Naked cameras
Scientists say the danger from radiation is amplified
by the fact that Chandra and XMM use large mirrors to focus low-energy protons
into essentially naked cameras.
Chandra suffered
partial degradation of eight of ten one-inch-square silicon chips, shortly
after launch in 1999, that reduced the telescope’s ability to distinguish between
different X-ray energies, or "colors," Chandra scientists said last October.
"No one realized that low-energy protons would
scatter off of Chandra's X-ray mirrors in the direction of the focal plane [of
the camera] with such a high efficiency," said Paul Plucinsky of the Chandra
X-ray Observatory Center, at the Harvard-Smithsonian Center for Astrophysics.
Plucinsky and other Chandra and XMM scientists met recently in Europe to discuss
the radiation threat.
"Our models were sufficient for the environment
in the [radiation] belts; we now have to improve our understanding of what is
happening further out on the orbit," Plucinsky said. "In particular we must
continue to monitor closely the long-term cumulative effect of this radiation.
But so far we are still on target to continue Chandra operations for at least
10 years."
Researchers are using the orbiting observatories
to study the gusts. One of the XMM's cameras has proven more robust than the
others and has been used to monitor the low-energy particles. When it detects
a high rate of incoming protons, it shuts the other instruments off until the
coast is clear. Meanwhile, it is measuring the radiation and even generating
images of it.
"It probably will help us understand the frequency
and range of events which occur when the Earth's magnetic field loops and coils
under the influence for the dynamic solar wind," said David Lumb, an XMM calibration
scientist. He added that researchers who study Earth's magnetosphere would most
likely benefit from the measurements, a data boon that wasn't anticipated at
the telescope's launch.
"Plenty of ESA, NASA and other scientists are eager
to use the serendipitous measurements to fill in the gaps of their knowledge,"
Lumb told SPACE.com.
Other craft
There are far more spacecraft in the sky during
this solar maximum than there were when the last one hit, including the International
Space Station (ISS).
During a November
radiation storm, ISS crew members set up a radiation-monitoring device inside
the Russian-built modules as a precaution. The portable device would sound an
alarm if it sensed radiation that reached a preset level, and crew members would
move to the a part of the Zvezda service module that offers the most protection.
So far, the alarm has not sounded.
Even spacecraft downstream from the Sun's energy
are at risk. During a Nov. 9 solar storm, the Stardust spacecraft was forced
into safe mode by solar weather. At the time, the craft was 130 million
miles (48.3 million kilometers) from the Sun -- 1.4 times as far from the star
as Earth.
advertisement
