Illustration of the JWST operating in the extreme coldness of space. Credit: NASA Illustration of the JWST operating in the extreme coldness of space. Credit: NASA

NASA's giant cryogenic chamber is ready for the JWST

Sen— The latest vital stage in advancing the James Webb Space Telescope (JWST) has come with the upgrade of a vast NASA thermal-vacuum chamber that was once used to test Apollo spacecraft.

Chamber A at Johnson Space Center is 16.8 metres wide and 27.4 metres high and is the only "room" big enough to hold the giant successor to Hubble in conditions like those in deep space.

Engineers have completed eight years of work to design and rebuild the facility at Houston, Texas, to make it suitable for cryogenic testing. A three-week test that lowered the temperature inside to 11 Kelvin (-262 C) showed that the systems perform better than imagined.

The JWST, which is due to launch on an Ariane 5 rocket from Europe's spaceport at Kourou, French Guiana, in 2018, is the size of a tennis court, and with a cost of $8 billion it is important to ensure it will work in its harsh space environment.

Chamber A has been used to test all space vehicles and components for major space programmes since the Apollo Moon missions. But to make it cold and clean enough for the JWST with its honeycomb of 18 perfect mirrors, several modifications had to be made.

Most significantly, the entire system for supplying liquid nitrogen to the chamber interior was redesigned and re-plumbed. The number of valves was cut from more than a hundred valves, all presenting potential reliability risks, to fewer than two dozen of a new, more efficient design. The result will not only keep working even during a power cut or a hurricane, but uses less than half the amount of liquid nitrogen as before.

Chamber A at Johnson Space Center

The vast Chamber A at Johnson Space Center with its door open. Credit: NASA

Next step, following the chamber's completion, will be to install a clean room zone right in front of it. This work, due to begin in February will allow engineers to begin testing parts of the JWST as they start to arrive at Johnson. Around half a dozen of these tests will have been carried out before the complete telescope undergoes a test in 2017.

Mary Cerimele, manager for the JWST Chamber A modifications project said: "This series of tests leading up to the final test of the flight unit will go a long way toward reducing the technical risks that naturally accompany such a technologically ambitious science mission." 

Following controversial cost overruns that saw the JWST project threatened with cancellation and a campaign to save it, all seems back on track for the observatory which will travel to a point four times further away from Earth than the Moon. It has been designed to sit in sync with Earth at what is called a Lagrangian Point that is gravitationally stable with us as we both orbit the Sun.

Its segmented mirror, 6.5 metres in diameter will gather more than five and a half times as much light as Hubble, though in the infrared, to find the first galaxies that formed in the early Universe, and peer through dusty clouds to see stars forming planetary systems.

Two other significant milestones in developing the JWST were achieved in May, with the arrival of Europe's Mid-Infrared Instrument (MIRI) at the Goddard Space Flight Center in Greenbelt, Maryland, and then the Fine Guidance Sensor/Near-Infrared Imager and Slitless Spectrograph (FGS/NIRISS) from Canada in July.


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