Human Risks and Safety

Throughout the history of manned spaceflight, both astronauts and cosmonauts have experienced both short term and long term effects from their time away from Earth’s gravity. In the relatively short period the Apollo astronauts traveled to the Moon and back, mostly short term effects were experienced, but the longer periods spent on the ISS have shown some long term effects that can be detrimental to Mars-bound space explorers.

The human cardiovascular system circulates fluids through the body, pushing against gravity to prevent blood from pooling in the legs and bringing blood to the brain. In the microgravity of space, the cardiovascular system is not taxed as hard, triggering a fluid shift. As fluids move up from the lower body to the trunk, the heart rate increases and blood pressure rises. Astronauts experience puffy faces, headaches, nasal congestion and skinny “bird” legs as a result. Additionally, over a third of all astronauts experience some form of motion sickness in space because of the blood circulation changes. Symptoms of space sickness, including nausea and vomiting, headaches, malaise and dizziness, usually subside within 2 or 3 days.

Some evidence suggests that microgravity causes astronauts’ red blood cells to change. The red blood cells appear to change shape in space, becoming more spherical, and fewer cells populate bone marrow. Cells do return to normal once back under Earth-normal gravity however, even after a long-term mission.

Astronauts returning from missions have been found to be more prone to infec­tion, both viral as well as bacterial and fungal. Long term studies in space and Antarctica have shown that isolation and sleep deprivation may result in a weakened T-lymphocyte system, leading to compromised immunity. A high probability of increased allergy symptoms has been noted. The immune system is unable to adapt under microgravity conditions. A future Mars-bound crew will need a supply of antibacterial, anti-fungal, and antiviral drugs and medications. A Mars mission that extends beyond 6 months will mean these drugs will reach their expiration dates, thus inviting the need for some pharmaceutical capability onboard. A shorter 39-day-to-Mars mission reduces this risk.

A well known effect of microgravity is the atrophy the muscular structure. Astronauts onboard the ISS counter these effects by exercising up to 2 hours a day.

The microgravity of space triggers the human body to excrete calcium and phos­phorus (in urine and feces), resulting in rapid bone loss. On the shorter duration Apollo missions, the calcium and phosphorus loss was minimal, and the Apollo astronauts quickly recovered their bones density. A 2 year or longer Mars mission can result in an astronaut’s bone density loss to be equivalent to a lifetime on Earth. Like osteoporosis on Earth, bone loss in space can lead to fractures, weakness and painful urinary stones. The most dramatic changes occur in the heel bone, femoral neck, lumbar spine and pelvis. Exercise in space and upon return can help slow the loss, but it will take 2 years or more of dedicated, consistent training upon return to repair it. Artificial gravity would also serve to mitigate this problem if it is a part of the mission design.

All Apollo missions conducted the Light Flashes Experiment in an effort to explain the flashes of light that seem to appear behind the astronaut’s eyelids. The result of the experiment showed that galactic cosmic rays passed through the astro­naut’s brains causing the retinal flashes. These flashes are just symptomatic of a much larger problem. Cosmic rays and the radiation effects of solar flares expose astronauts to high levels of ionizing radiation. The Apollo astronauts were fortunate that during their missions, other than the light show they experienced when they closed their eyes, no solar flares occurred. A solar flare had the potential of causing the loss of the LM crew on the lunar surface. The LM construction and the lunar spacesuits provided minimal radiation shielding.

Unrelated to the light flashes, medical doctors and scientists are showing some concern over a possible loss of eyesight from extended microgravity exposure. NASA has reported that 15 male astronauts returning from extended missions in space have experienced confirmed visual and anatomical changes during or after long-duration flights. It is continuing to be studied, with current thought being related to ocular fluid shifts due to microgravity as a contributing factor.

The radiation in deep space can damage atoms in human cells, leading to decreased immunity and a higher risk of cataracts, cancer, heart disease, damage to the central nervous system and brain damage. Recognize that Mars does not have a global magnetic field to shield the planet from solar radiation particles, nor does it have a thick atmosphere to help filter out cosmic rays. Long-term exposure to ion­izing radiation in open space and on the planet surface is a significant concern for the crew of the Mars mission.

The Radiation Assessment Detector (RAD) aboard the Mars rover Curiosity produced detailed measurements of the absorbed dose, and dose equivalent from galactic cosmic rays, and solar energetic particles en route and from the surface of Mars. The numbers from the RAD are startling high. For the round trip, based on Curiosity’s RAD data, an astronaut would receive radiation from both cosmic gamma rays and solar activity approximately 0.66 Sv during a 180 day flight to Mars.

A 500 day exposure on the surface of Mars would result in each astronaut receiv­ing approximately 1 Sv. Long-term population studies have shown that exposure to radiation increases a person’s lifetime cancer risk; exposure to a dose of 1 Sv is associated with a 5 % increase in fatal cancer risk. NASA has established a 3 % increased risk of fatal cancer as an acceptable career limit for astronauts in low earth orbit, such as extended stays on the ISS. NASA has not established a limit for deep space missions.

A number of solutions are being explored to help protect astronauts, including antioxidant-rich foods, such as blueberries and strawberries and close monitoring of radiation levels combined with the use of radiation shields. Protection from solar flares, however, poses a technological problem that is solvable at the price of addi­tional weight of protective shielding.

Astronauts returning to Earth risk low blood pressure. A sudden reintroduction of gravity makes the blood in astronauts’ bodies rush down, resulting in dizziness and lightheadedness. Tiny muscles in veins that send blood uphill can atrophy after prolonged periods of microgravity, and can fail to push blood back up to the heart. Astronauts can experience fainting or be unable to remain standing. Mir cosmo­nauts had to be carried off their landing craft by stretcher due to the severe drop their blood pressure following long missions. A prolonged mission to Mars will result in returning astronauts needing to drink salt water to increase the volume of fluids in their bodies, wear G-suits (rubberized full body suits which are inflated to squeeze the extremities) or potentially use new drugs to increase blood pressure.

Apollo moon missions took several days to transition from Earth orbit to the Moon, with the Earth within of a few days reach and communications links with only a handful of seconds latency. The manned mission to Mars will not have those luxuries. The travel time to and from Mars will be measured in terms of months or years, not days. Communication latency will be measured in terms of a maximum of 22 minutes, not seconds.

Medical aid for Space Shuttle missions and ISS missions can be accommodated with near real-time communications, on board supplies, and in an emergency, a relatively timely re-entry and return to Earth. A Mars mission, as it progresses towards its goal, will not have the luxury of a quick and timely return to Earth in case of medical emergency. Any real-time communications to guide the crew through a medical procedure will be severely handicapped by the communications delay because of the distance.

A different medical philosophy is required, utilizing lessons learned from the Apollo, Space Shuttle, long-term Antarctic, and ISS experiences. Five decades of American and Russian spaceflight have yielded a greater understanding of space medicine and the effects of weightlessness on the human body. The development of a comprehensive Mars healthcare system will allow for autonomous health care, with a combination of advanced medical instrumentation, medical training of the crew, and the possible selection of a medical doctor for inclusion as part of the Mars crew. It will need to support the Mars crew members for both the journey to and from Mars, and surface activities. The medical system must accommodate a wide array of human illness and conditions, while being prepared for emergencies caused by accidents. In addition, the medical system will incorporate both environ­mental monitoring and exercise countermeasures to ensure wellness and maintain crew health.

The return to Earth from Mars will likely require a quarantine period for the same reasons the crews of Apollo 11, 12, and 14 experienced. It is unknown if there is any microbial life on Mars, harmful or otherwise. A quarantine in an environment external to Earth would be prudent to avoid any possible contamination of Earth. A likely site might be at or near an established Moon base. Isolation could be conducted on an Earth-orbital quarantine module, perhaps in conjunction and monitored by personnel with the ISS.