Radiation Risks in a Mission to Mars for a Solar Particle Event Similar to the AD 993/4 Event

Within the past decade, evidence of excess atmospheric 14C production in tree rings, coupled with an increase in annually resolved measurements of 10Be in Arctic and Antarctic ice cores, have indicated that an extremely large solar particle event (SPE) occurred in AD 993/4. The production of cosmogenic nuclei, such as 36Cl in consonance with 10Be, indicate that the event had a very energetic “hard” particle spectrum, comparable to the event of February 1956. Herein, we estimate the potential radiation risk to male and female crew members on a mission to Mars that would occur from such an SPE. Critical organ doses and effective doses are calculated and compared with NASA space radiation limits for an SPE comparable to the AD 993/4 event, occurring during the transit phase to Mars, or while the crew members are operating on the surface of Mars. Aluminum shielding, similar in thickness to a surface lander, a spacecraft, and a storm shelter area within the spacecraft, are assumed for the transit phase. For surface operations, including the shielding provided by the atmosphere of Mars, shielding comparable to a spacesuit, enclosed rover, and a surface habitat are assumed. The results of our simulations indicate that such an event might have severe consequences for astronauts in transit to Mars. However, on the surface of Mars, the atmosphere provides some protection against an event similar to the 993/4 SPE. In general, the results show that additional shielding may be required for some of the assumed shielding scenarios.

Health care for deep space explorers

[Formula: see text] There is a growing desire amongst space-faring nations to venture beyond the Van Allen radiation belts to a variety of intriguing locations in our inner solar system. Mars is the ultimate destination. In two decades, we hope to vicariously share in the adventure of an intrepid crew of international astronauts on the first voyage to the red planet. This will be a daunting mission with an operational profile unlike anything astronauts have flown before. A flight to Mars will be a 50-million-kilometre journey. Interplanetary distances are so great that voice and data communications between mission control on Earth and a base on Mars will feature latencies up to 20 min. Consequently, the ground support team will not have real-time control of the systems aboard the transit spacecraft nor the surface habitat. As cargo resupply from Earth will be impossible, the onboard inventory of equipment and supplies must be planned strategically in advance. Furthermore, the size, amount, and function of onboard equipment will be constrained by limited volume, mass, and power allowances. With less oversight from the ground, all vehicle systems will need to be reliable and robust. They must function autonomously. Astronauts will rely on their own abilities and onboard resources to deal with urgent situations that will inevitably arise. The deep space environment is hazardous. Zero- and reduced-gravity effects will trigger deconditioning of the cardiovascular, musculoskeletal, and other physiological systems. While living for 2.5 years in extreme isolation, Mars crews will experience psychological stressors such as loss of privacy, reduced comforts of living, and distant relationships with family members and friends. Beyond Earth’s protective magnetosphere, the fluence of ionising radiation will be higher. Longer exposure of astronauts to galactic cosmic radiation could result in the formation of cataracts, impaired wound healing, and degenerative tissue diseases. Genetic mutations and the onset of cancer later in life are also possible. Acute radiation sickness and even death could ensue from a large and unpredictable solar particle event. There are many technological barriers that prevent us from carrying out a mission to Mars today. Before launching the first crew, we will need to develop processes for in-situ resource utilisation. Rather than bringing along large quantities of oxygen, water, and propellant from Earth, future astronauts will need to produce some of these consumables from local space-based resources. Ion propulsion systems will be needed to reduce travel times to interplanetary destinations, and we will need systems to land larger payloads (up to 40 tonnes of equipment and supplies for a human mission) on planetary surfaces. These and other innovations will be needed before humans venture into deep space. However, it is the delivery of health care that is regarded as one of the most important obstacles to be overcome. Physicians, biomedical engineers, human factors specialists, and radiation experts are re-thinking operational concepts of health care, crew performance, and life support. Traditional oversight of astronaut health by ground-based medical teams will no longer be possible, particularly in urgent situations. Aborting a deep space mission to medically evacuate an ill or injured crew member to Earth will not be an option. Future crews must have all of the capability and responsibility to monitor and manage their own health. Onboard medical resources must include imaging, surgery, and emergency care, as well as laboratory analysis of blood, urine, and other biospecimens. At least one member of the crew should be a broadly trained physician with experience in remote medicine. She/he will be supported by an onboard health informatics network that is artificial intelligence enabled to assist with monitoring, diagnosis, and treatment. In other words, health care in deep space will become more autonomous, intelligent, and point of care. The International Commission on Radiological Protection (ICRP) has dedicated a day of its 5th International Symposium in Adelaide to the theme of Mars exploration. ICRP has brought global experts together today to consider the pressing issues of radiation protection. There are many issues to be addressed: Can the radiation countermeasures currently used in low Earth orbit be adapted for deep space? Can materials of low atomic weight be integrated into the structure of deep space vehicles to shield the crew? In the event of a major solar particle event, could a safe haven shelter the crew adequately from high doses of radiation? Could Martian regolith be used as shielding material for subterranean habitats? Will shielding alone be sufficient to minimise exposure, or will biological and pharmacological countermeasures also be needed? Beyond this symposium, I will value the continued involvement of ICRP in space exploration. ICRP has recently established Task Group 115 to examine radiation effects on the health of astronaut crew and to recommend exposure limits. This work will be vital. Biological effects of radiation could not only impact the health, well-being, and performance of future explorers, but also the length and quality of their lives. While humanity has dreamed of travel to the red planet for decades, an actual mission is finally starting to feel like a possibility. How exciting! I thank ICRP for its ongoing work to protect radiation workers on Earth. In the future, we will depend on counsel from ICRP to protect extraterrestrial workers and to enable the exploration of deep space.