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The Next Generation Space Telescope (NGST) will include a suite of three observational instruments, including a Near Infrared multi-object Spectrograph (NIRSPEC). To achieve multi-object capability, the spectrograph must be equipped with a slit mask to position small apertures on a number of astronomical targets simultaneously.
Unlike most ground based spectrographs, the NIRSPEC slit mask must be reconfigurable, so that it can be adapted and reused for each observation. Although a great deal of work has been put into the development of mirror and shutter arrays using MEMS technology, these devices are currently unproven and risky in space environments. Therefore, a Mechanically Actuated Reconfigurable Slit mask (MARS) is being developed by the NRC - Herzberg Institute of Astrophysics as an alternative in case MEMS devices do not achieve maturity in the required timeframe.
The MARS device creates 50 slits in an opaque mask by translating individual metal shutters within an array of precise guide tracks. When two adjacent shutters are brought close together, a slit is formed between them. A unique, robust, and high-resolution actuation scheme has been developed to individually position the metal shutters with micron accuracy. It is based on a combination of custom electromagnetic and piezoelectric actuators working in a coordinated sequence of movements. This scheme incorporates the key goals of reliability, redundancy and low heat dissipation in the focal plane of the instrument.
MARS has been modeled, and its principle components have been prototyped to test the feasibility of the concept. The model has undergone structural, thermal, electrical and magnetic analysis to ensure that it meets the restrictive requirements on mass, volume and launch survivability while maintaining very low power requirements and heat dissipation. The prototypes have shown that the MARS concept is a viable alternative for the NIRSPEC slit mask which is based on proven and stable technologies. Further development is underway to manufacture a prototype slit mask, and test its operation in a cryogenic (30 K) environment to simulate the actual conditions aboard NGST.
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