by Debbie Linton
Like ships on the ocean, satellites travel space’s vast ocean. Being hundreds or even thousands of miles above the earth doesn’t make satellites immune from the effects of weather … space weather, that is. The environment of space is anything but stable. In fact, it’s quite turbulent.
Space weather is used to describe the effect of the sun and the solar wind across the expanse of space. When this weather is agitated and rough, satellites can be damaged or their systems disrupted. If those satellites are supporting warfighter communications, the results can be devastating.
When the world welcomed the new millennium with parties and global celebrations, it also ushered in the height of the solar maximum’s 23d cycle. The sun, as does the earth, has its seasons, but the sun’s major cycle of seasons takes 11 earth years. The solar cycle can be described as an 11-year time period that determines the space environmental "season." Just as thunderstorms occur on earth more frequently during the summer, the solar maximum is the period during that 11-year solar cycle when the number of sunspots (strong magnetic regions on the sun) is the greatest. The last solar maximum occurred in 1989.
|The peak of the 11-year solar cycle is on us now. Agencies such as the National Oceanic and Atmospheric Agency chart the cycle's progression by observing the number of sunspots. Over the past 300 years, the average number of sunspots has waxed and waned in an 11-year sunspot cycle.|
During the solar maximum, the number and intensity of solar storms increase. This affects the earth and the satellites in orbit around the earth. Sunspots, appearing as blemishes, are caused by magnetic disturbances on the sun’s surface.
A sunspot is often referred to as a magnetic "storm." As this storm grows stronger, the sunspot erupts in a solar flare and ejects streams of subatomic particles along with solar wind (known as plasma), cosmic rays, X-rays and gamma rays into space. These flares – which explode from the sun’s surface – are the largest and most violent events in the solar system. The magnetic energy generated by solar flares can reach the equivalent of about 40 billion Hiroshima-sized atomic bombs. Solar flares give off radiation that includes X-rays, ultraviolet rays and charged particles called protons and electrons.
Another source of solar material in space is a "coronal mass ejection." CMEs are violent eruptions of enormous gas bubbles that occur in the outer solar atmosphere. When a CME occurs, billions of tons of energy particles are spewed out into the interplanetary medium (the area between the sun and the planets) at hypersonic speeds.
|The solar surface is constantly active; a CME can be seen in this photo. A large CME can contain more than a billion tons of matter than can be accelerated to several million miles per hour in a spectacular explosion.|
Energy and charged particles can reach earth one to four days after a solar event. They buffet the magnetosphere, earth’s invisible magnetic field extending far out into space, and can result in geomagnetic storms. During a geomagnetic storm, this solar energy is transferred to the magnetosphere, causing earth’s magnetic field to change rapidly in direction and intensity. The interaction between the solar wind and earth’s magnetic field results in the creation of the aurora borealis and aurora australis, magnificent bands of color widely known as the Northern and Southern Lights, respectively.
|Aurora australis (Southern Lights) over the South Pole Station, Antartica.|
|Aurora australis shot from Kangaroo Island, South Australia.|
|Aurora borealis (Northern Lights) at Anchorage, Alaska.|
Solar energy can amplify currents flowing through the atmosphere and in electrical wires on earth. The surge of extra current can blow out transformers, disrupt communications, overload power systems and leave millions of people stranded and in the dark.
Satellites orbiting earth are particularly vulnerable to blasts of solar energy resulting from the sun’s tantrums. Of course, the effects vary according to the satellite orbit, its position relative to certain regions in space and the stage of the 11-year sunspot cycle. If there’s enough response time, satellites can sometimes be turned so the impact to internal systems can be minimized. But it doesn’t always happen.
When satellites are in the path of the blasts, there’s no way to ignore the consequences of these solar cyclones. Effects can range from simple upsets that are easily recovered from to total mission failure. For instance, in November 1982 the GOES-4 weather satellite was temporarily disabled for 45 minutes after the arrival of high-energy protons from a solar flare. In January 1984, two Anik Canadian satellites were disabled due to the elevated activity of high-energy electrons in the magnetosphere. At the same time, the Intelsat-K satellite experienced wobbling and a short outage of service.
In August 1993, solar disturbances apparently were the cause of temporary pointing errors in five orbiting Intelsats. On Jan. 11, 1997, AT&T experienced a massive power failure in its Telstar 401 satellite. A few hours before Telstar 401 began showing signs of difficulties, the GOES-8 satellite also began to malfunction. Meanwhile, solar energy particles had just arrived hours before.
When the earth gets hit with huge amounts of ultraviolet radiation from geomagnetic storms, the upper atmosphere heats up. This heated air rises, and the density of lower satellite orbits (about 1,000 kilometers) increases significantly. This causes drag to increase on satellites; they slow down and gravity pulls them in towards earth. Unless these satellites are boosted into higher orbits, they’ll fall and eventually burn up in earth’s atmosphere. Remember Skylab? It was a victim of premature entry just because of higher than expected solar activity.
More recently, the Japanese Advanced Satellite for Cosmology and Astrophysics went into safe mode on July 15, 2000. The satellite lost its attitude, and its power dropped to critical levels because its solar arrays were no longer properly aligned towards the sun. The problem appeared to be the result of a chain reaction. Solar activity caused an increase in atmospheric drag. The drag applied a torque to the spacecraft, sending it into a spin.
For satellites, the most destructive ingredient of solar storms seems to be in high-energy electrons rather than the other types of particles. These electrons do their damage by producing "deep dielectric charging" in unprotected parts of the satellite. So why aren’t satellite manufacturers protecting these critical systems? In one word: money. The cost of shielding a satellite, its associated weight and the calculated risk of actually having a satellite damaged due to solar blasts is a gamble engineers must consider when designing a satellite.
Although satellite components are manufactured to withstand high total doses of radiation, it’s currently impossible to design and build a satellite that’s entirely immune to variations in the space environment. The long-term effects of solar activity on satellites include an accelerated deterioration of solar arrays and other components on the spacecraft that can result in a shortened life for the satellite.
It’s entirely possible and quite likely that during the next few years, satellite-communications systems may experience signal fluctuations, blackouts and communications outages because of space-weather effects. Communications in the frequency range between 245 megahertz and three gigahertz (very high frequency to ultra-high frequency) – a range the Defense Department uses widely – appear to be very vulnerable to solar activity. Army units, particularly those in northern regions, who have SATCOM equipment should know and understand this – and most importantly, should know how to find out if they might be victims of a space environmental disturbance. Your commander’s inability to communicate over his AN/PSC-5 Spitfire radio might just be due to the sun and not operator headspace!
The same solar-weather-related changes that affect communications also affect the time it takes signals to traverse the ionosphere. The abnormal time delays introduce position errors and decrease the accuracy and reliability of the Global Positioning System, which is used for many range-finding and navigational purposes.
Agencies such as the National Oceanic and Atmospheric Agency and the Solar and Heliospheric Observatory can observe and predict solar activity’s impact on the earth. Army leaders responsible for communications should be aware of how to retrieve the results of NOAA’s and SOHO’s observations and take appropriate action if at all possible.
Real-time space-weather advisories are posted at the Space Environmental Center’s website. Information includes space-weather watches and warnings, progression of the solar cycle, level of activity in geomagnetic storms, solar-radiation storms and radio blackouts.
Also, the website visitor may view, based on location, tracking and data retrieval from satellites gathering solar-weather information. For instance, a unit in Alaska can check to see what level of radiation activity has been detected that could affect communications in their operations area.
Data dumps from the satellites are done every 15 minutes.
Another great website for learning about space weather and its effects on satellites belongs to 55th Space Weather Squadron at Schriever AFB, Colo. There are also links to daily space-weather forecasts and detailed diagrams showing affected areas.
In summary, space-weather-related disruptions to SATCOM systems have wide-ranging effects – from interrupted phone calls to disruption of automated teller machines and problems in global economic transactions. For the warfighter, the failure of critical communications systems in times of crises can be life- and mission threatening. Before deployment, leaders with SATCOM equipment should make a point to minimize the adverse impacts weather could have on their communications and operational readiness – the solar weather, that is!
Ms. Linton works for Information Technology and Applications Corporation’s Fort Gordon, Ga., branch, as contract support to the military SATCOM project manager and Training and Doctrine Command’s SATCOM systems manager. She’s a retired Signal Corps major who began her career as an Army air-traffic controller and completed it as an Army SATCOM architect. She has continued her satellite architectural work as a civilian and is author of the Army’s SATCOM architecture book, distributed annually by PM-Milsatcom.
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Army Communicator is part of Regimental Division, a division of Office Chief of Signal.