10th December 2013

Giant telescope being developed by DARPA

By using lightweight "membrane optics" instead of traditional glass, a new generation of space telescopes could be deployed that reach sizes of 20 metres (68 foot) or larger.

As the need for higher-resolution orbital imagery expands, glass mirrors are fast approaching the point where they will be too large, heavy and costly for even the largest of today's rockets to carry to orbit. DARPA's Membrane Optical Imager for Real-Time Exploitation (MOIRE) program seeks to address these challenges by developing technologies that would make orbital telescopes much lighter, more transportable and more cost-effective. Currently in its second and final phase, the program recently successfully demonstrated a ground-based prototype that incorporated several critical technologies, including new lightweight polymer membrane optics to replace glass mirrors.

Instead of reflecting light with mirrors or refracting it with lenses, MOIRE's membrane optics diffract light. Roughly the thickness of household plastic wrap, each membrane serves as a Fresnel lens — it is etched with circular concentric grooves like microscopically thin tree rings, decreasing from hundreds of microns at the centre, down to only 4 microns at the outside edge. The diffractive pattern focuses light on a sensor that the satellite translates into an image.

MOIRE technology houses the membranes in thin metal "petals" that would launch in a tightly-packed configuration roughly 20 feet in diameter. Upon reaching its destination orbit, a satellite would then unfold the petals to create the full-size, multi-lens optics. The envisioned diameter of 68 feet (about 20 metres) would be the largest telescope optics ever made — dwarfing the glass mirrors contained in the world's most famous telescopes. This behemoth would be even larger than the 16-metre ATLAST observatory planned for 2025.

Looking down from geostationary orbit, it is believed a satellite using MOIRE optics could see approximately 40 percent of the Earth’s surface at once. It could focus on a 10 km-by-10 km region at 1-metre resolution and provide real-time video of this entire area at one frame per second. In its ground-based tests, MOIRE has achieved a technological first for membrane optics by nearly doubling their efficiency, from 30 percent to 55 percent.

Lt. Col. Larry Gunn, DARPA program manager: "Membrane optics could enable us to fit much larger, higher-resolution telescopes in smaller and lighter packages. In that respect, we're 'breaking the glass ceiling' that traditional materials impose on optics design. We're hoping our research could also help greatly reduce overall costs and enable more timely deployment using smaller, less expensive launch vehicles."

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