According to Medical News Today, "gravity affects blood circulation and the musculoskeletal system, among other things", which means "the effects of microgravity could prevent astronauts, and their bodies, from performing necessary functions in space."
Space travel can also increase the risk of high blood pressure and cardiac arrhythmia and atrophy.
Even on a short trip, tourists would still have to deal with exposure to radiation, cosmic rays and extreme cold, as described by Kelly.
Some studies believe that just one particle of the cosmic rays "has the power to charge through human tissue and destroy DNA, raising the risk of mutations and cancer".
The close quarters involved in space travel could also pose a problem, as bacteria is easily shared when people are in close proximity.
As with more conventional forms of travel, passengers could also be affected by motion sickness and disorientation, which can "affect vision, cognition, balance and motor control".
- nzherald.co.nz