Although the antenna must fit during launch into a space not much bigger than a tall kitchen trash can, it must unfold so precisely that the surface shape of the mesh is accurate within about an eighth of an inch.

The mesh dish is edged with a ring of lightweight graphite supports that stretch apart like a baby gate when a single cable is pulled, drawing the mesh outward.

“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. We have a very stable and robust system now,” the SMAP instrument manager said.

SMAP’s radar uses the antenna to transmit microwaves towards Earth and receive the signals that bounce back, called backscatter.

The microwaves penetrate a few inches or more into the soil before they rebound. Changes in the electrical properties of the returning microwaves indicate changes in soil moisture, and also tell whether or not the soil is frozen.

Using a complex technique called synthetic aperture radar processing, the radar can produce ultra-sharp images with a resolution of about one to three kilometres.

The SMAP will be the fifth NASA Earth science mission launched within the last 12 months.

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