NASA scientists are gearing up for the launch of its new instrument that can monitor the moisture of the Earth's soil from space.

On Dec. 30, the U.S. space agency announced the scheduled launch of its Soil Moisture Active Passive (SMAP) instrument from the Vandenberg Air Force Base in California on Jan. 29. The instrument, which was designed to accurately measure the level of moisture in our planet's soil, is made up of three main parts: a radiometer, a radar and the largest rotating mesh antenna to be deployed into space.

The antenna, which scientists have dubbed the spinning lasso is what makes SMAP different from other satellites that NASA already has in orbit. One side of the antenna is attached to an arm of the satellite just like a cowboy's lariat. SMAP spins this antenna like a giant lasso swung at about 14 revolutions per minute.

Measuring 19.7 feet in diameter, the antenna was designed in a way that it could be stowed into a one foot by four feet space for launch but it needs to unfold precisely within one-eighth of an inch once SMAP is already in orbit to avoid resolution issues.

"Making sure we don't have snags, that the mesh doesn't hang up on the supports and tear when it's deploying -- all of that requires very careful engineering," said SMAP instrument manager Wendy Edelstein. "We test, and we test, and we test some more. We have a very stable and robust system now."

The satellite's radar will use the antenna for transmitting microwaves towards Earth, where these penetrate into soil and bounce back to SMAP high above the planet, a phenomenon known as backscatter. The changes in the electrical properties of the microwaves that bounce back from Earth would indicate the changes in the soil's moisture as well as tell if the soil is frozen.

SMAP project manager Kent Kellogg said that the objective is to come up with global maps of soil moisture as well as of the freeze and thaw state every two to three days. Once SMAP starts to work at altitude of 426 miles, it is anticipated to help with drought and flood monitoring as well as provide food productivity insights. 

"It will give very useful new regional observations of soil moisture conditions, which will be important for drought monitoring and a wide range of applications related to agriculture," said Forrest Melton, from the Ecological Forecasting Lab at NASA Ames Research Center.

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