July 10, 2013
NASA Is Doing Some ‘Webb Spinning’
NASA is spinning a "Webb," and it is not about a spider, it's about a part of the James Webb Space Telescope that is being "spin-tested" in a centrifuge to prove it can withstand the rigors of space travel.
In the video institute host Mary Estacion takes the viewer to the giant centrifuge chamber at NASA's Goddard Space Flight Center in Greenbelt, Md., where the telescope's Integrated Science Instrument Module was tested in an environment to simulate the acceleration forces it will endure during launch.
The instrument module, known as ISIM, is one of three major elements that make up the Webb telescope flight system. ISIM will house Webb's four main instruments, which will detect light from distant stars and galaxies, and planets orbiting other stars. Basically, the structure provides support for Webb's cameras and other instruments.
Estacion interviewed Bill Chambers, centrifuge project engineer at NASA Goddard, who explains why the center has the world's largest centrifuge. Goddard's 140-foot-diameter centrifuge can accelerate a 2.5-ton payload up to 30 g, that is, 30 times Earth's normal gravity -- well beyond the force experienced in a launch. The most intense roller-coasters in the world top out at about 5 g, and then only for brief moments. The Webb equipment can experience between 6 g and 7 g because of vibration.
In the video, Estacion also talked with Eric Johnson, ISIM structure manager at NASA Goddard, about why the centrifuge was used and the stresses the machine will impose on the instrument module. Johnson explained that the module was tested at seven times Earth's gravity to simulate the pull it will experience during launch, "and then when it gets to zero g way out in space, we have to show that it's the same shape as it was here on Earth."
Usually in centrifuge testing, engineers run the tests a little beyond actual environment conditions. They take the structural loading conditions that they expect to see during launch and then raise them up 25 percent. Instruments should be able to handle actual conditions if they hold up to the increased, simulated experience. Two 1,250-horsepower motors power the centrifuge, which can spin up to 156 mph, more than 30 rotations per minute.