Animation of the Soil Moisture Active Passive spacecraft spinning its antenna while orbiting Earth.Youtube video

This Thursday, March 19, NASA's latest mission will begin preparation for its next great milestone: making the wicked-amazing antenna rotate.

A number of spacecraft have rotating parts, such as the RapidScat mission and the Global Precipitation Measurement (GPM) mission, but those don't hold a candle to the dynamics of Soil Moisture Active Passive (SMAP).

SMAP's antenna is 20 feet in diameter. The larger the antenna, the more complex its behavior can be, which makes it more difficult to control. Just imagine swinging a 20-foot baseball bat over your head. Yikes!

Right now the antenna is locked in position until the mission "ops" (operations) team completes its checks of the entire instrument's function and confirms operability. They have taken measurements with the radar and the radiometer. They know the instruments are working by comparing the measurements to how they were tested on the ground before launch. The signals look appropriate; they're seeing what's expected. But the antenna's fixed position means it's measuring only a small strip of the ground below.

Once the antenna starts to spin, we'll be able to measure a much larger area and monitor soil moisture around the entire Earth every two to three days.

These are the three steps to achieving "spin up":

1. Engineers unlock the antenna.

2. A few days later, they spin the antenna slowly.

3. They gradually spin it faster.

At each step, they'll verify how it's performing. The engineers will then conduct a more comprehensive checkout of the instrument's systems. With the antenna spinning, they'll get to see the instrument's full performance for the first time.

After the spinning checkouts are completed ... Voilà! Bibbidi bobbidi boo! SMAP will start mapping global soil moisture and return data!

I look forward to your comments.

- Laura

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TAGS:EARTH, SMAP, SOIL MOISTURE, SPACECRAFT, CLIMATE,

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