New visions for space telescopes

NASA stumbled into a rare bit of good luck recently when the National Reconnaissance Office did some housecleaning. NRO decided that a pair of space-qualified 2.4 m telescopes dating from the late 1990s were no longer suitable for their original mission in spy satellites. So NRO offered the surplus optics to one of its poorer relations, NASA, for use in new space-based instruments. 

Unexpected hand-me-downs can bring opportunity, like the the piles of Scientific American and Sky & Telescope that came with a house my family rented when I was in high school. Astronomers and NASA scientists are pondering what to do with the windfall. The f/8 Cassegrain telescopes lack instruments, electronics, or spacecraft, but NRO long ago paid for the optics, saving NASA serious money. The Study on Applications for Large Space Optics workshop held February 5 and 6, 2013, in Huntsville, AL heard and discussed 34 proposals for building new instruments around the mirrors. They will be narrowed to six proposals and submitted to NASA management in May.

The range of ideas is impressive. Adaptive optics can do wonders on the ground, but ultraviolet astronomy must remain above the atmosphere, so three proposals call for studying the ultraviolet sky. Other common themes are spectroscopy, planetary science inside the solar system, and attempts to image challenging targets including extrasolar planets.

Bare-bones surplus telescopes inherited by NASA (Government work not subject to copyright)

Some proposals are intriguing. Alfred McEwen of the University of Arizona (Tucson, AZ) envisions the Mars Orbiting Space Telescope, and  Zachary Bailey of the Jet Propulsion Laboratory (Pasadena, CA) proposes "high-resolution surface science at Mars."  Rebecca Farr of the NASA Marshall Space Flight Center (Huntsville, AL) proposes using both mirrors as a deep-space binocular telescope stationed at the Lunar L2 Lagrange point.

Not everything is exactly a telescope. Abhijit Biswas of JPL wants to use a mirror as an optical communications node in space. J. H. Clemmons of the Aerospace Corp. (El Segundo, CA) wants to use one in a lidar to explore the Earth's thermosphere.  Richard Eastes of the University of Central Florida (Orlando, FL) has a plan for "Atmospheric TeleConnections on Earth."

There are plenty more listed on the program, and NASA will be recording the proceedings for later viewing. The ideas are not fully formed, of course, and some seem to duplicate others. But there are enough bright ideas to make one hope that NRO can find more goodies sitting in storage for its needy relatives.

Source:  http://science.nasa.gov/salso/telescope-characteristics-and-capabilities/

Display technology getting ahead of the market

Peter Jackson's decision to shoot The Hobbit at 48 frames per second brought optical technology into many holiday-party conversations, at least among technologists and movie buffs. Together with demonstrations of video screens with horizontal resolution of 8000 pixels, it raises the question of whether the cutting edge of large-screen display technology is getting too far ahead of the market.

From the production side, it makes sense to record a movie in the best quality available at reasonable cost. It's easy to reduce resolution or frame rate to current mass-distribution standards. Theaters can charge extra for the highest quality screenings, as they have done for 3D. And archival copies should be compatible with the next generation or two of technologies.


From the display side, reviewers had mixed reactions. They found some parts spectacular, but sometimes too revealing. As Lucy O'Brien wrote on the gaming site IGN.com, "The problem with doubling the frame-rate in The Hobbit is a problem of scrutiny; you can see all its tricks."

The push for higher video screen resolution comes largely from the consumer electronics industry. Aided by government mandates to convert to digital broadcasting, the industry persuaded the public to switch to flat-panel high-definition televisions showing 720 or 1080 lines, corresponding to widths of 1280 or 1920 pixels respectively. But the public largely passed on 3D television, and in uncertain times they have been slow to step up to larger screens, so manufacturers have slashed prices to bolster sales.

Two ultra-high-definition formats are in development. One that doubles resolution is called 4K, for a nominal width of 4000 pixels (actually 3840 x 2160 pixels). An alternative called 8K quadruples resolution to a nominal width of 8000 pixels (actually 7680 x 4320 pixels). Some 4K equipment is available, and 8K has been demonstrated. However, big challenges remain, writes Pete Putman of Display Daily, including lack of production equipment and cameras, high screen costs, and the need for much more bandwidth to carry the larger files.

Unlike 3DTV, ultra-high-def won't give you a headache or require special glasses. It makes sense for future-proofing video production, and it could be a selling point for video venues or sports bars.  But for now, ultra-high-def has gotten far ahead of the home television market, which is getting to like today's low prices.

Bright future for silicon

The Wiley-VCH journal ChemPhysChem issued an embargoed press release embargoed early on the morning of November 21, 2012, heralding "a bright future for silicon." Just eight hours later, they lifted the embargo, citing "early reporting" of the research by Brian Korgel of the University of Texas (Austin, TX) and colleagues.

Embargo breaks often indicate hot stories, and the headline hinted at an important step toward the elusive goal of efficient light emission from silicon. Yet the next line was more muted: "Ordered nanocrystal arrays may provide a new platform to study and tailor the light-emitting properties of silicon." What is the real story?

Silicon is a wonderful material for electronics, but its photonic uses have been hobbled by an indirect bandgap that makes it very hard for electrons dropping into the valence band to release their energy as photons. That leaves silicon far behind III-V compounds like gallium arsenide for LEDs and diode lasers. Yet silicon is far ahead of other semiconductors in electronics, and companies like Intel (Santa Clara, CA) want to integrate photonics into their integrated circuits.

So far they have demonstrated "silicon lasers" by optically pumping Raman lines in silicon and III-V diode laser chips bonded to silicon. Both were important advances. But neither met the real goal--electrically powered emitters based on silicon that could be integrated into standard semiconductor chip production processes.

In their ChemPhysChem paper, Korgel and colleagues take a different approach, tapping the bright luminescence produced by silicon quantum dots. They write that their major achievement is devising a chemical technique that causes self-assembly of "the first colloidal Si nanocrystal superlattices." Self-assembly is essential because individual dots are too small to fabricate by conventional photolithography, and transmission electron microscope images show the dots are closely spaced in regular face-centered-cubic arrangements (see photo).

TEM image silicon nanocrystals in the 111-oriented (c) and 112-oriented (d) plans, with depictions of the crystalline structures shown in insets. (Courtesy Yixuan Yu et al., ChemPhysChem, Wiley-VCH Verlag GmbH & Co. KGaA, http://dx.doi.org/10.1002/cphc.201200738 [2012]. Reproduced with permission)

The authors say that covalent bonds with the hydrocarbon solvent make the silicon-nanocrystal superlattices stable to 350 degrees Celsius, higher than other similar superlattices. That's encouraging news, because self-organized nanocrystals are a promising fresh approach to structuring silicon to emit light more efficiently. But so far electrical excitation--sought for integrated optoelectronics--has far to go to match the efficiency of optical excitation of isolated silicon quantum dots. So Korgel is understandably optimistic about having "a new playground for understanding and manipulating the properties of silicon in new and unique ways," and is appropriately cautious in not claiming silicon lasers are just around the corner.