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Last Post 3/19/2012 10:34 AM by  Kris Sigsbee
Solar Radiation Effects
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Anonymous





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3/19/2012 9:27 AM

    This article about a falling Russian satellite (http://news.discovery.com...descent-120217.html) says that the satellite has been exposed to too much solar radiation. Why would there be more solar radiation at an orbit closer to Earth as opposed to the planned orbital distance?

    Additionally, have solar storms ever caused problems in our ground based electrical grid?

    Tags: Radiation Belts, Power Grid, solar radiation storms, Communications Satellites

    Claire Raftery



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    3/19/2012 10:22 AM
    This would be the case if the effects of radiation were uniform around the Earth. If that was the case then all we would have to worry about was the radial distance. However, there are pockets of high radiation that exist and from what I can gather, it is one of these that is causing the problem. The satellite was originally meant to be at an inclination of about 20 degrees to the equator. However, the failed rocket left it at an inclination of 50 degrees. That means it is probably passing through a region called the South Atlantic Anomaly (SAA - http://en.wikipedia.org/w...th_Atlantic_Anomaly) which is a well known pocket of radiation due to the proximity of the Earth's Van Allen belt to the Earth's surface. There are plenty of satellites that pass through this belt, however they all have sufficient protection to avoid damage from the radiation. It is my assumption that the failed satellite does not have these protections because it was never meant to pass through them in the first place. In answer to your second question, yes they have. One of the more notable events was the Quebec blackout of 1989. You can read more about it here: http://www.nasa.gov/topic...es/sun_darkness.html

    Kris Sigsbee



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    3/19/2012 10:34 AM

    Hello,

    The article you mentioned is actually rather vague about the source of the radiation that damaged the Express -- AM4 telecommunications satellite. However, based upon what I know about the Sun and the Earth's magnetosphere, I think this satellite was most likely damaged by high energy particles in the Earth' radiation belts, NOT solar radiation. The radiation belts were discovered by a scientist from the University of Iowa named James Van Allen shortly after the launch of the first U.S. satellite, Explorer 1. Scientists here at the University of Iowa are currently working on instruments for the Radiation Belt Storm Probes, which will be launched this fall.

    According to another article I found about the Express-AM4 satellite, it was originally supposed to be launched into an elliptical orbit with an apogee of 35,786 kilometers (about 5.6 Earth radii, 1 Earth radii = 6378 km) and a perigee of 5,210 kilometers (0.8 Earth radii), with an inclination of 20.5 degrees. Apogee is the furthest distance from the Earth in an orbit, and perigee is the closest. From that location the satellite was supposed to use its own power to circularize its orbit into geostationary position about 36,000 kilometers (still about 5.6 Earth radii) over the equator. The radiation belts actually consist of an inner belt and an outer belt. Most communications satellites are in geostationary orbits that fall within the outer radiation belt, which is most intense between 4-5 Earth radii. High-energy, "killer" radiation belt electrons can damage the computer chips on these satellites, but fortunately the outer radiation belt is highly variable and the most intense electrons are found only during geomagnetic storms.

    The Express-AM4 satellite actually ended up in a much lower orbit with an apogee of 20,317 kilometers (3.2 Earth radii), a perigee of 1,007 kilometers (0.15 Earth radii) and an inclination relative to the equator of 51.3 degrees. This would have placed it inside the inner radiation belt, which is between 1.2 to 3 Earth radii. However, when solar activity is stronger or in geographical areas such as the South Atlantic Anomaly (SAA), the inner boundary may go down to a few hundred kilometers above the Earth's surface. The inner radiation belt is more steady than the outer belt, and satellites in this region can be affected by both high energy protons and electrons. The International Space Station, which has an orbital inlication of 51.6 degrees needs to have special shielding to deal with high energy protons when it travels through the South Atlantic Anomaly. I don't know for sure, but I would take a guess that the Express-AM4 satellite ended up in an orbit inside the inner radiation belt that occasionally took it throught the South Atlantic Anomaly and exposed it to higher radiation levels than the satellite was designed to withstand.

    Solar storms like coronal mass ejections (CMEs), solar flares, or solar proton events do not directly damage our electrical power grids on the Earth. Not all solar storms (CMEs, solar flares, etc.) are aimed at Earth and produce geomagnetic storms. However, if a CME is aimed towards the Earth and has the right magnetic field characteristics, it can cause a geomagnetic storm that produces huge electrical currents in Earth's magnetic field. These electrical currents have damaged electric power grids on Earth. The most famous example is a geomagnetic storm that occurred in March 1989, which you can read about here -

    http://en.wikipedia.org/wiki/March_1989_geomagnetic_storm

    Kris

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