Hubble’s Heir will Orbit at the Lagrange Point 1 Million Miles from Earth


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Imagine a place colder than Pluto where rubber behaves like glass and where most gasses are liquid. The place is called a Lagrange point where the James Webb Space Telescope will orbit.

NASA engineers have created a unique engineering marvel called the ISIM structure that recently survived exposure to extreme cryogenic temperatures, proving that the structure will remain stable when exposed to the harsh environment of space. 

The ISIM, or the Integrated Science Instrument Module Flight Structure, will serve as the structural "heart" of the James Webb Space Telescope. The ISIM is a large bonded composite assembly made of a light weight material that has never been used before to support high precision optics at the extreme cold temperatures of the Webb observatory.

At the Lagrange Point, the Webb telescope can observe the whole sky while always remaining in the shadow of its tennis-court-sized sunshield. Webb's components need to survive temperatures that plunge as low as 27 Kelvin (-411 degrees Fahrenheit), and it is in this environment that the ISIM structure met its design requirements during recent testing. 

"It is the first large, bonded composite space flight structure to be exposed to such a severe environment," said Jim Pontius, ISIM lead mechanical engineer at NASA's Goddard Space Flight Center.

When fully integrated, the roughly 2.2-meter (more than 7 feet) ISIM will weigh more than 900 kg (nearly 2000 lbs) and must survive more than six and a half times the force of gravity. The ISIM structure holds all of the instruments needed to perform science with the telescope in very tight alignment. Engineers at NASA Goddard had to create the structure without any previous guidelines. They designed this one-of-a-kind structure made of new composite materials and adhesive bonding technique that they developed after years of research.

"We engineered from small pieces to the big pieces testing all along the way to see if the failure theories were correct. We were looking to see where the design could go wrong," Pontius explained. "By incorporating all of our lessons learned into the final flight structure, we met the requirements, and test validated our building-block approach."

The Mechanical Systems Division at NASA Goddard performed the 26-day test to specifically test whether the car-sized structure behaved as predicted as it cooled from room temperature to the frigid — very important since the science instruments must maintain a specific location on the structure to receive light gathered by the telescope's 6.5-meter (21.3-feet) primary mirror. If the contraction and distortion of the structure due to the cold could not be accurately predicted, then the instruments would no longer be in position to gather data about everything from the first luminous glows following the big bang to the formation of star systems capable of supporting life.

The same testing facility will be used to test other Webb telescope systems, including the telescope backplane, the structure to which the Webb telescope's 18 primary mirror segments will be bolted when the observatory is assembled.

Casey Kazan via NASA and EurekaAlert.org

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