Interplanetary Travel Help
As of this writing, humans have paid live visits to one other world in the Universe besides the Earth: our own Moon. We have sent robotic probes to the surfaces of Venus and Mars. We have flown remotely controlled vessels past the outer planets.
It is one thing to send a machine to, say, Titan, the largest moon of Saturn. It is another matter to send people there. Machines can survive without air, water (H 2 O), or food. Machines can tolerate far more radiation than can human beings, and they can put up with long periods of zero gravity. Humans are more fragile. In order to travel in interplanetary space, astronauts will need vessels equipped to keep them alive and safe so that they can reach their destinations and return to live normal lives thereafter. They also will have to realize that there are certain perils they cannot completely avoid.
An interplanetary journey will require months or years, given the propulsion technology we have right now. Even if nuclear-fusion engines are developed, a trip to the outermost planets will take weeks or months. Can we design a space vessel that will keep its occupants alive and well for this length of time? Tests conducted to date suggest that we can. Both the Americans and the Russians have sent people to Earth-orbiting space stations and let them stay there for periods comparable with those required for interplanetary travel.
There’s one big difference between spending a long time in Earth orbit and spending the same amount of time en route to and from another planet. This difference is the ease of supply renewal. If something goes wrong with the International Space Station, we can send some technicians in a Space Shuttle to fix the problem. If the food goes bad or the H 2 O-recycling system goes awry, help is just a shuttle away. This won’t be the case for vessels halfway between Earth and Saturn.
How will future astronauts and cosmonauts bail themselves out of trouble when Earth-based help is not immediately available? One idea involves redundancy, also known as the buddy system . Rather than sending only one vessel on an interplanetary quest, we could send two identical vessels with two crews. Each vessel would carry sufficient supplies for twice the number of travelers on board (plus a little extra to allow for unexpected delays). In this way, if something bad happens to one ship, all the astronauts could get into the other one while the affected vessel is repaired or, at worst, abandoned.
Human beings can tolerate fairly long periods of weightlessness, known as zero-g , although it is not known if a person could survive in that environment indefinitely. There are serious health consequences. One problem is loss of mineral matter from the bones. Even with heavy exercise, an astronaut loses calcium from the bones when the bones are not required to support the body against the force of gravity. This weakens the skeleton so that when the astronaut returns to Earth, bone fractures can occur easily. In addition, the calcium, which is excreted in the urine, can cause kidney stones. Muscle wasting also takes place. Cardiopulmonary (heart and lung) functions decline. An astronaut in zero- g gets out of shape fast.
Artificial gravity will be a necessity for the well-being of astronauts who travel among the planets. This could be done by rotating a large, wheel-shaped vessel around the axis that points in its direction of travel. Another method, which takes advantage of the buddy system, would involve tethering two identical vessels together with a strong cable and spinning the whole assembly like a huge baton (Fig. 19-5). If the cable is a few hundred meters long, such a tethered assembly does not have to revolve very fast to provide an acceleration force of 1 g , equivalent to the gravity at the surface of the Earth.
Using small rockets in each ship, the spin rate would be adjusted to get astronauts accustomed to whatever gravitational force they would encounter at their destination. Computers would take care of the navigation. It would take a while for the travelers to get used to looking out the windows without getting dizzy. Casual stargazing would be done only for amusement, if at all.
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