Saturday, February 13, 2010

Lasers, Solar flares and GPS's oh my!

The United States successfully used an airborne laser to destroy a mock ballistic missile Thursday, the "first directed-energy lethal-intercept demonstration against a liquid-fuel-boosting ballistic missile target from an airborne platform," according to the U.S. Missile Defense Agency.

"The revolutionary use of directed energy is very attractive for missile defense, with the potential to attack multiple targets at the speed of light, at a range of hundreds of kilometers and at a low cost per intercept attempt compared to current technologies," Reuters quoted the agency.

But history shows that the military has for a long time offered rosy pronouncements on missile defense. A closer look at that history suggests that this week's successful test of the airborne laser (ABL) – a
laser weapon mounted on a modified 747 jet – is unlikely to meaningfully shore up the country's defense any time soon.

Related Reads
Strategic Defense Initiative Wiki
HOE Homing Overlay Experiment 

Solar flares will most likely wreak havoc on GPS signals

The sun's activity isn't usually a hot topic around these parts, but when it threatens to derail satellite navigation services around the world, it must surely take center stage. UK researchers have corroborated Cornell's 2006 warning that our solar system's main life-giver is about to wake up and head toward a new solar maximum -- a period of elevated surface activity and radiation. It is precisely that radiation, which can be perceived in the form of solar flares, that worries people with respect to GPS signaling, as its effects on the Earth's ionosphere are likely to cause delays in data transmission from satellites to receivers and thereby result in triangulation errors. Still, it's more likely to be "troublesome than dangerous," but inaccuracies of around 10 meters and signal blackouts that could last for hours are being forecast in the absence of any intervening steps being taken. So yes, you now have another reason not to trust your GPS too much.

Satellites advertise their exact position, and the precise time at which they are sending it

The signal travels through the outer atmosphere, the ionosphere; its speed depends on how much the Sun's radiation and particle winds are affecting the ionosphere's composition

A receiver on Earth determines how long the signals took to arrive from a number of satellites, calculating the position from the time differences

In 2011 or 2012, when the sun reaches its next solar maximum, scientists expect it to cause a 90 percent GPS signal drop for several hours.

Scientists and grad students from Cornell University envision this horrific day as a "nightmare situation," given that all planes will likely have GPS signaling by that time. However, they think the best remedy is to be aware of the problem and operate GPS systems with the knowledge that they may fail during a solar flare.

What is a Solar Flare?

A flare is defined as a sudden, rapid, and intense variation in brightness. A solar flare occurs when magnetic energy that has built up in the solar atmosphere is suddenly released. Radiation is emitted across virtually the entire electromagnetic spectrum, from radio waves at the long wavelength end, through optical emission to x-rays and gamma rays at the short wavelength end. The amount of energy released is the equivalent of millions of 100-megaton hydrogen bombs exploding at the same time! The first solar flare recorded in astronomical literature was on September 1, 1859. Two scientists, Richard C. Carrington and Richard Hodgson, were independently observing sunspots at the time, when they viewed a large flare in white light.

As the magnetic energy is being released, particles, including electrons, protons, and heavy nuclei, are heated and accelerated in the solar atmosphere. The energy released during a flare is typically on the order of 1027 ergs per second. Large flares can emit up to 1032 ergs of energy. This energy is ten million times greater than the energy released from a volcanic explosion. On the other hand, it is less than one-tenth of the total energy emitted by the Sun every second.

There are typically three stages to a solar flare. First is the precursor stage, where the release of magnetic energy is triggered. Soft x-ray emission is detected in this stage. In the second or impulsive stage, protons and electrons are accelerated to energies exceeding 1 MeV. During the impulsive stage, radio waves, hard x-rays, and gamma rays are emitted. The gradual build up and decay of soft x-rays can be detected in the third, decay stage. The duration of these stages can be as short as a few seconds or as long as an hour.

Solar flares extend out to the layer of the Sun called the corona. The corona is the outermost atmosphere of the Sun, consisting of highly rarefied gas. This gas normally has a temperature of a few million degrees Kelvin. Inside a flare, the temperature typically reaches 10 or 20 million degrees Kelvin, and can be as high as 100 million degrees Kelvin. The corona is visible in soft x-rays, as in the above image. Notice that the corona is not uniformly bright, but is concentrated around the solar equator in loop-shaped features. These bright loops are located within and connect areas of strong magnetic field called active regions. Sunspots are located within these active regions. Solar flares occur in active regions.

The frequency of flares coincides with the Sun's eleven year cycle. When the solar cycle is at a minimum, active regions are small and rare and few solar flares are detected. These increase in number as the Sun approaches the maximum part of its cycle. The Sun will reach its next maximum in the year 2011, give or take one year.

A person cannot view a solar flare by simply staring at the Sun. (NEVER LOOK DIRECTLY AT THE SUN! EYE DAMAGE CAN RESULT.) Flares are in fact difficult to see against the bright emission from the photosphere. Instead, specialized scientific instruments are used to detect the radiation signatures emitted during a flare. The radio and optical emissions from flares can be observed with telescopes on the Earth. Energetic emissions such as x-rays and gamma rays require telescopes located in space, since these emissions do not penetrate the Earth's atmosphere.

Related / Interesting Reads
Sat-nav devices face big errors as solar activity rises BBC News
Solar flares to ruin cab journeys - The Inquirer

Solar Flares Could Seriously Disrupt GPS Receivers -
Potential of GPS Failure Overblown, Says Air Force, Vendors
Morphogenesis - Priestessing on the edge of chaos: Sun Spots, Solar Flares and Geomagnetic Storms 
Satellite could predict Katrina-style solar storms - San Jose Mercury News 

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