A manned mission to Mars is slated for as early as 2024, but there are serious health risks that must be mitigated in order for such a mission to be successful. The most pressing risk identified by NASA is radiation exposure. Instead of stunting our spirit of exploration, there is an urgent need to develop effective radioprotection strategies to send humans to Mars on the order of decades, and not centuries. The health risks associated with deep space travel stem from fairly fundamental biology questions. Hence, the same radioprotection solutions we’d develop to go to Mars (or any other planet) would likely have considerable medical applications here on Earth—think new drugs, regenerative medicine, and gene editing.
The health hazards associated with space travel, such as microgravity, solar radiation, isolation, and harsh environments, are all greatly elevated on the long journey to our planetary neighbor. In deep space, though, the radiation risk is especially glaring. Once we leave the shield of our Earth’s magnetosphere, astronauts will be exposed to high-energy, ionizing radiation, called galactic cosmic radiation or cosmic rays. Cosmic rays are especially damaging compared to the forms of space radiation we see closer to Earth, as they cause a high rate of double-stranded DNA breaks in cells, a type of damage extremely difficult for the body to repair, if at all.
The short-term health effects of high-energy radiation are anticipated to be most pronounced in brain, heart, and immune systems. Over time, radiation greatly elevates cancer risk. As humans have yet to experience chronic exposure to cosmic rays, the precise health consequences for a Mars mission remain largely unknown, but the radiation problem is clearly defined.
Currently there are no space-compatible shielding materials to safely block out cosmic rays. So, pending a materials science breakthrough, what can we do to help our bodies resist damage? And, how might those solutions help meet terrestrial medical needs of today? There are broad strategies identified by an international panel that could produce radioprotection tools on the order of decades, namely: drug development, human hibernation, and tissue engineering.
The most rapid approach is to determine if there are any new or existing drugs that could help protect against the effects of galactic cosmic rays, otherwise known as “radioprotectant drugs.” These drugs most often work by decreasing cellular damage and/or improving DNA repair. There are many candidates under investigation, but more hands are needed at the lab bench to fully vet and identify leading compounds, and accelerate development. In a therapeutic radioprotection success story, the drug amifostine was FDA approved to protect healthy cells during radiation therapy in head and neck cancer patients. Amifostine has many undesirable side effects and is quickly degraded in the body, making it unsuitable for a deep space mission, but its example highlights how the same advances to protect people in space could be used to improve radiation oncology therapies. And further, if the drugs were exceptionally safe, as they’d likely need to be for a long-term space mission, they may even have applications in mitigating risks from routine diagnostic radiation such as CT scans.
Another approach to increasing human survival in space is to dramatically slow down metabolism in order to decrease risks of radiation damage from cosmic rays. This model of “biostasis,” in which astronauts would be put into a recoverable hibernation-like state, would mitigate both radiation and general health risks in deep space. This may seem to be a niche value proposition; however, it is of great relevance to trauma care. DARPA recently launched a biostasis program specifically aimed at developing such technologies, not for space, but for the purpose of increasing survival following battlefield injury. To date, the best technology we’ve had to slow metabolism is to quite literally cool people down, using a technique called therapeutic hypothermia. Precise and controlled mechanisms of slowing metabolism could also extend to civilian cases of trauma, infection, or cardiac arrest.
Tissue engineering and regenerative medicine may also play a key role in helping to mitigate the medium to long term effects of cosmic ray exposure by replacing damaged cells and tissues. Given that every ten minutes someone is added to the U.S. national transplant waiting list, the need to mature this area of science is palpable. The precursors to lab-grown replacement tissue are also of relevance to both space and medical applications in terms of testing new treatments. This is best exemplified by NASA’s Vascular Tissue Challenge, a prize awarded in conjunction with the New Organ Alliance to teams able to create lab-grown, metabolically active, vascularized tissue models. Furthermore, the cellular changes associated with radiation damage are remarkably similar to cellular aging, suggesting breakthroughs here may have applications in attenuating aging and promoting human longevity here on Earth.
In the long run the most promising space-enabling approach may be to optimize and edit the human genome to engineer the most space-compatible expression of ourselves: this is in progress but on a 300-500 year timeline. Other approaches seek to eliminate our bodies altogether. The “whole brain emulation” approach seeks to create brain-computer interfaces to upload our minds onto computers. By translating the human experience into an inorganic substrate, and freeing us of our mortal coil, it certainly solves the space compatibility issue, but in turn generates a whole host of moral and ethical questions. However, with either engineering genomes or connecting minds to computers, the research powering these ideas could be transformative for healthcare. For example, such science would potentially enable us to make humans cancer resistant or revolutionize the treatment of many neurological disorders.
Ensuring the long-term survival of humanity is contingent on becoming an interplanetary species. But, in a world that primarily rewards short-term horizons, it is understandably difficult to motivate widespread research on seemingly abstract topics like radioprotecting humans for space travel. By reframing the space radiation problem as one that serves the long-term goals of humanity but also has very real, imminent applications for medical care on earth, we hope to motivate interest in mitigation work. The potential benefits for human health are many, and those must be communicated in order to help a broader audience of researchers, organizations, and entrepreneurs get on board.