NIRSpec can obtain simultaneous spectra of more than 100 objects using the Micro-Shutter Assembly (MSA) (see figure below). It will be the first spectrograph in space that has this capability.
- Tiny cells (microshutters) measuring 100 μm x 200 μm arranged in a waffle-like grid.
- Micro-Shutter Assembly (MSA) has these grids arranged in four quadrants each containing 365 shutters along the dispersion axis (x-axis) and 171 shutters along the spatial axis (y - axis).
- Every shutter has a row electrode and a column electrode so that it can be individually controlled and can be opened or closed to view or block a portion of the sky.
- The aperture of an open shutter is ~0.20" x 0.45" projected onto the sky.
The MSA shutters are opened and closed by sweeping a permanent magnet across the array. In the orientation depicted in the figure, the magnet arm sweeps upward to open shutters, and downward to close them. The magnet arm is located on the front side of the MSA; i.e., towards the sky. As the magnet sweeps upwards away from the NIRSpec OA, its magnetic field pulls on the magnetic stripes on the shutter doors and swings the shutters open into their “egg crates”. As shown in Figure 4.2-5, the open shutters are latched and held open by electrostatic forces until they are electronically released. Positive voltages are applied to the 365 row electrodes (+V2), and negative voltages are applied to the 171 column electrodes (-V1). The voltages described below for opening and addressing an array are nominal voltages. Since each array is unique, each quadrant uses an individually optimized voltage in the range from ±12 to ±36 V.