Both coming and going, spaceflight can threaten tourists' health, with potential dangers from higher gravitational forces during acceleration, and space motion sickness that strikes some people in low and zero-gravity.
Too little information
Outside of the Earth's protective magnetosphere, space radiation might also pose a risk, possibly to implanted medical devices.
And a hidden threat might be the unpredictable ways people act while confined in a ship in this new situation.
But the experts' bottom-line message? There's too little information now to definitively answer the question of who is fit for this kind of travel.
"We don't have a specific list of conditions that would be disqualifying, but certainly uncontrolled medical problems (whether it's hypertension or heart disease or lung disease, or many other conditions), would most likely cause concern and result in disqualification," Dr. Tarah Castleberry, an assistant professor of aerospace medicine at the University of Texas Medical Branch in Galveston, told Reuters Health.
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Castleberry and her colleagues are a part of an academic network created by the U.S. Federal Aviation Administration to assess challenges in commercial spaceflight.
Recently in the quarterly journal New Space they published an outline of what remains to be done to understand the health risks.
Forces of acceleration
So far, most data on the risk of spaceflight comes from professional astronauts. But space tourists will likely be a much more diverse group, with a broader range of health conditions.
Earlier this year, researchers from Castleberry's group ran 335 volunteers through a centrifuge that simulates the forces of acceleration in spaceflight.
Most had one of five medical conditions: hypertension, diabetes, back or neck problems, cardiovascular or lung disease.
No one suffered significant damage or setbacks from the experience, the researchers reported in July 2014 in the journal Aviation, Space and Environmental Medicine.
The most common complaint was grayout, the blurred vision that is a precursor to blackout, which occurred in more than two-thirds of the volunteers. Twenty percent had nausea, and six percent had chest discomfort.
With historical data so limited, it's difficult to make predictions, the researchers say.
They have drawn up a shopping list of tools that could answer some of these questions and offset risks. Their to-do list includes setting medical standards for spaceflight crew and developing training and risk management systems. They also want to create a health database to collect information from space tourists.
Fliers could potentially wear monitoring devices, the researchers say – but most off-the-shelf products are not up to the task. New devices may have to be developed to track heart rate, breathing, skin temperature and other useful measurements.
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Those measures may start to fill the gap in medical knowledge about this new endeavour, but more study and more scientific publication is needed.
"The aerospace medical profession is one of the smallest and least published fields in scientific literature," Drs. Natacha Chough and Rebecca Blue, also at the University of Texas Medical Branch, wrote in a New Space editorial.
The problem with the lack of data may be compounded by the public's high expectations for safety.
Excellent safety measures
"The only real reference point right now is commercial air travel, and we are a victim of our own excellent safety measures," says Dr. Clay Cowl, chair of the Division of Preventive, Occupational and Aerospace Medicine at Mayo Clinic in Rochester Minnesota, who was not involved in Castleberry's research.
Image: Virgin Galactic's Space Ship 2
Read: Link between astronauts and osteoporosis
"My fear is that public tolerance for a bad outcome is not like it was when we introduced the public to regular flight in fixed-wing aircraft. There were a lot of health risks at that time before we came up with things like pressurised cabins, before we came up with ways to mitigate the problems with travelling at altitude."
Something that's a nuisance on the ground can become an emergency during the flight. Indigestion, for example, could become a medical concern as pockets of gas trapped in the body expand at high altitudes, Cowl says.
And unexpected behaviour could become a problem if the flight triggers a phobia or a passenger gets angry.
Read: Are you afraid of flying?
"In credit to the groups thinking about space flight, my opinion is that we're going to have to figure out ways to mitigate potential side effects of this travel as much as possible because I don't know what the public appetite is going to be to tolerate in-flight emergencies and catastrophes," Cowl said.
Notes: It would currently cost you around $40 million to get as far as ISS, though the price should come down if commercial space travel takes off. Sub-orbital flights, which are brief trips up to around 100-160km, providing a few minutes of weightlessness, views of the curved earth below and stars above, would cost a mere $200 000. Companies like Space Adventures are taking bookings for as early as next year.
Space Travel agent Paul Klein offers Virgin Galactic space travel charters for $1.25 million which includes an exclusive spaceflight for you and up to 5 friends, 6 seats for the price of 5.
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