The Irait Telescope And The Mirnir Amica Camera

The IRAIT project is part of an international collaboration (Italy-Spain-France) led by the Perugia University and is based on a fully robotic 80 cm ALT-AZ telescope. The final optical and mechanical configuration of the telescope is now defined and a preliminary sketch is given in Figure 2. The telescope is integrated into a modified ISO20 container and a hydraulic system provides the opening and closing mechanism of the structure. The telescope secondary will allow the chopper function to be commanded by the camera controller.

One of the Nasmyth focal stations will be equipped with AMICA (Antarctic Multiband Infrared Camera), a NIR/MIR double armed camera operating in the J, H, K, L, M, N, Q photometrical bands.

Infrared Mechanical Chopper
Figure 2. The Perugia University IRAIT Antarctic telescope. The complete structure fits a standard container.

A preliminary optomechanical design of the camera is shown in Figure 3. Taking advantages from the large difference in pixel size between the NIR and MIR detectors, a single TMA (Three Mirror Anastigmatic) system with fixed magnification has been designed to illuminate the selected detector. Detector selection is commanded by a simple step-motor driven flat flip-mirror. A second advantage of this simple optical system is a single stepmotor driven filter wheel placed in the reimaged pupil that switches between filters for both channels. Both mechanisms, flip-mirror and filter-wheel, are driven by cryogenic motors (Phytron) working at optical bench and radiation shield temperatures (about 55 K°) and avoiding the presence of mechanical feed-through.

Detectors will be mounted on dedicated housings cooled by conductive straps connected to the second stage of a Sumitomo GM cryocooler. The optical-bench and shield will be cooled by the first stage of the cryocooler. Resulting electro-optical parameters of the camera are given in Table 1.

Under these conditions the MIR detector provides diffraction-limited Rayleight sampling at ^=8.57 ^m.

Figure 3. A preliminary sketch of AMICA showing the entrance window, the TMA mirror system and the two motor driven parts: a flip-mirror and the single filter wheel.

Figure 3. A preliminary sketch of AMICA showing the entrance window, the TMA mirror system and the two motor driven parts: a flip-mirror and the single filter wheel.

Table 1. Main electro-optical parameters for the NIR/MIR channels of AMICA.

MODE

Detector

Pixel number

Pixel size

Pixel sampling

Well capacity

Work Temp.

NIR

Raytheon In:Sb

256x256

30 y

0.54" /pixel

1.5x105 e/pixel

7 K°

MIR

DSR Si:As

128x128

75 y

1.34" /pixel

107 e/pixel

30 K°

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