NASA’s Moisture Active Passive (SMAP) instrument is all set to measure the moisture lodged in Earth’s soils with an unprecedented accuracy and resolution. The instrument’s consists of three main parts – a radar, a radiometer and the largest rotating mesh antenna ever deployed in space.
It is scheduled for launch on January 29. 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, the US space agency said in a statement.
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 centimeters) for launch.
Wendy Edelstein of NASA’s Jet Propulsion Laboratory, Pasadena, California, SMAP instrument manager said, “We call it the spinning lasso.” He said that the antenna is attached on one side to an arm with a crook in its elbow, which spins around the arm at about 14 revolutions per minute (one complete rotation every four seconds).
He added, “The antenna caused us a lot of angst, no doubt about it.”
While SMAP’s radar uses the antenna to transmit microwaves toward Earth and receive the signals that bounce back called backscatter, SMAP’s radiometer detects differences in Earth’s natural emissions of microwaves that are caused by water in soil.
As per the statement by NASA, combining the radar and radiometer signals allow scientists to take advantage of the strengths of both technologies while working around their weaknesses.
The SMAP will be the fifth NASA Earth science mission launched within the last 12 months.