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AUG 2016

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45 CompositesWorld.com SMAP Deployable Reflector Design temperature of a plot of soil, you can quickly estimate what the water content is down to about 4% accuracy, which is pretty incredible," explains Kent Kellogg, JPL's SMAP project manager. He notes that the L-band radar is much less accurate but contrib- utes high resolution. "e real aperture resolution of the radio- meter, which is basically the spot size it reads on Earth, is 40 km," says Kellogg. "But with the radar, we can generate what's called a synthetic aperture by making a series of measurements as the satel- lite is orbiting overhead." Kellogg says this creates a virtual antenna that's much larger than the 6m reflector, improving the radar's resolution to as fine as 1 km. us, the accuracy of dish size and shape are key. Kellogg likens it to a parabolic mirror with a flashlight out in front at the focal point. All the light rays are collected by the mirror into a focused beam, Illustration / Karl Reque Northrop Grumman SMAP Deployable Reflector Dish › A 6m-diameter composite reflector frame that could be collapsed into a 1.83m by 0.36m envelope for launch, weigh less than 13 kg and then deploy as expected in the zero-gravity LEO environment. › A composite boom stiff enough to extend the reflector 3.35m off the spacecraft's spin deck at a 40° angle and to hold the antenna in expected alignment without distortion at 14.6-rpm rotation speeds. › The reflector boom assembly (RBA) corrects the spin-induced constant pointing error (caused by centripetal forces) by 350 millidegrees, and accounts for a 2-cm deflection in the reflector tip furthest from the boom.

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