NASA has completed testing of the James Webb Space Telescope in icy conditions after 100 days. This checks whether the instruments can withstand the conditions in the room.
According to the space telescope’s project manager, Bill Ochs, the cryogenic tests were a great success. The project’s scientists tested the optical telescope and its integrated science instrument module for 100 days to ensure they function properly in the extreme cold and vacuum of space.
An important alignment test was also performed with the eighteen mirror elements of the primary mirror of the James Webb Space Telescope. These mirror parts, each in the shape of a hexagon, must be brought into exactly the right position in space via actuators so that the eighteen mirror segments together form a mirror of 6.5 meters. This movement is extremely precise: each mirror element will be shifted per step over a distance comparable to 1/10,000 of the diameter of a hair.
Before the tests could begin, all air had to be removed from the test room. This took a week. After that, the project’s scientists began to bring the temperature of the chamber, telescope, and instruments down to cryogenic temperatures; that process took thirty days.
Not to scale.
In space, the telescope operates at -233 degrees Celsius; the telescope must be very cold to pick up the faint infrared light from distant space objects. The so-called mid-infrared instrument, a spectrograph that mainly analyzes the light from warm exoplanets, must even operate in -266 degrees Celsius. A special cooling system has been installed for this.
Completing the test in cold conditions is one of the most important steps leading up to the launch of the device. The launch is likely to take place in the spring of 2019. The new telescope should complement the Hubble Space Telescope.
The James Webb Space Telescope will not orbit the Earth like the Hubble, but rather orbit the Sun, at a distance of 1.5 million kilometers from Earth. This point is also called the Lagrange point L2. In that spot, the telescope stays out of the shadows of the Earth and the Moon. The sun shield blocks the light and heat of the sun, earth and moon. This is necessary so that the telescope can detect infrared light from distant objects as well as possible. Incidentally, at the front of the sunshade it is 85 degrees Celsius, while the telescope on the other side of the sunshade operates in -233 degrees Celsius.