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In astronomy, multi-object spectrometers (MOS) provide an efficient means to gather large samples of spectral data. Digital Micromirror Devices (DMDs) can be used as programmable slit masks in a MOS. There is strong interest in using DMDs in space-based MOS instruments. Our team has been carrying out an environmental test campaign to qualify eXtended Graphic Array (XGA) DMDs for space deployment. The environmental tests have included mechanical shock and vibration, low temperature, heavy ion radiation, proton radiation, and gamma radiation testing. In each of the tests, the devices were able to withstand the expected conditions of a space mission without adverse effects. Initial gamma radiation testing was performed on fourteen XGA DMDs during June of 2018. Ten of the devices were active and four passive (unbiased) during gamma irradiation. Passive devices accumulated a total ionizing dose (TID) of up to 76 krad(Si) without showing adverse effects. The active devices began to exhibit the appearance of non-latching micromirrors at a TID of 16-19 krad(Si). Non-latching mirrors recovered after annealing at room temperature for as little as 24 hours. The DMDs subjected to the harshest testing conditions were completely recovered after six months. A distinct difference in the pattern of non-latching mirrors was observed between commercial-off-the-shelf (COTS) DMDs with their original windows and re-windowed DMDs. In this work, we present a second round of gamma radiation testing performed on XGA DMDs at the NASA Goddard Space Flight Center in June 2019. One of the main purposes of this testing was to further investigate the differences in TID effects observed between the COTS and re-windowed DMDs. This testing also investigated the use of high temperature annealing to accelerate the recovery of non-latching mirrors. Additionally, DMDs which had previously been irradiated in an unbiased state were tested again while active during gamma irradiation. This work finalizes our efforts to qualify XGA DMDs for use in space and provides a better understanding of the effects of TID on the devices.
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