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Of these 34 risks, three are potential obstacles: radiation, severity (or lack thereof), and the need for surgery or a complicated medical procedure.
The gravity of the situation.
Let’s explore the problem of gravity.
Some science fiction writers in the mid-20th century speculated that zero gravity would be vital: blood would flow more easily; arthritis would be a thing of the past; back pain would be cured forever; and aging itself would slow down. So, bring grandma for the ride. We had hints from the beginning of the space program that such an optimistic scenario was not true. The astronauts returned from a few days of weightlessness feeling weak. But they recovered; and many thought, well, maybe it’s not that bad. Then we spend more time in space. Russians on the Mir space station for months appeared to have some serious and prolonged health problems upon their return. However, the Russians were tight-lipped about the health of their cosmonauts, so we never knew for sure. Many of these cosmonauts, defended as heroes, were rarely seen in public after their return. It was the ISS missions that got the message across: Long-term exposure to zero gravity is detrimental to human health on many levels. Congratulations to NASA for that.
Before continuing, you should first define some terms. Zero gravity, while visually convenient, may be a misnomer in the context of near-Earth activity. Astronauts on the ISS do not live in the absence of gravity. Rather, they are in free fall, forever falling on the horizon and missing Earth. The ISS and other satellites are not floating in space because they have escaped the pull of Earth’s gravity; they stay up there due to their excellent horizontal speed. The ISS is moving at 17,500 miles per hour. If it somehow came to a complete stop, it would fall straight to Earth, and the astronaut, crib and all would descend. The Earth’s gravitational pull, in fact, keeps the satellites moving in orbit as a perfectly balanced counter force, in a downward motion, to the lateral motion established during launch. Without Earth’s gravitational pull (if Earth suddenly and magically disappeared), the satellites would shoot in a straight line. Therefore, the most accurate terms to describe the lack of feeling of gravity on board the ISS are microgravity and weightlessness. However, even these terms are neither perfect nor synonymous. Astronauts on the ISS have weight, about 90 percent of their weight on Earth, which is just 200 miles below their feet. They would be much lighter on the Moon, actually, at only 16 percent of their weight. Absolute zero gravity is not achievable, because gravity is the force of attraction between two objects. But in deep space, away from the gravitational pull of any moon, planet, or star, gravity dims to near zero. I tend to use the terms zero gravity, microgravity, and weightlessness interchangeably in the context of space travel.
Our understanding of the effect of gravity on the body has only two data points: one and zero. On Earth, we live with a gravitational pull of 1G. In the ISS, astronauts live in 0G. We really don’t know anything in between. Air Force pilots can accelerate their planes so fast that they experience forces of 5G or more, sometimes causing them to pass out. That’s five times the force of Earth’s normal gravity, which pushes blood out of their brains. But such forces usually last only a few seconds; pilots do not live in a hypergravity environment. And anyway, we don’t care too much about forces greater than 1G because every place we want to go in our Solar System (L2 orbit, Moon, Mars, etc.) has a gravitational force less than 1G.
