WISE Observatory Sensor Nears Delivery
By Guy Norris 
Space Dynamics Laboratory (SDL), a nonprofit research and development corporation owned by Utah State University, is preparing to deliver the main sensing unit of NASA's upcoming Wide-field Infrared Survey Explorer (WISE) to Ball Aerospace for integration into the spacecraft.
SDL pioneered the "solid hydrogen" cooling technology at the heart of the WISE spacecraft, which is due to be launched in November to survey the entire sky in four mid-infrared bands spanning from 2.8 to 26 microns.
The intense cooling capability of the SDL system will provide WISE with more than a thousand times the infrared sensitivity of any previous mission, and enable it to collect millions of overlapping images from which astronomical objects will be catalogued.
According to NASA, WISE will measure the diameters of more than 100,000 asteroids in the solar system, and provide a complete inventory of nearby young stars as well as of the debris disks associated with planetary systems around older nearby stars. Additionally, WISE will look for cool, dim brown dwarf stars as well as far distant ultra-luminous infrared galaxies. The images will provide the essential star catalog for the James Webb Space Telescope.
Following the completion of payload vibration and solid hydrogen testing at the start of the year, the sensor was recently returned to SDL for verification of calibration. "We passed those tests and the system is going through the final few tests," SDL director Doug Lemon says. "It will then go to Ball in the next few weeks for integration on the bus, before being sent to Vandenberg Air Force Base, Calif., later in the summer."
The Wise payload, measuring just more than six feet tall and weighing nearly 80 pounds, is derived from earlier exploratory spacecraft designs, including Spirit III and Wire. The unit's chief feature is an almost 16-inch-diameter, all-reflective imaging telescope housed in a two-stage, solid-hydrogen cryostat. Hydrogen in a slush-like consistency is held within the cryostat in a metallic sponge-type mesh.
Although WISE is initially aimed at a six-month mission, "we think we can hold it cool for 13 months, so you could probably get two whole trips around the sun," Lemon says. Images from the telescope will be captured on four 10242 focal plane arrays; two arsenic-doped silicon arrays and two mercury-cadmium-telluride arrays.
Artist's concept of WISE: NASA
