Developing a Custom Tip-Tilt Positioning Stage for an Astronomical Spectrograph

Table of Contents

Near InfraRed Robert Stobie Spectrograph RSS-NIR
nPoint Tip-Tilt Stage
About nPoint


nPoint developed and produced a custom tip-tilt piezo stage for the Robert Stobie Spectrograph (RSS) in collaboration with the Astronomy Department at the University of Wisconsin Madison.

The RSS is a first-generation, multi- purpose spectrograph on SALT, which is a 10m class telescope in Sutherland, South Africa. It is mounted at the key focus and benefits of direct access to the nominal 8’ field of view.

Near InfraRed Robert Stobie Spectrograph RSS-NIR

The Near InfraRed Robert Stobie Spectrograph (RSS-NIR) is a near-infrared arm constructed on the original instrument to extend its capabilities of the RSS.

RSS-NIR is developed with a large range of capabilities, which include medium band imaging, Fabry-Perot narrow-band imaging, long-slit and multi-slit grating spectroscopy and polarimetry.

The versatile RSS results in a complex mechanical design. RSS-NIR includes a cooled (-40°C) disperser area and camera. A large number of mechanisms are required by the multiple mode changes and the inaccessibility of RSS’s prime focus location and cooled mechanisms require large magazines to reduce the frequency of change-outs.

Furthermore, gravity loading needs to be withstood by the instrument in flexure due mostly to rho-rotation at the 37° inclination of the telescope.

nPoint Tip-Tilt Stage

The tip-tilt stage offered by nPoint is used to position the fold mirror in the instrument in order to compensate for any image motion induced by flexure as the instrument and telescope tracks the sky.

The mirror and mounting hardware load is approximately 3kg. The stage is built out of Invar36 to maintain precision and eliminate drift under varying temperature conditions.

The system makes use of capacitive sensors as feedback for position monitoring and has a travel range of +/-1mrad in tilt and tip axes of motion. The unloaded resonant frequency of the stage is approximately 1KHz and was designed to maintain a relatively high resonant frequency (~330Hz) even with the mirror load.

About nPoint

nPoint, Inc. specializes in piezo actuator driven flexure stages available in one, two or three axes of motion. Our ultra-precision motion control scanners and controllers provide users with the highest level of performance available in the marketplace.

With design and production facilities located in Middleton, WI and distribution channels throughout the world, nPoint provides each of our customers the same outstanding service regardless of the application.

Our product lines include standard products consisting of upgrade kits for your AFM and stand alone research instruments, a growing list of OEM applications and custom design for your unique research application. Let nPoint be your complete nanopositioning solution provider.

This information has been sourced, reviewed and adapted from materials provided by nPoint.

For more information on this source, please visit nPoint.

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