Design and Measurements of the BOLT-1B Joint Steps

The Boundary Layer Transition (BOLT-1B) flight experiment was designed to study hypersonic boundary-layer transition on a geometry with low-curvature concave surfaces with highly swept leading edges. Due to hypersonic boundary layer transition being notoriously sensitive to surface roughness, a significant effort was made to control and document roughness for the BOLT-1B flight. The mechanical design featured two joint steps on the upstream half of the BOLT geometry that were the dominant focus of roughness measurements and documentation. Novel methods to measure small magnitude step heights of sounding rocket flight experiments were developed and measurements were made during fabrication, environmental testing, and preflight checkout. Initial results confirm that the step heights were all rearward-facing and within desired design limits to accommodate differential thermal expansion in flight. The step height magnitude and distributions around the azimuth were quantified for multiple joints of the flight experiment.