NASA’s Upcoming SMAP Mission Critical to Understanding Earth’s Soil Moisture Influence on Weather and Climate

NASA's Soil Moisture Active Passive (SMAP) mission will produce high-resolution global maps of soil moisture to track water availability around our planet and guide policy decisions. Image Credit: NASA/JPL-Caltech

NASA’s Soil Moisture Active Passive (SMAP) mission will produce high-resolution global maps of soil moisture to track water availability around our planet and guide policy decisions.
Image Credit: NASA/JPL-Caltech

Five new earth science missions launched in the last 12 months will wrap up with liftoff of NASA’s Soil Moisture Active Passive (SMAP) mission at the end of January, a mission which will produce high-resolution global maps of water located in Earth’s soil, providing data on the fresh water availability around our planet to help give scientists a better understanding of agricultural productivity, climate change, and weather.

Launched in 2014 to study climate and weather on Earth were NASA’s Global Precipitation Measurement (GPM), Orbiting Carbon Observatory (OCO)-2, and ISS-RapidScat. As for 2015, NASA’s Cloud-Aerosol Transport System (CATS) is scheduled to launch this weekend, on the SpaceX CRS-5 Commercial Resupply Services (CRS) mission to the ISS, and SMAP is scheduled to launch from Vandenberg Air Force Base in California on Jan. 29. This concludes an incredibly big year for the space agency, because NASA hasn’t launched this many earth science missions in over a decade.

The $916 million SMAP mission will provide data on water’s last place of hiding on Earth—in the soil. Water is a requirement for life (as we know it) and the daily activities we perform as humans. Some 97 percent of the Earth’s water is in the oceans, with the remaining majority locked in the polar ice caps; only a very small fraction of Earth’s water is locked in the soil and present in the form of fresh water in lakes and rivers. But that small fraction of soil moisture has a huge impact on our future water resources, as well as climate change and weather forecasting over a long period of time, and having an understanding of how these changes may affect food production, drought, and water supply is important for policy makers and many industries (such as agriculture).

We must understand the details of how water moves within and between the atmosphere, the oceans, and the land if we are to predict changes to our climate and the availability of water resources,” said Michael Freilich, director of NASA’s Earth Science Division in Washington in a January 2014 release. “Coupled with data from other ongoing NASA missions that measure sea-surface salinity and that detect changed in underground aquifer levels, with GPM and SMAP we will have unprecedented measurements of our planets vital water cycle.”

Christine Bonniksen, SMAP program executive with the Science Mission Directorate’s Earth Science Division at NASA Headquarters, talks to the media during the SMAP media briefing at NASA Headquarter on January 8 2015.  Image credit: NASA/Aubrey Geminani

Christine Bonniksen, SMAP program executive with the Science Mission Directorate’s Earth Science Division at NASA Headquarters, talks to the media during the SMAP media briefing at NASA Headquarter on Jan. 8, 2015.
Image credit: NASA/Aubrey Geminani

According to NASA’s SMAP mission overview, the uncertainties on current climate models disagree on whether there will be more or less water regionally in the future when compared to today. Climate models will be enabled and brought into agreement on the future availability of water resources because of SMAP data, and these reasons led the Committees Water Resources Panel to give SMAP the highest mission priority within its field of interest. The mission is also one of four first-tier missions recommended by the National Research Council’s Committee on Earth Science and Applications from Space.

NASA held a media briefing on SMAP this past Thursday, Jan. 8, at NASA Headquarters in Washington, D.C. A panel of scientists and program managers spoke to members of the media about the mission and its function.

This dual instrument was key to the National Academies of Science Earth Science 2007 Decadal Survey ranking of this as a tier one mission,” said Christine Bonniksen, SMAP program executive with the Science Mission Directorates Earth Science Division at NASA Headquarters. “NASA is very excited by the fact we’re able to launch this within 10 years of receiving that recommendation.”

NASA’s Science Mission Directorate engages with the science community to identify and put priority to the leading-edge scientific questions. They do this through the National Research Council (NRC), which conducts studies to provide a community consensus on the important questions asked by NASA and other government entities. NASA states that the most comprehensive of these studies in these areas of NASA’s research are decadal surveys. NASA and partners ask the NRC once every 10 years to look a decade into the future and select areas of research, observations, and the supposed missions to make those observations.

In an AmericaSpace article announcing the arrival of SMAP at Vandenberg Air Force Base (AFB) in October 2014, it was noted that in order to meet all of the missions requested science objectives laid out in the Decadal Survey, SMAP’s definition team had to implement a design similar to a previously small mission that was cancelled due to budget costs, called Hydros. Based on the Hydros design, “SMAP will utilize a single, large, 6-meter-wide, deployable gold mesh antenna that will be shared by the missions two science instruments: a synthetic aperture radar and a passive radiometer which will be operating in the L-band frequency range of the microwave spectrum between 1.20-1.41 and GHz, where the Earth’s atmosphere is highly transparent. Mounted on top of a moving platform that will be constantly spinning at a rate of 14-RPM, SMAP’s antenna will produce a conical-shaped scanning beam which will continuously image a large 1,000-km-wife swatch of the surface as the satellite will be circling the Earth from its planned 685-km-high, high-inclination near-polar, Sun-synchronous orbit.”


VIDEO CREDIT: NASA / JPL

This special orbit will allow SMAP to scan the top five centimeters of soil on the surface of the Earth in 2-3 days. The measurements provide unique information relevant to a variety of disciplines including climate, carbon cycle, hydrology, and the meteorological, environmental, and ecology applications communities. Throughout SMAP’s three-year mission, scientists will have invaluable data regarding the global coverage of soil moisture and freeze/thaw measurements.

Kent Kellogg, SMAP project manager at NASA JPL, explained the launch sequence of the satellite in the media briefing at NASA Headquarters on Thursday. SMAP will launch on Jan. 29 from Space Launch Complex-2 at Vandenberg AFB in California atop United Launch Alliance (ULA) Delta II rocket. Once the rocket’s first stage is spent the second stage will fire, then go quiet for, “a fairly long unpowered coast period, followed by a brief second burn of the second stage which will deposit us very close to our final science orbit,” said Kellogg. “As soon as we separate from the second stage we’ll release the solar array, stabilize the spacecraft, and initiate communication with the ground through TDRS. We should achieve a power positive condition on the observatory as early as 8 minutes after separation, or it could take as long as 50 minutes depending on the configuration and orientation of the spacecraft after separation.”

Two views of the SMAP Observatory, showing the Instrument (upper portion) and Spacecraft (lower portion) with the large antenna and solar array stowed for launch. This compact shape is needed to fit comfortably inside the launch vehicle’s protective fairing. (Image Credit: NASA)

Two views of the SMAP Observatory, showing the Instrument (upper portion) and Spacecraft (lower portion) with the large antenna and solar array stowed for launch. This compact shape is needed to fit comfortably inside the launch vehicle’s protective fairing. (Image Credit: NASA)

SMAP’s team on the ground will spend the first two weeks checking out the spacecraft’s systems. Then they will begin the deployment sequence for the large reflector boom antenna. This antenna deploys in two steps, starting 16 days after launch, which takes approximately 16 minutes. Twenty days after launch, the large antenna will unfurl at 12 inches in diameter and it will “bloom” out to around 7 feet in diameter, and then the power deployment will deploy the antenna out to its largest size of 6 meters (20 feet) in diameter. The process, according to Kellogg, takes about 30 minutes to complete. They will spend several days making sure the deflector is rightfully deployed and SMAP is behaving as they expected it to. Once the antenna is deployed, they will observe the instruments, perform final adjustments, and then begin the process of spinning the antenna up approximately 50 days after launch. The antenna is SMAP’s most prominent feature and the “eye” of the instrument.

The antenna and its gold-plated wire screen focus the radio frequency (RF) energy collected by the observatory’s radar and radiometer, and the area measured on Earth is a 40 km (25 mile) area in diameter. According to the SMAP specifications fact sheet, this is the smallest area for which SMAP directly measures soil moisture, which is then reduced to 1 km (0.5 miles) using a radar process called “aperture synthesis.” The antenna works somewhat like a handheld flashlight. Located at the base of the antenna boom, the feedhorn lights up the massive reflector that creates a narrow beam to illuminate the Earth below. The beam is tilted at a 40 degree angle, that way the spot on the Earth is shifted about 500 km (310 miles) from right under SMAP. The spot moves in a 1000-km (620-mile) diameter around the observatory when the antenna spins. This creates the wide band of measurement that is essential to SMAP when measuring the entire Earth every 2-3 days. The observatory’s 14.6-RPM spin rate insures that the radar and radiometer measurement timing is continuous around the circle.

As SMAP maps Earth’s surface, the data is stored by the spacecraft’s computer memory and then transmitted to waiting NASA ground stations two to three times every orbit. Once the data is received on ground, the SMAP instrument data are moved over internet links to the observatory’s science data processing system at JPL. The data will undergo much calibration and processing to create the freeze/thaw and soil moisture measurements.

SMAP will return approximately 135 Terabytes of information from orbit over its three-year mapping mission, although—if history is any indication—SMAP will hopefully be in service for a lot longer than three years, especially since the satellite is not restricted by the use of liquid propellants.

 

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