Fine Guidance Sensors-Tunable Filter and Guider

The Fine Guidance Sensors-Tunable Filter (FGS-TF) consists of two components with different functions: a camera and a "guider," which helps point the telescope. The FGS-TF camera is able to focus on extremely specific portions of the light being emitted by an object. Other cameras also focus on specific wavelengths, but they can select from only a few. FGS-TF can choose from a wide array of wavelengths.

Parallel plates situated in the camera widen or narrow to capture the particular wavelength scientists are interested in studying. The chosen wavelength can be anywhere within the 1.6 to 4.9 micrometer range, with an accuracy better than 1 percent.

FGS-TF will look at the internal workings of galaxies, examining their structure and looking for gas disks in the centers of galaxies that could harbor black holes. It'll examine protoplanetary objects — disks of dust that may become planets someday — and examine the speed of their rotation and their structure. Coronographs will allow FGS-TF to block out bright light to examine protoplanetary disks around stars, and perhaps even planetary systems around stars.

FGS-TF will also be able to discover which molecules and elements are present in clouds of dust and gas, and their energy level. It can help determine the density and temperature of the gas, and what's happening to it.

Balancing act

The FGS Guider helps point the telescope. To lock onto an object, the telescope finds a guide star, a star located close to the field of view that contains the object to be studied. As long as the telescope points at that star, it also points at the object to be studied.

But the telescope, adrift in space and affected by solar radiation, its own moving parts, and other various stresses, tends to wander. The FGS Guider has an imaging camera that detects this movement by measuring the position of the guide star many times per second . When it detects motion, it orders the telescope to shift to keep the telescope pointed at the guide star.

Click on image to enlarge.

Click on image to enlarge.