<title>Optical Alignment Of A 0.5 Meter Ultra-Violet Spectrometer For Apollo 17</title>

Abstract

A 0.5 m Ebert spectrometer of high sensitivity (Figure 1) was de-signed, fabricated and calibrated by the Johns Hopkins University. It was mounted on Apollo 17 for research on the ultra-violet spectrum of the lunar atmosphere, with W. G. Fastie of the Physics Department as Principal Investigator. The Ultra-Violet Spectrometer (UVS) 5169 was designed for operation in the range 1175 A to 1675 X, but had zero transmission for all wavelengths in air. A method was developed for aligning subassemblies (using visible light) in such a way that the assembled instrument would be aligned in the ultra-violet to an accuracy of 2 with maximum efficiency, In the Vacuum Optical Bench (VOB), the efficiency and wavelength calibration were determined. If required, a small AX correction could then be made with a precision of 0.5 which would be verified during final VOB calibration. An alignment procedure using precision optical tooling will be described. Enough of the optical and mechanical features will be given to show how the basic objective was attained, and also how the inherent flexibility of the instrumentation proved useful in the rapid diagnosis and correction of several problems which were encountered. This program was a joint effort by the Physics Department and the Applied Physics Laboratory of the University. The UVS was mounted in the SIM bay of Apollo 17 (Figure 2), where it could be operated in several modes for specific investigations. These include observing:1. resonance re-radiation from the lunar atmosphere below the command module against the dark lunar surface just beyond the sunset line; or above the orbit by rolling the module 180°; 2. the UV reflectivity of the lunar surface under solar illumina-tion; 3. galactic Lyman Alpha (Lc)radiation scattered from the moon's surface on the night side; 4. galactic La during translunar coast; 5. the hydrogen halo around the earth during trans-lunar coast. The UVS S169 operated successfully during December 1972, with results to be published by the Principal Investigator.