Spectrographs in space

Two spacecraft built by the Johns Hopkins University Applied Physics Laboratory carried a total of six spectrographs into space early in 1996; five were on the Midcourse Space Experiment and one was on the Near Earth Asteroid Rendezvous Spacecraft (NEAR). Flight spectrographs have also been delivered for the Defense Meteorological Satellite Program and the Global Ultraviolet Imaging spectrograph (GUVI) is currently being built for the TIMED satellite. These eight instruments, while on four different spacecraft and working in different spectral ranges extending from 115 nm out to 2700 nm, were based on only two optical designs. The five spectrographs on the MSX used the same design and the DMSP, NEAR, and GUVI used an identical optical layout even though the wavelength range changed from the vacuum ultraviolet to the infrared. This paper reviews the performance parameters and optical designs of these instruments and shows how minor optical changes made it possible to use the identical mechanical design for a range of applications. Rather than create a unique design for each application, modification of an existing design resulted in a saving of cost, time, and testing. In spite of the plagiarized designs each instrument is fully capable of meeting all of its scientific objectives. Designs for future missions follow the same concept; a basic optical layout is prepared and is then modified to meet the field-of-view, spectral range, and capability requirements of a mission. Some proposed concepts for future spacecraft are also described.