How Does WIRE Work?

The WIRE instrument is a cryogenically-cooled 30 cm Ritchey-Chretien telescope system that illuminates two arsenic-doped silicon infrared detector arrays.  A  two-stage solid hydrogen cryostat maintains the optics colder than 19 K and the detector arrays below 7.5 K.  The optical system consists of the telescope primary and secondary mirrors, a dichroic beamsplitter, one optical passband filter, and baffles.  The two channels of the instrument cover broad bands centered near 12 microns and 25 microns; the 25 micron band is the primary one for detecting starburst galaxies.  The instrument contains no moving parts. 

A cutaway view is shown  below as well as further explanations of each component.

  Cutaway of WIRE Instrument

The Pegasus Launch Fairing is part of the Pegasus XL rocket that will propel WIRE into orbit.  For a better view, see Pegasus Fairing Accommodations or Orbital's Expanded View of the Pegasus XL.

The Star Tracker keeps track of a star or set of stars to keep the spacecraft properly oriented.  See Ball Aerospace and Technologies Corporation for a better explanation of Star Trackers.

The Primary and Secondary Tank Vents allow the venting of excess pressure from the Primary and Secondary Hydrogen Tanks. 

The Primary Hydrogen Tank contains solid hydrogen and is used to keep the detector arrays at a temperature less than 7.5 K (-265 Celsius). 

The Secondary Hydrogen Tank also contains solid hydrogen.  It is used to cool the instruments optics to 12 K (-254 Celsius).   Both tanks make up the dual stage cryostat.

The Dichroic Beam Splitter divides the incoming light into two colors: 12 and 25mm are the two colors.  They are two different wavelengths of light that are both in the infrared region of the electromagnetic spectrum.

The Focal Plane Arrays are the eyes of the telescope.  There are two FPAs; one that detects radiation at 12mm, and one that detects at 25mm.  The radiation reaches each of the FPAs after it has been divided by the beam splitter.  See Boeing for a more detailed explanation of Focal Plane Arrays.

The Spacecraft Bus is simply the spacecraft minus the instrument.  The spacecraft is the entire observatory as it is launched into orbit and consists of the instrument and the Spacecraft Bus.

The Vapor Cooled Shields and Fiberglass Support Tubes are structural components of the instrument that are cooled by vapor from the cryostat.

The Ejectable Cover provides protection for the instrument and will be ejected once the science experiment is ready to begin.

The Aperture Shade prevents the Sun's visible light from entering the instrument and interfering with the experiment.

The Primary and Secondary Mirrors in this arrangement are characteristic of Cassegrain reflector telescopes.  This Ritchey-Chretien telescope is a Cassegrain design.  The 30 cm diameter primary mirror reflects the incoming radiation to the much smaller seconary mirror, which then redirects the radiation to the beam splitter.


Last Updated: 12/2/98