Before the completed telescope is sent into space, a million miles from Earth, it will be tested in a thermal-vacuum chamber (below) at NASA’s Johnson Space Center in Houston. The chamber is 19.8 meters in diameter and 36.6 meters high. Its door alone weighs 40 tons.
Thus far, the chamber has been used mostly to test objects destined for low Earth orbit, so it will need to go through a series of modifications before it can simulate the cold temperatures the James Webb telescope will experience. New helium-cooled panels will be added to existing panels cooled by liquid nitrogen, allowing the chamber to reach a temperature of 30 to 35 K. The helium will also carry heat away from the panels.
The telescope will be put into the chamber by means of a mobile crane. Bringing the chamber and telescope to the desired temperature will take 30 to 40 days.
NASA engineers plan to start testing the telescope in 2010.