Tiny shutters open on deep space

NASA engineers and scientists building the James Webb Space Telescope have used ‘microshutters,’ tiny doorways that will allow the telescope to see further than ever before.

The microshutters will enable scientists to mask unwanted light from foreground objects so the telescope can focus on the faint light of the first stars and galaxies that formed in the universe. The Webb Telescope will launch in the next decade and will be the first to use this technology.

In December 2006, the microshutters passed environmental testing to demonstrate that they can withstand the rigors of launching and placement in deep space. NASA's Goddard Space Flight Centre designed, tested and built the instrument technology. The microshutters will work in conjunction with the telescope's Near Infrared Spectrograph that is being built by the European Space Agency.

Each of the 62,000 shutters measures 100 by 200 microns, or roughly the width of three to six human hairs. The shutters are arranged in four identical grids that have a layout of 171 rows by 365 columns. These shutter grids are in front of an eight million-pixel infrared detector that records the light passing through the open shutters.

Astronomers using ground-based telescopes first take a picture of the sky and map all the objects in which they are interested. They then create a mask resembling a sieve to place on the telescope so that only the light from areas of interest can reach the telescope's detectors.

In space, the Webb Telescope will have a wide field of view, and its deep, long observation of the sky will contain millions of light sources. Microshutters allow scientists to remotely and systematically block out light that they do not want, allowing the large-format detector to measure infrared spectra optimally. Previously, masks of space telescopes only covered large regions of a field of view at any one time.

‘The microshutters provide a conduit for faint light to reach the telescope detectors with very little loss,’ said Harvey Moseley, the Microshutter Principal Investigator at Goddard. ‘The shutters allow us to perform spectroscopy on up to 100 targets simultaneously. We will be able to see deeper in less time.’

Each shutter grid array is etched from a single piece of silicon, leaving a sculpture of cavities and doorframes with microscopic hinges and moving doors. The tiny shutters are laced with magnetic cobalt-iron strips.

A passing magnet will open all the doors, pulling them down into the cavity. While the doors are opened, engineers can apply a combination of voltages to keep the selected microshutters open. The remainder close when the magnet moves away.

The microshutters must perform at a temperature of -233 degrees Celsius, which is the temperature of the near infrared spectrograph.

The microshutters are needed for observing distant, faint sources. Hubble's Ultra-Deep Field provides the deepest view of the universe, an image containing tens of thousands of light sources. Some of these light sources are relatively close and some are from an era just after galaxies and stars formed. To go deeper, scientists need to mask the brighter, closer sources and focus only on the most distant. The same microshutter technology also will efficiently reveal faint features in relatively nearby star fields, where scientists will analyse multiple sources at once.

‘The microshutters are a remarkable engineering feat that will have applications both in space and on the ground, even outside the realm of astronomy in biotechnology, medicine and communications,’ said Moseley.