Soldering Away - Soldering Irons in Space

Image courtesy NASA. 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.

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.

The Expedition 7 crew, which returned to Earth in 2003, fashioned the wire into L-shapes, loops, parallel threads, and other shapes in preparation for the experiment to be performed during Expedition 8 which lasted until April 2004.

While the experiment happened, the researchers were able to watch it unfold live at NASA's Telescience Center at the Marshall Space Flight Center in Huntsville, Alabama. Watching to see the differences in how the solder flows and the shapes it assumes in space, which offers clues to the fundamental physics of molten solder.

The live interaction allowed 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."