AUG 2016


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AUGUST 2016 44 CompositesWorld FOCUS ON DESIGN Precision design for deployable space structures Enabling SMAP mission success, unprecedented design requirements were deftly managed using composites in the largest unfurling and rotating reflector to date. » In 2015, NASA's Jet Propulsion Laboratory (JPL, Pasadena, CA, US) launched the Soil Moisture Active/Passive (SMAP) mission to measure ocean salinity and soil moisture from low-Earth orbit (LEO). SMAP's single spacecraft used new instrumentation, comprising an L-band radar and an L-band radiometer with a shared feedhorn and a 6m mesh reflector dish. e reflector is cantilevered out from the spacecraft by a 3.35m long articulated boom. e feedhorn, reflector and boom assembly (RBA) rotate at 14.6 rpm, so that a 1,000-km-wide swath on Earth's surface can be measured continuously, enabling complete scanning of the planet's surface every three days. "e requirements for the rotating RBA on SMAP were unprece- dented in scope," says Daniel Ochoa, the product development manager at Northrop Grumman Astro Aerospace (Carpinteria, CA, US) and part of the engineering team responsible for the final design. "Not only did the deployable RBA have to be exceptionally light and stable to minimize deflection during high-speed rotation, it also had to have extremely accurate and predictable mass properties when spinning." Established in 1958 as Astro Aerospace, Ochoa's group is now a business unit of Northrop Grumman Aerospace Systems (Redondo Beach, CA, US). "Our deployable antennas and struc- tures are orbiting the Earth, the Moon and Mars, and traveling beyond our Solar System on the Voyager spacecraft, still measuring the effects of solar winds and magnetic fields 35 years after launch," he says. With a 100% success rate in mission deployments, the group understood the design challenge SMAP presented. "SMAP is the largest rotating reflector, as well as the largest mass-balanced reflector, ever built. We've built reflectors 12m in diameter, but they don't spin." e dish was designed to be deployable, furled into a small space — 1.83m by 0.36m — for launch, and then, after entry into orbit, unfurled to form a precise reflective surface. Precise, accurate focus in motion To the SMAP's L-band radiometer, very dry soil on Earth appears to be about 300 º K. Very moist soil shows as roughly 100 º K. ese are not physical temperatures, but the temperature of naturally occurring L-band emissions from Earth's surface. "By measuring the brightness By Ginger Gardiner / Senior Editor Soil Moisture Active/Passive (SMAP) mission enabler NASA/JPL's SMAP spacecraft features a deployable reflector dish that rotates to optimize its ability to measure ocean salinity and soil moisture on Earth's surface. It can scan the Earth's entire surface every three days. The measurements now provide data that will help scientists to better understand and predict global processes that link Earth's water, energy and carbon cycles. Source | Northrop Grumman Astro Aerospace

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