Alongside the well-known hazards of space – freezing temperatures, crushing pressures, isolation – astronauts also face risks from radiation, which can cause illness or injure organs.Though not believed to be an imminent threat to current missions, astronauts may one day face radiation from solar winds and galactic cosmic rays. How much radiation, what kind, and what the anticipated health impacts of this exposure would be to astronauts are open questions among space agencies.Jeffery Chancellor, a research scientist in the Department of Physics and Astronomy at Texas A and M University and a PhD candidate in the applied physics program there, has spent more than a decade studying these questions as part of four NASA missions. Recently, collaborating with physician and astronaut Serena Aunon-Chancellor (NASA/University of Texas Medical Branch) and Associate Director of NASA’s Human Research Program for Exploration Research Planning John Charles (NASA), Chancellor examined the health implications of space radiation exposure in low-altitude polar orbits.
The researchers used as a test case the Manned Orbiting Laboratory (MOL), about which mission documents were recently declassified.The MOL was conceived in 1963 and underwent planning from 1965 to 1969, but never actually flew.”It was such a unique orbital profile,” Chancellor said. “Polar, low altitude… I couldn’t guestimate what the effects would be. So, I decided to take a step back and apply advanced computational and numerical methods to this mission profile.”They found that the relatively minimal shielding of the MOL program’s space vehicle and its high inclination polar orbit would have left the crew susceptible to high exposures of cosmic radiation and solar particle events. Had the mission continued through 1972, astronauts would have faced toxic doses of radiation during a massive solar event.
Eyes In The Skies
The Manned Orbiting Laboratory was conceived as an experimental laboratory for human spaceflight, but was recast as a secret reconnaissance platform in 1965 during the height of the Cold War. The vehicle would have travelled in low-earth orbit and passed repeatedly over the northern and southern polar regions to better spy on the Soviet Union. This type of orbit incurs greater radiation exposure than orbits closer to the equator because it is less protected by the Earth’s gravitational field.
In August 1972 – three years after the MOL mission planning was discontinued due to the emergence of cheaper, unmanned satellites – the Earth experienced a historically large solar particle event. Chancellor wondered how typical radiation would have impacted MOL pilots who orbited for 30 days in the thin-shielded vessel and how a massive event like the one in 1972 would have affected someone caught in flight.
The researchers focused on radiation from two sources: solar winds and galactic cosmic rays. Some space radiation is believed to pass through the walls of shuttles, while some barrages the shielding and causes a cascade of loose metal ions. A portion passes through the body; the rest deposits its energy on the skin or even inside the body, affecting the organs.
Determining the radiation levels that MOL pilots would have experienced behind the vehicle’s light-weight shielding entailed a good deal of data mining, extrapolation and simulation. Chancellor and his collaborators modeled the MOL’s orbit profile, the space weather and geomagnetic forces from those years, and the particle and heavy ion transport that such a trajectory would have encountered.
Combining these factors, sampling them, and simulating them thousands of times on TACC’s Lonestar5 supercomputer, Chancellor and his collaborators found that, under normal conditions, the MOL crew would have endured 113.6 millisievert (mSv; a measure of radiation dosage) to their skin and 41.6 mSv to blood forming organs (for instance, bone marrow or lymph nodes) during a 30-day flight – well within the exposure limits for NASA astronauts.However, during the “worst-case scenario” of the 1972 solar storm, their skin would have been exposed to 1,770 mSv, while their organs would have experienced 451 mSv, both of which exceed NASA exposure limits.Based on animal studies, Chancellor and his colleagues anticipate that such exposure would have caused nausea, vomiting, fatigue, and possibly skin burns to crew. Without prompt instigation of medical countermeasures, the risks could have been even more severe.