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James Webb Space Telescope- Canada’s FGS Successfully Used in Mirror Alignment Phase

The Fine Guidance Sensor (FGS) on the James Webb Space Telescope, a mission-critical element designed and built in Canada, was used in tracking mode for the first time as part of the telescope’s mirror alignment process.

On February 13, the Webb team performed “Line of Sight” testing that confirmed the FGS’s ability to “lock on” to a specific guide star in tracking mode. This mode allows the FGS to transmit highly precise information to Webb’s positional system 16 times per second.

The successful FGS operation is the latest in a series of smooth manoeuvres for the massive observatory. After its launch on December 25, 2021, the telescope underwent a delicate, month-long unfolding process as it travelled to its final destination, the second Lagrange point (L2).

Most recently, the team released an image mosaic of Webb seeing its first star: it shows 18 views of the same star – one for each of the 18 hexagonal segments that make up Webb’s primary mirror.

In the coming weeks, with the help of the FGS, each mirror segment will be carefully adjusted to “stack” these views and calibrate the rest of the telescope’s optical elements, to ultimately create a highly focused image of a single star.

The months-long mirror alignment process affords time for Webb’s scientific instruments to shed heat. Because Webb will perform its observations in infrared light, its sensitive instruments, like Canada’s NIRISS, must be extremely cold. They will gradually cool to an operating temperature of about -233 degrees Celsius.

Once the instruments have reached the correct temperature, Canada’s FGS will be used throughout their commissioning, set to begin around the end of April 2022.

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