BEELION-dollar lasso snaps, NASA mapper blind in one eye

The active radar portion of the “spinning lasso” antenna attached to NASA's SMAP satellite, launched in January, has stopped functioning and can't be recovered.

Luckily for the space agency, it doesn't put an end to the entire near-billion-dollar mission, because the other half of the spacecraft's mission, a radiometer instrument, is still functioning. This passive instrument continues to receive, using the same lasso antenna as the active instrument used.

SMAP – the Soil Moisture Active Passive observatory – is an earth-sensing mission that ran two instruments. The “lasso”, a six-metre mesh that circled every four seconds, mapped soil moisture with radar signals.

These penetrated a few centimetres into the soil, and backscatter of the returning signals would indicate the amount of soil moisture in areas about a mile wide at a time.

The passive instrument, a radiometer, picks up microwave signals emitted from wet soils. When the two were both working, their measurements could be compared to each other.

Alas, in July, the radar antenna stopped transmitting data, with NASA determining that there was a problem with its high power amplifier.

More than a month's work followed as ground crews tried to diagnose the problem and reproduce it in laboratories. On August 24, they tried to re-start the unit, but failed.

That's led the agency to concede that the antenna can't be revived, and the mission will just have to continue without it using the passive collector.

That crimps the mission somewhat, but NASA reckons it will still get good data from the passive instrument:

“Without the radar, the mission's resolving power will be limited to regions of almost 25 miles (40 kilometers) for soil moisture and freeze-thaw. The mission will continue to meet its requirements for soil moisture accuracy and will produce global soil moisture maps every two to three days,” NASA says.

Other measurements have been identified since the mission began, including sea surface salinity, and detection of high winds on the ocean surface.

“NASA has appointed a mishap investigation board to conduct a comprehensive review of the circumstances that led to the HPA anomaly in order to determine how the anomaly occurred and how such events can be prevented on future missions. JPL also will convene a separate failure review board that will work with the NASA investigation”, the statement says. ®