Red risks for a journey to the red planet: The highest priority human health risks for a mission to Mars

Abstract

NASA's plans for space exploration include a return to the Moon to stay-boots back on the lunar surface with an orbital outpost. This station will be a launch point for voyages to destinations further away in our solar system, including journeys to the red planet Mars. To ensure success of these missions, health and performance risks associated with the unique hazards of spaceflight must be adequately controlled. These hazards-space radiation, altered gravity fields, isolation and confinement, closed environments, and distance from Earth-are linked with over 30 human health risks as documented by NASA's Human Research Program. The programmatic goal is to develop the tools and technologies to adequately mitigate, control, or accept these risks. The risks ranked as "red" have the highest priority based on both the likelihood of occurrence and the severity of their impact on human health, performance in mission, and long-term quality of life. These include: (1) space radiation health effects of cancer, cardiovascular disease, and cognitive decrements (2) Spaceflight-Associated Neuro-ocular Syndrome (3) behavioral health and performance decrements, and (4) inadequate food and nutrition. Evaluation of the hazards and risks in terms of the space exposome-the total sum of spaceflight and lifetime exposures and how they relate to genetics and determine the whole-body outcome-will provide a comprehensive picture of risk profiles for individual astronauts. In this review, we provide a primer on these "red" risks for the research community. The aim is to inform the development of studies and projects with high potential for generating both new knowledge and technologies to assist with mitigating multisystem risks to crew health during exploratory missions.

Fig. 1. The five main hazards of spaceflight and the space exposome.

a The key threats to human health and performance associated with spaceflight are radiation, altered gravity fields, hostile and closed environments, distance from Earth, and isolation and confinement. From these five hazards stem the health and performance risks studied by NASA’s Human Research Program. b The space exposome considers the summation of an individual’s environmental exposures and their interaction with individual factors such as age, sex, genomics, etc. - these interactions are ultimately responsible for risks to the human system. Images used in this figure are courtesy of NASA.

Fig. 2. NASA human system risks—likelihood and consequence rating scale.

NASA uses an evidence-based approach to assess likelihood and consequence for each documented human system risk. The matrix used for classifying and prioritizing human system risks has two sets of consequences—the left side shows consequences for in-mission risks while the right side is used to evaluate long-term health consequences (Romero and Francisco).

Fig. 3. Galactic cosmic rays are qualitatively different from X-rays or gamma-rays.

a HZE ions produce dense ionization along the particle track as they traverse a tissue and impart distinct patterns of DNA damage compared to terrestrial radiation such as X-rays. γH2AX foci (green) illuminate distinct patterns of DNA double-strand breaks in nuclei of human fibroblast cells after exposure to b gamma-rays, with diffuse damage, and c HZE ions with single tracks. Image credits: NASA (a) and Cucinotta and Durante (b and c).

Fig. 4. The hallmarks and emerging hallmarks of cancer.

Shown are the enabling characteristics and possible mechanisms of radiation damage that lead to these changes observed in all human tumors. (Adapted from Hanahanand Weinberg).

Fig. 5. Cardiovascular disease is a human systems risk.

In blue are the known risk factors for CVD and in black are the other spaceflight stressors that may also contribute to disease development. Image used in this figure is courtesy of NASA.

Fig. 6. Reduced dendritic spine density in the rodent medial prefrontal cortex 15 weeks following exposure to cosmic radiation.

Representative digital images of 3D reconstructed dendritic segments (green) containing spines (red) in unirradiated (0 cGy) and irradiated (5 and 30 cGy) mice brains. Multiple comparisons show that total spine numbers (left bar chart) and spine density (right bar chart) are significantly reduced after exposure to 5 or 30 cGy of ¹⁶O particles. Data are expressed as mean ± SEM. *P < 0.05, **P < 0.01 versus control; ANOVA. Adapted from Parihar et al.. Permission to reproduce open-source figure per the Creative Commons Attribution 4.0 International License. https://creativecommons.org/licenses/by/4.0.

Fig. 7. Onboard the ISS, NASA astronaut Peggy Whitson collects images of the back of the eye during a routine screening check.

Image courtesy of NASA.

Fig. 8. Potential pathways for SANS.

Image created with BioRender.com.

Fig. 9. The “Journals” study of in-flight behavioral responses.

Example bar graph showing distribution of journal entries related to general adjustment to the spaceflight enivronment during each quarter of an ISS mission.

Fig. 10. The NASA Human Research Exploration Analog.

HERA is used to simulate environments and mission scenarios analogous to spaceflight to investigate a variety of behavioral and human factors issues. Images courtesy of NASA.

Fig. 11. A depiction of the relationship of nutrition with exploration missions.

Many of the physiological systems and performance characteristics that are touched by nutrition are shown in white text, while the unique elements of spacecraft and space exploration are shown in red text.

Fig. 12. Resistance exercise devices on the ISS.

Sunita Williams exercising on the iRED (a), and on a later mission, Sandy Magnus exercises on the much improved ARED device (b). Images courtesy of NASA.