Arnold teams provide NASA with test data

Published Feb. 1, 2007
By Philip Lorenz III
Arnold Engineering Development Center

ARNOLD AIR FORCE BASE, Tenn. -- Two teams at Arnold Engineering Development Center's Hypervelocity Wind Tunnel 9 recently were involved in tests for NASA's next crew exploration vehicle.

One team made use of conventional and advanced measurement techniques during the NASA-sponsored aerothermal testing on a scale model of the space agency's new Orion, the projected spacecraft that will send a new generation of explorers to the moon. Orion is part of the Constellation Program to send human explorers to other destinations in the solar system.

The test objective was to obtain heating data over the model's surface covering the full operational range of the facility at Mach 8 and 10 freestream conditions.

Unlike the development of the Apollo capsule where the database was populated entirely using experimental data, the Orion database is being developed using advanced computational fluid dynamic techniques. The experimental data will be used to validate the computational fluid dynamic models for NASA's Orion database development.

According to Joe Coblish, project group team leader at Tunnel 9, the facility's unique high Mach number and high pressure capabilities allowed NASA to obtain data on the vehicle, "which they were not able to obtain in any other facility."

A second Tunnel 9 team provided support by pushing the use of Temperature Sensitive Paint to its limits during the project's final phase. The goal was to further develop and demonstrate Temperature Sensitive Paint's effectiveness and viability to collect test data in Tunnel 9's unique high-temperature and high pressure hypersonic environment.

Temperature Sensitive Paint is a system that includes a special paint, an ultra-violet illumination source and a sensitive-charge coupled-device camera to obtain surface temperature data. The paint is applied to the model in two layers--a white undercoat and the Temperature Sensitive Paint layer. The white undercoat provides a uniform reflective surface for the Temperature Sensitive Paint. The illumination source excites the Temperature Sensitive Paint layer, which fluoresces a bright red color with its intensity inversely proportional to the surface temperature on the model.

According to Joe Norris, Aerospace Testing Alliance's Temperature Sensitive Paint developmental lead at Tunnel 9, Temperature Sensitive Paint is a more efficient way to collect heat transfer data than the traditional way of using discrete sensors.

"TSP allows us to use what is described as a global mapping technique to get the desired parameter --heat transfer in this case --from the entire surface of the test article," said Mr. Norris. "It's effectively like acquiring data from tens of thousands of thermocouples."

Mr. Norris said the team at Tunnel 9 had to deal with some technical challenges not experienced at other facilities working with Temperature Sensitive Paint and Pressure Sensitive Paint.

"Tunnel 9's unique combination of relatively short run times and high heating rates presents challenges that are unique in the world of TSP/PSP," he said. "High quality, high output, stable illumination fields are needed to combine with high-end scientific grade CCD cameras to take images at frame rates fast enough to calculate heat transfer."

Orion is scheduled to make a first manned mission no later than 2014 as the follow-on to the space shuttle, due to be retired in 2010.