Scientists Say Sun Is the Culprit In Sidelining Satellites, Toasters
For earthbound motorists, early spring's nor'easters were an annoyance. For Telesat Canada, the sun's "nor'easter" was a disaster.
On March 26, one of two solar panels on the company's $300 million ANIK-E1 satellite suddenly failed, silencing half the signals the craft was relaying across Canada.
At first, the cause was thought to be a meteor or a design failure. But a team of American scientists using a network of special satellites now points to a solar-wind storm as the likely culprit.
At a time when activities on Earth are more dependent on satellites for everything from communications to aircraft navigation, an intense international effort is under way to monitor and forecast "space weather" - the sun's impact on Earth's magnetic field and radiation belts.
ANIK's troubles occurred as a solar-wind storm - a burst of electrons and protons from the sun - fed and fattened Earth's radiation belts, enveloping the satellite in high-energy particles that overloaded some of the craft's circuits.
"It was a devastating loss," says Daniel Baker, director of the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder. Nor was ANIK alone, he says. Several other satellites, including classified military craft, had problems.
Satellites are not the only vulnerable pieces of hardware. Intense solar storms can disrupt radio signals and sideline toasters. In March 1989, a powerful magnetic storm knocked out electricity to the entire province of Quebec, affecting 6 million people. Sporadic blackouts occurred as far south as New Mexico.
Researchers also point out that radiation from intense solar storms can affect high-altitude aircraft such as supersonic airliners and even lower-altitude airliners flying over polar routes.
Had the Russian MIR space station been at a higher position in its orbit at the time of the March 1989 storm, the cosmonauts on board could have faced serious problems, says Harlan Spence, an associate professor of astronomy at Boston University's Center for Space Physics.
"When the earth's magnetic field rattles anywhere, it rattles everywhere," says Ernest Hildner, director of the National Oceanic and Atmospheric Administration's space environment center, Boulder, Colo.
With almost clocklike regularity, new spacecraft are being launched to monitor the sun's surface, the charged particles it sends out, and the effect those particles have on Earth's magnetosphere, the region of space affected by Earth's magnetic field.
Later this month, for example, four unmanned craft are scheduled for launch atop an Ariane rocket. Known as Cluster, the four craft will travel in unison to measure conditions in the relatively thin boundary region between the solar wind and the magnetosphere. They represent the final link in a series of International Solar Terrestrial Physics missions designed to give researchers a complete look at the sun's influence on near-Earth space.
Others series projects include:
*The Polar mission. Launched in February, the US Polar craft is orbiting Earth over the poles to monitor conditions throughout the planet's magnetic field. The high point of its orbit is over the North Pole, where it peers down at auroras. Data from Polar helped unravel the mystery of ANIK's partial blackout, says Dr. Baker, who heads one team of researchers using the satellite.
The team's conclusions are contained in a draft report being prepared for NASA.
*The Solar Heliospheric Observatory mission. Launched in December, SOHO is a joint effort between NASA and the European Space Agency. The satellite orbits a point roughly 1.6 million miles from Earth where the gravitational effects of sun and Earth cancel each other. The position gives the craft an unimpeded view of the sun. At a press briefing last week, researchers reveled in the first images from SOHO, which enabled them to clearly see features on the sun's surface that could only be inferred before.
*The WIND mission. Launched in 1994 and placed in an elongated orbit that puts it upwind of Earth for relatively brief periods, WIND measures the particle flows and magnetic fields of the solar wind.
*The Geotail mission. The flow of solar wind stretches the magnetosphere into a comet-like tail. Built by Japan and launched by NASA in 1992, Geotail measures conditions throughout the magnetosphere downwind of Earth.
In addition, Russia has two Interball satellites orbiting: one to monitor auroras and the other to measure conditions in the magnetosphere's tail. Additional sunwatching spacecraft are planned for next year and beyond, including placing a WIND-like craft in an orbit similar to SOHO's for continuous coverage.
Yet with all this hardware, "we're still in the feeling-the-elephant stage" of understanding space weather, says Patricia Reiff, professor of space physics and astronomy at Rice University in Houston.
The ultimate goal is to develop an ability not only to see the solar events that generate the solar-wind storms, researchers say, but also to give detailed forecasts about the strength and duration of storms at various altitudes. With the sun heading into the next active period in its 11-year sunspot cycle, which should peak around 2000, the demand for better space-weather forecasting is expected to grow.