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WISE prior to its mission into orbit |
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| General information | |
|---|---|
| NSSDC ID | 2009-071A |
| Organization | NASA/JPL |
| Major contractors | Ball Aerospace Lockheed Martin Space Dynamics Laboratory SSG Precision Optronics, Inc. |
| Launch date | 2009-12-14 14:09:33 UTC |
| Launched from | Space Launch Complex 2W Vandenberg Air Force Base Lompoc, California |
| Launch vehicle | Delta II 7320-10 |
| Mass | 750 kg (1,650 lb) |
| Type of orbit | Sun-synchronous polar Inclination: 97.5° |
| Orbit height | 525 km (326 mi) |
| Orbit period | 95 minutes, 15 times per day |
| Location | Low Earth Orbit |
| Wavelength | 3.4, 4.6, 12, 22 μm bands |
| Diameter | 0.4 m |
| Website | wise.ssl.berkeley.edu |
Wide-field Infrared Survey Explorer (WISE) is a NASA infrared-wavelength astronomical space telescope launched on December 14, 2009,[1][2][3] and decommissioned/hibernated on February 17, 2011 when its transmitter was turned off.[4] The US$320 million mission launched an Earth-orbiting satellite with a 40 cm (16 in) diameter infrared telescope, which performed an all-sky astronomical survey with images in 3, 5, 12 and 22 μm wavelength range bands, over 10 months.[5] The initial mission length was limited by its hydrogen coolant, but a secondary post-crygenic mission continued for four more months.[4][6]
By October 2010, WISE hydrogen coolant and original NASA funding ran out, and the proposed WISE warm mission, using remaining functionality, was not approved by NASA.[6] Rather than abandon the spacecraft, the NASA Planetary division stepped in with funding for a shorter fourth month mission extension called NEOWISE, to search for small solar system bodies close to Earth's orbit.[6]
WISE served as a replacement for the Wide Field Infrared Explorer (WIRE), which failed within hours of reaching orbit in March 1999.[7] In certain measurements, WISE is over 1,000 times more sensitive than prior infrared space surveys such as IRAS, AKARI, and COBE's DIRBE.[8]
During its active mission it found dozens of previously unknown asteroids every day.[9] Over 33,500 new asteroids and comets were discovered, and over 154,000 solar system objects were observed by WISE by October 2010.[10]
Results of the full survey are scheduled to be released by March 2012.[11]
The first Earth Trojan asteroid was discovered using WISE data, announced on July 27, 2011.[12][13]
A new type of star called Y dwarfs are discovered with WISE, announced August 23, 2011.[14][15]
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The mission was planned to create infrared images of 99 percent of the sky, with at least eight images made of each position on the sky in order to increase accuracy. The spacecraft was placed in a 525 km (326 mi), circular, polar, sun-synchronous orbit for its 10 month mission, during which it has taken 1.5 million images, one every 11 seconds.[16] The satellite orbited above the terminator, its telescope pointing always to the opposite direction to the Earth, except for pointing towards the Moon, which was avoided, and its solar cells towards the Sun. Each image covers a 47-arcminute field of view, which means a 6 arcsecond resolution. Each area of the sky was scanned at least 10 times at the equator, the poles were scanned at theoretically every revolution due to the overlapping of the images.[17] The produced image library contains data on the local Solar System, the Milky Way Galaxy, and the more distant universe. Among the objects WISE studied are asteroids, cool, dim stars such as brown dwarfs, and the most luminous infrared galaxies.
Stellar nurseries, which are covered by interstellar dust, are detectable in infrared, since at this wavelength electromagnetic radiation can penetrate the dust. Thus galaxies of the young Universe and interacting galaxies, where star formation is intensive, are bright in infrared. On this wavelength the interstellar gas clouds are also detectable, as well as proto-planetary discs. WISE satellite was expected to find at least 1,000 of those proto-planetary discs.
WISE was not able to detect Kuiper belt objects, as their temperature is too low.[18] It was able to detect any objects warmer than 70-100 Kelvins. A Neptune-sized object would be detectable out to 700 AU, a Jupiter-mass object out to one light year (63,000 AU), where it would still be within the Sun's zone of gravitational control. A larger object of 2–3 Jupiter masses would be visible at a distance of up to seven to ten light years.[18]
At the time of planning, it was estimated that WISE would detect about 300,000 main-belt asteroids, of which approximately 100,000 will be new, and some 700 near-Earth objects including about 300 undiscovered. That translates to ~1000 new Main-belt asteroids per day, and 1-3 NEOs per day. The peak of magnitude distribution for NEOs will be about 21-22 V. WISE would detect each typical Solar system object 10-12 times over about 36 hours with the interval of 3 hours.[17]
Construction of the WISE telescope was divided between Ball Aerospace & Technologies (spacecraft, operations support), SSG Precision Optronics, Inc. (telescope, optics, scan mirror), DRS and Rockwell (focal planes), Lockheed Martin (cryostat, cooling for the telescope), and Space Dynamics Laboratory (instruments, electronics, and testing). The program is managed through the Jet Propulsion Laboratory.[6]
The WISE spacecraft was built by Ball Aerospace and Technologies Corp. in Boulder, Colorado. The spacecraft is derived from the Ball Aerospace RS-300 spacecraft architecture, particularly the NEXTSat spacecraft built for the successful Orbital Express mission launched on March 9, 2007. The flight system has an estimated mass of 560 kg (1,200 lb). The spacecraft is three-axis stabilized, with body-fixed solar arrays. It uses a high-gain antenna in the Ku band to transmit to the ground through the TDRSS geostationary system. Ball also performed the testing and flight system integration.
WISE surveyed the sky in four wavelengths of the infrared band, at a very high sensitivity. Its detector arrays have 5-sigma sensitivity limits of 120, 160, 650, and 2600 microjanskies (µJy) at 3.3, 4.7, 12, and 23 micrometres (aka microns).[8] This is a factor of 1,000 times better sensitivity than the survey completed in 1983 by the IRAS satellite in the 12 and 23 micrometres bands, and a factor of 500,000 times better than the 1990s survey by the Cosmic Background Explorer (COBE) satellite at 3.3 and 4.7 micrometres.[8] On the other hand, IRAS could also observe 60 and 100 micron wavelengths, which WISE does not.[19]
The primary mission lasts ten months: one month for checkout, six months for a full-sky survey, then an additional three months of survey until cryogenic coolant runs out. The partial second survey pass will facilitate the study of changes (e.g. orbital movement) in observed objects.[20]
On November 8, 2007, the House Committee on Science and Technology's Subcommittee on Space and Aeronautics held a hearing to examine the status of NASA's Near-Earth Object (NEO) survey program. The prospect of using WISE was proposed by NASA officials.[21]
NASA officials told Committee staff that NASA plans to use WISE to detect near-Earth objects in addition to performing its science goals. It was projected that WISE could detect 400 NEOs (or roughly 2 percent of the estimated NEO population of interest) within its one-year mission.
By May 27, 2010, WISE discovered 12,141 previously unknown asteroids, of which 64 were considered near-Earth, and 11 new comets.[22] This grew to 113 near-Earth asteroids and 16 comets by August 26, 2010.[23] Two unambiguous brown dwarfs have been detected, although their distances are unknown, as well as some brown dwarf candidates.[24]
By October 2010, over 33,500 new asteroids and comets were discovered, and nearly 154,000 solar system objects were observed by WISE.[10] Out of this total on that date, 136 new NEA, PHA, & Comets were discovered.[25] Out of these, 19 were new potentially hazardous asteroids, celestial objects both more likely to hit Earth and cause significant destruction (not to be confused with the more common but less dangerous Near Earth object (NEO)).[25] As of Oct 2010, there are 1,151 PHA are known, including those found by WISE.[26]
Discovery of an ultra-cool brown dwarf, WISEPC J045853.90+643451.9, about 10 to 30 light years away from Earth, was announced in late 2010 based on early data.[27] In July 2011 it was announced that WISE had discovered the first Earth trojan asteroid, 2010 TK7.[28]
The WISE Mission is led by Dr. Edward L. Wright of the University of California, Los Angeles. The mission has a long history under Wright's efforts, and was first funded by NASA in 1999 as a candidate for a NASA Medium-class Explorer (MIDEX) mission under the name Next Generation Sky Survey (NGSS). The history of the program from 1999 to date is briefly summarized as follows:
The launch of the Delta II rocket carrying the WISE spacecraft was originally scheduled for December 11, 2009. This attempt was scrubbed to correct a problem with a booster rocket steering engine. The launch was then rescheduled for December 14, 2009.[34] The second attempt launched on time at 14:09:33 UTC (06:09 local PST) from Vandenberg Air Force Base in California. The rocket successfully placed the WISE spacecraft into the planned polar orbit at an altitude of 326 miles (525 km) above the Earth.[3]
The WISE spacecraft underwent a month long checkout after launch, which found all spacecraft systems functioning normally and both the low and high rate data links to the operations center working properly. The instrument cover was successfully jettisoned on December 29, 2009.[35] The first light image from WISE was released on January 6, 2010. It was an eight-second exposure taken in the direction of the Carina constellation showing infrared light in false color from three of WISE's four wavelength bands: Blue, green and red corresponding to 3.4, 4.6, and 12 micrometres, respectively.[36] On January 14, 2010, the WISE mission started its official sky survey.[37] The WISE group's bid for continued funding for an extended "warm mission" scored low by a NASA review board, in part because of a lack of outside groups publishing on WISE Data. Such a mission would have allowed use of the 3.4 and 4.6 micrometres detectors after the last of cryo-coolant had been exhausted, with the goal of completing a second sky survey to detect additional objects and obtain parallax data on putative brown dwarf stars. Rather than see the 320 million dollar spacecraft abandoned, the NASA Planetary Division stepped in as an alternate source of funding in October 2010.[6]
In October 2010, the NASA Planetary Division saved the spacecraft from termination with a 400 000 US$ one month program extension called "Near-Earth Object WISE" (NEOWISE).[6] If the one month post-cryogenic mission proved a success, it would be extended for an additional three months- it was, and the mission continued.[4] The focus of the extended mission was to look for asteroids and comets close to Earth orbit, using the remaining post-cryogenic detection capability. Two of four detectors on WISE work without cryogen.[6] In February 2011, NASA announced that NEOWISE had discovered many new objects in the Solar System, including 20 comets.[38] The spacecraft was put into hibernation on February 1, 2011.[4]
On April 14, 2011, a preliminary release of WISE data was made public, covering 57 percent of the sky observed by the spacecraft.[39]
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