Optical and Mechanical Design of a Telescope for Lunar Spectral Irradiance Measurements from a High-Altitude Aircraft
Clarence J. Zarobila, Steven E. Grantham, Steven W. Brown, John T. Woodward IV, Stephen E. Maxwell, Dana R. Defibaugh, Thomas C. Larason, Kevin Turpie
We have designed a non-imaging telescope for measurement of the spectral irradiance of the moon. The telescope was integrated into a wing pod of a NASA ER-2 research aircraft to measure lunar spectral irradiance during flight. The telescope and support system were successfully flown in August 2018 at altitudes near 21 km and at speeds of approximately 760 kmh . The wing pod in which the telescope is mounted has an opening through which the moon can be observed. The mount exposes the telescope to high winds, low pressures, temperatures exceeding -60 C, and vibrations both due to flight and to the motion of the aircraft on the ground. This required a telescope design with high thermal stability and high resistance to shock. The optical design of the telescope is optimized to have high throughput and spatially uniform transmission from 380 nm to 1000 nm over a field of view about twice the angular size of the moon as viewed from the earth. The light from the telescope is introduced into an integrating sphere which destroys the image and the polarization. Herein we present an overview of the instrument and support system with emphasis on the telescope design.