This month we reached a significant project milestone with one small step: the first part of the NRT arrived in our offices in Liverpool!
The autoguider (AG) system is responsible for measuring the offset from the telescope's pointing and the object's location. These measurements feed into the robotic telescope control system to perform fine guiding with an accuracy of <0.1-0.2 arcseconds. The AG relies on a camera, fed by a lens system, that takes images of the sky. The NRT AG field of view is large enough to almost guarantee a guide star in any random pointing. With the AG positioned outside of the science field, it takes images and records the difference in position of the stars in the field between subsequent integrations. These measurements are then passed to the telescope control system to correct for pointing offsets.
Our AG system has a strict guiding accuracy requirement to suit our ambitious science cases. The AG system interfaces with almost every aspect of the NRT telescope system such as the structure, optics and telescope and robotic control software. As such it is a great place to start understanding and prototyping the NRT!
At the NRT project's recent preliminary design review, the team was pleased to report that the AG design was near completion, with off-the-shelf components identified for purchase. We are using the same detectors as those that have been recently deployed on the LT for the MOPTOP polarimeter. The camera is an sCMOS-based PCO Edge-4.2 and is to be put through a series of tests including comparison of lab data and simulations by NRT Instrument Scientist Dr. Éamonn Harvey.
The package contains two boxes: one with the camera itself and the second the ancillary equipment. The additional equipment consists of power cable, USB3 connector and a PCI Express USB3 card. The camera itself can be air- or water-cooled and has a fitting to accommodate F-mount lenses. This allows for the easy fitting of Nikon-type lenses, which are well designed and readily available off-the-shelf.
The AG itself will perform closed-loop tracking for both sidereal (distant) and non-sidereal (Solar System/ nearby) objects. The AG’s ~3.5 arcminute field of view will allow for a bright star to be located in almost any pointing, therefore allowing blind pointing of the telescope for a sidereal object. This is possible with either single object centroiding or full-frame guiding, without the need to solve the world co-ordinate system (WCS) fitting of AG images. Tracking non-sidereal objects is more of a challenge, and the exact techniques we will use are still be be decided. Our AG testbed will help us make that choice, and so our journey continues.