  may also be made of other materials without such properties. The fill port body  1202  may also include a passageway  1228  that passes through the threaded body portion  1224  and the lower flange portion  1222  in order to lift gas to pass from one end of the passageway to the other. 
     The fill port body retaining nut  1204  includes internal threading  1240 . The internal threading  1240  is complementary to threading of the threaded body portion  1224  of the fill port body  1202 . In this regard, the fill port body  1202  may be secured to a portion of the top cap  201  and a portion of the envelope  210  (shown most clearly in  FIG. 15 ) of balloon  200  via the fill port retaining nut  1204  and envelope sealing O-ring  1232 . 
     The fill tube cap  1206  includes internal threading  1260  that is complementary to the threading of the threaded body portion  1224 . The fill tube cap also includes a contact surface  1262  configured to contact the lip  1114  of the flange portion  1110 . 
     Filling apparatus  1200  may also include a fitting (not shown) attached to the open first end  1104  of the pinch-off tube assembly  1100 . This fitting may be configured similar to fitting  402  of  FIG. 4 . In this regard, the fitting may be fixed to the open first end  1104  of the tubular portion  1102  by braze welding or other connection techniques. The fitting may be configured to connect the filling apparatus  1200  with a lift gas fill source in order to fill a high altitude balloon such as balloon  200  with lift gas. 
       FIG. 16  is a close up view of box  1300  of  FIG. 13 . Although not shown as such, envelope sealing O-ring  1232  is compressed by the force of fill port body retaining nut  1204  on the top cap  201  and balloon envelope  210 . This compression force on the envelope sealing O-ring  1232  creates a seal between the balloon envelope  210 , and the fill port body  1202 . In addition, this force may also compress the thin flexure section  1230 . In some examples, this thin flexure section  1230  may be compressed as much as the O-ring by the force of the fill port body retaining nut  1204  on the top cap  201 . For instance, the thin flexure section  1230  may have a cross section of approximately 0.125 in and may be compressed a distance on the order of 0.015 in or more or less. The thing flexure section  1230  may keep the O-ring in place at temperatures well below the O-ring&#39;s elastic temperature (e.g. at −50 degrees Celsius where the O-ring loses its elastic characteristics and becomes ridged) such that the seal is maintained. Thus, the envelope sealing O-ring  1232  may be made of materials other than flouroscilicone or other materials well suited to low temperature environments. 
       FIG. 17  is a close up view of box  1310  of  FIG. 13 . Although not shown as such, O-rings  1126  and  1128  compressed within the grooves  1116  and  1118 , respectively, between the plug  1112  and an interior surface of fill port body  1202 . The minimum and maximum compression values may be approximately 15 and 19 percent of the cross sectional width of the ring (measured though line  1802  of  FIG. 18 ), respectively. The compressed O-rings each form a seal between the plug  1112  of the filling apparatus  1100  and the fill port body retaining nut  1204 . In this regard, only a single O-ring may be required to provide a sufficient seal, however the second O-ring may provide for further protection against leaks should the first O-ring fail. 
     As noted above, the low temperatures in the stratosphere can cause various components of the filling apparatus  1200  to change shape. For example, the O-rings may lose their shape at −80 degrees Celsius, shrinking within the grooves a distance on the order of 0.001 of an inch. Similarly, the other components of the filling apparatus  1200  may also shrink. Such shrinkage may cause very small leaks in the balloon envelope  210  which can allow lift gas to escape. As noted above, this can be problematic for long term (e.g. weeks or months or more) flights in the stratosphere. The amount of shrinkage may be determined using the coefficient of thermal expansion for each of the materials used in the filling apparatus. 
     However, the seals between the filling apparatus  1100  and the fill port body retaining nut  1204  may enable continuous seal contact well below the elastic temperature of the O-rings. For example, the materials and dimensions selected for the O-rings, fill port body, and plug may be selected such that the change in the cross sectional area of the grooves is equal to the change in the cross sectional area of the grooves. Table 1 below provides example dimensions, materials, and coefficients of thermal expansion (CTE) for such materials. Assuming zero elasticity of the O-ring material below −20 degrees Celsius, any movement would be due to the thermal coefficient of expansion at or below this temperature. The combination of components in Table 1 provide for complementary changes in the shapes of these components below −20 degrees Celsius, expected conditions in the stratosphere. In other words, the change in the distance between the grooves and the fill port body is approximately equal to the change in the diameter of the O-ring thereby reducing the likelihood of even small leaks around these O-rings during a flight in the stratosphere. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Example Dimensions, Materials and CTEs 
               
            
           
           
               
               
               
               
            
               
                 Component 
                 Dimension 
                 Material 
                 CTE 
               
               
                   
               
               
                 O-rings 1106  
                 0.139 ± 0.003 inch 
                 flouroscilicone 
                  810 ppm/K 
               
               
                 and 1108 
                 diameter cross section of 
                   
                   
               
               
                   
                 O-ring for a #244 O-ring 
                   
                   
               
               
                   
                 (e.g., measured through 
                   
                   
               
               
                   
                 line 1802 of FIG. 18 
                   
                   
               
               
                   
                 when uncompressed and 
                   
                   
               
               
                   
                 at SATP) 
                   
                   
               
               
                 Plug 1112 
                 1.780 inch diameter 
                 304 Stainless  
                 17.3 ppm/K 
               
               
                   
                 cross section at the 
                 Steel 
                   
               
               
                   
                 grooves 1116 and 1118 
                   
                   
               
               
                   
                 (e.g., measured through 
                   
                   
               
               
                   
                 line 1804 of FIG. 18 
                   
                   
               
               
                   
                 when uncompressed and 
                   
                   
               
               
                   
                 at SATP) 
                   
                   
               
               
                 Fill port body  
                 2.007 inch diameter 
                 Delrin ® 
                  122 ppm/K 
               
               
                 1202 
                 interior cross section 
                   
                   
               
               
                   
                 (e.g., measured through 
                   
                   
               
               
                   
                 line 1806 of FIG. 18 
                   
                   
               
               
                   
                 at SATP) 
               
               
                   
               
            
           
         
       
     
     As with filling apparatus  300 , filling apparatus  1200  may be attached to a balloon envelope during the manufacturing of the balloon. For example, before the balloon envelope is completed, a hole may be cut into a portion of the balloon envelope material using any conventional cutting technique. In addition, a hole may be made in the cap, for example during or after the material of the cap is form. These holes may be aligned with one another, and the various components of filling apparatus  1200  may be connected to one another (as shown in  FIGS. 13 and 14 . 
     Referring to  FIG. 15 , the balloon envelope  210  includes a hole  1502  and cap  201  includes hole  1504  which may be cut or formed as discussed above. The size and shape of these holes generally corresponds to a width of threaded body portion  1224  of the fill port body  1202  but are no larger than a diameter of the sealing o-ring  1232  and the lower flange portion  1222 . 
     In order to attach the filling apparatus  1200  to the balloon envelope and cap, the hole  1502  in the balloon envelope  210  may be aligned with the hole  1504  in the cap  201  as shown in  FIG. 15 . The threaded body portion  1224  of the fill port body  1202  is placed through the holes  1502  and  1504  from what will become the interior of the balloon envelope  210 . The lower flange portion  1222  does not pass through the holes  1502  and  1504  but makes contact with what will become an interior surface of the balloon envelope  210 . 
     The pinch-off tube assembly  1100  may then be placed within passageway  1228  of the fill port body  1202  until lip  1114  contacts a top portion of the threaded body portion  1224 . O-rings  1126  and  1128  are compressed within the grooves  1116  and  1118  and against an internal surface of the threaded body portion  1224  as shown in  FIGS. 13 and 14 . In this regard, as noted above, O-rings  1126  and  1128  may each form an air tight seal with the threaded body portion  1224 . 
     Before or after the plug  1112  of pinch-off tube assembly  1100  is placed within passageway  1228 , the fill port body retaining nut  1204  is then placed over the threaded body portion  1224 . For example, the fill port body retaining nut  1204  may be screwed onto the threaded body portion via the complementary threading of internal threading  1240 . As the fill port body retaining nut  1204  is tightened against the cap  201 , sealing O-ring  1232  creates an air tight seal against what will become the interior surface of the balloon envelope  210 . 
     In order to further secure the pinch-off tube assembly  1100  to the fill port body  1202 , the fill tube cap  1206  is placed over the tubular portion  1102  and onto the threaded body portion  1224  of the fill port body  1202 . The fill tube cap  1206  may be secured to the threaded body portion  1224  via internal threading  1260  and the threading of the threaded body portion. The fill tube cap  1206  may also secure the pinch-off tube assembly  1100  in place by contact between surface  1262  and the lip  1114  of the flange portion  1110 . 
     Once the fill port body is secured to the balloon envelope material, the balloon envelope and balloon may be completed as described above in order to produce a completed balloon. In this regard, the pinch-off tube assembly  1100  may be secured to the fill port body before or after the balloon envelope and balloon are completed. In addition, in some examples, before, during, and after assembly of the filling apparatus to the balloon envelope and cap, high vacuum grease may be applied to all or some of the components of the filling apparatus  1200 . 
     Once the filling apparatus and the completed balloon are assembled, the completed balloon may then be inflated using the filling apparatus  1200 . As with the filling apparatus  400  and the example of  FIG. 8 , the completed balloon envelope and filling apparatus  1200  may then be attached to a lift gas fill source via the fitting (not shown) in order to fill the envelope with lift gas. Thus, lift gas may progress from the lift gas fill source, through the passageways of the tubular portion and the fill port body, and into the balloon envelope in order to inflate the chamber of the balloon envelope. Again, the O-rings provide air tight seals in order to prevent gas from escaping during inflation. 
     Once a desired level of inflation has been reached, the filling apparatus  1200  may be pinched off, for example, using a cold welding process as described above.  FIG. 19  is an example  1900  of filling apparatus  1200  after it has been welded shut. In this example, the open end  1104  (not shown) has been removed from the filling apparatus  1200  and an air tight seal  1902  is formed. As with the example of filling apparatus  400 , the section of the tubular portion  1102  associated with the open end  1104  may be still attached to lift a gas fill source via the fitting. This section may be removed from lift gas fill source and discarded. Air tight seal  1902  as well as the seals of each of the O-rings  1126 ,  1128 , and  1226  may prevent lift gasses from escaping from the completed balloon envelope during use of the balloon even in high-altitude environments as described above. 
     Flow diagram  2000  of  FIG. 20  is an example flow diagram of some of the aspects described above which may be used to manufacture a high-altitude balloon having a balloon envelope using a filling apparatus such as filling apparatus  1200 . In this example, a fill port body is inserted through an opening in material of an incomplete balloon envelope and cap at block  2002 . The fill port body has a flange. The fill port body is secured to the incomplete balloon envelope and the cap at block  2004 . The incomplete balloon envelope is then completed such that the flange and the surface of the material are located within a chamber of the completed balloon envelope configured to receive lift gas at block  2006 . A pinch-off tube assembly is attached to the fill port body at block  2008 . Again, as noted above, the pinch-off tube assembly may be attached before or after the incomplete balloon envelope is completed. 
     Flow diagram  2100  of  FIG. 21  is an example flow diagram of some of the aspects described above which may be used to fill a high-altitude balloon with lift gas. In this example, a filling apparatus is connected to a fitting at block  2102 . The fitting is connected to a first end of a tube. The filling apparatus is connected to a balloon envelope and a cap portion of a balloon. The envelope is filled with the lift gas using the filling apparatus at block  2104 . As noted above, in some examples, the lift gas may include hydrogen. The tube is pinched off such that the tube is separated from the filling apparatus at block  2106 . The pinching off may include a cold welding process which reduces a likelihood of combustion of the lift gas. The welding may also prevent the lift gas from escaping from the envelope after the filling. 
     Unless otherwise stated, the foregoing alternative examples are not mutually exclusive, but may be implemented in various combinations to achieve unique advantages. As these and other variations and combinations of the features discussed above can be utilized without departing from the subject matter defined by the claims, the foregoing description of the embodiments should be taken by way of illustration rather than by way of limitation of the subject matter defined by the claims. In addition, the provision of the examples described herein, as well as clauses phrased as “such as,” “including” and the like, should not be interpreted as limiting the subject matter of the claims to the specific examples; rather, the examples are intended to illustrate only one of many possible embodiments. Further, the same reference numbers in different drawings can identify the same or similar elements.