Introduction

The Wide-field Infrared Survey Explorer, or WISE, will scan the entire sky in infrared light, picking up the glow of hundreds of millions of objects and producing millions of images. The mission will 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. Its vast catalogs will help answer fundamental questions about the origins of planets, stars and galaxies, and provide a feast of data for astronomers to munch on for decades to come.

Thanks to next-generation technology, WISE's sensitivity is hundreds of times greater than its predecessor, the Infrared Astronomical Satellite, which operated in 1983.

WISE will join two other infrared missions in space -- NASA's Spitzer Space Telescope and the Herschel Space Observatory, a European Space Agency mission with important NASA participation. WISE is different from these missions in that it will survey the entire sky. It is designed to cast a wide net to catch all sorts of unseen cosmic treasures, including rare oddities.

The closest of WISE's finds will be near-Earth objects, both 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. 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. WISE data will also reveal new information about the composition of near-Earth objects and asteroids -- are they fluffy like snow or hard like rocks, or both?

The next closest targets for WISE are dim stars called brown dwarfs. These Jupiter-like balls of gas form like stars but fail to gather up enough mass to ignite like stars. The objects are cool and faint, and nearly impossible to see in visible light. WISE should uncover about 1,000 in total, and will double or triple the number of star-like objects known within 25 light-years of Earth. What's more, if a brown dwarf is lurking closer to us than the closest known star, Proxima Centauri, WISE will find it and the little orb will become famous for being the "closest known star."

The most distant objects that will stand out like ripe cherries in WISE's view are tremendously energetic galaxies. Called ultraluminous infrared galaxies, or ULIRGs, these objects shine with the light of up to a trillion suns. They crowd the distant universe, but appear virtually absent in visible-light surveys. WISE should find millions of ultra-luminous infrared galaxies, and the most luminous of these could be the most luminous galaxy in the universe.

Other nuggets to come out of the WISE survey will be newborn stars; disks of planetary debris around young stars; a detailed look at the structure of our Milky Way galaxy; clusters of galaxies in the far universe and more. The most interesting finds will lay the groundwork for follow-up studies with other missions, such as NASA's Spitzer Space Telescope, the Herschel Space Observatory, NASA's Hubble Space Telescope, NASA's upcoming SOFIA airborne telescope and NASA's upcoming James Webb Space Telescope. Powerful ground-based telescopes will also follow up on WISE discoveries.

As with past all-sky surveys, surprises are sure to come. For example, one of the most surprising finds to come out of the Infrared Astronomical Satellite mission was the discovery of excess infrared light around familiar stars like Vega and Fomalhaut. Astronomers soon determined that the excess light comes from pulverized rock in disks of planetary debris. The findings implied that rocky planets like Earth could be common. Today hundreds of astronomers study these debris disks, and Hubble recently captured an actual photograph of a planet orbiting Fomalhaut within its disk.

WISE will orbit Earth at an altitude of 525 kilometers (326 miles), circling Earth via the poles about 15 times a day. A scan mirror within the WISE instrument will stabilize the line of sight so that snapshots can be taken every 11 seconds over the entire sky. Each position on the sky will be imaged a minimum of eight times, and some areas near the poles will be imaged more than 1,000 times.

The mission's sensitive 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 a chilly 17 degrees Kelvin (minus 429 degrees Fahrenheit).

After a one-month checkout period, the infrared surveyor 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. 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.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Wide-field Infrared Survey Explorer for NASA's Science Mission Directorate, Washington. The mission's principal investigator, Edward L. (Ned) Wright, is at UCLA. The mission was competitively selected in 2002 under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp, Boulder, Colo. Science operations and data processing will take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

History
Instruments

Telescope

The WISE telescope has a 40-centimeter-diameter (16-inch) aperture and is designed to continuously image broad swaths of sky at four infrared wavelengths as the satellite wheels around Earth. The four wavelength bands are 3.4, 4.6, 12 and 22 microns. The field of view is 47-arcminutes wide, or about one-and-a-half times the diameter of the moon.

The telescope was built by L-3 SSG-Tinsley in Wilmington, Mass. Its design uses a total of 10 curved and two flat mirrors, all made of aluminum and coated in gold to improve their ability to reflect infrared light. Four of the mirrors form an image from the 40-centimeter primary mirror onto the flat scan mirror. The scan mirror moves at a rate that exactly cancels the changing direction of the spacecraft on the sky, allowing freeze frame images to be taken every 11 seconds. The scan mirror then snaps back to catch up with the craft as it continues to survey the sky.

The remaining mirrors form a focused image of the sky onto the detector arrays. Before reaching the arrays, the light passes through a series of flat "dichroic" filters that reflect some wavelengths and transmit others, allowing WISE to simultaneously take images of the same part of the sky at four different infrared wavelengths.

The image quality, or resolution, of WISE is about six arcseconds in its 3.4, 4.6 and 12 micron bands, meaning that it can distinguish features one six-hundredth of a degree apart. At 22 microns, the resolution is 12 arcseconds, or one three-hundredth of a degree. This means WISE can distinguish features about five times smaller than the Infrared Astronomical Satellite could at 12 and 25 microns, and many hundred times smaller than NASA's Cosmic Background Explorer could at 3.5 and 4.9 microns.

Detectors

Light gathered by WISE's telescope is focused onto what is called a focal plane, which consists of four detector arrays, one for each infrared wavelength observed by WISE. Each of the detector arrays contain about one million pixels (1,032,256 to be exact). This is a giant technology leap over past infrared survey missions. The Infrared Astronomical Satellite's detectors contained only 62 pixels in total.

The 3.4- and 4.6-micron detectors convert light to electrons using an alloy made of mercury, cadmium and tellurium. The electrons from each of the million-plus pixels are measured on the spot every 1.1 seconds, and the result sent to the instrument electronics. These detector arrays, a type known as the HAWAII 1RG, were manufactured by Teledyne Imaging Systems, Camarillo, Calif. They need to be warmer than the rest of the instrument to improve their performance. The 12- and 22-micron detectors sense light using silicon mixed with a tiny amount of arsenic. They have readout electronics specially developed for the low-temperatures of WISE and were manufactured by DRS Sensors & Targeting Systems, Cypress, Calif.

Cryostat

Because WISE is designed to detect infrared radiation from cool objects, the telescope and detectors must be kept at even colder temperatures to avoid picking up their own signal. The WISE telescope is chilled to 12 Kelvin (minus 261 degrees Celsius or minus 438 degrees Fahrenheit) and the detectors for the 12- and 22-micron detectors operate at less than 8 Kelvin (minus 265 degrees Celsius or minus 447 degrees Fahrenheit). The shorter wavelength 3.4- and 4.6-micron detectors operate at a comparatively balmy 32 Kelvin (minus 241 degrees Celsius or minus 402 degrees Fahrenheit). To maintain these temperatures, the telescope and detectors are housed in a cryostat, essentially a giant Thermos bottle.

The WISE cryostat, manufactured by Lockheed Martin Advanced Technology Center, Palo Alto, Calif., has two tanks filled with frozen hydrogen. The colder, or primary cryogen tank, the smaller of the two tanks, cools the 12- and 22-micron detector arrays. To achieve this low operating temperature, a larger 12-Kelvin secondary tank protects the primary tank from nearly all the heat from the outer structure of the cryostat, which is comparatively warm at about 190 Kelvin (minus 83 degrees Celsius or minus 117 degrees Fahrenheit). This secondary tank also cools the telescope and the 3.4- and 4.6-micron detectors. Small heaters are used to warm the 3.4- and 4.6-micron detectors from 12 to 32 Kelvin.

It is important to maintain a vacuum inside the cryostat when it is cold and on the ground; otherwise air would freeze inside it. It would become a giant popsicle. A deployable aperture cover seals the top of the cryostat while on the ground to prevent air from getting in. After WISE is safely in orbit, a signal is sent to eject the aperture cover. Three pyrotechnic separation nuts will fire, and the cover will be pushed away from the spacecraft.

An aperture shade is mounted at the top of the telescope to shield the open cryostat system from the sun and Earth's heat.

The expected lifetime of WISE’s frozen hydrogen supply is 10 months. Since it takes WISE six months to survey the sky, this is enough cryogen to complete one-and-a-half surveys of the entire sky after a one-month checkout period in orbit.

Mission

The Wide-field Infrared Survey Explorer, or WISE, will scan the entire sky in infrared light, picking up the glow of hundreds of millions of objects and producing millions of images. The mission will 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. Its vast catalogs will help answer fundamental questions about the origins of planets, stars and galaxies, and provide a feast of data for astronomers to munch on for decades to come.

Thanks to next-generation technology, WISE's sensitivity is hundreds of times greater than its predecessor, the Infrared Astronomical Satellite, which operated in 1983.

WISE will join two other infrared missions in space -- NASA's Spitzer Space Telescope and the Herschel Space Observatory, a European Space Agency mission with important NASA participation. WISE is different from these missions in that it will survey the entire sky. It is designed to cast a wide net to catch all sorts of unseen cosmic treasures, including rare oddities.

The closest of WISE's finds will be near-Earth objects, both 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. 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. WISE data will also reveal new information about the composition of near-Earth objects and asteroids -- are they fluffy like snow or hard like rocks, or both?

The next closest targets for WISE are dim stars called brown dwarfs. These Jupiter-like balls of gas form like stars but fail to gather up enough mass to ignite like stars. The objects are cool and faint, and nearly impossible to see in visible light. WISE should uncover about 1,000 in total, and will double or triple the number of star-like objects known within 25 light-years of Earth. What's more, if a brown dwarf is lurking closer to us than the closest known star, Proxima Centauri, WISE will find it and the little orb will become famous for being the "closest known star."

The most distant objects that will stand out like ripe cherries in WISE's view are tremendously energetic galaxies. Called ultraluminous infrared galaxies, or ULIRGs, these objects shine with the light of up to a trillion suns. They crowd the distant universe, but appear virtually absent in visible-light surveys. WISE should find millions of ultra-luminous infrared galaxies, and the most luminous of these could be the most luminous galaxy in the universe.

Other nuggets to come out of the WISE survey will be newborn stars; disks of planetary debris around young stars; a detailed look at the structure of our Milky Way galaxy; clusters of galaxies in the far universe and more. The most interesting finds will lay the groundwork for follow-up studies with other missions, such as NASA's Spitzer Space Telescope, the Herschel Space Observatory, NASA's Hubble Space Telescope, NASA's upcoming SOFIA airborne telescope and NASA's upcoming James Webb Space Telescope. Powerful ground-based telescopes will also follow up on WISE discoveries.

As with past all-sky surveys, surprises are sure to come. For example, one of the most surprising finds to come out of the Infrared Astronomical Satellite mission was the discovery of excess infrared light around familiar stars like Vega and Fomalhaut. Astronomers soon determined that the excess light comes from pulverized rock in disks of planetary debris. The findings implied that rocky planets like Earth could be common. Today hundreds of astronomers study these debris disks, and Hubble recently captured an actual photograph of a planet orbiting Fomalhaut within its disk.

WISE will orbit Earth at an altitude of 525 kilometers (326 miles), circling Earth via the poles about 15 times a day. A scan mirror within the WISE instrument will stabilize the line of sight so that snapshots can be taken every 11 seconds over the entire sky. Each position on the sky will be imaged a minimum of eight times, and some areas near the poles will be imaged more than 1,000 times.

The mission's sensitive 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 a chilly 17 degrees Kelvin (minus 429 degrees Fahrenheit).

After a one-month checkout period, the infrared surveyor 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. 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.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Wide-field Infrared Survey Explorer for NASA's Science Mission Directorate, Washington. The mission's principal investigator, Edward L. (Ned) Wright, is at UCLA. The mission was competitively selected in 2002 under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp, Boulder, Colo. Science operations and data processing will take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

Orbital Insertion
Orbit

NASA's Wide-field Infrared Survey Explorer, or WISE, launched into Earth orbit at 6:09 a.m. PST (9:09 a.m. EST) Dec. 14, 2009, rocketing away from Vandenberg Air Force Base in California aboard a Delta II launch vehicle.

Once WISE was on its own in orbit, it sent a signal back to Earth through the Tracking and Data Relay Satellite System. With its cooling unit and solar arrays activated, the the 1,485-pound spacecraft was ready to begin its scientific mission.

WISE: Mapping the Infrared Sky

From a vantage point 500 km above Earth's surface, WISE will survey the entire sky at infrared wavelengths, creating a cosmic clearinghouse of hundreds of millions of objects that will be catalogued and provide a vast storehouse of knowledge about the solar system, the Milky Way, and the universe. By the end of its six-month mission, WISE will have taken nearly 1,500,000 pictures covering the entire sky.

Launch Information

Spacecraft: Wide-field Infrared Survey Explorer (WISE)
Launch Vehicle: United Launch Alliance Delta II 7320
Launch Site: Vandenberg Air Force Base - SLC 2
Launch Date: Dec. 14, 2009
Launch Time: 6:09 a.m. PST (9:09 a.m. EST)

Science
Sapcecraft

The WISE spacecraft is about the height and weight of a big polar bear, only wider. It measures 2.85 meters tall (9.35 feet), 2 meters wide (6.56 feet), 1.73 meters deep (5.68 feet) and weighs 661 kilograms (1,433 pounds). It is composed of two main sections: the instrument and the spacecraft bus.

The Space Dynamics Laboratory in Logan, Utah, designed, fabricated and tested the instrument. They also manufactured the electronics used to control the instrument and perform onboard processing of the detector images.

The spacecraft bus was built by Ball Aerospace & Technologies Corp, Boulder, Colo. Ball was also responsible for integrating the instrument to the spacecraft bus and testing the completed spacecraft.

 

 

The instrument includes a 40-centimeter-diameter (16-inch) telescope and four infrared detectors containing one million pixels each, all kept cold inside an outer cylindrical, vacuum-tight tank filled with frozen hydrogen, called a cryostat. Some say the whole assembly looks like a giant Thermos bottle, while others see a resemblance to the Star Wars robot R2-D2. After launch, the hydrogen vents on the cryostat are opened and the instrument cover is ejected. Once these events have occurred, a scan mirror in the telescope will be the only moving instrument part.

At the bottom of the instrument is a three-axis stabilized, eight-sided spacecraft bus that houses the computers, electronics, battery and reaction wheels needed to keep the observatory operating and oriented correctly in space. Two star trackers for precision pointing are mounted on the sides of the spacecraft bus. A fixed solar panel that provides all the spacecraft's power is mounted on one side of the bus, and a fixed high gain antenna for transmitting science images to the ground is mounted on the opposite side. The bus structure is composed of an aluminum skin backed by aluminum honeycomb panels. It has no deployable parts -- the only moving parts are four reaction wheels used to maneuver the satellite.

The base of the spacecraft structure includes a “soft-ride” system of springs to reduce stress from the rocket on the satellite. A metal clamp band attaches the second stage of the rocket to the base of the satellite, and is released to allow the spacecraft to separate from the launch vehicle in orbit.

Other News
Other News

"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," said 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."

NASA's asteroid initiative will be the first mission to identify, capture and relocate an asteroid. It represents an unprecedented technological feat that will lead to new scientific discoveries and technological capabilities that will help protect our home planet. The asteroid initiative brings together the best of NASA's science, technology and human exploration efforts to achieve President Obama's goal of sending humans to an asteroid by 2025.

Launched December 2009 to look for the glow of celestial heat sources from asteroids, stars and galaxies, WISE made about 7,500 images every day during its primary mission from January 2010 to February 2011. As part of a project called NEOWISE, the spacecraft made the most accurate survey to date of NEOs. NASA turned most of WISE's electronics off when it completed its primary mission.

Because asteroids reflect but do not emit visible light, infrared sensors are a powerful tool for discovering, cataloging and understanding the asteroid population. Depending on an object's reflectivity, or albedo, a small, light-colored space rock can look the same as a big, dark one. As a result, data collected with optical telescopes using visible light can be deceiving.

During 2010, NEOWISE observed about 158,000 rocky bodies out of approximately 600,000 known objects. Discoveries included 21 comets, more than 34,000 asteroids in the main belt between Mars and Jupiter, and 135 near-Earth objects.

The WISE prime mission was to scan the entire celestial sky in infrared light. It captured more than 2.7 million images in multiple infrared wavelengths and cataloged more than 560 million objects in space, ranging from galaxies faraway to asteroids and comets much closer to Earth.