By DEAN M. PETERS, Consulting Editor

In my June column, titled Welding and Space, I invited readers to open a dialogue with us concerning the subject of welding in space. I can't say that the fabric of cyberspace was strained by the volume of e-mails the June column elicited, but among those that responded was Dr. Graeme Aston, director of the Electric Propulsion Laboratory Inc. in Monument, Colorado.

He and his wife, Dr. Martha B. Aston, developed what they call Safe Potential Arc Channel Enhanced (SPACE) welding in the 1990s. This system uses an electrode-less plasma weld head, and its development was funded by NASA's Marshall Space Flight Center.

But before we get too far into that, some background information is appropriate. During the 1990s, NASA had a cooperative venture with the Paton Welding Institute of Kiev, Ukraine. This was the International Space Welding Experiment, and its purpose was to demonstrate the ability to weld in space using technology developed by Paton.

The technology included a device called the universal hand tool, an electron beam welding instrument that is integrated onto a support structure located in the space shuttle cargo bay.

The International Space Welding Experiment originally was scheduled to fly in October of 1997. However, its trip aboard the space shuttle was scrubbed as a result of a re-evaluation of space shuttle missions that followed a series of negative events on a prior mission.

Although the universal hand tool apparatus was tested successfully in space in the 1980s by Russian cosmonauts on Salyut 7 missions, and despite American astronauts having tested the International Space Welding Experiment equipment under water, the equipment was returned to the Ukraine when NASA's lease agreement for it expired.

Enter the Astons' Safe Potential Arc Channel Enhanced welding system, which was the first effort made to develop an American space welding technology.

Here's how it works: A low power plasma discharge is established within the Safe Potential Arc Channel Enhanced weld head using less than 60V. With the work piece biased 20V to 30V positive relative to the weld head, a dense welding arc column is drawn to the work piece. A magnetic field constricts this arc to increase energy density at the melt zone. Modulation of this magnetic field aids in melt zone mixing since the gas flow rate is too low to promote significant convective heat transfer. No electrodes are used in the Safe Potential Arc Channel Enhanced weld head, so no adjustments or maintenance are required.

The weld head operates at arc power levels up to 4kW and its power transfer efficiency is more than 90 percent. This is critical because active weld head cooling in space is impractical.

The prototype Safe Potential Arc Channel Enhanced weld head and accompanying systems are self-contained and are designed to be powered by a 60V battery pack. In addition to welding, the Safe Potential Arc Channel Enhanced system could be configured to perform metal cutting, fluxless brazing, surface coating and surface cleaning.

It may be someday that the Safe Potential Arc Channel Enhanced system will be tested in the environment for which it was intended, but as of now, NASA has no plans to do so, and is instead focusing on adhesive metal joining technologies.

Dean Peters is principle at Syntactical Communications, Cleveland, Ohio. Peters formerly was chief editor of Welding Design & Fabrication, Gases & Welding Distributor, and Foundry Management & Technology magazines. He may be reached at dpeters@penton.com