The all sky surveys done by the Palomar Observatory Schmidt, the European Southern Observatory Schmidt, and the United Kingdom Schmidt, the InfraRed Astronomical Satellite, and the Two Micron All Sky Survey have proven to be extremely useful tools for astronomy with value that lasts for decades. The Wide-field Infrared Survey Explorer (WISE) is mapping the whole sky following its launch on 2009 December 14. WISE began surveying the sky on 2010 January 14 and completed its first full coverage of the sky on July 17. The survey will continue to cover the sky a second time until the cryogen is exhausted (anticipated in 2010 November). WISE is achieving 5σ point source sensitivities better than 0.08, 0.11, 1, and 6 mJy in unconfused regions on the ecliptic in bands centered at wavelengths of 3.4, 4.6, 12, and 22 μm. Sensitivity improves toward the ecliptic poles due to denser coverage and lower zodiacal background. The angular resolution is 6. 1, 6. 4, 6. 5, and 12. 0 at 3.4, 4.6, 12, and 22 μm, and the astrometric precision for high signal-to-noise sources is better than 0. 15.

The Wide Field Infrared Survey Explorer is a NASA Medium Class Explorer mission to perform a high-sensitivity, high resolution, all-sky survey in four infrared wavelength bands. The science payload is a 40 cm aperture cryogenically cooled infrared telescope with four 1024 2 infrared focal plane arrays covering from 2.8 to 26 µm. Mercury cadmium telluride (MCT) detectors are used for the 3.3 µm and 4.6 µm channels, and Si:As detectors are used for the 12 µm and 23 µm wavelength channels. A cryogenic scan mirror freezes the field of view on the sky over the 9.9-second frame integration time. A two-stage solid hydrogen cryostat provides cooling to temperatures less than 17 K and 8.3 K at the telescope and Si:As focal planes, respectively. The science payload collects continuous data on orbit for the seven-month baseline mission with a goal to support a year-long mission, if possible. As of the writing of this paper, the payload subassemblies are complete, and the payload has begun integration and test. This paper provides a payload overview and discusses instrument status and performance.

Thc Widc-Ficld Infrared Explorer (WIRE) is a Small Explorer (SMEX) mission that will fly in the fall of 1998. The WIRE In SSJOfl OOSCS tO conduct a 4-month survey of more than 100 degree2 of sky using I 2-and 25-jtm detectors. The instrumcnt requires cryogenic cooling of iLS focal planes (<7.5 K) and telescope (<18 K) in order to achieve the required performance sensitivity. In addition, because of the SMEX nature of the experiment, the mass of the cryostat must be less than t() kg. The ITflOSL mass efficient system meeting the lifetime requirement was determined to be a dual stage HJ H2 cryosLat. The føci1 planes arc conduciivcly cooled by the primary H2 (6.76 K) while the telescope is cooled by the secondzir H2 (1 2 K). The secondary H2 also protects the primary H2 by intercepting the parasitic heat loads. This paper dcscrihcs the dcsiizn and performance of the Hil H2 cryostat.

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The Wide Field Infrared Survey Explorer is a NASA Medium Class Explorer mission to perform and all-sky survey in four infrared wavelength bands. The science payload is a cryogenically cooled infrared telescope with four 1024^2 infrared focal plane arrays covering from 2.8 to 26 microns. Advances in focal plane technology and a large aperture allow an all-sky survey to be performed with high sensitivity and resolution. Mercury cadmium telluride (MCT) detectors, cooled to 32 K, are used for the two midwave channels, and Si:As detectors, cooled to < 8.3 K, are used for the two long wavelength channels. Cooling for the payload is provided by a two-stage solid hydrogen cryostat providing temperatures <17K and < 8.3K at the telescope and Si:As focal planes, respectively. The science payload supports operations on orbit for the seven month baseline mission with a goal to support a 13 month extended mission if available. This paper provides a payload overview and discusses instrument requirements and performance.