NASA today said its Wide-field Infrared Survey Explorer spacecraft successfully popped the cover off its infrared telescope and began “celestial treasure hunt” mission of sending back what will be millions of images of space.
The WISE lens cap served as a safety system keeping the ultra-sensitive lens and telescope system safe until the spacecraft positioned itself correctly in orbit. The cap also served as the top to a Thermos-like bottle that chilled the instrument. WISE’s infrared telescope and detectors are kept chilled inside a Thermos-like tank of solid hydrogen, called a cryostat. This prevents WISE from picking up the heat, or infrared, signature of its own instrument. The solid hydrogen, called a cryogen, is expected to last about 10 months and will keep the WISE telescope at a minus 429 degrees Fahrenheit, NASA stated.
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According to NASA, scientists are now adjusting the rate of the spacecraft to match the rate of a scanning mirror. To take still images on the sky as it orbits around Earth, WISE will use what NASA calls a scan mirror to counteract its motion. Light from the moving telescope's primary mirror will be focused onto the scan mirror, which will move in the opposite direction at the same rate. This lets the mission take "freeze-frame" snapshots of the sky every 11 seconds. That's about 7,500 images a day, NASA stated.
The space agency says the WISE spacecraft will circle Earth over the poles, scanning the entire sky one-and-a-half times in nine months. The idea behind the mission is to uncover objects never seen before, including the coolest stars, the universe's most luminous galaxies and some of the darkest near-Earth asteroids and comets.
After a one-month checkout period, WISE will spend six months mapping the whole sky. It will then begin a second scan to uncover even more objects and to look for any changes in the sky that might have occurred since the first survey, according to NASA. This second partial sky survey will end about three months later when the spacecraft's frozen-hydrogen cryogen runs out. Data from the mission will be released to the astronomical community in two stages: a preliminary release will take place six months after the end of the survey, or about 16 months after launch, and a final release is scheduled for 17 months after the end of the survey, or about 27 months after launch.
WISE will also scan for near-Earth objects, such as asteroids and comets, with orbits that come close to crossing Earth's path. The mission is expected to find hundreds of these bodies and hundreds of thousands of additional asteroids in our solar system's main asteroid belt, NASA stated. By measuring the objects' infrared light, astronomers will get the first good estimate of the size distribution of the asteroid population. This information will tell us approximately how often Earth can expect an encounter with a potentially hazardous asteroid, NASA said.