IMAGE:TRMM observes the 3-D rain structure of Hurricane Katrina on Aug. 28, 2005, including the red spikes known as hot towers that appear where the storm is most intense. The... view more

In 1997 when the Tropical Rainfall Measuring Mission, or TRMM, was launched, its mission was scheduled to last just a few years. Now, 17 years later, the TRMM mission has come to an end. NASA and the Japan Aerospace Exploration Agency (JAXA) stopped TRMM's science operations and data collection on April 8 after the spacecraft depleted its fuel reserves.

TRMM observed rainfall rates over the tropics and subtropics, where two-thirds of the world's rainfall occurs. TRMM carried the first precipitation radar flown in space, which returned data that were made into 3-D imagery, enabling scientists to see the internal structure of storms for the first time.

TRMM also carried a microwave imager, a state-of-the-art instrument that had the highest resolution images of rainfall at the time. Together with three other sensors - the Visible and Infrared Scanner (VIRS), the Lightning Imaging Sensor (LIS), and the Clouds and the Earth's Radiant Energy System (CERES) instrument - scientists used TRMM data to explore weather events, climate, and Earth's water cycle.

The cutting-edge TRMM instruments arrived in orbit at the right time to take advantage of the explosion of computing power and major advances in data-sharing.

"In the early 1990s, sharing data consisted of nine-track data tapes in the mail," said research meteorologist George Huffman at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "By the time you got to the 2000s, it became possible to actually share data online. Once we got that piece in place, people were asking, 'Oh, can you send me that data?' Eventually they wanted to see it all the time."

Scientists at Goddard originally intended TRMM's data to be used purely for precipitation research, but before long, people and organizations outside NASA were using it for a variety of purposes.

"The data were being heavily used for tropical cyclone monitoring and forecasting," said TRMM Project Scientist Scott Braun at Goddard. "It was being used for flood detection and monitoring. It was also used for drought monitoring, disease monitoring -- where diseases are most prevalent in areas of heavy precipitation and flooding."

The scientific community considered TRMM's data so critical to research and many practical applications that in 2001, at the end of TRMM's primary mission, NASA wanted to extend the mission for as long as possible.

TRMM's original flight altitude was optimized for the precipitation radar. To obtain precipitation profiles through the depth of the lower atmosphere and to concentrate the measurements in the tropics, the orbit was confined to 35 degrees north to 35 degrees south latitude at an altitude of 350 km (217.5 miles). At this altitude, Earth's atmosphere is still sufficiently dense to cause drag on the spacecraft, slowing it down, which progressively lowers its altitude.

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The TRMM rainfall mission comes to an end after 17 years