[The following is my comment to a New York Times article.]
I became an amateur astronomer at 15 and worked as an aerospace engineer for thirty years on mostly NASA projects, occasionally even rubbing shoulders with an astronaut or two. I spent several years working on Viking, the original project to put two spacecraft on Mars. I think highly of all or efforts to get and maintain a human presence in space. However, I have never though that long-term missions such as putting an astronaut on Mars would be worth trying until we have someway of creating artificial gravity. And once on Mars the problem doesn’t go away. Gravity on the surface of Mars is only one-third of that on Earth. The Moon of course is even worse. Only one-sixth of Earth’s gravity.
To understand the true significance of this, I think to we have to realize that not just mankind but all life and life’s process evolved under the influence of gravity at a specific level. The fact that humans walk upright speaks to a concept that is meaningless in zero gravity. The shape of the human body is a tribute to gravity. To speak of colonies where humans would live for extended periods without some form of gravity approaching that of Earth’s to me is unthinkable. To put an astronaut out in zero-G space, and then patch up the body to make it tolerate the condition for years or perhaps even permanently I see as a futile exercise. We should understand and know how to treat the conditions, but in the end, astronauts need gravity. It is indelibly a part of who we are.