Contents

### **Preface XI**


Preface

to a cellular, even molecular, level.

ter their return to Earth.

as a universal species becomes evident.

All living organisms on Earth are subject to the influence of gravity. This gravitational force has dictated their anatomy and physiology over millions of years, including that of human beings. Therefore, if humans were "dolls" made of modelling clay, the mould would be gravity.

Removing the effect of Earth's gravitational force alters all organic functioning. One of the first responses to space flight is the inability of the vestibular system to cope with the ab‐ sence of gravity and, consequently, body spatial orientation. A disease called space motion sickness, which is characterized by impairment of performance, nausea, vomiting and a dif‐ fuse malaise, occurs in astronauts and lasts for the first 72 hours of a space mission. In the weightless environment of space, a headward shift of blood and body fluids progressively happens over the course of weeks and deeply affects the cardiopulmonary and neuro-oph‐ thalmic systems, remodelling heart and lung function as well as vascular pressures in the brain and cardiovascular system. When astronauts return to Earth, the cardiovascular sys‐ tem, already adapted to microgravity, causes concern by succumbing to orthostatic intoler‐ ance and decreasing exercise aerobic capacity. In space, humans develop anaemia and the immune system is depressed, showing that weightlessness affects human physiology down

In 3 to 5 days, the body begins to adapt to the space environment, and within 6 weeks, it starts to work in accordance with its new setting. Some systems, however, do not adapt fa‐ vourably. The mechanical unloading of muscles and bones in space affects the musculoske‐ letal system, causing significant atrophy, especially in the anti-gravitational groups of muscles in the back and legs. It is believed that the normal process of bone formation and resorption is disturbed, resulting in loss of bone mass, primarily in the lower body. The de‐ crease in bone mass is a huge concern, as the loss can range from 1% to 2% of total bone mass per month, impacting on astronauts' health, not only in space but also particularly af‐

At 27,000 km/h, a spacecraft completes an orbit around the Earth every 90 minutes, which affects the circadian rhythm of the astronaut. Seeing the world through a little window in‐ side the confines of a spacecraft obviously has implications for human psychology. Emotion‐ al issues related to isolation and confinement can also have a significant impact on crewmembers, a situation that is likely to be exacerbated by the increased duration and dis‐ tance from Earth that an interplanetary trip to Mars will bring. The concept of our finitude

We benefit on Earth from the protection provided by the atmosphere and magnetic field of our planet, which shields us from much of the radiation present in outer space. However, when humans leave this cocoon, they become exposed to space radiation that can have dele‐

