Houston, We Have a Solution
New research aboard the space station aims to adapt a tried-and-true repair tool to weightlessness
In the unforgiving environment of space, a successful solder-repair to, say, navigation hardware or an oxygen pump could mean the difference between life and death.
Right: Astronaut James Voss uses a soldering iron onboard the International Space Station.
"Surprisingly, relatively little is known about the unique physics of soldering in microgravity," says Richard Grugel, a scientist at NASA's Marshall Space Flight Center who specializes in the solidification of metals.
Melted solder behaves differently in space. In the microgravity aboard a spacecraft, molten solder doesn't "feel" a downward pull as it does on Earth, so surface tension becomes more prominent and causes blobs of liquid solder to flow differently. In other words, soldering techniques that work on the ground may not form proper joints in orbit.
Below: A scanning electron micrograph of solidified solder on a wire. The precise angle at which the solder meets the wire is driven by forces such as surface tension, gravity, and wetting of the wire. Removing the effects of gravity lets physicists better understand these other influences. Image courtesy NASA.
"How prevalent are these gas bubbles in joints soldered in space? We need to find out, and perhaps find some way to get those gas bubbles out so that we can make good joints that won't break," Grugel says.
The experiment is straightforward: metal wires will be soldered together in various arrangements, reflecting common geometries important for making repairs. Space station crewmembers will use a soldering iron to join these wires with lead-tin solder.
While the shuttle fleet is grounded, room for sending research equipment and materials up to the space station is severely limited. The ISSI experiment was selected in part because it requires no "up-mass" sent to the station from the ground. The space station already has a soldering kit onboard and coils of silver-coated copper wire.
Right: The experiment will be performed with reshaped wire (top frame) and a soldering kit (bottom frame) aboard the space station. Image courtesy NASA.
While the experiment happens, the researchers will be able to watch it unfold live at NASA's Telescience Center at the Marshall Space Flight Center in Huntsville, Alabama. They'll be watching to see the differences in how the solder flows and the shapes it assumes in space, which will offer clues to the fundamental physics of molten solder.
If they see something unexpected, the live interaction will allow them to suggest procedure changes to the station crew members in real-time. After the samples are returned to Earth, the scientists will cut open the joints to see how many gas bubbles were trapped during the process, and they'll test how strong the joints are.
"We should be able to gain a window into how surface tension effects soldering in microgravity," Grugel says. "This will help lay a foundation for the future of in-space fabrication and repair."
In Space Soldering Investigation (ISSI) -- information on the experiment from NASA's Office of Biological & Physical Research
In Space Soldering Investigation fact sheet -- from the Marshall Space Flight Center
"A better theoretical understanding of the physics of molten solder will help close the book on lead-based solder as well as open the door for industry's newer work with lead-free solders," Grugel says. "Microgravity research is a good way to explore that physics."
Above: Hardened solder on a wire. Notice how the solder has been pulled downward by gravity, and the gold-colored flux has accumulated at the bottom of the drop. Image courtesy NASA.
Other soldering in microgravity research: by Imperial College, London; by the Ursa Astronomical Association in Finland; experiments at the 2.2 second drop tower at NASA's Glenn Research Center.
A New Look at Molten Metals in Space -- (Science@NASA) Scientists discuss ways to peer inside solid materials
Hoolder electronics -- downloadable instructional videos, from NASA's Goddard Space Flight Center
Research on the ISS -- information about other science experiments currently aboard the International Space Station
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