If you want to go to space for any significant duration of time, you should be prepared to suffer from a number of maladies. The zero-gravity (or microgravity) environment of space is catastrophic, in many ways, to the normal, everyday functions of the human body. Without that gravity to orient ourselves, pull down on our organs, and provide that resistance that forces our body to build and maintain strong bones and muscles, all sorts of problems arise for human bodies: problems that compound and worsen the longer we remain in space.
There’s a big reason that most astronauts only spend a relatively short period of time in space: our bodies degrade in a great many ways in the zero-gravity environment of space, leaving us less fit to succeed at life on Earth when we return. One way around that problem would be to generate artificial gravity in space. After all, one of the biggest insights that Einstein ever had was the equivalence principle: the recognition that gravity was just another form of acceleration, and that an observer experiencing that acceleration would have no way of telling whether it was gravitational or non-gravitational.
So could we use a specific type of rotating, low-cost artificial acceleration — with two separate craft connected by a tether — to provide that artificial gravity? That’s what John Tomlinson wants to know, writing in to ask: “How long would a Kevlar cable need to be for astronauts to feel centripetal acceleration as comfortable as gravity? Why don’t we send up a mile-long Kevlar cable, stretch it between two capsules, spin it up, and have artificial gravity?” In principle, we could do it.
In principle, we could even make it equivalent to Earth’s surface gravity in strength. But in practice, it faces some major obstacles. Here on Earth, in the gravitational field of our planet, there is no way to “shield” ourselves from the gravitational influence of Earth, as there are no gravitationally negative charges/masses/forms of energy.
This closed room experiences free-fall conditions, where the observers in the room experience no net acceleration relative to their surroundings. From within the room, one cannot tell whether you’re at rest or in constant motion, only that your acceleration relative to your surroundings is zero, as you experience the sensation of weightlessness. NASA has long known that the long-term, cumulative effects of spaceflight on the human body are both profound and overwhelmingly negative.
In fact, when they quantify them in modern times, they use the acronym RIDGE, for the adverse effects of: Radiation can be dealt with by providing significant layers of shielding and by remaining inside the influence of Earth’s magnetosphere and van Allen belts. Isolation has been shown to only affect a selection of astronauts, and only over the short-term, as the current record-holder for the longest duration in space for a single spaceflight, Valeri Polyakov, demonstrated aboard Mir from 1994-5. Distance and environment are not necessarily dealbreakers, as these are largely psychological effects that can be mitigated with any number of interventions, or simply by selecting people who aren’t as adversely affected by them as most.
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