SMAP Radar Failure Leaves Big Hole in Mission

NASA and the scientific community are trying to stay upbeat and positive following the failure of one of the two main instruments on the agency’s Soil Moisture Active Passive (SMAP) satellite, saying the mission will soldier on and conduct meaningful science with its remaining sensor.

That’s well and good, but there’s no whitewashing the reality that a billion-dollar mission now will not meet its basic science objectives.

For reasons NASA has yet to determine, or at least fully disclose, SMAP’s active radar sensor suffered a component failure and ceased operating in July, just two months after the high-priority Earth science mission, which launched in January, completed on-orbit testing.

NASA announced Sept. 2 that it had ended efforts to resuscitate the sensor, designed to bounce radio signals off Earth to make high-resolution soil moisture maps. The agency said the otherwise healthy spacecraft would carry on with its passive radiometer instrument, which has much-coarser spatial resolution than the radar but takes more-accurate moisture readings.

SMAP was designed to create high-fidelity global maps, updated every two to three days, of soil moisture and freeze/thaw states to help scientists better understand how both factor into seasonal and climate changes. The mission, also expected to aid the prediction of floods, drought, agricultural productivity and weather, was one of four endorsed for implementation in the near term by the National Research Council in its 2007 decadal survey of Earth science priorities.

“Although some of the planned applications of SMAP data will be impacted by the loss of the radar, the SMAP mission will continue to produce valuable science for important Earth system studies,” Dara Entekhabi, SMAP science team lead at the Massachusetts Institute of Technology in Cambridge, said in statement that accompanied NASA’s release of the bad news.

NASA Earth Science Director Michael Freilich struck a similar tone, suggesting that even the degraded mission satisfies at least some of the scientific objectives laid out in the decadal survey. “Measurements of the radiometer-only SMAP mission will advance that science and form the basis for a host of applications consistent with the recommendations in the decadal survey,” he said.

Both statements are no doubt technically correct, but they understate the consequences of losing the active radar.

As outlined by NASA, the baseline science requirements of the mission are fairly clear: soil moisture measurements with a spatial resolution of 10 kilometers at three-day average intervals; freeze/thaw-state measurements at 3-kilometer resolution; and continuous collection of both over a three-year period. The ability to achieve those resolutions was largely dependent on the radar, whose data were to be combined with the lower-resolution but more moisture-sensitive readings from the radiometer.

It doesn’t take an Earth or climate scientist to see that a radiometer-only mission falls short of those requirements. According to mission literature, freeze/thaw-state measurements, important for understanding the global carbon cycle, were almost entirely dependent on the active radar.

NASA is developing new algorithms to enhance the value of the radiometer-only data, and scientists now believe that sensor can also be used for freeze/thaw-state measurements. Scientists have also raised the possibility of relying on satellites operated by Europe and Japan to replace the radar measurements, although the viability of this option is unclear.

Much credit is due to NASA and the SMAP science team for making the best of a bad situation. If their assessments of what can be accomplished with the radiometer are correct, then obviously there is meaningful science to be salvaged from the mission, even it falls well short of the initial objectives.

But the fact that NASA is not pursuing a replacement mission, despite the high priority assigned to SMAP, likely is due more to budget reality than — as Mr. Freilich suggested — the quality of the radiometer data. Funding for new missions, in particular billion-dollar-class Earth science missions, is tough to come by, and that would be the case even if members of Congress’ Republican majority were more enthusiastic about climate change research.

That leaves NASA and scientists to contemplate what might have been, notwithstanding their admirable salvage efforts.

Volker Liebig, director of Earth observation at the European Space Agency, which is utilizing SMAP’s unfurlable antenna technology — this hardware was not implicated in the radar failure — for its Biomass spacecraft, called the loss of SMAP’s radar a “very sad day” for NASA and the Earth science community. “I am not aware of any similar instrument being built anywhere else,” he said. “It is a real loss.”


Brian Berger is editor in chief of and the SpaceNews magazine. He joined in 1998, spending his first decade with the publication covering NASA. His reporting on the 2003 Space Shuttle Columbia accident was...