Ascent modeling of scientific balloon missions is particularly sensitive to accurate knowledge of the balloon lifting gas mass. Transient distortions of the balloon body effectively increase drag beyond classical solid body data. Further, experimenters have reported an increase in virtual mass with developing flow relative to the accepted inviscid determination at incipient flow.In support of the National Aeronautics and Space Administration (NASA) Balloon Program, small scale balloons (175 m3) were flown with varying lifting gas and total system mass. Stow Away Special (SAS) instrument packages were developed to measure and record acceleration and temperature data during these tests. Top fitting and instrument payload accelerations were measured from launch to steady state ascent and through ballast drop transients. The development of the small (5×7.5×15 m3), light weight (.5 kg.), self-powered SAS is discussed along with mathematical models developed to determine gas mass, drag and virtual mass coefficients.