In Space Soldering Investigation (ISSI) - 09.26.18

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Without gravity, gas bubbles form pores in a soldering joint can reduce its strength. In this experiment, astronauts solder different sets of materials (small wires wrapped with solder in different configurations) while taking video images. By looking at the soldering process and microscopically examining the different samples, it will be possible to determine better methods for soldering in space.
Science Results for Everyone
Spacecraft repair often requires good old, low-tech soldering. On Earth, gas bubbles in soldered joints can reduce thermal and electrical conductivity or start cracks. In microgravity, these bubbles have less chance to escape and weak joints become a bigger problem. Astronauts soldered different sets of materials on the International Space Station (ISS) while researchers viewed video images in real time. Researchers observed unexpected flux movement when heated solder formed a small droplet spinning around the larger solder drop. This behavior cannot be duplicated on Earth. Further analysis of the solder samples on Earth will help determine better methods for soldering in space.

The following content was provided by Richard N. Grugel, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details


Principal Investigator(s)
Richard N. Grugel, Ph.D., NASA Marshall Space Flight Center, Huntsville, AL, United States

Information Pending

Intel Corporation, Santa Clara, CA, United States
Vanderbilt University, Nashville, TN, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)

Research Benefits
Information Pending

ISS Expedition Duration
April 2003 - April 2005

Expeditions Assigned

Previous Missions
ISSI is a unique investigation that has not been conducted in microgravity before.

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Experiment Description

Research Overview

  • Soldering is an important general technique that may be needed for repair of spacecraft either in orbit or on the way to the Moon or Mars.
  • On Earth, soldering depends on gravity and convection for proper solidification, joint shape, joint integrity and microstructure. Some detrimental gas bubbles or void spaces form in the solder joint at contact surfaces. These voids reduce the thermal and electrical conductivity as well as provide sites for crack initiation.
  • In the reduced gravity environment on orbit, bubbles have less chance to escape and weaker joints are more of a problem than on Earth.
  • In this experiment, soldering is done on a set of samples that were systematically selected to have pore development, surface wetting and shape formation. The soldering process is observed using a video camera and then the samples will eventually return to Earth for critical evaluation.

ISS Science Challenge Student Reflection

ISS Science Challenge Selected Project
I chose to research the In Space Soldering Experiment (ISSI) because I found it to be extremely relevant to the goal of maintaining a human presence in space. I also found it to be important in the development of repair capabilities in deep space, which could be crucial to a crew's survival and a mission's success.  Another reason why I chose ISSI was because I have experience with soldering, and I thought that ISSI was more relatable because of this experience.  Through researching ISSI, I learned about the effects of gravity on soldering, and how a microgravity environment can magnify these effects. I found it really interesting and exciting that this research will be used to develop better soldering techniques that could make in-flight repair of spacecraft more effective. I also learned about temperature gradients and thermo capillary flow, two subjects that I plan to study and learn more about after researching ISSI.
-Kelly, Grade 9, H.H. Dow High School, Midland, Michigan

The In-space Soldering Experiment (ISSI) is another payload that was rapidly developed after the Columbia accident to provide a lowmass experiment using hardware already on board station. It was designed to promote understanding of joining techniques, shape equilibrium, wetting phenomena, and micro-structural development in space. Its primary objective was to better understand the effects and consequences of soldering in a microgravity environment such as that found on ISS. In Earth’s gravity, soldering has a defined behavior and is reliant on gravity and convection to assist in solidification, joint shape, integrity, and microstructure. Unfortunately, on Earth detrimental gas bubbles (void spaces) are still found in the solder joint and at contact surfaces. These voids reduce the thermal and electrical conductivity and provide sites for crack initiation. Bubbles have less chance to escape in the reduced-gravity environment of space and, therefore, are likely to be more of a problem. To better understand this potential problem, a systematic series of soldering samples was designed to investigate and understand porosity development, surface wetting, and equilibrium shape formation. After the samples were heated on orbit, they were returned to Earth for property testing and metallographic examination.

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Space Applications
The ISSI payload provides unique insight into microgravity soldering methods, which could play a fundamental role in maintaining the International Space Station as well as provide understanding of repair capabilities on future missions to the Moon and to Mars.

Earth Applications
The study of soldering in space could lead to better soldering techniques here on Earth.

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Operational Requirements and Protocols

The experiments are being conducted in the ISS Maintenance Work Area (MWA), which serves to contain the smoke produced and the debris created during the soldering procedure. The soldering iron used is that already available on space station. It runs off of a rechargeable battery and can heat up to 315.6 degrees C (600 degrees F). After soldering, the samples will be returned to Earth.

The ISS Maintenance Work Area (MWA) is set up with a video camera mounted to observe the procedure. Then the samples of wire wrapped in solder (called coupons) are heated with the soldering iron.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Five soldering sessions resulted in 86 samples. The experiment samples were returned to the investigator team in late 2005, and were evaluated both nondestructively and then destructively.

Real-time downlink video of the experiment yielded direct observation of the solder melting, equilibrium shape attainment by the liquid, and flux movement. The flux movement was particularly noteworthy because it was entirely unexpected. When the flux was released from the solder during heating, it formed a droplet that spun around the larger solder drop. This surprising movement is driven by thermocapillary flow induced by the temperature gradient. This type of behavior cannot be duplicated on Earth. (Evans et al. 2009)

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Results Publications

    Grugel RN, Cotton LJ, Segre PN, Ogle JA, Funkhouser G, Parris F, Murphy L, Gillies D, Hua F, Anilkumar AV.  The In-Space Soldering Investigation (ISSI): Melting and Solidification Experiments Aboard the International Space Station. 44th Aerospace Sciences Meeting and Exhibit. Reno, NV; 2006

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Ground Based Results Publications

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ISS Patents

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Related Publications

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Related Websites
NASA Fact Sheet

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image View of the In Space Soldering Investigation (ISSI) experiment set up inside the Maintenance Work Area (MWA) containment system. A clamp holding three wire test samples or coupons is visible along with a video camera and solder iron. This test is designed to see how different configurations of metal alloy wire hold together after soldering. The test was conducted in the Destiny U.S. Laboratory. (NASA Image)
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image Astronaut and Science Officer Mike Fincke conducts tests for the In Space Soldering Investigation (ISSI) inside the Maintenance Work Area (MWA) containment system onboard the U.S. Lab Destiny. Mike's arms are in the MWA gloves as he works. (NASA Image)
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image The solder, heated, became a molten blob with a droplet of rosin clinging tight to the outside. It's the behavior of the rosin that amazed. As the temperature increased, the droplet began to spin, round and round, faster and faster, like a miniature carnival ride. (NASA)
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image View of solder sample for the In-Space Soldering Investigation (ISSI) experiment in the U.S. Laboratory/Destiny. (NASA Image)
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image Thermocapillary force causes flux and bubbles to coalesce at the junction, weakening the joint. (NASA Image)
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image Gas bubbles in the molten solder that often rise to the surface and disappear on Earth can remain suspended within the liquid in orbit. That's because the pull of gravity is the force behind buoyancy, so in microgravity bubbles don't necessarily rise. These tiny bubbles become trapped within the solder as it solidifies, making the joint less effective and more prone to breakage. (NASA Image)
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image A Scanning Electron Microscopy (SEM) photo of a solder joint cutaway view showing a uniformly filled joint without bubbles. (NASA Image)
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image 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. (NASA Image)
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