Stanford Research Systems
Sunnyvale, CA

The Robotic External Leak Locator (RELL) — a collaboration between NASA's Johnson Space Center and Goddard Space Flight Center — was launched to the International Space Station in 2015. RELL's instruments provide directionally sensitive measurements of the amount and kinds of gases present.

The SRS RGA100 quadrupole mass spectrometer from Stanford Research Systems was part of the RELL system. Robot operators maneuvered the Dextre robot arm to position RELL within 12” of the leak to collect measurements for several days. By moving the device around suspect areas outside of the station, NASA was able identify the source of ammonia leaks from heat exchangers. The project was so successful that NASA and SRS are currently working to devise an improved system.

The RELL instrument, being unwrapped by astronaut Kate Rubins, was held at the end of the ISS robot arm.

A drawback of the current approach is that the instrument has to be stored inside the ISS and taken outside when needed — a time-intensive task. The improved instrument would live in what NASA is calling a “Dog House” — a protective structure outside the ISS in vacuum, saving the transition time.

By taking samples, RELL established baseline readings for amounts and kinds of gases that are normally present outside the station. In recent operations on the ISS, robotic operators were twice able to test and confirm the ability of the RELL to “smell” in space.

These baseline readings matched what engineers expected, but RELL detected an ammonia signature during the final portion of testing. Using the RELL instruments, operators successfully located a small leak from the station's ammonia coolant loop and confirmed that it was not a safety concern. Later, they were able to return and more precisely characterize the leak. This valuable data helped station operators vent and isolate the leaking line from the coolant loop and successfully stop the leak.

Operators were able to identify the ammonia source — an isolation valve for the ammonia cooling loop on the station. With the data gathered, personnel on the ground were able to determine the leak posed no risk to the station or astronauts onboard.

Later, ground controllers returned RELL to take high-resolution scans from a variety of angles to identify the specific location of the leak. Assisted by RELL's precise data, station managers choreographed a spacewalk that saw astronauts perform tests to gather additional data that would inform a plan to solve the leak issue. Afterwards, station operators successfully vented and isolated the leaking hose connection from the rest of the cooling system. The station team was able to confirm the leak had stopped and the ammonia coolant loop was intact.

To date, RELL has logged nearly 190 total hours in space, completed thousands of scans, and continuously demonstrated its value aboard the space station. RELL is currently inside station, ready to return outside when needed.

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