[Oct. 22, 2023: Staff Writer, The Brighter Side of News]
Aircraft crews today, though not subjects of myth, confront the Icarian dilemma in the form of radiation exposure at high altitudes. (CREDIT: Creative Commons)
In Greek mythology, Daedalus cautioned his son, Icarus, "Don't fly too close to the sun," warning that soaring too high would melt the wax affixing his wings, while flying too low would let the sea's dampness weigh him down. This ancient tale parallels modern challenges in commercial aviation, albeit in a more scientifically complex context: the occupational hazard of aviation radiation exposure.
Aircraft crews today, though not subjects of myth, confront the Icarian dilemma in the form of radiation exposure at high altitudes. The Earth's atmosphere acts as a protective layer, absorbing a significant portion of space radiation, but this shield thins as one ascends. This scenario leaves flights at customary cruising altitudes, especially long-haul flights, exposed to increased levels of cosmic radiation.
This radiation primarily stems from two sources: galactic cosmic rays (GCRs) and solar energetic particles (SEPs). While GCRs, high-energy particles originating from outside our solar system, present a relatively stable threat, SEPs, associated with solar flares and coronal mass ejections (CMEs), are far more unpredictable and potentially more dangerous.
SEPs, associated with solar flares and coronal mass ejections (CMEs), are far more unpredictable and potentially more dangerous. (CREDIT: VICTOR HABBICK VISIONS/SCIENCE PHOTO LIBRARY/GETTY IMAGES)
Regulatory bodies have established guidelines aiming to mitigate these risks. Notably, the dose rates from GCRs remain manageable, not exceeding 10 µSv/h at the typical flight altitude of 12 km, well within acceptable occupational exposure limits. However, the sporadic nature of large solar particle events, which emit SEPs, can complicate this regulatory landscape.
The Cost-Benefit Analysis of Radiation Mitigation:
A fundamental question arises when these solar events occur: do the potential consequences justify the economic costs of taking protective actions? Current protocols in the event of heightened radiation exposure include lowering altitude, altering flight paths, or even cancelling flights—each option carrying substantial costs.
Yosuke Yamashiki, from Kyoto University, leads a research team dedicated to addressing this cost-benefit conundrum. Their analysis, detailed in the journal Scientific Reports, focuses on assessing eight flight routes during five distinct ground level enhancements (GLEs)—unexpected surges in radiation recorded by terrestrial detectors.
"During a large solar particle event, we observe sudden SEP influxes with dose rates exceeding 2 mSv/h," Yamashiki explains, emphasizing the rarity and transient nature of these events. For context, 2 mSv is twice the annual radiation exposure limit recommended for flight crews, a benchmark set to minimize long-term health risks.
Through their research, Yamashiki's team concluded that for airlines to justify implementing countermeasures, the maximum radiation dose and dose rate from significant GLE events would need to surpass 1.0 mSv and 80 µSv/h, respectively. However, their frequency analysis revealed that GLEs capable of inducing such levels occur only about once every 47 years for the maximum dose and once every 17 years for the maximum dose rate, rendering them exceedingly infrequent.
Exposure to cosmic rays when on board an aircraft is an important topic, not only for airline workers such as flight attendants and pilots, but also for general passengers. (CREDIT: Kyoto University)
National standards, like those from Japan's Radiation Council, further illustrate this point. The council recommends a maximum annual radiation exposure of 5 mSv for airline crews and 1 mSv for passengers. The disparity between these guidelines and the actual frequency of threatening GLE events suggests that current mitigation efforts, and their associated costs, might exceed what's necessary for the safety of passengers and crew.
The Economic Perspective:
Rerouting or delaying flights, especially long-haul ones, incurs significant expenses—around $1,500 per event. When extrapolated to the scale of global commercial aviation, these costs become astronomical. "There's no denying the potentially debilitating effects of radiation exposure," states Yamashiki, "but the data suggest that current measures may be over-compensating for the actual risks."
The Emergence of Space Tourism:
The conversation takes an even more intriguing turn with the advent of space tourism. Companies like SpaceX, Virgin Galactic, and Blue Origin are propelling humanity into a new era of recreational space travel. However, this introduces a new variable into the radiation exposure equation: the absence of Earth's atmospheric protection.
The research team underscores the necessity of quantifying radiation threats for these novel aerospace ventures. They advocate for using their established methods to assess risks, propose reduction measures, and develop mitigation strategies tailored to the unique parameters of space travel.
Yet, concrete recommendations demand more precise risk assessments, necessitating detailed operational plans from these pioneering companies. "The risk of solar radiation exposure is expected to be higher in the space travel plans... It will be even more important to quantify the risk using the method developed in this study," the team elaborates in their report.
The study, "Probabilistic Risk Assessment of Solar Particle Events Considering the Cost of Countermeasures to Reduce the Aviation Radiation Dose," represents a critical step forward in understanding the interplay between science and economics in aviation safety.
Blue Origin’s New Shepard crew (L-R) Oliver Daemen, Jeff Bezos, Wally Funk, and Mark Bezos pose for a picture near the booster after flying into space in the Blue Origin New Shepard rocket on July 20, 2021. (CREDIT: Joe Raedle/Getty Images)
The findings prompt a re-evaluation of current practices, potentially steering regulatory policies towards more data-driven decision-making. Furthermore, as we stand on the cusp of civilian space travel, the research sets the stage for ensuring that these historic leaps for mankind are not only awe-inspiring but also fundamentally safe.
The tale of Icarus and Daedalus resonates with humanity's timeless desire to soar yet also heeds caution. As we navigate this modern Icarian landscape, the balance we strike between ambition and safety will define not only our skies but also the very future of human exploration.
For more science news stories check out our New Discoveries section at The Brighter Side of News.
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