DARPA shoots for 20 meter folding space telescope

The DARPA MOIRE program will create the first-ever images using lightweight membrane optics, which could help redefine how we build, launch and use orbital telescopes.

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. Membrane optics traditionally have been too inefficient to use in telescope optics. MOIRE has achieved a technological first for membrane optics by nearly doubling their efficiency, from 30 percent to 55 percent. The improved efficiency enabled MOIRE to take the first images ever with membrane optics.

While the membrane is less efficient than glass, which is nearly 90 percent efficient, its much lighter weight enables creating larger lenses that more than make up the difference. The membrane is also substantially lighter than glass. Based on the performance of the prototype, a new system incorporating MOIRE optics would come in at roughly one-seventh the weight of a traditional system of the same resolution and mass. As a proof of concept, the MOIRE prototype validates membrane optics as a viable technology for orbital telescopes.

MOIRE would have 70 times the collecting area of the Hubble and would have over 8 times the diamter

“Membrane optics could enable us to fit much larger, higher-resolution telescopes in smaller and lighter packages,” said Lt. Col. Larry Gunn, DARPA program manager. “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.”

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, with the grooves hundreds of microns across at the center 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 20 meters (about 68 feet) would be the largest telescope optics ever made and dwarf the glass mirrors contained in the world’s most famous telescopes.

From GEO, it is believed, a satellite using MOIRE optics could see approximately 40 percent of the earth’s surface at once. The satellite would be able to focus on a 10 km-by-10 km area at 1-meter resolution, and provide real-time video at 1 frame per second.

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