Soldering in space holds surprises

rk wrote:

Soldering in space holds surprises


http://www.aiaa.org/aerospace/images...ookmarch05.pdf

Very interesting. It shows that we need to be sure that we really
understand even mundane (that's not the right word, I'm sure)
things in space. It also suggests something useful to do with
ISS in the years ahead.

Here's a couple of excerpts from the story:

Soldering in space holds surprises
AEROSPACE AMERICA/MARCH 2005
Edward D. Flinn

[EXCERPTS]


There is nothing routine about working in space, as
astronaut Mike Fincke found out when he did some
soldering onboard the International Space Station (ISS).

Richard Grugel, a materials scientist at NASA Marshall,
watched his video monitor in disbelief. A transmission from
the ISS was playing. The scene: Astronaut Fincke touches the
tip of a soldering iron to a wire wrapped with rosin-core
solder. The solder, heated, becomes a molten blob with a
droplet of rosin clinging tightly to the outside. As the
solder melts, it is the behavior of the rosin that amazes
Grugel. As the temperature increases, the droplet begins to
spin, round and round, faster and faster, like a miniature
carnival ride.

"What a surprise," says Grugel. "I have never seen anything
quite like it."

Grugel is the principal investigator of the In-Space Soldering
Investigation (ISSI). Fincke was conducting the ISSI program
at the time of the discovery. The program's purpose is to find
out how solder behaves in a weightless environment. This is
important information for astronauts: If something breaks
during a long trip to Mars, they will likely reach for a
soldering iron to repair it.

[snip]

Many of the methods used to build and repair equipment on Earth
must now be adapted for space. ISS crews have tools for making
small repairs, but little research has been conducted on the
best ways to manufacture and repair equipment in space.

In the low-gravity environment inside the orbiting space station,
surface tension influences materials and fluids more strongly
than it does on Earth. Fluids that would splatter and spill to
the ground on Earth form drops held together by surface tension.
Left uncontained, these drops float through the air in space.
Convection and surface tension are two forces that influence how
a fluid moves or flows. Both play roles in fabrication and repair
techniques such as soldering and welding. Soldering involves
melting a metal or metal alloy, usually lead or tin. The molten
material is applied and flows between surfaces or joints of
materials that are being held together. When it cools and
solidifies, the solder joins the materials together. On orbit,
however, gravity is balanced by the equal but opposite centrifugal
force or orbital rotation, thus eliminating convection and leaving
surface tension to be the dominant force influencing flow.

[snip]