Abstract:
Space vehicles such as space stations are often constructed as segmented inflatable structures which are susceptible to being punctured by small meteoric materials, resulting in small insidious leaks which are difficult to locate and repair. A method and apparatus are described in which a differential pressure transducer is positioned between segments of the space vehicle. Atmospheric gas pressure of all segments is continuously monitored. Analysis is performed on any pressure differentials which are determined to exist between adjacent segments. Detection of small leaks initiates an automatic isolation of the leaking segment. Detection of catastrophic leaks initiates an emergency evacuation of personnel from the affected segment.

Description:
BACKGROUND OF THE INVENTION 
     This invention generally relates to methods and apparatus for reliably detecting leaks in exterior walls of a segmented space station or vehicle. More particularly the invention relates to rapidly identifying a segment in which a leak has developed and isolating the affected segment from other segments of the vehicle. 
     Exploration of space is being carried out with vehicles which are inflatable structures. These vehicles are carried into an orbiting location in space in a deflated state. After reaching an orbital location, the vehicle is inflated into an enlarged configuration. Typically, these inflatable structures employ flexible materials as their outer walls. Flexible wall materials are susceptible to damage from meteoric particles. Consequently, there is a need to anticipate air leaks and provide a system to locate and repair such leaks in these vehicles. 
     In the prior art, manned vehicles such as the former Russian space station Mir, and the International Space Station, were constructed as a collection of segments which could be isolated from one another so that adverse effects of detected leakage could be isolated from a remainder of the vehicle. But leak detection is extra challenging for segmented manned space structures. The presence of multiple segments that are all attached and open to each other requires not only detecting the presence of a leak, but also identifying the location of the leak, i.e., in which segment the leak is occurring. 
     Large leaks are easily detected by monitoring cabin pressure and watching for rapid changes in that cabin pressure. Small leaks, while not presenting as immediate of a danger to crew life as large leaks, still are of grave concern and require detection, isolation, and repair in a timely manner. Even though the leak may be in only one segment, the pressure in all the segments decreases since the segments are all open to each other. As air rushes out of the leaking segment, air from neighboring segments rushes in to replace the lost air. The result is a decreasing cabin pressure in all segments. In the prior art, such small leaks in segmented space structures are detected by closing off and isolating each individual segment, one by one. The segments must be hermetically sealed from one another. If the pressure in the non-isolated segments holds steady while the pressure in the isolated segment continues to decrease, then the leak has been determined to be in the isolated segment. However, for slow leaks in a vehicle having multiple connected segments, identification of the location of the leaks in this manner can be a very time consuming process. Analysis of any one segment may require work effort that extends over a period of 48 hours or more. In a multi-segmented structure, identification and repair of a leak may require hundreds of hours of work effort. Throughout this extended time, atmospheric gas continues to escape from the vehicle. 
     As can be seen, there is a need for simple and accurate method and apparatus for discerning the presence of a leak in any particular segment of an inflatable manned space vehicle. Additionally, it is important that such a system can rapidly produce leak location information. It is also important that such a system have a capability for detecting small leaks. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention an inflatable space vehicle comprises a first segment and a second segment adjacent to the first segment, each of the segments having an atmospheric gas therein, a differential pressure transducer adapted to monitor a differential in an atmospheric gas pressure in the first segment and an atmospheric gas pressure in the second segment, and an isolation barrier adapted to isolate the first segment from the second segment and thereby preclude flow of the atmospheric gas between the first segment and the second segment, the isolation barrier being in an open position in the absence of the differential. The isolation barrier is adapted to automatically close in the presence the differential. 
     In another aspect of the present invention an apparatus for mitigating atmospheric gas leakage from a segmented space vehicle comprises a differential pressure transducer positioned so that a first sensor of the transducer is adapted to sense atmospheric gas pressure in a first segment of the vehicle and a second sensor of the differential pressure transducer is adapted to sense atmospheric gas pressure in a second segment, a control panel adapted to continuously monitor pressure differential between the first and second segments, and an isolation barrier adapted to prevent gas flow between the first and the second segment. The isolation barrier is adapted to close when a differential is detected between atmospheric gas pressure in the first segment and atmospheric gas pressure in the second segment. 
     In still another aspect of the present invention a method for mitigating leakage of atmospheric gas from segmented manned space vehicles comprises the steps of continuously monitoring atmospheric gas pressure differential between a first and a second segment of the vehicle, closing an isolation barrier between the first segment and second segment to preclude atmospheric gas flow therebetween and to produce an isolated segment when said atmospheric gas pressure differential is detected, analyzing the atmospheric gas pressure differential to determine if the differential increases over time, producing a warning signal if such a determination is made, and opening the isolation barrier after the warning signal is produced so that any personnel in the isolated segment may exit said segment. 
     In yet another aspect of the present invention a method for mitigating atmospheric gas leakage in segmented manned space vehicles comprises the steps of positioning a differential pressure transducer so that a first sensor of the transducer is adapted to sense atmospheric gas pressure in a first segment of the vehicle and a second sensor of the differential pressure transducer is adapted to sense atmospheric gas pressure in a second segment, continuously monitoring atmospheric gas pressure differential between the first and second segments, and isolating the first segment from the second segment when a differential is detected between atmospheric gas pressure in the first segment and atmospheric gas pressure in the second segment. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a portion of a segmented space vehicle which may embody the present invention; 
         FIG. 1A  is a sectional view taken along the lines A-A of  FIG. 1  showing an open isolation barrier in accordance with the present invention; 
         FIG. 1B  is a sectional view taken along the lines A-A of  FIG. 1  showing a closed isolation barrier in accordance with the present invention; 
         FIG. 2  is a schematic illustration that displays a series of steps that comprises a method for mitigating adverse effects of space vehicle leaks in accordance with the present invention. 
         FIG. 3  is a graph that illustrates a relationship between inter-segment pressure differentials and time in the context of a leaking segment; 
         FIG. 4  is a graph that shows a time-expanded portion of the graph of  FIG. 3 ; and 
         FIG. 5  is a schematic illustration that displays a series of steps that comprises a method for mitigating adverse effects of space vehicle leaks in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     The present invention may be useful in mitigating adverse effects of leakage in inflatable segmented structures. In that regard the invention is particularly useful for leak detection in segmented inflatable manned space vehicles. For illustrative purposes, the following description includes an example of the inventive apparatus and method that may be employed in detecting and initiating corrective measures to control leakage of atmospheric gas from a space vehicle. However, it is understood that other applications can be substituted for the inventive leak mitigation methods and apparatus. 
     In the prior art, small leaks in inflatable segmented space vehicles were not immediately detected. Their presence typically became known only after a general reduction of pressure was observed throughout the entire space vehicle. In these instances, atmospheric gas pressures among all of the segments would become equalized and identification of a leaking segment became difficult. The present invention may provide accurate and timely information about the presence of a leak in any segment of a multi-segment space vehicle. When this timely information is provided, a leaking segment may be quickly isolated from other segments of the vehicle. Timely leak information may be provided by continuously monitoring differential atmospheric pressure between adjacent segments of the vehicle. Detection of a pressure differential may begin a sequence of events in which a potentially leaking segment may be quickly isolated. An initial isolation of the segments may produce a condition in which an existence of a leak may be confirmed. An increasing differential in pressure may be indicative of a confirmed leak. Absence of change in differential pressure may be indicative of an anomaly that is not a leak. 
     The present invention may overcome a need to perform exhaustive and time-consuming manual leak detection work on manned space vehicles. The inventive technique may be particularly effective because leaks may be detected quickly and air loss associated with those leaks may be substantially reduced. 
     Referring now to  FIG. 1 , a portion of a space vehicle, designated by the numeral  10 , is shown schematically. The space vehicle  10  may be comprised of a plurality of segments. By way of example, two of these segments are illustrated in  FIG. 1 . A first segment  12  and a second segment  14  are shown in an adjacent relationship. A normally-open airlock  16  may be interposed between the first segment  12  and second segment  14 . The airlock  16  may be provided with a first isolation barrier  18  and a second isolation barrier  19 . The space vehicle  10  may comprise a differential pressure transducer  20  interposed between the first segment  12  and the second segment  14 . The differential pressure transducer may be provided with a first sensor  20 A and a second sensor  20 B. The first sensor  20 A may be adapted to sense atmospheric gas pressure in the first segment  12 . The second sensor  20 B may be adapted to sense atmospheric gas pressure in the second segment  14 . The first segment  12  may be provided with a first control panel  22 . The second segment  14  may be provided with a second control panel  23 . 
     For purposes of illustration, an outer wall  24  of the first segment  12  is shown to have a leak location  26 . Additionally, for purposes of illustrating the efficacy of the present invention, the air lock  16  may be in an open position to allow for ease of movement of personnel between the segment  12  and the segment  14 . 
     In operation, the apparatus shown in  FIG. 1  may perform a leak mitigation function in the presence of a loss of atmospheric gas at the leak location  26 . Atmospheric gas, i.e., gas required for life support, may begin to flow out of the space vehicle  10  at the leak location  26  in the first segment  12 . This outward flow of atmospheric gas may produce an overall change in pressure within the space vehicle  10 . But, the flow of atmospheric gas may produce, within the first segment  12 , a slightly greater change in pressure than that which develops throughout the space vehicle  10 . The differential pressure transducer  20  may detect a differential between a first atmospheric pressure in the first segment  12  as compared to a second atmospheric pressure in the second segment  14 . When a differential is detected between the first and the second atmospheric pressures, the differential pressure transducer  20  may produce a pressure differential signal that may be conveyed to the first control panel  22  in the first segment  12 . The first control panel  22  may in turn produce a closure signal  22 - 1  that may be conveyed to the first isolation barrier  18  in the first segment  12 , which isolation barrier  18  may be in an open state as shown in  FIG. 1A  Responsively to the closure signal  22 - 1 , a closure member  18 - 1  of the first isolation barrier  18  may close, as shown in  FIG. 1B ; thereby isolating the first segment  12  and precluding any further flow of atmospheric gas from the second segment  14  into the first segment  12 . 
     When flow of atmospheric gas into the first segment  12  is blocked by closure of the first isolation barrier  18 , atmospheric gas pressure in the first segment  12  may begin to change at a rate that may be more rapid than the change of pressure detected prior to closure of the first isolation barrier  18 . This more rapid rate of change of atmospheric pressure may occur because the overall mass of atmospheric gas in the first segment  12  may diminish. An increase in rate of change of atmospheric pressure within the first segment  12  may provide confirmation that a leak within the outer wall  24  of first segment  12 . 
     If, on the other hand, the pressure in the first segment  12  remains substantially unchanged after closure of the first isolation barrier  18 , the differential pressure transducer  20  may provide a false-alarm signal to the first control panel  22  which in turn provides a opening signal to the first isolation barrier  18  which may cause the first isolation barrier  18  to open. 
     Referring now to  FIG. 2 , a schematic diagram illustrates a sequence of events that may be associated with detection of a potential leak in the first segment  12  according to one embodiment of a method  200  of the present invention. In a step  202  a pressure differential may be detected by the differential pressure transducer  20  of  FIG. 1 . In a step  204  a pressure differential signal from the differential pressure transducer  20  may be analyzed within the first control panel  22  of  FIG. 1 . If a detected pressure differential is deemed to be large and indicative of a catastrophic leak, a warning signal may be produced in a step  206 . In this event, any personnel who are present in the leaking first segment  12  may quickly leave that segment in a step  208 . In a step  210 , the first isolation barrier  18  may be closed after all personnel have exited the leaking first segment  12 . Cessation of the warning signal by the exiting personnel also may occur in the step  210 . By way of example, a catastrophic leak may be one that produces a pressure differential of about 0.1 psia or more in a time period of about one minute or less. In other words, a catastrophic leak may be deemed to exist when a rate of increase in pressure differential exceeds about 0.1 psia in about one minute or less. 
     If the analysis of step  204  determines that a potential leak is not catastrophic, then a different series of events may be implemented (e.g., steps  212 - 220 ). In this case, in a step  212 , the first isolation barrier  18  may be closed in response to a closure signal from the first control panel  22 . Thus, in the event of a small leak, i.e., a non-catastrophic leak, the first isolation barrier  18  may be automatically closed without an intervening evacuation of personnel. In other words, closure may occur quickly within a time less than about four minutes. 
     After closure of the isolation barrier  18  in step  212 , the differential pressure transducer  20  and the control panel  22  may begin to determine, in a step  214 , if atmospheric gas pressure is changing in the first segment  12  at a rate different from that of the adjacent second segment  14 . If such a rate of change is indicative of a leak, then in a step  216 , the isolation barrier  18  may be opened, and the sequence of steps  206  through  210  may be initiated. Evacuation of personnel may proceed in a step  208  and the first segment  12  may be isolated until a leak repair plan may be implemented in a step  222 . 
     If, on the other hand, the analysis of step  214  fails to confirm that a leak exists in the isolated first segment  12 , i.e., pressure change rate may be below a predetermined value, then in a step  218 , the first isolation barrier  18  may be opened and the differential pressure transducer  20  may return to a monitoring mode in a step  220  without any evacuation of personnel from the first segment  12 . In other words, the present invention advantageously provides for a rapid analysis of virtually any minor pressure differential to be performed without disrupting normal activities of personnel in the space vehicle  10 . 
     The series of steps shown in  FIG. 2  provides an efficient and effective method  200  for continuously determining whether or not any segment of the space vehicle  10  has developed a leak. When the method  200  is employed, there may never be a need to perform the arduous segment by segment isolation and leak checking that has been required in prior art leak location methods. 
     The method of monitoring for leaks of the present invention as discussed above may be seen to be particularly useful when consideration is given to the difficulty of detecting small leaks in segmented space vehicles. These difficulties can be better understood by referring to  FIG. 3 . 
     In  FIG. 3 , a graph  300  illustrates a relationship that may exist between time and a differential between atmospheric gas pressure in the first segment  12  and atmospheric gas pressure in the second segment  14  in the event of a loss of atmospheric gas at the leak location  26 . A graph line  302  may reflect a typical pressure differential/time relationship in a leaking segment of a multi-segmented space vehicle in which atmospheric gas may freely flow between the first and second segments  12  and  14 , respectively. An ordinate/y axis  304  of the graph  300  displays pressure differential in a range from zero to 0.08 psia. An abscissa/x axis  306  of the graph  300  displays time in a range between zero and 1000 minutes. 
     The graph line  302  may display operational characteristics of a typical one of the differential pressure transducers  20  of  FIG. 1 . The differential pressure transducer  20  may comprise a digital quartz pressure diaphragm (not shown) that may be employed to measure absolute pressure within a vehicle located in space, wherein one side of the diaphragm may be referenced to a standard or reference pressure value, while cabin pressure, or other pressure to be measured, may be applied to the other side of the diaphragm. In an exemplary embodiment of the present invention, a first side of the diaphragm of the differential pressure transducer  20 , which first side may comprise the sensor  20 A, may be exposed to the atmosphere of the first segment  12 , and a second opposite side of the diaphragm, which second side may comprise the sensor  20 B, may be exposed to the atmosphere of the second segment  14 . 
     The graph  300  portrays a condition in which a small leak may have developed in the outer wall  24  of the first segment  12 . The graph line  302  may have a sharp spike  308 . The spike  308  may represent a phenomenon which may occur when the first segment  12  begins to leak. A pressure differential of about 0.07 psia may develop during a short period of time. This short period of time typically may be between about 4 to 10 minutes. After the spike  308  develops, the pressure differential may begin to diminish exponentially. After a time of about 800 minutes, the pressure differential may be substantially undetectable. 
       FIG. 4  shows the spike  308  of the graph line  302  in a time-expanded format.  FIG. 4  more readily illustrates that the spike  308  may develop within about a first 10 minutes of existence of a differential between the atmospheric gas pressure in the first segment  12  and the atmospheric gas pressure in the second segment  14 . The graph line  302  of  FIGS. 3 and 4  illustrates the value of performing an analysis of a potentially leaking condition in the very early stages of detection of such a pressure differential. It may be desirable to produce an isolation of the leaking segment while the pressure differential is high enough to be readily detectable. Typical differential pressure transducers have a limited sensitivity. They function well when measuring pressure differences that are least as large as about 0.2 to about 0.4 psia. Pressure differences which are readily detectable typically occur in a very early stage of a leaking condition. Consequently, quick action produces the most accurate and useful analytical results. 
     Referring now to  FIG. 5 , it may be seen that rapid acquisition of information relating to possible leakage may be used to initiate a series of steps of a method  500  which may be implemented in one of the space vehicles  10  even if the isolation barriers  18  and  19  are not adapted to respond automatically to closure signals from the control panels  22  and  23 . In a step  502 , the spike  308  of  FIG. 3  may be detected by the differential pressure transducer  20  of  FIG. 1 . In a step  504 , this detection may be recorded in either of the control panels  22  or  23  of  FIG. 1 . In a step  506 , a warning signal may be generated. As a non-limiting example, the warning signal generated in the step  506  may be an audible signal. The warning signal generated in the step  506  may be detectable or sensed by crew members/vehicle personnel throughout the entire space vehicle  10 . In a step  508 , a manual evaluation of conditions may be performed by personnel in the space vehicle  10 , and corrective action such as manual isolation of the affected segment and analysis and/or repair of a leak may be implemented. 
     The methods and apparatus described above may be particularly useful in mitigation of adverse effects of small leaks in segmented space vehicles. Nevertheless, the present inventions may also have utility in the context of mitigating the effects of large or catastrophic leaks. In the case of large leaks a warning signal such as that of step  206  in  FIG. 2  may be produced whenever a pressure differential greater than about 0.1 psia develops in a time period less than about one minute. 
     It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.