Ultrasonic Background Noise Test (UBNT) - 09.17.14
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Science Objectives for Everyone
The Ultrasonic Background Noise Test (UBNT) detects high-frequency sounds generated by hardware on the U.S.-built portions of the International Space Station. Identifying sources of noise will aid in development of a leak locating system, which would detect the high-pitched sound of air leaking through a pressurized wall. To detect leaks, the system would have to tell the difference between harmless background sounds and potentially dangerous air leakage.
Science Results for Everyone
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Technology Demonstration Office (TDO)
ISS Expedition Duration
September 2012 - Ongoing
Previous ISS Missions
- The goal of the Ultrasonic Background Noise Test (UBNT) investigation is the development of an automated leak location system, which is based on the detection of high frequency (ultrasonic) noise that is generated by air leaking through a pressure hull. In order to develop such an automated system, we must ensure that other high frequency sources are identified and characterized.
- During this investigation the plan is to install the hardware first within the US Lab followed by the Node 3 module at a later time. Once installed in a given module, the hardware samples the high frequency sound domain periodically during normal ISS operations. The data is then processed and down-linked to the ground for further evaluation. Understanding and characterizing this kind of information teaches the designers how to create a monitoring system that accounts for these extraneous noise sources.
- Such information provides a critical element of control in our steps to develop a leak location system. Everyone is familiar with the phenomenon of being in a large group of people and having trouble hearing someone nearby because of the high levels of background noises. Locating a pressure hull leak within a busy and noisy spacecraft cabin is the same problem, just at a higher frequency. Once we have characterized these background noises we plan to use that information as a component of a system to locate the origin of critical leak generated noises.
The DIDS hardware represents a unique capability as a small, ultra-low powered, high speed, four channel digitizer module box that can be programmed to trigger on a threshold signal or on a predetermined schedule. This unit can record all four channels of data for approximately 9 msec. at around 800 to 900 Kilosamples/sec. with approximately 14 bits resolution. It operates off two “AA” batteries, which should last for up to 6000 measurements, including downloading of data or 5 years. These units communicate wirelessly with a laptop computer. With the sensors that we are using, we can record signals from below 30KHz up to 350KHz. By installing these devices on the pressure wall, where a leak signal might exist, there is the possibility that we can detect and locate the source of a leak signal provided that station equipment and instrumentation does not produce an inordinate amount of sounds over the 30KHz to 350KHz range. We expect to find frequencies where station hardware does not produce ultrasonic signals, so those frequency ranges will allow us to locate leaks. (Note: Ultrasonic leaks within station hardware on ground have been measured to produce ultrasonic signals over a very wide range of frequencies.)
Seven units of this hardware will be installed throughout the US Lab, while six units of this hardware will be installed throughout the Node 3. A single SSC within each ISS module will control all the DIDS units within that module. Once the units are installed in a given module, we intend to upload a simple file that the crewmembers can run, which will program the DIDS units to record at a future time a specific series of data (probably over one or two days time) that sample the ultrasonic fields within the pressure wall. During this period of time, the DIDS units will run independently of the SSC computer.
It is expected that the amount of data taken will be very large, and much of it will not be of interest. For efficiency, we intend to only download data that suggests a significant source of noise. In order to know what to download, first a brief summary of the data will be downloaded and reviewed. Based on those results, a small amount of the overall data will be downloaded for ground review. To implement this two-step download process, first a short file will be uploaded from ground with specific instructions for the flight software to initiate the summary download. The resulting summary file will be downlinked to ground for evaluation, and based on the summary results, specific files will be targeted for download for investigation. For the specific data files download operation, another configuration file will be uploaded to the station. Crewmembers can then run the flight software to download the requested data for subsequent downlink to the ground for the UBNT team to analyze. The download operations will require that the software be running on the SSC so that the computer can receive the data. On the ground, this data will be reviewed and correlated with station operations that might have occurred spatially nearby and in the same time frame. From this set of data, we hope to understand the nature of the ultrasonic background noises in the ISS. Another advantage from this test is that a leak location system will very likely use similar instrumentation as the DIDS hardware, but with slightly different flight software, so this investigation provides us with valuable experience with testing this type of hardware as the basis of a future leak location system.
The UBNT experiment uses a small four channel, high speed digitizing, wireless data recorder powered by two AA batteries to record sounds in a range between 30KHz and 350KHz, frequencies that are above the human hearing range, but are below the minimum frequencies of AM radio. By analyzing the source of sounds in these frequencies, the UBNT recording device could detect possible spacecraft pressure leaks. Data from this experiment could assist in development of an automated leak detection system for the ISS or future long-duration spacecraft.
Listening for ultrasonic clues can be a new way to measure the pressure integrity of many pressurized systems, from the chemical and nuclear industries to oceanic research. It can be used to ensure tight seals in facilities that use high-pressure or vacuums, and it could serve as an added safeguard in areas where human access might be limited.
Once the system is installed, the plan is to perform a check out by capturing background noises during standard ISS operations. This check out involves having a crewmember initiate a software test (the configuration of that test having been uploaded previously). Once the test is complete, the crewmember is asked to initiate a download of the summary file data (the configuration file for the summary data to be downloaded also having been uploaded previously). The data summary file will be reviewed on ground and a subsequent data download configuration file will be uploaded as needed. A crewmember will be asked to operate the software to download all data as needed. That process is to be repeated several times per module (US Lab and Node 3) for the duration of the investigation.
Unstow and install the DIDS unit, battery, and antenna to structure using Velcro. Attach the sensors, glued to Kapton® tape to the pressure wall at the desired location. Connect the DIDS USB antenna device to the SSC in the appropriate module. Configure and initiate software for operating the system. There are six functions that the crewmember can execute from the SSC. Once a function is selected, the crewmember will be asked to select a previously uploaded file in order to configure the program for the selected function. When taking data, the DIDS hardware runs independent of the SSC. Downloading of data (a separate program operation) will require the SSC to be actively running the program to receive the data.
Image shows an example of the UBNT system in operation.
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Image shows DIDS hardware: 1) DIDS sensor unit, 2) antenna/cable, 3) 4 transceiver/cables, 4) SSC Transceiver.
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