The temperature of Chamber A at NASA’s Johnson Space Centre in Houston has begun to rise, signalling the beginning of the end of James Webb Space Telescope’s cryogenic testing.
Engineers began to warm the chamber to bring the Webb telescope back to room temperature – the last step before the chamber’s massive, monolithic door unseals and Webb emerges in October.
“Engineers will perform the warming gradually to ensure the safety of the telescope, its science instruments and the supporting equipment,” explained Randy Kimble, an Integration and Test Project Scientist for the Webb Telescope at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Once the chamber and its contents are warmed to near room temperature, engineers will begin to pump gaseous nitrogen (N2) into the chamber until it is once again at one atmosphere of pressure (at sea level) and no longer a vacuum.”
The engineers are using heaters to incrementally warm the inside of the chamber. In addition to this, they will warm the two enveloping shrouds, which previously had frigid cryogens (substances used to produce extremely cold temperatures) flowing through them.
In addition to the heaters, the engineers will gradually raise the temperature of the helium gas flowing through the inner most shroud. Carl Reis, the Test Director for Webb’s cryogenic testing at Johnson, said the temperature of that shroud will reach about 68 degrees Fahrenheit (about 20 degrees Celsius / 293 kelvins) before the Chamber A door opens. He added that the engineers will stop the flow of liquid N2 into the outermost shroud, allowing the liquid N2 already inside the shroud to “boil off” as it warms.
The team tested Webb in the airless cold of Chamber A because, in the vacuum of space, the telescope must be kept extremely cold in order to be able to detect the infrared light from very faint, distant objects. Warm objects emit infrared radiation, and any excess warmth could give false signals to the telescope. The cryogenic testing ensured all of Webb’s components, including its science instruments and mirrors, worked as expected in a space-like environment.
Webb next journey is to Northrop Grumman in Redondo Beach, California, where it will be integrated with the spacecraft and sunshield, thus forming the completed observatory. Once there, it will undergo more tests during what is called “observatory-level testing.” This testing is the last exposure to a simulated launch environment before flight and deployment testing on the whole observatory.
The James Webb Space Telescope, the scientific complement to NASA’s Hubble Space Telescope, will be the most powerful space telescope ever built. This engineering marvel is designed to unravel some of the greatest mysteries of the universe, from discovering the first stars and galaxies that formed after the big bang to studying the atmospheres of planets around other stars. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).