The International Space Station (ISS) is in some ways like most homes -- over time, it occasionally requires repairs. When the ammonia cooling system on the exterior of the ISS springs a leak, however, tracking down its location is by no means an easy task.
Small leaks are identified by the loss of mass/pressure within the system, but determining the leak's actual location is a time-consuming process for astronauts -- and it can involve a spacewalk.
So researchers and engineers from SRS, a manufacturer of test instruments, and NASA's Johnson Space Center and Goddard Space Flight Center teamed up to create an "Ammonia Leak Locator."
Matthew S. Kowitt, a physicist and project manager working at SRS, and colleagues will describe the new tool and its capabilities at the AVS 62nd International Symposium & Exhibition, held Oct. 18-23 in San Jose, Calif.
The team's Ammonia Leak Locator is crafted around a commercial residual gas analyzer (RGA). Typically, a RGA is connected to a researcher's high-vacuum chamber, with the probe end of the RGA inside the vacuum chamber, and the support electronics hanging outside in the room. "Our approach was to take that configuration and turn it inside out," said Kowitt.
To do this, they designed and built a gas-tight chamber to protect the instrument's support electronics. This chamber is filled with dry air -- at a pressure of about 1 atm -- to prevent the electronics package from overheating, while the high-vacuum probe end of the RGA is specifically designed to protrude out of the chamber so it can perform gas sampling.
The entire assembly will be held by the space station's robotic arm to expose the RGA probe to the outside vacuum of space near the space station. "By scanning the instrument across the length of the station and pointing it toward suspected leaks, we hope to identify the location of possible ammonia leaks via the mass spectrum signature of ammonia molecules," Kowitt explained.
This tool provides the ISS with a new option when faced with dreaded cooling system problems. "As a demonstration project, we don't know if it will work as planned, but in terms of its capability, it's quite exciting," said Kowitt.
One of the biggest surprises the team has encountered is the task of getting the tool up to the ISS. "The first version of our instrument was ready for launch in mid-2014," Kowitt noted. "Unfortunately, that unit was onboard the Orbital Sciences rocket that failed shortly after launch October 28, 2014, at Wallops Flight Facility in Virginia. Fortunately, we built multiple spares and a new unit is fully integrated and awaiting launch later this year."
Adapting a commercial-off-the-shelf (COTS) instrument for spaceflight proved to be an interesting challenge for the team as well. "The COTS RGA we used, the SRS RGA100, has a long track record of high reliability during the past 20 years," Kowitt said. "But the instrument needed some minor reconfigurations to fit the form factor needed by NASA. Balancing how many 'one-off' changes to make and realizing that each change was taking the instrument farther away from its high-reliability COTS heritage was a constant struggle."
In the end, the electronics and probe "were left virtually unmodified, and a new interconnect was designed to mate the two in the configuration necessary for fitting into the space station's air lock and robot arm," he explained.
The key motivating factors behind choosing a commercial RGA for this project were, not surprisingly, speed and cost. "The total time between when the project first started and the unsuccessful Orbital launch was less than two years," Kowitt pointed out.
Beyond serving as a potentially important tool for dealing with coolant leaks, "the RGA should help give us a better understanding of the space environment immediately outside the station -- it can provide a good indication of what's outgassing from the surfaces of the station," Kowitt said. "It can also tell us more about the background environment -- the very low residual atmosphere at that altitude -- through which the station is flying."
Next up: space! The instrument is currently scheduled to head to the ISS onboard an unmanned commercial resupply mission "Orb-4," being launched on an Atlas-5 rocket in late 2015.
Upon its arrival at the ISS, the Ammonia Leak Locator will be unloaded into the crew's area and stored until it can be scheduled for a trip outside through an airlock and connected to the robotic arm. Then, it will "undergo a period of testing to demonstrate its performance on orbit outside the ISS, and we'll develop potential strategies for leak location," Kowitt added.
Following initial testing, the instrument will remain onboard as a tool for the ISS operating team -- stowed, but ready to help locate any future coolant system leaks.
Presentation VT-WeA7, "The Deployment of a Commercial RGA to the International Space Station," is at 4:20 p.m. on Wednesday, Oct. 21.
Materials provided by AVS: Science & Technology of Materials, Interfaces, and Processing. Note: Content may be edited for style and length.
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