Despite being made to withstand radiation emitted from solar flares, a storm caused by the sun earlier this month may have temporarily knocked American military satellites offline, according to General William Shelton, head of the Air Force's Space Command.
The energy particles associated with two solar storms March 9 and 10 may have caused what are called "single event upsets" on military satellites. "The timing is such that we say this was likely due to [solar radiation]," Shelton told reporters at a Defense Writers Group breakfast Thursday. Although it's impossible to tell exactly what caused the events—essentially a temporary reboot of satellite instrumentation software—solar storms are known to wreak havoc on satellites.
"We're very concerned about solar activity," he said. Military satellites are "hardened [to withstand radiation], but maybe in some cases, not every part is as hard as we would like it to be."
That's because building a satellite to withstand solar storms is costly, which is why NASA says commercial satellites are often most vulnerable. Yihua Zheng, head of NASA's Space Weather Services at Goddard Space Flight Center in Greenbelt, Md., says each satellite is built to withstand a different level of radiation, and that there's a "cost-benefit analysis" to radiation hardening during a satellite's development. Most mission-critical military satellites are built to sustain short bursts of solar radiation. Satellites "can reset and come back online." But if the solar storm is lengthy, the damage could be severe enough that the satellite's software won't be able to reboot.
"Most of the satellites are built for this," she says. "They should be OK."
In recent years, the military has become more reliant on satellites operated by the Air Force's Space Command, Shelton said. "Space capability is integral to everything [the military does]," he said, "from GPS targeting and communications to incoming missile warnings for our troops overseas."
Shelton said the outages following this month's solar storms didn't affect any missions. "There were dire predictions preceding [these flares]," he said. "We didn't see it to that degree."
Zheng says NASA alerts the Air Force whenever a solar flare is incoming, and they have about 20 minutes of advance notice to de-activate sensitive instruments onboard satellites.
"They can turn sensitive instruments off as a preventative measure," she says. "They can go into a 'safe mode.' Once the storm dies down, they can turn it back on." Shelton says that NASA's close relationship with the Air Force space command gives them good "advance notice of when a solar storm is headed our way."
NASA says the recent wave of solar storms is only likely to intensify through the end of 2012, but Shelton believes the military's satellites will be able to withstand any future storms.
"I don't believe that anything—short of something truly catastrophic, that would be catastrophic to those of us on Earth as well, I don't believe there's a scenario where we'd wholesale lose spacecraft," Shelton said.