The astronomical community continues to be interested in suitable programmable slit masks for use in multi-object spectrometers (MOSs) on space missions. There have been ground-based MOS utilizing digital micromirror devices (DMDs) and they have proven to be highly accurate and reliable instruments. This paper summarizes the results of a continuing study to investigate the performance of DMDs under conditions associated with space deployment. This includes the response of DMDs to radiation, to the vibration and mechanical shock loads associated with launch, and the operability of DMD under cryogenic temperatures. The optical contrast ratio and a study of the long-term reflectance of a bare device have also been investigated. The results of the radiation testing demonstrate that DMDs in orbit would experience negligible heavy-ion induced single event upset (SEU) rate burden; we predict SEU rate of 5.6 micromirrors per 24 hours. Vibration and mechanical shock testing was performed according to the NASA General Environmental Verification Standard (GEVS); no mirrors failed in the devices tested. The results of low temperature testing suggest that DMDs are not affected by the thermal load and operate smoothly at temperatures at least as low as 78 K. The reflectivity of a bare DMD did not measurably change even after being exposed to ambient conditions over a period of 13 months. The measured contrast ratio (on state vs off state of the DMD micromirrors) was greater than 6000:1 when illuminated with an f /4 optical beam. Overall, DMDs are extremely robust and promise to provide a reliable alternative to micro shutter arrays (MSA) to be used in space as remotely programmable slit masks for MOS design.
Digital micromirror devices (DMDs) are commercial micro-electromechanical systems, consisting of millions of mirrors which can be individually addressed and tilted into one of two states (±12 • ). These devices were developed to create binary patterns in video projectors, in the visible range. Commercially available DMDs are hermetically sealed and extremely reliable. Recently, DMDs have been identified as an alternative to microshutter arrays for space-based multi-object spectrometers (MOS). Specifically, the MOS at the heart of the proposed Galactic Evolution Spectroscopic Explorer (GESE) uses the DMD as a reprogrammable slit mask. Unfortunately, the protective borosilicate windows limit the use of DMDs in the UV and IR regimes, where the glass has insufficient throughput. In this work, we present our efforts to replace standard DMD windows with custom windows made from UV-grade fused silica, low-absorption optical sapphire (LAOS) and magnesium fluoride (MgF 2 ). We present transmission measurements of the antireflection coated windows and the reflectance of bare (window removed) DMDs. Furthermore, we investigated the long-term stability of the DMD reflectance and experiments for coating DMD active area with a layer of pure aluminum (Al) to boost reflectance performance in the UV spectral range (200−400 nm).
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