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Guiding Light: Canada's Contribution to the JWST

Canada is designing and building one of Webb's four science instrument packages, which actually consists of two parts: high-sensitivity cameras known as the Fine Guidance Sensor (FGS), and the Tunable Filter Imager (TFI), both built by COM DEV for the Canadian Space Agency. The Canadian Project Scientist for Webb is Dr. John Hutchings of the Herzberg Institute of Astrophysics, National Research Council of Canada. Dr. René Doyon, of the Université de Montréal is the principal investigator for TFI. Canada is also providing functional support of the science operations for Webb.

The Fine Guidance Sensor engineering test unit being prepared for cryogenic testing at the CSA's David Florida Lab in Ottawa
(Credit: CSA-COM DEV)

Both the Fine Guidance Sensor and the Tunable Filter Imager will be located behind the telescope's main mirror, and will be cooled to minus 240 degrees Celsius (just a few tens of degrees above Absolute Zero) to increase Webb's sensitivity to infrared light.

In exchange for the Canadian Space Agency's contribution, Canadian astronomers will be guaranteed 5% of the telescope's observation time for scientific research throughout Webb's expected 5-10 year lifespan.

The Fine Guidance Sensor: Keeping Webb on Target

Canada is providing Webb's Fine Guidance Sensor (FGS), as well as one of the telescope's four science instruments called the Tunable Filter Imager (TFI). Both are being built by COM DEV International for the Canadian Space Agency. The Fine Guidance Sensor consists of two specialized cameras that are critical to Webb's ability to “see”: they will work like a guiding scope to allow Webb to locate its celestial targets, determine its own position and remain pointed at an object so that the telescope can collect high-quality data. The FGS will measure the position of guide stars with incredible precision, pinpointing them with an accuracy of one millionth of a degree (3.5 milli-arcseconds). Canada gained key knowledge in building pointing systems (specifically, the fine error sensor) on the FUSE mission, which contributed to Canada's expertise in designing Webb's FGS.

The Tunable Filter Imager (TFI)

The Tunable Filter Imager is housed in the same package as the Fine Guidance Sensor, but functions independently to achieve different goals. The TFI's unique capabilities will allow astronomers to peer through clouds of dust to see stars forming and planetary systems, possibly even exoplanets (planets outside our Solar System).

Animation
Take a closer look at the engineering
models of the Canadian science package.
(Credit: CSA).

The Tunable Filter Imager is essentially a sophisticated spectrometer—a finely tuned camera that can break down images of celestial objects into very precise wavelengths (or colours) of infrared light. Each specific segment of light can provide astronomers with different kinds of information about the object they are observing. For instance, by decomposing the light emitted from a galaxy or nebula, astronomers will be able to determine the chemical compounds and atoms present to learn more about the composition of the object.

TFI will also be able to search for exoplanets, and may be able to discern more information about their composition and possibly even their atmospheres. Since planets are much fainter than their star, they are very difficult to detect in the star's glare. To solve this problem, the Tunable Filter Imager will use a technique called coronography (which means that the light from the star will be masked out so that astronomers can see what is in the star's proximity). The TFI also carries a unique non-redundant mask that has the best capability of imaging faint bodies very close to bright ones.