Visual photometric experiment - A Getaway Special payload aboard STS-042

Abstract

Visible-light sensors were flown aboard the Space Shuttle hi order to measure, without contamination by atmospheric airglow, the zodiacal light (sunlight reflected from interplanetary dust). A photomultiplier tube and four selectable optical filters constituted the primary sensor. This filter-wheel photometer was supplemented by two video cameras, which imaged star fields for aspect determination and provided an assessment of contaminating radiation. The suite of instruments was configured as part of a Getaway Special (GAS) experiment, in order to obtain the measurements at the lowest possible cost. As a GAS payload, the instruments were required to operate nearly autonomously. The payload had no gimbaled optics and no influence on the attitude timeline of the space shuttle. Only the enabling and disabling of data collection in accordance with prelaunch scheduling was controlled by the GAS payload specialist. Despite these limitations, the diffuse character of the zodiacal light permitted the serendipitous measurements described here. Several scans across the zodiacal dust plane were recorded, and provided peak brightness values for the zodiacal light at several solar elongation angles. A preliminary analysis of data redundantly recorded on a VHS audio track indicates ratios of zodiacal-light brightness in three spectral bands that are comparable to solar brightness ratios, confirming a result obtained previously with a balloon-based experiment.