In 1966 Carruthers built, and in 1969 received a patent (US3478216) for, an image converter that turned images made from light of very short wavelengths into electron images. This enabled capturing an entire spectrum in a single exposure, and was more robust than traditional ultraviolet films because it used reflective cathodes rather than transmissive cathodes. On the first test flight of the image converter in 1970, it captured a far ultraviolet spectrum which was the first detection of molecular hydrogen in space. His design detected an upper limit to the amount of molecular hydrogen that exists in the interstellar medium, answering numerous questions astronomers were asking at that time about what was then referred to as the "missing mass" problem.