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Technical innovations spin NASA's SMAP into space

30 December 2014

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It's active. It's passive. And it's got a big, spinning lasso. Scheduled for launch on 29 January 2015, NASA's Soil Moisture Active Passive (SMAP) instrument will measure the moisture lodged in Earth's soils with an unprecedented accuracy and resolution.

The instrument's three main parts are a radar, a radiometer and the largest rotating mesh antenna ever deployed in space.

Remote sensing instruments are called "active" when they emit their own signals and "passive" when they record signals that already exist. The mission's science instrument ropes together a sensor of each type to corral the highest-resolution, most accurate measurements ever made of soil moisture -- a tiny fraction of Earth's water that has a disproportionately large effect on weather and agriculture.

To enable the mission to meet its accuracy needs while covering the globe every three days or less, SMAP engineers at NASA's Jet Propulsion Laboratory in Pasadena, California, designed and built the largest rotating antenna that could be stowed into a space of only one foot by four feet (30 by 120 centimetres) for launch. The dish is 19.7 feet (6 metres) in diameter.

Source: National Aeronautics and Space Administration (NASA)

Image credit: NASA - Artist's concept of SMAP

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