Protecting humans in space
For humans working within a potentially hazardous radiation environment, three primary safety measures are implemented. First, continuous monitoring of the human’s radiation exposure is undertaken to ensure that permitted daily, yearly, and lifetime exposure limits are not exceeded. Second, physical barriers are employed to provide shielding to moderate exposure. And, third, the human is able to be removed from the radiation environment when permitted exposure limits are approached or anticipated. When lifetime exposure limits are reached, permanent removal is employed.
Following this successful terrestrial experience, the radiation safety measures that will be undertaken in space include:
- All people in space will use continuous radiation monitoring to track exposure to ensure that permitted exposure limits are not exceeded.
- All human space habitats, spacesuits, and spaceships will include passive radiation shielding to provide permitted levels of space radiation under normal space radiation circumstances. Active radiation shielding using electromagnetic fields—a new technology currently under development—will also be employed as it matures.
- Long-term human presence in space will generally be limited to those regions where lower radiation environments exist and/or suitable protection is provided. LEO at low orbital inclinations is one example. Lunar bases buried to provide substantial radiation protection are another example.
- Human activities within higher radiation environments or during times of increased radiation will be limited. For example, EVAs in LEO will generally not be undertaken during orbital passage through the South Atlantic Anomaly. As robotic teleoperation improves, this will be primarily used for routine “outside” work.
- Space habitats located within increased radiation environments (e.g., GEO) will include additional radiation protection and individual human exposure limits will be adjusted to reflect the increased radiation levels.
- Space habitats and spaceships will include radiation storm cellars. These will use high levels of passive shielding and, in the future, active shielding to protect against increased levels of radiation exposure, such as major solar events. Space sensor observation of the sun will be increased to provide additional warning of forthcoming extreme solar activity.
- Age restrictions may be imposed on workers.
- If lifetime radiation limits are reached, the person is returned to the Earth.
The radiation environment in space is variable, driven by changes in the sun’s radiation output and cosmic radiation. As with all natural environments, while most variations are within ranges that are practical to address through engineering design, some exceed practical bounds. Ships at sea occasionally experience rogue waves that exceed the wave height for which the ships can practically be built. When such rogue waves are encountered, the ship and crew may be lost. Aircraft operate with the risk that flying through a flock of large birds can cause all engines to lose power leading to the crash of the aircraft. While very rare, this has been known to happen. Yet, they don’t prevent us from conducting commercial operations in these environments.
The magnitude and frequency of extreme levels of the sun’s radiation output is under scientific investigation. Such solar “storms” impact electrical power generation systems on the Earth and will impact human space activities. Part of becoming a true spacefaring nation is improving our understanding of the space environment and how to engineer acceptable radiation safety into our habitats and spaceships. Just as with the extension of other human activities into new and potentially dangerous environments, our rate of progress in civilizing space will depend on our ability to engineer acceptably safe human environments in space.
The primary problem, today, with protecting humans in space is the limitation on the mass that can be economically transported to space to provide adequate radiation protection. Fortunately, the use of increased levels of passive radiation shielding to protect permanent human space facilities, including storm cellars in spaceships, will become the norm with the establishment of a spacefaring logistics infrastructure. Couple improved shielding with improved space environmental sensing—especially for predicting major sunspot activity that can significantly increase harmful solar radiation—and humanity’s ability to safely and routinely live and work in space’s radiation will be significantly improved.