The Effects of an Unsteady Reduced Gravity Environment on the Soldering Process

摘要

An improved understanding of the effects of reduced gravity is important to applications of soldering during both current and future human space missions. Recently, we conducted a series of manual soldering experiments aboard NASA's KC-135 reduced gravity aircraft. This paper focuses on the interpretation of the unsteady (g-jitter) acceleration environment measured aboard the aircraft as it affects the experimental results. The results presented here use a through-hole geometry that was soldered with the same hardware that is currently on orbit aboard the International Space Station. As presented elsewhere, we observed significant changes in porosity and geometry of solder joints formed in reduced gravity. Based on acceleration measurements during periods when the solder was molten, we examined a data filtering technique to determine the influence of g-jitter on our data. The results of this filter indicate that joint geometry is largely unaffected by the unsteady variations in acceleration as seen aboard the KC-135. We deduced that the increase in voids observed in low gravity can be described by decreases in buoyancy driven bubble motion. An acceleration environment which oscillates about zero gravity further increases joint porosity by keeping bubbles within the joint. Additionally, by examining some partial gravity results we observed that acceleration levels near Martian levels and higher result in porosity data sets similar to our normal gravity results. This suggests the existence of a threshold acceleration level below which gravitational effects become important for joint porosity in the though-hole geometry. The techniques and interpretations presented in this paper may be beneficial to others using the KC-135 research aircraft.