FEATURE ASTRONOMY
separation. The mirror will also be segmented to reduce mass, and the instrument suite replaced with a single, prime focus imaging camera. ‘Major telescopes are ideal testbeds for technologies that can later be commercialised,’ commented Copperwheat. Liverpool JMU has partnerships with optical and engineering experts in the Merseyside area and beyond. Additionally, these projects raise the profile of the optical science, with students developing skills that they take outside of academia.
Near-IR Camera for the James Webb Space Telescope
➤ vacuum cryostat’s thick window, behind which sits the 3.2 billion pixel detector system. Few places in the world can manufacture an
eight metre glass mirror, but the LSST’s combined primary and tertiary mirrors were uniquely fabricated out of a single piece of glass. The University of Arizona’s Stuart Observatory Mirror Lab developed a technique by which molten glass is spun within an oven to achieve the rough shape; this is then cooled, solidified, and subsequently finished to its precise final figure. ‘The interesting thing for a telescope building
project is that the primary-tertiary mirror pair was finished well ahead of schedule and is now being stored in a box. That’s never happened before,’ said Chuck Claver, LSST systems scientist with the LSST Project.
Optical components for projects like the
LSST are competitively bid by industry. ‘Some optics drive innovation at various companies; for example, the secondary mirror being built by Harris Corporation can’t be tested all at once,’ Claver remarked. Harris demonstrated that they could stitch the metrology together to validate surface quality. It behoves them to apply that ability to other projects. Further, the 1.6m-diameter front lens of LSST’s camera is ‘huge for a refractive optic’, according to Claver. ‘It will be the largest refractive optic ever put into service for astronomy. Achieving high performance surfaces over large optics opens a new parameter space for the photonics industry.’
Small and sweet
Smaller scopes lend themselves to optics developments, too. The two-metre Liverpool Telescope, a joint
20 ELECTRO OPTICS l JUNE 2016
venture between the UK’s Liverpool John Moores University and Royal Greenwich Observatory, became operational in January 2004 on the Canary Island of La Palma, Spain. Apart from being fully robotic, so that it requires no human operator, it is set apart from most other telescopes by its instrumentation and enclosure. A rotating fold mirror, which reflects the
converging beam near the telescope’s focus, allows seven science instruments to be simultaneously mounted and permanently available. It takes under a minute to switch between instruments. Further, the clamshell enclosure provides all-sky access, enabling rapid response to targets of opportunity. In contrast, conventional domes often limit reaction speeds. The telescope is entirely
responsible for opening and closing itself, scheduling science operations, and
Testing and metrology Huge projects like these lead to the commercial availability of better-performing products that otherwise may not have been invented. For example, astronomy has driven new CCD types, now used in medical imaging and consumer cameras. The commercial remote-sensing market has also been helped by the development of imaging equipment for high-resolution commercial satellites.
Until now, running a laser for adaptive optics required specialised personnel on site and on shift, attending the laser and adjusting it continuously
safely shutting down in the event of weather or technical issues. The critical scheduler system chooses observations entered into the queue based on science priority and conditions. ‘Some systems are easier to roboticise and operate reliably than others. Instrument cryogenic cooling can be particularly troublesome,’ explained Chris Copperwheat, astronomer in charge. Plans for a second four-metre successor, comprising a fast design using novel materials to reduce structure mass while maintaining stiffness are under way. ‘Fast’ means a focal ratio of ~f/1.5; which enables a small primary-secondary mirror
Component suppliers take their cues from the latest trends. For Edmund Optics that means adaptive optics. While Edmund does not manufacture products specifically for astronomy, their mirrors and filters are purchased for use in adaptive optics systems. Customers use Edmund products on test benches, for designing systems before building versions for a telescope. ‘We get a lot of requests for filters and eyepieces from amateurs who want to customise their own telescopes,’ noted Daniel Adams, applications engineer. Metrology systems designers also benefit. McPherson, manufacturer of photometers and spectrometers, recently sent a new ultraviolet spectrophotometer system for optical coating
metrology to NASA Goddard. They optimised performance in the ‘deep’ ultraviolet region (90-169nm), designed to work with wavelengths beyond those of conventional deuterium lamps. The spectrophotometer system will most likely help to develop, inspect and qualify optical materials and coatings used for very high altitude and extraterrestrial space flight missions. ‘NASA’s newest heliophysics satellite, the Ionospheric Connection Explorer, uses the same type of 1m monochromator that McPherson just shipped to NASA,’ said McPherson’s Erik Schoeffel. l
@electrooptics |
www.electrooptics.com
Lockheed Martin
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