What are some of the ethical considerations of sending humans into space?

The adventure of space travel readily captures the imagination. Countless books, movies, and television shows have been created around the theme. In practical terms, the scientific and medical advancements spurred by the space program have aided humanity at large. Technologies as diverse as LEDs, advanced artificial limbs, and plane de-icing systems owe something of their creation to the aerospace industry. The possible colonization of Mars will doubtless spark even more innovation. However, such a momentous undertaking cannot ignore the ethical issues raised by sending human beings into space for the time required for the trip. Considerations include physical and mental health as well as the probability of catastrophe and the response to it.
The human skeletal system and microbiome are normally under conditions of consistent gravity and atmospheric protection from solar and cosmic radiation. These will be largely lacking on any prolonged expedition. Muscle weakness and bone demineralization already trouble astronauts. Longer exposure can potentially worsen these issues. Little research has been done regarding the effects of radiation on human gut bacteria, and a healthy microbial colony is essential to proper nutrition and overall health.
With current technologies, any Mars-bound craft will be small and cramped compared with what people are used to on Earth. The psychological balance of the crew is essential. Lack of privacy and close living conditions during the long journey could threaten astronaut mental health and essential group cohesivity.
Finally, the response to an emergency or its practical impossibility cannot be overlooked. It would be extremely difficult, if not impossible, to come to the astronauts' aid in case of emergency, making any dangers faced far starker.
https://spinoff.nasa.gov/Spinoff2008/tech_benefits.html

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