temperatures. These images complemented earlier images from STS-96 and further validated the approach and methods, but again did not capture boundary-layer transition on the windward side. The requirement of being relatively close to the ground track was also emphasized in order to be able to best characterize transition on the windward surface.
Figure 5. STS-103, raw image.
Figure 6. STS-103 reduced temperatures.
Development of the Mobile Aerial Tracking and Imaging System
The ISAFE results showed that these types of ground-based measurements were a very valuable tool to gather accurate windward global aeroheating measurements. It was, however, a time- and labor-intensive undertaking to field the MDA/ISTEF mounts, especially when multiple locations were needed to account for possible different ground tracks from different reentry orbits. Also, the MDA/ISTEF mounts were heavily utilized and significant lead time was often necessary to schedule them. Since the ISTEF mounts had significantly more capability than was needed for the ISAFE experiment, the idea emerged of developing a smaller, simpler setup that was tailored for reentry vehicle heating measurements. This would reduce the time and effort to field a system, and could result in reduced cost, possibly leading to a system that could be rapidly fielded to account for orbital variation at reentry and also one in which multiple systems could be fabricated that could be located at several strategic locations to account for reentry ground track variation. Based on the results from ISAFE the 12.5-inch (31.75 cm) aperture telescope offered good results for its size. Much larger optics (for example, 24-inch aperture) become more difficult to field and are much more expensive. A system was designed that employed as much off-the-shelf hardware as possible to minimize cost and development time.
METHODOLOGY AND APPROACH
System Design Philosophy
The design philosophy was to develop a system that was mobile, rapidly deployable, rugged, and relatively inexpensive. To that end, compromises had to be made. Commercial-off-the shelf (COTS) components and equipment previously designed for another purpose were used whenever possible. This made it possible to put together a system quickly for significantly less cost.