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Fact sheet number: FS-2003-09-116-MSFC
Release date:

In Space Soldering Investigation (ISSI)

Experiment Name: In Space Soldering Investigation (ISSI)

Mission: Uses materials presently on-board the Space Station; experiment conducted during Space Station Expedition 7 and/or Expedition 8

Experiment Location: Maintenance Work Area in Destiny Laboratory Module

Principal Investigators: Dr. Richard Grugel, NASA Marshall Space Flight Center, Huntsville, Ala., Dr. Fay Hua, Intel Corporation, Santa Clara, Calif., and Dr. A.V. Anilkumar, Vanderbilt University, Nashville, Tenn. NASA

Project Manager: Lucinda Murphy NASA Marshall Space Flight Center, Huntsville, Ala.


Many of the methods used to build and repair equipment on Earth must now be adapted for space. International Space Station 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 has a greater influence on materials and fluids than 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 forces play a role 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. However, on-orbit, 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.

On Earth possible gas bubbles inside solder are lighter, and convection causes them to rise to the surface and separate from the molten fluid. In space, another method must be used to remove the bubbles from the soldering metal. If too many bubbles become trapped, the solder is weakened and the joined parts could separate.

The goal of this study is to investigate solder flows and the quality and strength of solder connections formed in the absence of convection. Hopefully this will lead to a better understanding of fabrication and repair methods for use in space.

Experiment Operations

The investigation will use hardware already available on the Space Station. For small on-orbit repairs, the astronaut tool kit includes a battery-operated soldering iron that heats up to 315.6 degrees Celsius (600 degrees Fahrenheit.) The soldering iron has special safety features, such as a holder that protects the user from burns.

The experiment will be conducted inside the International Space Station Maintenance Work Area -- a portable workbench with a tabletop that measures 36 inches by 25 inches. When not in use, it is folded and stored inside a drawer.

The Maintenance Work Area can be used most anywhere throughout the Station. An astronaut unfolds it and clamps it to a slotted mechanism similar to seat tracks found in cars or airplanes. The tracks are located on the sides of most of the floor-to-ceiling racks inside the Station.

To contain debris during cutting, drilling, filing, or soldering, a clear, plastic cover can be placed around the workbench. Gloveports on the sides and ends of the workbench's plastic cover and a front flap that unzips allow both crew members to use the soldering iron or other tools at the same time. The Station's vacuum can be attached to capture and dispose of particles or liquids that are 6 microns in diameter or larger. One challenging aspect of soldering in space is that any smoke created during the heating will not easily disperse, possibly leaving the operator unable to see the work piece. In the Maintenance Work Area, this problem will be avoided by using the vacuum.

The crew will perform several tests connecting metal alloy wires of various configurations together with solder. These test pieces, or coupons, are designed to evaluate the effectiveness of different geometries typical of the kinds of operations that might be required in future.

Investigators on Earth will monitor the experiment from the Telescience Center at NASA's Marshall Center. By viewing video, they will be able to observe the soldering operation as the crew works on samples.

The samples will be returned to Earth for examination. Tests will include a microscopic evaluation of the structures of the solder joints, and how they compare with those done in the laboratory on Earth. The tensile strength will be measured in specially designed coupons.


The International Space Station must be maintained for its lifetime of a decade or longer. This orbiting home and workplace never returns to the ground, so all repairs must be made in space.

Conducting repairs in space is challenging. Tools and loose materials must be tethered or restrained so that they don't float away. Crew members must anchor themselves so they have a steady hand when making repairs. Particles of debris created during drilling, filing, and other operations must be collected and disposed of so they do not contaminate the crew's living environment.

Besides the soldering iron, other tools used for repairs inside the Space Station include ratchets, sockets, screw drivers, wrenches, pliers, hacksaws, chisels, files, hammers and even a sewing kit. Special tool kits allow astronauts to repair electronics, fiber optics, and fluid lines.

The more Space Station crews work with tools in space, the easier future repairs will be. Experiments like this one provide a systematic method for studying how to improve tools and repair procedures. This information can be used to design future tools and develop the best procedures for repairing equipment in the unique environment inside an orbiting spacecraft.

More Information

More information on this experiment and other Space Station experiments is available at:

Steve Roy
Public Affairs Office
(256) 544-0034

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