James Webb Space Telescope still has 2 months before awakening; NASA scientist reveals why

The James Webb Space Telescope, which recently got all its instruments aligned with its primary mirrors, has yet to pass a crucial test that would take another couple of months. Webb's instruments are currently undergoing the thermal stability test, meaning testing at extreme temperatures, although they have reached the final phase of commissioning. In a NASA statement, the lead commissioning scientist for Webb, Scott Friedman explained that the engineers would now measure the detailed performance of the instruments, which would take two months from now. 

Webb's instruments to undergo rigorous testing

The successor of the Hubble telescope, Webb will have its instruments undergo, what Friedman calls, the "last group of activities" before its awakening. Webb has four instruments- Near-Infrared Camera (NIRCam), Near-Infrared Spectrograph (NIRSpec), Mid-Infrared Instrument (MIRI) and the Fine Guidance Sensor/Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS). Each of these instruments has been powered up and safely cooled and their mechanisms and detectors have been operated.

Friedman said that in the next step, the mission team will begin an extensive suite of calibrations and characterisations of the instruments using an astronomical source. Recently, the engineers used a sun-like star to align the primary and secondary mirrors of the telescope. Through a similar practice, the scientists will measure how much of the light that enters the telescope reaches the detectors and is recorded. NASA has noted that there is a loss of light with each reflection by the mirrors within each instrument since no detector records every photon that arrives.

"We will also measure the sharpness of the stellar images, what astronomers call the ‘point spread function'. Measuring the point spread function within each instrument at different wavelengths provides an important calibration for interpreting the data," Friedman said. The lead scientist said that Webb's accuracy will also be tested by pointing the telescope toward moving targets. "Observing these requires that the observatory change its pointing direction relative to the background guide stars during the observation. We will test this capability by observing asteroids of different apparent speeds using each instrument," he added.

Image: Twitter/@NASAWebb