Preliminary evaluation of the vibration environment within JS']JSC Chamber A using a simultaneous phase-shifting interferometer

The vibration environment in and around the Space Environment Simulation Laboratory Chamber A at the Johnson Space Center was recently characterized via accelerometer measurements in support of the thermal-vacuum testing of the James Webb Space Telescope (JWST). Interferometric measurements were also conducted in order to (i) evaluate the ability to make valid measurements with a high speed interferometer within the chamber, (ii) coarsely evaluate the vibration sources, and (iii) provide some correlation between the accelerometer data & the interferometer data. A simultaneous phase-shifting interferometer was used for the measurements. Measurements were made, using a 2" collimated beam & return flat, at various places in and around the chamber, including: across the high-bay floor outside the chamber, across the payload table at the ground floor level of the chamber, from the top of the chamber to the payload table, and from the top to the P floor catwalk. Measurements were made in quiet mode, with a roughing pump on, with exhaust fans on, and with both the pump & fans on. Accelerometer data was taken simultaneously with the interferometer data. The fringe motion was well within capture range of the interferometer for all measurements. The fringes were the most stable across the payload table and the least stable from the top to the catwalk, but the difference was not extreme. The quality of the interferometer data was essentially the same for all configurations (top-to-bottom, top-to-catwalk, etc.) and cases (pump/fans on/off). The results of these measurements will be used to help implement the thermal-vacuum testing of the JWST.