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 infrared James Webb Space Telescope will orbit following its scheduled launch in 2014.
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.
"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.
The James Webb Space Telescope (JWST), scheduled to launch in 2014, is the successor to the Hubble Space Telescope and the key to almost every big question that astronomers hope to answer in the coming decades. Without the JWST, the bulk of the science goals listed in the 2010 decadal survey, released this August, will be unattainable, according to Nature.com.
The JWST's 6.5-metre primary mirror, nearly three times the diameter of Hubble's, will be the largest ever launched into space. The telescope will rely on a host of untried technologies, ranging from its sensitive light-detecting instrumentation to the cooling system that will keep the huge spacecraft below 50 kelvin. And it will have to operate perfectly on the first try, some 1.5 million kilometres from Earth — four times farther than the Moon and beyond the reach of any repair mission. If the JWST — named after the administrator who guided NASA through the development of the Apollo missions — fails, the progress of astronomy could be set back by a generation.