Study finds high-energy electrons in space may be to blame for some satellite failures

September 16, 2013 by Jennifer Chu
Study finds high-energy electrons in space may be to blame for some satellite failures
Credit: NASA

Is your cable television on the fritz? One explanation, scientists suspect, may be the weather—the weather in space, that is. MIT researchers are investigating the effects of space weather—such as solar flares, geomagnetic storms and other forms of electromagnetic radiation—on geostationary satellites, which provide much of the world's access to cable television, Internet services and global communications.

Geostationary satellites orbit at the same rate as the Earth's rotation, essentially remaining above the same location throughout their lifetimes. These satellites are designed to last up to 15 years, during which time they may be bombarded by charged particles. Most satellites cover sensitive electronics with layers of protective shielding, but over time, radiation can penetrate and degrade a satellite's components and performance.

"If we can understand how the environment affects these satellites, and we can design to improve the satellites to be more tolerant, then it would be very beneficial not just in cost, but also in efficiency," says Whitney Lohmeyer, a in MIT's Department of Aeronautics and Astronautics.

Lohmeyer is working with Kerri Cahoy, an assistant professor of , to understand how sensitive components are to the weather conditions in space, and how may contribute to failures.

In a paper published in the journal Space Weather, the team analyzed space weather conditions at the time of 26 failures in eight geostationary satellites over 16 years of operation. The researchers found that most of the failures occurred at times of high-energy electron activity during declining phases of the . This particle flux, the scientists theorize, may have accumulated in the satellites over time, creating internal charging that damaged their amplifiers—key components responsible for strengthening and relaying a signal back to Earth.

Lohmeyer says a better understanding of space weather's effects on satellites is needed not just for current fleets, but also for the next generation of communications satellites.

"Users are starting to demand more capabilities," Lohmeyer notes. "They want to start video-streaming data, they want to communicate faster with higher data rates. So design is changing—along with susceptibilities to space weather and radiation that didn't used to exist, but are now becoming a problem."

Space-weather disconnect

Today, engineers design satellites with space weather in mind, using radiation models to predict how much radiation a satellite may be exposed to over its lifetime. Cahoy notes that a satellite's radiation exposure may vary depending on its orbit. For instance, some orbits are more dangerous than others; engineers choose components that can survive and operate in such environments.

"But space weather is a lot more dynamic than models predict, and there are many different ways that can wreak havoc on your satellite's electronics," Cahoy adds. "The hard part about satellites is that when something goes wrong, you don't get it back to do analysis and figure out what happened."

To add another layer of complication, Lohmeyer points out a "disconnect" between satellite engineers and space-weather forecasters.

"The space-weather community provides forecasting mechanisms for companies to help them better operate their satellites, and they may say, 'Space-weather activity is incredibly high right now, we're putting out a warning,'" Lohmeyer says. "But engineers and operators don't really understand what this implies."

Lohmeyer's primary goal, she says, is to bridge the gap between the space-weather community and satellite engineers.

Reading the space forecast

To establish a better understanding of space weather's effects on satellite equipment, Cahoy and Lohmeyer partnered with Inmarsat, a telecommunications company based in London. The researchers analyzed more than 665,000 operational hours of telemetry data from eight of the company's satellites, including temperature and electric-current measurements from the satellites' solid-state amplifiers. From these data, the researchers analyzed scientific space-weather data coinciding with 26 anomalies from 1996 to 2012, the majority of which were considered "hard failures"—unrecoverable failures that may lead to a temporary shutdown of the spacecraft.

The team noted the dates and times of each failure, and then analyzed the weather conditions leading up to each failure, using observations from multiple space-weather satellites. Such observations included solar-flare activity and geomagnetic storms.

Specifically, the researchers analyzed the Kp index, a measurement of geomagnetic activity that is represented along a scale from zero to nine. Satellite engineers incorporate the Kp index into radiation models to anticipate space conditions for a particular spacecraft's orbit. However, as the team found, most of the amplifier failures occurred during times of low geomagnetic activity, with a Kp index of three or less—a measurement that engineers would normally consider safe. The finding suggests that the Kp index may not be the most reliable metric for radiation exposure.

Instead, Cahoy and Lohmeyer discovered that many amplifiers broke down during times of high-energy electron activity, a phenomenon that occurs during the solar cycle, in which the sun's activity fluctuates over an 11-year period. The flux of high-energy electrons is highest during the declining phase of the solar cycle—a period during which most amplifier failures occurred.

Lohmeyer says that over time, such high-energy electron activity may penetrate and accumulate inside a satellite, causing internal charging that damages amplifiers and other electronics. While most satellites carry back-up amplifiers, she notes that over an extended mission, these amplifiers may also fail.

"Once you get into a 15-year mission, you may run out of redundant amplifiers," Lohmeyer says. "If a company has invested over $200 million in a , they need to be able to assure that it works for that period of time. We really need to improve our method of quantifying and understanding the space environment, so we can better improve design."

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1 / 5 (8) Sep 16, 2013
There is nothing good on cable television. We could only hope that solar flares destroyed every television and cable network in existence
2 / 5 (4) Sep 16, 2013
How is this news? Spurious switch off are considered to be caused mainly by electrons even in Space Mission Design first edition.
1 / 5 (10) Sep 17, 2013
Re: "But space weather is a lot more dynamic than models predict"

I say this about every single day on these forums within the context of Hannes Alfven's critique of the way in which astrophysicists are applying MHD to cosmic plasmas. It appears that when the context is satellite failures from transient events, it's okay to critique the MHD models. But, when the context is the science of the cosmos and the electromagnetic nature of cosmic plasmas, such statements are apparently heresy.

Let's say it again for good measure: MHD models which cannot even support the formation of E-fields or electric currents will fail to properly predict the transient events which can disrupt satellites. But, these transient events do much more than disrupt satellites. A plasma model which could not even support the lighting of a fluorescent or neon bulb has no business being applied to the cosmos. The suggestion that cosmic plasmas cannot support electrodynamic behavior is in truth a political act.
5 / 5 (1) Sep 18, 2013
The suggestion that cosmic plasmas cannot support electrodynamic behavior is in truth a political act

You know, the proper term you are looking for is MHD - magnetohydrodynamic. Electrodynamics would be only the fields and currents. MHD is inclusive of ED, but adds the interaction of a fluid medium.

To suggest that anyone denies MHD in plasma is ignorant. Just who are you talking about?

I think you have it backwards. Nobody denies MHD. I think the problem here is that you refuse to accept that gas laws, gravity, conservation of energy and momentum, etc. ALSO still apply to plasma. You cannot ignore all the other laws of physics just because you think MHD is cool.

Your plasma rivers in intergalactic space just don't have any evidence to support them. Your theory is based on Alfven's outdated refusal to accept GR. It's funny that you paint him as a revolutionary, when he was actually a traditionalist refusing to accept the new theory of GR.
5 / 5 (1) Sep 18, 2013
But GSwift, Ancient mystics spoke of leylines traversing the cosmos. Surely that's proof positive that modern physics doesn't know anything about anything and is too short sighted to try to include effects as simple as maxwell's equations to simulations of stars and galaxies. The ancient mystics said so. They were more in touch with nature than us modern peoples, what with our health, and extended lifespans and modern communications equipment and farming techniques...
1 / 5 (4) Sep 26, 2013
One of the reasons plasma is classified as a distinct state of matter is because it does not follow gas laws and its properties of velocity distribution are often non-maxwellian. Maybe a refresher course on what plasma is and the amazing range it exists in would help some of you get your minds around it. Then take a look at some of the data coming back from our probes.

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