NASA brings WISE probe out of retirement to hunt asteroids
By David Szondy
August 25, 2013
NASA will be putting another eye on potentially dangerous asteroids in September when it reactivates the retired Wide-field Infrared Survey Explorer (WISE). The space telescope, which was deactivated in 2011, will use its infrared instruments to carry out a survey of near-Earth asteroids that may pose a threat to our planet.
Sitting in a solar-synchronous orbit 525 km (326 mi) above the Earth, WISE circles the globe once every 95 minutes. Its new three-year mission starting in September focuses on searching for asteroids that might pose a threat to Earth or that may be targets for an asteroid exploration mission as part of the US asteroid initiative. NASA anticipates that the unmanned probe will find up to 150 new near-Earth objects (NEO) and will study the size, albedo and thermal properties of 2,000 more.
Weighing 750 kg (1,650 lb), WISE was launched atop a Delta II booster on December 14, 2009 from Space Launch Complex 2W at Vandenberg Air Force Base in California. It’s primary instrument is a 40 cm (16 in) infrared telescope with four infrared detectors at a resolution of one million pixels each. At the time of launch, this was supercooled down to as low as 7.6 K by inserting it inside a cryostat containing solid hydrogen.
During its primary mission, WISE carried out an all-sky survey at infrared wavelengths from 3 to 25 μm. It collected 2.7 million images of 560 million objects until its hydrogen coolant ran out in October 2010. After that, it carried on with the NEOWISE four-month mission extension, which continued the survey at reduced capabilities.
According to NASA, WISE has already conducted the most accurate survey to date of NEOs. Its infrared sensors are excellent for assessing the characteristics of asteroids. However, since they can only be seen by reflected light, the telescope works best with near-Earth objects. By the time it was decommissioned on February 17, 2011, WISE had studied about 158,000 rocky bodies out of 600,000 known NEOs, discovered 21 comets, over 34,000 asteroids and 135 NEOs. With this track record, NASA believes that WISE can still play a part in asteroid surveys.
"The WISE mission achieved its mission's goals and as NEOWISE extended the science even further in its survey of asteroids. NASA is now extending that record of success, which will enhance our ability to find potentially hazardous asteroids, and support the new asteroid initiative," says John Grunsfeld, NASA's associate administrator for science in Washington. "Reactivating WISE is an excellent example of how we are leveraging existing capabilities across the agency to achieve our goal."