- 10:10 AM

From the Sawin Lab to NASA: Uses of Very Long Vacuum Tubes

Brett A. Cruden, NASA Ames University Affiliated Research Center, NASA Ames Research Center, Mail Stop 223-2, Moffett Field, CA 94035

Professor Sawin and his group have pioneered plasma-materials interactions for over 25 years. Work in the Sawin lab has included plasma characterization and spectroscopy, among other things. The cornerstone of the Sawin lab since the mid-90s has been a long Vacuum Sample Transfer (VAST) Tube, that was used to mimic cluster processing, allowing treatment and analysis of samples without ambient exposure.

This talk will review current and recent work at NASA Ames in the Electric Arc Shock Tube (EAST) facility being applied to the design of NASA's new crew exploration vehicle, drawing some parallels to experiences and knowledge gained in the Sawin lab. The EAST facility was built over 40 years ago for the Apollo program and has been used since to characterize radiative conditions of shock waves, similar to the conditions encountered during re-entry into the earth and other planetary atmospheres. Shock wave plasmas are produced in the EAST by dumping up to 1.2 MJ of energy at 40 kV via a high pressure (100 psi) arc into a volume of 1.3 L. The arc creates a pressure shock that travels down the tube, ionizing and dissociating a driven gas, and can be measured spectroscopically. While this presents a very different plasma regime from low temperature materials processing plasmas, the basic principles of plasma physics and spectroscopic characterization still apply. Present tests in the EAST facility are focused on tests simulating earth re-entry for the new Orion spacecraft. These tests are of high importance to the new vehicle heat shield design because models predict that radiative heating by the shockwave will constitute a significant fraction (i.e. more than half) of the overall heat load seen by the spacecraft. The current test condition operates at velocities near 10 km/s with air pressures of 0.1-1.0 torr. The spectra obtained are primarily comprised of atomic O and N emission in the near IR and N2 and CN impurity emissions in the UV/visible. Of particular emphasis in the most recent studies is in the vacuum ultraviolet. Simulations have predicted VUV emission to account for approximately half of the total energy flux. Preliminary measurement and model validation in this spectral region will be presented.