Flare path: protecting infrastructure from space weather
Here comes the sun: engineers are beginning to understand how space weather could affect today’s technology
The Northern Lights are normally confined to the highest latitudes within the Arctic Circle, but one day in 1859 the shimmering curtains of light descended far down the globe. Miners in the Rockies thought the bright light behind the mountains was the breaking dawn, clocks being harder to come by than alcohol. The display reached as far south as the Caribbean.
While the auroral displays provoked wonder, for telegraph workers in Europe and North America the night was terrifying. The systems went haywire. Operators recoiled from electric shocks. Pylons emitted showers of sparks. Telegraph paper spontaneously caught fire. Some telegraph systems seemed to send and receive messages even though they had been disconnected from their power supplies.
In London, an amateur astronomer called Robert Carrington saw the news of these occurrences and began to think. The previous day, while observing the sun, he had seen a bright flash seeming to erupt from the edge of the solar disc. Could this be connected with the aurora and the strange electrical disturbances?
Carrington was the first to make the connection between the activity of the sun and geomagnetic storms, and the 1859 event, now known as the Carrington Superstorm, is the most powerful solar storm ever recorded. We now know a great deal more about solar storms, and we know they are not uncommon - the most recent happened only two weeks ago, on Valentine’s Day, and was intense enough to momentarily overwhelm the detectors on NASA’s Solar Dynamics Observatory satellite. We also know that the activity of the sun waxes and wanes according to an 11-year cycle, which has links to phenomena such as sunspots, the dark areas caused by magnetic fluctuations preventing the passage of hot plasma to the solar surface.
However, we are only now starting to come to grips with the implications of the sun’s behaviour on the technology that underpins a large proportion of our lives. While we know that solar storms of varying intensities will continue to occur, and events of the magnitude of the Carrington Superstorm have happened before, the effects of such a storm today could be much more far-reaching.
Back in the 19th century, society was mainly dependent on mechanical power in various different forms. Electricity had only recently begun to take hold in a few applications and its widespread use had yet to begin. But today, we’re almost entirely reliant on electricity, and its cousin electromagnetism, in the form of radio, microwaves and other wireless data transmission techniques. It just so happens that these are the very forms of energy produced by the sun, and this is why solar storms could have such far-reaching effects on today’s infrastructure. As we begin to realise just how interconnected these systems are, we are trying to understand the sun’s effects and how to prevent the worst outcomes.
Solar activity is now increasing after hitting the lowest point on the cycle in 2005; the next solar maximum will occur in 2013. However, the regular highs and lows of the cycle are no guide to the actual intensity of the sun’s activity, according to Prof Cathryn Mitchell of Bath University’s department of electrical and electronic engineering, a specialist in the sun’s effect on GPS, which is one of the most vulnerable systems. ’There’s a lot of variability of the level of activity of each cycle,’ Mitchell said. ’Sunspot activity is a non-stationary process, which means that we can’t predict what’s going to happen in the future by looking at what’s happened in the past.’
Records do exist, however, and they are surprisingly detailed. Records of the strength of magnetic fields were kept in the UK as far back as 1846, and the British Geological Survey has just released a 160-year archive for study. ’There are more than a quarter of a million records in the archive, many on crumbling photographic paper,’ said geo-information specialist Bob McIntosh. ’Preserving these records is essential for the future and for enabling access to the public and scientists alike.’ Head of geomagnetism Alan Thompson added: ’The Carrington Storm caused fires and electrocuted workers at telegraph stations, but what else is there in these records we might find? How might such events affect today’s power grid, if they were to occur again?’
There are three categories of solar effects - commonly known as space weather - on Earth-based infrastructure and orbital systems, Mitchell said. The first comes from electromagnetic radiation. Solar flares produce intense bursts of X-rays. Although the Earth’s surface is shielded from X-rays by its magnetic field and the atmosphere, the radiation will knock electrons out of the gas molecules in the tenuous upper layers of the atmosphere. This will create radio activity that can interfere with satellite signals, especially from GPS. Moreover, in a phenomenon only discovered in 2005, the sun can sometimes produce radio bursts in the same frequency band as GPS and acts as a natural signal jammer. There is no way of predicting these events and no possible early-warning system, Mitchell said, because no warning can travel faster than the speed of light.
The Carrington Storm caused fires and electrocuted workers at telegraph stations. How might such events affect today’s power grid, if they were to occur again?
Alan Thompson, head of geomagnetism, British Geological Survey
Solar flares can also eject sub-atomic particles from the sun, in a phenomenon known as coronal mass ejection (CME). Bursts of protons can erupt from the sun at 0.8 of the speed of light. ’For unshielded satellites and astronauts, these can be very dangerous,’ Mitchell said. ’They also cause irregularities in the ionosphere, the shell of free electrons and ions up to 1,000km above the Earth’s surface, and these can diffract GPS signals and cause them to break up.’ This effect, known as scintillation, was thought to be relatively unimportant, she added, as GPS applications tend to rely on a reading from several satellites and it was thought that a scintillation event would only affect one satellite at a time. ’However, last year a solar event switched off all the satellites over a large area of Alaska.’ Scintillation can last up to a few days after a solar storm.
The third effect is the most severe, caused by a phenomenon called plasma clouds, which are formed by dissociated electrons and protons. When these hit the Earth’s atmosphere, they cause ionospheric storms that can affect electricity distribution infrastructure by inducing large currents in transmission cables, feeding back to transformers, similar to the phantom currents in the telegraph lines in 1859. ’A plasma storm jammed GPS across polar regions recently,’ Mitchell said. ’The ionosphere was ionised over North America, the ions were dragged over the polar regions and then dumped over Europe, causing scintillation that broke up GPS signals all over the continent.’
Large-scale systems across our economy are generally cobbled together from existing systems that weren’t necessarily designed with that application in mind
Mike Hapgood, Rutherford Appleton Laboratory
Effects on GPS are among the most worrying results of space weather, and not just because of navigation. In fact, GPS is one of the prime examples of system interconnectedness. One of its most important uses is, in fact, in timing. Clocks on GPS satellites are used to handle the handover of mobile phone calls from cell to cell; they’re used to schedule aircraft landings as well as in guiding aircraft; and they’re an integral part of financial transactions, including share dealing and currency exchange. ’Large-scale systems across our economy are generally cobbled together from existing systems that weren’t necessarily designed with that application in mind,’ said Mike Hapgood of the Rutherford Appleton Laboratory. ’It’s rare for something to be designed and implemented as a fully integrated system.’ Because of this, he said, GPS has become hugely important, incorporated into many safety-critical, and potentially vulnerable, systems. ’The clocks on these systems are all synched to GPS, but the way to mitigate the risk posed by space weather is relatively straightforward. You need an accurate clock on the base station so you only have to synch occasionally, which will make sure that stations are resilient for, say, a month.’
In other cases, mitigation of space weather effects is best done by accurate modelling. UCL’s Marek Ziebart, an expert in the prediction and analysis of satellite orbits, explained that a satellite’s behaviour is influenced by a complex mixture of a number of factors, including the gravitational fields of the sun, Earth and moon, and even the other planets. After these come the effects of radiation. Electromagnetism transfers momentum to spacecraft, which is known as radiative pressure, and the effect of the sun is the next biggest influence after gravity. ’If you ignored solar radiative pressure, even without solar storms, after 12 hours your prediction would be out by 200m,’ he said.
Positioning is vital to GPS, Ziebart added. ’GPS is entirely predicated on knowing the orbit of your spacecraft and being sure the clock is accurate,’ he said. ’It would not work if you couldn’t predict where the spacecraft is going to be a couple of hours ahead.’
The orbits of the GPS constellation are managed by the Second Space Operations Squadron of the US Air Force (known as 2SOPS), based in Colorado. According to Ziebart, 2SOPS does not model the effect of radiative forces on the spacecraft in great detail. ’If you ignore these things, your ability to predict your orbit for a long time gets degraded,’ he said. This problem is being made less acute by the building of more satellite tracking stations. ’The more widely distributed the stations are, the less problem there is with scintillation,’ Ziebart added.
GPS is entirely predicated on knowing the orbit of your spacecraft and being sure the clock is accurate,’ he said. ’It would not work if you couldn’t predict where the spacecraft is going to be a couple of hours ahead
Marek Ziebart, UCL
Positioning is perhaps even more vital for the scientific community. ’If you’re trying to measure sea level, the polar icecaps or plate tectonics, or build a tsunami warning system, having your satellite position a centimetre out from where you think it is will have a significant effect,’ Ziebart said. Factoring in the effect of the extra radiation or of particle collisions from solar activity is an important step.
Most observers agree, however, that predictions of infrastructure apocalypse in the press are overstated. ’People sometimes say that if we lose the signal from GPS then the internet will fail,’ said Hapgood. ’I don’t believe that’s true.’ The risk shouldn’t be understated though. ’Insurance companies worry about one-in-200-year risks,’ he added. ’And there was a big storm in 1999 that was a one-in-60-year event. We’re looking at events that might happen once or twice in the lifetime of major electricity infrastructure, such as transformers. It is something that has to be considered.’
ray of fright
Cosmic rays are believed to be the biggest source of error in digital technologies
While increasing activity from the sun is a major focus of concern, there are also problems associated with the periods of low activity. The solar wind protects the Earth from bombardment by cosmic rays - high-energy particles that originate outside the solar system. ’When solar activity is low, cosmic ray activity goes up, and that’s a big issue with aviation,’ said Mike Hapgood from the Rutherford Appleton Laboratory. ’If a particle passes through a chip in a processing system, it can flip the bits, and that can change the data or the software response in an uncontrolled way.’
Cosmic ray hits are estimated by Intel to be the biggest source of error in digital technologies in systems both in the air and on the ground. They have been blamed for incidents such as one in 2008, when a Qantas Airbus A330 went into two rapid dives, losing 650ft and 400ft in rapid succession in a matter of seconds.
’For safety-critical systems, the main response is to make sure that we have at least triple redundancy,’ Hapgood said. ’If you get a hit on one processing train, then the other two can outvote it.’ Another option might be to increase the shielding around safety-critical electronics. But Hapgood added: ’You can’t wrap an aircraft in lead shielding. The question is, if you have a severe cosmic ray episode or a severe solar storm, is there a chance that there would be sufficient hits to break that redundancy?’
Studies are under way to assess the vulnerability of the computer control systems inside vehicles. ’This is a serious issue because we don’t understand all the implications of electronics in cars, in this context,’ Hapgood said. ’The last thing you want is for a cosmic ray to set off your airbags on the motorway.’