High-resolution ultraviolet spectrograph for sounding rocket measurements of planetary emission line profiles

Abstract

We constructed a high-resolution imaging spectrograph for use as a payload in a sounding rocket experiment. The spectrograph employs a modified Ebert-Fastie design with a LiF objective prism and a replica of an El echelle grating developed for the Space Telescope Imaging Spectrograph. The instrument has a 5-arcmin-long adjustable width entrance aperture with two identical secondary apertures separated from the primary by ±2 arcmin. The secondary apertures are intended for simultaneous measurement of the sky background. The spectrograph has been optimized for measurement of the 221st order of Lyman-α at a resolution of 0.03 to 0.04 A. The detector system is a two-dimensional photon counting device that employs a microchannel plate intensifier and a wedge and strip anode readout. The spectrograph is used as a focal plane instrument of the Jupiter Telescope, a Cassegrain telescope constructed exclusively for use as a sounding rocket payload. The Jupiter Telescope is self-pointed, employing image motion compensation to achieve 2- to 3-arc sec image quality. The telescope/spectrograph payload was launched from the White Sands Missile Range on May 4, 1991, to observe the H Lyman-α line profile spatially resolved across the disk of Jupiter in the North-South (polar) and East-West (equatorial) directions, and to measure the H Lyman-α emission line profile from interplanetary hydrogen associated with the local insterstellar medium.