A new report commissioned by NASA highlights many of the risks connected with one of the agency's major goals: putting more humans in space for longer periods of time.
Space missions with humans have grown far longer and more complex since the early days of the space program. NASA's One Year Mission, launched in March 2015, will keep astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko on the International Space Station for a full year. Nearly twice as long at the typical ISS mission, the One Year Mission is in part designed to help NASA understand the effects of living in a weightless environment with tightly limited resources.
The 2015 Review of NASA's Evidence Reports on Human Health Risks, released Thursday, is the third of five such documents produced by a committee of researchers at the National Academies of Science, Engineering and Medicine.
The review's recommendations include that NASA:
The reports are being done at NASA's request to further the agency's understanding of how it can improve safety and quality of life for travelers on space missions, especially longer ones where the health effects of celestial travel are less well understood and potentially more severe.
Each report in NASA's Human Research Program takes a sample of the agency's studies and identifies both areas where research is solid, as well as potential research problems or questions that still need to be addressed.
Apart from longer trips to the ISS, NASA is also evaluating the feasibility of setting up bases or outposts on the moon, deep space missions to bodies such as near-Earth asteroids, and travel to other planets, such as Mars.
"I think it would be fair to say the context in which all of this is happening is there will be longer tours of duty and longer missions," said committee chair Carol E.H. Scott-Conner, a doctor and professor of surgery at the University of Iowa Carver College of Medicine.
There are myriad risks an astronaut faces in space — from muscle and bone loss to psychological health to nutrition, and risks change based on the type of mission or activity an astronaut undertakes. "Space travel is so complex and difficult, and space is such an unforgiving environment, that it is almost impossible to identify any one thing that is a greater risk than anything else," Scott-Conner told CNBC
Muscle loss is a well-documented problem in environments with little or no gravity — astronauts in space typically spend two hours a day working out simply to compensate for it. NASA has estimated that muscle size and function can decline 20 to 40 percent without countermeasures.
Space can also affect the body's ability to take up oxygen — a key indicator of aerobic fitness — and can impair the body's ability to regulate blood pressure.
Astronauts can injure themselves while performing tasks or suffer excessive radiation exposure, especially while donning space suits and working outside a vehicle or space station. NASA has been working on new spacesuits in part to reduce the risk of injury or sickness while on space walks or venturing outside vehicles.
There are also food supply and nutrition issues. Food can spoil during long missions, it can lack needed nutrients, and it can even bore or frustrate astronauts when it tastes bad or lacks variety.
Space travel brings logistical challenges that can ruin even the best-laid plans. In one case noted in the review, food supplies prestocked at the International Space Station went to waste or lost quality over time as the number of astronauts traveling to the ISS declined.
Despite the challenges, Scott-Conner said she is impressed with space travel's extraordinary safety record, and the potentially useful advances in research and technology that have been made by public institutions and the private sector.
Breakthroughs can come from unlikely places. For example, with respect to food supplies, the review notes that three-dimensional printing may help "enhance the variety and freshness of foods that might be produced during long term missions."
Russian cosmonaut Valery Polyakov still holds the record for the longest space mission at 438 days, which he set while stationed at the Mir Space Station from 1994-1995.