Oct. 25, 2013: The next time you step onto an
airplane, consider the following: In any given year, the pilot of your
aircraft probably absorbs as much radiation as a worker in a nuclear
power plant.
And you are about to follow him wherever he goes.
The FAA classifies pilots as "occupational radiation workers." Flying
high above Earth with little atmosphere to protect them, they can absorb
significant doses of cosmic rays and solar radiation. During a typical
polar flight from Chicago to Beijing, for instance, a pilot is exposed
to the equivalent of two chest x-rays. Multiplied over the course of a
career, this can cause problems such as increased risk of cancer and
possibly cataracts.
Passengers have reason to be concerned, too.
"A 100,000 mile frequent flyer gets about 20 chest x-rays," points
out Chris Mertens, a senior research scientist at NASA Langley Research
Center. "This is true regardless of the latitude of the flights."
It’s worth noting that even people on the ground absorb some
radiation. Cosmic rays and their by-products are so powerful, they can
reach all the way down to Earth’s surface, giving a person at sea level
the equivalent of one chest x-ray every 10 days or so.
On a plane, however, dose rates increase 10-fold or more. The
exposure depends on factors ranging from the altitude and latitude of
the flight path (polar routes are irradiated most) to sunspot counts and
solar activity (a powerful solar storm can boost radiation levels a
hundredfold). To help airline companies safeguard passengers and
personnel, NASA is developing an experimental tool to predict exposures
in real time. Mertens is the PI of the system, called NAIRAS--short for
"Nowcast of Atmosphere Ionizing Radiation for Aviation Safety."
A NAIRAS model shows radiation levels over the northern hemisphere on Oct. 25, 2013. More
Mertens notes that the number of flights over the poles has
skyrocketed in recent years. Airlines prefer polar routes for
international travel because they are shorter and have reduced head
winds, creating fuel savings of tens of thousands of dollars per flight.
However, Earth's poles are where the radiation problem can be most
severe. Our planet's magnetic field funnels cosmic rays and solar
energetic particles over the very same latitudes where airlines want to
fly. On a typical day when the sun is quiet, dose rates
for international flights over the poles are 3 to 5 times higher than
domestic flights closer to the equator.
If a flight controller wants to know the situation around the poles
right now,
NAIRAS can help. It is, essentially, an online global map of radiation
dose rates for different flight paths and altitudes. Maps are produced
in near real-time by a computer at Langley, which combines cutting-edge
physics codes with realtime measurements of solar activity and cosmic
rays.
“We are still in an experimental phase,” he says. “The ultimate
goal of the NAIRAS effort is to adopt a paradigm similar to terrestrial
weather forecasting.”
The value to the airlines is clear. The ability to fly over the
poles can save $35,000 to $40,000 per flight in fuel costs alone. On
the other hand, altering course to avoid a polar radiation storm can
cost as much as $100,000. A forecasting tool like NAIRAS can help the
airlines make the right decision.
Of even greater importance to Mertens is the human factor. “Back
in 2004, I went to a workshop on space weather and aviation. A pilot
from American Airlines stood up to address the audience: ‘Look,’ he
said, ‘we are classified as radiation workers, we are the most exposed
than any other group, yet we know the least of all the groups.’ That
was a turning point for me. I wanted to do something to help pilots
better understand what they are flying into.” And so NAIRAS was born.
Mertens and colleagues are about to publish a paper in the journal
Space Weather
comparing NAIRAS predictions to actual radiation measurements onboard
airplanes. “The results are encouraging,” he says, “but we still have
work to do.”
Credits:
Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit: Science@NASA
