Satellite Safe Zone – Not So Safe

The beauty of science is that nothing is for certain. There are times when scientists think they have something figured out and then nature throws them for a loop. Just such an event happened last fall when the Sun erupted in some massive, record-shattering explosions that hurled billion of tons of electrified gas toward Earth.

Scientists realize that space is dangerous for unprotected satellites and astronauts, but they thought that they had found a small safe zone around Earth’s radiation belt — a shelter from these dangerous solar storms. It turns out that when the solar storm is strong enough, even this safe zone can become a major hot zone for dangerous radiation.

Image Right: In October 2003, huge bursts of plasma generated powerful electric fields, pushing Earth’s outer atmosphere (plasmasphere), into interplanetary space. Without the plasmasphere in the safe zone (gap between the two rings), a new, intense radiation belt formed in the region. The red ring represents the potential orbit of a satellite. In some periods it travels through the gap, but at the storm’s peak, the gap is filled in with radiation. Credit: NASA

“Space weather matters — we now know that no matter what orbit we choose, there is the possibility that a spacecraft could get blasted by a significant dose of radiation. We need to take this into account when designing spacecraft. We also need to the ability to continuously monitor space weather so satellite operators can take protective measures during solar storms,” said Dr. Daniel Baker, Director of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder.

Image Left: In this view, the plasmasphere (shown in green) is blown out to the magnetopause (gray barrier), the main point of contact between the solar wind and Earth’s protective magnetic field lines. Visualization is based on data from the IMAGE spacecraft.  Credit: NASA

The region is more of a gap between the two Van Allen radiation belts that surround Earth. The two belts resemble one donut inside the other. The belts are comprised of high-speed electrically charged particles trapped in the Earth’s magnetic field. It can almost be thought of as a giant umbrella in space shielding Earth from these space events.

Image Right: The safe zone appears as a gap between the inner and outer ‘donut,’ beginning about 7,000 km (4,350 miles) and ending about 13,000 km (8,110 miles) above the Earth’s surface. Credit: NASA

The safe zone is considered prime real estate for satellites in “middle Earth orbits” because they would be exposed to relatively small doses of radiation and cost less to build. While there are currently no satellites in that particular orbit, many are being seriously considered including some from the Air Force.

To call the Sun active in late October / early November is an understatement. Within a two-week period, the Sun released an unusually high number of coronal mass ejections (CMEs) into space, and experienced explosions many times more powerful than anything ever observed. For some perspective, flares are usually ranked by number and class. A large flare might be X-2, for example. The Nov. 4 flare was ranked X-28, although more precisely, “off the scale” because it was hard to get an exact measurement. To add to the drama, the Sun is headed into its period of minimum activity within its 11-year cycle, making the number and intensity of the fall flares unusually high. The maximum and most active period occurred around 2000-2001.

Image Left: From Oct. 22 to Nov. 4, 2003, at least eight solar shocks reached Earth, severely disturbing its protective magnetic field and affecting orbiting spacecraft. The SOHO spacecraft tracked the explosions in the Sun’s outer atmosphere, or corona. Credit: NASA/ESA

Fortunately the science community has a number of satellites to track solar comings and goings. The Solar, Anomalous and Magnetospheric Particle Explorer (SAMPEX) satellite flies through the Van Allen radiation belts, taking measurements of the particle types and their energy and abundance. It observed the formation of a new belt in the safe zone on Oct. 31, 2003. That new belt made the safe zone hazardous for more than five weeks until the radiation was able to drain away and be absorbed by our Earth’s atmosphere. Other satellites helped researchers track the solar storms as they generated auroras on Earth, and spread out to Mars, Jupiter, Saturn, and the very edges of the solar system

Image Right: Advanced warning saved a lot of spacecraft and power grids on Earth from serious damage. Aircraft were rerouted, and astronauts on the International Space Station took temporary shelter. This data from SAMPEX is overlaid on a grid showing the ISS orbits and its frequent interaction with the radiation. Credit: NASA/LASP

“This was an extreme event, a natural experiment that will be used to better understand how radiation belts work,” summed up Dr. Baker. “We were fortunate to have a suite of spacecraft in place to observe this event. This is why it’s important to systematically and continuously observe space weather, because there is always the potential to be surprised by nature.”