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Instrument Support Structure

Gemini South ISS
Instrument support structure at Gemini South (as of January 2011)

Instruments are mounted at the Cassegrain focus on the instrument support structure (ISS). Each ISS is a stiff cube that itself houses the Acquisition and Guidance Unit which contains the Acquisition Camera and Peripheral Wavefront Sensors (guiders). A science fold mirror mounted inside the ISS can be rotated to send the light from the telescope to any of four side-looking ports, or can be retracted so that the light goes to the up-looking port.

Each ISS is attached to the telescope via the Cassegrain rotator, which may be oriented at any desired position angle and which normally rotates during observations to compensate for rotation of the field of the alt-az telescope.

The current (as of January 2011) assignment of instruments to ISS ports is:

Instrument Name Location Orientation
GMOS-N Gemini North Side-Looking
GNIRS Gemini North Side-Looking
GCAL Gemini North Side-Looking
ALTAIR Gemini North Side-Looking
NIRI, MICHELLE, or NIFS Gemini North Up-Looking
GMOS-S Gemini South Side-Looking
Canopus(AO) Gemini South Side-Looking
GCAL Gemini South Side-Looking
NICI Gemini South Up-looking
GSAOI Gemini South Side-Looking

Other instrument assignments may include: