Testing of digital micromirror devices for space-based applications

Scientists conceiving future space missions are interested in using DMDs as a multi-object spectrometer (MOS) slit mask. The main uncertainties in utilizing DMDs in a space-based instrument are associated with their operational longevity given the exposure to high levels of proton radiation and their ability to operate at low temperatures. Since a favored orbit is at the second Lagrangian point (L2), it is important to determine how long such Micro-Electrical Mechanical Systems (MEMS) would remain operational in the harsh L2 radiation environment, which primarily consists of solar protons and cosmic rays. To address this uncertainty, we have conducted DMD proton testing at the Lawrence Berkeley National Laboratory (LBNL) 88” Cyclotron. Three DMDs were irradiated with high-energy protons (20- 50MeV) with energies sufficient to penetrate the DMD package’s optical window and interact electrically with the device. After each irradiation step, an optical test procedure was used to validate the operability of each individual mirror on the DMD array. Each DMD was irradiated to a wide range of dosage levels and remained 100% operable up to a total dose of 30 krads. In addition, a few single event upsets were seen during each irradiation dose increment. To determine the minimal operating temperature of the DMDs, we placed a DMD in a liquid nitrogen dewar, and cooled it from room temperature to 130 K. During this test, the DMD was illuminated with a light source and monitored with a CCD camera. Additionally, the temperature was held constant at 173 K for 24 hours to test landing DMD patterns for long periods of time. There was no indication that extended periods of low temperature operation impact the DMD performance. Both of these results point to DMDs as a suitable candidate for future long duration space missions.