If humans live on the moon some day, they might turn on theweather forecast just as they do on Earth. But in space, they won't fear rainstorms, but sun storms.
During a solarradiation storm, the sun emits huge sprays of charged particles that candisable satellites and would harm humans in space if they're not properlyprotected. Although these storms are notoriously difficult to predict,a new method of forecasting storms can give up to an hour's warning.
The technique relies on measurements taken by the NASA/ESASOHO (Solar and Heliospheric Observatory) spacecraft in orbit around the sun. SOHO,launched in 1995, has been near death more than once, but clever engineers,working with the equivalent of electronic duct tape and more than a dash ofluck, have kept it running well beyond its expected lifetime. And now the probeis making fresh contributions to solar weather forecasting.
The new technique relies on SOHO's ComprehensiveSuprathermal and Energetic Particle Analyzer (COSTEP), which monitors theradiation coming from the sun.
Scientists analyzed the data COSTEPrecorded from sun storms during the first six years of the spacecraft's launch,and compiled a matrix that can predict a full-blown storm is coming after the less-dangerousfirst wave arrives. Because there is about an hour's lag time between the earlyarrival of electrons, and the eventual onslaught of more-damaging protons, thisnew forecast system gives people and spacecraft enough time to take cover.
The method was described in the journalSpace Weather, and went online just in time for the recent launch of theSTS-122shuttle mission.
On Earth, people are protected from the brunt of solarradiation by our planet's atmosphere and magnetic field. Even astronautsorbiting the Earth on the InternationalSpace Station are shielded from much of it since Earth's magnetic fieldextends far enough to cover them. The astronauts do retreat to aradiation-shielded part of the station during severe storms, however.
But when people venture beyond our planet's protectivebubble, they will really be at risk of severe health effects from solar stormradiation. It was a concern even during brief lunar missions in the Apollo era.
"We know what happens when humans are exposed to a lotof radiation ? Hiroshima and Nagasaki have given us an example," said ArikPosner, a senior research scientist at Southwest Research Institute in SanAntonio, Texas, who developed the new forecast technique. "Humans areconstantly hit by some sort of radiation, even on Earth, at very low levels. Butwhat happens when you increase the radiation level slightly? We don?t know. Butthe best thing to do is limit exposure."
The most damaging solar-storm radiation particles arefast-moving protons. These energetic particles can destroy human tissue andbreak strands of DNA.
The radiation is also dangerous for spacecraft. When aspeeding particle hits electronics, it can cause bits to change from zeroes toones or vice versa, prompting program malfunctions. If power is knocked out, asatellite can fail completely.
Scientists don't fully understand the physics behind solarstorms. They know they are closely related to the cycles of the sun's magneticfield, and that they emerge from relatively cool, intensely magneticregions of the solar surface called sunspots. The magnetic field is alwayschanging ? about every 11 years its magnetic north pole becomes the south pole,and vice versa. As the polarity cycles and regional instabilities develop, thesun's magnetic field lines get twisted and tangled, resulting in big knots ofextremely strong magnetism.
Although the exact mechanism isn't known, somehow thesemagnetic field events are tied to eruptions of matter and energy.
"We don?t have a really good idea of exactly how theseprocesses happen," Posner said. "It's a very active area ofresearch."
Huge explosions on the sun accelerate charged particles tonear light-speed. The lighter particles, electrons, can speed up more easily,so they reach SOHO's radiation detector first. This allows the spacecraft togive humans about an hour's advance notice before the heavier protons and ionsarrive and wreak havoc.
"The detector can only say that there is already anevent in progress," Posner told SPACE.com. "It cannot predict one beforeit starts. But it does give you a tool to forecast these events."
After Posner and his collaborators designed the matrix topredict a coming storm, they tested it on the sun storm record from 2003, ayear that did not comprise the initial data set on which the matrix was based. Whenit measured an increase in high-speed electrons, the program was able tosuccessfully predict that a solar storm was coming. It forecasted all fourmajor storms of 2003 with advance warnings ranging from 7 to 74 minutes.
SOHO is a joint project between NASA and the European SpaceAgency (ESA). Three times it has seemed to be a doomed mission. During the mostrecent scare, in 2003, a stuck motor drive would not permit the craft's primaryantenna to move. The antenna is used for transmitting pictures and data back toEarth, and it must be pointed toward the planet. Scientists feared lengthyblackout periods.
Engineers employed some tricks, including flipping the craftupside down during portions of its orbit, to get the data flowing again.
In 1998, changes in the spacecraft's software inadvertentlysent it into a flat spin. The electricity-providing solar panels turned edge-onto the Sun, and SOHO lost power. It could not orient itself or maintain itstemperature ? critical in the frigid environment of space.
The mission appeared doomed.
After nearly three months, with much perseverance by theground team, contact was re-established and the craft's orientation was fixed.Sunlight hit the panels, and SOHO was back.
Later in 1998, another problem nearly ended the missionagain. The craft's last navigational gyro failed.
"In a race against time and a depletingmaneuvering-fuel supply," explained SOHO Project Scientist Bernhard Fleckof ESA, engineers had to develop a software patch to get the craft back inoperation without the gyro. New software was developed in early 1999 to allow aspacecraft to maintain attitude without gyros. Engineers sent it up,"making SOHO the first 3-axis stabilized spacecraft to be operated withoutany gyros," Fleck said.
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