VIRUS: A hugely replicated integral field spectrograph for HETDEX

We present the visible integral-field replicable unit spectrograph (VIRUS), the basis of the Hobby-Eberly telescope dark energy experiment (HETDEX); a survey of a 5 Gpc3 volume at 1.8 < z < 3.7 that will constrain the evolution of dark energy. VIRUS consists of 145 copies of a simple unit spectrograph, deployed on the HET. Industrial replication will allow VIRUS to be built quickly, at considerable cost-savings, with substantial risk-mitigation, compared to conventional instruments. VIRUS will cover 30 sq. arcmin per observation and detect 14 million resolution elements per exposure, an order of magnitude larger than existing instruments. VIRUS can complete HETDEX in about 100 nights observing.