NASA Goddard Space Flight Center
NASA GAMMA-RAY BURST SATELLITE TEAM ASSEMBLES WORLD'S LARGEST TELESCOPE MASK
The team behind the NASA gamma-ray burst satellite called Swift has completed construction of a massive "coded aperture mask," the largest such device ever built, marking another milestone on its path to a 2003 launch.
The mask will be key in pinpointing the location of gamma-ray bursts, the most powerful events in the Universe whose origins have remained a mystery because the bursts fade within seconds, too quickly to precisely locate and investigate in detail with previous satellites.
The gamma rays that pass through Swift's coded aperture mask will create a shadow upon the gamma-ray detectors below, allowing scientists to trace the location of gamma-ray bursts with great accuracy based on the shape of the shadow. The mask, the size of a standard piece of plywood (4 by 8 feet, or 1.2 by 2.4 meters), comprises approximately 52,000 tiny lead squares spaced in a computer-generated random pattern.
"Each of the 52,000 tiles was hand-placed 'upside down,'" said Danielle Vigneau, the lead engineer for the team that designed and built this coded aperture mask at NASA Goddard Space Flight Center. "We then used a thin coat of wet adhesive to bond all of the tiles to the panel simultaneously as the panel was lowered down on top of the tiles."
Unlike other forms of light, gamma rays penetrate right through focusing mirrors. Thus, this shadowing technique is needed to determine the location of a gamma-ray source. Gamma rays will only pass through the gaps between the lead tiles.
The mask together with a set of gamma-ray detectors, totaling 32,768 pieces of cadmium-zinc-telluride each measuring four square millimeters are the main components of Swift's Burst Alert Telescope (BAT). BAT will locate hundreds of bursts to better than 4-arcminute accuracy and provide enhanced sensitivity to faint bursts that earlier detectors have missed.
BAT will relay positions of bursts within 15 seconds to ground-based and other space-based observatories. And during this time, Swift's other two instruments -- the X-ray Telescope and Ultraviolet/Optical Telescope -- will zoom in upon the BAT detection and provide arcsecond positioning. This will provide for crucial follow-up observations of the burst's lower-energy afterglow, which can last for days to weeks. The data from the BAT will also produce a sensitive hard x-ray (high-energy) all-sky survey about 20 times deeper than previous surveys and uncovering over 400 new supermassive black holes.
Swift is a key component of NASA's Structure and Evolution of the Universe theme, which seeks answers to key questions in present-day astrophysics, including what powered the Big Bang, what is the nature of space and time, and what is the Universe made of.
For this coded aperture mask project, NASA Goddard and Swales Aerospace, Inc., in Beltsville, Md., developed the detailed mask design; Composite Optics, Inc., in San Diego manufactured the honeycomb panel; and the Johns Hopkins University Applied Physics Laboratory in Baltimore manufactured the lead tiles. Mike Schoolman of NASA Goddard is the lead technician for the coded aperture mask.
Swift was selected in October 2000 as a medium-class explorer mission (MIDEX). Swift, an international collaboration with partners in Italy and Great Britain, will operate for two years or more following launch. Dr. Neil Gehrels from NASA's Goddard Space Flight Center is the Principal Investigator for the Swift Mission.
A detailed description of Swift is available at: http://swift.gsfc.nasa.gov.
For an image of the coded aperture mask, refer to: