ISS - International Space station patch.
Dec. 22, 2015
Nobody wants a spacecraft to spring a leak – but if it happens, the best thing you can do is locate and fix it, fast. That’s why NASA launched the International Space Station (ISS) Robotic External Leak Locator (IRELL), a new tool that could help mission operators detect the location of an external leak and rapidly confirm a successful repair.
Image above: The IRELL tool could help mission operators sniff out and locate potential leaks that might occur on the space station thermal control system. Image Credits: NASA/Chris Gunn.
The IRELL launched to the space station aboard the fourth Orbital ATK Commercial Resupply Services Flight (CRS-4). The tool will be put through a series of tests to evaluate its performance and determine its capabilities as a leak locator for the orbiting space laboratory.
If IRELL’s concept is proven successful, the robotic tool could potentially greatly reduce the time that astronauts spend on spacewalks finding and repairing external leaks on the ISS. Future versions of IRELL could also potentially support other programs and vehicles operating in low Earth orbit and beyond.
Helping the ISS Operate Optimally
Just as coolant in your car cools its engine, ammonia is circulated through a huge system of pumps, reservoirs and radiators on the space station to cool all of its complex life support systems, spacecraft equipment and science experiments. The coolant system contains thousands of feet of tubing and hundreds of joints. Throughout its lifetime, this system has experienced tens of thousands of thermal cycles through each orbital night and day and the normal wear and tear of 15 years in service. The station also has to contend with micrometeoroids: tiny objects whizzing through space at speeds that can easily exceed 20,000 mph – and that can cause unwanted, microscopic holes in spacecraft equipment.
Image above: Engineers from the Satellite Servicing Capabilities Office at NASA’s Goddard Space Flight Center prepare the IRELL for flight. Image Credits: NASA/Chris Gunn.
Over time, there have been intermittent component failures and leaks in the ammonia cooling loop. Astronauts have undertaken spacewalks to help diagnose, troubleshoot and replace components within the complex active thermal control system. Without a way to robotically locate the leak with high accuracy, astronauts have used valuable spacewalk time to inspect and isolate a potential leak site before addressing the problem at hand.
Working together, the Engineering Directorate at NASA’s Johnson Space Center (JSC) and the Satellite Servicing Capabilities Office (SSCO) at NASA’s Goddard Space Flight Center (GSFC) developed the IRELL for the ISS Program to allow ground-based operators to robotically locate leaks so astronauts could dedicate their time and energy to other duties on-orbit.
“This was a fantastic collaborative effort with Johnson,” says Benjamin Reed, deputy project manager of SSCO. “Their team knows the ISS structure inside and out. Every step of the way, we co-designed the IRELL so that it would be precisely ‘the right tool for the job.’”
How the IRELL Works
Two instruments working in sync give the IRELL its ammonia-detecting superpowers. The first sensor, explains Dino Rossetti, the SSCO IRELL Instrument Integration Lead, is a small mass spectrometer. Designed for use in a vacuum, it measures the atomic masses of the molecules present to create a “mass spectrum” reading. From this spectrum, analysts can distinguish between gases that are naturally present in the orbital environment versus ammonia, which could only be coming from the ISS itself. Far more sensitive than a human nose, the instrument can detect ammonia from a football field’s length away.
Image above: Mission Control room at Johnson Space Center from which Dextre operations are commanded. Image Credit: NASA.
The second instrument is an ion vacuum pressure gauge. True to its name, this device measures total pressure in space. It cannot distinguish between different gas molecules, but it can sniff for a large leak up close and locate a leak’s position to within a few inches. If the mass spectrometer is overcome by a sizeable leak, the gauge also offers an alternate method of detection.
After IRELL’s arrival at ISS, the Canadian Dextre robot – completely controlled by ground operators at Johnson – will pick up the tool for an initial series of tests. During subsequent operations, Dextre will point the IRELL toward the space station’s cooling lines while a NASA team monitors from Earth. That’s when the game of “Hot and Cold” begins. When the tool is pointed at a leak, the tool’s signal goes up. The closer the tool comes to the leak source, the higher the reading becomes. When not in use, the instrument will be stored within the ISS.
A Tale of Two Centers
As they locked down the tool’s technical design, the combined Goddard and Johnson teams focused on delivering IRELL quickly and cost-efficiently.
“The challenge,” said Rossetti, “was to identify and incorporate the right sensors and ruggedize the entire instrument, in a cost effective way, for the space environment.”
They also wanted to put the IRELL on a delivery truck 18 months after the designers’ pens touched paper – an incredibly tight timeline for a brand new space tool.
Image above: NASA astronauts Chris Cassidy (right) and Tom Marshburn are seen on a 2013 spacewalk to inspect and replace a pump controller box on the International Space Station's far port truss (P6) leaking ammonia coolant. Image Credit: NASA.
To accelerate the process, the team used an off-the-shelf mass spectrometer called a “residual gas analyzer” developed by Stanford Research Systems. Working with NASA, the company modified their existing design for use in IRELL’s mass spectrometer so NASA wouldn’t have to start from scratch. The ion gauge was also an off-the-shelf device that the team repackaged to fit within the instrument housing.
Through every phase of development, the IRELL project drew heavily from the combined NASA team experience. With a long history of cutting-edge mission planning and operations, the Johnson team is responsible for keeping the immense, orbiting research asset operating safely and reliably for global use. Robotic tools like the IRELL can help them to monitor the space station’s vital signs and prescribe efficient maintenance.
Image above: Controlled by a team at NASA’s Johnson Space Center (JSC), the Canadian Space Agency’s Dextre robot will point IRELL toward the station’s cooling lines. A NASA ground team will monitor the signals from Earth. Image Credits: NASA/Goddard Spaceflight Center.
Jesse Buffington, the IRELL project manager at JSC, explained that, “The IRELL is a critical capability that will mitigate risk for ISS and will also establish a capability that future extended duration exploration missions beyond low-Earth orbit will benefit from.”
In creating the IRELL, SSCO leveraged the experience they gained building and executing the multi-phased Robotic Refueling Mission (RRM), an experiment on the space station that is successfully demonstrating robotic tools, technologies and techniques to service spacecraft that were not designed for in-flight repair. Prior to SSCO’s formation in 2009, its core team spent 26 years building more than 300 tools for astronauts to repair and upgrade the Hubble Space Telescope.
“It is very exciting,” said Buffington, “to see the talent and dedication of so many people come together across NASA and our International Partners to create new tools and techniques like the Leak Locator. This new capability will be there to help ensure the ISS can safely operate well into the next decade and point the way for future spacecraft addressing similar concerns.”
Robotic External Leak Locator (IRELL): http://ssco.gsfc.nasa.gov/irell.html
Satellite Servicing Capabilities Office (SSCO): http://ssco.gsfc.nasa.gov/robotic_refueling_mission.html
Robotic Refueling Mission (RRM): http://ssco.gsfc.nasa.gov/robotic_refueling_mission.html
For more information about International Space Station (ISS), visit:
Space Station Research and Technology:
Images (mentioned), Text, Credits: NASA/Jennifer Harbaugh/GSFC/Peter Sooy.
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