With the failure of its active radar less than a year into the mission, NASA’s Soil Moisture Active Passive observatory is crippled but functional. Thankfully, the passive radiometer is still working perfectly, salvaging the satellite.
Launch of the SMAP observatory on January 31, 2015 from Vandenberg Airforce Base in California. Image credit: NASA/Bill Ingalls
The Soil Moisture Active Passive (SMAP) observatory launched on January 31, 2015. It hit the right orbit and deployed properly, downlinking first calibrated data in April. That data is still being processed by NASA, but we should be seeing initial maps of global soil moisture levels this month and a full data release by November. But this summer, something went terribly wrong.
Water volume in the top 5 centimeters (2 inches) of soil from April 15 to April 22, 2015. Wetter areas are blue, drier areas are yellow, and frozen areas are white. Image credit: NASA/SMAP/Mika McKinnon
Like any good horror movie, the first indicator was mild. An anomaly cropped up at 2:16pm on July 7th, with SMAP halting radar transmissions. Everything else continued normally, and the spacecraft kept collecting data with its passive radiometer.
The mission team tried troubleshooting the problem. And poked at it, and prodded, and finally figured out that an anomaly in the low-voltage power supply was causing problems for the radar’s high-power amplifier. Without the amplifier to boost power levels of the radar pulse to over 500 watts, the scattered energy would be far too spread out to be measured by the satellite. Yet even after identifying the source of the problem, the radar instrument stayed in safe mode. After a summer of troubleshooting, the team tried to power up the radar unit August 24th. They failed.
Finally, they surrendered to the inevitable: On September 2, 2015, SMAP’s mission scientists declared the radar unit lost. The active and passive instruments were designed to complement each other, but the mission is still possible even with the radar dead. Relying only on the passive radiometer, the observatory’s resolution is fuzzier, dropping from areas 9 kilometers (5.6 miles) across for soil moisture or 3 kilometers (1.9 miles) for freeze-thaw regions to a much coarser 40 kilometers (25 miles) for each characteristic. That, and “Active” part of the observatory’s name is now a painfully lingering relic of potential science now lost.
Data from field measurements of soil moisture are essential for calibrating the satellite data. Image credit: Amy McNally
The SMAP observatory collected nearly three months of data with all instruments functioning, more with just the passive instruments. The data tracks soil moisture and freeze-thaw conditions, an entirely novel dataset for researchers investigating our planet’s water, earth, and carbon cycles. Scientists are also finding ways to use the radiometric data to monitor sea surface salinity and surface wind speeds.
The observatory is in the first year of its planned three-year mission, with the possibility of extensions prolonging the mission after that. Once it hits its stride, it’ll be able to produce global maps every two to three days.